A Simplified Kinetic Model for the Enantioselective Hydrogenationof 1-Phenyl-1,2-Propanedione over Ir/TiO2in the Presence of aChiral Additive

This communication proposes a preliminary simplifiedkinetic model for the hydrogenation of 1-phenyl-1,2-propanedionethat can render up to eight compounds, involving regioselectivity andenantioselectivity. The catalytic system comprises two functionalities;the heterogeneous catalyst (Ir/TiO2)playstheroleforthehydrogenation, whereas the adsorption/binding to the active site isplayed by a chiral molecule (cinchonidine), added to the reactionmixture. The reaction occurs at room temperature and total pressureof 40 bar. The product distribution shows competitive parallel andseries pathways with up to 12 possible reactions. Despite thecomplexity of both reaction and catalyst system, a simplified kinetic model was able to predict the concentrations profiles. Themodel assumes the reactions to be apparentfirst order in the concentrations of reactant and intermediate products, while the kineticconstants include all other effects (partial pressure of hydrogen, solvent and catalyst effects, and the concentration of the chiraladditive). The concentration profiles were well-modeled with low residual values. The errors in the kinetic constants (k-values) weresmall for all relevant parameters of the main reaction pathways. Twok-values are nil, which is the lower bound imposed in themodel, suggesting that these reaction pathways are likely negligible. The positive outcome from this simplified model suggests thatthe process can be formally treated as afirst-order irreversible homogeneous catalyzed reaction, despite a heterogeneous catalyst wasemployed (with a modifier). Despite the promising results, the model must be extended for a more general applicability, orconditions where it is applicable.

Automated summary

This study proposes a simplified kinetic model for the hydrogenation of 1-phenyl-1,2-propanedione, which can accurately predict concentration profiles despite the complexity of the reaction and catalyst system. The model suggests that the process can be formally treated as a first-order irreversible homogeneous catalyzed reaction.