Oxidation reactions of thiodiglycolic acid: a pulse radiolysis study
The transient optical absorption spectrum produced on pulse radiolysis of an N2O saturated aqueous solution (pH 3.0–10.0) of thiodiglycolic acid has been assigned to the α-thio radical, HO2CH2C–S–ĊHCO2H, formed by hydrogen atom abstraction from the parent compound by hydroxyl radicals. The absorption maximum (285 nm) and extinction coefficient (1.6 × 103 dm3 mol–1 cm–1) are found to be independent of solute concentration over the range 8.0 × 10–5-8.0 × 10–2 mol dm–3 and pH (1.0–10.0) of the solution. The rate constant for the reaction of hydroxyl radicals with thiodiglycolic acid has been determined to be 4.1 × 109 dm3 mol–1 s–1 and the product species decays by second-order kinetics with a rate constant of 1.6 × 109 dm3 mol–1 s–1 Strong oxidizing agents such as (CH3I)2+˙, Cl2–˙, CH3İOH, and SO4–˙ have been found to oxidize thiodiglycolic acid with the formation of a transient species with λmax 280 nm, the rate constants being 6.7 × 109, 4.9 × 108, 6.9 × 109, and 2.7 × 109 dm3 mol–1s–1 respectively. The transient optical absorption spectrum (λmax= 280, 380 nm) obtained on pulse radiolysis of a nitrogen saturated solution of thiodiglycolic acid in 1,2-dichloroethane has been assigned to a radical cation derived from this solute.