Acetic anhydride ( acetic anhydride ), ( C H 3 C O ) 2 O is a colorless liquid with a pungent odor , soluble in benzene , diethyl ether and other organic solvents. It finds very wide application in industry and organic synthesis.
| Acetic anhydride [1] [2] [3] [4] | |
|---|---|
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| Are common | |
| Systematic name | acetic anhydride |
| Abbreviations | Ac 2 O |
| Traditional names | acetic anhydride, ethane anhydride acetylacetate acetyl oxide |
| Chem. formula | (CH 3 CO) 2 O |
| Rat formula | C 4 H 6 O 3 |
| Physical properties | |
| condition | colorless clear odorless liquid |
| Molar mass | 102.09 g / mol |
| Density | 1,0820 g / cm³ |
| Surface tension | 0.03265 N / m |
| Dynamic viscosity | 901 Pa · s |
| Ionization energy | 965 kJ / mol |
| Conductivity | 4.8 · 10 –7 S / m |
| Thermal properties | |
| T. melt. | –73.1 ° C |
| T. bale. | 139.6 ° C |
| T. aux. | 52.5–53 ° C |
| T. svpl. | 316 ° C |
| Etc. blast | 2.7-10.3% |
| Cr. pace. | 295.8 ° C |
| Cr. pressure | 45.4 atm |
| Like heat resistant. | 168.2 30 ° C J / (mol · K) |
| Thermal conductivity | 0.2209 · 10 –3 W / (m · K) |
| Enthalpy of Education | –624.42 w , –576.1 steam kJ / mol |
| Enthalpy of melting | 10.5 kJ / mol |
| Enthalpy of boiling | 276.7 [ specify ] kJ / mol |
| Sublimation Enthalpy | 48.3 kJ / mol |
| Steam pressure | 0.4 20 ° C , 1.7 40 ° C , 5.2 60 ° C , 13.3 80 ° C , 28.7 100 ° C , 53.3 120 ° C atm |
| Chemical properties | |
| Solubility in water | 12 g in 100 g of cold water |
| Dielectric penetration. | 20.5 |
| Optical properties | |
| Refractive index | 1,3906 |
| Structure | |
| Dipole moment | 2.8 D |
| Classification | |
| Reg. CAS number | 108-24-7 |
| PubChem | |
| Reg. EINECS number | |
| Smiles | |
| Inchi | |
| Reg. EC number | 203-564-8 |
| RTECS | |
| Chebi | 36610 |
| UN number | |
| ChemSpider | |
| Security | |
| MPC | 21 mg / m 3 |
| LD 50 | 1.78-5 mg / kg |
| R phrases | R10 , R20 / 22 , R34 |
| S-phrases | S26 , S36 / 37/39 , S45 |
| H phrases | H226 , H302 , H314 , H332 |
| P-phrases | P280 , P305 + P351 + P338 , P310 |
| GHS icons |    |
| NFPA 704 |  2 2 one |
Content
Industrial Production Methods
Deprecated Methods
Historically, the first method for the synthesis of acetic anhydride was based on the conversion of sodium acetate CH 3 COONa to acetyl chloride CH 3 COCl under the action of inorganic chloride (usually thionyl chloride SOCl 2 , sulfuryl chloride SO 2 Cl 2 or phosphoryl chloride POCl 3 ). In the second stage, the resulting acetyl chloride reacted with an excess of sodium acetate with the formation of acetic anhydride [5] .
In another approach, acetic acid was converted into acetic anhydride under the action of phosgene in the presence of aluminum chloride [5] .
Other methods were previously used, for example, the decomposition of ethylidene diacetate into acetaldehyde and acetic anhydride in the presence of acid catalysts , as well as the catalytic reaction of vinyl acetate with acetic acid. Currently, these processes are not used in industry. The main methods of preparation are the reaction of ketene with acetic acid, the oxidation of acetic aldehyde and the carbonylation of methyl acetate [5] .
Getting from ketene
This synthesis method consists of two stages: the thermal decomposition of acetic acid to ketene and the reaction of ketene with acetic acid. The first stage proceeds in the gas phase at a temperature of 700-750 ° C in the presence of trace amounts of triethyl phosphate . Coils made of refractory steel alloys ( Sicromal , 25% Cr , 20% Ni , 2% Si ) are used as a reactor. A method has also been developed for the preparation of ketene by the decomposition of acetone , but this method has no industrial value.
Then, the obtained ketene is absorbed by glacial acetic acid, resulting in crude acetic anhydride, which is subjected to fractional distillation. During distillation, several fractions are collected: pregon (1%, consists of acetic acids and lighter impurities, for example, acetone and methyl acetate ), fraction I (~ 10%, a mixture of acetic acid and acetic anhydride) and pure anhydride. The purity of acetic anhydride obtained in this way does not exceed 99% (the rest is acetic acid), since the product is partially decomposed during distillation.
The synthesis of acetic anhydride from ketene is used by many companies. To obtain 100 kg of acetic anhydride, 122 kg of acetic acid is required. The method does not create serious environmental problems: the by-product gases are burned in the furnace and provide the temperature necessary for the first stage; there is no sewage problem [6] .
Acetic Aldehyde Oxidation
Acetic anhydride can be obtained by liquid-phase oxidation of acetaldehyde in air, while the formation of peracetic acid occurs in the first stage, which then reacts with the second molecule of acetaldehyde to form acetic anhydride.
Essential for this process are the rapid removal of water from the reaction mixture and the use of a suitable catalyst . The reaction always forms a mixture of acetic anhydride and acetic acid; the latter is formed as a result of decomposition of the target product with water . Since hydrolysis largely proceeds at temperatures above 60 ° C, the process is carried out between 40 ° C and 60 ° C. As the catalysts, acetates of manganese , copper , cobalt , nickel or copper salts of fatty acids are used .
The reaction is exothermic , therefore, requires effective cooling. The main cooling method is to add low-boiling solvents, usually methyl acetate or ethyl acetate , to the reaction mixture. In addition to the heat dissipation function, these solvents allow the water to be removed from the mixture, since they boil in the form of an azeotropic mixture with water.
In practice, a mixture of acetaldehyde and ethyl acetate (1: 2) is used, which is oxidized with air when 0.05-0.1% cobalt acetate and copper acetate (1: 2) are added at 40 ° C. The ratio of acetic anhydride and acetic acid in the resulting product is 56:44, while in the oxidation in the absence of ethyl acetate it is only 20:80 [7] .
Methyl Acetate Carbonylation
The disadvantage of thermal decomposition of acetic acid to ketene is the need for significant energy costs. In addition, processes based on the use of synthesis gas , which, in turn, are obtained from methane , are industrially useful. An example is the industrial production of acetic acid from methanol , by Monsanto .
In 1973, Halcon patented a method for carbonylation of methyl acetate in the presence of a rhodium catalyst to produce acetic anhydride. The process proceeds in the liquid phase at a temperature of 160-190 ° C and a partial pressure of carbon monoxide (II) CO equal to 2-5 MPa. Methyl acetate, which is formed as a by-product upon receipt of acetic acid from methanol and CO, is used as a raw material. The crude product is distilled to give 99% pure acetic anhydride. The first plant using this process was launched in 1983 [8] .
Laboratory methods for obtaining
In the laboratory, acetic anhydride is obtained by the reaction of acetyl chloride with anhydrous sodium acetate . A reaction of acetic acid with inorganic anhydrides and acid chlorides ( SO 2 Cl 2 , SOCl 2 , COCl 2 , N 2 O 4 , POCl 3 ) is also used [1] .
Laboratory Cleaning
Sufficiently purified acetic anhydride can usually be obtained by distillation with an effective reflux condenser . Impurities of acetic acid are removed by boiling with calcium carbide CaC 2 or by heating with magnesium chips (80–90 ° С, 5 days). The dehydration of acetic anhydride is carried out over sodium wire for a week. Acetic anhydride can also be purified by azeotropic distillation with toluene . A quick purification method consists of shaking acetic anhydride with P 2 O 5 , then with potassium carbonate and fractional distillation [9] .
Physical Properties
Acetic anhydride is a colorless, clear, mobile liquid with a pungent odor. It is soluble in benzene , diethyl ether , ethanol , chloroform , acetic acid , tetrahydrofuran , and to a limited extent in cold water. When dissolved in water and alcohols , slow decomposition occurs, which accelerates upon heating [1] [10] .
Chemical Properties
Acetic anhydride is often used in acylation reactions (in this case, acetylation ), which involve a wide range of different compounds [11] .
- In particular, alcohols react with acetic anhydride, while acetic acid is released, and the bases (for example, sodium acetate ) and strong acids act as catalysts.
- Amines also enter the acylation reaction, and for them this reaction proceeds faster than for alcohols. Anilines can also be acetylated: usually this reaction is used to protect the amino group connected to the aromatic cycle from oxidation .
- Acetic anhydride is used to acylate aromatic hydrocarbons by the Friedel-Crafts reaction , for example, the reaction of benzene with acetic anhydride in the presence of a catalyst produces acetophenone .
- Inorganic acids also undergo acetylation reactions. Thus, in the interaction of acetic anhydride with nitric acid , acetyl nitrate is formed - a nitrating reagent, which is used in fine organic synthesis. Mixed esters with acetic anhydride give sulfuric acid , sulfonic acids and hydrochloric acid .
- Oxides can also be acetylated to form the corresponding acetates . Various salts, acetylenides , and alcoholates also react with acetic anhydride.
- Peroxides under the action of acetic anhydride form peracetic acid ( hydrogen peroxide ) or acetyl peroxide (CH 3 CO) 2 O 2 .
Another important property of acetic anhydride is its ability to take water in chemical reactions. This property is widely used in organic synthesis, as well as in the chemical industry. In particular, acetic anhydride is used as a dewatering agent in the production of RDX . Also, under the action of acetic anhydride, oximes lose water, turning into nitriles . In addition, acetic anhydride is involved in many cyclization reactions [12] .
Acetic anhydride enters into the Perkin reaction and other reactions of carbonyl compounds [5] .
Spectral data
- Mass spectrometry . The mass of the molecular ion of acetic anhydride is equal to 102, however, as a result of its fragmentation, peaks with m / z equal to 43 and 15 are also formed [13] .
- NMR spectroscopy . The protons of acetic anhydride in the 1 H NMR spectrum have a chemical shift of 2.219 ppm (solvent CDCl 3 ). Two signals are observed in the 13 C NMR spectrum: at 22.07 ppm for carbon atoms of the methyl group and at 166.63 ppm for carbon atoms of the carbonyl group [13] .
- UV spectroscopy . The maximum absorption of acetic anhydride is 217 nm [10] .
Usage
Industrial Use
About 80% of acetic anhydride synthesized in industry is used for the production of cellulose acetate [14] .
Use in Organic Synthesis
- It is used in organic synthesis as an acylating and water-taking agent.
- It is a precursor in the production of heroin and other drugs of the opioid group, in connection with which the turnover of acetic anhydride in the Russian Federation, Belarus, Ukraine and some other states is legally limited .
See also
- Carboxylic acid anhydrides
- Acetic acid
Notes
- ↑ 1 2 3 Chemical Encyclopedia / Ed. I. L. Knunyantsa. - M: Big Russian Encyclopedia, 1992. - V. 5. - S. 33. - ISBN 5-85270-039-8 .
- ↑ Ullmann, 2000 , p. 239-240.
- ↑ Dean JA Lange's Handbook of Chemistry. - McGraw-Hill, 1999 .-- ISBN 0-07-016384-7 .
- ↑ Sigma-Aldrich. Acetic Anhydride, ReagentPlus, ≥ 99% . Date of treatment May 2, 2013. Archived on May 10, 2013.
- ↑ 1 2 3 4 Ullmann, 2000 , p. 244.
- ↑ Ullmann, 2000 , p. 244-246.
- ↑ Ullmann, 2000 , p. 247-248.
- ↑ Ullmann, 2000 , p. 248-249.
- ↑ Amarego WLF, Chai CLL Purification of Laboratory Chemicals. - Sixth ed. - Elsevier, 2009. - P. 90. - ISBN 978-1-85617-567-8 .
- ↑ 1 2 Ullmann, 2000 , p. 240.
- ↑ Ullmann, 2000 , p. 241-242.
- ↑ Ullmann, 2000 , p. 243.
- ↑ 1 2 Spectral Database for Organic Compounds SDBS . Date of treatment May 4, 2013. Archived on May 10, 2013.
- ↑ Speight JG Chemical Process and Design Handbook. - McGraw-Hill, 2002 .-- P. 2.15. - ISBN 0-07-137433-7 .
Literature
- Held H., Rengst A., Mayer D. Acetic Anhydride and Mixed Fatty Acid Anhydrides // Ullmann's Encyclopedia of Industrial Chemistry. - Wiley, 2000. - DOI : 10.1002 / 14356007.a01_065 .
- Hoelz LVB Synlett Spotlight 291. Acetic anhydride (Ac 2 O) // Synlett. - 2009. - No. 15 . - S. 2547-2548 . - DOI : 10.1055 / s-0029-1217816 .
- Kim DH Acetic anhydride as a synthetic reagent ( J. ) // J. Het. Chem. - 1976. - Vol. 13 , no. 2 . - P. 179-194 . - DOI : 10.1002 / jhet.5570130201 .