A kinetic study on the reductive opening of the diphenylmethylene acetal in methyl 2,3-O-diphenylmethylene-α-l-rhamnopyranoside

Abstract

Reductive opening of the diphenylmethyl acetal in methyl 2,3-O-diphenylmethylene-α-l-rhamnopyranoside has been investigated by kinetic studies, and the results have been compared to those recently obtained by quantum chemical calculations. In contrast to the previous theoretical calculations which related only to the presumably rate limiting step of the reductive opening, the reaction system LiAlH(4), AlCl(3), and the title compound consists of at least four simultaneous reactions. Nevertheless, reasonable agreement can be found between the activation Gibbs free energy obtained from kinetic measurements and the theoretically calculated ones in spite of the experimental errors and the approximate nature of theoretical calculations.

Oxidation and Reduction

“…The reaction system LiAlH 4 , AlCl 3 , featured at least four simultaneous reactions of the title compound, whereas the quantum-chemical calculations had considered the 'presumably' rate-limiting step of the reductive opening, Nevertheless, there was reasonable agreement between the activation Gibbs free energy obtained from kinetic measurements and those calculated theoretically, in spite of the experimental errors and the approximate nature of theoretical calculations. 395 Linear free energy relationships (LFERs) were developed to correlate the rate constants reported in the literature for HO • -initiated reactions in aqueous phase with the theoretically calculated free energies of activation for H-atom abstraction from a C-H bond, and HO • addition to alkenes. The theoretical method used ab initio QM Gaussian 1-3 calculations for gas-phase reactions and a solvation method, COSMO-RS theory, to establish the impact of water.…”