CATALYTIC SYNTHESIS OF GLYCOLIC ACID AND ITS METHYL ESTER FROM GLYOXAL

Abstract

Glycolic acid is practically non-toxic to humans, has bactericidal properties and a weak odor, which makes it widely used in food (as a flavoring and preservative) textile (as a dye and tanning agent), cosmetics and pharmaceuticals (as a keratolytic and a skin care agen). Glycolic acid can also be converted to biodegradable polymer with good mechanical properties and excellent biocompatibility, wich is used for different medical applications. In industry, glycolic acid is obtained by carbonylation of formaldehyde using as catalysts quite aggressive acids (H2SO4, HCl, HF), hydrolysis of hydroxyacetonitrile under the influence of acids (H2SO3, H3PO3) or the enzyme nitrilase and saponification of chloroacetic acid with a double excess of alkali (NaOH, KOH). In addition to the non-ecological nature of used raw materials for this process there is a problem associated of purification of the product especially from homogeneous catalysts. The process of obtaining glycolic acid and its methyl ester from glyoxal over a number of solid acid and basic catalysts based on mixed oxides of aluminum, tin, titanium, zirconium, and magnesium has been studied. In study, commercially available 40% aqueous solution of glyoxal, anhydrous glyoxal trimer (Sigma-Aldrich, 95%) and methanol (99%, Merck) were used. Catalytic experiments were carried out in rotated steel autoclave (60 rpm) for 0.5–5 hours at temperatures of 100–170 °C. It is shown that the synthesized oxide catalysts after 5 h of reaction at 100 °C provide up to 98% conversion of an aqueous solution of glyoxal to glycolic acid with a selectivity of 83–100%.It was found that over the studied basic catalysts the undesirable oligomerization process of the formed glycolic acid occurred to a lesser extent and as a result the yield of monoglycolic acid was much higher (60–69%) than over acid catalysts (28–40%). The most selective MgO-ZrO2 catalyst after 1 h of the reaction at 150 °C of methanolicglyoxal solution provides almost 100% yield of methyl glycolate.