Detoxification of hexachlorobenzene by dechlorination with potassium-sodium alloy.

Dechlorination of hexachlorobenzene (HCB) was achieved by a liquid potassium-sodium (K-Na)-alloy. HCB in a cyclohexane/benzene solution (22 mmol/l, 4.67 g/l as chlorine) was dechlorinated by almost 100% after a 30-min reaction, indicating high reactivity of K-Na alloy and high proton donating power of cyclohexane. Decreasing orders of chlorobenzenes identified after a 15-min reaction, by amount were 1,2,3,4->1,2,3,5->1,2,4,5- for tetrachlorobenzenes, 1,2,4->1,2,3->1,3,5- for trichlorobenzenes, and 1,4->1,3->1,2- for dichlorobenzenes. It was hypothesized that once one chlorine atom in HCB was replaced with a proton, the adjacent chlorine atom to the proton tended to be replaced with another hydrogen atom. A total of 63 PCBs formed via the Wurtz-Fittig reaction were identified as by-products in the sample after a 15-min reaction. Among PCBs found, 2,3',4',5-tetrachlorobiphenyl, which was a product from 1,2,4-trichlorobenzene formed via the Wurtz-Fittig reaction, was detected in relatively high concentration (48.9 nmol/ml). The sample obtained from a reaction mixture after 30 min contained only 14 PCBs in trace amounts, indicating that the PCBs formed were also further dechlorinated by K-Na alloy. Non-chlorinated compounds--such as methylbenzene, dimethylbenzene, dimer of tetrahydrofuran, and dicyclohexyl (dimer of cyclohexane)--were also identified in the samples. A method using K-Na alloy developed in the present study dechlorinated satisfactorily HCB at room temperature.