Hydrogen evolution from organic "hydrides"

New concepts of hydrogen storage are being explored for applications from portable power to transportation for the future hydrogen economy. The exergonic evolution of hydrogen gas at room temperature via catalysis from reduced organic compounds was studied. Hydrogen elimination from 2-(1,3-dimethylbenzimidazoline-2-yl)benzoic acid comprised the catalyzed reaction between the "hydride" from the unique C-H of the imidazolidine and a "proton" from the carboxyl group. This reactivity was confirmed by the reaction of 1,3-dimethyl-2-phenylbenzimidazoline (3) with acetic acid or benzoic acid under an inert atmosphere in the presence of finely divided palladium to afford hydrogen and the phenylbenzimidazolium cation. Compound 3 was stable toward these acids for days when no catalyst was present. 1,3-Dimethylbenzimidazoline (5) evolved hydrogen in the presence of acetic or benzoic acid and catalyst, similar to compound 3. Ambient-temperature hydrogen formation from benzimidazolidines and carboxylic acids was strongly favored and using hydrogen pressure alone to drive the reaction backwards would be extremely difficult. Water was sufficiently acidic for Pd-catalyzed hydrogen evolution from compounds 3 and 5. However, in the presence of water, the reactions were far more complex than the reactions involving carboxylic acids due to further reactions of water and hydroxide with the phenylbenzimidazolium and 1,3-dimethylbenzimidazolium cations. This is an abstract of a paper presented in the ACS Fuel Chemistry Meeting Fall 2005 (Washington, DC Fall 2005).