| Chlorinated solvents, notably chlorinated ethylenes that have been used as dry-cleaning and degreasing solvents, are ubiquitous in our groundwater. Both biotic and abiotic remediation methods employing reactive metal centers have been proven to effectively remove these contaminants from groundwater, however a sound understanding of the mechanism in these systems is generally lacking. Mechanistic studies of these systems can be complicated due to their complex structure, heterogeneous nature and sensitive reaction conditions. The objective of this thesis is the investigation of metal-mediated dechlorination reaction mechanisms through the advancement of model complex development and mechanistic probing techniques. First, the synthesis and characterization of a new phosphine ligated iron(0) complex designed for use as a zero-valent iron (ZVI) model was presented. Accordingly, the corresponding iron-chloride and iron-hydride complexes were also prepared and characterized due to their potential as products in dechlorination reactions. Next, the iron(0) model complex was utilized in dechlorination reactions and mechanistic investigations that were found to support a C-Cl oxidative addition pathway followed by beta-Cl elimination. The relative rates of reaction for CEs with this complex were also determined and found to follow a trend of faster reaction with more highly chlorinated ethylenes. In chapter four cobaloxime, a well-established model for cobalamin, was studied in its reaction with TCE by stable carbon isotope analysis via isotope ratio-mass spectrometry. The results showed a very large enrichment factor of -36.1 per mille for this nucleophilic-vinylic substitution that corresponds to a C-Cl bond cleavage in the rate determining step. Finally, in the fifth chapter, in an effort to advance the potential application of chlorine isotope analysis for reactions involving TCE, a study on the fragmentation of TCE in an electron impact ion source is described. In this investigation, 35Cl-labeled TCE was prepared and analyzed by EI GC-MS to show that fragmentation by electron impact ionization is indiscriminant towards C-Cl bonds, thus lending support to the use of fragment ions for the calculation of chlorine isotope effects for reactions with TCE. |
