Surface active ionic liquid assisted metal-free electrocatalytic-carboxylation in aqueous phase: a sustainable approach for CO2 utilization paired with electro-detoxification of halocarbons

Abstract

Electrocarboxylation of halocarbons is a promising green synthetic strategy for capture, fixation and utilization of CO₂ for the synthesis of high-added-value industrial compounds. However, the unparalleled kinetic/thermodynamic stability and solubility concerns of CO₂ and halocarbons warrant the use of appropriate (often precious metal based) electrocatalytic electrodes and environmentally non-green solvent systems to drive this otherwise kinetically slow electrochemical process. Herein we demonstrate that owing to their unique solubility and excellent electrocatalytic properties, the aqueous micellar solutions of imidazolium-based surface active ionic liquids (SAILs) can be used for the efficient and selective electrocatalytic-carboxylation of halocarbons to produce carboxylic acids. Specifically, we present results from our detailed electrochemical investigations regarding the electroreductive cleavage of the C–X bond and electrocarboxylation of 9-bromoanthracene (9-BAN) and chloroacetonitrile (CAN) in buffered (pH 7, phosphate buffer) micellar solutions of 1-dodecyl-3-methyl-imidazolium chloride ([DDMIM][Cl]). We demonstrate that the unique ability of [DDMIM][Cl] micelles to stabilize the electrogenerated reactive intermediates facilitates a novel reaction pathway that ensures selective and efficient electrocatalytic-reductive carboxylation of 9-BAN and CAN. The presented results clearly establish that besides allowing for the electrocarboxylation of halocarbons in aqueous green electrolytes, the use of SAILs ensures electrochemical fixation of CO₂ at practically low cost current and potential conditions imposed over metal free, economically viable and electrochemically robust carbon electrodes. The use of SAILs is reported to improve the faradaic efficiency (∼95%) and reduce the chances of undesired side product reactions which continue to be a major concern in the state of art electro-carboxylation processes. The presented approach we opine offers a promising avenue toward design of eco-green pathways in the direction of CO₂ fixation and electro-organic synthesis of a diverse range of value-added products from water insoluble halocarbons (toxic pollutants) in aqueous media.