Stereoselective hydrogenation of Paracetamol to trans-4-acetamidocyclohexanol on carbon-supported Ru-M (M =Co, Ni) bimetallic catalysts

This paper describes the results obtained on the catalytic hydrogenation of Paracetamol (4-acetamidophenol), carried out at 393 K, over carbon-supported Ru, Co and Ni based monometallic catalysts, and over graphite-supported Ru-M (M = Co, Ni) bimetallic catalysts. A comparative study of the effect of the different supported-metal catalysts and of the applied reduction temperature has been carried out. Two selectivity parameters have been controlled: the production of by-products and the trans-cis composition of 4-acetamidocyclohexanol (stereoselectivity). Characterisation of the catalysts was performed by temperature-programmed reduction (TPR) and CO volumetric chemisorption. It was found that the hydrogenation reaction of Paracetamol is structure sensitive, since intrinsic activity and selectivity values are modified with variations in the metallic particle sizes. Generally, the catalytic activity, under our experimental conditions, follow the trend: Pt < Pd < Ni much less than Co < Ru. The production of secondary compounds derived of hydrogenolytic cleavage (N-cyclohexylacetamide) and/or of partial hydrogenation reactions (4-acetamidocyclohexanone), depends on the active metal: Ni < Ru < Co, among other factors. Concerning the stereoselectivity (trans to cis ratio), among the monometallic catalysts Co exhibited the highest T/C ratio, with the overall sequence: Co > Ni > Ru. Finally, the bimetallic catalysts, particularly those of Ru-Ni, show an improved stereoselectivity (T/C ratio) in comparison with the corresponding counterparts. (C) 2004 Elsevier B.V. All rights reserved.