A spectroscopic investigation into the reaction of sodium tetrathionate with cysteine

A spectroscopic investigation into the reaction of sodium tetrathionate with cysteine at pH 5 both at the boil and at room temperature has been carried out. The Raman and infrared spectra of the model compounds cysteine, cysteine-S-sulfonate, cysteine-S-thiosulfonate, sodium thiosulfate and sodium sulfite were also obtained and vibrations involving the sulfur atoms were analyzed in detail. These results were utilized in the interpretation of the spectra obtained from tetrathionate–cysteine reaction mixtures. The reaction supernatants were analyzed by high performance thin layer chromatography while the precipitates were analyzed gravimetrically. It was found that during the reaction, the thiol groups of cysteine are oxidised to give predominantly cysteine-S-sulfonate. Cystine was also detected but was determined gravimetrically to be a minor reaction product. No significant amounts of cysteine-S-thiosulfonate were detected. The reaction is accompanied by the formation of elemental sulfur and a small amount of sulfite. Major reaction pathways are put forth that are consistent with the experimental data.