Marked influence of minute amounts of water on the selectivity of alkylation site of sodium 2-naphtholate (ambident anion) in aprotic solvent

It has been established that solvation is an integral part of most bimolecular reactions in solution. In particular, Parker¹ has demonstrated that the reactivities of anionic species are dramatically affected by the solvation through hydrogen bonding with protic solvent species. The marked activation of anionic species observed in dipolar aprotic solvents has since been attributed to the desolvation effect, that is, exclusion of hydrogen bond forming molecules from the reaction center.¹ On the other hand, the reaction rate in dipolar aprotic solvents has been believed to be affected little by small amounts (several millimolar) of remaining water, ^2-4 since dipolar aprotic solvent molecules (i.e., hygroscopic molecules) can compete with reacting anions as acceptors for water molecules.³ It was found, however, that the rate constants for the nucleophilic reactions of oxyanions are affected by a water concentration of less than 1 M, and the plots of rate constants vs. [H₂O] increased exponentially with decreasing water concentration.^5-7 The influence of small amounts of water on the reaction rate is an old but still controversial problem.