One-Pot Synthesis of Propylene Carbonate through Tandem Epoxidation-Cycloaddition Reaction from Propylene and CO₂

The direct synthesis of propylene carbonate (PC) through a tandem epoxidation-cycloaddition reaction from propylene and CO2 is considered a highly promising industrial process due to its streamlined procedure, atomic efficiency, cost-effectiveness, and inherent safety. In this work, we investigated the thermal stability of oxidants critical for the tandem epoxidation-cycloaddition reaction, aiming to determine the optimal oxidant between hydrogen peroxide (H2O2) and cumene hydroperoxide (CHP). This evaluation is particularly significant given the tendency of oxidants to decompose at a higher temperatures required for the cycloaddition reaction. Our findings indicate that CHP is a superior oxidant for facilitating the tandem epoxidation-cycloaddition coupling at high reaction temperatures, due to its higher decomposition temperature (122 °C) compared to H2O2 (40 °C). Furthermore, we present for the first time a one-pot synthesis of PC through a tandem epoxidation-cycloaddition reaction using CHP as the oxidant for the epoxidation step, achieving PC yield of 79.8%. Additionally, a plausible reaction mechanism for this tandem epoxidation-cycloaddition reaction of propylene and CO2 is proposed, based on experimental observations and supported by density functional theory (DFT) calculations. Specifically, DFT calculations reveal that the synergistic effect between hydroxyl groups and Br– promotes the ring-opening of propylene oxide (PO).