Acetic anhydride



Acetic anhydride
IUPAC name Ethanoyl ethanoate
Other names Acetic anhydride
Acetic acid anhydride
Acetylacetate
Acetyl oxide
Acetic oxide
Ethanoic anhydride
Identifiers
CAS number 108-24-7
RTECS number AK1925000
SMILES CC(=O)OC(=O)C
InChI InChI=1/C4H6O3/c1-3(5)
7-4(2)6/h1-2H3
Properties
Molecular formula C4H6O3
Molar mass 102.1 g/mol
Appearance clear liquid
Density 1.08 g/cm³, liquid
Melting point

−73.1 °C

Boiling point

139.8 °C

Solubility in water 2.6% by weight; rapidly reacts to
form acetic acid
Hazards
EU classification Corrosive (C)
R-phrases R10, R20/22, R34
S-phrases S45
Flash point 54 °C
Related Compounds
Related acid anhydrides Propionic anhydride
Related compounds Acetyl chloride
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Acetic anhydride is the acetic acid, which is formed by its reaction with the moisture in the air.

Production

Acetic anhydride is produced by methyl acetate:[1]

CH3CO2CH3 + CO → (CH3CO)2O

This process involves the conversion of methyl acetate to Monsanto acetic acid synthesis, which also involves a rhodium catalyzed carbonylation of methyl iodide, is at least partially aqueous.

To a decreasing extent, acetic anhydride is also prepared by the reaction of ketene with acetic acid. Ketene is generated by dehydrating acetic acid at elevated temperatures.

Due to its low cost, acetic anhydride is purchased, not prepared, for use in research laboratories.

Uses

Ac2O is mainly used for the cellulose acetate for photographic film and other applications.

In general alcohols and amines are acetylated.[2] For example, the reaction of acetic anhydride with ethanol is:

(CH3CO)2O + CH3CH2OH → CH3CO2CH2CH3 + CH3CO2H

Often a base such as Lewis acidic scandium salts are also effective catalysts.[3]

morphine, acetic anhydride (known as 'AA' in clandestine chemistry circles) is listed as a DEA List II Precursor,[4] and restricted in many other countries.

Hydrolysis

Acetic anhydride dissolves in water to approximately 2.6% by weight.[5] Aqueous solutions have limited stability because, like most acid anhydrides, acetic anhydride hydrolyses to give acetic acid:[6]

(CH3CO)2O + H2O → 2 CH3CO2H

Safety

  Acetic anhydride is an irritant and flammable. Because of its reactivity toward water, alcohol foam or carbon dioxide are preferred for fire suppression.[7] The vapour of acetic anhydride is harmful.[8]

Notes and references

  1. ^ Zoeller, J. R.; Agreda, V. H.; Cook, S. L.; Lafferty, N. L.; Polichnowski, S. W.; Pond, D. M. "Eastman Chemical Company Acetic Anhydride Process" Catalysis Today (1992), volume 13, pp.73-91. doi:10.1016/0920-5861(92)80188-S
  2. ^ Science is Fun…. Chemical of the Week. Retrieved on 2006-03-25.
  3. ^ Macor, J.; Sampognaro, A. J.; Verhoest, P. R.; Mack, R. A. "(R)-(+)-2-Hydroxy-1,2,2-Triphenylethyl Acetate" Organic Syntheses, Collected Volume 10, p.464 (2004). http://www.orgsyn.org/orgsyn/pdfs/V77P0045.pdf
  4. ^ ChemGuide. Acid Anhydrides. Retrieved on 2006-03-25.
  5. ^ British Petroleum. Acetic Anhydride: Frequently Asked Questions (PDF). Retrieved on 2006-05-03.
  6. ^ Celanese. Acetic Anhydride: Material Safety Data Sheet (PDF). Retrieved on 2006-05-03.
  7. ^ Data Sheets. International Occupational Safety and Health Information Centre. Retrieved on 2006-04-13.
  8. ^ NIOSH. Pocket Guide to Chemical Hazards. Retrieved on 2006-04-13.

See also
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Acetic_anhydride". A list of authors is available in Wikipedia.