Electrochemistry of organophosphorus compounds. I. Electroreduction of tris(p-nitrophenyl) phosphate

The electroreduction of tris(p-nitrophenyl) phosphate has been investigated by polarography, cyclic voltammetry, coulometry, and esr. A mechanism for the reduction based on an initial two-electron transfer followed by cleavage of the oxygen-carbon bond is proposed. The cleaved nitrophenyl rings condense to give 4,4'-dinitrobiphenyl as a product during controlled-potential reduction. lthough the electrochemical oxidation and reduction A of organic nitrogen compounds have been widely investigated, relatively few studies have been concerned with phosphorus compounds. Because of the widespread use of organophosphorus compounds as biocides, plasticizers, and additives, and a fundamental interest in the mechanisms of oxidation and reduction of this class of compounds, for example, in biological systems, we have undertaken a systematic investigation of their electrochemical behavior. Tris(pnitropheny1) phosphate (TNP) [(NOzC6H,0)3P=0] was chosen as a model compound for an initial study, because of the well-known behavior of nitro aromatic compounds in aprotic media,2 and because of the practical interest in nitro-substituted organosphorus compounds as insecticides. Recently Gulick and Geske have reported the polarographic reduction of a number of nitrophenyl phosphates in nonaqueous media during a study of the electron spin resonance (esr) spectra of anion radicals (1) To whom correspondence and request for reprints should be directed. (2) See, for example, (a) A. H. Maki and D. H. Geske, J. Chem. Phys., 33, 825 (1960); (b) J. Q. Chambers and R. N. Adams, J. Electroanal. Chem.. 10. 400 (1965). and references contained therein. (3) W. M. Gulick,' Jr., and D. H. Geske, J . Am. Chem. Soc., 88, 2928 (1966). derived from these compounds. No investigation of the mechanism of the reaction or of reactions following the electron transfer was reported. A few electrochemical studies concerned with the development of polarographic methods for the analysis of such compounds as Malathion [ S ( 1,Zdicarbethoxyethyl) 0,O-dimethyl dithiophosphate] and Parathion (0,O-diethyl 0-p-nitrophenyl thiophosphate) have also been