Iodide Reduction of Sulfilimines. 3. Evidence of a Minor Role for Catalysis by Hydrogen Bonding in the Decomposition of Sulfurane Intermediates

Article abstract of DOI:10.1021/ja00240a035

The iodide reduction of N-(substituted benzoyl or benzenesulfonyl)-S,S-dimethylsulfilimine ylides (aqueous solution, 25 deg C, μ = 1.0 with KCl) is first order with respect to iodide concentration in the pH range 0.5-5; the order with respect to the proton is slightly > 1.0.The solvent deuterium isotope effect for the reduction of N-(4-chlorobenzoyl)-S,S-dimethylsulfilimine ylide is k_H/k_D = 0.6.Electron-withdrawing groups in the leaving group accelerate the rate of the reaction and give β_l.g. value of -0.67.General acid catalysis is observed in the reduction reaction with Broensted α values of 0.15 and 0.29 for 4-methoxybenzamide and 4-chlorobenzenesulfonamide leaving groups, respectively.The value of β_l.g. increases with decreasing strength of the catalyzing acid and the term p_xy = (δβ_l.g./δpK_a^HA) = (δα/δpK_a^l.g.) ca. +0.05.The solvent deuterium isotope effect on the general catalyzed reduction reaction is small (k_BH/k_BD = 1.32) and independent of acid strength.For the solvent-catalyzed reaction, it is suggested that the rate-limiting step involves diffusion apart of the amide anion-iodosulfonium cation pair.It is concluded, however, that the observed general catalysis does not arise from hydrogen bonding effects in a preassociation-type mechanism, but rather it involves proton transfer that is concerted with S-N bond cleavage.