A method for photocatalytic reduction of oxalate to glycolate

Abstract

The application relates to a method for photocatalytic reduction of oxalate to glycolate. The method can convert oxalate into corresponding glycolate under irradiation by using a semiconductor material as a photocatalyst through a selective hydrogenation reduction reaction. The application adopts a photocatalytic strategy, uses a semiconductor such as carbon nitride as a photocatalyst, and has the advantages of green, non-toxic, excellent environmental compatibility, simple and efficient overall catalytic system, low catalyst consumption, rapid and high-selectivity conversion of oxalate to glycolate under mild reaction conditions, and significant technical advantages and industrial application potential.

Description

Technical Field

[0001] This invention belongs to the field of catalytic chemical engineering and fine chemical synthesis technology, specifically relating to a method for the photocatalytic reduction of oxalate esters to produce methyl glycolate and its derivatives, a key monomer of biodegradable polyglycolic acid (PGA). Background Technology

[0002] Converting coal resources into bulk chemicals and further upgrading them into high-value-added fine chemical products is one of the important ways to achieve the clean and efficient utilization of coal resources. Among them, the further production of dimethyl oxalate (DMO) from coal-to-syngas is a mature and important technical route in the modern coal chemical industry. According to statistics, the global actual production of dimethyl oxalate was approximately 2 million tons in 2025, and it is expected to reach more than 3 million tons by 2030, demonstrating a vast industrial scale and development potential.

[0003] Methyl glycolate is a key monomer for biodegradable polyglycolic acid (PGA) materials. It can be directly polymerized into GGA in a one-step process, and has significant applications in environmental materials, pharmaceuticals, and chemicals. Therefore, converting coal-based dimethyl oxalate into methyl glycolate is a core technological pathway to achieve high-value utilization of this bulk chemical and extend the coal chemical industry chain.

[0004] Currently, various methods exist for the conversion of dimethyl oxalate to methyl glycolate using thermocatalysis. However, these thermocatalytic technologies all require high-temperature, high-pressure hydrogen reaction conditions, resulting in high energy consumption, low operational safety, easy catalyst sintering, and complex production processes. These limitations make it difficult to meet the industrial demands for green chemistry and low-carbon development. Therefore, developing a green, sustainable, safe, and low-energy-consumption conversion process is a pressing technical problem that needs to be solved in the field of high-value coal chemical industry.

[0005] The purpose of this invention is to overcome the shortcomings of traditional thermocatalytic processes and provide a photocatalytic conversion process. This process is driven by light energy and uses semiconductor materials as catalysts, enabling the efficient and directional conversion of oxalate esters to glycolate esters at room temperature and pressure. Compared to thermocatalytic processes, this process offers milder reaction conditions, lower energy consumption, higher safety, superior product selectivity, and is green and sustainable, possessing promising industrial application prospects and commercial promotion value. Summary of the Invention

[0006] The present invention aims to provide a method for preparing methyl glycolate and its derivative esters, a key monomer of biodegradable polyglycolic acid (PGA) materials, and to provide a catalyst that can efficiently catalyze the conversion of oxalate esters into glycolate esters.

[0007] The technical solution of the present invention: This invention provides a method for the photocatalytic reduction of oxalate to glycolate. The method employs a photocatalytic reduction process, using a semiconductor material as a catalyst under light energy drive, to reduce oxalate in a certain amount of reaction solvent, selectively converting it into the corresponding glycolate.

[0008] The oxalate has the structural formula R. 1 -OOC-COO-R 2 The structural formula of the corresponding product, glycolate, is R. 1 -OOC-CH2OH or R 2 -OOC-CH2OH (where R) 1 or R 2 It includes methyl, ethyl, propyl, butyl, isopropyl, tert-butyl, pentyl, hexyl, allyl, cyclopropyl, cyclohexyl, benzyl, phenyl, naphthyl, and benzene rings with various substituents, etc.

[0009] Derivative esters related to dimethyl oxalate (where R) 1 R 2 All compounds (including methyl groups and their substituted derivatives) belong to the oxalate class of compounds. Their core commonality is that the molecule contains an oxalate diester structure (-OOC-COO-), with only the R substituent group being present. 1 R 2 There are differences; the oxalate esters mentioned belong to the oxalate diester class of compounds, and their molecules all contain a -OOC-COO- core structure, with only the substituent R. 1 R 2 Despite the differences, all of these compounds can be used as reaction substrates in this invention and have similar photocatalytic activity.

[0010] The wavelength range of the excitation light described above is 100 to 1500 nm.

[0011] The semiconductor materials described above that can be used as catalysts include, but are not limited to, carbon nitride-based catalysts (including carbon nitride, carbon nitride supported by transition metals or noble metals); cadmium-based catalysts (including cadmium oxide, cadmium sulfide, cadmium carbonate, and cadmium oxide and cadmium sulfide supported by transition metals or noble metals); titanium-based catalysts (including titanium dioxide, titanium dioxide supported by transition metals or noble metals, and titanium dioxide modified with heteroatoms); zinc-based catalysts (including zinc oxide, zinc sulfide, and zinc oxide and zinc sulfide supported by transition metals or noble metals); bismuth-based catalysts (including bismuth oxide, bismuthates, bismuth sulfide, and bismuth oxide, bismuthates, and bismuth sulfide supported by transition metals or noble metals, and bismuth catalysts modified with heteroatoms); tungsten-based catalysts (including tungsten trioxide, tungstates, tungsten sulfide, and tungsten trioxide and tungstates supported by transition metals or noble metals, and tungsten catalysts modified with heteroatoms); and metal oxide series (including single metal oxides, ...). Composite metal oxides, as well as metal oxides supported by transition metals or noble metals and modified with heteroatom doping, such as aluminum oxide, copper oxide, zirconium oxide, manganese oxide, chromium oxide, cerium oxide, titanium-zirconium composite oxides, cerium-zirconium composite oxides, etc.; metal sulfide series (including single metal sulfides, composite metal sulfides, as well as metal sulfides supported by transition metals or noble metals and modified with heteroatom doping, such as molybdenum sulfide, cobalt sulfide, nickel sulfide, copper sulfide, selenium sulfide, tellurium sulfide, lead sulfide, indium zinc sulfide, indium copper sulfide, cobalt-molybdenum sulfide, nickel-cobalt sulfide, etc.); semiconductor heterojunction systems (including heterojunctions formed by any two or more of the above semiconductors, such as TiO2 / C3N4, TiO2 / ZnInS, C3N4 / CdS, TiO2 / CdS, ZnO / CdS, BiVO4 / WO3, C3N4 / TiO2 / CdS, Ag / TiO2 / CdS, etc.).

[0012] The reaction temperature of this system is 10–80 °C, and the reaction pressure is 0.1–0.2 MPa. The reaction atmosphere can be air or an inert atmosphere. The reaction time is 0.1–48 h. The mass fraction of the semiconductor catalyst relative to the oxalate ester is 0.1–100 wt%.

[0013] A solvent needs to be added to the reaction system. The solvent used is one or more of the following: dimethyl sulfoxide, 1,4-dioxane, ethyl acetate, toluene, dichloromethane, tetrahydrofuran, N,N-dimethylformamide, acetonitrile, water, and alcohols (including aliphatic alcohols, alicyclic alcohols, aromatic alcohols, and various substituted derivatives of the above alcohols such as alkyl-substituted, halogen-substituted, alkoxy-substituted, and hydroxyl-substituted, covering monohydric alcohols, dihydric alcohols, and polyhydric alcohols). The reaction is stirred during the process.

[0014] The beneficial effects of this invention are: This invention enables the efficient and targeted conversion of oxalate esters to glycolate esters. The resulting methyl glycolate can be directly used as a key monomer for the polymerization of biodegradable polyglycolic acid (PGA), providing a new pathway for the high-value-added production of coal chemical products and the supply of biodegradable polymer raw materials. This invention employs a photocatalytic conversion strategy, using semiconductors such as carbon nitride as photocatalysts. The reaction system is green, environmentally friendly, and exhibits excellent environmental compatibility. The overall catalytic system is simple and efficient, requiring low catalyst dosage. It achieves rapid and highly selective conversion of oxalate esters to glycolate esters under mild reaction conditions, demonstrating significant technological advantages and industrial application potential. Attached Figure Description

[0015] Figure 1 Image of the product methyl glycolate and its corresponding mass spectrometry chromatogram.

[0016] Figure 2 : Mass spectrum qualitative analysis of the product ethyl glycolate.

[0017] Figure 3 : Mass spectrum qualitative analysis of the product butyl glycolate.

[0018] Figure 4 : Mass spectrum qualitative analysis of the product benzyl glycolate. Detailed Implementation

[0019] The present invention will now be described through specific embodiments, but the implementation of the present invention is not limited to these embodiments: Examples 1-18: 0.5 mmol dimethyl oxalate, 5 mg carbon nitride, and 2 mL solvent were added to a 10 mL photoreactor. The reactor was sealed under atmospheric pressure and air atmosphere, and the reaction was carried out at room temperature under 365 nm light source irradiation for a certain period of time. Qualitative analysis of the obtained samples was performed using gas chromatography-mass spectrometry (GC-MS), and quantitative analysis was performed using gas chromatography. The results are detailed in Table 1.

[0020] Table 1 Optimization of Reaction Conditions

[0021] As shown in Table 1, carbon nitride as a catalyst exhibits high reactivity in various solvents when used to catalyze the preparation of methyl glycolate from dimethyl oxalate, indicating that the reaction is adaptable to a variety of solvent systems. Under optimized conditions of 40 W irradiation and 24 h of reaction, the conversion rate of dimethyl oxalate can reach 100%, and the selectivity of methyl glycolate is as high as 98%. See the attached image for the physical image of the product methyl glycolate and its corresponding qualitative spectral density. Figure 1 .

[0022] Examples 19-58: 0.5 mmol of dimethyl oxalate, a certain amount of catalyst, and 2 mL of water were added to a 10 mL photoreactor. The reactor was sealed under atmospheric pressure and air atmosphere, and the reaction temperature was room temperature. The reaction was carried out for a certain period of time under irradiation with light sources of different wavelengths, with the irradiation power fixed at 40 W. Qualitative analysis of the obtained samples was performed using gas chromatography-mass spectrometry (GC-MS), and quantitative analysis was achieved by gas chromatography. The results are detailed in Table 2.

[0023] Table 2. Effects of different catalysts on the catalytic reaction

[0024] As shown in Table 2, various semiconductor materials exhibit excellent catalytic activity as catalysts and can respond to a wide range of light spectral ranges. Furthermore, the reaction activity is further enhanced after loading metals onto the semiconductor materials, indicating that this photocatalytic system has excellent versatility and can be adapted to various types of catalytic systems. See the appendix for the physical image and corresponding qualitative spectral spectrum of the product methyl glycolate. Figure 1 .

[0025] Examples 59-85: A certain amount of different reaction substrates, 5 mg of carbon nitride, and 2 mL of water were added to a 10 mL photoreactor. The reactor was sealed under atmospheric pressure and air atmosphere, and the reaction temperature was room temperature. The reaction was carried out for a certain time under irradiation with a 365 nm, 40 W light source. Qualitative analysis of the obtained samples was performed using gas chromatography-mass spectrometry (GC-MS), and quantitative analysis was performed using gas chromatography. The results are detailed in Table 3.

[0026] Table 3 Catalytic effects of different reaction substrates and their dosages

[0027] As shown in Table 3, all 14 substrates examined exhibited excellent reactivity, indicating that the photocatalytic system possesses excellent substrate versatility and can efficiently reduce various oxalate compounds to their corresponding glycolates. Detailed qualitative spectral analyses of some glycolate products are attached. Figure 2-4 .

[0028] The qualitative analysis of the product was performed using gas chromatography-mass spectrometry, and the retention time was compared with that of the standard sample; the quantitative analysis was performed using gas chromatography with the internal standard method.

[0029] Conversion rate = (moles of oxalate converted / moles of oxalate added) × 100% Selectivity = (moles of glycolate / moles of converted oxalate) × 100%.

Claims

1. A method for the photocatalytic reduction of oxalate to glycolate, characterized in that, Under light irradiation, using semiconductor materials as catalysts, a selective hydrogenation reduction reaction is carried out in the reaction solvent to convert oxalate esters into glycolate esters.

2. The method for photocatalytic reduction of oxalate to glycolate according to claim 1, characterized in that, The oxalate has the general formula R 1 -OOC-COO-R 2 The structure, whose catalytic reduction product is the corresponding glycolate, has the general structural formula R. 1 -OOC-CH2OH or R 2 -OOC-CH2OH; where R 1 R 2 Each can be independently methyl, ethyl, propyl, butyl, isopropyl, tert-butyl, pentyl, hexyl, allyl, cyclopropyl, cyclohexyl, benzyl, phenyl, naphthyl, or substituted phenyl.

3. The method for photocatalytic reduction of oxalate to glycolate according to claim 1, characterized in that, The wavelength range of the excitation light under the illumination conditions is 100 to 1500 nm.

4. The method for photocatalytic reduction of oxalate to glycolate according to claim 1, characterized in that, The semiconductor material is a carbon nitride-based, cadmium-based, titanium-based, zinc-based, bismuth-based, tungsten-based, metal oxide-based, metal sulfide-based, or semiconductor heterojunction-based material.

5. The method for photocatalytic reduction of oxalate to glycolate according to claim 4, characterized in that, The carbon nitride system is one or more of carbon nitride, transition metal, and noble metal supported carbon nitride; The cadmium system is one or a mixture of two or more of cadmium oxide, cadmium sulfide, cadmium carbonate, cadmium oxide supported by transition metals or noble metals, and cadmium sulfide supported by transition metals or noble metals. The titanium system comprises one or more of the following: titanium dioxide, titanium dioxide supported by transition metals or noble metals, and titanium dioxide modified by heteroatom doping. The zinc system is one or a mixture of two or more of zinc oxide, zinc sulfide, zinc oxide supported by transition metals or noble metals, and zinc sulfide supported by transition metals or noble metals. The bismuth system comprises one or more of the following: bismuth oxide, bismuthate, bismuth sulfide, bismuth oxide supported by transition metals or noble metals, bismuthate supported by transition metals or noble metals, bismuth sulfide supported by transition metals or noble metals, and bismuth catalysts modified with heteroatom doping. The tungsten-based catalyst is one or a mixture of two or more of the following: tungsten trioxide, tungstate, tungsten sulfide, tungsten trioxide supported by transition metals or noble metals, tungstate supported by transition metals or noble metals, and heteroatom-doped modified tungsten-based catalysts. The metal oxide series comprises one or more of the following: single metal oxides, composite metal oxides, transition metal or noble metal supported, and heteroatom-doped modified metal oxides; The metal sulfide series comprises one or more of the following: single metal sulfides, complex metal sulfides, transition metal or noble metal supported, and heteroatom-doped modified metal sulfides; The semiconductor heterojunction series refers to heterojunctions formed by any two or more semiconductors from the above-mentioned carbon nitride, cadmium, titanium, zinc, bismuth, tungsten, metal oxide, and metal sulfide series.

6. The method for photocatalytic reduction of oxalate to glycolate according to claim 4, characterized in that, The metal oxide series includes one or more of the following: aluminum oxide, copper oxide, zirconium oxide, manganese oxide, chromium oxide, cerium oxide, titanium-zirconium composite oxide, and cerium-zirconium composite oxide; the metal sulfide series includes one or more of the following: molybdenum sulfide, cobalt sulfide, nickel sulfide, copper sulfide, selenium sulfide, tellurium sulfide, lead sulfide, indium zinc sulfide, indium copper sulfide, cobalt-molybdenum sulfide, and nickel-cobalt sulfide.

7. The method for photocatalytic reduction of oxalate to glycolate according to claim 1, characterized in that, The reaction atmosphere is air or an inert atmosphere; the reaction temperature is 10–80 °C; the reaction pressure is 0.1–0.2 MPa; and the reaction time is 0.1–48 h.

8. The method for photocatalytic reduction of oxalate to glycolate according to claim 1, characterized in that, The semiconductor catalyst used accounts for 0.1-100 wt% of the oxalate ester.

9. The method for photocatalytic reduction of oxalate to glycolate according to claim 1, characterized in that, The reaction solvent is one or a mixture of two or more of the following: dimethyl sulfoxide, 1,4-dioxane, ethyl acetate, toluene, dichloromethane, tetrahydrofuran, N,N-dimethylformamide, acetonitrile, water, and alcohols; the reaction is stirred during the process.

10. The method for photocatalytic reduction of oxalate to glycolate according to claim 1, characterized in that, The alcohols are aliphatic alcohols, alicyclic alcohols, aromatic alcohols, and one or more combinations of alkyl substitution, halogen substitution, alkoxy substitution, and hydroxyl groups of the above alcohols.

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