Kinetic Studies of the Solvolyses of 4-Nitrophenyl Phenyl Thiophosphorochloridate

Abstract

Rates of solvolyses of 4-nitrophenyl phenyl thiophosphorochloridate (4-N<TEX>$O_2$</TEX>PhOP(S)(Cl)OPh, <TEX>$\underline{1}$</TEX>) in ethanol, methanol, and aqueous binary mixtures incorporating ethanol, methanol, acetone, and 2,2,2-trifluroethanol (TFE) are reported. Thermodynamic parameters were determined at several temperatures in three representative solvents. The extended Grunwald-Winstein equation was applied to 29 solvents and the correlation coefficient (R) showed 0.959. The sensitivities (l = 1.37 and m = 0.62) are similar to those obtained for diphenyl thiophosphorochloridate ((<TEX>$PhO)_2$</TEX>PSCl, <TEX>$\underline{2}$</TEX>), diphenyl phosphorochloridate ((<TEX>$PhO)_2$</TEX>POCl, <TEX>$\underline{3}$</TEX>), diphenyl phosphinic chloride (<TEX>$Ph_2$</TEX>POCl, <TEX>$\underline{4}$</TEX>), and diphenyl thiophosphinic chloride (<TEX>$Ph_2$</TEX>PSCl, <TEX>$\underline{5}$</TEX>). The solvolytic reaction mechanism of 4-nitrophenyl phenyl thiophosphorochloridate (<TEX>$\underline{1}$</TEX>) is suggested to be proceeded a <TEX>$S_N$</TEX>2 process as previously reported result. The activation enthalpies are shown as slightly low as <TEX>${\Delta}H^{\neq}\;=\;9.62\;to\;11.9\;kcal{\cdot}mol^{-1}$</TEX> and the activation entropies are shown as slightly high negative value as <TEX>${\Delta}S^{\neq}\;=\;-34.1\;to\;-44.9\;cal{\cdot}mol^{-1}{\cdot}K^{-1}$</TEX> compared to the expected <TEX>$S_N$</TEX>2 reaction mechanism. Kinetic solvent isotope effects are accord with a typical <TEX>$S_N$</TEX>2 mechanism as shown in the range of 2.41 in MeOH/ MeOD and 2.57 in <TEX>$H_2O/D_2O$</TEX> solvent mixtures.