Concurrent production and purification of glycolic acid from mixed esters via selective hydrolysis reactions catalyzed and thermodynamically promoted by MgO

Methyl glycolate (MG) in the presence of methyl levulinate (MLE) was selectively converted into magnesium glycolate via MgO-mediated hydrolysis reactions under mild conditions. The conversion of MG reached 95.2% while that of MLE was 15.1%, with reaction selectivity of 100%. After facile isolation procedures, the magnesium glycolate was readily transformed into glycolic acid, monomer of biodegradable plastic, with recovery rate of 90.2%. The basic sites with medium strength on MgO dominated the catalytic activity. The precipitation of magnesium glycolate led to the shift of chemical equilibrium for MG hydrolysis. DFT calculation results showed that the energy barriers for MG hydrolysis were smaller than those for MLE hydrolysis by 46-47 kJ/mol. Both the shift of chemical equilibrium and lower energy barriers contributed to the much higher reactivity of MG compared to MLE. This paper sheds light on the selective hydrolysis of esters and complete hydrolysis of an ester.