NEIGHBORING GROUP PARTICIPATION IN ORGANIC REDOX REACTIONS. 13. INTRAMOLECULAR INTERACTION OF THE β-PHOSPHONIC ACID GROUP IN THE AQUEOUS IODINE OXIDATION OF THIOETHERS AND DISULFIDES.¹ GENERATION OF A PHOSPHONIC-PHOSPHORIC ANHYDRIDE

Abstract

The oxidation of the phosphonic acid-thioether, 2-methylthioethanephosphonic acid (MTEP) and the oxidative-cleavage of the phosphonic acid-disulfide (PED) by aqueous iodine are accelerated by neighboring-group participation. The pH profiles indicate that in both cases it is the dianionic form of the phosphonate group which is responsible for accelerations of 10⁶ and 10² in the reactions of MTEP and PED. respectively, compared to analogs without neighboring groups. The oxidative cleavage of PED in the presence of phosphate buffer generates ca. 30% of a hydrolytically stable, mixed phosphonic-phosphoric anhydride, which makes the proposed cyclic sulfenic-phosphonic anhydride intermediate one of the more efficient phosphate-coupling agents in aqueous solution. In contrast, no mixed anhydride is generated during the oxidation of MTEP in phosphate buffer.