Reactions of hydrogen atoms with α-(alkylthio) carbonyl compounds. Time-resolved ESR detection and DFT calculations

The pulse radiolysis of acidic aqueous solutions of 2-(methylthio)ethanoic acid and S-ethylthioacetone yields acetic acid radicals, ^˙CH₂COOH, and acetone radicals, ^˙CH₂-C(O)CH₃, respectively. These radicals were identified by time-resolved electron spin resonance. Based on the analogy to previous work on α-(methylthio)acetamide where acetamide radicals were identified in similar situations, the mechanism of the reactions is assigned as bimolecular homolytic substitution (S_H2). Support for this assignment is given by density functional theory (DFT) calculations and radical-scavenging experiments with tert-butanol. DFT computations were made on the thermo-chemistry of the S_H2 reaction pathway and on the various alternatives to S_H2 such as H-abstraction/β-scission.