Role of water in determining organic reactivity in aqueous binary solvents

Abstract

Abstract Kinetic data for organic reactions in various binary water-organic solvent mixtures were collected and quantitatively analysed in terms of linear-free-energy relationships by using tert-butyl chloride (2-chloro-2-methylpropane) solvolysis as the reference system. Linear similarity plots for these kinetic data were determined for solvent systems ranging from pure water mixtures up to considerable amount of cosolvent, and 161 similarity coefficients were calculated from slopes of these plots. The existence of these linear plots demonstrated that the solvent effects are of some common nature in all analysed reaction mixtures independent of the reaction type and the cosolvent used. Therefore it was concluded that the observed effects could be connected to the specific solvating properties of water, which govern reactivity even in significant dilution of water by an organic cosolvent. This conclusion was supported by the linear interrelationship between the slopes of similarity plots of different reactions, and hydrophobicity parameters log P of the reacting compounds. The relative solvent effects observed in binary water-organic solvent mixtures were for the first time directly related to the structure of reacting compounds.