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

Hexachlorocyclohexane isomers (α-, β-, γ- and δ-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 α-, γ- and δ-HCH to trichlorobenzenes (TCBs) was complete within 5 min at room temperature, but β-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 °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 °C.