Effect of Solvent Polarity Properties on the Selectivity and Activity for 3,4-Dichloronitrobenzene Hydrogenation over Pd/C Catalyst

Abstract:

Several representative solvents classified in three categories: 1) aprotic apolar solvents: 2) protic solvents; 3) aprotic polar solvents were chosen to investigate the effect on the catalytic activity and selectivity for the selective hydrogenation of 3,4-dichloronitrobenzene (3,4-DCNB) over Pd/C catalyst. The solvent polarity increases the hydrogenation rate apparently, but also increases the selectivity to 3-chloroaniline and 4-chloroaniline from dehalogenation reaction. The solvents with the high polarity and hydrogen-bond donation capability can generate the strong interaction and the H-bond with nitro group of 3,4-DCNB, and then promote the activation and polarization of nitro group. However, on basis of the result of water as solvent, the higher hydrogenation rate in polarity solvents, to a larger extent, may be attributed to the increase of the amount of reactive chemisorbed hydrogen resulting from the dissociative chemisorption of aprotic polar solvents over the activated metal surface. At the same time, this is why the selectivity to 3-chloroaniline and 4-chloroaniline from dehalogenation reaction increase obviously with the increase of solvent polarity, because the amount of reactive chemisorbed hydrogen on the catalytic activated sites exceeds the needs of nitro group reduction and then surplus hydrogen reacts with the C-X bond.

• Periodical: Advanced Materials Research (Volumes 396-398)
• Pages: 2379-2383
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.396-398.2379
• Online since: November 2011
• Authors: Chun Shan Lu, Jing Hui Lu, Lei Ma, Qun Feng Zhang, Xiao Nian Li
• Keywords: 3.4-Dichloronitrobenzene, Aromatic Haloamines, Pd/C, Selective Hydrogenation

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DOI: 10.1016/j.apcata.2004.08.025