Pulse- and X-radiolysis of 2-mercaptoethanol in Aqueous Solution

Summary

Aqueous solutions of 2-mercaptoethanol have been irradiated with pulses of 4 MeV electrons and with 240 kVp x-rays. The specific rate-constants for reactions of hydroxyl radicals, hydrated electrons and hydrogen atoms with the thiol were found to be 6·5 × 10⁹, 1·2 × 10¹⁰ and 2 × 10⁹ M⁻¹ sec⁻¹, respectively. Reaction products have been identified by gas chromatography and functional group analysis as hydrogen peroxide, hydrogen sulphide, acetaldehyde, ethanol and dithiodiglycol. Yields were determined quantitatively by spectrophotometric means after the addition, where necessary, of suitable reagents. Radical scavengers such as acetone have been used to isolate effects due to the various primary species. In the absence of oxygen, dithiodiglycol was formed with G up to 5 while hydrogen peroxide was formed in very small yield. In oxygenated solutions, dithiodiglycol and hydrogen peroxide were formed in equal yields with G values up to about 30, while hydrogen sulphide and ethanol had yields up to G ∼ 1. A reaction mechanism is proposed, involving 2-hydroxyethyl, thiyl and organo-sulphur-peroxy radicals. A role for thiols as ‘radiation-protectors’ is suggested.