Journal of the American Chemical Society p. 3435 - 3440 (1982)
Update date:2022-08-11
Topics:
Stone, Paul G.
Cohen, Saul G.
Rate constants, kir, quantum yields, φred, and effects of thiol have been studied in the photoreduction of fluorenone by amines in benzene.Hydroxyethylamines show increased φred as compared with unsubstituted ethyl analogues, φred ca.0.8 with triethylamine, but ca.2, the maximum theoretical value, with triethanolamine and 2-(diethylamino)ethanol.Abstraction is predominantly from unsubstituted ethyl groups in the latter, and increased kir and φred are attributed to solvation by hydroxyl, present only at the reaction site, of polar intermediates or transition states.Secondary amines have high kir and low φred, 0.01-0.2, attributed to predominant abstraction of H from N and disproportionation of ketyl and aminyl radicals.This reduction is strongly catalyzed by aliphatic thiol, as aminyl radical abstracts H from S and thiyl radical abstracts H from α-C of amine.Primary amines have low kir and φred.This reduction is not catalyzed by thiol, indicating that H is not abstracted by triplet fluorenone from N of primary aliphatic amines.Aniline inhibits this reduction, but aniline plus thiol leads to strong catalysis.Triplet fluorenone abstracts H from N of aniline, anilino radical abstracts H from S of thiol, and thiol abstracts H from α-C of amine, leading to effective reduction.Thiol catalysis may be diagnostic for the formation of aminyl radicals.Inhibition and catalysis by thiols are discussed.
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