THIONO COMPOUNDS. 9. USE OF SPECTRA TO STUDY INTERMEDIATES IN THE OXIDATION OF THIONO PHOSPHORUS, COMPOUNDS

Abstract

Intermediates in the oxidation by m-chloroperoxybenzoic acid (MCPBA) of 13 structurally different thiophosphoramides and phosphorothioates were studied at -25°C to 0°C using NMR, EPR, UV. IR and Raman spectra. The lifetimes of intermediates ascertained by NMR varied from a few minutes to many hours at the same temperature and were longer for thiono esters than for amides, for aryl than for alkyl constituents, and for electron-donating substituents on aryl groups than for electron-withdrawing groups. The major ³¹P NMR peaks for all intermediates appeared in the same region, about midway between the resonances of the P(S) starting materials and the P(O) products, indicating close structural similarity to one another for the intermediates; the range of 13-33 ppm for the major peaks indicates that the intermediates are tetracoordinate and supports phosphonium polysulfide structures for them of the type R₃PS_x (26, Scheme 1), or perhaps R₃POS_x. UV spectra also afforded support for polysulfide structures, since typical absorption develops and then disappears. Raman, ³¹P NMR, and UV spectra are consistent with longer-term presence of bisphosphonium species (e.g. 25, from reactions of 26; Scheme 1). EPR spectra gave no indication of homolysis.

Key Words:

• Phosphorothioates
• Raman Spectra
• Infrared Spectra
• Thionophosphorus
• NMR Spectra
• Thiophosphoramides