Electron spin resonance study of radiation-induced radicals in polycrystalline aromatic carboxylic acids containing a thioether group

Radicals and radical ions formed on gamma-radiolysis of aromatic carboxylic acids containing a thioether group in the polycrystalline state at 77 K and on subsequent warming over the temperature range of 95-293 K were identified using the electron spin resonance technique. In all carboxylic acids studied, monomeric sulfur radical cations (X-S-. -Y- COOH) and radical anions formed by an addition of an electron to the carboxyl group (X-S-Y-COOH)(.-) were detected at 95K. On further warming over the 150-293K range various S-centered radicals (XS.) and C-centered radicals were observed. The results are discussed in terms of the following competitive reaction pathways,: fragmentation, decarboxylation, and deprotonation of the parental monomeric sulfur radical cations. Carbon dioxide was identified and quantified (G = 0.2-3.5) in all carboxylic acids exposed to gamma-radiation. (C) 2004 Elsevier Ltd. All rights reserved.