An Efficient Continuous Flow Synthesis for the Preparation of N-Arylhydroxylamines: Via a DMAP-Mediated Hydrogenation Process

Abstract

The selective hydrogenation of nitroarenes to N-arylhydroxylamines is an important synthetic process in the chemical industry. It is commonly accomplished by using heterogeneous catalytic systems that contain inhibitors, such as DMSO. Herein, DMAP has been identified as a unique additive for increasing hydrogenation activity and product selectivity (up to >99%) under mild conditions in the Pt/C-catalyzed process. Continuous-flow technology has been explored as an efficient approach toward achieving the selective hydrogenation of nitroarenes to N-arylhydroxylamines. The present flow protocol was applied for a vast substrate scope and was found to be compatible with a wide range of functional groups, such as electron-donating groups, carbonyl, and various halogens. Further studies were attempted to show that the improvement in the catalytic activity and selectivity benefited from the dual functions of DMAP; namely, the heterolytic H2 cleavage and competitive adsorption.

Efficient room-temperature hydrogenation of nitroaromatic compounds to primary amines using nitrogen-doped carbon-supported palladium catalysts

“…Post-treatment methods involve the preparation of carbon materials followed by the introduction of nitrogen from a nitrogen source, such as NH 3 . 25–27 However, the nitrogen content in post-treated carbon materials is usually deficient and unevenly distributed. Therefore, the more common approach is to directly pyrolyze N -containing precursors.…”