I&EC 19 |
| Mechanically alloyed palladized magnesium has successfully been shown to dechlorinate polychlorinated biphenyls (PCBs). A variety of single congener studies have been performed in an attempt to deduce the reaction mechanism by which the dechlorination occurs in methanol. Monochlorinated congener (PCB-1, PCB-2, PCB-3) studies in both methanol and water (9:1 water:methanol) show different relative rates of dechlorination, suggestive of solvent specificity in the mechanism. Also suggestive of solvent specificity is that different final products are seen in both solvents. Use of isotopically labeled methanol-d in the degradation of PCB-151 has indicated that hydrogen exhibits a primary kinetic isotope effect (kh/kd>2), indicating that it is involved in the rate-determining step of the reductive dehalogenation process. Based upon experimental data, a free-radical substitution similar to that of an SRN1 mechanism is proposed, where atomic hydrogen abstracts chlorine from the PCBs in a homolytic bond-cleavage. An aryl radical would be produced which can then be attacked by a second hydrogen radical in a termination step. Subsequent dechlorination can continue in this matter until biphenyl is reached, at which point the degradation would be halted. |
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Environmental Applications of Nanoscale and Microscale Reactive Particles
1:30 PM-5:30 PM, Sunday, April 6, 2008 Morial Convention Center -- Rm. 223, Oral
Division of Industrial & Engineering Chemistry |