Metal-Free N-Doped Carbon Catalyst Derived from Chitosan for Aqueous Formic Acid-Mediated Selective Reductive Formylation of Quinoline and Nitroarenes

Abstract

A chitosan-derived metal-free N-doped carbon catalyst was synthesized and investigated for selective reductive formylation of quinoline to N-formyl-tetrahydroquinoline and nitroarenes to N-formyl anilides via aqueous formic acid (FA)-mediated catalytic transformation. FA dissociated on the catalyst surface and acted as a hydrogenating and formylating source for selective N-formylation of N-heteroarenes. The carbonized catalyst prepared at 700°C offered the best activity. A 92% yield of N-formyl-tetrahydroquinoline after 14 h and >99% yield for N-formyl anilide after 12 h at 160°C were obtained. The excellent catalytic activity was correlated with the type of “N” species and the basicity of the catalyst. Density functional theory calculations revealed that a water-assisted FA decomposition pathway (deprotonation and dehydroxylation) generated the surface adsorbed H and HCOO species, required for the formation of N-formylated products. In addition, the selective formation of N-formyl-tetrahydroquinoline and Nformyl anilides was explained by a comprehensive reaction energetics analysis.