Comparative study of 1,3-dibromo-5,5-dimethylhydantoin assisted and conventional synthesis of benzimidazole derivatives and the solvent effects on spectroscopic properties

A small library of benzimidazoles with a range of side-chain substituents have been synthesized through the condensation reaction of o-phenylenediamine derivatives and several other commercially available materials. The reactions were catalyzed by either 4M HCl or 1,3-dibromo-5,5-dimethylhydantoin (DBDMH). The compounds synthesized using DBDMH as the catalyst required a shorter reaction time, the yield was higher and the workup procedure was not as tedious as those produced using 4M HCl as the catalyst. The structural elucidations of synthesized compounds have been confirmed through spectroscopic analysis. 13C NMR analysis of some of the synthesized compounds showed that the appearance of carbon signals in the NMR spectrum is affected by the nature of the NMR solvent and temperature.The exchange-induced broadening of the 13C NMR signal was probably facilitated by the intermolecular proton exchange between the NH of the benzimidazole and the H2O present in the DMSO-d6 solvent.   Key words: 1,3-dibromo-5,5-dimethylhydantoin, benzimidazole, solvent-effect, structure elucidation, synthetic method.