Abstract
We report on the manufacture of a state-of-the-art heterogeneous non-noble metal catalyst, which is based on a molecularly well-defined phosphine-tagged cobalt corrole complex. This precursor compound is readily synthesized from convenient starting materials while the active material is obtained through wet-impregnation of the pertinent metalliferous macrocycle onto carbon black followed by controlled pyrolysis of the loaded carrier material under an inert gas atmosphere. Thus, the obtained composite was then applied in the heterogeneous hydrogenation of various nitroarenes to yield a vast array of valuable aniline derivatives that were conveniently isolated as their hydrochloride salts. The introduced catalytic protocol is robust and user-friendly with the entire assembly of the reaction set-up enabling the conduction of the experiments on the laboratory bench without any protection from air.
Highlights
The synthesis of aniline from nitroarenes is a highly relevant industrial process considering the high demand of aromatic amines for the production of pharmaceuticals, dyestuffs, agrochemicals, and isocyanates for making polyurethanes
CoCorrPPh3 -support composite was finely grinded using mortar and pestle, upon which the formed powder was carefully pyrolyzed in an Austromat® 624 furnace at the required temperature (Ar atmosphere, 2 h)
The catalyzed hydrogenation reactions were carried out in glass vials (4 mL), each of which was charged with solid CoCorrPPh3 @Vulcan-800 (12 mg, if not stated otherwise, i.e., 0.5 mol% based on a bulk Co content of 1.16% by weight), nitro compound (0.5 mmol), solvent (2 mL), as well as a magnetic stirring bar—in that order and without any protection from air
Summary
The synthesis of aniline from nitroarenes is a highly relevant industrial process considering the high demand of aromatic amines for the production of pharmaceuticals, dyestuffs, agrochemicals, and isocyanates for making polyurethanes. The given nitro reduction is realized through the stoichiometric Béchamp reaction, which deploys highly corrosive hydrochloric acid and excess iron powder [1] Since this route produces a significant amount of inorganic waste, it is worthwhile, for both economic and ecological reasons, to resort to catalytic methods utilizing H2 gas as the principal reductant. The use of nitrogen-rich (chelating) N-donor ligands is an effective tool for the preparation of decent heterogeneous catalysts that are activated through controlled thermal heat treatment of a molecularly well-defined metal complex
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