Solvation Accounts for the Counterintuitive Nucleophilicity Ordering of Peroxide Anions.

The nucleophilic reactivities (N, sN ) of peroxide anions (generated from aromatic and aliphatic peroxy acids or alkyl hydroperoxides) were investigated by following the kinetics of their reactions with a series of benzhydrylium ions (Ar2 CH+ ) in alkaline aqueous solutions at 20 °C. The second-order rate constants revealed that deprotonated peroxy acids (RCO3- ), although they are the considerably weaker Brønsted bases, react much faster than anions of aliphatic hydroperoxides (ROO- ). Substitution of the rate constants of their reactions with benzhydrylium ions into the linear free energy relationship lg k=sN (N+E) furnished nucleophilicity parameters (N, sN ) of peroxide anions, which were successfully applied to predict the rates of Weitz-Scheffer epoxidations. DFT calculations with inclusion of solvent effects by means of the Integral Equation Formalism version of the Polarizable Continuum Model were performed to rationalize the observed reactivities.