A Pd confined hierarchically conjugated covalent organic polymer for hydrogenation of nitroaromatics: catalysis, kinetics, thermodynamics and mechanism

Herein, we propose a fast and scalable synthesis of a triazine based hierarchically conjugated covalent organic polymer under solvent and additive free conditions through a single step process. The synthesized material CCTP (Cyanuric Chloride-Thiourea-Polymer) was thoroughly characterized by various physicochemical techniques. The CCTP exhibited regular sponginess and excellent chemical as well as thermal stability. The solvent and additive free approach for CCTP synthesis provides a sustainable alternative for classical solvothermal methods. The CCTP was immobilized with Pd (0) and subsequently a heterogeneous material Pd@CCTP was obtained, which was used as an efficient catalyst for the hydrogenation of nitroarenes. The rate constant andE(a)were measured to be 2.08 x 10(-2)s(-1)and 15.67 kJ mol(-1)respectively and thereafter other thermodynamic parameters like Delta H, Delta Sand Delta Gfor the hydrogenation ofp-nitrophenol were also calculated. The obtained results indicate that the catalytic hydrogenation ofp-nitrophenol is a non-spontaneous and endothermic process. We have also investigated the effect of surfactants (NH4OH, FA, and N-2) on the reaction performance, and consequently NH4OH and FA both slow down the reaction while N(2)doesn't affect the reaction medium. Further, we calculated the rate constant for the hydrogenation of 2,4-dinitrophenol and 2,4,6-trinitrophenol. An array of nitroarenes were further reduced to extend the substrate scope at RT; high TOFs were observed. Besides, Pd@CCTP showed excellent reusability in hydrogenation reactions without evident performance falloff.