Kinetics and mechanism of condensation reactions of thiobenzamides and N-substituted thioureas

摘要

The condensation reaction of thiobenzamides and of N-substituted thioureas in dimethyl sulfoxide or in methanol, innthe presence of the mixture DMSO–Hu0001–Xu0002 (X = Cl, Br) produces 1,2,4-thiadiazole derivatives. Kinetic investigationnemphasizes the importance of the presence of dimethyl sulfoxide, of halide ions and of an acidic catalyst. For reactionsnof thiobenzamide, the bromide ion increases the reaction rate 150 times more than the chloride ion. The presence ofnelectron-donating groups on the starting thioamidic group enhances the reactivity. Reported data indicate that thenmixture DMSO–Hu0001–Xu0002 produces a positive halogen species. The proposed mechanism involves the formation ofnthe N-halogenated thioamides (or N-substituted thioureas) in the rate-determining step. The reactivity ofnthionicotinamide S-oxide is also reported and discussed..