The Direct Electrosynthesis of L-Cysteine Free Base

L-Cysteine is an important amino acid used in hair waving formulations, as a nutritional supplement and as an intermediate in the synthesis of several pharmaceuticals. The world market for this amino acid is estimated at 1000 tons/year which is almost entirely produced by the electrochemical reduction of L-cystine in acid solution. The electrochemical route starts with L-cystine, which is a naturally occurring material usually extracted from hair or feathers by acid hydrolysis. The idea of a distillable electrolyte is not a new one, indeed the excess hydrochloric acid used in the conventional preparation of L-cysteine is distilled off; however, this still leaves the acid salt as the product. A graphite cathode was also found to perform well at conversions up to 49%. Zinc gave current efficiencies greater than 100%, due to chemical reduction by zinc metal occurring alongside the electrochemical reduction, as demonstrated by the corrosion of the zinc electrode.