Experimental and computational determination of Brønsted coefficients for equilibrium transfer of the O , O ‐dimethyl phosphorothioyl group between oxyanion nucleophiles

An experimental determination of the β Eq value for equilibrium transfer of the O,O ‐dimethyl phosphorothioyl group between oxyanion nucleophiles in water and methanol at 25 °C is presented. The respective β Eq values in the two solvents are experimentally the same at −1.45 ± 0.08 and −1.39 ± 0.12. Based on the observation that the Brønsted correlation for the nucleophilic reaction of phenoxides in water with substrate 1d (dimethyl 4‐nitrophenyl phosphorothioate, p K a HOAr of 7.14) is linear over the entire range of phenoxides employed (5.53 ≤ p K a Nu  ≤ 12.38), the reaction for phenoxide nucleophiles displacing phenoxide leaving groups is probably concerted. The obtained data allow one to calculate, for a symmetrical transition state involving 2,4,5‐trichlorophenoxide as a nucleophile and leaving group, an approximately 60% P–OAr cleavage and about 40% P–Nuc bond formation. A computational method is presented for the rapid prediction of the β Eq values for such processes in water and methanol, and the results are compared with known values from the literature. Copyright © 2011 John Wiley & Sons, Ltd.