Catalysis of Organic..

Robitaille, Clément, Chapuzet and Lessard 28132. Chemoselective Hydrogenation of NitroCompounds to the Corresponding Amines onRaney® Copper CatalystsSimon Robitaille, Geneviève Clément, Jean Marc Chapuzet and Jean LessardAbstractLaboratoire de Chimie et Electrochimie Organiques, Département de Chimie,Université de Sherbrooke, Sherbrooke, Québec, J1K 2R1 CanadaJean.Lessard@USherbrooke.caThe selectivity of the electrocatalytic hydrogenation (ECH) method for the reductionof nitro compounds to the corresponding amines is compared with that of reductionby Raney copper (RCu) alloy powder in alkaline aqueous ethanol. In the formermethod, chemisorbed hydrogen is generated in situ by electrochemical reduction ofwater. In the latter method (termed “chemical catalytic hydrogenation” (CCH)),chemisorbed hydrogen is also generated in situ but by reduction of water byaluminium (by leaching of the alloy). Finally, the selectivity and efficiency of theelectrochemical reduction of 5-nitro-indoles, -benzofurane, and -benzothiophene atRCu electrodes in neutral and alkaline aqueous ethanol is compared with that of theclassical reduction with zinc in acidic medium.IntroductionThe electrocatalytic hydrogenation (ECH) of a nitro group to the correspondingamine in neutral or basic aqueous or mixed aqueous-organic media is described byequations [1] to [7] where M represents an adsorption site of the catalyst and M(H)chemisorbed hydrogen, and M(RNO 2 ), M(RNH(OH) 2 ), and M(RNHOH) representor/and[1] 6H 2 O + 6e + M 6M(H) + 6OH[2] RNO 2 + MM(RNO 2 )[3] M(RNO 2 ) + 2 M(H) M(RNH(OH) 2 )[4] M(RNH(OH) 2 ) + 2 M(H) M(RNHOH) + H 2 O[5] M(RNH(OH) 2 )M(RNO) + H 2 O[6] M(RNO) + 2 M(H) M(RNHOH) + H 2 O[7] M(RNHOH) + 2 M(H) M(RNH 2 ) + H 2 OM + RNH 2