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 ‐MeC 6 H 4 OKwith 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.