Relay transesterification strategy for direct synthesis of high-purity glycolide from methyl glycolate

High-purity glycolide is a key monomer for the synthesis of biodegradable polyglycolic acid. Here, we report a relay transesterification strategy for synthesizing high-purity glycolide directly from methyl glycolate, by using behenyl alcohol as a recyclable transesterification agent. This strategy achieves an average purity of 99.3% for glycolide without forming oligomers, and thus can avoid the energy-intensive purification required in the conventional route. Mechanistic studies indicate that methyl glycolate is first converted into behenyl glycolate via hetero-intermolecular transesterification during the relay transesterification process, and then the behenyl glycolate undergoes a homo-intermolecular transesterification to form behenyl dimer glycolate, which then undergoes intramolecular backbiting transesterification to yield glycolide and behenyl alcohol.