Ethanol → Ethyl 4,5,6,7-tetrahydro-1H-benzo[d]imidazole-6-carboxylate

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Reaction Steps

A mixture of 10.0 g of sulfate of benzimidazole-5-carboxylic ethyl ester, 5.0 g of 5% palladium-carbon catalyst, and 100 ml of ethanol was stirred in hydrogen for five hours under the conditions of 135° C. and 50 kg/cm2, cooled, then filtered to separate the catalyst, and distilled to expel the ethanol. The residue of the distillation was neutralized with an aqueous sodium bicarbonate solution and extracted with chloroform. The chloroform layer was dried over anhydrous magnesium sulfate and then distilled to expel chloroform and obtain 6.9 g of 4,5,6,7-tetrahydrobenzimidazole-5-carboxylic ethyl ester. This ester and 200 ml of 6N hydrochloric acid added thereto were refluxed together for seven hours. The hydrochloric acid solution was concentrated to dryness, crystallized by addition of acetone, separated by filtration, and then dried to obtain 6.9 g of hydrochloride of 4,5,6,7-tetrahydrobenzimidazole-5-carboxylic acid.

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