Dechlorination of lindane in the multiphase catalytic reduction system with Pd/C, Pt/C and Raney-Ni

Abstract

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.

Degradation of lindane from aqueous solutions using iron sulfide nanoparticles stabilized by biopolymers

“…Hence, iron nanoparticles are stabilized by supports, which prevent their agglomeration [13,14] or by synthesizing bimetallic iron particles having an outer shell of a non-corroding metal such as Pt, Pd, etc. [15,16]. The use of iron nanoparticles in drinking water may pose a hitherto unknown health risk.…”

Pd/C-catalyzed hydrodehalogenation of aromatic halides in aqueous solutions at room temperature under normal pressure

“…Reduction is usually mediated by a transition-metal catalyst (Ni, Pd, Rh, Pt) and is performed with molecular hydrogen, metal hydrides or hydrogen sources such as hydrazine, formic acid and its salts, etc. [7][8][9][10][11][12][13][14][15]. For most dehalogenation reactions of aromatic halides in liquid phase, it was general to select organic solvents as the reaction medium.…”

Multiphasic Heterogeneous Catalysis Mediated by Catalyst‐Philic Liquid Phases

“…The product using the multiphasic system was benzene, obtained within one hour. 90 The base initially promoted HCl elimination from HCH to yield trichlorobenzene, which then underwent the usual hydrodechlorination reaction. Dieldrin (which belongs to the 12 POPs banned by the Stockholm convention and is in the same class of other pesticides named 'drins' such as aldrin and endrin) possesses six aliphatic chlorine atoms on a polycyclic skeleton.…”