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In this paper, we explored the synthesis of benzimidazole by the reaction of DMF and o-phenylenediamine. In the process of catalyst screening, we found that 4-amino-3-hydroxybenzoic acid, benzoic acid, and benzene-1,3,5-tricarboxylic acid could catalyze the reaction. Moreover, the calcium 4-amino-3-hydroxybenzoate and CO2 could more effectively catalyze the reaction, the synergistic effect of CO2 and 4-amino-3-hydroxybenzoic acid calcium salt can increase the yield of benzimidazole from 28% to 94%.