Synthesis of New Vitamin B12 Model Complexes for Mechanistic Studies of the Reductive Dechlorination of Chlorinated EthylenesEPA Grant Number: U916107
Title: Synthesis of New Vitamin B12 Model Complexes for Mechanistic Studies of the Reductive Dechlorination of Chlorinated Ethylenes
Investigators: Fritsch, Joseph M.
Institution: University of Minnesota - Twin Cities
EPA Project Officer: Klieforth, Barbara I
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $133,716
RFA: STAR Graduate Fellowships (2003) Recipients Lists
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Chemistry and Materials Science
The objectives of this research project are to: (1) develop a deeper understanding of chlorinated ethylene (CE) reductive dehalogenation mechanism by Vitamin B12 through the synthesis of novel model complexes, including complexes containing new -ketiminate ligands with pendant donor groups; and (2) study the mechanism of aqueous CE reductive dehalogenation by structurally similar Vitamin B12 mimics.
Synthesis of novel cobalt complexes of new, monoanionic, tetradentate, aza ligands will supplement existing Vitamin B12 model complexes and allow for a new approach to the study of the CE reductive dehalogenation. CEs (perchloroethylene, trichloroethylene, dichloroethylene, and vinyl chloride) are reductively dechlorinated by Vitamin B12—a cobalt containing corrin macrocycle, of which the Co(I) oxidation state is the reactive species. Few cobalt complexes of monoanionic, tetradentate, aza ligands have been studied, and new -ketiminate ligands with pendant donor groups will be used to prepare new complexes. These complexes will be fully characterized during this research. The complexes will be useful for investigation into CE degradation. Any isolable Co(I) complexes will allow for the study of the individual CE reduction steps. Isolation and characterization of volatile and inorganic products will be valuable to understanding the reaction pathway.
In addition, synthetic Vitamin B12 mimics represent an opportunity to find new aqueous reductive dehalogenation catalysts. Cobalt porphyrin complexes have been assessed as viable CE degradation catalysts in batch reactors, and the reduced products were analyzed with gas chromatography with flame ionization detection. Kinetic studies of the factors governing the dehalogenation rate were studied. Also, UV-Vis spectroscopy was used to study the reaction because there are known absorbance maxima for cobalt complexes in different oxidation states. Investigation into the mechanism of catalyst oxidation state cycling and CE degradation pathways currently is underway.
This work will lead to new, highly active dechlorination catalysts with tunable properties, which will make them more useful for engineered dechlorination systems. In addition, the insights gained regarding the dechlorination mechanism may allow for the selective production of nontoxic, benign dechlorination products.