Abstract: | The recent experiments on the chloride-assisted dealkylation of alkylcobalamins by a variety of oxidants (IrCl , AuCl , Fe(H2O)5Cl2+, and PtCl ), which are scattered in several previous publications, and their general kinetic characteristics are summarized. The kinetic studies are also extended to include the dealkylations of (methylaquo)?3,5,6-trimethylbenzimidazolylcobamide and protonated base-off ethylcobalamin by IrCl (1.0M Cl?) and by Fe(III) ions at 0.1M Cl?, and the demethylation of (methylaquo)?3,5,6-trimethylbenzimidazolylcobamide by AuCl (1.0M Cl?). This extension is in an effort to substantiate the general mechanism which has been previously proposed for these oxidative dealkylations. The general kinetic characteristics are described in terms of a preassociation of the reactants, followed by a rate-determining electron-transfer process to yield the R-B radical, which then undergoes further reactions to produce the products observed. The overall reactions are discussed within the framework of chlorine-bridging inner sphere electron-transfer reactions. |