A closed cycle for esterifying aromatic hydrocarbons with CO₂ and alcohol

The ability to functionalize hydrocarbons with CO₂ could create opportunities for high-volume CO₂ utilization. However, current methods to form carbon-carbon bonds between hydrocarbons and CO₂ require stoichiometric consumption of very resource-intensive reagents to overcome the low reactivity of these substrates. Here, we report a simple semi-continuous cycle that converts aromatic hydrocarbons, CO₂ and alcohol into aromatic esters without consumption of stoichiometric reagents. Our strategy centres on the use of solid bases composed of an alkali carbonate (M₂CO₃, where M⁺ = K⁺ or Cs⁺) dispersed over a mesoporous support. Nanoscale confinement disrupts the crystallinity of M₂CO₃ and engenders strong base reactivity at intermediate temperatures. The overall cycle involves two distinct steps: (1) CO₃^2--promoted C-H carboxylation, in which the hydrocarbon substrate is deprotonated by the supported M₂CO₃ and reacts with CO₂ to form a supported carboxylate (RCO₂M); and (2) methylation, in which RCO₂M reacts with methanol and CO₂ to form an isolable methyl ester with concomitant regeneration of M₂CO₃.