Compounds containing the benzimidazole moiety have a wide range of pharmaceutical applications. More than 61,000 individual compounds containing the 2-(phenyl)-1H-benzimidazole substructure have been reported to Chemical Abstract Services of which nearly 19,000 include reports of their biological properties. Among these are 330 compounds containing the 2-(4-nitrophenyl)-1H-benzimidazole substructure and 8800 compounds containing the 2-(4-chlorophenyl)-1H-benzimidazole substructure. Reported biological effects of these compounds include anticancer and antibacterial applications. Given the wide range of compounds and their potential importance in the development of pharmaceuticals, effective and rapid methods of synthesis must be developed and refined. In this work, a series of transition metal catalysts were synthesized using a one-pot microwave method including cobalt, copper, and iron contained in phthalocyanine, tetra-2,3-pyridinoporphyrazine, tetra-3,4-pyridinoporphyrazine, and tetrapyrazinoporphyrazine ring systems. The catalysts were used in the one-pot synthesis of 2-(4-nitrophenyl)-1H-benzimodazole and 2-(4-chlorophenyl)-1H-benzimidazole from o-phenylenediamine and, respectively, p-nitrobenzaldehyde and p-chlorobenzaldehyde in refluxing ethanol. The results were compared to those obtained by the synthesis of the benzimidazoles using ammonium chloride as the catalyst and refluxing in ethanol according to a published method. Isolated yields of 2-(4-nitrophenyl)-1-H-benzimidazole ranged from 65 – 84% using each of 12 catalysts while refluxing for 30 minutes and an isolated yield of 75±2% was obtained using ammonium chloride as the catalyst while refluxing for 120 minutes. Only when iron(II)tetrapyrazinoporphyrazine was used as the catalyst was a statistically lower yield (64±3%) observed compared to the ammonium chloride catalyzed reaction (P = 0.004). Three catalysts, cobalt(II)tetrapyrazinoporphyrazine, cobalt(II)-2,3-tetrapyridinoporphyrazine, and copper(II)-tetra-3,4-pyradinoporphyrazine produced statistically higher yields (P = 0.01, 0.009, and 0.0004 respectively). The largest yield, 84±3%, was obtained with copper(II)-tetra-3,4-pyridinoporphyrazine as the catalyst. Synthesis of 2-(4-chlorophenyl)-1H-benzimidazole has been completed using copper(II)phthalocyanine as the catalyst and studies using 11 additional catalysts are ongoing. NMR and FTIR analyses of the products are consistent with the literature.

Catalytic synthesis of substituted benzimidazoles using metal phthalocyanines, pyridinoporphyrazines, and pyrazinoporphyrazines

255th National Meeting (2018)

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