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Synthesis and Reactivity of New Benzimidazolylcarbamates

Fátima P. Norberto 1,2Susana P. Santos 1,2Jim Iley 3Daniel A. Silva 1,2Margarida C. Real 1

1. University of Lisbon, Science Faculty, Department of Chemistry and Biochemistry (DQB/FCUL), Edif. C8, Campo Grande, Lisbon 1749-016, Portugal
2. CQB, FCUL, Campo Grande Bloco C-8, Lisbon 1749-016, Portugal
3. Chemistry Department (POCRG), The Open University, Milton Keynes MK76AA, United Kingdom

Abstract

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 25o 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 AAc2 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 BAc2 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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Presentation: poster at 18th Conference on Physical Organic Chemistry, Posters, by Daniel A. Silva
See On-line Journal of 18th Conference on Physical Organic Chemistry

Submitted: 2006-05-31 16:36
Revised:   2009-06-07 00:44