An efficient and green method for synthesis of 2 substituted benzimidazoles has been described. Despite previous methods being available in literature for synthesis of such compounds, the ease of operation, use of common and non-toxic solvent and cheap catalyst (NH4Cl) are the highlights of this new methodology.
The general procedure involves the reaction of o-phenylene diamine with a range of substituted aldehydes in the ratio 1:2 in ethanolic medium and in presence of NH4Cl to afford. The procedure is depicted in scheme 1 and the results summarized in Table 1.
- The method is very easily reproducible. The reaction times were found to be around 3 hours for most of the reactions.
- As noted by the authors in the section “Results and Discussion”, the results replicated the observation that the aliphatic aldehydes did not yield more than 10% while the aryl ketones did not react with diamine.
- The novelty of this method is the selective formation of 2 substituted benzimidazoles only without the formation of 1,2 disubstituted ones as side products.
- The catalyst used is one of the cheapest chemicals available in labs.