The 2-aminobenzimidazole ring system represents the core structure of a number of biologically significant molecules and its derivatives have been found to possess a wide spectrum of biological activity. Particularly, alkyl benzimidazole-2-carbamates show potent fungicide [1] and anti- helmintic activity, [2, 3] being Carbendazim® a good example of a successful market fungicide. Nevertheless, there are, to our knowledge, no studies on aryl benzimidazole-1-carbamates, either in terms of synthesis, bioactivity or chemical reactivity. So, in the sequence of our on- going work about aryl carbamates we decided to synthesize new 2-aminobenzimidazole-1-carbamates (1a-e, 2). Synthesis of new 2-aminobenzimidazole-1-carbamates was accomplished by carbamoylation of 2-aminobenzimidazole using different substituted phenyl chloroformates. The aqueous hydrolysis of the new compounds was examined in the pH range 1-13 at 25^o C. The evaluated kinetic parameters led to the conclusion that up to pH 4 reaction proceeds by a bimolecular attack of water to the N- protonated substrate, via an A_Ac2 mechanism with specific acid catalysis. This is the first time this behaviour is described for carbamates, and can be ascribed to the higher basicity of the benzimidazolyl moiety when compared with the carbonyl oxygen. For higher values of pH, the results are consistent with a B_Ac2 mechanism with nucleophilic catalysis, but while between pH 4 and pH 7 water acts as the nucleophile, for pH > 7 the hydroxide ion is the acting species.

[1] H. Loewe, J. Urbanietz, R. Kirsch, D. Duewell, Canadian Patent 31, 780 1978. (C:A. 81 13512)

[2] M. Novak, M. Hardy, W. S. Evans, B. J. Blackburn, D. Ankrom, J. Parasitol. 1982, 68, 1165.

[3] M. Novak, B. J. Blackburn, Experientia 1981, 37, 250.

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