Synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material

A synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material, comprising following steps:

• step (I) synthesis of catalysts comprising:
• a) placing a compound A, a compound B, mesitylene and 1,4-dioxane into a reaction vessel;
• b) mixing the contents of the reaction vessel evenly;
• c) adding acetic acid to the reaction vessel;
• d) de-aerating the contents of the reaction vessel;
• e) vacuum sealing the reaction vessel;
• f) placing the reaction vessel in an oven for heating;
• g) filtering precipitates from the reaction vessel;
• h) washing the precipitates with a Soxhlet extractor;
• i) vacuum drying the precipitates;
• and
• j) obtaining solid catalysts;
• wherein a structural formula of the compound A is:
• wherein R1 ═OH, CH3, OCH3, C2H5, F, Cl, Br or I;
• wherein compound B is:
• step (II) synthesis of lactide by confinement effect catalysis comprising:
• a) adding the catalysts obtained in step (I), solvents, and lactic acid to a reaction vessel for reaction;
• b) cooling down the reaction vessel slowly after the reaction;
• c) filtering the contents of the reaction vessel after the reaction;
• d) washing the contents of the reaction vessel after the reaction;
• e) removing the solvents from the contents of the reaction vessel after the reaction at low pressure;
• and
• f) obtaining crude lactide;
• step (III) lactide purification comprising:
• a) conducting liquid-liquid extraction on the crude lactide obtained in step (II) with methylbenzene and water,
• b) combining organic phases of the liquid-liquid extraction,
• c) removing the solvents of the combined organic phases at low pressure, and
• d) obtaining lactide,
• wherein in step (I) a mole ratio between the compound A and the compound B is 4:7;
• a volume ratio among the mesitylene, the 1,4-dioxane, and the acetic acid is 15:5:1;
• and a mole ratio between the compound A and the mesitylene is 1:25;
• wherein in step (I) the method for de-aerating comprises freeze-pump-thaw cycling;
• wherein in step (I) the conditions for heating in the oven comprise 80° C. for 3 days;
• wherein in step (I) the conditions for washing with the Soxhlet extractor comprise specifically:
• washing four hours with THF and acetone;
• and conditions for vacuum drying comprise:
• 80° C. for 12 hours;
• wherein lactic acid in step (II) comprises L-lactic acid of 90 percent purity;
• wherein the solvents in step (II) comprise methylbenzene or ortho-xylene;
• wherein a mass ratio between the catalysts and the lactic acid is 1:10, and a weight/volume ratio of the catalysts and the solvents is 1:1 g/cm3;
• wherein reaction conditions in step (II) comprise:
• reaction time of 5 hr and reaction temperature 120° C.;
• wherein in step (II) washing is done by washing with acetonitrile.