The use of diethylene glycol in the synthesis of 2,2'-bibenzimidazole from o-phenylenediamine and oxalic acid

Abstract

One- and two-step syntheses of 2,2'-bibenzimidazole were compared. Diethylene glycol was used as solvent that provides good solubility of the substrates. The limitation of the one-step preparation is the formation of the by-product, fluoflavine. The two-step synthesis proceeds with the separation of the intermediate product, 1,4-dihydroquinoxaline-2,3-dione, and the final product is only 2,2'-bibenzimidazole. The total yield of the two-step synthesis is above 85%.