Photochemistry of polyhaloarenes 9. characterization of the radical anion intermediate in the photodehalogenation of polyhalobenzenes
Freeman, P.K.; Ramnath, N.
Journal of Organic Chemistry 56(11): 3646-3651
1991
ISSN/ISBN: 0022-3263 DOI: 10.1021/jo00011a037
Accession: 007653189
The product-determining intermediate in the photodehalogenation of polyhalobenzenes has been characterized by generating excimers and radical anions within a micellar core and by formation of corresponding radical anions by electron transfer from lithium p,p'-di-tert-butylbiphenyl radical anion (LiDBB). The photodechlorination of pentachlorobenzene (1; 254 nm, CH3CN) produces 1,2,3,5-tetrachloro- (2), 1,2,4,5-tetrachloro- (3), and 1,2,3,4-tetrachlorobenzene (4). The regiochemistry of this reaction is compared with that observed in the photodechlorination of 1 in a micellar solution of hexadecyltrimethylammonium bromide (CTAB) with occupancy numbers (n) principally < 2 and .gtoreq. 2. Further comparisons with photodechlorination of 1 in a micellar CTAB solution (n < 2) in the presence of triethylamine, as well as photodechlorination in CH3CN in the presence of triethylamine, were used to characterized unencumbered radical anions. The regiochemistries observed in photolytic dehalogenations of 1, 2, 1,2,4-trichlorobenzene, and pentafluorobenzene in the presence of triethylamine are in good agreement with those realized in the radical anion fragmentations induced by electron transfer from LiDBB.