Efficient synthesis of mixed aliphatic benzoic anhydrides in a two-phase system

The reactions of benzoyl chloride and different aliphatic sodium carboxylates catalyzed by pyridine derivatives in a two-phase water/organic solvent system were studied. The effects of catalyst structure, initial concentration of catalyst and carboxylate ion in the aqueous phase, temperature, and polarity of organic solvent on the formation rate and yield of mixed anhydride were investigated in detail. 4-methylpyridine N-oxide, 4-methoxypyridine N-oxide, 4-morpholinopyridine N-oxide, and 4-dimethylaminopyridine were used as catalysts. A higher reaction rate was achieved with use of 4-methylpyridine N-oxide. In contrast to literature data, it was found that the reaction between ionic intermediate and carboxylate ion is a rate-determining step rather than the reaction of ionic intermediate formation. Both linear and branched carboxylates were used to study the effect of carboxylate ion structure on the reaction rate and yield of the mixed anhydrides.