Dechlorination of DDT Mediated by Bimetallic Systems

Abstract

DDT dechlorination efficiencies of bimetallic systems, namely, Mg°-Zn, Mg°-Ni, and Mg°-Co were compared. All the systems transformed DDT with efficiencies exceeding 98% within 24 h. Based on GC-ECD and GC-MS analyses a step-wise and sequential dechlorination of DDT by Mg°-Zn system in 1:1 water acetone phase via 1,1 dichloro, 2,2- bis (p-chlorophenyl) ethane (DDD), 1, chloro, 2,2 bis (p-chlorophenyl) ethane (DDMS) to 2,2 bis (p-chlorophenyl) ethane (DDNS) was noted. Accumulation of DDNS as the end product indicates that all three alkyl chlorine atoms of DDT were removed by Mg°-Zn system. Mg°-Co also showed almost complete removal of DDT in water-acetone phase that was accompanied by the accumulation of DDD followed by a decline in its concentration as a function of time. On the other hand, Mg°-Ni system exhibited inefficient removal of DDT in water-acetone phase. In pure acetone phase, Mg°-Co system and Mg°-Ni dechlorinated DDT with the accumulation of DDE and DDMU as end products following 24 h of reaction. The presence of surfactants or organic solvents is required to ensure solubilization of DDT. Also addition of acid is essential to provide sufficient protons for efficient reductive dechlorination via hydrogenation. Advantage of Mg° based dehalogenation reactions is that they occur at high rates under ambient temperatures, and pressure and oxygen need not be excluded in the reaction phase. Our studies revealed that Mg°-Zn is the best option among all tested systems due to its high reactivity and low cost, and may be used to treat DDT contaminated water.