SPONTANEOUS REACTIONS AND REDUCTION BY IODIDE OF PEROXYNITRITE AND PEROXYNITRATE - MECHANISTIC INSIGHT FROM ACTIVATION PARAMETERS

Thermal and pressure activation parameters are reported for the decomp osition of peroxynitrate, isomerization of peroxynitrite, and their re duction by iodide in aqueous solutions, The spontaneous decomposition reactions are characterized by activation enthalpies of ca. 16 kcal/mo l, activation entropies close to zero, and significantly positive acti vation volumes between 7 and 10 cm(3)/mol, These parameters suggest th at the rearrangement of both peroxo species, leading to intermediates of increased partial molar volume, must include partial bond cleavage. The iodide-induced reduction reactions are characterized by significa ntly smaller activation enthalpies, negative activation entropies betw een -19 and -23 cal/(mol . K), and negative activation volumes between -6 and -11 cm(3)/mol. These parameters suggest that bond formation be tween the redox partners occurs before electron transfer and favors an inner-sphere mechanism. The results are discussed regarding mechanism s based on ambient kinetic data suggested in the literature.