RESUMO
The C-C coupling of methane (CH4) and carbon dioxide (CO2) to generate acetic acid (CH3COOH) represents a highly atom-efficient chemical conversion, fostering the comprehensive utilization of greenhouse gases. However, the inherent thermodynamic stability and kinetic inertness of CH4 and CO2 present obstacles to achieving efficient and selective conversion at room temperature. Our study reveals that hydroxyl radicals (·OH) and hydrated electrons (eaq-) produced by water radiolysis can effectively activate CH4 and CO2, yielding methyl radicals (·CH3) and carbon dioxide radicals (·CO2-) that facilitate the production of CH3COOH at ambient temperature. The introduction of radiation-synthesized CuO-anchored TiO2 bifunctional catalyst could further enhance reaction efficiency and selectivity remarkably by boosting radiation absorption and radical stability, resulting in a concentration of 7.1 mmol·L-1 of CH3COOH with near-unity selectivity (>95%). These findings offer valuable insights for catalyst design and implementation in radiation-induced chemical conversion.
RESUMO
The preparation of high value-added boronic acids from cheap and plentiful carboxylic acids is desirable. To date, the decarboxylative borylation of carboxylic acids is generally realized through the extra step synthesized redox-active ester intermediate or in situ generated carboxylic acid covalent derivatives above 150 °C reaction temperature. Here, we report a direct decarboxylative borylation method of carboxylic acids enabled by visible-light catalysis and that does not require any extra stoichiometric additives or synthesis steps. This operationally simple process produces CO2 and proceeds under mild reaction conditions, in terms of high step economy and good functional group compatibility. A guanidine-based biomimetic active decarboxylative mechanism is proposed and rationalized by mechanistic studies. The methodology reported herein should see broad application extending beyond borylation.