Acetic anhydride (boiling point: 139.5, density: 1.0820) may be produced by three different methods. The first procedure involves the in situ production from acetaldehyde of peracetic acid, which in turn reacts with more acetaldehyde to yield the anhydride.

CH3CH=O + O2 ? CH 3C(=O)OH
CH3C(=O)OH + CH3CH=O ? CH3C(=O)O(O=)C CH3 + H2O

In the preferred process, acetic acid (or acetone) is pyrolyzed to ketene, which reacts with acetic acid to form acetic anhydride.

CH3C(=O)OH ? CH2=C=O + H2O
CH2=C=O + CH3C(=O)OH ? CH3C(=O)O(O=)C CH3

Another process to make acetic anhydride involves carbon monoxide insertion into methyl acetate (Fig. 1).

CH3C(=O)OCH3 ? CH3C(=O)O(O=)CCH3

Approximately 80 percent of acetic anhydride is used as a raw material in the manufacture of cellulose acetate.

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