Electrochemical carboxylation is an organic electrosynthesis technique where CO2 is coupled with one or more organic molecules to form carboxylic acids. Here, we show that process intensification and selectivity enhancements are simultaneously achieved by performing electrochemical carboxylation in CO2-eXpanded electrolytes (CXE)a class of media that accommodates multimolar concentrations of CO2 in organic solvents at modest pressures. We observed that electrochemical carboxylation of acetophenone does not occur at ca. 1 atm (0.2 MPa) CO2 headspace pressure. Instead, acetophenone hydrogenation was dominant, producing the undesired 1-phenylethanol as the major product. However, in the CXE media (at 1.4–4.2 MPa CO2 headspace pressure), (±)-atrolactic acid was the major product with a maximum faradaic efficiency of 72% observed at 2.8 MPa. Achieving the pressure-tunable carboxylation results from the high liquid-phase CO2 concentrations afforded by the CXE media. At CO2 pressures exceeding 2.8 MPa, we observed a lower rate of carboxylation, which is attributed to the decreased electrolyte polarity at progressively greater liquid-phase CO2 concentrations present at higher pressures.

We shed light on the mechanism and rate-determining steps of the electrochemical carboxylation of acetophenone as a function of CO2 concentration by using a robust finite element analysis model that...

We shed light on the mechanism and rate-determining steps of the electrochemical car- carboxylation of acetophenone as a function of CO2 concentration, by using robust finite element analysis model that incorporates each reaction step. Specifically, we show that the first electrochemical reduction of acetophenone is followed by the homogeneous chemical addition of CO2. The electrochemical reduction of the acetophenone-CO2 adduct is more facile than that of acetophenone, resulting in an Electrochemical-Chemical-Electrochemical (ECE) reaction pathway that appears as a single voltammetric wave. These modeling results pro- vide new fundamental insights on the complex microenvironment in CO2-rich media that pro- duces an optimum electrochemical carboxylation rate as a function of CO2 pressure.