Solvation Accounts for the Counterintuitive Nucleophilicity Ordering of Peroxide Anions.

The nucleophilic reactivities (N, s ) 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 (Ar CH ) in alkaline aqueous solutions at 20 °C. The second-order rate constants revealed that deprotonated peroxy acids (RCO ), 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=s (N+E) furnished nucleophilicity parameters (N, s ) 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.