Complete Degradation Method of PCBs Using Catalytic Dechlorination Reaction

脱氯反应具有合成和环境潜力。由于芳香族氯化物的脱氯不容易实现，开发这种脱氯的新方法仍然是人们非常感兴趣的。最近，我们报道了在Pd/C催化的加氢体系中加入含氮碱(如NH3、吡啶、乙酸铵)，化学选择性地抑制了苄基醚的氢解，并顺利地加氢了其他可还原官能团，如烯烃、CBZ、苄基酯叠氮化合物等。在对Pd/C-胺的化学选择性加氢反应的研究过程中，我们发现Pd/C的催化剂活性与我们预期的相反，对于芳香族氯化物的加氢脱氯反应具有很好的选择性。胺和溶剂的选择被发现是极其重要的。在常温常压下可对多种芳香族氯化物进行彻底脱氯，除相应的芳香烃和胺盐酸盐外，未检测到其他产物。在环境中可能发现的各种氯代芳香族化合物中，多氯联苯等化合物作为污染物受到了更多的关注。补救这类污染物的努力一直是许多报告的主题，但总的来说，审查的范围仅限于应用。另一方面，我们的脱氯方法完全适用于在常温常压下销毁多氯联苯。

Dechlorination reactions have synthetic and environmental potential. Since the dechlorination of aromatic chlorides cannot readily be achieved, the development of new methodology for such dechlorination remains of great interest. Recently we have reported that addition of a nitrogen containing base (e.g. NH_3, pyridine, ammonium acetate) to a Pd/C-catalyzed hydrogenation system chemoselectively inhibited the hydrogenolysis of a benzyl ether with smooth hydrogenation of other reducible functionalities such as olefin, cbz, benzyl ester azide and so on. During the course of our study on the chemoselective hydrogenations using Pd/C-amine combination, we found that the catalyst activity of Pd/C was marvelously and selectively activated toward the hydrodechlorination of aromatic chlorides by the addition of appropriate amines, contrary to our expectation. The choice of amine and solvent was found to be extremely important. A wide range of aromatic chlorides could be thoroughly dechlorinated under ambient temperature and pressure and no products other than corresponding aromatic hydrocarbon and hydrochloride of amine have been detected. Among the variety of chlorinated aromatic compounds, which may be found in the environment, some compounds such as PCBs have been the subjects of more attention than others as pollutants. The attempts to remedy such pollutants have been the subject of numerous reports but, in general, the scopes of reviews have been limited to applications. On the other hand, our dechlorination method was perfectly applicable to the destruction of PCBs under ambient temperature and pressure.