Dechlorination of ␥-hexachlorocyclohexane (lindane) is carried out in the multiphase catalytic system, composed by isooctane and aqueous KOH phases, a phase transfer agent (Aliquat 336) and a metal catalyst, e.g. 5% Pd/C, 5% Pt/C, or Raney-Ni. At 50• C and atmospheric pressure the full conversion of lindane to 1,2,4-tricholorobenzene (1,2,4-TCB) is achieved in 5-10 min via the base assisted dehydrochlorination, followed by the metal catalyzed hydrodechlorination with hydrogen to benzene. Aqueous KOH and Aliquat 336 strongly affect the reaction: if present together they co-promote both dehydrochlorination and hydrodechlorination steps; if KOH is absent, the reaction is forced to follow a different catalytic pathway, which involves a removal of a pair of chlorines at every reaction step by zerovalent metal followed by reduction of metal with hydrogen. This is proven by the formation of 3,4,5,6-tetrachlorocyclohex-1-ene and 5,6-dichlorocyclohexa-1,3-diene as intermediates in the reaction over Raney-Ni, and by the absence of TCBs in the reactions on all the catalysts studied. The final yield of benzene via this pathway can be achieved in shorter times than in a system with KOH. The presence of Aliquat 336 in the isooctane-water system produces a 10-fold rate increase, the presence of alkaline water is also important since it avoids catalyst poisoning by neutralizing the hydrochloric acid formed.

Selectivity and product distribution of hydrodechlorination (HDCl) of dieldrin and DDT are studied in different liquid phase systems, namely in: (1) in ethanol; and (2) in the supported ionic liquid heterogeneous catalytic system (multiphase system), composed by the organic phase and aqueous KOH, a quaternary ammonium ionic liquid promoter (Aliquat 336), and a metal catalyst, e.g. 5% Pd/C, 5% Pt/C, or RaneyNi. At 50 8C and atmospheric pressure of hydrogen, a quantitative hydrodechlorination of DDT in the biphasic system with ionic liquid layer is achieved in 40 min and in 4 h with Raney-Ni and Pd/C, respectively, while the reaction on Pt/C or on Pd/C without Aliquat 336 is slow. Dieldrin undergoes partial dechlorination, with high selectivity achievable only for its mono-and bi-dechlorination products. Dechlorination pathways and reactivity of different types of organic chlorine atoms versus the catalyst nature and other conditions are discussed. #

Hydrodechlorination of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), pentachlorophenol (PCP), and p-chlorobenzoic acid with hydrogen gas over 5% Pd/C or Raney-Ni was studied in different liquid phase systems: (1) ethanol or ethanol-aqueous KOH; (2) in the multiphase system, composed by an organic phase and aqueous KOH and containing a quaternary ammonium salt (Aliquat 336). Under mild conditions (50 8C and atmospheric pressure of hydrogen) quantitative hydrodechlorination of 2,4,5-T is achieved in 1-4 h over Raney-Ni or Pd/C in the multiphase system or in the ethanol-aqueous KOH solution. PCP reacts selectively giving the dechlorinated phenolate in several hours in the system made of aqueous KOH (with Raney-Ni or Pd/C) or in several minutes in the presence of a small amount of Aliquat 336 solution in isooctane (1-4 molar% of Aliquat 336), where Aliquat 336 promotes the phase-transfer of polychlorinated anion. The reaction rates versus conditions, process localization, and the role of the ionic liquid environment are discussed. #