Molecular interactions with CO2 for controlling the regioselectivity of liquid phase hydrogenation of 2,4-dinitroaniline

Abstract

The catalytic hydrogenation of 2,4-dinitroaniline using a 0.5 wt% Pt/TiO₂ catalyst was investigated in a multiphase medium of tetrahydrofuran (THF) pressurized by CO₂ at different pressures and at 323 K. When CO₂ pressure was increased, the overall rate of hydrogenation simply decreased but the selectivity to the desired product of 4-nitro-1,2-phenylenediamine increased. The noticeable enhancement of the selectivity to 4-nitro-1,2-phenylenediamine can be explained by chemical reactivities of CO₂ molecules. In situ high-pressure FTIR and molecular simulations demonstrate that the dissolved CO₂ molecules may interact with amino groups of the substrate and weaken the intra-hydrogen bonding between the amino and 2-nitro groups, which results in the change in the relative reactivity of the two nitro groups, yielding the desired product in a higher selectivity. The change in the intra- and inter-molecular interactions between the substrate and CO₂ molecules was theoretically examined by DFT calculations.