Acetic anhydride

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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 139.9 °C
Dipole moment ? D
Hazards
MSDS External MSDS
EU classification Corrosive (C)
NFPA 704
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)
[Chemical infoboxInfobox disclaimer and references]

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.

Contents

1 Properties
2 Production

2.1 Acetic acid condensation
2.2 Alcohol and

3 Uses
4 Reactions
5 Safety
6 Notes and references
7 See also

Properties

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

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 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

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

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

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.

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	139.9 °C
Dipole moment	? D
Hazards
MSDS	External MSDS
EU classification	Corrosive (C)
NFPA 704
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) [Chemical infoboxInfobox disclaimer and references]