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Illustrative is the acetylation of aniline. First aniline is dissolved in water using one equivalent of hydrochloric acid. This solution is subsequently treated, sequentially, with acetic anhydride and aqueous sodium acetate. Aniline attacks acetic anhydride followed by deprotonation of the ammonium ion: Acetate then acts as a leaving group:
Hippuric acid, the benzamide derivative of glycine, cyclizes in the presence of acetic anhydride, condensing to give 2-phenyl-oxazolone. [3] This intermediate also has two acidic protons and reacts with benzaldehyde, acetic anhydride and sodium acetate to a so-called azlactone. This compound on reduction gives access to phenylalanine. [4]
Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH 3 CO) 2 O. Commonly abbreviated Ac 2 O , it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis .
Acetic anhydride. This reagent is common in the laboratory; its use cogenerates acetic acid. [7] [10] Acetyl chloride. This reagent is also common in the laboratory, but its use cogenerates hydrogen chloride, which can be undesirable. [8] Ketene. At one time acetic anhydride was prepared by the reaction of ketene with acetic acid: [11]
The following figure shows the reaction mechanism: [2] Reaktionsmechanismus Albright-Goldman-Oxidation. First, dimethyl sulfoxide (1) reacts with acetic anhydride to form a sulfonium ion. It reacts with the primary alcohol in an addition reaction. Furthermore, acetic acid is cleaved, so that intermediate 2 is formed. The latter reacts upon ...
Aniline and its ring-substituted derivatives react with nitrous acid to form diazonium salts. One example is benzenediazonium tetrafluoroborate. Through these intermediates, the amine group can be converted to a hydroxyl (−OH), cyanide (−CN), or halide group (−X, where X is a halogen) via Sandmeyer reactions.
Modern variations on the Dakin–West reaction permit many enolizable carboxylic acids – not merely amino acids – to be converted to their corresponding methyl ketones. For example, β-aryl carboxylic acids can be efficiently converted to β-aryl ketones by treatment of an acetic anhydride solution of the acid with catalytic N-methylimidazole.
Examples: synthesis of N-vanillyl nonanamide, also known as synthetic capsaicin; synthesis of benzamide from benzoyl chloride and a phenethylamine; synthesis of flutamide, a nonsteroidal antiandrogen; acylation of a benzylamine with acetyl chloride (acetic anhydride is an alternative)