Limitations of the Transition State Variation Model. Part 8. Dual Reaction Channels for Solvolyses of 3,4-Dimethoxybenzenesulfonyl Chloride

• Published in: Bulletin of the Korean Chemical Society 2007, Vol.28 (12), p.2377-2381
• Main Authors: Koo, In-Sun, Kwon, Eun-Ju, Choi, Ho-June, Yang, Ki-Yull, Park, Jong-Keun, Lee, Jong-Pal, Lee, Ikc-Hoon, Bentley, T. William
• Format: Article
• Language: Korean
• ISSN: 0253-2964; 1229-5949

Solvolyses of 3,4-dimethoxybenzenesulfonyl chloride (DSC) in water, D2O, CH3OD, and in aqueous binary mixtures of acetone, acetonitrile, 1,4-dioxane, ethanol, methanol, and 2,2,2-trifluoroethanol (TFE) have been investigated at 25.0 oC. Kinetic solvent isotope effects (KSIE) in water and in methanol and product selectivities in alcohol-water mixtures are also reported. The Grunwald-Winstein plot of first-order rate constants for the solvolyic reaction of DSC with YCl shows marked dispersions into separated lines for various aqueous mixtures. With use of the extended Grunwald-Winstein equation, the l and m values obtained are 1.12 and 0.58 respectively for the solvolyses of DSC. The relatively large magnitude of l is consistent with substantial nucleophilic solvent assistance. From Grunwald-Winstein plots the rate data are dissected approximately into contributions from two competing reaction channels. This interpretation is supported for alcohol-water mixtures by the trends of product selectivities, which show a maximum for ethanol-water mixtures. From the KSIE of 1.45 in methanol, it is proposed that the reaction channel favored in methanolwater mixtures and in all less polar media is general-base catalysed and/or is possibly (but less likely) an addition-elimination pathway. Also, the KISE value of 1.35 for DSC in water is expected for SN2-SN1 processes, with minimal general base catalysis, and this mechanism is proposed for solvolyses in the most polar media.