A kinetic study of the reactions on some disulphides with sodium sulphite

Abstract

The kinetics of the reactions of cystine, oxidized glutathione, diacetylcystine ester, diformylcystine and [beta][beta]''-di-thiodipropionic acid with sodium sulfite were studied. The reaction above pH 9 is a simple reversible bimolecular reaction, but below pH 9 the mechanism is complex. The dlsulfide bonds of these compounds react with SO32- ions but not HSO3 ions. The rates of reaction with SO32- ions are dependent on the net charge in the vicinity of the di-sulfide bonds. A net negative charge, due to COO groups, causes a large decrease in rate constant. The pK values of the thiol groups of N-acetyl-cysteine ester, N-formylcysteine and -mercaptopropionic acid have been calculated from equilibrium data. The heats of ioniza-tion of the thiol groups of these 3 compounds were approximately + 6000 cal.