Synthesis of lactide from alkyl lactates catalyzed by lanthanide salts

Cerium salt exhibited a highest catalytic activity in the conversion of ethyl and isopropyl oligolactates into lactide. A maximum yield of the target product was reached at the concentration of CeCl₃·7H₂O ranging from 1 to 4 mol% relative to the lactide units in ethyl and isopropyl oligolactates. A gradual reduction of the pressure from 50 to 5 Torr along with the temperature increase from 180 to 230°C during depolymerization resulted in the product containing up to 94% lactide.