Acid-Catalyzed Hydrolysis of 1,1-Bis(methylthio)ethene. Buffer- and Thiol-Dependent Changes in the Rate-Determining Step

Article abstract of DOI:10.1021/ja00348a043

Acid-catalyzed hydrolysis of 1,1-bis(methylthio)ethene has been studied kinetically in 10percent aqueous acetonitrile at 30 deg C.The rate increased with buffer concentration, showing saturation at higher concentrations.Addition of 2-mercaptoethanol had little influence on the rate at the limiting zero buffer concentration, but it greatly accelerated the reaction in buffer solutions and followed a saturation curve.It was concluded that the rate-determining step is largely the protonation of the double bond at zero buffer concentration (k₂/k_-1 = 3.13) but it changes to the attack of water on the intermediate carbenium ion as the buffer concentration increases.The 1H NMR spectral analysis of the reaction products in 80percent CH3CN-D2O showed that the H-D isotope exchange at the 2-position of the substrate occurred extensively in a formate buffer but only moderatly in a DCl solution during the hydrolysis.