The formation of anhydrides in the Mitsunobu reaction

Article abstract of DOI:10.1016/S0040-4020(97)00010-0

Treatment of benzoic acid with triphenylphosphine and diisopropyl azodicarboxylate in THF or acetonitrile, results in the formation of benzoic anhydride. A significant solvent effect was observed for this reaction. Anhydride formation did not occur however with the more acidic p-nitrobenzoic acid. Relative rate and competition experiments suggest that the improved yields observed when p-nitrobenzoic acid is used instead of benzoic acid in the Mitsunobu esterification reaction are due to competitive anhydride formation in the latter case.