Acetic anhydride

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Structural formula
Structural formula of acetic anhydride
Surname Acetic anhydride
other names
  • Acetic anhydride
  • Ac 2 O
  • Ethanoic anhydride
Molecular formula C 4 H 6 O 3
Brief description

colorless, pungent smelling liquid

External identifiers / databases
CAS number 108-24-7
EC number 203-564-8
ECHA InfoCard 100.003.241
PubChem 7918
Wikidata Q407775
Molar mass 102.09 g · mol -1
Physical state



1.08 g cm −3

Melting point

−73 ° C

boiling point

140 ° C

Vapor pressure
  • 5.06 h Pa (20 ° C)
  • 9.49 hPa (30 ° C)
  • 17.0 hPa (40 ° C)
  • 29.9 hPa (50 ° C)
Refractive index

1.3901 (20 ° C)

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
02 - Highly / extremely flammable 06 - Toxic or very toxic 05 - Corrosive


H and P phrases H: 226-302-331-314-335
P: 210-260-280-303 + 361 + 353-305 + 351 + 338-312
  • DFG : 5 ml m −3 , 21 mg m −3
  • Switzerland: 5 ml m −3 or 20 mg m −3
Thermodynamic properties
ΔH f 0

−624.4 kJ / mol

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Acetic anhydride ( acetic anhydride ), also abbreviated to Ac 2 O, is a chemical compound from the group of acid anhydrides with the empirical formula C 4 H 6 O 3 . It is an acetic acid derivative that results from the condensation of two acetic acid molecules . The carboxy groups of two molecules of acetic acid combine with the elimination of water .


In the laboratory

In the laboratory , acetic anhydride can be synthesized by reacting acetyl chloride with sodium acetate with the elimination of sodium chloride :

Laboratory synthesis of acetic anhydride

Instead of sodium acetate, another alkali salt of acetic acid can also be used.

Industrial manufacture

Large-scale production takes place through dehydration (elimination of water) of acetic acid at 800 ° C:

Dehydration of acetic acid to acetic anhydride

Rapid cooling and separation of the products is necessary during the synthesis, otherwise the reverse reaction to form acetic acid can take place.

Another possibility is the carbonylation of methyl acetate using the Tennessee-Eastman process :

Tennessee Eastman Acetic Anhydride Process 2.png

Part of the product stream is converted back into methyl acetate with methanol and returned to the process. The synthesis of acetic anhydride therefore only requires CO and methanol. The main catalysts used are rhodium and iridium complexes. The conversion takes place at increased CO pressure and temperatures around 200 ° C.


Chemical properties

Like other acid anhydrides, acetic anhydride can also be reacted with alcohols to form the corresponding esters and with ammonia or with amines to form the corresponding amide .

When placed in water, the compound initially dissolves and is then split into acetic acid by hydrolysis . The splitting takes place much faster in hot water than in cold water and is base or acid catalyzed. The solubility in cold water is 13.6%.

Safety-related parameters

Acetic anhydride forms flammable vapor-air mixtures. The compound has a flash point of 49 ° C. The explosion range is between 2.0% by volume (85 g / m³) as the lower explosion limit (LEL) and 10.2% by volume (430 g / m³) as the upper explosion limit (UEL). According to the vapor pressure function, the lower explosion point is 46 ° C. The maximum explosion pressure is 7 bar. The limit gap width was determined to be 1.17 mm. This results in an assignment to explosion group IIA. The ignition temperature is 330 ° C. The substance therefore falls into temperature class T2.


Acetic anhydride is the most commercially important aliphatic anhydride . Around one million tons are produced every year. It is mainly used for the reaction with alcohols to form acetates . Frequent areas of application are the production of cellulose acetate , N-acetyl-4-aminophenol (paracetamol) and acetylsalicylic acid as well as for the absoluteization of glacial acetic acid . It is also essential in the manufacture of heroin , which is why many countries are trying to curb the manufacture of this semi-synthetic drug by controlling access to acetic anhydride . In the Basic Materials Monitoring Act , it is listed in category 2, so production, import, export and trade from a quantity of 100 liters are subject to registration.

In synthetic chemistry, acetic anhydride is often used to create protective groups that convert an alcohol into a less reactive ester .

Diacetyl peroxide , which as a free radical generator in polymerization reactions is used, can be of acetic anhydride and sodium metaborate - peroxidhydrat manufacture.

In a mixture with sulfuric acid (9 parts acetic anhydride to 1 part sulfuric acid) it is used for acetolysis .

Acetic anhydride is also used to acetylate wood , a wood modification to improve the properties (e.g. moisture resistance) of coniferous wood .

Individual evidence

  1. a b Entry on acetic anhydride. In: Römpp Online . Georg Thieme Verlag, accessed on December 25, 2014.
  2. a b c d e f g h i j k l m n o p q Entry on acetic anhydride in the GESTIS substance database of the IFA , accessed on July 29, 2017(JavaScript required) .
  3. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-4.
  4. Entry on Acetic anhydride in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  5. Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 108-24-7 or acetic anhydride ), accessed on November 2, 2015.
  6. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-26.
  7. Claudia Synowietz (Ed.): Paperback for chemists and physicists . founded by Jean d'Ans, Ellen Lax. 4th edition. Volume II: Organic Compounds . Springer, Berlin 1983, ISBN 3-540-12263-X .
  8. ^ A b c d E. Brandes, W. Möller: Safety-related parameters - Volume 1: Flammable liquids and gases , Wirtschaftsverlag NW - Verlag für neue Wissenschaft GmbH, Bremerhaven 2003.