The Influence of solvent and crown polyethers on the nucleophilic reactivity of potassium tert-Butylperoxide,potassium tert-Butoxide,and some other oxygen bases

The rates of reaction of t-BuOOK, t-BuOK, n-BuOOK, and p-MeC₆H₄OKwith p-nitrophenyl diphenylphosphinate 1 and with p-nitrophenyl benzoate 2 have been measured in toluene both in the absence and in the presence of crown polyether dicyclohexyl-18-crown-6 3a . The rates of nucleophilic displacementon 1 by HOO^?, t-BuOO^?, and some “nonalpha” oxyanions in water have also been determined. Solvent transfer from water to toluene results in increasing the nucleophilic reactivity of the t-butyl hydroperoxide anion. Rate ratios Q_Qa are given which allow one to estimate the enhanced reactivity of t-BuOO^? (an α-nucleophile) compared to oxygen nucleophiles of comparable base strength toward 1 and 2 . These are for substrate 1 , Q_α (water) ? 6.5 and Q_α (toluene) ? 2.7; for substrate 2 , Q_α (water) ? 5.5 and Q_α (toluene) ? 5. The hypothesis is advanced that solvation is not a major factor in determining the α-effect of the t-butylhydroperoxide anion.