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 beta-methylthio-alpha-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.
Bernasconi
C F
CF
Contribution from the Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, USA.
Ketner
R J
RJ
Ragains
M L
ML
Chen
X
X
Rappoport
Z
Z