A method for photocatalytic hydrogen transfer reduction to cleave aryl ethers at room temperature

Abstract

The present invention discloses a method for photocatalytic hydrogen transfer reduction cleavage of aryl ethers at room temperature. This method uses Pt / TiO2 as a photocatalyst, diaryl ethers and aryl alkyl ethers as aryl ether substrates, simple aliphatic alcohols as solvents and hydrogen donors, hydrochloric acid as an acid catalyst, and a 370 nm LED as a light source. Under an anaerobic atmosphere at room temperature, hydrogen transfer from simple aliphatic alcohols to aryl ethers is achieved, thereby the aryl ethers undergo reductive cleavage to obtain cyclohexane and cyclohexanol products. The aryl ether substrate, Pt / TiO2 catalyst, catalytic amount or equivalent amount of hydrochloric acid, and aliphatic alcohol are placed in a quartz reaction tube. After replacing the gas atmosphere with nitrogen or argon, it is sealed and stirred under light for 1 - 12 hours to obtain cyclohexane and cyclohexanol products. Compared with conventional aryl ether hydrogenation methods, this method has the characteristics of operating at room temperature, without the need for hydrogen, using primary alcohols as hydrogen sources, and using heterogeneous photocatalysts, and the experiment is simple and easy to operate.

Description

Technical Field

[0001] The present invention relates to a method for photocatalytic hydrogen transfer reduction cleavage of aryl ethers at room temperature, belonging to the technical field of biomass refining. Background Art

[0002] Lignin is the most abundant renewable aromatic polymer resource in nature and can be converted into bio-oil liquid fuel that can replace traditional petroleum through various catalytic means. However, due to the high oxygen content of bio-oil, it has poor physicochemical properties such as poor thermal stability and low energy density, and needs to be further hydrodeoxygenated to be effectively utilized. Aryl ether structures are widely present in lignin and its preliminary depolymerization products. Due to the high bond energy of the carbon-oxygen bond in aryl ethers, hydrocracking often requires high temperature (100 - 300 °C) and high-pressure hydrogen (0.1 - 30 MPa). The use of high-pressure hydrogen not only causes waste of resources but also poses certain safety hazards. In recent years, some thermal catalytic hydrogen transfer deoxygenation methods have been developed, that is, using alcohols, acids or water as hydrogen donors to achieve the reduction of aryl ethers without the need for hydrogen. However, these methods still require high temperature to activate the hydrogen donor or the catalyst.

[0003] The present invention is committed to developing a strategy for selectively catalytic hydrodeoxygenation of lignin-based oxygenates under mild conditions (room temperature, no external hydrogen). Through semiconductor photocatalytic technology, hydrogen is activated and released from alcohol molecules at room temperature, and the hydrogen is in-situ transferred to the aryl ether substrate through metal sites. Under the synergistic action of an acid catalyst, the aryl ether preferentially undergoes carbon-oxygen bond cleavage, and then aromatic ring hydrogenation occurs, so as to obtain cyclohexane products with high selectivity, accompanied by a small amount of cyclohexanol secondary products. Developing a green, safe and mild-condition method for reducing aryl ethers has important guiding significance for the development and utilization of pulping waste - lignin to prepare fuels. Summary of the Invention

[0004] In order to overcome the above technical defects, the object of the present invention is to provide a method for photocatalytic hydrogen transfer reduction cleavage of aryl ethers at room temperature. Under room temperature and 370 nm light irradiation conditions, using Pt / TiO2 as the photocatalyst, diaryl ethers and aryl alkyl ethers as aryl ether substrates, simple aliphatic alcohols as solvents and hydrogen donors, and hydrochloric acid as the acid catalyst, the transfer of hydrogen from simple aliphatic alcohols to aryl ethers is realized in an anaerobic atmosphere, so that the aryl ethers undergo reduction cleavage to obtain cyclohexane and cyclohexanol products.

[0005] The method for photocatalytic hydrogen transfer reduction cleavage of aryl ethers at room temperature according to the present invention is represented by the following reaction equation:

[0006]

[0007] Wherein: R1 is selected from -H, methoxy or alkyl; R2 is selected from aryl, alkyl.

[0008] It includes the following operations: using aryl ether as a substrate, reacting in a fatty alcohol solvent at room temperature, under light irradiation and anaerobic conditions in the presence of a photocatalyst and an acid catalyst to obtain cyclohexane and cyclohexanol products;

[0009] Furthermore, in the above technical solution, it further includes the following operations: sequentially putting a fatty alcohol solvent, aryl ether as a substrate, a Pt / TiO2 catalyst, and a hydrochloric acid catalyst into a quartz tube container, filling it with a protective gas and then sealing it, irradiating it with a lamp within a certain wavelength range for T1 hours under room temperature and stirring conditions to cause the reduction cleavage of aryl ether and obtain cyclohexane and cyclohexanol products.

[0010] Furthermore, in the above technical solution, the main reduction product of the aryl ether is cyclohexane or substituted cyclohexane, and the secondary product is cyclohexanol or substituted cyclohexanol.

[0011] Furthermore, in the above technical solution, the fatty alcohol is selected from one of methanol, ethanol, isopropanol, n-propanol, ethylene glycol, or glycerol. The preferred solvent is isopropanol.

[0012] Furthermore, in the above technical solution, the aryl ether is selected from one of diphenyl ether, anisole, isopropoxybenzene, phenoxyethylbenzene, guaiacol, 2-methoxy-4-propylphenol, 2,6-dimethoxy-4-propylphenol, 3-(4-hydroxy-3-methoxyphenyl)-1-propanol.

[0013] Furthermore, in the above technical solution, the photocatalyst is Pt / P25TiO2 prepared by the sodium borohydride reduction method.

[0014] Furthermore, in the above technical solution, the Pt loading is 0.5 - 6 wt%. The preferred value is 4 wt%.

[0015] Furthermore, in the above technical solution, the acid catalyst is hydrochloric acid.

[0016] Furthermore, in the above technical solution, the protective gas is selected from one of normal pressure nitrogen or normal pressure argon.

[0017] Furthermore, in the above technical solution, the wavelength range is 360 - 390 nm. The preferred wavelength is 370 nm.

[0018] Furthermore, in the above technical solution, the value of T1 is 1 - 12. The preferred value is 12 hours.

[0019] Furthermore, in the above technical solution, the molar concentration of the aryl ether substrate is 0.05 - 0.15 mol / L. The preferred value is 0.1 mol / L.

[0020] Further, in the above technical solution, the molar concentration of the hydrochloric acid is 0.1 mol / L.

[0021] Further, in the above technical solution, the mass concentration of the photocatalyst is 5 - 10 g / L.

[0022] Advantages of the invention:

[0023] 1. The present invention uses transfer hydrogenation under light irradiation to replace the traditional high-temperature and high-pressure hydrogen conditions to achieve the reduction cleavage of aryl ethers, which has the advantages of being green, safe, mild in conditions, requiring lower equipment and being simple in operation.

[0024] 2. The present invention uses fatty alcohols as both a solvent and a hydrogen donor, and fatty alcohols can also be obtained from biomass refining. Therefore, this process gets rid of the dependence on traditional petroleum-based chemicals and prepares fuels from pure biomass-based raw materials, greatly increasing the sustainability of this process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the principle of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Example 1

[0027] Weigh 5 mg of 4 wt%-Pt / TiO₂ catalyst and 17 mg of diphenyl ether in a 6 mL quartz tube, use 1 mL of isopropanol as a solvent, add 100 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid, displace with argon for 6 - 7 times, and irradiate with a 365 nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample with an organic filter membrane, dilute the filtrate with ethanol and analyze it by gas chromatography. The product yield is shown in Table 1.

[0028] Example 2

[0029] Weigh 5 mg of 2 wt%-Pt / TiO₂ catalyst and 17 mg of diphenyl ether in a 6 mL quartz tube, use 1 mL of isopropanol as a solvent, add 100 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid, displace with argon for 6 - 7 times, and irradiate with a 365 nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample with an organic filter membrane, dilute the filtrate with ethanol and analyze it by gas chromatography. The product yield is shown in Table 1.

[0030] Example 3

[0031] Weigh 5 mg of 1 wt%-Pt / TiO₂ catalyst and 17 mg of diphenyl ether in a 6-mL quartz tube, use 1 mL of isopropanol as the solvent, add 100 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid, displace with argon 6 - 7 times, and irradiate with a 365-nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample using an organic filter membrane, dilute the filtrate with ethanol, and analyze it using gas chromatography. The product yields are shown in Table 1.

[0032] Example 4

[0033] Weigh 5 mg of 4 wt%-Pt / TiO₂ catalyst and 17 mg of diphenyl ether in a 6-mL quartz tube, use 1 mL of ethanol as the solvent, add 100 μL of an ethanol solution of 1.2 mol / L hydrochloric acid, displace with argon 6 - 7 times, and irradiate with a 365-nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample using an organic filter membrane, dilute the filtrate with ethanol, and analyze it using gas chromatography. The product yields are shown in Table 1.

[0034] Example 5

[0035] Weigh 5 mg of 4 wt%-Pt / TiO₂ catalyst and 17 mg of diphenyl ether in a 6-mL quartz tube, use 1 mL of methanol as the solvent, add 100 μL of a methanol solution of 1.2 mol / L hydrochloric acid, displace with argon 6 - 7 times, and irradiate with a 365-nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample using an organic filter membrane, dilute the filtrate with ethanol, and analyze it using gas chromatography. The product yields are shown in Table 1.

[0036] Example 6

[0037] Weigh 5 mg of 4 wt%-Pt / TiO₂ catalyst and 17 mg of diphenyl ether in a 6-mL quartz tube, use 1 mL of glycerol as the solvent, add 100 μL of a glycerol solution of 1.2 mol / L hydrochloric acid, displace with argon 6 - 7 times, and irradiate with a 365-nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample using an organic filter membrane, dilute the filtrate with ethanol, and analyze it using gas chromatography. The product yields are shown in Table 1.

[0038] Example 7

[0039] Weigh 5 mg of 4 wt%-Pt / TiO2 catalyst and 17 mg of diphenyl ether in a 6 mL quartz tube, use 1 mL of isopropanol as the solvent, add 50 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid, displace with argon 6 - 7 times, and irradiate with a 365 nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample using an organic filter membrane, dilute the filtrate with ethanol, and analyze it using gas chromatography. The product yields are shown in Table 1.

[0040] Example 8

[0041] Weigh 5 mg of 4 wt%-Pt / TiO2 catalyst and 17 mg of diphenyl ether in a 6 mL quartz tube, use 1 mL of isopropanol as the solvent, add 20 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid, displace with argon 6 - 7 times, and irradiate with a 365 nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample using an organic filter membrane, dilute the filtrate with ethanol, and analyze it using gas chromatography. The product yields are shown in Table 1.

[0042] Example 9

[0043] Weigh 5 mg of 4 wt%-Pt / TiO2 catalyst and 17 mg of diphenyl ether in a 6 mL quartz tube, use 1 mL of isopropanol as the solvent, add 10 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid, displace with argon 6 - 7 times, and irradiate with a 365 nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample using an organic filter membrane, dilute the filtrate with ethanol, and analyze it using gas chromatography. The product yields are shown in Table 1.

[0044] Example 10

[0045] Weigh 5 mg of 4 wt%-Pt / TiO2 catalyst and 10.8 mg of anisole in a 6 mL quartz tube, use 1 mL of isopropanol as the solvent, add 100 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid, displace with argon 6 - 7 times, and irradiate with a 365 nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample using an organic filter membrane, dilute the filtrate with ethanol, and analyze it using gas chromatography. The product yields are shown in Table 1.

[0046] Example 11

[0047] In a 6 mL quartz tube, 5 mg of 4 wt%-Pt / TiO₂ catalyst and 13.6 mg of cumene hydroperoxide were weighed, 1 mL of isopropanol was used as a solvent, 100 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid was added, and the mixture was purged with argon 6 - 7 times. Under stirring at 600 rpm and at room temperature, it was irradiated with a 365 nm LED lamp for 12 h. After the reaction, an internal standard was added, the sample was filtered using an organic filter membrane, and the filtrate was diluted with ethanol and analyzed by gas chromatography. The product yields are shown in Table 1.

[0048] Example 12

[0049] In a 6 mL quartz tube, 5 mg of 4 wt%-Pt / TiO₂ catalyst and 19.8 mg of phenethyl phenyl ether were weighed, 1 mL of isopropanol was used as a solvent, 100 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid was added, and the mixture was purged with argon 6 - 7 times. Under stirring at 600 rpm and at room temperature, it was irradiated with a 365 nm LED lamp for 12 h. After the reaction, an internal standard was added, the sample was filtered using an organic filter membrane, and the filtrate was diluted with ethanol and analyzed by gas chromatography. The product yields are shown in Table 1.

[0050] Example 13

[0051] In a 6 mL quartz tube, 5 mg of 4 wt%-Pt / TiO₂ catalyst and 12.4 mg of guaiacol were weighed, 1 mL of isopropanol was used as a solvent, 100 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid was added, and the mixture was purged with argon 6 - 7 times. Under stirring at 600 rpm and at room temperature, it was irradiated with a 365 nm LED lamp for 12 h. After the reaction, an internal standard was added, the sample was filtered using an organic filter membrane, and the filtrate was diluted with ethanol and analyzed by gas chromatography. The product yields are shown in Table 1.

[0052] Example 14

[0053] In a 6 mL quartz tube, 5 mg of 4 wt%-Pt / TiO₂ catalyst and 16.6 mg of 2-methoxy-4-propylphenol were weighed, 1 mL of isopropanol was used as a solvent, 100 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid was added, and the mixture was purged with argon 6 - 7 times. Under stirring at 600 rpm and at room temperature, it was irradiated with a 365 nm LED lamp for 12 h. After the reaction, an internal standard was added, the sample was filtered using an organic filter membrane, and the filtrate was diluted with ethanol and analyzed by gas chromatography. The product yields are shown in Table 1.

[0054] Example 15

[0055] Weigh 5 mg of 4 wt%-Pt / TiO2 catalyst and 16.6 mg of 2,6-dimethoxy-4-propylphenol in a 6 mL quartz tube. Use 1 mL of isopropanol as the solvent, add 100 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid, displace with argon 6 - 7 times, and irradiate with a 365 nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample using an organic filter membrane, dilute the filtrate with ethanol, and analyze it using gas chromatography. The product yields are shown in Table 1.

[0056] Example 16

[0057] Weigh 5 mg of 4 wt%-Pt / TiO2 catalyst and 18.2 mg of 3-(4-hydroxy-3-methoxyphenyl)-1-propanol in a 6 mL quartz tube. Use 1 mL of isopropanol as the solvent, add 100 μL of an isopropanol solution of 1.2 mol / L hydrochloric acid, displace with argon 6 - 7 times, and irradiate with a 365 nm LED lamp for 12 h under stirring at 600 rpm and room temperature. After the reaction, add an internal standard, filter the sample using an organic filter membrane, dilute the filtrate with ethanol, and analyze it using gas chromatography. The product yields are shown in Table 1.

[0058] Table 1 Evaluation results of photocatalytic transfer hydrogenation for the reduction of aryl ethers

[0059]

[0060]

[0061]

[0062]

[0063] The present invention uses transfer hydrogenation under light irradiation to replace the traditional high-temperature and high-pressure hydrogen conditions to achieve the reductive cleavage of aryl ethers, which has the advantages of being green, safe, mild in conditions, having lower equipment requirements, and being simple to operate. In addition, the present invention uses fatty alcohols as both the solvent and the hydrogen donor, and fatty alcohols can also be obtained from biomass refining. Therefore, this process gets rid of the dependence on traditional petroleum-based chemicals and prepares fuels from pure biomass-based raw materials, greatly increasing the sustainability of this process.

[0064] The above examples describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above examples. What is described in the above examples and the specification only illustrates the principle of the present invention. Without departing from the principle of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for photocatalytic hydrogen transfer reduction cleavage of aryl ethers at room temperature, characterized in that, It includes the following operations: Using aryl ether as the substrate, reacting in a fatty alcohol solvent at room temperature, under light irradiation and in an anaerobic condition in the presence of a Pt / TiO₂ photocatalyst and a hydrochloric acid catalyst to obtain cyclohexane compounds and cyclohexanol compounds; Among them, the aryl ether is selected from one of diphenyl ether, anisole, isopropoxybenzene, phenoxyethylbenzene, guaiacol, 2-methoxy-4-propylphenol, and 2,6-dimethoxy-4-propylphenol; The cyclohexane compounds are selected from cyclohexane or propylcyclohexane; The cyclohexanol compounds are selected from cyclohexanol or 3-propylcyclohexanol; When the aryl ether is diphenyl ether, anisole, isopropoxybenzene, phenoxyethylbenzene or guaiacol, the products are cyclohexane and cyclohexanol; When the aryl ether is 2-methoxy-4-propylphenol or 2,6-dimethoxy-4-propylphenol, the products are propylcyclohexane and 3-propylcyclohexanol.

2. The method for photocatalytic hydrogen transfer reduction cleavage of aryl ethers at room temperature according to claim 1, characterized in that: It also includes the following operations: Sequentially putting the fatty alcohol solvent, the aryl ether substrate, the Pt / TiO₂ catalyst, and the hydrochloric acid catalyst into a quartz tube container, filling with a protective gas and then sealing, irradiating with a lamp within a certain wavelength range for 1 - 12 hours under room temperature and stirring conditions, causing the reduction cleavage of the aryl ether to obtain cyclohexane compounds and cyclohexanol compounds.

3. The method for photocatalytic hydrogen transfer reduction cleavage of aryl ethers at room temperature according to claim 1, wherein: The fatty alcohol is selected from one of methanol, ethanol, isopropanol, n-propanol, ethylene glycol or glycerol.

4. The method for photocatalytic hydrogen transfer reduction cleavage of aryl ethers at room temperature according to claim 1, wherein: The photocatalyst is Pt / P25TiO₂ prepared by the sodium borohydride reduction method.

5. The method for photocatalytic hydrogen transfer reduction cleavage of aryl ethers at room temperature according to claim 4, wherein: The Pt loading is 0.5 - 6 wt%.

6. The method for photocatalytic hydrogen transfer reduction cleavage of aryl ethers at room temperature according to claim 2, wherein: The protective gas is selected from one of normal pressure nitrogen or normal pressure argon.

7. The method for photocatalytic hydrogen transfer reduction to cleave aryl ethers at room temperature according to claim 2, wherein: The wavelength range is 360 - 390 nm.

8. The method for photocatalytic hydrogen transfer reduction to cleave aryl ethers at room temperature according to claim 1, wherein: The molar concentration of the aryl ether substrate is 0.05 - 0.15 mol / L.

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