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 degrees C; 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 (k1RS), k(-1)RS, the second to the conversion of the intermediate to products (k2RS). In most cases all of the rate constants (k1RS, k(-1)RS and k2RS 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 k1OH for nucleophilic attack on the substrate; in this case the tetrahedral intermediate remains at steady-state levels under all conditions.