Unraveling structure-reactivity relationships in SNV reactions:: Kinetics of the reactions of methoxybenzylidenemalononitrile, 2-(methylthiobenzylidene)-1,3-indandione, 2-(benzylthiobenzylidene)-1,3-indandione, and methyl β-methylthio-α-nitrocinnamate with OH- and thiolate ions in aqueous DMSO

The kinetics of the title reactions were determined in 50% DMSO-50% water (v/v) at 20 OC; n-BuS-, HOCH2CH2S-, and MeO2CCH2S- were used as thiolate ions. The reactions with the thiolate ions gave rise to two separate kinetic processes. The first refers to rapid, reversible attachment of RS- to the substrate leading to a tetrahedral intermediate (k(1)(RS), k(-1)(RS)), the second to the conversion of the intermediate to products (k(2)(RS)). In most cases all of the rate constants (k(1)(RS), k(-1)(RS) and k(2)(RS)) could be determined. In combination with results from previous studies, a detailed discussion regarding the effects of activating substituents and leaving groups on rate and equilibrium constants as well as on intrinsic rate constants is presented. The reaction with OH- only allowed a determination of k(1)(OH) for nucleophilic attack on the substrate; in this case the tetrahedral intermediate remains at steady-state levels under all conditions.