Photochemistry of Polyhaloarenes. 12. The Photochemistry of Pentachlorobenzene in Micellar Media

Article abstract of DOI:10.1021/jo00036a017

The dependence of the reciprocal of the quantum yield for the photohydrodechlorination of pentachlorobenzene (1) in aqueous 0.100 M hexadecyltrimethylammonium bromide (CTAB) solution upon the reciprocal of the microconcentration of 1 and upon the reciprocal of the probability for excited state 1 reacting with ground-state 1 provides a linear correlation at high microconcentrations of 1.The regiochemistry of the photohydrodechlorination process in CTAB favors formation of 1,2,4,5-tetrachlorobenzene to a significantly smaller extent than is observed in the analogous process in acetonitrile solution in the presence of triethylamine.The bromotetrachlorobenzene byproduct is formed in the photolysis in the following composition: 1-bromo-2,3,4,5-tetrachloro- (5) : 2-bromo-1,3,4,5-tetrachloro- (6) : 3-bromo-1,2,4,5-tetrachlorobenzene (7) = 9.7 : 66.7 : 23.3.In a trapping experiment carried out during an irradiation of 1 in CH3CN/ H2O (8:2) in the presence of excess KBr at 254 nm, bromotetrachlorobenzenes (5:6:7) were formed in a ratio of 11.3 : 66.8 : 21.9.These experiments are rationalized by proposing that product in these micellar photohydrodechlorination reactions is formed by fission of triplet-state 1 and a competing process which involves conversion of triplet-state 1 to triplet excimer which then undergoes fragmentation.