Acetic anhydride

From Wikipedia, the free encyclopedia

Acetic anhydride

General
Systematic name	Ethanoyl ethanoate
Other names	Acetic anhydride Acetic acid anhydride Acetylacetate Acetyl oxide Acetic oxide Ethanoic anhydride
Molecular formula	C₄H₆O₃
SMILES	CC(=O)OC(=O)C
Molar mass	102.1 g/mol
Appearance	clear liquid
CAS number	[108-24-7]
Properties
Density and phase	1.08 g/cm³, liquid
Solubility in water	2.6% by weight; rapidly reacts to form acetic acid
Melting point	−73.1 °C
Boiling point	139.8 °C
Dipole moment	? D
Hazards
MSDS	External MSDS
EU classification	Corrosive (C)
NFPA 704	2 2 1 W
R-phrases	R10, R20/22, R34
S-phrases	S1/2, S26, S36/37/39, S45
Flash point	54 °C
RTECS number	AK1925000
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related acid anhydrides	Propionic anhydride
Related compounds	Acetic acid 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, formally known as ethanoic anhydride and commonly abbreviated Ac₂O, is one of the simplest of acid anhydrides. With the chemical formula (CH₃CO)₂O, it is a widely used reagent in organic synthesis. It is a colorless liquid that smells strongly of vinegar (acetic acid) due to its reaction with the moisture in the air.

1 Properties
2 Production
3 Uses
4 Reactions
5 Safety
6 Notes and references
7 See also
8 External links

[edit] Properties

Acetic anhydride dissolves in water to approximately 2.6% by weight^[1]; however, it is not possible to keep a solution of acetic anhydride because it decomposes within a few minutes (the exact time being dependent upon the temperature) into a solution of acetic acid^[2].

[edit] Production

Acetic anhydride is produced by condensation of acetic acid. In 2006, ca. 25%of the global production of acetic acid was consumed for this process.^[3]

Acetic anhydride can also be prepared by the reaction of acetyl chloride with sodium acetate:

H₃C-C(=O)Cl + H₃C-COO⁻ Na⁺ → Na⁺Cl⁻ + H₃C-CO-O-CO-CH₃

[edit] Uses

Ac₂O is widely used for acetylation of alcohols and amines. ^[4] Illustrative applications include the production of cellulose acetate, which is used for clothing. Aspirin, acetyl salicylic acid, is prepared by the acetylation of salicylic acid. Heroin, diacetylmorphine, is prepared by the acetylation of morphine. For this reason, acetic anhydride is listed as a DEA List II Precursor. Acetic Anhydride is also used in the production of some types of photographs, negatives and motion pictures.

[edit] Reactions

Hydrolysis of acetic anhydride produces acetic acid slowly at room temperature:

(CH₃CO)₂O + H₂O → 2CH₃COOH

Acetic anhydride also reacts under gentle heating with alcohols to form acetic acid and an ester. ^[5] For example, the reaction of acetic anhydride with ethanol is:

(CH₃CO)₂O + CH₃CH₂OH → CH₃COOCH₂CH₃ + CH₃COOH

Here, the ester produced is ethyl acetate. Often a base such as pyridine is added to function as catalyst.

[edit] Safety

Corrosive

Acetic anhydride is corrosive, an irritant, and flammable. Because of its reactivity toward water, alcohol foam or carbon dioxide are preferred for fire suppresion. ^[6]

The vapour of acetic anhydride is harmful, potentially necessitating cardiopulmonary resuscitation (CPR).^[7]

[edit] Notes and references

^ British Petroleum. Acetic Anhydride: Frequently Asked Questions (PDF). Retrieved on May 3, 2006.
^ Celanese. Acetic Anhydride: Material Safety Data Sheet (PDF). Retrieved on May 3, 2006.
^ Greener Industry. Ethanoic Acid – Major Uses. Retrieved on March 25, 2006.
^ Science is Fun…. Chemical of the Week. Retrieved on March 25, 2006.
^ ChemGuide. Acid Anhydrides. Retrieved on March 25, 2006.
^ Data Sheets. International Occupational Safety and Health Information Centre. Retrieved on April 13, 2006.
^ NIOSH. Pocket Guide to Chemical Hazards. Retrieved on April 13, 2006.