Solvent effect on the rate of ester interchange of p-nitrophenyldiethylphosphate

The reaction of p-nitrophenyldiethylphosphate with sodium phenolate takes place readily in aprotic polar solvents. Bimolecular rate constants of this reaction increase with increased concentration of the phenolate in such solvents as dimethylsulfoxide (DMSO), dimethylformamide (DMF), or hexamethylphosphoric amide (HMPA), but decrease in acetonitrile or acetone; this is caused by the association of sodium phenolate, and the different reactivities of free ions and ion pairs. The addition of 18-crown-6 to the reaction mixture decreases the reaction rate, because of the reduced reactivity of the complex formed by the crown ether with the phenolate ion pair.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1968–1972, September, 1991.