邻氯硝基苯在Pd/C催化剂上加氢反应机理及添加Cu对邻氯苯胺选择性的影响

本文研究了邻氯硝基苯在5%Pd/C催化剂上加氢为邻氯苯胺和苯胺的反应机理。结果表明,在常压下,邻氯苯胺和苯胺的选择性分别为~70%和~30%,且不随转化率增加而变化。在加压(1.0 Mpa)条件下,也有类似规律。因此,说明邻氯苯胺和苯胺分别是两个平行反应的产物。通过测定该反应各步骤的初始反应速率,进一步证实了这一结论。在认识反应机理的基础上,制备出可有效抑制脱氯的Cu-Pd/C双金属催化剂,在不加脱氯抑制剂的情况下,可使邻氯硝基苯加氢制备邻氯苯胺的选择性提高到96%以上。

Mechanism of hydrogentation of o-chloronitrobenzene over Pd/C and the effect of copper on selectivity of o-chloroaniline in the reaction

Reaction mechanism of hydrogenation of o-chloronitrobenzene to o-chloroaniline and aniline over 5% Pd/C was investigated. It was shown that the selectivity of o-chloroaniline and aniline were～ 70% and～ 30%, respectively, under atomosphere. More importantly,the seleetivities remained almost constantly with increasing conversion of ochloronitrobenzene. Similar results were observed under elevated perssure (1.0 Mpa). These results indicated that o-chloroaniline and aniline were formed from two parallel reactions. The initial reaction rates of diferent reactions were measured, which further confirmed the paralle reaction mechanism. Based on the proposed mechanism, a Cu-Pd/C bimetallic catalyst was prepared and applied in hydrogenation of o-chloroonitrobenzene to o-chloroaniline. Thus, selectivity of o-chloroaniline was improved to higher than 96%, owing to the inhibiting effect of copper on hydro-dechlorination reaction.