Photochemistry of Pesticides, 12 [1] On the Photoconversion of l,3-Dihydro-2H-benzimidazole-2-thione, 2(3H)-Benzothiazolethione, and 2-Chlorobenzothiazole

The photoreactivity of l,3-dihydro-2H-benzim idazole-2-thione ( la ) and 2(3H )-benzothiazolethione ( lb ) has been studied in several solvents in the presence of oxygen with or without methylene blue as a sensitizer. The corresponding disulfides (5a , b), 2-oxo derivatives (2a , b), benzimidazole and benzothiazole (11a, b), and elem ental sulfur have been characterized as the main products. The UV irradiation of the disulfides 5a , b results in the formation of the same product pattern as the thiones la , b. Photolysis of 2-chlorobenzothiazole (12) in acetonitrile gives a mixture of 2b , 2,2'-dibenzothiazole (13). while photolysis of 12 in ethanol yields 2b and l i b . Products and mechanisms are discussed and compared with previous studies in this area.