New phenomenon in competitive hydrogenation of binary mixtures of activated ketones over unmodified and cinchonidine-modified Pt/alumina catalyst

Competitive hydrogenations of eight binary mixtures of ethyl pyruvate (EP), methyl benzoylformate (MBF), ketopantolactone (KPL), pyruvic aldehyde dimethyl acetal (PA) and trifluoroacetophenone (TFAP) on platinum/alumina catalysts unmodified (racemic hydrogenation) and modified by cinchonidine (chiral hydrogenation) were studied under the experimental conditions of the Orito reaction. Reaction rates of chiral and racemic hydrogenations were determined and relative adsorption coefficients were calculated. In the competitive chiral hydrogenation of EP + MBF, EP + TFAP and KPL + MBF binary mixtures a new phenomenon was observed: namely the EP and KPL are hydrogenated faster than MBF and TFAP, whereas in racemic one the MBF and TFAP are hydrogenated faster than EP or KPL. Effects of the activated ketones structure on their reactivity and the stability of the surface complexes are discussed. It was found that differences in rate enhancement are caused by the differences both in the adsorptivity and in the reactivity of adsorbed substrates and adsorbed intermediate complexes.

In competitive hydrogenations of binary mixtures of several activated ketones over Pt catalyst modified by cinchonidine (CD) substrates 1 are hydrogenated faster than substrates 2, whereas over unmodified catalyst substrates 2 are hydrogenated faster than substrates 1. It was found that differences in rate enhancement are caused by differences both in the adsorptivity and in the reactivity of adsorbed substrates and adsorbed intermediate complexes.Figure optionsDownload as PowerPoint slideResearch Highlights
► Competitive hydrogenations of activated ketones on modified Pt/Al2O3 were studied.
► Reaction rates of chiral and racemic hydrogenations were determined.
► The values of the relative adsorption coefficients were calculated.
► These values may be inverted in the chiral with respect to racemic hydrogenations.