Structure and Kinetics of Organic Acid Radicals Formed in Reaction with OH Radicals.

The study investigated OH-derived radicals from certain organic acids employed in nuclear fuel processing and separation using EPR spectroscopy and quantum chemistry methods. Hydroxyl radicals were generated through a Fenton-like reaction within the EPR resonator under both acidic and basic conditions, allowing for the detection of neutral and radical anions, respectively. The spectral assignment and analysis were conducted using a combination of literature data and quantum chemical calculations employing DFT theory with B3LYP or LPBE functionals and the L2a_3 basis set. The reaction of the OH radical with lactic and glycolic acids yielded primary C-centered radicals through hydrogen abstraction from these acids. In contrast, the OH radical exclusively generated secondary radicals from oxalic acid, whereas for citric acid, it resulted in both primary and secondary species induced by decarboxylation. The EPR spectrum of acetohydroxamic acid, upon reaction with the OH radical, displayed a complex pattern featuring primary N-type and N-O-type radicals. The decay pathways of the generated radicals were primarily attributed to radical-radical reactions, with the extracted reaction rate constants generally falling within the typical range observed for such reactions. The EPR parameters calculated for potential radicals using B3LYP and LPBE functionals with L2a_3 basis set demonstrated good accuracy for neutral radicals, albeit requiring minor adjustments for radical anions.