Nucleophilic Attack vs. General Base Assisted Hydrolysis in the Reactions of Acetic Anhydride with Primary and Secondary Amines. pH-Yield Studies in the Recognition and Assessment of the Nucleophilic and General Base Reactions

The reaction of a set of primary and secondary amines with acetic anhydride in water at 25 o C gave variable yields of the N-substituted acetamide in seven of the eight amines studied. The yield of the amide as a function of pH revealed the incursion in most cases of a general base assisted hydrolyse of the acetic anhydride by the amine. From the pK a 's of the amines and k w and k OH for acetic anhydride (the specific rates for the reaction of the anhydride Nth water and hydroxide, respectively), both k DN (for the formation of the acetamides) and l GB (for the general base assisted hydrolysis) may be readily evaluated by fitting the pH-yield data to pH-yield or pH-product ratio profiles