38836-40-7Relevant articles and documents
Catalysis by Aliphatic Thiols in Photoreduction of Benzophenone by Amines and Alcohols
Stone, Paul G.,Cohen, Saul G.
, p. 1719 - 1725 (1981)
The quantum yield of photoreduction of benzophenone by aliphatic thiol is low, ca. 0.03.However, the photoreduction by primary and secondary aliphatic amines, which contain α-C-H (and N-H), is markedly catalyzed by low concentrations (ca. 1E-2 M) of aliphatic thiol, while it is retarded by aromatic thiol.The catalysis is greater at high concentrations of ketone and amine and passes through a maximum with increasing concentration of thiol.Photoreduction by tertiary amines is retarded by both aromatic and aliphatic thiols. tert-Butylamine and aniline, which lack α-C-H, lead to ketyl and N-centered aminyl radicals, which disproportionate, regenerating ketone and amine.These amines retard photoreduction by amines which possess α-H, and aliphatic thiol greatly decreases this retardation.Acceleration by thiol is ascribed to a sequence of hydrogen atom abstractions, by N-centered aminyl radical from thiol, with rate constant >1E5 M-1s-1, and by thiyl radical from α-C of amine, with rate constant >1E3 M-1s-1.These reactions convert a disproportionating N-centered radical to a reducing C-centered radical.The tert-butylamine-retarded reduction by benzhydrol, but not that by 2-propanol, is accelerated by aliphatic thiol.Retardation and acceleration by thiols in photoreduction by amines and alcohols are discussed in terms of competing free radical reactions and are related to the S-H bond strengths of aromatic and aliphatic thiols, the reactivities of the related thiyl radicals, the ease of abstraction of H from α-C of alcohols and amines, and the reactivities of α-hydroxyalkyl and α-aminoalkyl radicals.
