Benzimidazole Reaction Lab Report

3.1. Influence of the catalyst on synthesis of Benzimidazole Initially, we began with catalyst free reaction by stirring reaction mixture of a and b in ethanol at room temperature. Additionally, several reactions were performed using various catalysts in different reaction conditions and results are summarized in Table 1. The catalyst free reaction fails to produce selective benzimidazole and conversion of reactants in long reaction time and obtained only 21 % conversion with 13 % selective yield of c after 48 h reaction time (Table I, Entry 1). Later on, the same reaction performed at 80oC reaction temperature in ethanol without any catalyst. This reaction obtained 21% improved yield in 24h reaction time with number of known side products (Table I, Entries 2). Moreover, same catalyst free reaction was also carried out in same condition by replacing of ethanol by DMF to see the effect of
This reaction with L-Proline not only showed poor yield but also obtained some known side products with the benzimidazole [20-22]. However, under similar reaction condition we have also used poly phosphoric acid (PPA) and Sc(OTf)3 as catalyst for the benzimidazole formation in ethanol. These reaction results obtained, 61% and 28% selective yield of benzimidazole in 12 h reaction time (Table I, Entries 7 and 8). Furthermore, the reactions with PPA and Sc(OTf)3 having certain drawbacks such as long reaction time, in-efficient yield and highly expensive catalysts and lengthy product separation process. Additionally, we have also tested ZnSO4 as catalyst for the same reaction in same reaction condition. This catalyst also fails to obtain good to efficient yield of respective c and ended with 47% yield in 12 h reaction time (Table I, Entry