Reductive dehalogenation of perchloroethylene and trichloroethylene with vitamin B12 mimics

Since Vitamin B₁₂ is one of the most well-known reductive dehalogenation catalysts for perchloroethylene (PCE), a survey of structurally similar complexes was conducted to search for new catalysts. Dehalogenation activity was assayed by comparing the rates of PCE reduction by test complexes with those obtained with B₁₂. While several common B₁₂ model complexes failed to show catalytic activity, tetrakis-(4-carboxyphenyl)-porphyrin cobalt, (TCPP)Co, demonstrated dechlorinating behavior superior to Vitamin B₁₂. Kinetic profiles were used to find the absolute rate constant of dechlorination of PCE and TCE by (TCPP)Co under a variety of conditions. The rate law was first order in PCE as indicated by the first order decay reaction profile. The concentration of catalyst was varied over the range of 5.1-20.4 μM against PCE, and the degradation rate constant was first order in catalyst. The PCE degradation rate constant was independent of reductant concentration from 1.28 to 16 mM, indicating that the rate limiting step is zero order for bulk reductant. (TCPP)Co demonstrated superior dechlorination activity compared to B₁₂. This is an abstract of a paper originally presented at the 225th ACS National Meeting (New Orleans, LA 3/23-27/2003).