Nuclear magnetic resonance investigations of iminium ion intermediates, part 7. Structure and mechanism of formation of the intermediates in the reactions between amides and CSCl2 or PSCl3 or between thioamides and COCl2, POCl3, or PSCl3

Abstract

Previous studies of the reactions between amides and Lewis acids (COCl₂, SOCl₂, POCl₃) have been extended to reactions involving amides with PSCl₃ or CSCl₂ and thioamides with POCl₂ or PSCl₃. The products and intermediates were identified using ¹H, ¹³C, and ³¹P n.m.r. spectroscopy. Kinetic and variable temperature n.m.r. experiments have permitted the elucidation of the reaction mechanisms. The experiments also demonstrated exchange processes between the amides or thioamides and the iminium salts. Although the products are of various types a general feature is equilibria between the amide + PSCl₃ and the thioamide + POCl₃. The reactivities are highly dependent on the structure of the starting amide or thioamide, the polarity of the solvent, and the nature of the Lewis acid.