A method for preparing glyoxylic acid by copper-catalyzed oxidation of glyoxal

Abstract

The present application discloses a method for preparing glyoxylic acid by copper-catalyzed oxidation of glyoxal. The method comprises the following steps: dispersing glyoxal, a copper catalyst, and a cocatalyst in a solvent, and performing an oxidation reaction under an air atmosphere to obtain glyoxylic acid. The present invention uses oxygen in the air as an oxidant and a copper salt as a catalyst to prepare glyoxylic acid, which has the advantages of inexpensive and easily available catalyst, mild reaction conditions, good selectivity, high conversion rate, simple operation, etc., is easy to carry out industrial production, and has potential industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of organic synthesis, and particularly relates to a method for preparing glyoxylic acid by copper-catalyzed oxidation of glyoxal. Background Art

[0002] Glyoxylic acid is an important chemical. It is the simplest aldehyde acid, having the properties of both aldehyde and acid. Industrial products are usually 40% aqueous solution or high-purity crystalline glyoxylic acid monohydrate crystals. Glyoxylic acid has a wide range of applications and is an important chemical raw material, organic synthesis intermediate and biochemical reagent, and its applications involve fields such as daily necessities, cosmetics, pesticides, and pharmaceuticals. For example, glyoxylic acid can be used to synthesize vanillin (Hansen E H, Moller B L, Kock G R, et al., Denovo biosynthesis ofvanillin in fission yeast (Schizosaccharomyces pombe) and baker's yeast (Saccharomyces cerevisiae)[J].Appl.Environ Microb.,2009,75(9):2765 - 2774), ethyl vanillin (Nobel Dominique.Process for para-hydroxyalkylation of hydroxylatedaromatic compounds[P].US:5430183,1994,01,12) and allantoin (Sohn J R,Seo DH.Preparation of new solid superacidcatalyst,zirconium sulfate supported onγ-alumina andactivity for acid catalysis[J].Catal. Today,2003,87(4):219 - 226), etc., for use in cosmetics and daily necessities; it can also be used to prepare pharmaceutical intermediates such as p-hydroxyphenylglycine, p-hydroxyphenylacetamide, p-hydroxyphenylacetic acid, p-hydroxyphenylhydantoin (Degner D, Pander H J, Siegel H.4-Tert-butoxyphenyl glycinenitrile and methods for D-(-)-and L-(+)-4-hydrophenylglycine:DE, 3002543[P].1981,06,30); it can also be used to prepare the corrosion and scale inhibitor 2-hydroxyphosphonoacetic acid.

[0003] There are many industrial production methods for glyoxylic acid at present, mainly including: 1) The glyoxal nitric acid oxidation method (Pozdniakov, M.A., Salikov, A.S., Botvin, V.V., Poleshchuk, O.K., & Filimoshkin, A.G. Features of homogeneous oxidation of glyoxal to glyoxylic acid. Russ. Chem. B. 2019, 68(4), 802-808; Pozdniakov, M.A., Zhuk, I.V., Salikov, A.S., Botvin, V.V., & Filimoshkin, A.G. Synthesis of Glyoxylic Acid by Glyoxal Oxidation in the Presence of Hydrohalic Acids. Russ. J. Appl. Chem., 2022, 93(10), 1571-1577); 2) The oxalic acid electrolytic reduction method (Zhao, F., Yan, F., Qian, Y., & Xu, Y. Roughened TiO2 film electrodes for electrocatalytic reduction of oxalic acid to glyoxylic acid. J. Electroanal. Chem., 2013, 698, 31-38); 3) The maleic anhydride ozonation method (Caprio, V., Insola, A., & Silvestre, A.M., Glyoxal ozonation process in aqueous solution. Ozone-Sci. Eng., 1989, 11(3), 271-280); 4) The hydrogen peroxide oxidation method (Demirel S., Lehnert K., Lucas M., et al., Use of renewables for the production of chemicals: Glycerol oxidation over carbon supported gold catalysts. Appl. Catal. B., 2007, 70(1): 637-643), etc.However, there are still various deficiencies in these methods. For example, in the glyoxal nitric acid oxidation method, due to the use of excessive nitric acid as an oxidant, the requirements for the reaction device are very high, and NO2 is easily generated, and its emission will seriously pollute the environment; while the oxalic acid reduction method has problems such as high power consumption and low current efficiency; the ozone oxidation and hydrogen peroxide oxidation methods also have disadvantages such as high requirements for equipment and large investment costs (Pozdniakov, M.A., Zhuk, I.V., Lyapunova, M.V., Salikov, A.S., Botvin, V.V., Filimoshkin, A.G. Glyoxylic acid: synthesis, isolation, and crystallization. Russ. Chem. Bull., Int. Ed., 2019, 68(3), 472 - 479). Therefore, it is of great significance to develop new methods and technologies for the synthesis of glyoxylic acid that are green, environmentally friendly and highly economical.

[0004] Oxygen is the most inexpensive, readily available, and green oxidant. Developing the use of oxygen as an oxidant to oxidize glyoxal is an ideal method for preparing glyoxylic acid. Although certain progress has been made in the research of this method, all relevant reports have used noble metal catalysts such as palladium and gold as catalysts (Jia, M. L., Liu, C. X., Wang, J., Bao, S., & Bao, Z., Catalytic oxidation of glyoxal to glyoxalic acid over Au-Pd alloy nanoparticles on hydrotalcite. Kineti. Cata., 2014, 55(5), 671-675; Hermans, S., Deffernez, A., & Devillers, M. Au–Pd / C catalysts for glyoxal and glucose selective oxidations. Appl. Catal. A-Gen., 2011, 395(1-2), 19-27; Liu, J., Qin, F., Huang, Z., Huang, L., Liao, Z., Xu, H., & Shen, W. Selective oxidation of glyoxal to glyoxalic acid by air over mesoporous silica supported Pd catalysts. Catal. Lett., 2019, 149(7), 1894-1902; Hermans, S., Thiltges, F., Deffernez, A., & Devillers, M. Molybdenum oxoanions as dispersing agents in the preparation of Pd / C catalysts for the selective oxidation of glyoxal. Catal. lett., 2012, 142(5), 521-530; Pozdniakov, M. A., Rubtsov, K. V., Rasskazova, L. A., & Filimoshkin, A., Glyoxylic acid separation from products of glyoxal oxidation in the form of its calcium salt. Adv. Mater. Res., 2015, 108(5), 74-78), resulting in high production costs and a decline in the industrial application value of these methods.

[0005] Therefore, developing inexpensive, readily available and highly efficient metal catalysts to achieve the efficient oxidation of glyoxal to glyoxylic acid using oxygen as the oxidant is the key to developing a new green and economical technology for the production of glyoxylic acid. Summary of the Invention

[0006] In order to overcome the above problems, the object of the present invention is to provide a method for the oxidation of glyoxal to glyoxylic acid catalyzed by copper.

[0007] The following technical solutions are adopted in the present invention.

[0008] A method for the oxidation of glyoxal to glyoxylic acid catalyzed by copper, comprising the following steps: dispersing glyoxal, a copper catalyst and a co-catalyst in a solvent, and carrying out an oxidation reaction in an air atmosphere to obtain glyoxylic acid.

[0009] Specifically, glyoxal, a copper catalyst and a co-catalyst are dispersed in a solvent, heated and reacted in an air atmosphere, and glyoxylic acid is obtained through separation and purification.

[0010] The chemical reaction equation for the synthesis of glyoxylic acid is:

[0011]

[0012] Preferably, the molar ratio of glyoxal, the copper catalyst and the co-catalyst is 1:0.05 - 0.1:0.3 - 0.5.

[0013] Preferably, the copper catalyst is at least one of copper trifluoromethanesulfonate, cuprous trifluoromethanesulfonate, copper sulfate, copper nitrate, copper trifluoroacetate, copper chloride, cuprous iodide, copper acetate, copper acetylacetonate.

[0014] More preferably, the copper catalyst is copper trifluoromethanesulfonate.

[0015] Preferably, the co-catalyst is at least one of 2,2,6,6-tetramethylpiperidine oxide, 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide, 4-oxo-2,2,6,6-tetramethylpiperidine oxide.

[0016] More preferably, the co-catalyst is 2,2,6,6-tetramethylpiperidine oxide.

[0017] Preferably, the solvent is at least one of water, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, dimethyl sulfoxide, acetone.

[0018] More preferably, the solvent is acetonitrile.

[0019] Preferably, the oxidation reaction is carried out at 50°C - 70°C for 12h - 24h.

[0020] Preferably, the oxidation reaction is carried out under the condition that the air pressure is one atmosphere (1 atm).

[0021] Preferably, the oxidation reaction is carried out under stirring conditions, and the stirring rate is 200 rpm to 600 rpm.

[0022] In the present invention, by using oxygen in the air as a mild oxidant and inexpensive copper salt as a catalyst, the selective oxidation of one aldehyde group in glyoxal is realized, avoiding the over-oxidation problem caused by using traditional strong oxidants such as nitric acid, and greatly improving the selectivity of the reaction.

[0023] The beneficial effects that can be produced by this application include:

[0024] The method for preparing glyoxylic acid from glyoxal provided by this application uses oxygen in the air as an oxidant and copper salt as a catalyst to prepare glyoxylic acid, without the need to use noble metal catalysts. The method of the present invention has the advantages of inexpensive and easily available catalyst, mild reaction conditions, good selectivity, high conversion rate, simple operation, etc., is easy to carry out industrial production, and has potential industrial application prospects and good economic benefits. Detailed implementation manners

[0025] The following further illustrates the specific implementation of the present invention in conjunction with embodiments, but the implementation and protection of the present invention are not limited thereto. It should be noted that for the processes not specifically described in detail below, those skilled in the art can implement or understand them with reference to the prior art. For reagents or instruments without indicating the manufacturer, they are regarded as conventional products that can be obtained through commercial purchase.

[0026] Example 1:

[0027] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal includes the following steps:

[0028] Take 114 ul (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as a solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 96%, and the selectivity of glyoxylic acid is 99%.

[0029] Example 2:

[0030] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal includes the following steps:

[0031] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0212 g (10 mol%) of copper(I) trifluoromethanesulfonate, add 3 mL of acetonitrile as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 95%, and the selectivity of glyoxylic acid is 99%.

[0032] Example 3:

[0033] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0034] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0290 g (10 mol%) of copper(II) trifluoroacetate, add 3 mL of acetonitrile as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 92%, and the selectivity of glyoxylic acid is 99%.

[0035] Example 4:

[0036] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0037] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.0781 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0134 g (10 mol%) of copper(II) chloride, add 3 mL of acetonitrile as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 88%, and the selectivity of glyoxylic acid is 99%.

[0038] Example 5:

[0039] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0040] Take 114 μl (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0159 g (10 mol%) of copper sulfate, add 3 mL of acetonitrile as a solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 68%, and the selectivity of glyoxylic acid is 99%.

[0041] Example 6:

[0042] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0043] Take 114 μl (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0187 g (10 mol%) of copper nitrate, add 3 mL of acetonitrile as a solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 62%, and the selectivity of glyoxylic acid is 99%.

[0044] Example 7:

[0045] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0046] Take 114 μl (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.0861 g (0.5 mmol) of the co-catalyst 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as a solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 92%, and the selectivity of glyoxylic acid is 99%.

[0047] Example 8:

[0048] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0049] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.0851 g (0.5 mmol) of the cocatalyst 4-oxo-2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 88%, and the selectivity of glyoxylic acid is 99%.

[0050] Example 9:

[0051] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0052] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add only 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 8%, and the selectivity of glyoxylic acid is 95%.

[0053] Example 10:

[0054] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0055] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the cocatalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0180 g (5 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 72%, and the selectivity of glyoxylic acid is 99%.

[0056] Example 11:

[0057] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0058] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the cocatalyst 2,2,6,6-tetramethylpiperidine N-oxide and 0.0289 g (8 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as a solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 85%, and the selectivity of glyoxylic acid is 99%.

[0059] Example 12:

[0060] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0061] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.3 mmol) of the cocatalyst 2,2,6,6-tetramethylpiperidine N-oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as a solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 75%, and the selectivity of glyoxylic acid is 99%.

[0062] Example 13:

[0063] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0064] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.4 mmol) of the cocatalyst 2,2,6,6-tetramethylpiperidine N-oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as a solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 87%, and the selectivity of glyoxylic acid is 99%.

[0065] Example 14:

[0066] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0067] Take 114 μl (1 mmol) of a 40% aqueous glyoxal solution in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of dimethyl sulfoxide as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, add water to the reaction stock solution and extract with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 92%, and the selectivity of glyoxylic acid is 99%.

[0068] Example 15:

[0069] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0070] Take 114 μl (1 mmol) of a 40% aqueous glyoxal solution in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of water as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, dilute the reaction stock solution with water and then extract with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 16%, and the selectivity of glyoxylic acid is 99%.

[0071] Example 16:

[0072] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0073] Take 114 μl (1 mmol) of a 40% aqueous glyoxal solution in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of N,N-dimethylformamide as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, add water to the reaction stock solution and extract with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 40%, and the selectivity of glyoxylic acid is 95%.

[0074] Example 17:

[0075] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0076] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of tetrahydrofuran as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 60 °C and react for 18 h. After the reaction is completed, water and ethyl acetate are added to the reaction stock solution for extraction to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 47%, and the selectivity of glyoxylic acid is 96%.

[0077] Example 18:

[0078] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0079] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 50 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 42%, and the selectivity of glyoxylic acid is 99%.

[0080] Example 19:

[0081] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0082] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the co-catalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as the solvent, stir, and under the condition of an air pressure of 1 atm, heat up to 70 °C and react for 18 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 98%, and the selectivity of glyoxylic acid is 92%.

[0083] Example 20:

[0084] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0085] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the cocatalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as a solvent, stir, and under the condition of an air pressure of 1 atm, raise the temperature to 60 °C and react for 12 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 62%, and the selectivity of glyoxylic acid is 99%.

[0086] Example 21:

[0087] A method for synthesizing glyoxylic acid by copper-catalyzed oxidation of glyoxal, comprising the following steps:

[0088] Take 114 μL (1 mmol) of an aqueous glyoxal solution with a mass fraction of 40% in a 25 mL screw-cap test tube, add 0.078 g (0.5 mmol) of the cocatalyst 2,2,6,6-tetramethylpiperidine oxide and 0.0361 g (10 mol%) of copper trifluoromethanesulfonate, add 3 mL of acetonitrile as a solvent, stir, and under the condition of an air pressure of 1 atm, raise the temperature to 60 °C and react for 24 h. After the reaction is completed, the reaction stock solution is rotary evaporated to remove the acetonitrile solvent, diluted with water, and then extracted with ethyl acetate to obtain an aqueous glyoxylic acid solution. The conversion rate of glyoxal is 97%, and the selectivity of glyoxylic acid is 97%.

[0089] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing glyoxylic acid by copper-catalyzed oxidation of glyoxal, characterized in that, It includes the following steps: Glyoxal, a copper catalyst, and a co-catalyst are dispersed in a solvent, and an oxidation reaction is carried out under an air atmosphere. Glyoxylic acid is obtained through separation and purification. The molar ratio of glyoxal, the copper catalyst, and the co-catalyst is 1:0.05 - 0.1:0.3 - 0.

5. The copper catalyst is at least one of copper trifluoromethanesulfonate, cuprous trifluoromethanesulfonate, and copper trifluoroacetate. The co-catalyst is at least one of 2,2,6,6-tetramethylpiperidine-N-oxide, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxide, and 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxide. The solvent is at least one of acetonitrile and dimethyl sulfoxide. The oxidation reaction is carried out at 60°C - 70°C, and the reaction time is 18h - 24h.

2. The method for preparing glyoxylic acid by copper-catalyzed oxidation of glyoxal according to claim 1, characterized in that, The reaction equation is: 。 3. The method for preparing glyoxylic acid by copper-catalyzed oxidation of glyoxal according to claim 1, characterized in that, The air pressure of the oxidation reaction is 1 atm.

4. The method for preparing glyoxylic acid by copper-catalyzed oxidation of glyoxal according to claim 1, characterized in that, The oxidation reaction is carried out under stirring conditions.

5. The method for preparing glyoxylic acid by copper-catalyzed oxidation of glyoxal according to claim 1, wherein The stirring rate is 200 rpm - 600 rpm.

Images