Pd/C-catalyzed practical degradation of PCBs at room temperature

The catalytic degradation method of polychlorinated biphenyls (PCBs) using the palladium on activated carbon–triethylamine (Pd/C–Et3N) system under ambient hydrogen pressure and temperature was developed. Aroclor® 1254, Aroclor® 1248, 10% Aroclor® 1254 in paraffin oil and PCBs from capacitor could be completely dechlorinated to afford biphenyl and Et3N·HCl. Fifteen pure PCB congeners, including the highly toxic co-planar PCBs, were smoothly dechlorinated to biphenyl within 1 or 2 h using 10% Pd/C (10% of substrate weight) and Et3N (1.2 equiv. vs. Cl numbers). However, the dechlorination of the fully ortho-substituted PCB congeners was delayed and chlorine atoms on the ortho-positions still remained under the hydrogenation conditions, but these PCB congeners are only slightly present in the commercial PCB mixture. The Pd/C–Et3N–H2 system offers a simple, safe, and inexpensive degradation method of PCBs under mild reaction conditions.