Chemistry

Oxidation of tertiary amines to amine oxides

Oxidation of tertiary amines to amine oxides


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

  • chemistry
    • General Chemistry
    • Inorganic chemistry
    • Organic chemistry
    • Physical chemistry
    • Analytical chemistry
    • technical chemistry
    • Macromolecular Chemistry
    • Theoretical chemistry
    • Chemical information
    • Chemoinformatics
    • toxicology
  • Organic chemistry
    • Basics
    • Chemical bond
    • Alkanes
    • Alkenes
    • Alkynes
    • Hydrocarbons
    • Stereochemistry
    • Oxidation reactions
    • Reduction reactions
    • Alcohols
    • Ether
    • Sulphides
    • Haloalkanes
    • Carboxylic acids
    • Carbonyl compounds
    • Organometallic compounds
    • Keto-enol
    • Aromatic chemistry
    • Heterocycles
    • substitution
    • Addition reactions
    • Elimination
    • Radical chemistry
    • Reaction mechanisms
    • Pericyclic reactions
    • Substances
  • Oxidation reactions
  • Oxidation of tertiary amines to amine oxides

Oxidation of Tertiary Amines to Amine Oxides: Introduction

Reaction principle:

Tertiary amines are easily oxidized to amine oxides by hydrogen peroxide or a peroxycarboxylic acid. Hydrogen peroxide is reduced to water or the peracid to carboxylic acid.

Example:

Fig.1

Use:

Mainly synthesis of alkenes by oxidation of amines with subsequent Cope elimination.

<Seite 1 von 6>

<Seite 1 von 6>

Table of contents

  • introduction
  • mechanism
  • Use in the laboratory
  • Practical implementation
  • Practice quiz
  • Bibliography

20 min.

Preparation and review

  • Required basics
  • Further learning units

About the learning unit

Authors

  • Prof. Dr. Rainer Herges
  • Kirsten Klose

Book recommendations

  • E-mail
  • PDFBuy this chapter as a PDF
    "Payment method: ClickandBuy"

Photooxygenation

Photooxygenation, Photo-oxidation, the reaction of molecules with molecular oxygen when light is absorbed. There are two types.

1) Type I reaction: The substrate is activated photochemically, with the formation of a start radical which is converted in a radical chain reaction with molecular triplet oxygen, as in thermal auto-oxidation. This P. is often sensitized, e.g. B. by carbonyl compounds. Examples of this type are the P. of primary and secondary alcohols (formation of carbonyl compounds) and of tertiary aliphatic amines (to imines and aldehydes).

2) Type II reaction: Reaction of photochemically generated singlet oxygen with substrates that are in the ground state.

Reader opinion

If you have any comments on the content of this article, you can inform the editors by e-mail. We read your letter, but we ask for your understanding that we cannot answer every one.

Dr. Andrea Acker, Leipzig
Prof. Dr. Heinrich Bremer, Berlin
Prof. Dr. Walter Dannecker, Hamburg
Prof. Dr. Hans-Günther Däßler, Freital
Dr. Claus-Stefan Dreier, Hamburg
Dr. Ulrich H. Engelhardt, Braunschweig
Dr. Andreas Fath, Heidelberg
Dr. Lutz-Karsten Finze, Grossenhain-Weßnitz
Dr. Rudolf Friedemann, Halle
Dr. Sandra Grande, Heidelberg
Prof. Dr. Carola Griehl, Halle
Prof. Dr. Gerhard Gritzner, Linz
Prof. Dr. Helmut Hartung, Halle
Prof. Dr. Peter Hellmold, Halle
Prof. Dr. Günter Hoffmann, Eberswalde
Prof. Dr. Hans-Dieter Jakubke, Leipzig
Prof. Dr. Thomas M. Klapötke, Munich
Prof. Dr. Hans-Peter Kleber, Leipzig
Prof. Dr. Reinhard Kramolowsky, Hamburg
Dr. Wolf Eberhard Kraus, Dresden
Dr. Günter Kraus, Halle
Prof. Dr. Ulrich Liebscher, Dresden
Dr. Wolfgang Liebscher, Berlin
Dr. Frank Meyberg, Hamburg
Prof. Dr. Peter Nuhn, Halle
Dr. Hartmut Ploss, Hamburg
Dr. Dr. Manfred Pulst, Leipzig
Dr. Anna Schleitzer, Marktschwaben
Prof. Dr. Harald Schmidt, Linz
Dr. Helmut Schmiers, Freiberg
Prof. Dr. Klaus Schulze, Leipzig
Prof. Dr. Rüdiger Stolz, Jena
Prof. Dr. Rudolf Taube, Merseburg
Dr. Ralf Trapp, Wassenaar, NL
Dr. Martina Venschott, Hanover
Prof. Dr. Rainer Vulpius, Freiberg
Prof. Dr. Günther Wagner, Leipzig
Prof. Dr. Manfred Weissenfels, Dresden
Dr. Klaus-Peter Wendlandt, Merseburg
Prof. Dr. Otto Wienhaus, Tharandt


Hydrobromides

Hydrobromide is a collective term for the organochemical class of salts that hydrobromic acid (HBr) forms with basic organic compounds. Often, hydrobromides are salts of primary, secondary or tertiary amines that are formed in a neutralization reaction with hydrobromic acid (HBr):

The reaction is analogous to the reaction of ammonia with HBr, in which ammonium bromide (NH4Br) forms. Like all bromides, hydrobromides contain the bromide anion (Br -) and are therefore salts. Compared to their parent compounds (mostly amines), hydrobromides are usually more soluble in water and can be more easily purified by recrystallization. The hydrobromides of amines are significantly more stable and more resistant to aging - recognizable by their discoloration - than the free basic amines.

In the case of complex molecules with several basic reacting functional groups (see alkaloids, lysine), in which the protonated group cannot be precisely defined, hydrobromides are often represented graphically as follows:

Forms when organic diamines react with excess hydrobromic acid Dihydrobromidescontaining two equivalents of hydrobromic acid (HBr) bound in a salt-like manner.

In addition, hydrobromids are formed from basic amino acids, amino acid esters and alkaloids. A number of medicinal substances (examples: dextromethorphan, fenoterol, galantamine, salsolinol) are commercially available as hydrobromides. [Wick cough syrup ® (D)] and Homatropin [Homatropin POS ® 1 & # 160% (D)] are further examples. & # 911 & # 93 The drugs scopolamine & # 912 & # 93 and eletriptan & # 913 & # 93 are also used as hydrobromides. & # 914 & # 93


Illumina

Tartaric acid
Potassium iodide

Execution:

20 mg of basic bismuth (III) nitrate, 25 mg of tartaric acid and 400 mg of potassium iodide are dissolved in 2 ml of water (this solution is also known as Dragendorff's reagent, but cannot be stored for a long time and must therefore always be freshly prepared). Then the sample dissolved in water or ethanol is added. An orange-red precipitate (possibly with a time delay) indicates alkaloids and tertiary amines.

Dragendorff's reagent is disposed of as inorganic waste.

In a weakly acidic environment, an orange-yellowish, water-soluble tetraiodobismuthate complex is formed from excess bismuth (III) and potassium iodide:

Alkaloids and tertiary amines are protonated by tartaric acid:

With the tetraiodobismutate anion, an ion pair is formed which, due to its "bulkiness", cannot be hydratized and which precipitates:


Blank sample (left) and sample


The resulting precipitate after settling (caffeine was used)

Contribution by frankie & raquo Saturday May 22, 2010, 2:40 pm

What did you use as a probe? Caffeine, nicotine?

Contribution by Archeopteryx & raquo Saturday May 22nd 2010, 5:23 pm

Contribution by lemmi & raquo Sunday January 29th 2012, 7:22 pm

Since I have dealt with Dragendorff's reagent (DR) in more detail, I would like to make a few comments on this older thread (which, based on the number of comments so far, does not seem to have met with too much interest).

First of all, there are many different regulations for DR - there are 5 variants in the European Pharmacopoeia alone! The one used here by @Archaeopteryx was not yet known to me and it would be interesting to know where it comes from.

The tetraiodobismuthate anion is only stable in an acidic environment or in the presence of complexing substances that lower the concentration of free Bi 3+ in the solution. When diluting a pure K [BiI4] Solution with neutral water, the complex is split and orange-brown cloudiness or precipitates (a mixture of basic bismuth iodides) arise even without the presence of alkaloids. The pharmacopoeias (DAB and Ph. Eur.) Therefore prescribe that the solution to be tested for alkaloids must be acidified before the addition of DR. This note is missing in the experiment described.

In general there are two different Greuppen from DR, one with the addition of acetic acid, the other (like here) with tartaric acid. The latter are more stable when diluted with water, but the production does not result in a clear solution, instead potassium hydrogen tartrate (Weinstein) precipitates, as shown here (I carried out the experiment today with the amounts of substance given here in a 3 times larger amount):

The reagent must therefore be filtered (this note is missing in the description of the experiment). Contrary to what is stated in the description, it is also quite durable if it is stored protected from light.

The other thing that struck me as surprising was that @Archeopteryx got a precipitate with caffeine. Caffeine and purines in general are known to react poorly or not at all with Dragendorff (which is why other spray reagents are used to make them visible in thin layer chromatography). More detailed information (salt used, amount) would be of interest here. I performed the reaction with caffeine and quinine here:

5 ml of distilled water were used in each case and 0.5 ml of DR were added each time (prepared according to the instructions given in this thread). On the far left the blank sample with only water. In the middle, a spatula tip of dissolved caffeine citrate + 0.5 ml of 1N HCl was added. On the right a very small spatula tip of quinine + 0.5 ml of 1N HCl had been added.

As you can see, it arises with caffeine no precipitate while quinine forms a strong orange precipitate. If you want to try the very sensitive detection of quinine, you can use tonic water for it.

About my experiments with DR, I allow myself to refer again to VC - there I described the use of a DR with acetic acid (according to the European Pharmacopoeia):

"Everything should be made as simple as possible. But not easier." (A. Einstein 1871-1955)

"If you only understand chemistry, you don't really understand it either!" (G.C. Lichtenberg, 1742 - 1799)

"The most dangerous worldview is the worldview of the people who have never seen the world." (Alexander v. Humboldt, 1769 - 1859)


Description Primary, secondary and tertiary alcohols

Primary, secondary and tertiary alcohols

Alcohols - Definition

Alcohols are not aromatic Hydrocarbons with one or more Hydroxyl groups (OH groups).

Alcohols - Examples
Methanol, Ethanol, Propanol and Butanol are examples of alcohols, the number of carbon atoms increasing in the list.

Classification - alcohols

Valence of alcohols
Alcohols can be in monohydric or polyhydric alcohols to be grouped. This happens according to the number of OH groups. Alcohols with one OH group are referred to as monohydric and alcohols with at least two OH groups as polyhydric. Dihydric alcohols are called Diols and trivalent as Triplet designated. Alcohols with four or more OH groups are considered Polyols designated.

Number of non-hydrogen neighbors
In addition, alcohols can be differentiated according to the number of non-hydrogen neighbors of the carbon atom on which the OH group is located. One divides into primary, secondary and tertiary alcohols a. Structure - alcohols

Why is there a distinction between primary, secondary and tertiary alcohols?
Example:
In propanol, the OH group can either be on the first carbon atom or on the second carbon atom. To differentiate, the first case is propan-1-ol (1-propanol) and the second case propan-2-ol (2-propanol). It's about Isomerswhose physical properties differ slightly and can be called primary and secondary alcohols.

Primary alcohols - definition

What is primary alcohol?
A primary alcohol is an alcohol in which the OH group is on a primary carbon atom. A primary carbon atom is a carbon atom that is only connected to one other carbon atom.
Primary alcohol - example: 1-propanol

Secondary alcohols - definition

What is secondary alcohol?
at secondary alcohols the carbon atom on which the OH group is located is linked to two carbon atoms.
Secondary alcohol - example: 2-propanol

Tertiary alcohols - definition

What is tertiary alcohol?
at tertiary alcohols the C atom that carries the OH group is bonded to three other carbon atoms.
Tertiary alcohol - example: tert-butanol

Primary, secondary and tertiary alcohols - properties and reactions

  • the Acid starch has the following sequence for alcohols:
    Methanol & gt primary & gt secondary & gt tertiary
  • the Basicity however, has the following order:
    Methanol & lt primary & lt secondary & lt tertiary
  • The more an alcohol is, the more acidic it is Hydrogen atoms sit on the carbon atom on which the OH group is located. The more an alcohol is, the more basic it is Carbon atoms sit on the carbon atom on which the OH group is located.
  • Oxidation of alcohols:
    A primary alcohol becomes one through oxidation aldehyde. For example, the aldehyde becomes ethanal from ethanol with elimination of water. A secondary alcohol becomes one through oxidation Ketone. Tertiary alcohols, on the other hand, cannot be oxidized under mild conditions.

Primary, Secondary and Tertiary Alcohols - Detection

One method for the analytical differentiation of alcohols is the so-called Lucas sample. A solution of concentrated hydrochloric acid and zinc chloride is added to the alcohol, with three possible observations:
1. Immediate milky cloudiness
2. Milky cloudiness after about 5 minutes
3. Milky cloudiness only after warming
During the test, the alcoholic group is exchanged for a chlorine atom. The chloroalkane is less soluble in water than the alcohol, which is why it becomes cloudy. The rate of reaction is in good agreement with the basicity of the alcohol:
tertiary & gt secondary & gt primary & gt methanol

This video

In this video we want to divide the alcohols into primary, secondary and tertiary. The position of the hydroxyl group in the alcohol molecule serves as a distinguishing feature. It is also important whether the carbon chain is straight or branched. We get to know the different reaction behavior of the different alcohols - be it the reaction with an alkali metal, the splitting off of water or a mild oxidation. Finally, let's look at a popular evidence. Have fun!


Determination of the "Ziegler activity" of organoaluminum compounds with physical indexing

The application of a titration method with thermometric indexing to determining the content of organoaluminum compounds with an automatic self-registering apparatus is described. The formation of molecular compounds with ethers and tertiary amines as well as solvolysis with alcohols are suitable as titration reactions. With certain titrants it is possible to determine several substances in one step. When using primary alcohols, a simple relative method, independent of the weight and titer, results from the separate recording of the first and second alcoholysis level.

The slope of the titration curve at the beginning of the addition of the titrant is a measure of the magnitude of the exothermicity of the reaction and was used to determine it. The method is self-normalizing with regard to the concentration, so that the two highly air-sensitive substances, unavoidable inactive impurities, cannot falsify the result. As an example, the enthalpy changes in the formation of the triethylamine of some aluminum alkyl compounds were determined.


Table of contents

Chlorination is one of the oldest known substitution reactions in chemistry. The French chemist Jean-Baptiste Dumas investigated the substitution of hydrogen by chlorine in the effects of chlorine on candle wax and acetic acid as early as 1830. [1] He demonstrated that for every mole of chlorine introduced into a hydrocarbon, one mole of hydrogen chloride was formed, and he noticed the photosensitivity of this reaction. [2]

Theodor Grotthuss wrote the first work on the influence of light on the speed of chemical reactions. As early as 1819 Grotthuss published a treatise on the chemical effectiveness of light and formulated the law of photochemical absorption. As a result, only that fraction of the incident radiation causes an effect in a physico-chemical system that is absorbed by this system, reflected and transmitted radiation has no effect. [3]

Through the work of Max Planck published in 1900 it was known that light consists of discrete quanta. [4] This could explain the excitation of a single chemical reaction by a light quantum, but not the quantum yield of reactions such as photochlorination. The idea that these reactions could be chain reactions originated from Max Bodenstein in 1913. He assumed that when two molecules react, not only the end product of the reaction can arise, but also unstable, reactive intermediates, the can continue a chain. [5]

Because of the importance of the reaction in understanding chemistry, substitution patterns, and the resulting derivatives, chemists have studied the reaction in depth. However, photochlorination could only be transferred to chemical-industrial practice when, towards the end of the nineteenth century, cheap chlorine was available from chlor-alkali electrolysis. [6]

Chlorinated alkanes were first used in throat sprays. Around 1914 to 1918, these contained relatively large amounts of chlorinated alkanes as solvents for chloramine T. In 1929, Sharpless Solvents Corporation commissioned the first industrial photochlorination plant for the chlorination of pentane. [7] The commercial production of chlorinated paraffins for use as high pressure additives in lubricants began around 1930. [8] Around 1935 the process was technically stable and commercially successful. [7]

But it wasn't until the years after World War II that a major build-up of photochlorination capacity began. By 1950 the United States was producing over 800,000 tons of chlorinated paraffinic hydrocarbons. The main products were ethyl chloride, carbon tetrachloride and methylene chloride. [9] Because of concerns about health and environmental problems such as the ozone depletion behavior of volatile chlorine compounds, the chemical industry developed alternative processes that managed without chlorinated compounds. As a result of the replacement of chlorinated products with non-chlorinated ones, the global production volume fell considerably over the years. [8] [10]

Since only absorbed light triggers a photochemical primary reaction, one of the reaction partners has to absorb this light in every photochemical reaction. In the case of photochlorination, the chlorine is the absorbing reactant. Chlorine absorbs light in a wavelength range of around 250 to 450 nanometers, corresponding to absorption in the long-wave ultraviolet and in the visible violet spectral range. [11] For the homolytic splitting of chlorine, an energy of 244 kilojoules per mole is necessary. [12]

According to the photochemical equivalence law, every absorbed photon causes a primary photochemical reaction. [13]

Inserting the values ​​results in a value for the wavelength of 491 nanometers, which the incident light may have at most in order to cause chlorine to split. The absorption maximum of chlorine is around 340 nanometers. [14] Light of this wavelength radiates an energy of about 377 kilojoules per mole and is therefore more than sufficient for photolysis of the chlorine.

For photochemical processes it is important how the number of converted molecules relates to the number of absorbed light quanta. This ratio is called the quantum yield (QA) at a certain wavelength of light. The ratio of converted molecules of the light-absorbing substance N n (λ) < displaystyle N_( lambda)> to the number of absorbed photons N ν < displaystyle N _ < nu >> is calculated as:

The quantum yield should not exceed the value 1 in the photochemical primary process, the absorption of the light quantum. In the case of photochlorination, however, this ratio is not equal to or less than 1, but is often considerably greater because of the secondary processes in which the same substances are formed as in the primary photochemical process. [14]

Substitution reaction edit

The substitution of hydrogen atoms in a hydrocarbon is purely statistical, with tertiary hydrogen atoms reacting faster than secondary ones and these react faster than primary ones. At a temperature of 30 ° C, the relative reaction rates of primary, secondary and tertiary hydrogen atoms are roughly 1 to 3.25 to 4.43. [14] A rearrangement of the carbon skeleton does not take place, but all possible monochlorides are always formed. [15]

When exposed to light, the reaction takes place with the participation of alkyl and chlorine radicals as chain carriers according to the following scheme:

C l 2 → h ν C l ⋅ + ⋅ C l (K e t t e n s t a r t) < displaystyle mathrm < xrightarrow > Cl < cdot> + < cdot> Cl quad (chain start)>> C l ⋅ + R H ⟶ ⋅ R + H C l (K e t t e n f o r t p f l a n z u n g) < displaystyle mathrm + RH longrightarrow < cdot> R + HCl quad (chain propagation)>> R ⋅ + C l 2 ⟶ ⋅ C l + R C l (K e t t e n f o r t p f l a n z u n g) < displaystyle mathrm + Cl_ <2> longrightarrow < cdot> Cl + RCl quad (chain propagation)>> C l ⋅ + ⋅ R ⟶ R C l (K e t t e n a b b r u c h) < displaystyle mathrm + < cdot> R longrightarrow RCl quad (chain termination)>> C l ⋅ + ⋅ C l ⟶ C l 2 (K e t t e n a b b r u c h) < displaystyle mathrm + < cdot> Cl longrightarrow Cl_ <2> quad (chain termination)>>

The chain is terminated by the recombination of chlorine radicals to form molecular chlorine on the vessel wall. [16] Impurities such as oxygen, which is found in electrochemically obtained chlorine, also cause chain termination.

With photochlorination there is no rearrangement of the carbon chain and all possible monochlorides and multiply chlorinated compounds are formed. [15] However, the target products of photochlorination are mostly the monosubstituted chlorinated hydrocarbons. The formation of multiply substituted products can be reduced within limits by working with a large excess of hydrocarbons or by diluting the chlorine with nitrogen.

The selectivity of photochlorination with regard to a substitution of primary, secondary or tertiary hydrogen atoms can be determined by the interaction of the chlorine radical with the solvent, such as benzene, tert-Butylbenzene or carbon disulfide, can be controlled. [17] The formation of a complex from benzene and the chlorine radical reduces the reactivity towards a free chlorine radical, which increases the selectivity of the photochlorination. [18] The range of the ratio of substituted primary to secondary hydrogen atoms obtained by the choice of solvent is from 1: 3 to 1: 31. [19] At higher temperatures, the reaction rates of primary, secondary, and tertiary hydrogen atoms become the same. Therefore, the photochlorination is usually carried out at lower temperatures. [15]

Addition reaction edit

The addition of chlorine to benzene also takes place as a radical chain reaction: [20]

C l 2 → h ν C l ⋅ + ⋅ C l (K e t t e n s t a r t) < displaystyle mathrm < xrightarrow > Cl < cdot> + < cdot> Cl quad (chain start)>> C l ⋅ + C 6 H 6 ⟶ ⋅ C 6 H 6 C l (K e t t e n f o r t p f l a n z u n g) < displaystyle mathrm + C_ <6> H_ <6> longrightarrow < cdot> C_ <6> H_ <6> Cl quad (chain propagation)>> ⋅ C 6 H 6 C l + C l 2 ⟶ ⋅ C l + C 6 H 6 C l 2 (chain propagation) < displaystyle mathrm << cdot> C_ <6> H_ <6> Cl + Cl_ <2> longrightarrow < cdot> Cl + C_ <6> H_ <6> Cl_ < 2> quad (chain propagation)>> […] ⋅ C 6 H 6 C l 5 + C l 2 ⟶ ⋅ C l + C 6 H 6 C l 6 (chain propagation) < displaystyle mathrm << cdot> C_ <6> H_ <6> Cl_ <5> + Cl_ <2> longrightarrow < cdot> Cl + C_ <6> H_ <6> Cl_ <6> quad (chain propagation)>> C l ⋅ + ⋅ C l ⟶ C l 2 (chain termination) < displaystyle mathrm + < cdot> Cl longrightarrow Cl_ <2> quad (chain termination)>>

The reaction is carried out at a temperature of 15 to 20 ° C. When the conversion is from 12 to 15%, the reaction is terminated and the reaction mixture is worked up. [20]

The starting materials (reactants) for photochlorination can be either gaseous or liquid hydrocarbons. In the case of liquid starting materials, chlorine is introduced with stirring. Pure gas reactions, such as the photochlorination of methane, are in principle possible; the temperature rise in a gas phase reaction must largely be absorbed by the specific heat capacities of the gases involved, which limits the conversion. [21] In general, it is necessary to bring the reactants close to the light source in order to obtain the highest possible light yield. For this purpose, the reaction mixture can be irradiated with a suitable light source directly or in a side arm of a reactor through which there is flow. Gaseous hydrocarbons are introduced into an inert solvent and made to react there under irradiation with chlorine. [22]

A disadvantage of photochemical processes is the low efficiency of converting electrical energy into radiant energy of the required wavelength. In addition to radiation, light sources generate a lot of heat, which in turn requires cooling. In addition, most light sources emit polychromatic light, although only monochromatic light is required. [23] However, a high quantum yield offsets these disadvantages. The quantum yield for the photochlorination of the n-Heptane is, for example, about 7000. [24] In technical systems for photochlorination, the quantum yield is about 100. In contrast to thermal chlorination, which can use the heat generated by the reaction, the photochemical method of operation requires constant supply of energy to maintain the reaction. [22]

The presence of inhibitors such as oxygen or nitrogen oxides must be avoided. Excessive chlorine concentrations lead to excessive absorption in the vicinity of the light source and have a detrimental effect. [19] Working at low temperatures is advantageous because side reactions are avoided, since the selectivity is increased, and since gaseous reactants are less expelled from a solvent, which increases the yield. Before the reaction, some of the starting materials can be cooled to such an extent that the heat of reaction is absorbed without further cooling of the mixture. In the case of gaseous or low-boiling starting materials, it is necessary to work under pressure. Due to the large number of possible raw materials, a large number of processes have been described. [25] [26] The photochlorination is usually carried out in a stirred tank reactor, a bubble column reactor or a tubular reactor, which, depending on the target product, are followed by further processing stages. In the case of the stirred tank reactor, the lamp, which is usually shaped as an elongated cylinder, is provided with a cooling jacket and immersed in the reaction solution. Tube reactors are quartz or glass tubes that are irradiated from the outside. The stirred tank variant has the advantage that no light is lost to the environment. However, the light intensity drops rapidly with distance from the light source due to adsorption by the reactants. [22]

The influence of the radiation on the reaction speed can often be determined by a power law based on the quantum current density, i.e. the moles of light quanta (earlier in the unit Einstein measured) per area and time. One goal when designing reactors is therefore to determine the most economically advantageous dimensioning in terms of optimizing the quantum current density. [28]

Chlorinated products can be converted into further intermediate and end products via a variety of reactions, for example by hydrolysis into alcohols or by reaction with alkali metal cyanides into nitriles, which can be hydrolyzed with water to carboxylic acids or reduced with hydrogen to amines. By conversion with metallic magnesium in Grignard reactions, carbon skeletons can be built up via the intermediate stage of alkyl magnesium halides. [29] In Friedel-Crafts alkylations, chloroalkanes are used to prepare alkyl aromatics. [30]

Chlorinated paraffins edit

Chlorinated paraffins can be produced from alkanes by photochlorination. Compared to thermal chlorination, the risk of the formation of secondary products through thermolysis, for example through the splitting off of hydrogen chloride, is very low. Due to the radical course of the reaction, the selectivity is low and mixtures of several chlorinated paraffins with a complex composition are formed. The degree of chlorination varies, and the exact composition of the resulting product mixtures is often not known. The world annual production was 300,000 tons in 1985 since then the production volumes in Europe and North America are declining. In China, on the other hand, production rose sharply. In 2007, China produced over 600,000 tons of chlorinated paraffins, in 2004 the amount was still below 100,000 tons. [32]

The chlorinated paraffins have the general formula CxH(2xy+2)Cly and are divided into three groups. The low molecular weight chlorinated paraffins are the short-chain chlorinated paraffins (Short chain chloroparaffins (SCCP)) with 10 to 13 carbon atoms, followed by the medium-chain chlorinated paraffins (Medium chain chloroparaffins (MCCP)) with carbon chain lengths of 14 to 17 carbon atoms and the long-chain chlorinated paraffins (Long chain chloroparaffins (LCCP)), where the carbon chain length is greater than 17 carbon atoms. About 70% of the chlorinated paraffins produced are MCCPs with a degree of chlorination of 45 to 52%. The remaining 30% are divided equally between SCCP and LCCP. [8th]

the Short chain chloroparaffins are highly toxic and easily accumulate in the environment. The European Union has classified the SCCP as a category III carcinogen and has restricted its use. [33]

Benzyl Chloride, Benzal Chloride, and Benzotrichloride Edit

The photochlorination of the side chain of toluene enables the production of mono- to trichlorinated products, the most important representative of which is benzyl chloride. Converted into benzyl alcohol, it serves as an intermediate product in the manufacture of plasticizers. By converting it into benzyl cyanide with subsequent hydrolysis, phenylacetic acid is finally obtained. [34] [35]

The disubstituted benzal chloride is the raw material for the production of benzaldehyde. Benzaldehyde is used as a pure substance to give foods an almond odor. [36] As an intermediate product, it is used in the production of malachite green and other dyes. [37] The trisubstituted benzotrichloride is hydrolyzed to synthesize benzoyl chloride: [38]

Benzoyl chloride can be converted into the corresponding esters by reaction with alcohols. With sodium peroxide, it reacts to form benzoyl peroxide, a radical initiator for polymerizations. However, the atom economy of these syntheses is low, since stoichiometric amounts of salts are obtained.

Chloromethane edit

An example of photochlorination at low temperatures and under normal pressure is the chlorination of methyl chloride to methylene chloride. The liquefied methyl chloride, which boils at −24 ° C, is mixed with chlorine in the dark and then irradiated with a mercury vapor lamp. The resulting methylene chloride has a boiling point of 41 ° C and is later separated from the methyl chloride by distillation. [39]

The photochlorination of methane has a lower quantum yield than the chlorination of methylene chloride. The resulting high use of light results in direct further chlorination of the intermediate products, so that mainly carbon tetrachloride is formed. [39]

Monochlorononane and dodecane edit

Monochlorononane reacts in a Friedel-Crafts alkylation with phenol to form nonylphenol and can be further converted to nonylphenol ethoxylates by ethoxylation. These nonionic surfactants are used as emulsifiers and as detergents and cleaning agents. Due to their xenoestrogenic properties, the use of nonylphenol ethoxylates and nonylphenols has been severely restricted in the EU. [40]

Another target product is monochlorododecane, which also reacts with benzene in a Friedel-Crafts alkylation to form a detergent raw material, linear alkylbenzene, which is further processed into sodium dodecylbenzenesulfonate. When dodecane is photochlorinated, the formation of undesired 1-isomers can be suppressed by choosing a suitable solvent such as benzene. [18] In the meantime, the production of alkylbenzene usually takes place via the hydrogen fluoride-catalyzed reaction of 1-dodecene with benzene. [41]

Chlorinated Polymers Edit

Polyethylene, dissolved in carbon tetrachloride, can be converted photochemically in a polymer-analogous reaction into a chlorinated polyolefin, which is used as an impact modifier to improve the notched impact strength of polyvinyl chloride. Polyvinyl chloride films can be further chlorinated at room temperature by photochlorination. The non-chlorinated methylene groups of the polymer are chlorinated. The quantum yield in reactions between polymers in the solid phase and chlorine is typically in the region of 1, since a chain reaction is not possible or only possible to a limited extent in this case. [42]

Polyolefin membranes made from polyethylene, polypropylene and polystyrene films can be chlorinated in the solid phase by photochlorination to form membranes with a chlorine content of up to 12%. This improves gas permeation, wettability and water permeability. [43]

Hexachlorocyclohexane edit

In the photochlorination of benzene, of the eight possible isomers, the four α-, β-, γ-, δ-hexachlorocyclohexane isomers are formed on a larger scale. These are all in a chair conformation and differ in the occupation of axial and equatorial positions in the molecule. Only the γ-isomer, which contains three chlorine atoms in the axial and three in the equatorial position and is produced in concentrations of 10 to 18%, shows an insecticidal effect. [20] It is separated from the other isomers by extraction processes, which are further processed to trichlorobenzene by dehydrochlorination. The technically pure γ-isomer is still used as an insecticide outside the EU under trade names such as lindane and gammexane. [20]

Other products edit

By photochlorination of ethylene carbonate, vinylene carbonate can be converted into monochloroethylene carbonate with subsequent dehydrochlorination, for example with triethylamine (NEt3), to win. Vinylene carbonate is a reactive monomer for homopolymerization and copolymerization, for example with isobutyl vinyl ether. [44]

Small traces of trichlorosilane in ultra-pure tetrachlorosilane can be removed by photochlorination. [27]

Utilization of Hydrogen Chloride Processing

Hydrogen chloride can be used for further chlorination, for example by the addition reaction of hydrogen chloride onto an olefinic double bond, by esterification of alcohols or by oxychlorination of alkanes and olefins. The hydrogen chloride formed during the photochlorination of methane can be selectively converted to methyl chloride, for example by esterification with methanol. [45] At elevated temperatures, catalysis also produces methylene chloride.

Radiation Chemical Chlorination Edit

Instead of ultraviolet light, gamma radiation is also used to start radical chains in chlorination. The chemical combine Bitterfeld carried out the dry post-chlorination of PVC in the fluidized bed, the so-called PC chlorination, using radiation chemistry. [46] The long-lived isotope cobalt-60 was used as a source of gamma radiation. [47]

Sulfochlorination Edit

The sulfochlorination first described by Cortes F. Reed in 1936 takes place under almost identical conditions and the same reaction procedure as conventional photochlorination. [48] ​​In addition to chlorine, sulfur dioxide is also introduced into the reaction mixture. The products are alkylsulfonyl chlorides that are processed into surfactants. [49]

As with photochlorination, hydrogen chloride is produced as a by-product. Since a direct sulfonation of the alkanes is hardly possible, this reaction has proven to be useful. Due to the chlorine bound directly to the sulfur, the resulting products are extremely reactive. The by-products in the reaction mixture are alkyl chlorides, which are formed by pure photochlorination, as well as multiple sulfochlorinated products. [50]

Photobromination edit

The photobromination with elemental bromine also proceeds according to a radical mechanism analogous to photochlorination. In the presence of oxygen, some of the hydrogen bromide formed is oxidized to bromine, which leads to an increased yield. [51] Because the elemental bromine is easier to dose and the higher selectivity of the reaction, photobromination is preferred to photochlorination for work on a laboratory scale. For industrial applications, however, bromine, which is only contained in small quantities in seawater and released from it by oxidation with chlorine, is usually too expensive. [52] [53] Instead of elemental bromine is also suitable N-Bromosuccinimide as a brominating agent. [54] The quantum yield of photobromination is usually much lower than that of photochlorination.


Table of contents

CO2 was one of the first gases to be given a name. The Flemish chemist Johan Baptista van Helmont (1580–1644) observed that the mass of charcoal decreased during combustion because the mass of the remaining ash was less than that of the charcoal used. His interpretation was that the rest of the charcoal had turned into an invisible substance that he gas or Alcohol sylvestre ("Forest Spirit") called. [19]

The Scottish physician Joseph Black (1728–1799) studied the properties of CO2 more thorough. In 1754 he found out that adding acids to calcium carbonate solutions releases a gas, which he does fixed air ("Fixed / fixed air") called. [20] He realized that this was heavier than air and did not support combustion processes. When this gas was introduced into a solution of calcium hydroxide, it was able to generate a precipitate. With this phenomenon he showed that carbon dioxide occurs in the breath of mammals and is released through microbiological fermentation. His work proved that gases can be involved in chemical reactions and contributed to the case of the phlogiston theory. [21]

Joseph Priestley succeeded in producing soda water for the first time in 1772 by adding sulfuric acid to a calcareous solution and dissolving the resulting carbon dioxide in a beaker of water. [22] William Brownrigg had recognized the connection between carbon dioxide and carbonic acid earlier. In 1823, Humphry Davy and Michael Faraday liquefied carbon dioxide by increasing the pressure. [23] Henry Hill Hickman operated animals from 1820, which was achieved painlessly after inhaling carbon dioxide to achieve anesthesia. He also described the physiological processes during anesthesia. [24] The first description of solid carbon dioxide comes from Adrien Thilorier, who opened a pressurized container with liquid carbon dioxide in 1834 and found that the spontaneous evaporation takes place with cooling, which leads to solid CO2 leads. [25]

Carbon dioxide is found in the atmosphere, the hydrosphere, the lithosphere, and the biosphere. The carbon exchange between these earth spheres takes place largely through carbon dioxide. Around 2015 there were around 830 gigatons (830 billion tons) of carbon in the atmosphere in the form of carbon dioxide. [26] The hydrosphere contains around 38,000 gigatons of carbon in the form of physically dissolved carbon dioxide as well as dissolved hydrogen carbonates and carbonates. The lithosphere contains by far the largest proportion of chemically bound carbon dioxide. Carbonate rocks such as calcite and dolomite contain around 60,000,000 gigatons of carbon. [27] In addition, large amounts of carbon are stored in permafrost areas such as the tundras of the Arctic and Antarctic polar regions, in boreal coniferous forests or high mountains and in moors. [28] [29] [30]

Occurrence in the atmosphere and man-made climate change

Carbon dioxide is a naturally occurring trace gas in the earth's atmosphere that has an impact on the climate, but its concentration increases, in particular due to the burning of fossil fuels. Ice core data indicated that the atmospheric CO2Values ​​in the past 420,000 years up to the beginning of industrialization in the middle of the 18th century fluctuated between 190 ppm during the height of the ice ages and 280 ppm during the warm periods. [31]

With industrialization, human activities led to a sharp increase in the amount of carbon dioxide in the atmosphere, which continues. Between 1750 and 1958 (the beginning of systematic measurements by Charles David Keeling) the CO rose2-Value initially moderate to 315 ppm, and then increased to 401 ppm by 2015. [32] The concentration exceeded the threshold of 400 ppm (0.04% by volume of the total gas envelope of the earth) on May 9, 2013 in the local daily mean, as measured by the National Agency for Ocean and Atmospheric Research (NOAA) of the United States on the Mauna Loa (Hawaii). [33] The monthly, global mean value measured by NOAA first exceeded the 400 ppm limit in March 2015, [34] in February 2018 this value was 408 ppm (provisional status, as the data from the previous year was still being checked will). [35] Finally, the data for 2017 show a new record high of 405.5 ppm, which is 46 percent above the pre-industrial value. [36] In 2018, a new record high was reached again at 407.8 ppm. [16] The main sources are the burning of fossil fuels for energy production and in the industrial sector. The release of carbon dioxide stored in soils and forests through changes in land use, for example through clearing of forests, also contributes to the increase to a much lesser extent. In 2014, energy use and industrial use of fossil fuels as well as land use accounted for 70% and 5%, respectively, of total man-made greenhouse gas emissions (measured in carbon dioxide equivalents). [37]

The total mass of carbon dioxide in the atmosphere is around 3000 gigatons or around 800 Gt carbon (the ratio of the molar masses of CO2 to C is rounded 44:12). The concentration varies seasonally and locally, especially near the ground. In urban areas the concentration is generally higher, in closed rooms the concentration can be up to ten times the average value. [38]

Carbon dioxide absorbs part of the thermal radiation (infrared radiation), while the shorter-wave part of the solar radiation can pass through almost unhindered. An absorbent body also emits according to its temperature. These properties make carbon dioxide a so-called greenhouse gas. After water vapor, carbon dioxide is the second most effective of the greenhouse gases in terms of its proportion, although the specific effectiveness of methane and ozone are higher. All greenhouse gases together increase the mean temperature on the earth's surface from around −18 ° C to +15 ° C due to the natural greenhouse effect. Carbon dioxide has a relatively large share in the overall effect and thus contributes to the earth-friendly climate. [39]

The proportion of carbon dioxide in the earth's atmosphere has been subject to considerable fluctuations over the course of the earth's history, which have various biological, chemical and physical causes. 500 million years ago, the concentration of carbon dioxide was at least ten times higher than it is today. [40] As a result, the CO2-Concentration steadily decreased and was around 300 million years ago during the Permocarbonic Ice Age, at the transition from the Carboniferous to the Permian, averaged around 300 ppm [41] and fell briefly in the early Permian to a low of probably 100 ppm [42] during the Mesozoic moved the CO2-Level mostly between 1,000 and 2,000 ppm, in order to fall well below 1,000 ppm in the Modern Earth Age, after a climatic optimum in the early Eocene, [43] up to the beginning of the Cenozoic Ice Age about 34 million years ago. [44]

For at least 800,000 years, the carbon dioxide content has always been below 300 ppm. [45] [46] The carbon dioxide concentration in the last 10,000 years has remained relatively constant at 300 ppm. The balance of the carbon dioxide cycle was thus balanced during this time. With the beginning of industrialization in the 19th century, the amount of carbon dioxide in the atmosphere increased. The current concentration is likely the highest in 15 to 20 million years. [47] In the period from 1960 to 2005, the carbon dioxide content rose by an average of 1.4 ppm per year. [48] ​​In 2017, the 10-year average increase was a good 2 ppm per year. [49]

The anthropogenic, i.e. man-made carbon dioxide emissions amount to around 36.3 gigatons annually [48] and are only a small proportion of the carbon dioxide, which comes mainly from natural sources, of around 550 gigatons annually. [50] However, since the natural carbon sinks have the same amount of CO2 resume, the carbon dioxide concentration remained relatively constant before industrialization. About half of the additional carbon dioxide is absorbed by the biosphere and the oceans (this leads to their acidification), so that these now absorb more carbon dioxide than they give off. [51] As a result, since 1982 there has been a "greening" of the earth (Leaf Area Index), as has been proven by satellite data from NASA. [52] However, more recent data suggest that this greening, which was observed until the late 20th century, then stopped and, as a result of a larger saturation deficit (more drought), an opposing trend developed, ie. H. the earth is currently losing vegetation. [53] The other half of the carbon dioxide emitted remains in the atmosphere, where it leads to a measurable increase in concentration, which Charles Keeling was able to demonstrate for the first time in the early 1960s with the Keeling curve named after him.

It is widely recognized scientifically that there is a statistically significant human impact on climate that is the primary cause of global warming. This warming is most likely largely due to the anthropogenic amplification of the natural greenhouse effect through the emission of greenhouse gases. [54] The additionally produced carbon dioxide has a share of about 60% in the intensification of the greenhouse effect. [55] [56]

Luxembourg, Belgium and Switzerland have the highest CO per capita2-Footprint across Europe. [57] The consequences of global warming should be reduced through climate protection.

Occurrence in oceans

The water of the oceans contains carbon dioxide in dissolved form and as carbonic acid in equilibrium with hydrogen carbonates and carbonates. The amount dissolved changes with the season, as it depends on the temperature and salinity of the water: Cold water dissolves more carbon dioxide. Since cold water has a higher density, the carbon dioxide-rich water sinks into deeper layers. Only at pressures above 300 bar and temperatures above 120 ° C (393 K) is it the other way round, for example in the vicinity of deep geothermal vents. [58]

The oceans contain about 50 times as much carbon as the atmosphere. The ocean acts as a large carbon dioxide sink and absorbs around a third of the amount of carbon dioxide released by human activities. [59] In the upper layers of the oceans, it is partially bound by photosynthesis. As the solution of carbon dioxide increases, the alkalinity of the salt water decreases, which is known as acidification of the oceans and is very likely to have negative consequences for the ecosystems of the oceans. Many sea creatures are sensitive to fluctuations in the acidity of the oceans. Acidification events in the history of the earth have led to mass extinctions and a sharp decline in biodiversity in the world's oceans. Organisms that build up calcium carbonate structures are particularly affected, as this dissolves as the acidity of the oceans increases. Corals, mussels and echinoderms such as starfish and sea urchins are particularly vulnerable. [60]

Among other things, it is feared that this will have a negative effect on the formation of mussel shells, among other things. [61] [62] These effects are already visible in coral reefs and certain oyster farms. Increasing acidification is expected to have greater ecological consequences. [60] On the other hand, there are indications that an increased carbon dioxide concentration stimulates some species to increase the production of mussel shells. [63]

Occurrence in fresh water

Aerobic bacteria and animals living in the (under) water consume oxygen and CO2 exhaled. If there is sufficient contact with the atmosphere, this gas can be released into the air and oxygen can be absorbed at the same time. A surface that freely adjoins the air and is free of ice or oil is beneficial, as are wave movements, turbulence with air, i.e. the formation of foam and spray, water currents that also include deeper layers and wind. Without sufficient gas exchange, a body of water can also be oxygen-poor and CO2-become rich. They say "it tips over".

Due to special geological conditions, fresh water can be loaded with considerable amounts of carbon dioxide from volcanic sources, such as water from mineral springs or in lakes on extinct volcanoes, so-called maars. Under the pressure of great water depth, CO2 be dissolved in a much higher mass concentration than under atmospheric pressure on the surface of the water. If a lake is not (sufficiently) traversed by water or driven by wind and / or heat convection currents, it becomes more CO2 entered from below, can be transported upwards as mixing and diffusion, then CO is formed2-rich deep water that has the potential to cause catastrophic CO2-Release to the air. A local outgassing once triggered locally under water leads to the rise of a body of water, the relief of hydrostatic pressure that takes place in the process intensifies the outgassing. This self-reinforcing process can lead to the release of large amounts of CO2 that can kill humans and animals near the lake.

One of these natural disasters occurred in 1986 at Lake Nyos in Cameroon.[64] The lake is located in an old volcanic crater in the Oku volcanic area. A magma chamber feeds the lake with carbon dioxide and saturates its water. Probably triggered by a landslide in 1986, large amounts of carbon dioxide were released from the lake, killing around 1,700 residents and 3,500 livestock in the surrounding villages. Another catastrophe occurred in 1984 at Lake Manoun, the water of which is saturated with carbon dioxide by a similar mechanism. 37 people were killed in this carbon dioxide release. The Kiwu Lake in Central Africa also has high concentrations of dissolved gases in its deep water. It is estimated that around 250 km³ of carbon dioxide is dissolved in this lake. [65]

Extraterrestrial occurrence

The atmosphere of Venus consists of 96.5% carbon dioxide, has about 90 times the mass of the earth's atmosphere and a pressure of about 90 bar. The high proportion of carbon dioxide is one of the causes of the strong greenhouse effect. In addition, the distance from the sun is on average 41 million kilometers shorter than the earth, which leads to a surface temperature of around 480 ° C. [66] With a share of 95%, carbon dioxide also makes up the main part of the Martian atmosphere. [67] At the Mars poles, atmospheric carbon dioxide is partially bound as dry ice. Due to the low atmospheric pressure of around seven millibars, the greenhouse effect only leads to an increase of around 5 K, despite the high carbon dioxide content. The atmospheres of the outer planets and their satellites contain carbon dioxide, the origin of which is impacts from comets such as Shoemaker-Levy 9 and cosmic dust is attributed. [68] [69] Using the instruments of the Hubble Space Telescope, NASA found carbon dioxide on extrasolar planets such as HD 189733 b. [70]

Carbon dioxide is found both in interstellar space and in protoplanetary disks around young stars. [71] The formation occurs through surface reactions of carbon monoxide and oxygen on water ice particles at temperatures around −123 ° C (150 K). When the ice evaporates, the carbon dioxide is released. [72] The concentration in free interstellar space is relatively low, as reactions with atomic and molecular hydrogen form water and carbon monoxide. [73]

Carbon dioxide is produced when carbon-containing fuels are burned, especially fossil fuels. Around 36 gigatons (billion tons) of carbon dioxide are produced around the world each year and are released into the atmosphere. Processes to separate the carbon dioxide and to store it in deep rock layers are currently (2016) at the beginning of their development and are not yet ready for series production. Their effectiveness and profitability, especially in sustainable energy systems, are being critically assessed. [74]

Carbon dioxide is produced when carbon reacts with oxygen:

Technically, carbon dioxide is produced when coke is burned with excess air. In coal gasification and the steam reforming of natural gas, carbon dioxide is produced, among other things, as a product of the water-gas shift reaction in synthesis gas production.

For use in ammonia synthesis and in methanol production, for example, the synthesis gas is washed using the Rectisol process, which means that large amounts of carbon dioxide are produced in a very pure form. [76] [77] As a by-product, carbon dioxide is produced when burning lime. Subsequent purification via the formation of potassium carbonate to hydrogen carbonate and subsequent release by heating, around 530 million tons per year are obtained.

In the laboratory, carbon dioxide can be released from calcium carbonate and hydrochloric acid, for example in a Kipp apparatus. The device was previously used in laboratories. The method is rarely used any more, as carbon dioxide is available in gas bottles or as dry ice. [78]

Carbon dioxide is also extracted from the air using the direct air capture (DAC) process.

Physical Properties

At normal pressure below −78.5 ° C, carbon dioxide is present as a solid, known as dry ice. If this is heated, it does not melt, but sublimates, i.e. it changes directly into the gaseous state of aggregation. It therefore has no melting point and no boiling point under these conditions.

The triple point at which the three phases solid, liquid and gaseous are in thermodynamic equilibrium is at a temperature of −56.6 ° C and a pressure of 5.19 bar. [4]

The critical temperature is 31.0 ° C, the critical pressure 73.8 bar and the critical density 0.468 g / cm³. [4] Below the critical temperature, gaseous carbon dioxide can be compressed to a colorless liquid by increasing the pressure. [79] At room temperature, a pressure of around 60 bar is required for this.

Solid carbon dioxide crystallizes in the cubic crystal system in the space group Pa 3 (room group no. 205) Template: room group / 205 with the grid parameter a = 562.4 pm. [80]

Carbon dioxide absorbs electromagnetic radiation mainly in the spectral range of infrared radiation and is stimulated to vibrate molecules. Its effect as a greenhouse gas is based on this property.

The solubility in water is comparatively high. At 20 ° C under normal pressure, the saturation is in equilibrium with the pure carbon dioxide phase at 1688 mg / l. For comparison, the solubility of oxygen or nitrogen is shown below: with a pure oxygen phase, saturation is reached at 44 mg / l and with a pure nitrogen phase at 19 mg / l. [81] Under standard conditions, the density of carbon dioxide is 1.98 kg / m³. [82]

Molecular Properties

The carbon dioxide molecule is linear, all three atoms are in a straight line. The carbon is bound to the two oxygen atoms with double bonds, with both oxygen atoms having two lone pairs of electrons. The carbon-oxygen distance is 116.32 pm. [79] The carbon-oxygen bonds are polarized by the different electronegativities of carbon and oxygen, but the electrical dipole moments cancel each other out due to the molecular symmetry, so that the molecule has no electrical dipole moment. The (bending) vibration mode of the molecule, in which the carbon atom moves perpendicular to the axis and the oxygen atoms in the opposite direction (and vice versa), corresponds to an infrared wavelength of 15 μm. This 15 μm radiation is the main component the effect of carbon dioxide as a greenhouse gas. [83]

Chemical properties

Carbon dioxide is an incombustible, acidic and colorless gas at low concentrations it is odorless, at high concentrations you can perceive a pungent to sour odor, [84] although there are people who have this (similar to hydrocyanic acid, for example) Cannot perceive smell. Carbon dioxide dissolved in water forms carbonic acid (H.2CO3), whereby more than 99% of the carbon dioxide is only physically dissolved, the aqueous solution therefore reacts slightly acidic. The carbonic acid as such and the dissolved carbon dioxide are in equilibrium with their dissociation products (species) hydrogen carbonate (Bicarbonate, HCO3 -) and carbonate (CO3 2−), which are in a proportion to each other depending on the pH value. In water, this equilibrium is predominantly on the side of carbon dioxide and hydrogen carbonate ions are only formed to a small extent. If the oxonium ions (H.3O +) is trapped by adding a lye with hydroxide ions (OH -), so the quantitative ratio shifts in favor of carbonate.

Carbon dioxide is a very weak oxidizing agent. Base metals such as magnesium, which act as strong reducing agents, react with carbon dioxide to form carbon and metal oxides according to: [85]

Due to the positive partial charge on carbon, carbon dioxide reacts as an electrophile in the carboxylation of carbon nucleophiles such as metal alkynylidene or alkyl magnesium compounds to form a carbon-carbon bond. Carbon dioxide reacts with phenolates to form phenol carboxylic acids.

In industry, carbon dioxide is used in a variety of ways. It is inexpensive, non-flammable and is used physically as a compressed gas, in liquid form, solid as dry ice or in supercritical phase. The chemical industry uses carbon dioxide as a raw material for chemical synthesis. This CO2 originates z. B. from fertilizer production, where it is very pure, or from exhaust gases that require downstream cleaning to remove unwanted accompanying substances. [86]

Use in food technology

Carbon dioxide contained in beverages stimulates the taste sensory cells when drinking, which has a refreshing effect. In drinks such as beer or sparkling wine, it is produced through alcoholic fermentation, in others such as lemonade or soda water it is added artificially or natural mineral water containing carbon dioxide is used. During production, carbon dioxide is pumped into the drink under high pressure, around 0.2% of which reacts with water to form carbonic acid, while most of it dissolves as a gas in the water. As a food additive, it bears the designation E 290. [87] In private households, carbon dioxide from pressure cartridges is passed through the drink to be enriched with soda makers.

Baker's yeast develops carbon dioxide through the fermentation of sugar and is used as a leavening agent in the production of yeast dough. Baking powder, a mixture of sodium hydrogen carbonate and an acid salt, releases carbon dioxide when heated and is also used as a leavening agent. [88]

In winemaking, dry ice is used as a coolant to cool freshly picked grapes without diluting them with water, thus avoiding spontaneous fermentation. The winemakers in Beaujolais use carbonic acid maceration to produce the Beaujolais Primeur. [89]

In addition to the temperature, the composition of the atmosphere plays an important role in the storage of fruit and vegetables. In the warehouses of fruit producers and retailers, apples have been stored in controlled atmospheres for many decades. The realization that ripening fruit consumes oxygen and gives off carbon dioxide and that an atmosphere without oxygen brings ripening to a standstill goes back to the early 19th century. In the 1930s, a warehouse was first set up in Great Britain with the ability to regulate the levels of oxygen and carbon dioxide in the air. [90] The economic importance of precisely adapted controlled atmospheres in fruit storage is considerable. By adding carbon dioxide to the atmosphere, the shelf life can be extended by months, thus reducing dependence on imports from warmer regions for part of winter and spring. On the other hand, an improper addition of carbon dioxide can cause defects in the pulp and render an entire inventory or container shipment worthless. [91] The biochemical processes that lead to the delayed maturity have not yet been deciphered. It is currently assumed that both the slowing down of the maturation process and the formation of the various types of damage are controlled by stress reactions at the cellular level. [90]

Fruit, vegetables and mushrooms packaged in foil for the retail trade, [92] unprocessed or cut, are provided with a protective atmosphere in order to extend the shelf life and so as not to lose the impression of freshness on the way to the consumer. Today, meat, fish and seafood, pasta, baked goods and dairy products are also offered in this way. The proportion of carbon dioxide in the protective atmosphere is significantly higher in packaged products that are not intended to be stored for months than in stored fruit and vegetables (1–5%, rarely up to 20%), for which carbon dioxide can cause damage. Typical proportions are 20% carbon dioxide for beef, 50% for veal, pork and pasta, 60% for baked goods and 80% for fish. Packaging under pure carbon dioxide is avoided, however, since it would promote the development of pathogenic, anaerobic germs and in many cases would impair the color and taste of the products. Determining the optimal protective atmosphere for a product is the subject of intensive research in the food industry. [93] [94]

Supercritical carbon dioxide has a high solubility for non-polar substances and can replace toxic organic solvents. It is used as an extraction agent, for example for the extraction of natural substances such as caffeine in the production of decaf Coffee through decaffeination. [95]

Technical use

Because of its oxygen-displacing properties, carbon dioxide is used as an extinguishing agent for fire extinguishing purposes, especially in hand-held fire extinguishers and automatic extinguishing systems. CO2Extinguishing systems flood the entire room with carbon dioxide to protect silos or storage halls for flammable liquids. This led to repeated accidents, some of which resulted in death from suffocation. [96] A study by the US Environmental Protection Agency (EPA) identified 51 accidents between 1975 and 1997 with 72 fatalities and 145 injuries. [97]

As a refrigerant, carbon dioxide is used under the designation R744 in vehicle and stationary air conditioning systems, in industrial refrigeration, supermarket and transport refrigeration and in beverage machines. [98] It has a large volumetric cooling capacity and thus a higher efficiency for a given volume. Carbon dioxide is more environmentally friendly because its global warming potential is only a fraction of that of synthetic refrigerants. In contrast to these, it does not contribute to ozone depletion. Carbon dioxide is also used in air conditioning systems for vehicles. [99] In gas-cooled nuclear reactors of the type AGR, carbon dioxide is used as a coolant.

Carbon dioxide is used as a protective gas in welding technology, either in its pure form or as an additive to argon or helium. At high temperatures it is thermodynamically unstable, which is why it is not called an inert gas, but an active gas. [100]

With the carbon dioxide laser, laser gas, a mixture of nitrogen, helium and carbon dioxide, flows continuously through the discharge tube. In addition to the solid-state lasers, these gas lasers are among the most powerful lasers in industrial use with outputs between 10 watts and 80 kilowatts. The efficiency is around 10 to 20%. [101]

In liquid form, carbon dioxide is traded in pressurized gas cylinders. There are two types: Riser bottles for withdrawing liquids and bottles without risers for withdrawing gaseous carbon dioxide. [102] Both must be vertical for removal. The riser cylinder is always operated without, the other with a pressure reducing valve. As long as there is still liquid carbon dioxide in the pressure bottle, the internal pressure is only dependent on the temperature. A measurement of the fill level is therefore only possible with both types of bottle using a weighing system. The removal speed is limited by the fact that the liquid carbon dioxide has to evaporate again in the bottle due to the absorption of heat from the environment in order to build up the pressure corresponding to the temperature again.

The sublimation of dry ice creates a white mist from the cold carbon dioxide-air mixture and condensing humidity, which serves as a stage effect. There are also fog cooling attachments for evaporator fog machines that run on liquid carbon dioxide. [103]

Increasingly, carbon dioxide is being used in conjunction with an automatable blasting process in order to produce high-purity surfaces. With its combination of mechanical, thermal and chemical properties, carbon dioxide snow, for example, can loosen and remove various types of surface contamination without leaving any residue. [104]

Supercritical carbon dioxide is used as a solvent for cleaning and degreasing, for example wafers in the semiconductor industry and textiles in dry cleaning. [105] Supercritical carbon dioxide is used as a reaction medium for the production of fine chemicals, for example for the production of flavorings, since isolated enzymes often remain active and, in contrast to organic solvents, no solvent residues remain in the products.

In tertiary oil production, supercritical carbon dioxide is used to flood oil reservoirs in order to flush oil to the surface from greater depths. [106]

Heat pipes filled with carbon dioxide are used to provide geothermal heat and are more energy efficient than brine cycles.

Use as a chemical raw material

In the chemical industry, carbon dioxide is used primarily for the production of urea through conversion with ammonia. In the first step, ammonia and carbon dioxide react to form ammonium carbamate, which in the second step further reacts to form urea and water. [107]

Formamide is obtained by reduction with hydrogen. Reaction with amines such as dimethylamine gives dimethylformamide. [108]

By reacting carbon dioxide with sodium phenolate, the Kolbe-Schmitt reaction produces salicylic acid. [109]

Ethylene carbonate is produced by reacting with ethylene oxide. In the OMEGA process, this is converted into monoethylene glycol with water in a highly selective manner.

The reaction of carbon dioxide with a Grignard reagent leads to carboxylic acids, e.g. B .:

The telomerization of carbon dioxide with two molecules of 1,3-butadiene under homogeneous palladium catalysis leads to fine chemicals such as lactones under mild reaction conditions. [107]

In the Solvay process, carbon dioxide is used to produce soda (sodium carbonate). Some metal carbonates such as lead carbonate, which are obtained, for example, by reacting the metal hydroxides with carbon dioxide, are important as pigments.

With a high oil price and low electricity prices for renewable energies, for example from wind power and solar systems, it could be worthwhile in the future to use carbon dioxide for other applications such as methane production in power-to-gas systems (Sabatier process) and methanol production (Power -to-Liquid) with hydrogen from electrolysis. [110] Further potential fields of application would be the production of formic acid and synthesis gases for the production of fuels (power-to-fuel) and chemical raw materials (power-to-chemicals). This can be done via a Fischer-Tropsch synthesis or the direct use together with ethylene oxide or propylene oxide for the production of polyols and polymers such as polyurethanes or polycarbonates. For thermodynamic reasons, however, the use of carbon dioxide is currently mostly uneconomical.

Carbon dioxide recycling

In addition to the separation and storage of carbon dioxide, research is aimed at converting the carbon dioxide that arises from the combustion of fossil fuels into usable compounds and, if possible, back into energy sources. Compounds such as methanol [111] and formic acid can already be produced by reduction. [112]

The synthesis of urea is also possible. A French research team is investigating the organocatalytic conversion to formamide or its derivatives. [113] [114] Since the process energy has to be supplied, these processes are not suitable for the economical production of energy carriers. Scientists at RWTH Aachen University developed a homogeneous catalytic process for the production of methanol from carbon dioxide and hydrogen under pressure with a special ruthenium-phosphine complex in which the catalyst and starting materials are in solution. [115] Likewise, a continuous process for the production of formic acid with an organometallic ruthenium complex was developed in which carbon dioxide plays the dual role of reactant and, in supercritical form, as the extractive phase for the formic acid formed. [116] In another variant developed by a Spanish research group, carbon dioxide can be converted via an iridium-catalyzed hydrosilylation and captured in the form of a silyl formate from which formic acid can be easily separated. This reaction, which could already be carried out on a gram scale, takes place under very mild reaction conditions, is very selective and has a high conversion. [117]

In the “Coal Innovation Center”, RWE and Brain AG are researching how microorganisms CO2 convert. [118]

Other uses

Carbon dioxide was routinely used as an anesthetic in humans, especially in the United States, until the 1950s [119] and was rated as very satisfactory. This method is no longer used in traditional anesthesia for humans, as more effective, inhalable anesthetics have been introduced.

This method is still used today for stunning animals for slaughter. [120] Pigs are let down in groups with an elevator system into a pit, the atmosphere of which contains at least 80% carbon dioxide, and lose consciousness in it. This process is controversial and is subject to intensive efforts to improve animal welfare. [121] [122] [123] Fish are anesthetized by introducing gaseous carbon dioxide or by adding carbonated water. [124] In Germany, stunning slaughter animals with carbon dioxide is only permitted for pigs, turkeys, day-old chicks and salmon fish. [125]

In the context of animal euthanasia, carbon dioxide is used for killing. In Germany, the application is limited to small laboratory animals, also for purposes such as the procurement of feed animals in animal husbandry. [126] However, the legality of such animal killings without prior stunning is questioned. [127] For officially ordered killing of livestock, the club, carbon dioxide may also be used to kill other animals if a special permit is available. [128] The Veterinary Association for Animal Welfare (DVT) describes this method as suitable for poultry. [129]

Carbon dioxide is used as a laxative in suppositories. The reaction of sodium dihydrogen phosphate and sodium hydrogen carbonate during the dissolution of the suppository releases carbon dioxide and stretches the intestine, which in turn triggers the stool reflex. [130]

In carbon dioxide fertilization, it is used as a fertilizer in greenhouses. The reason is the carbon dioxide deficiency caused by photosynthetic consumption when there is insufficient fresh air, especially in winter when the ventilation is closed. The carbon dioxide is introduced either directly as a pure gas or as a combustion product from propane or natural gas. This achieves a coupling of fertilization and heating. The possible increase in yield depends on how strong the lack of carbon dioxide is and how strong the light is available for the plants. [131] Carbon dioxide is used in aquaristics as a fertilizer for aquatic plants (CO2Diffuser). By adding organic matter, the carbon dioxide content in the water can be increased through inhalation at the expense of the oxygen content. [132]

The gas is used to catch blood-sucking insects and vectors that use the carbon dioxide found in the breath to find hosts, such as mosquitoes. It is released from dry ice, from gas cylinders or from the combustion of propane or butane and attracts insects near the intake opening of special traps. [133] The gas is also used in the cultivation of microorganisms, especially for strictly (strictly) anaerobic bacteria that can only grow under anoxic conditions. You can be in a CO2-Incubate the incubator, which is supplied by a gas bottle. In addition to strictly anaerobic bacteria, there are also so-called capnophilic bacteria, which require a proportion of 5–10 percent by volume of carbon dioxide in the surrounding atmosphere to grow. They are often cultivated in a closable anaerobic pot into which a commercially available reagent carrier is placed, the chambers of which are filled with sodium hydrogen carbonate and tartaric acid or citric acid. Moistening - similar to the principle of baking powder - generates CO2 released. [134]

Effect on animals and people

Too high a proportion of carbon dioxide in the air we breathe has harmful effects on animals and humans. These are not only based on the displacement of oxygen in the air. DIN EN 13779 divides the room air into four quality levels depending on the carbon dioxide concentration. At values ​​below 800 ppm, the indoor air quality is considered to be good, values ​​between 800 and 1000 ppm (0.08 to 0.1% by volume) are considered to be medium, and values ​​of 1000 to 1400 ppm are considered to be of moderate quality. At values ​​above 1400 ppm, the indoor air quality is considered to be low. [135] For comparison: the CO is in the global mean2- The proportion of air at around 400 ppm by volume, however, fluctuates strongly regionally, depending on the time of day and the season.

The maximum workplace concentration for a daily exposure of eight hours per day is 5000 ppm. [136] At a concentration of 1.5% (15,000 ppm) the respiratory time volume increases by more than 40%.

Due to the significantly increased CO2-Concentrations and / or lack of ventilation in rooms with comparatively clean ambient air can, according to studies, lead to a strong and avoidable impairment of brain performance - especially in decision-making and complex strategic thinking - in rooms such as classrooms. [137] [138]

Carbon dioxide dissolved in the blood activates the breathing center of the brain in a physiological and slightly increased concentration.

In significantly higher concentrations, it leads to a reduction or elimination of the reflex breathing stimulus, initially to respiratory depression and finally to respiratory arrest. [139] From about 5% carbon dioxide in the inhaled air headaches and dizziness occur, with higher concentrations accelerated heartbeat (tachycardia), rise in blood pressure, shortness of breath and unconsciousness, the so-called carbon dioxide anesthesia. Carbon dioxide concentrations of 8% lead to death within 30 to 60 minutes. [140] [141] An accumulation of carbon dioxide in the blood is called hypercapnia.

Accidents occur again and again in wine cellars, feed silos, wells and cesspools due to high carbon dioxide concentrations. [82] Fermentation processes produce considerable amounts of carbon dioxide there, in the fermentation of one liter of must, for example, around 50 liters of fermentation gas. Often several people fall victim to fermentation gas poisoning because the helpers inhale carbon dioxide themselves during the rescue attempt and become unconscious. Rescuing an injured person from suspected carbon dioxide situations is only possible by professional emergency responders with self-contained breathing apparatus. [142]

If adequate ventilation is not provided, natural carbon dioxide sources in caves and mine tunnels can create high concentrations of the gas. These are then close to the ground, so that smaller animals in particular can suffocate. For example, the dog grotto in Italy has a carbon dioxide concentration of around 70%. [143]

The carbon dioxide concentration in the blood influences its pH value and thus has an indirect effect on the oxygen balance. The carbonic acid-bicarbonate system, a carbonic acid-bicarbonate buffer, represents about 50% of the total buffer capacity of the blood, which is catalyzed by the enzyme carbonic anhydratase. [144]

At a lower pH value, the oxygen-binding capacity of the red blood pigment hemoglobin is reduced. With the same oxygen content in the air, hemoglobin therefore transports less oxygen. The Bohr effect and the Haldane effect describe this fact. [145]

Effect on plants

On plants, a slightly increased carbon dioxide concentration has the effect of carbon dioxide fertilization, since the plants during photosynthesis for the carbon dioxide assimilation CO2 require. However, excessively high concentrations are also harmful to plants. For C3 plants, the optimum is usually between 800 and 1000 ppm, but for C4 plants it is only just over 400 ppm. The C4 plant maize as an indicator plant showed CO at 10,000 ppm2 streaks on their leaves after a six-day exposure period. [146] Changes in the nutritional composition (proteins, micronutrients and vitamins) were found in rice. Protein, iron, zinc, vitamins B1, B2, B5 and B9 take with excessively increasing CO2-Concentration decreases, while vitamin E increases. Such a reduction in the quality of plant foods would exacerbate the global malnutrition problem. [147]

Plants and photosynthetic bacteria absorb carbon dioxide from the atmosphere and convert it into carbohydrates such as glucose through photosynthesis under the action of light and absorption of water.

This process simultaneously releases oxygen from the decomposition of water. The resulting carbohydrates serve as an energy source and building material for all other biochemical substances such as polysaccharides, nucleic acids and proteins. Carbon dioxide thus provides the raw material for the formation of all biomass in the primary production of ecosystems. [149]

The breakdown of biomass through aerobic respiration is, in reverse to the process of photosynthesis, linked to the formation of carbon dioxide and the consumption of oxygen. [150]

All organisms in an ecosystem breathe continuously, while photosynthesis is tied to the availability of light. This leads to a cyclical increase and decrease of carbon dioxide in the daily and seasonal rhythm depending on the different light intensities.

In water bodies, the carbon dioxide concentration also fluctuates according to the daily and seasonal rhythms mentioned. Carbon dioxide is in a chemical equilibrium with the other dissolved carbonic acid species, which essentially determines the pH value in the water. The chemical equilibrium of the dissociations of ammonium / ammonia, nitrite / nitrous acid, sulphide / hydrogen sulphide and other acid-base pairs, which are noticeable through the toxicity for the organisms in the water, depend on the pH value. [152]

If the supply of carbon dioxide in a body of water is exhausted through photosynthesis, which is noticeable by a pH value close to 8.3, some types of algae and aquatic plants are able to obtain the required carbon dioxide from the dissolved hydrogen carbonate, whereby they release hydroxide ions, so that the pH value becomes more and more alkaline. In nutrient-rich waters such as carp ponds, the pH value can then rise to 12, with the corresponding health consequences for the fish, for example carp gill necrosis. [153]

In 2012, scientists from the Biodiversity and Climate Research Center calculated for the first time in a joint study with other institutions that cryptogamous layers of lichen, algae and moss bind around 14 billion tons of carbon dioxide annually in addition to nitrogen. They bind as much carbon dioxide as is released each year by forest fires and the burning of biomass worldwide. Fighting climate change with the help of the cryptogamous layers is not possible, however, because the extensive vegetation stores the greenhouse gas carbon dioxide for only a few years. [154] [155]

The storage and release of carbon dioxide in soils is important. The extent to which the release of soil organic carbon is influenced by the respective environmental conditions and other factors is currently largely unknown. However, the release is accelerated by warming, which has been shown in recent studies, and could have an impact on the climate. [156] A study published in 2019 shows that with a CO2Concentration above 1,200 ppm stratocumulus clouds break up into scattered clouds, which could further fuel global warming. [157]

With the indication of the CO2-Emission, different processes are made energetically and ecologically comparable. For this purpose, the release of carbon dioxide when burning fossil fuels is converted.

A simple detection of carbon dioxide is possible with an aqueous calcium hydroxide solution, the so-called lime water sample. For this purpose, the gas to be examined is introduced into the solution. If the gas contains carbon dioxide, it reacts with calcium hydroxide to form water and calcium carbonate (lime), which precipitates as a whitish solid and makes the solution cloudy.

With barium water, an aqueous barium hydroxide solution, the detection is more sensitive, since barium carbonate is less soluble than calcium carbonate.

In aqueous solution, carbon dioxide is determined by titration with 0.1 N sodium hydroxide solution up to a pH value of 8.3, the color change of the phenolphthalein indicator. The measurement of the acid binding capacity (SBV), the pH value and the electrical conductivity or the ionic strength enables the calculation of the carbon dioxide content from these parameters according to the dissociation equilibrium of the carbonic acid. The Severinghaus electrode, a pH electrode with a buffer solution made from sodium hydrogen carbonate, determines the carbon dioxide concentration of a solution by measuring the change in pH value. [158]

Carbon dioxide can be detected using infrared or Raman spectroscopy, whereby the asymmetrical stretching vibrations and tilting vibrations are infrared-active, while the symmetrical stretching vibrations at a wave number of 1480 cm −1 are Raman-active. [159] The measuring device used for this is called a non-dispersive infrared sensor.


DE102007027306A1 - Use of a bonding agent for fibers, in particular for their introduction into bitumen-containing masses - Google Patents

known in a variety of solutions. This is common to bind the filling fibers in various physical modifications to granular compacts or the so-called pellets.

In addition, the aim was to achieve a coarse distribution of the filler fibers in a flowable bitumen right from the start by adding the filler fibers in granulated form. The subsequent fine distribution should then take place through the granules that dissolve in the flowable bitumen. After the apprenticeship of

In addition, the aim was also to achieve a coarse distribution of the filling fibers in a flowable bitumen from the beginning by adding the filling fibers in granulated form. The subsequent fine distribution should then take place through the dissolving in the flowable bitumen granules.

the bitumen or asphalt or the road surface is mixed with a proportion of paraffin obtained by Fischer-Tropsch synthesis (FT paraffin) and this FT paraffin is added in the process for the production of such road surfaces. Therefore, according to the

a proportion of paraffin obtained by Fischer-Tropsch synthesis (FT-paraffin) is added to the bitumen or asphalt or the road surface and, in the process for producing such road surfaces, this FT paraffin is admixed.


Table of contents

CO2 was one of the first gases to be given a name. The Flemish chemist Johan Baptista van Helmont (1580–1644) observed that the mass of charcoal decreased during combustion because the mass of the remaining ash was less than that of the charcoal used. His interpretation was that the rest of the charcoal had turned into an invisible substance that he gas or Alcohol sylvestre ("Forest Spirit") called. [19]

The Scottish physician Joseph Black (1728–1799) studied the properties of CO2 more thorough. In 1754 he found out that adding acids to calcium carbonate solutions releases a gas, which he does fixed air ("Fixed / fixed air") called. [20] He realized that this was heavier than air and did not support combustion processes. When this gas was introduced into a solution of calcium hydroxide, it was able to generate a precipitate. With this phenomenon he showed that carbon dioxide occurs in the breath of mammals and is released through microbiological fermentation. His work proved that gases can be involved in chemical reactions and contributed to the case of the phlogiston theory. [21]

Joseph Priestley succeeded in producing soda water for the first time in 1772 by adding sulfuric acid to a calcareous solution and dissolving the resulting carbon dioxide in a beaker of water. [22] William Brownrigg had recognized the connection between carbon dioxide and carbonic acid earlier. In 1823, Humphry Davy and Michael Faraday liquefied carbon dioxide by increasing the pressure. [23] Henry Hill Hickman operated animals from 1820, which was achieved painlessly after inhaling carbon dioxide to achieve anesthesia. He also described the physiological processes during anesthesia. [24] The first description of solid carbon dioxide comes from Adrien Thilorier, who opened a pressurized container with liquid carbon dioxide in 1834 and found that the spontaneous evaporation takes place with cooling, which leads to solid CO2 leads. [25]

Carbon dioxide is found in the atmosphere, the hydrosphere, the lithosphere, and the biosphere. The carbon exchange between these earth spheres takes place largely through carbon dioxide. Around 2015 there were around 830 gigatons (830 billion tons) of carbon in the atmosphere in the form of carbon dioxide. [26] The hydrosphere contains around 38,000 gigatons of carbon in the form of physically dissolved carbon dioxide as well as dissolved hydrogen carbonates and carbonates. The lithosphere contains by far the largest proportion of chemically bound carbon dioxide. Carbonate rocks such as calcite and dolomite contain around 60,000,000 gigatons of carbon. [27] In addition, large amounts of carbon are stored in permafrost areas such as the tundras of the Arctic and Antarctic polar regions, in boreal coniferous forests or high mountains and in moors. [28] [29] [30]

Occurrence in the atmosphere and man-made climate change

Carbon dioxide is a naturally occurring trace gas in the earth's atmosphere that has an impact on the climate, but its concentration increases, in particular due to the burning of fossil fuels. Ice core data indicated that the atmospheric CO2Values ​​in the past 420,000 years up to the beginning of industrialization in the middle of the 18th century fluctuated between 190 ppm during the height of the ice ages and 280 ppm during the warm periods. [31]

With industrialization, human activities led to a sharp increase in the amount of carbon dioxide in the atmosphere, which continues. Between 1750 and 1958 (the beginning of systematic measurements by Charles David Keeling) the CO rose2-Value initially moderate to 315 ppm, and then increased to 401 ppm by 2015. [32] The concentration exceeded the threshold of 400 ppm (0.04% by volume of the total gas envelope of the earth) on May 9, 2013 in the local daily mean, as measured by the National Agency for Ocean and Atmospheric Research (NOAA) of the United States on the Mauna Loa (Hawaii). [33] The monthly, global mean value measured by NOAA first exceeded the 400 ppm limit in March 2015, [34] in February 2018 this value was 408 ppm (provisional status, as the data from the previous year was still being checked will). [35] Finally, the data for 2017 show a new record high of 405.5 ppm, which is 46 percent above the pre-industrial value. [36] In 2018, a new record high was reached again at 407.8 ppm. [16] The main sources are the burning of fossil fuels for energy production and in the industrial sector. The release of carbon dioxide stored in soils and forests through changes in land use, for example through clearing of forests, also contributes to the increase to a much lesser extent. In 2014, energy use and industrial use of fossil fuels as well as land use accounted for 70% and 5%, respectively, of total man-made greenhouse gas emissions (measured in carbon dioxide equivalents). [37]

The total mass of carbon dioxide in the atmosphere is around 3000 gigatons or around 800 Gt carbon (the ratio of the molar masses of CO2 to C is rounded 44:12). The concentration varies seasonally and locally, especially near the ground. In urban areas the concentration is generally higher, in closed rooms the concentration can be up to ten times the average value. [38]

Carbon dioxide absorbs part of the thermal radiation (infrared radiation), while the shorter-wave part of the solar radiation can pass through almost unhindered. An absorbent body also emits according to its temperature. These properties make carbon dioxide a so-called greenhouse gas. After water vapor, carbon dioxide is the second most effective of the greenhouse gases in terms of its proportion, although the specific effectiveness of methane and ozone are higher. All greenhouse gases together increase the mean temperature on the earth's surface from around −18 ° C to +15 ° C due to the natural greenhouse effect. Carbon dioxide has a relatively large share in the overall effect and thus contributes to the earth-friendly climate. [39]

The proportion of carbon dioxide in the earth's atmosphere has been subject to considerable fluctuations over the course of the earth's history, which have various biological, chemical and physical causes. 500 million years ago, the concentration of carbon dioxide was at least ten times higher than it is today. [40] As a result, the CO2-Concentration steadily decreased and was around 300 million years ago during the Permocarbonic Ice Age, at the transition from the Carboniferous to the Permian, averaged around 300 ppm [41] and fell briefly in the early Permian to a low of probably 100 ppm [42] during the Mesozoic moved the CO2-Level mostly between 1,000 and 2,000 ppm, in order to fall well below 1,000 ppm in the Modern Earth Age, after a climatic optimum in the early Eocene, [43] up to the beginning of the Cenozoic Ice Age about 34 million years ago. [44]

For at least 800,000 years, the carbon dioxide content has always been below 300 ppm. [45] [46] The carbon dioxide concentration in the last 10,000 years has remained relatively constant at 300 ppm. The balance of the carbon dioxide cycle was thus balanced during this time. With the beginning of industrialization in the 19th century, the amount of carbon dioxide in the atmosphere increased. The current concentration is likely the highest in 15 to 20 million years. [47] In the period from 1960 to 2005, the carbon dioxide content rose by an average of 1.4 ppm per year. [48] ​​In 2017, the 10-year average increase was a good 2 ppm per year. [49]

The anthropogenic, i.e. man-made carbon dioxide emissions amount to around 36.3 gigatons annually [48] and are only a small proportion of the carbon dioxide, which comes mainly from natural sources, of around 550 gigatons annually. [50] However, since the natural carbon sinks have the same amount of CO2 resume, the carbon dioxide concentration remained relatively constant before industrialization. About half of the additional carbon dioxide is absorbed by the biosphere and the oceans (this leads to their acidification), so that these now absorb more carbon dioxide than they give off. [51] As a result, since 1982 there has been a "greening" of the earth (Leaf Area Index), as has been proven by satellite data from NASA. [52] However, more recent data suggest that this greening, which was observed until the late 20th century, then stopped and, as a result of a larger saturation deficit (more drought), an opposing trend developed, ie. H. the earth is currently losing vegetation. [53] The other half of the carbon dioxide emitted remains in the atmosphere, where it leads to a measurable increase in concentration, which Charles Keeling was able to demonstrate for the first time in the early 1960s with the Keeling curve named after him.

It is widely recognized scientifically that there is a statistically significant human impact on climate that is the primary cause of global warming. This warming is most likely largely due to the anthropogenic amplification of the natural greenhouse effect through the emission of greenhouse gases. [54] The additionally produced carbon dioxide has a share of about 60% in the intensification of the greenhouse effect. [55] [56]

Luxembourg, Belgium and Switzerland have the highest CO per capita2-Footprint across Europe. [57] The consequences of global warming should be reduced through climate protection.

Occurrence in oceans

The water of the oceans contains carbon dioxide in dissolved form and as carbonic acid in equilibrium with hydrogen carbonates and carbonates. The amount dissolved changes with the season, as it depends on the temperature and salinity of the water: Cold water dissolves more carbon dioxide. Since cold water has a higher density, the carbon dioxide-rich water sinks into deeper layers. Only at pressures above 300 bar and temperatures above 120 ° C (393 K) is it the other way round, for example in the vicinity of deep geothermal vents. [58]

The oceans contain about 50 times as much carbon as the atmosphere. The ocean acts as a large carbon dioxide sink and absorbs around a third of the amount of carbon dioxide released by human activities. [59] In the upper layers of the oceans, it is partially bound by photosynthesis. As the solution of carbon dioxide increases, the alkalinity of the salt water decreases, which is known as acidification of the oceans and is very likely to have negative consequences for the ecosystems of the oceans. Many sea creatures are sensitive to fluctuations in the acidity of the oceans. Acidification events in the history of the earth have led to mass extinctions and a sharp decline in biodiversity in the world's oceans. Organisms that build up calcium carbonate structures are particularly affected, as this dissolves as the acidity of the oceans increases. Corals, mussels and echinoderms such as starfish and sea urchins are particularly vulnerable. [60]

Among other things, it is feared that this will have a negative effect on the formation of mussel shells, among other things. [61] [62] These effects are already visible in coral reefs and certain oyster farms. Increasing acidification is expected to have greater ecological consequences. [60] On the other hand, there are indications that an increased carbon dioxide concentration stimulates some species to increase the production of mussel shells. [63]

Occurrence in fresh water

Aerobic bacteria and animals living in the (under) water consume oxygen and CO2 exhaled. If there is sufficient contact with the atmosphere, this gas can be released into the air and oxygen can be absorbed at the same time. A surface that freely adjoins the air and is free of ice or oil is beneficial, as are wave movements, turbulence with air, i.e. the formation of foam and spray, water currents that also include deeper layers and wind. Without sufficient gas exchange, a body of water can also be oxygen-poor and CO2-become rich. They say "it tips over".

Due to special geological conditions, fresh water can be loaded with considerable amounts of carbon dioxide from volcanic sources, such as water from mineral springs or in lakes on extinct volcanoes, so-called maars. Under the pressure of great water depth, CO2 be dissolved in a much higher mass concentration than under atmospheric pressure on the surface of the water. If a lake is not (sufficiently) traversed by water or driven by wind and / or heat convection currents, it becomes more CO2 entered from below, can be transported upwards as mixing and diffusion, then CO is formed2-rich deep water that has the potential to cause catastrophic CO2-Release to the air. A local outgassing once triggered locally under water leads to the rise of a body of water, the relief of hydrostatic pressure that takes place in the process intensifies the outgassing. This self-reinforcing process can lead to the release of large amounts of CO2 that can kill humans and animals near the lake.

One of these natural disasters occurred in 1986 at Lake Nyos in Cameroon. [64] The lake is located in an old volcanic crater in the Oku volcanic area. A magma chamber feeds the lake with carbon dioxide and saturates its water. Probably triggered by a landslide in 1986, large amounts of carbon dioxide were released from the lake, killing around 1,700 residents and 3,500 livestock in the surrounding villages. Another catastrophe occurred in 1984 at Lake Manoun, the water of which is saturated with carbon dioxide by a similar mechanism. 37 people were killed in this carbon dioxide release. The Kiwu Lake in Central Africa also has high concentrations of dissolved gases in its deep water. It is estimated that around 250 km³ of carbon dioxide is dissolved in this lake. [65]

Extraterrestrial occurrence

The atmosphere of Venus consists of 96.5% carbon dioxide, has about 90 times the mass of the earth's atmosphere and a pressure of about 90 bar. The high proportion of carbon dioxide is one of the causes of the strong greenhouse effect. In addition, the distance from the sun is on average 41 million kilometers shorter than the earth, which leads to a surface temperature of around 480 ° C. [66] With a share of 95%, carbon dioxide also makes up the main part of the Martian atmosphere. [67] At the Mars poles, atmospheric carbon dioxide is partially bound as dry ice. Due to the low atmospheric pressure of around seven millibars, the greenhouse effect only leads to an increase of around 5 K, despite the high carbon dioxide content. The atmospheres of the outer planets and their satellites contain carbon dioxide, the origin of which is impacts from comets such as Shoemaker-Levy 9 and cosmic dust is attributed. [68] [69] Using the instruments of the Hubble Space Telescope, NASA found carbon dioxide on extrasolar planets such as HD 189733 b. [70]

Carbon dioxide is found both in interstellar space and in protoplanetary disks around young stars. [71] The formation occurs through surface reactions of carbon monoxide and oxygen on water ice particles at temperatures around −123 ° C (150 K). When the ice evaporates, the carbon dioxide is released. [72] The concentration in free interstellar space is relatively low, as reactions with atomic and molecular hydrogen form water and carbon monoxide. [73]

Carbon dioxide is produced when carbon-containing fuels are burned, especially fossil fuels. Around 36 gigatons (billion tons) of carbon dioxide are produced around the world each year and are released into the atmosphere. Processes to separate the carbon dioxide and to store it in deep rock layers are currently (2016) at the beginning of their development and are not yet ready for series production. Their effectiveness and profitability, especially in sustainable energy systems, are being critically assessed. [74]

Carbon dioxide is produced when carbon reacts with oxygen:

Technically, carbon dioxide is produced when coke is burned with excess air. In coal gasification and the steam reforming of natural gas, carbon dioxide is produced, among other things, as a product of the water-gas shift reaction in synthesis gas production.

For use in ammonia synthesis and in methanol production, for example, the synthesis gas is washed using the Rectisol process, which means that large amounts of carbon dioxide are produced in a very pure form. [76] [77] As a by-product, carbon dioxide is produced when burning lime. Subsequent purification via the formation of potassium carbonate to hydrogen carbonate and subsequent release by heating, around 530 million tons per year are obtained.

In the laboratory, carbon dioxide can be released from calcium carbonate and hydrochloric acid, for example in a Kipp apparatus. The device was previously used in laboratories. The method is rarely used any more, as carbon dioxide is available in gas bottles or as dry ice. [78]

Carbon dioxide is also extracted from the air using the direct air capture (DAC) process.

Physical Properties

At normal pressure below −78.5 ° C, carbon dioxide is present as a solid, known as dry ice. If this is heated, it does not melt, but sublimates, i.e. it changes directly into the gaseous state of aggregation. It therefore has no melting point and no boiling point under these conditions.

The triple point at which the three phases solid, liquid and gaseous are in thermodynamic equilibrium is at a temperature of −56.6 ° C and a pressure of 5.19 bar. [4]

The critical temperature is 31.0 ° C, the critical pressure 73.8 bar and the critical density 0.468 g / cm³. [4] Below the critical temperature, gaseous carbon dioxide can be compressed to a colorless liquid by increasing the pressure. [79] At room temperature, a pressure of around 60 bar is required for this.

Solid carbon dioxide crystallizes in the cubic crystal system in the space group Pa 3 (room group no. 205) Template: room group / 205 with the grid parameter a = 562.4 pm. [80]

Carbon dioxide absorbs electromagnetic radiation mainly in the spectral range of infrared radiation and is stimulated to vibrate molecules. Its effect as a greenhouse gas is based on this property.

The solubility in water is comparatively high. At 20 ° C under normal pressure, the saturation is in equilibrium with the pure carbon dioxide phase at 1688 mg / l. For comparison, the solubility of oxygen or nitrogen is shown below: with a pure oxygen phase, saturation is reached at 44 mg / l and with a pure nitrogen phase at 19 mg / l. [81] Under standard conditions, the density of carbon dioxide is 1.98 kg / m³. [82]

Molecular Properties

The carbon dioxide molecule is linear, all three atoms are in a straight line. The carbon is bound to the two oxygen atoms with double bonds, with both oxygen atoms having two lone pairs of electrons. The carbon-oxygen distance is 116.32 pm. [79] The carbon-oxygen bonds are polarized by the different electronegativities of carbon and oxygen, but the electrical dipole moments cancel each other out due to the molecular symmetry, so that the molecule has no electrical dipole moment. The (bending) vibration mode of the molecule, in which the carbon atom moves perpendicular to the axis and the oxygen atoms in the opposite direction (and vice versa), corresponds to an infrared wavelength of 15 μm. This 15 μm radiation is the main component the effect of carbon dioxide as a greenhouse gas. [83]

Chemical properties

Carbon dioxide is an incombustible, acidic and colorless gas at low concentrations it is odorless, at high concentrations you can perceive a pungent to sour odor, [84] although there are people who have this (similar to hydrocyanic acid, for example) Cannot perceive smell. Carbon dioxide dissolved in water forms carbonic acid (H.2CO3), whereby more than 99% of the carbon dioxide is only physically dissolved, the aqueous solution therefore reacts slightly acidic. The carbonic acid as such and the dissolved carbon dioxide are in equilibrium with their dissociation products (species) hydrogen carbonate (Bicarbonate, HCO3 -) and carbonate (CO3 2−), which are in a proportion to each other depending on the pH value. In water, this equilibrium is predominantly on the side of carbon dioxide and hydrogen carbonate ions are only formed to a small extent. If the oxonium ions (H.3O +) is trapped by adding a lye with hydroxide ions (OH -), so the quantitative ratio shifts in favor of carbonate.

Carbon dioxide is a very weak oxidizing agent. Base metals such as magnesium, which act as strong reducing agents, react with carbon dioxide to form carbon and metal oxides according to: [85]

Due to the positive partial charge on carbon, carbon dioxide reacts as an electrophile in the carboxylation of carbon nucleophiles such as metal alkynylidene or alkyl magnesium compounds to form a carbon-carbon bond. Carbon dioxide reacts with phenolates to form phenol carboxylic acids.

In industry, carbon dioxide is used in a variety of ways. It is inexpensive, non-flammable and is used physically as a compressed gas, in liquid form, solid as dry ice or in supercritical phase. The chemical industry uses carbon dioxide as a raw material for chemical synthesis. This CO2 originates z. B. from fertilizer production, where it is very pure, or from exhaust gases that require downstream cleaning to remove unwanted accompanying substances. [86]

Use in food technology

Carbon dioxide contained in beverages stimulates the taste sensory cells when drinking, which has a refreshing effect. In drinks such as beer or sparkling wine, it is produced through alcoholic fermentation, in others such as lemonade or soda water it is added artificially or natural mineral water containing carbon dioxide is used. During production, carbon dioxide is pumped into the drink under high pressure, around 0.2% of which reacts with water to form carbonic acid, while most of it dissolves as a gas in the water. As a food additive, it bears the designation E 290. [87] In private households, carbon dioxide from pressure cartridges is passed through the drink to be enriched with soda makers.

Baker's yeast develops carbon dioxide through the fermentation of sugar and is used as a leavening agent in the production of yeast dough. Baking powder, a mixture of sodium hydrogen carbonate and an acid salt, releases carbon dioxide when heated and is also used as a leavening agent. [88]

In winemaking, dry ice is used as a coolant to cool freshly picked grapes without diluting them with water, thus avoiding spontaneous fermentation. The winemakers in Beaujolais use carbonic acid maceration to produce the Beaujolais Primeur. [89]

In addition to the temperature, the composition of the atmosphere plays an important role in the storage of fruit and vegetables. In the warehouses of fruit producers and retailers, apples have been stored in controlled atmospheres for many decades. The realization that ripening fruit consumes oxygen and gives off carbon dioxide and that an atmosphere without oxygen brings ripening to a standstill goes back to the early 19th century. In the 1930s, a warehouse was first set up in Great Britain with the ability to regulate the levels of oxygen and carbon dioxide in the air. [90] The economic importance of precisely adapted controlled atmospheres in fruit storage is considerable. By adding carbon dioxide to the atmosphere, the shelf life can be extended by months, thus reducing dependence on imports from warmer regions for part of winter and spring. On the other hand, an improper addition of carbon dioxide can cause defects in the pulp and render an entire inventory or container shipment worthless. [91] The biochemical processes that lead to the delayed maturity have not yet been deciphered. It is currently assumed that both the slowing down of the maturation process and the formation of the various types of damage are controlled by stress reactions at the cellular level. [90]

Fruit, vegetables and mushrooms packaged in foil for the retail trade, [92] unprocessed or cut, are provided with a protective atmosphere in order to extend the shelf life and so as not to lose the impression of freshness on the way to the consumer. Today, meat, fish and seafood, pasta, baked goods and dairy products are also offered in this way. The proportion of carbon dioxide in the protective atmosphere is significantly higher in packaged products that are not intended to be stored for months than in stored fruit and vegetables (1–5%, rarely up to 20%), for which carbon dioxide can cause damage. Typical proportions are 20% carbon dioxide for beef, 50% for veal, pork and pasta, 60% for baked goods and 80% for fish. Packaging under pure carbon dioxide is avoided, however, since it would promote the development of pathogenic, anaerobic germs and in many cases would impair the color and taste of the products. Determining the optimal protective atmosphere for a product is the subject of intensive research in the food industry. [93] [94]

Supercritical carbon dioxide has a high solubility for non-polar substances and can replace toxic organic solvents. It is used as an extraction agent, for example for the extraction of natural substances such as caffeine in the production of decaf Coffee through decaffeination. [95]

Technical use

Because of its oxygen-displacing properties, carbon dioxide is used as an extinguishing agent for fire extinguishing purposes, especially in hand-held fire extinguishers and automatic extinguishing systems. CO2Extinguishing systems flood the entire room with carbon dioxide to protect silos or storage halls for flammable liquids. This led to repeated accidents, some of which resulted in death from suffocation. [96] A study by the US Environmental Protection Agency (EPA) identified 51 accidents between 1975 and 1997 with 72 fatalities and 145 injuries. [97]

As a refrigerant, carbon dioxide is used under the designation R744 in vehicle and stationary air conditioning systems, in industrial refrigeration, supermarket and transport refrigeration and in beverage machines. [98] It has a large volumetric cooling capacity and thus a higher efficiency for a given volume. Carbon dioxide is more environmentally friendly because its global warming potential is only a fraction of that of synthetic refrigerants. In contrast to these, it does not contribute to ozone depletion. Carbon dioxide is also used in air conditioning systems for vehicles. [99] In gas-cooled nuclear reactors of the type AGR, carbon dioxide is used as a coolant.

Carbon dioxide is used as a protective gas in welding technology, either in its pure form or as an additive to argon or helium. At high temperatures it is thermodynamically unstable, which is why it is not called an inert gas, but an active gas. [100]

With the carbon dioxide laser, laser gas, a mixture of nitrogen, helium and carbon dioxide, flows continuously through the discharge tube. In addition to the solid-state lasers, these gas lasers are among the most powerful lasers in industrial use with outputs between 10 watts and 80 kilowatts. The efficiency is around 10 to 20%. [101]

In liquid form, carbon dioxide is traded in pressurized gas cylinders. There are two types: Riser bottles for withdrawing liquids and bottles without risers for withdrawing gaseous carbon dioxide. [102] Both must be vertical for removal. The riser cylinder is always operated without, the other with a pressure reducing valve. As long as there is still liquid carbon dioxide in the pressure bottle, the internal pressure is only dependent on the temperature. A measurement of the fill level is therefore only possible with both types of bottle using a weighing system. The removal speed is limited by the fact that the liquid carbon dioxide has to evaporate again in the bottle due to the absorption of heat from the environment in order to build up the pressure corresponding to the temperature again.

The sublimation of dry ice creates a white mist from the cold carbon dioxide-air mixture and condensing humidity, which serves as a stage effect. There are also fog cooling attachments for evaporator fog machines that run on liquid carbon dioxide. [103]

Increasingly, carbon dioxide is being used in conjunction with an automatable blasting process in order to produce high-purity surfaces. With its combination of mechanical, thermal and chemical properties, carbon dioxide snow, for example, can loosen and remove various types of surface contamination without leaving any residue. [104]

Supercritical carbon dioxide is used as a solvent for cleaning and degreasing, for example wafers in the semiconductor industry and textiles in dry cleaning. [105] Supercritical carbon dioxide is used as a reaction medium for the production of fine chemicals, for example for the production of flavorings, since isolated enzymes often remain active and, in contrast to organic solvents, no solvent residues remain in the products.

In tertiary oil production, supercritical carbon dioxide is used to flood oil reservoirs in order to flush oil to the surface from greater depths. [106]

Heat pipes filled with carbon dioxide are used to provide geothermal heat and are more energy efficient than brine cycles.

Use as a chemical raw material

In the chemical industry, carbon dioxide is used primarily for the production of urea through conversion with ammonia. In the first step, ammonia and carbon dioxide react to form ammonium carbamate, which in the second step further reacts to form urea and water. [107]

Formamide is obtained by reduction with hydrogen. Reaction with amines such as dimethylamine gives dimethylformamide. [108]

By reacting carbon dioxide with sodium phenolate, the Kolbe-Schmitt reaction produces salicylic acid. [109]

Ethylene carbonate is produced by reacting with ethylene oxide. In the OMEGA process, this is converted into monoethylene glycol with water in a highly selective manner.

The reaction of carbon dioxide with a Grignard reagent leads to carboxylic acids, e.g. B .:

The telomerization of carbon dioxide with two molecules of 1,3-butadiene under homogeneous palladium catalysis leads to fine chemicals such as lactones under mild reaction conditions. [107]

In the Solvay process, carbon dioxide is used to produce soda (sodium carbonate). Some metal carbonates such as lead carbonate, which are obtained, for example, by reacting the metal hydroxides with carbon dioxide, are important as pigments.

With a high oil price and low electricity prices for renewable energies, for example from wind power and solar systems, it could be worthwhile in the future to use carbon dioxide for other applications such as methane production in power-to-gas systems (Sabatier process) and methanol production (Power -to-Liquid) with hydrogen from electrolysis. [110] Further potential fields of application would be the production of formic acid and synthesis gases for the production of fuels (power-to-fuel) and chemical raw materials (power-to-chemicals). This can be done via a Fischer-Tropsch synthesis or the direct use together with ethylene oxide or propylene oxide for the production of polyols and polymers such as polyurethanes or polycarbonates. For thermodynamic reasons, however, the use of carbon dioxide is currently mostly uneconomical.

Carbon dioxide recycling

In addition to the separation and storage of carbon dioxide, research is aimed at converting the carbon dioxide that arises from the combustion of fossil fuels into usable compounds and, if possible, back into energy sources. Compounds such as methanol [111] and formic acid can already be produced by reduction. [112]

The synthesis of urea is also possible. A French research team is investigating the organocatalytic conversion to formamide or its derivatives. [113] [114] Since the process energy has to be supplied, these processes are not suitable for the economical production of energy carriers. Scientists at RWTH Aachen University developed a homogeneous catalytic process for the production of methanol from carbon dioxide and hydrogen under pressure with a special ruthenium-phosphine complex in which the catalyst and starting materials are in solution. [115] Likewise, a continuous process for the production of formic acid with an organometallic ruthenium complex was developed in which carbon dioxide plays the dual role of reactant and, in supercritical form, as the extractive phase for the formic acid formed. [116] In another variant developed by a Spanish research group, carbon dioxide can be converted via an iridium-catalyzed hydrosilylation and captured in the form of a silyl formate from which formic acid can be easily separated.This reaction, which could already be carried out on a gram scale, takes place under very mild reaction conditions, is very selective and has a high conversion. [117]

In the “Coal Innovation Center”, RWE and Brain AG are researching how microorganisms CO2 convert. [118]

Other uses

Carbon dioxide was routinely used as an anesthetic in humans, especially in the United States, until the 1950s [119] and was rated as very satisfactory. This method is no longer used in traditional anesthesia for humans, as more effective, inhalable anesthetics have been introduced.

This method is still used today for stunning animals for slaughter. [120] Pigs are let down in groups with an elevator system into a pit, the atmosphere of which contains at least 80% carbon dioxide, and lose consciousness in it. This process is controversial and is subject to intensive efforts to improve animal welfare. [121] [122] [123] Fish are anesthetized by introducing gaseous carbon dioxide or by adding carbonated water. [124] In Germany, stunning slaughter animals with carbon dioxide is only permitted for pigs, turkeys, day-old chicks and salmon fish. [125]

In the context of animal euthanasia, carbon dioxide is used for killing. In Germany, the application is limited to small laboratory animals, also for purposes such as the procurement of feed animals in animal husbandry. [126] However, the legality of such animal killings without prior stunning is questioned. [127] For officially ordered killing of livestock, the club, carbon dioxide may also be used to kill other animals if a special permit is available. [128] The Veterinary Association for Animal Welfare (DVT) describes this method as suitable for poultry. [129]

Carbon dioxide is used as a laxative in suppositories. The reaction of sodium dihydrogen phosphate and sodium hydrogen carbonate during the dissolution of the suppository releases carbon dioxide and stretches the intestine, which in turn triggers the stool reflex. [130]

In carbon dioxide fertilization, it is used as a fertilizer in greenhouses. The reason is the carbon dioxide deficiency caused by photosynthetic consumption when there is insufficient fresh air, especially in winter when the ventilation is closed. The carbon dioxide is introduced either directly as a pure gas or as a combustion product from propane or natural gas. This achieves a coupling of fertilization and heating. The possible increase in yield depends on how strong the lack of carbon dioxide is and how strong the light is available for the plants. [131] Carbon dioxide is used in aquaristics as a fertilizer for aquatic plants (CO2Diffuser). By adding organic matter, the carbon dioxide content in the water can be increased through inhalation at the expense of the oxygen content. [132]

The gas is used to catch blood-sucking insects and vectors that use the carbon dioxide found in the breath to find hosts, such as mosquitoes. It is released from dry ice, from gas cylinders or from the combustion of propane or butane and attracts insects near the intake opening of special traps. [133] The gas is also used in the cultivation of microorganisms, especially for strictly (strictly) anaerobic bacteria that can only grow under anoxic conditions. You can be in a CO2-Incubate the incubator, which is supplied by a gas bottle. In addition to strictly anaerobic bacteria, there are also so-called capnophilic bacteria, which require a proportion of 5–10 percent by volume of carbon dioxide in the surrounding atmosphere to grow. They are often cultivated in a closable anaerobic pot into which a commercially available reagent carrier is placed, the chambers of which are filled with sodium hydrogen carbonate and tartaric acid or citric acid. Moistening - similar to the principle of baking powder - generates CO2 released. [134]

Effect on animals and people

Too high a proportion of carbon dioxide in the air we breathe has harmful effects on animals and humans. These are not only based on the displacement of oxygen in the air. DIN EN 13779 divides the room air into four quality levels depending on the carbon dioxide concentration. At values ​​below 800 ppm, the indoor air quality is considered to be good, values ​​between 800 and 1000 ppm (0.08 to 0.1% by volume) are considered to be medium, and values ​​of 1000 to 1400 ppm are considered to be of moderate quality. At values ​​above 1400 ppm, the indoor air quality is considered to be low. [135] For comparison: the CO is in the global mean2- The proportion of air at around 400 ppm by volume, however, fluctuates strongly regionally, depending on the time of day and the season.

The maximum workplace concentration for a daily exposure of eight hours per day is 5000 ppm. [136] At a concentration of 1.5% (15,000 ppm) the respiratory time volume increases by more than 40%.

Due to the significantly increased CO2-Concentrations and / or lack of ventilation in rooms with comparatively clean ambient air can, according to studies, lead to a strong and avoidable impairment of brain performance - especially in decision-making and complex strategic thinking - in rooms such as classrooms. [137] [138]

Carbon dioxide dissolved in the blood activates the breathing center of the brain in a physiological and slightly increased concentration.

In significantly higher concentrations, it leads to a reduction or elimination of the reflex breathing stimulus, initially to respiratory depression and finally to respiratory arrest. [139] From about 5% carbon dioxide in the inhaled air headaches and dizziness occur, with higher concentrations accelerated heartbeat (tachycardia), rise in blood pressure, shortness of breath and unconsciousness, the so-called carbon dioxide anesthesia. Carbon dioxide concentrations of 8% lead to death within 30 to 60 minutes. [140] [141] An accumulation of carbon dioxide in the blood is called hypercapnia.

Accidents occur again and again in wine cellars, feed silos, wells and cesspools due to high carbon dioxide concentrations. [82] Fermentation processes produce considerable amounts of carbon dioxide there, in the fermentation of one liter of must, for example, around 50 liters of fermentation gas. Often several people fall victim to fermentation gas poisoning because the helpers inhale carbon dioxide themselves during the rescue attempt and become unconscious. Rescuing an injured person from suspected carbon dioxide situations is only possible by professional emergency responders with self-contained breathing apparatus. [142]

If adequate ventilation is not provided, natural carbon dioxide sources in caves and mine tunnels can create high concentrations of the gas. These are then close to the ground, so that smaller animals in particular can suffocate. For example, the dog grotto in Italy has a carbon dioxide concentration of around 70%. [143]

The carbon dioxide concentration in the blood influences its pH value and thus has an indirect effect on the oxygen balance. The carbonic acid-bicarbonate system, a carbonic acid-bicarbonate buffer, represents about 50% of the total buffer capacity of the blood, which is catalyzed by the enzyme carbonic anhydratase. [144]

At a lower pH value, the oxygen-binding capacity of the red blood pigment hemoglobin is reduced. With the same oxygen content in the air, hemoglobin therefore transports less oxygen. The Bohr effect and the Haldane effect describe this fact. [145]

Effect on plants

On plants, a slightly increased carbon dioxide concentration has the effect of carbon dioxide fertilization, since the plants during photosynthesis for the carbon dioxide assimilation CO2 require. However, excessively high concentrations are also harmful to plants. For C3 plants, the optimum is usually between 800 and 1000 ppm, but for C4 plants it is only just over 400 ppm. The C4 plant maize as an indicator plant showed CO at 10,000 ppm2 streaks on their leaves after a six-day exposure period. [146] Changes in the nutritional composition (proteins, micronutrients and vitamins) were found in rice. Protein, iron, zinc, vitamins B1, B2, B5 and B9 take with excessively increasing CO2-Concentration decreases, while vitamin E increases. Such a reduction in the quality of plant foods would exacerbate the global malnutrition problem. [147]

Plants and photosynthetic bacteria absorb carbon dioxide from the atmosphere and convert it into carbohydrates such as glucose through photosynthesis under the action of light and absorption of water.

This process simultaneously releases oxygen from the decomposition of water. The resulting carbohydrates serve as an energy source and building material for all other biochemical substances such as polysaccharides, nucleic acids and proteins. Carbon dioxide thus provides the raw material for the formation of all biomass in the primary production of ecosystems. [149]

The breakdown of biomass through aerobic respiration is, in reverse to the process of photosynthesis, linked to the formation of carbon dioxide and the consumption of oxygen. [150]

All organisms in an ecosystem breathe continuously, while photosynthesis is tied to the availability of light. This leads to a cyclical increase and decrease of carbon dioxide in the daily and seasonal rhythm depending on the different light intensities.

In water bodies, the carbon dioxide concentration also fluctuates according to the daily and seasonal rhythms mentioned. Carbon dioxide is in a chemical equilibrium with the other dissolved carbonic acid species, which essentially determines the pH value in the water. The chemical equilibrium of the dissociations of ammonium / ammonia, nitrite / nitrous acid, sulphide / hydrogen sulphide and other acid-base pairs, which are noticeable through the toxicity for the organisms in the water, depend on the pH value. [152]

If the supply of carbon dioxide in a body of water is exhausted through photosynthesis, which is noticeable by a pH value close to 8.3, some types of algae and aquatic plants are able to obtain the required carbon dioxide from the dissolved hydrogen carbonate, whereby they release hydroxide ions, so that the pH value becomes more and more alkaline. In nutrient-rich waters such as carp ponds, the pH value can then rise to 12, with the corresponding health consequences for the fish, for example carp gill necrosis. [153]

In 2012, scientists from the Biodiversity and Climate Research Center calculated for the first time in a joint study with other institutions that cryptogamous layers of lichen, algae and moss bind around 14 billion tons of carbon dioxide annually in addition to nitrogen. They bind as much carbon dioxide as is released each year by forest fires and the burning of biomass worldwide. Fighting climate change with the help of the cryptogamous layers is not possible, however, because the extensive vegetation stores the greenhouse gas carbon dioxide for only a few years. [154] [155]

The storage and release of carbon dioxide in soils is important. The extent to which the release of soil organic carbon is influenced by the respective environmental conditions and other factors is currently largely unknown. However, the release is accelerated by warming, which has been shown in recent studies, and could have an impact on the climate. [156] A study published in 2019 shows that with a CO2Concentration above 1,200 ppm stratocumulus clouds break up into scattered clouds, which could further fuel global warming. [157]

With the indication of the CO2-Emission, different processes are made energetically and ecologically comparable. For this purpose, the release of carbon dioxide when burning fossil fuels is converted.

A simple detection of carbon dioxide is possible with an aqueous calcium hydroxide solution, the so-called lime water sample. For this purpose, the gas to be examined is introduced into the solution. If the gas contains carbon dioxide, it reacts with calcium hydroxide to form water and calcium carbonate (lime), which precipitates as a whitish solid and makes the solution cloudy.

With barium water, an aqueous barium hydroxide solution, the detection is more sensitive, since barium carbonate is less soluble than calcium carbonate.

In aqueous solution, carbon dioxide is determined by titration with 0.1 N sodium hydroxide solution up to a pH value of 8.3, the color change of the phenolphthalein indicator. The measurement of the acid binding capacity (SBV), the pH value and the electrical conductivity or the ionic strength enables the calculation of the carbon dioxide content from these parameters according to the dissociation equilibrium of the carbonic acid. The Severinghaus electrode, a pH electrode with a buffer solution made from sodium hydrogen carbonate, determines the carbon dioxide concentration of a solution by measuring the change in pH value. [158]

Carbon dioxide can be detected using infrared or Raman spectroscopy, whereby the asymmetrical stretching vibrations and tilting vibrations are infrared-active, while the symmetrical stretching vibrations at a wave number of 1480 cm −1 are Raman-active. [159] The measuring device used for this is called a non-dispersive infrared sensor.


Primary, secondary and tertiary alcohols

Start your free test phase quickly and easily
and improve your grades with fun!

Learning videos for all classes and subjectsthat explain the school material briefly and concisely.

increase your self-confidence in classby studying with our fun interactive exercises before tests and classwork.

learn with the printable worksheets on the go - Together with the accompanying videos, these worksheets enable a complete learning unit.

24h help from teacherswho always help when you need it.

89% of the students improve their grades with sofatutor

End the test phase online at any time

You have to be logged in to rate.

Wow, Thanks!
Give us your rating on Google! We are happy!


Video: 4 Stereochemistry of Quartenary ammomium salt, Amines, tertiary amine oxides. Nitrogen Compounds (May 2022).