METHOD OF PRODUCING GLYCOLIDE FROM GLYCOLIC ACID WITH HIGH CONVERSION.

Glycolide is an ester with limited applications due to its high hydrophilic properties. Nevertheless, these properties allow using glycolide as a basis to produce biodegradable polymers and products for medical purposes. To produce glycolide (1.4-dioxane-2.5-dione) synthesis from glycolic acid was chosen. The method contains polycondensation of glycolic acid, production of oligomer and its depolymerization. The developed method of glycolide production comprises the oligomerization and depolymerization stages with heating in vacuum. A 64-65% glycolic acid produced from 40% glyoxal (Newchem Ltd. (Tomsk, Russia)) was used for synthesis. Polycondensation of glycolic acid comprises water removal from glycolic acid in rotary film evaporator. Initially glycolic acid is put into rotary film evaporator. Then water removal is carried out at 120 degrees C and atmospheric pressure. It was stated that to receive high yields of glycolide (similar to 90%) it is necessary to perform water removal procedure for 3-4 hours gradually creating the vacuum to up to 300 Mmgh and increasing the temperature of the solution up to 140-150 degrees C. When 225-230 ml of distillate is received, the vacuum relief is carried out. 0.3-0.5% mass. of ZnO catalyst is added into the condensed glycolic acid. Then the mixture is supplied into the rotary evaporator. Vacuum is increased, the temperature is raised up to 175-185oC. Water removal is carried out for 4-6 hours. Then the heating of rotary evaporator is stopped, vacuum relief takes place and nitrogen supply is shut off. The reaction mass of oligomer is poured to the enamel capacity, the condensate of volatile compounds is poured to holding capacity. Oligoglycolic acid is formed as an intermediate product in pure glycolide synthesis. The cooled mass of oligomer is weighted, then 0.5-1.5% mass of Sb2O3 catalyst is added and the mixture is ground in mortar. The resulting mixture is loaded into the vacuum distillation unit. The nitrogen purging, heating of electromagnetic stirrer up to 270-280 degrees C as well as 10-15 Mmgh vacuum are used. The mixing of reaction mass is carried out by bubbling with dried nitrogen. Glycolic acid is removed in the form of transparent or yellowish oil in one hour after the start of the synthesis. The run-down drum was cooled with ice. The process is carried out until the releasing of crude glycolide is completed. The resulted product was crystallized in receiving flask. Depending on the quality of initial glycolic acid the crude glycolide with melting temperature of 70-75 degrees C was produced. The yield was similar to 90%. The purification of the received crude glycolide from oligomers, glycolic acid and other impurities was carried out using triple recrystallization from ethyl acetate. The drying of the product was carried out in vacuum drying box under nitrogen blanket at 45-50 degrees C. White crystals of glycolide with melting temperature of 95 oC were received. The further storage of glycolide is performed in airless and water-and vaporless atmosphere. It was shown that the resulting glycolide can be used to produce highly molecular polyglycolide (with molecular mass of more than 100,000), having wide application, as well as manufacture various copolymers, in particular, polyglycolide-lactide copolymer used to produce biodegradable sutures.