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Reaction Kinetics, Mechanisms and Catalysis, 2014, Volume 111, Issue 1, pp 115-121. János Németh, Árpád Kiss, Zoltán Hell.
Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, Budapest, 1521, Hungary.
Abstract
Aromatic nitro compounds can be reduced via transfer hydrogenation in the presence of Pd on basic supports in alcoholic sodium hydroxide yielding not only the appropriate amine, but the azobenzene and azoxybenzene intermediates as well. Depending on the support, the reaction time and the amount of sodium hydroxide added, both the intermediates and the amine can be produced with excellent selectivity.
Additional Information
The reduction of nitrobenzenes to aniline is a well-known procedure. In basic condition the intermediates of the reaction are azoxy- and azobenzenes. Herein we present a heterogeneous catalytic method for the selective synthesis of each intermediate or the aniline via transfer hydrogenation. The hydrogen source for the reduction was the alcohol (mostly ethanol) used as solvent. Two catalysts, developed earlier in our research group, were investigated in the reaction: palladium on 4A molecular sieve (Pd/4A) and on magnesium-lanthanum mixed oxide support (Pd/MgLaO). Pd/MgLaO was suitable for the preparation of the above mentioned intermediates and aniline as well, the selectivity depended on both the reaction time and the amount of base added. In the case of Pd/4A, aniline was not obtained, but for the preparation of azobenzene it was a robust method.
Further experiments with other nitrobenzene derivatives showed interesting results, too (Tetrahedron Letters, 2013, 54, 6094-6096.)
