New insights into the effect of base on the dechlorination of DDT in isopropanol-water over Pd/C catalyst under mild conditions

Catalytic dechlorination of DDT (1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane) over Pd/C catalyst under mild condition was carried out in 70% isopropanol-water (70/30, v/v). The dechlorination pathway of DDT over Pd/C catalyst and the reason for low dechlorination reactivity of DDT were investigated. It was found that there were three dechlorination pathways of DDT in the presence of NaOH: DDT-DDD-CDPB-DPB-DPE, DDT-DDE-BCPE-CPPE-DPE, and DDT-DDD-BCPE-CPPE-DPE. Notably, DPB, formed through the intermediate DDD molecule after losing two aromatic chlorines, led to the low dechlorination reactivity of DDT over Pd/C catalyst. Meanwhile, base could affect the dechlorination pathways of DDT, and thus influence the dechlorination reactivity of DDT over Pd/C catalyst. When strong bases were added, DDE and DDD were produced from the dehydrochlorination and hydrodechlorination of DDT, respectively. Yet, only DDD was formed when weak bases were added. When more NaOH was added, the dechlorination reactivity of DDT was apparently improved. And, NaOH addition also advanced formation of DDE, and affected the dechlorination pathways of DDT over Pd/C catalyst. On the basis of these results, we propose that DDT can be dechlorinated rapidly by means of altering the formation of DDE and DDD.