Enantioselective hydrogenation of (E)-alpha-phenylcinnamic acid with cinchonidine-modified Pd/TiO2: influence of solvents and additives

Both the enantioselectivity and activity of the hydrogenation of (E)-alpha- phenylcinnamic acid with cinchonidine-modified Pd catalysts are strongly so lvent dependent; polar solvents with higher solubility for the substrate ar e preferable. The simultaneous increases in the enantioselectivity and acti vity, also induced by the addition of either a small amount of water to apr otic solvents or an amine such as benzylamine, indicate that preferential a cceleration of the selective reaction has occurred, thus strongly suggestin g the importance of the product desorption step on the modified sites.