Efficient synthesis of dimethyl carbonate from methanol, propylene oxide and CO2 catalyzed by recyclable inorganic base/phosphonium halide-functionalized polyethylene glycol

Abstract

The cycloaddition of propylene oxide and CO₂ to form propylene carbonate promoted by a phosphonium salt covalently bound to polyethylene glycol (PEG), and the transesterification of propylene carbonate with methanol to dimethyl carbonate (DMC) mediated by PEG-supported K₂CO₃, were separately investigated. Inorganic base/phosphonium halide-functionalized PEG (K₂CO₃/BrBu₃PPEG₆₀₀₀PBu₃Br) was shown to be active for DMC synthesis from propylene oxide, CO₂ and methanol under mild reaction conditions, even under low CO₂ pressure (2 bar). The effects of various reaction variables on the activity and selectivity performance are discussed in detail. The catalyst was readily separated and reused, without catalyst leaching being detected by ³¹P NMR. Notably, excellent yields of DMC and complete conversion of propylene carbonate were reached under the optimized reaction conditions. This procedure was successfully applied to the synthesis of other dialkyl carbonates.