Premium
THE PHOTOREDUCTION OF METHYLENE BLUE BY AMINES—II. AN INVESTIGATION OF THE DECAY OF SEMIREDUCED METHYLENE BLUE
Author(s) -
Kayser R. H.,
Young R. H.
Publication year - 1976
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1976.tb06846.x
Subject(s) - methylene blue , chemistry , photochemistry , flash photolysis , methylene , amine gas treating , substituent , solvent , radical , reaction rate constant , methanol , kinetics , medicinal chemistry , organic chemistry , catalysis , photocatalysis , physics , quantum mechanics
— The decay of semireduced methylene blue (MB') formed in the photoreduction of the dye by aryl‐ and alkylamines was examined by flash photolysis. The second order decay of MB in methanol produced using arylamines and 1,4‐diazabicyclooctane as photoreducing agents led to complete regeneration of the dye and amine. The rate constants for a series of N.N‐dimethylanilines showed a small substituent effect ( p = 0.69 ± 0.16) compatible with recombination of MB' with arylamine derived radical cations. A study of the solvent effect on the recombination process revealed the importance of the stability of the radical cation toward the solvent and also indicated that the reaction approaches the rate of diffusion. The photoreduction of the dye by most alkylamines examined resulted in permanent bleaching of methylene blue. The second order decay of MB' produced using tertiary aliphatic amines led exclusively to formation of the leuco‐dye with no apparent regeneration of methylene blue; this process was tentatively assigned to a reaction of MB' with α‐amino radicals formed from the amine radical cation. It was concluded that the methylene blue‐sensitized photooxidation of amines involves a Type I process and possible mechanisms are discussed.