Synthesis of methyl glycolate by hydrogenation of dimethyl oxalate with P modified Co/SiO2 catalyst

A P-modified Co based catalyst was firstly reported in the selective hydrogenation of dimethyl oxalate(DMO) to methyl glycolate(MG) reaction and the synthesized Co8P/SiO2 exhibited 94.6% conversion of DMO and 88.1%...

Attaching onto or Inserting into an Intramolecular Hydrogen Bond: Exploring and Controlling a Chirality-Dependent Dilemma for Alcohols

Prereactive complexes in noncovalent organocatalysis are sensitive to the relative chirality of the binding partners and to hydrogen bond isomerism. Both effects are present when a transiently chiral alcohol docks on a chiral α-hydroxy ester, turning such 1:1 complexes into elementary, non-reactive model systems for chirality induction in the gas phase. With the help of linear infrared and Raman spectroscopy in supersonic jet expansions, conformational preferences are investigated for benzyl alcohol in combination with methyl lactate, also exploring p-chlorination of the alcohol and the achiral homolog methyl glycolate to identify potential London dispersion and chirality effects on the energy sequence. Three of the four combinations prefer barrierless complexation via the hydroxy group of the ester (association). In contrast, the lightest complex shows predominantly insertion into the intramolecular hydrogen bond, like the analogous lactate and glycolate complexes of methanol. The experimental findings are rationalized with computations and a uniform helicality induction in the alcohol by the lactate is predicted, independent on insertion into or association with the internal lactate hydrogen bond. p-Chlorination of benzyl alcohol has a stabilizing effect on association, because the insertion motif prevents a close contact between the chlorine and the hydroxy ester. After simple anharmonicity and substitution corrections, the B3LYP-D3 approach offers a fairly systematic description of the known spectroscopic data on alcohol complexes with α-hydroxy esters.

CATALYTIC SYNTHESIS OF GLYCOLIC ACID AND ITS METHYL ESTER FROM GLYOXAL

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.

Efficient Oxidation of Methyl Glycolate to Methyl Glyoxylate Using a Fusion Enzyme of Glycolate Oxidase, Catalase and Hemoglobin

Possessing aldehyde and carboxyl groups, glyoxylic acid and its ester derivatives serve as platform chemicals for the synthesis of vanillin, (R)-pantolactone, antibiotics or agrochemicals. Methyl glycolate is one of the by-products in the coal-to-glycol industry, and we attempted its value-added use through enzymatic oxidation of methyl glycolate to methyl glyoxylate. The cascade catalysis of glycolate oxidase from Spinacia oleracea (SoGOX), catalase from Helicobacter pylori (HpCAT) and hemoglobin from Vitreoscilla stercoraria (VsHGB) was firstly constructed, despite poor catalytic performance. To enable efficient oxidation of methyl glycolate, eight fusion enzymes of SoGOX, HpCAT and VsHGB were constructed by varying the orientation and the linker length. The fusion enzyme VsHGB-GSG-SoGOX-GGGGS-HpCAT was proved to be best, which reaction yield was 2.9 times higher than that of separated enzymes. The enzyme SoGOX was further subjected to directed evolution and site-saturation mutagenesis. The reaction yield of the resulting variant M267T/S362G was 1.9 times higher than that of the wild type. Then, the double substitution M267T/S362G was integrated with fusion expression to give the fusion enzyme VsHGB-GSG-SoGOXmut-GGGGS-HpCAT, which crude enzyme was used as biocatalyst. The use of crude enzyme virtually eliminated side reactions and simplified the preparation of biocatalysts. Under the optimized conditions, the crude enzyme VsHGB-GSG-SoGOXmut-GGGGS-HpCAT catalyzed the oxidation of 200 mM methyl glycolate for 6 h, giving a yield of 95.3%. The development of efficient fusion enzyme and the use of its crude enzyme paved the way for preparative scale application on enzymatic oxidation of methyl glycolate to methyl glyoxylate.