| Abstract
| - Kinetic data have been obtained for three distinct types of reactions of phthalimide N-oxyl radicals(PINO•) and N-hydroxyphthalimide (NHPI) derivatives. The first is the self-decomposition of PINO•which was found to follow second-order kinetics. In the self-decomposition of 4-methyl-N-hydroxyphthalimide (4-Me-NHPI), H-atom abstraction competes with self-decomposition in thepresence of excess 4-Me-NHPI. The second set of reactions studied is hydrogen atom transfer fromNHPI to PINO•, e.g., PINO• + 4-Me-NHPI ⇄ NHPI + 4-Me-PINO•. The substantial KIE, kH/kD =11 for both forward and reverse reactions, supports the assignment of H-atom transfer rather thanstepwise electron−proton transfer. These data were correlated with the Marcus cross relation forhydrogen-atom transfer, and good agreement between the experimental and the calculated rateconstants was obtained. The third reaction studied is hydrogen abstraction by PINO• from p-xyleneand toluene. The reaction becomes regularly slower as the ring substituent on PINO• is more electrondonating. Analysis by the Hammett equation gave ρ = 1.1 and 1.8 for the reactions of PINO• withp-xylene and toluene, respectively.
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