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	*
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	139.9 °C
Dipole moment	? D
Hazards
MSDS	External MSDS
EU classification	Corrosive (C)
NFPA 704
R-phrases	, ,
S-phrases	, , ,
Flash point	54 °C
RTECS number	AK1925000
Supplementary data page
Structure and properties	n, εr, 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) Chemical infobox

Acetic anhydride, also known as ethanoic anhydride, is one of the simplest of acid anhydrides. It has the chemical formula C₄H₆O₃ or (CH₃CO)₂O. Acetic anhydride is corrosive, flammable, and its vapour is irritating to the eyes and upper respiratory tract.

Properties

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Acetic anhydride is a colourless liquid and smells strongly of vinegar. The smell is due to a reaction with the moisture in the air forming acetic acid.

Acetic anhydride dissolves in water to approximately 2.6% by weight; 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.

Production

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Acetic acid condensation

The production of acetic anhydride by condensation of acetic acid is a major application using about 25% to 30% of the global production of acetic acid.

Alcohol and ester

Another synthesis of acetic anhydride is the reaction of acetyl chloride with sodium acetate:

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

Uses

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Common uses of acetic anhydride are in the production of clothes (cellulose acetate), in the chemical synthesis of aspirin (acetyl salicylic acid) from salicylic acid, and in the production of heroin (diacetylmorphine) from morphine. It is most widely used as a chemical reagent for acetylation.

Reactions

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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. 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 remove the acetic acid by-product.

Safety

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Acetic anhydride is corrosive and should be handled with care. Contact can cause delayed reaction burns and should be washed immediately with water. It is also moderately flammable therefore should not be used near an open flame. Water should not be used to fight a fire with acetic anhydride, alcohol foam or carbon dioxide are preferred as they will not react.

The vapour of acetic anhydride is corrosive to the mucous membranes of the respiratory tract and should be handled in a well-ventilated area. If the fumes are inhaled the person should be moved immediately to fresh air and medical attention sought. If the person is not breathing, cardiopulmonary resuscitation should be performed.

Notes and references

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See also

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Acid anhydride

Acid anhydrides

Essigsäureanhydrid | Anidride acetica | Acetanhidrīds | Azijnzuuranhydride | 無水酢酸 | Bezwodnik octowy | Уксусный ангидрид | Ättiksyraanhydrid