HYDROGENATION OF NITROBENZENE ON Au/ZrO2 CATALYSTS

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Abstract

The hydrogenation of nitrobenzene at 298K and pressure of 40 bar of H2 over zirconia supported Au catalysts has been studied. Three different procedures were used to prepare 1wt% of Au/ZrO2 catalysts: i) An impregnation method using HAuCl4 as gold precursor ii)Depositation precipitation of Au nanoparticles generated in the presence of urea and iii) Deposition of Gold nanoparticles generated in presence of cetryltrimethylammonium bromide (CTMABR) as surfactant. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, XRD, TEM and XPS techniques. The reactions were carried out in a stainless steel batch reactor using ethanol as solvent. The catalysts exhibits a higher selectivity to aniline, with low accumulation of intermediate products. The kinetic study displayed orders 1 respect to hydrogen pressure and to the substrate concentration (nitrobenzene), and the activation energy was 67.2 KJ/mol.

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Convergent Synthesis of Diverse Tetrahydropyridines via Rh(I)-Catalyzed C–H Functionalization Sequences

Tehetena Mesganaw, Jonathan Ellman (2014)

A Rh-catalyzed C–H bond activation/alkenylation/electrocyclization cascade reaction provides diverse 1,2-dihydropyridines from simple and readily available precursors. The reaction can be carried out at low (<1%) Rh-catalyst loadings, and the use of the robust, air-stable Rh precatalyst, [RhCl(cod)]2, enables the cascade reaction to be easily performed on the benchtop. The 1,2-dihydropyridine products serve as extremely versatile synthetic intermediates for further elaboration often without isolation. The addition of electrophiles under kinetic or thermodynamic conditions provides a wide range of iminiums. Subsequent addition of a nucleophile then generates a diverse array of differently substituted piperidine products. Additionally, [3 + 2] and [4 + 2] cycloadditions of the 1,2-dihydropyridine intermediate provides access to bridged bicyclic structures such as tropanes and isoquinuclidines. These concise reaction sequences enable the formation of highly substituted piperidines in synthetically useful yields with excellent diastereoselectivity.