Diethylene Glycol/NaBr catalyzed CO2 insertion into terminal epoxides: from batch to continuous flow

CO2 insertion reactions on terminal epoxides (styrene oxide, 1,2-epoxyhexane and butyl glycidyl ether) were performed in a binary homogeneous mixture comprising NaBr as the nucleophilic catalyst and diethylene glycol (DEG) as both solvent and catalyst activator (cation coordinating agent). The reaction protocol was initially studied under batch conditions either in autoclaves and glass reactors: quantitative formation of the cyclic organic carbonate products (COCs) were achieved at T=100 degrees C and p(0)(CO2)=1-40 bar. The process was then transferred to continuous-flow (CF) mode. The effects of the reaction parameters (T, p(CO2), catalyst loading, and flow rates) were studied using microfluidic reactors of capacities variable from 7.85 . 10(-2) to 0.157 cm(3). Albeit the CF reaction took place at T=220 degrees C and 120 bar, CF improved the productivity and allowed catalyst recycle through a semi-continuous extraction procedure. For the model case of 1,2-epoxyhexane, the (non-optimized) rate of formation of the corresponding carbonate, 4-butyl-1,3-dioxolan-2-one, was increased up to 27.6 mmol h(-1) equiv.(-1), a value 2.5 higher than in the batch mode. Moreover, the NaBr/DEG mixture was reusable without loss of performance for at least 4 subsequent CF-tests.