Dechlorination of hexachlorocyclohexanes with alkaline 2-propanol and a palladium catalyst.

Hexachlorocyclohexane isomers (alpha-, beta-, gamma- and delta-HCH) were dechlorinated in 2-propanol by means of stoichiometric reaction with NaOH and subsequent catalytic dechlorination over a supported palladium catalyst (Pd/C). When the HCH isomers (2-10 mmol/l) were reacted with a molar excess of NaOH ([NaOH]/[HCH]>9) in 2-propanol, transformation of alpha-, gamma- and delta-HCH to trichlorobenzenes (TCBs) was complete within 5 min at room temperature, but beta-HCH was less reactive. Analysis of TCB isomers produced from individual HCH isomers showed that 1,2,4-TCB was always predominant (70-90% of the product) and 1,2,3-TCB and 1,3,5-TCB were minor products. The produced TCBs were dechlorinated by subsequently adding Pd/C to the alkaline 2-propanol solution and heating at 55 degrees C for 3 h, resulting in the formation of benzene in high yield (>80%). Technical-grade HCH, which contains these four isomers, was successfully dechlorinated with NaOH and Pd/C at 55 degrees C.