Journal of the American Chemical Society p. 9699 - 9708 (1995)
Update date:2022-08-29
Topics:
Aveline, Béatrice M.
Kochevar, Irene E.
Redmond, Robert W.
The primary and subsequent photochemistry of four N-hydroxypyridine-2-thione esters has been investigated by laser flash photolysis (λexc = 355 nm). A simple, high-yield synthetic method is given for their preparation with high purity. UV irradiation of these ester compounds was shown to lead specifically to the formation of benzyl, diphenylmethyl, tert-butyl, and benzoyloxyl radicals in addition to the 2-pyridylthiyl radical. In all cases, the initial photoinduced nitrogen-oxygen bond cleavage was found to occur in high quantum yield (ΦN-O ≈ 0.5). The radical species generated by this process (2-pyridylthiyl radical and carbon-centered or oxygen-centered radicals) were characterized and their reactivity toward several radical scavengers has been studied. An efficient delayed depletion of the N-hydroxypyridine-2-thione esters was also observed, leading to overall bleaching quantum yields, ΦBl, close to unity. We have demonstrated that the delayed consumption of ground-state ester was due to the reaction of the 2-pyridylthiyl radical with its precursor, occurring with a rate constant, kr, of 3-4 × 109 M-1 s-1. This reaction, hitherto never proposed, leads to the formation of 2,2′-dipyridyl disulfide and further release of propagating radicals.
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