Solvent effects on the nucleophilic substitution reactions of p-nitrophenyl acetate with hydroxamate ions

Rate constants have been measured spectrophotometrically for the reactions of p-nitrophenyl acetate (PNPA) with some α-effect nucleophiles, i.e., acetohydroxamate, benzohydroxamate, and salicylhydroxamate ions in dimethylsulfoxide, dimethylformamide, 1,4-dioxane, and acetonitrile-water mixtures of varying compositions (10-80% v/v) at 27 °C (pH 7.7). All the three hydroxamates exert a large α-effect in H2O. The reactivity of hydroxamates towards PNPA depends upon the nature of substrate and solvents. The kinetic results have been explained on the basis of basicities (pKa), solvation effect, α-effect, and ground state destabilization.