A homogeneous redox catalytic process for the paired synthesis of L-cysteine and L-cysteic acid from L-cystine

Redox catalytic process involved in the paired electrosynthesis of L-cysteine and L-cysteic acid from L-cystine is investigated by cyclic voltammetric technique and also confirmed by preparative electrolysis. The cyclic voltammetric behaviour shows that in the catholyte, in situ deposited tin (Sn) surface acts as a redox catalyst for the electro-reduction of L-cystine to L-cysteine whereas in the anolyte, the electro-generated bromine acts as a homogeneous redox mediator to enhance the electro-oxidation of L-cystine. L-Cysteine hydrochloride monohydrate (L-cysteine) and L-cysteic acid are prepared from L-cystine by preparative electrolysis with high purity and high yield using graphite cathode and DSA anode. At optimum concentration of L-cystine with 1:1 concentration ratio (catholyte:anolyte), the material yield obtained for L-cysteine is above 80% and that for L-cysteic acid is close to 60% in the paired electrosynthesis process in the batch operation. Scope for further experiments in conversion efficiency is also discussed. (C) 2011 Elsevier Ltd. All rights reserved.