Hydrochloric Acid → 5-Oxo-5-(2-oxo-1,3-dihydrobenzimidazol-5-yl)pentanoic acid

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Reaction Steps

To a suspension of glutaric anhydride (3.42 g, 30 mmol) and benzimidazol-2(3H)-one (4.02 g, 30 mmol) in tetrachloroethane (100 ml), was added aluminium chloride from a freshly opened container (14.0 g, 105 mmol) in small portions. This mixture was heated to 120 C for 105 min, cooled to room temperature, then poured onto a mixture of ice (75 g) and concentrated hydrochloric acid (20 ml). The suspension was stirred overnight to break up solids that had formed. The tetrachloroethane was azeotropically distilled from the mixture with water under reduced pressure, leaving a brown solid suspended in an aqueous phase. The solid was filtered off and washed with dilute aqueous hydrochloric acid, then water. The solid was added to boiling aqueous sodium carbonate (5% w/v, 150 ml) and the solution filtered. Decolourizing charcoal was added to the cooled filtrate, which was then boiled for 5 min. The charcoal was removed by filtration, and the filtrate treated with concentrated hydrochloric acid until the pH of the solution was 4. The precipitated solid was allowed to stir overnight, filtered off, and dried in a vacuum oven at 50 C/20 mmHg until a constant weight was achieved (1.6 g of brown solid). Nmr indicates that some starting material still remains. Recrystallization of a portion of this solid from acetic acid, as indicated by Kosyakovskaya, did not afford recovery of any product. A portion of the brown solid (300 mg) was dissolved in aqueous sodium bicarbonate (5% w/v, 10 ml) and insoluble material removed by filtration. The filtrate was acidified with concentrated hydrochloric acid and the precipitate formed filtered off and dried at the pump (30 mg).

Provenance & Evidence