A Kinetic Study on Solvolysis of Diphenyl Thiophosphorochloridate

Abstract

Rates of solvolyses of diphenyl thiophosphorochloridate (<TEX>$(PhO)_2$</TEX>PSCl, 1) in ethanol, methanol, and aqueous binary mixtures incorporating ethanol, methanol, acetone and 2,2,2-trifluoroethanol (TFE) are reported. For four representative solvents, studies were made at several temperatures and activation parameters were determined. The 30 solvents gave a reasonably precise extended Grunwald-Winstein plot, correlation coefficient (R) of 0.989. The sensitivity values (l = 1.29 and m = 0.64) of diphenyl thiophosphorochloridate (<TEX>$(PhO)_2$</TEX>PSCl, 1) were similar to those obtained for diphenyl phosphorochloridate (<TEX>$(PhO)_2$</TEX>POCl, 2), diphenylphosphinyl chloride (<TEX>$Ph_2$</TEX>POCl, 3) and diphenylthiophosphinyl chloride (<TEX>$Ph_2$</TEX>PSCl, 4). As with the previously studied of 3~4 solvolyses, an <TEX>$S_N$</TEX> pathway is proposed for the solvolyses of diphenyl thiophosphorochloridate (1). The activation parameters, <TEX>${\Delta}H^{\neq}\;(=11.6{\sim}13.9\;kcal{\cdot}mol^{-1})\;and\;{\Delta}S^{\neq}\; (=\;-32.1\;{\sim}\;-42.7\;cal{\cdot}mol^{-1}{\cdot}K^{-1})$</TEX>, were determined, and they were in line with values expected for an <TEX>$S_N$</TEX>2 reaction. The large kinetic solvent isotope effects (KSIE, 2.44 in MeOH/MeOD and 3.46 in <TEX>$H_2O/D_2$</TEX>O) are also well explained by the proposed <TEX>$S_N$</TEX>2 mechanism.