The effect of water on the hydrogenation of o-chloronitrobenzene in ethanol, n-heptane and compressed carbon dioxide

Authors: Haiyang Cheng, Xiangchun Meng, Yancun Yu, Fengyu Zhao

Abstract:
Water as a clean solvent and promoter in the organic synthesis have attracted more attention, herein the effect of water was studied for the hydrogenation of o-chloronitrobenzene (o-CNB) over Pt/C and Pd/C catalysts in ethanol, n-heptane and compressed CO₂. Very interesting, the reaction rate decreased in ethanol, but increased in n-heptane and compressed CO₂ with the addition of water. The role of water in the reaction was mainly discussed from the experimental data and phase behavior analysis, one is to activate the functional group of NO₂ through the interactions via a hydrogen bonding, and the other is to affect the solubility of hydrogen in ethanol and n-heptane. The positive effect of the interaction between water and reactantsmay be counteracted by the negative effect of hydrogen solubility in ethanol. However, the concentration of o-CNB and hydrogen changed slightly in n-heptane with the addition of water, so the interaction of water with reactants may play a main role in improving the TOF. The combination of H₂O and CO₂ is more efficient than the pure H₂O, CO₂ and H₂O–n-heptane systems. The phase behavior may play important role also for the improved activity except for the interactions of H₂O and CO₂ with the reactants. o-CNB phase was expanded in the compressed CO₂ and so the concentration of H2 in o-CNB phase increased due to the miscible of CO₂ and H₂, resulting in the enhancement of reaction rate and the maximum conversion at pressure of 9 MPa CO₂, at which the volume was expanded to the largest one. The similar results were also obtained in the compressed CO₂ system without H₂O. In addition, the stability of Pt/C and Pd/C was studied in H₂O–n-heptane and H₂O–CO₂. As a result, the H₂O–CO₂ media and Pt/C catalyst is one of the most effective systems for the hydrogenation of o-CNB. 

Keywords:
o-chloronitrobenzene
Hydrogenation
Water
Compressed carbon dioxide

Published in: Applied catalysis A: General  (Volume 455, Pages 1-266, 30 March 2013)

Publisher: Elsevier

ISSN Information: 0926-860X

The effect of water on the hydrogenation of o-chloronitrobenzene in ethanol, n-heptane and compressed carbon dioxide

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