Amide formation formic anhydride

HCO2H, AC2O, 25°, 1 h, 78-90% yield.The use of formic acetic anhydride for esterification and amide formation has been reviewed. ... 

As mentioned above, the bis-amides 9a are used as precursors in the synthesis of Af-acylenamines. The conditions used for this reaction depend on the purpose of the synthesis and are described in numerous works, and reviewed in a series of articles35-37. The acid catalyst is usually concentrated sulfuric acid, but a successful application of 85% phosphoric, chlorosulfonic, methanesulfonic and formic acids was reported, and reactions were also conducted in the presence of anhydrous hydrogen chloride35. The solvents used are usually glacial acetic acid and chlorinated hydrocarbons. It is believed that the water necessary for the formation of the bis-amides under anhydrous conditions is obtained from conversion of the carboxylic acid to the anhydride, or even the sulfuric acid35. 

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