Studies on Reactions of the N-Phosphonium Salts of Pyridines. V. The Preparation of Carboxylic Amides and Esters by Means of the One-electron-transfer Oxidation of Phosphorous Acid and Its Esters in the Presence of Tertiary Amines

Abstract

Abstract The oxidation of phosphorous acid and its esters with an equimolar amount of mercurous chloride and half an equimolar amount of mercuric chloride was carried out in tertiary amines. On the treatment of the oxidation mixture with carboxylic acids, amines, and alcohols, followed by aminolysis, alcoholysis, or acidolysis, the corresponding carboxylic amides and esters were obtained in good yields, together with a nearly quantitative yield of metallic mercury. The yield was affected by the tertiary amines, the alkyl groups in the dialkyl phosphites, and the steric effect of the carboxylic acids. The reaction was proposed to proceed through the activation of carboxylic acids, amines, and alcohols via the N-phosphonium salts prepared by the oxidation. The electron-transfer processes involved in the oxidation were discussed on the basis of the yield of the amides obtained. These procedures were successfully extended to the preparation of peptides and active esters of amino acids, using diphenyl phosphite in pyridine.