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Oxidative Degradation of Thiaproline Derivatives in Aqueous Solutions Induced by • OH Radicals
Author(s) -
Pogocki Dariusz,
Bobrowski Krzysztof
Publication year - 2014
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.201300110
Subject(s) - chemistry , radical , aqueous solution , exergonic reaction , ascorbic acid , dicarboxylic acid , medicinal chemistry , photochemistry , carboxylic acid , radical substitution , organic chemistry , catalysis , food science
The participation of neighboring amino and carboxyl groups in thiazolidyne‐4‐carboxylic acid (thiaproline) and its two derivatives, thiazolidyne‐2‐carboxylic acid and thiazolidyne‐2,4‐dicarboxylic acid, is demonstrated during . OH‐radical‐induced oxidation in aqueous solutions. The reaction of . OH radicals with these compounds does not lead to the expected one‐electron oxidized sulfur‐centered radical cations and subsequently to the intermolecularly (S∴S)‐bonded dimeric radical cations (even at very high concentration of thiaprolines (>50 m M )), but rather to the elimination of CO 2 with the parallel formation of αN radicals. The latter radicals formed in thiaproline and thiazolidyne‐2,4‐dicarboxylic acid subsequently undergo β‐fragmentation of the CS bond, leading to the thiyl radicals (RS . ). The αN and RS . radicals were probed and quantified by one‐electron reduction of p ‐nitroacetophenone (PNAP) and by one‐electron oxidation of the monoanion of ascorbic acid (AH − ), respectively. The calculated stabilization enthalpies of the αN radicals show that the loss of CO 2 is thermodynamically a favorable process. The Gibbs free energies of β‐fragmentation processes in thiaproline and thiazolidyne‐2,4‐dicarboxylic acid are equal to −3.7 and −10.2 kJ mol −1 , respectively, showing that at room temperature both are exergonic. A general . OH‐radical‐induced oxidation mechanism of thiaproline derivatives in aqueous solutions is proposed.