Electrochemical reduction of trichloroethylene in an electrolyte based on acetonitrile and Bmim-BF4 ionic liquid: A computational perspective

Potential electrochemical detection and de-chlorination pathways of trichloroethylene (TCE) in acetonitrile (AN) with an ionic liquid (IL) co-solvent were investigated using computational methods. To our knowledge, no previous study systematically examined the thermodynamics and kinetics of the formation of possible reaction intermediates and products and structural properties in a similar non-aqueous electrolyte. Our findings provide direction for effective electrochemical detection and de-chlorination of TCE and other chlorinated compounds in non-aqueous media. This study predicts that electrochemical reaction pathways in absence of substantial proton concentration and with a sufficiently negative potential all result in acetylene. The dominating intermediate is chloroacetylene, but for a smaller fraction of reactions, trans-1,2-dichloroethylene (trans-DCE) is the intermediate instead. Each reduction step breaks one of the three CCl bonds initially, forming a radical. In the next steps, immediately following reductive dechlorination, limited stability of intermediate anions narrows intermediate compounds to chloroacetylene and some trans-DCE; both can be reduced further. Vinyl chloride (VC) is not generated. Full reduction of all intermediates results in acetylene, which will readily escape the solution. TCE and chloroacetylene do not evaporate from the solution as readily as AN, so full reduction of TCE is expected in this electrolyte. This feature is enabled by the IL content of the electrolyte. Most notably to this end, hydrogen of acetylene and chloroacetylene interact with the tetrafluoroborate (BF₄^-) anion. Our study takes a different perspective on electrochemical dechlorination or detection of TCE by assuming a blended aprotic solvent. These findings may lead to the design of better electrochemical systems for developing chemical sensors and more effective approaches to remediating organic pollutants.