Extracting chemical information from initial partial charges and electronic properties of reactants to predict order of chemical reactivity: Heterogeneous catalytic hydrogenation of homologue R-CO-X carbonyl compounds

Reactivity of various R-CO-X carbonyl compounds toward hydrogenation was compared on Re-Pt/Al2O3 catalyst containing 1 wt.% of both metals. In the R-CO-X carbonyl compounds the R is aliphatic, saturated and unsaturated group up to 16 carbon atoms or phenyl, while the group X refers to H, R′, OR′, OH, NH2, NR′ and NR′R″ i.e. aldehyde, ketone, ester, carboxylic acid, primary, secondary and tertiary carboxamides, respectively. The order of reactivity of >CO group toward hydrogenation in these different carbonyl compounds was demonstrated based on catalytic experiments and computational chemistry (molecular mechanics and ab initio calculations). Our theoretical calculations were based on computing various partial charges, bond-order and band gap on the carbonyl group of R-CO-X as a function of R and X. Our calculation has indicated that even a simple Mulliken partial charge analysis (an instant side result of the common Hartree-Fock calculation) on the carbonyl group of the gas phase R-CO-X can qualitatively predict its order of reactivity in the complex catalytic hydrogenation. Our calculation has also supported the experimental finding such that the effect of the chain size and length of group R on the reactivity is much smaller than that of group X in both, aliphatic and aromatic carbonyl compounds. However, the reactivity of aromatic carbonyl compounds (R = phenyl), as expected, is somewhat higher than that of aliphatic ones in the hydrogenation on Re-Pt/Al2O3 catalyst. The reactivity of carbonyl compounds followed the order: aldehydes > ketones > carboxamides > carboxylic acids > esters.