Reactions of acid anhydrides with nitrogen compounds

Carboxylic anhydrides are more powerful than the free acids as acylating agents and convert ammonia and primary and secondary amines into amides, generally smoothly and in very good yield. The equation 

Reaction conditions can be varied within wide limits. Merely mixing the amine and anhydride often sets off an exothermic reaction, but the mixture is usually heated subsequently for 1-2 hours on the steam-bath or under reflux. A solvent is not always needed when the reactants are liquid. 

Normally, however, a solvent is not dispensed with. For acetylations it may be an excess of the anhydride or glacial acetic acid may be used. Solvents of general utility are ether, light petroleum, benzene, and toluene dimethyl-formamide and pyridine have been used but less often use of alcohols is restricted to reactions at low temperatures. 

Formylation is best carried out with the readily accessible mixed anhydride of formic and acetic acid.721 

Aromatic anhydrides mostly react more slowly than aliphatic ones. For the analogous benzoylation of p-nitroaniline the amine is boiled with benzoic anhydride in benzene for 1.5 hours.720 

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