The kinetics of base catalyzed cyclization of 2,6-dinitrophenylsulfanyl ethanenitrile and 2,4,6-trinitrophenylsulfanyl ethanenitrile giving 2-cyano-7-nitrobenzo[d]thiazole-3-oxide and 2-cyano-5,7-dinitrobenzo[d]thiazole-3-oxide respectively was studied in methanolic methoxyacetate, acetate, trichlorophenoxide, N-methylmorpholine, and N-methylpiperidine buffers at 25 -C and I ¼ 0.1 mol L S1 . It was found that reaction involves both general acid and general base catalyses whose manifestation depends on the pK a of the acid-buffer component and the ratio of both buffer components. In weakly basic buffers the rate-limiting step is C-H bond breaking in the cyclic intermediate, while in strongly basic buffers the rate-limiting step is the general acid-catalyzed elimination of hydroxyl group from the intermediate.