Process for converting oxidized lignin and its model compounds into high value-added small organic molecules compounds

Abstract

The application discloses a method for converting oxidized lignin and model compounds thereof into high-value-added small organic molecular compounds, i.e. under the irradiation of ultraviolet light, oxidized lignin and model compounds thereof are degraded in alcohol solvents with an acid as an additive, and are converted into high-value-added small organic molecular compounds. The raw material of the application is simple and easy to obtain, the degradation process is green and environment-friendly (under normal temperature and pressure, without metal catalyst and photosensitizer), the conversion rate is high, and the yield is good. The application has a wide application prospect in the degradation and deep development and utilization of lignin.

Description

Technical Field

[0001] This invention relates to the field of agricultural and forestry biomass resource utilization and treatment, specifically to a method for converting oxidized lignin and its model compounds into high-value-added small organic molecule compounds, as well as aryl ketones and phenolic compounds. Background Technology

[0002] Timber resources are a widely distributed natural resource on the Earth's surface, characterized by their green and sustainable nature. Timber is mainly composed of cellulose, hemicellulose, lignin, and small amounts of sugars. Lignin, as the most abundant source of renewable aromatic compounds in nature, is often discarded as papermaking waste or burned for heat. Degrading lignin into smaller monomeric compounds yields high-value aromatic compounds, which can, to some extent, replace non-renewable fossil resources and achieve sustainable development. Lignin is a complex, irregular, and ether-bonded polymer, mainly composed of three monomers—S (eugenyl), G (guaiacyl), and H (p-hydroxyphenyl)—linked by 4-O-5, α-O-4, and β-O-4 bonds (as shown in the attached diagram). Figure 1 As shown in the figure, β-O-4 bonds account for more than 50% of the total CO bonds. Therefore, researching an efficient method for breaking β-O-4 bonds is of great significance for achieving lignin degradation.

[0003] The most common method for achieving lignin degradation is hydrogenation catalyzed by transition metals. These methods typically require high temperatures and do not allow the presence of free phenolic hydroxyl groups in the structure, which can lead to poor chemical selectivity of the products. For example, as early as 1938, Adkins' group used hydrogen to reduce lignin to cyclohexanols, and subsequently other groups also successfully degraded lignin to cyclohexanols or phenolic compounds.

[0004] In recent years, with the development of photocatalysis, methods for degrading lignin using light energy have also made some progress. Compared with traditional transition metal-catalyzed hydrogenation reactions, photocatalytic reactions offer milder conditions. In 2014, the photocatalytic breaking of the β-O-4 model CO bond in lignin was first reported, degrading 2-phenoxy-1-phenylethanol-1-ol into acetophenone and phenol. Subsequently, other groups have also developed different photocatalysts to successfully degrade 2-phenoxy-1-phenylethanol-1-ol into acetophenone and phenol. Looking at the above research results, it can be seen that their work mainly utilizes metal catalysts to degrade benzene lignin and its model compounds into small molecule organic compounds (such as phenol, cyclohexane, cyclohexanol, acetophenone, benzaldehyde, etc.). Such reactions face problems such as expensive metal catalysts, poor selectivity, and high reaction temperatures. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for converting oxidized lignin and its model compounds into high-value-added small organic molecule compounds. From the perspective of social sustainable development and green chemistry, this invention proposes a method for converting oxidized lignin into high-value-added small organic molecule compounds under metal-free conditions at room temperature, which has significant economic value and importance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for converting oxidized lignin and its model compounds into high-value-added small organic molecule compounds includes the following steps:

[0008] Oxidized lignin or model compounds and additives (0-5.0 equivalents) are added to a quartz reaction tube containing a magnetic stirrer. After deoxygenation, an alcohol solvent is added, and the reaction is carried out under ultraviolet light irradiation for 4-48 hours. After the reaction is completed, the degradation is analyzed to obtain the aforementioned small organic analytical compounds; wherein,

[0009] The structural unit of the oxidized lignin is:

[0010] The structural formula of the oxidized lignin model compound is:

[0011] The structural formula of the high-value-added organic small molecule compound is:

[0012] The structural formulas of aryl ketones are as follows: The structural formulas of phenolic compounds are:

[0013] In this context, R and R' are each independently a substituent group of aryl (ether), alkyl (oxy) group, ester group, or halogen.

[0014] Optionally, the aryl (ether) includes phenyl, p-methylphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 3,5-dimethoxyphenyl, or phenoxy; the alkyl (oxy) group includes methoxy, ethoxy, or tert-butyl; the ester group includes methyl ester or ethyl ester; and the halogen includes fluorine, chlorine, bromine, or iodine.

[0015] Optionally, the oxidized lignin is derived from straw, pine, fir, cypress, paulownia, poplar, birch, sycamore, etc.; preferably, the oxidized lignin is oxidized pine lignin.

[0016] Optionally, the illumination is ultraviolet light with a wavelength of 180-365nm, and preferably, the light source is a 254nm ultraviolet lamp.

[0017] Optionally, the alcohol solvent is methanol, ethanol, isopropanol, ethylene glycol methyl ether, cyclohexanol, or tert-butanol; preferably, the alcohol solvent is isopropanol; and the amount of the alcohol solvent is such that the concentration ranges of the oxidized lignin and its model compound are 1-50 mg / mL and 0.005-0.2 mmol / mL, respectively; preferably, the reaction concentrations of the oxidized lignin and its model compound are 8 mg / mL and 0.03 mmol / mL, respectively.

[0018] Optionally, the additives required in the reaction are hydrochloric acid, nitric acid, sulfuric acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, formic acid, acetic acid, propionic acid, or trifluoroacetic acid; preferably, the additive in the reaction is chloroacetic acid.

[0019] Furthermore, the reaction is carried out under the protection of an inert gas, the reaction temperature is 20-30℃, and the reaction time is 4-48h; preferably, the reaction temperature is 27℃, the reaction time is 6h, and the inert gas is argon.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1) The system of this invention is simple, has no metal catalyst, is easy to operate, has mild reaction conditions, high conversion rate, and good yield.

[0022] 2) This invention is also effective for lignin with complex structures and can efficiently degrade oxidized lignin. It has broad application prospects in the deep development and utilization of lignin. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This is a molecular structure diagram of lignin.

[0025] Figure 2 The 1H NMR spectrum is for 3,4-dimethoxyacetophenone.

[0026] Figure 3 The hydrogen spectrum of guaiacol. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0029] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0030] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0031] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0032] The raw materials used in this invention can be purchased from the market or synthesized using methods known in the art.

[0033] Example 1

[0034]

[0035] A suitable magnetic stir bar was placed in a dry quartz reaction tube (10 mL), and 0.1 mmol of 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)ethane-1-one was added. The reaction tube was then evacuated and purged with argon gas, and the purging was repeated three times. Under an argon atmosphere, 1 mL of ethanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and stirred for 6 hours. The reaction was then stopped. The reaction tube was removed from the reactor, concentrated, and separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2a and 3a. The proton NMR spectra of the products are shown in the attached figure. Figure 2 and 3 As shown.

[0036] Product 2a (yield: 45%): 1 H NMR (300MHz, CDCl3) δ7.68-7.48(m,2H),6.89(d,J=8.3Hz,1H),3.95(s,3H),3.94(s,3H),2.57(s,3H). 13 C NMR (151MHz, CDCl3) δ196.6,153.0,148.7,130.2,123.1,109.7,55.8,55.7,26.0.

[0037] Product 3a (yield: 55%): 1 H NMR (300MHz, CDCl3) δ6.98-6.90(m,1H),6.90-6.81(m,3H),5.61(s,1H),3.89(s,3H). 13 C NMR (75MHz, CDCl3) δ146.4,145.4,121.2,120.0,114.5,110.6,55.6.

[0038] Example 2

[0039]

[0040] A suitable magnetic stir bar was placed in a dry quartz reaction tube (10 mL), and 0.1 mmol of 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)ethane-1-one was added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, 1 mL of isopropanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and stirred for 6 hours. The reaction was then stopped, and the reaction tube was removed from the reactor. After concentration, the product was separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2a and 3a. Product 2a (yield: 60%); Product 3a (yield: 59%).

[0041] Example 3

[0042]

[0043] A suitable magnetic stir bar was placed in a dry quartz reaction tube (10 mL). 0.1 mmol of 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)ethane-1-one and 0.5 mmol of chloroacetic acid were added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, 1 mL of isopropanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and stirred for 6 hours. After the reaction was stopped, the reaction tube was removed from the reactor, concentrated, and separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2a and 3a. Product 2a (yield: 84%); Product 3a (yield: 76%).

[0044] Example 4

[0045]

[0046] A suitable magnetic stir bar was placed in a dry quartz reaction tube (10 mL). 0.1 mmol of 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)ethane-1-one and 0.15 mmol of chloroacetic acid were added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, 1 mL of isopropanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and stirred for 6 hours. After the reaction was stopped, the reaction tube was removed from the reactor, concentrated, and separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2a and 3a. Product 2a (yield: 78%); Product 3a (yield: 69%).

[0047] Example 5

[0048]

[0049] A suitable magnetic stir bar was placed in a dry quartz reaction tube (10 mL). 0.1 mmol of 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)ethane-1-one and 0.15 mmol of chloroacetic acid were added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, 3 mL of isopropanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and stirred for 6 hours. After the reaction was stopped, the reaction tube was removed from the reactor, concentrated, and separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2a and 3a. Product 2a (yield: 81%); Product 3a (yield: 71%).

[0050] Example 6

[0051]

[0052] A suitable magnetic stir bar was placed in a dry quartz reaction tube (10 mL). 0.1 mmol of 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)ethane-1-one and 0.15 mmol of chloroacetic acid were added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, 3 mL of isopropanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and stirred for 12 hours. After the reaction was stopped, the reaction tube was removed from the reactor, concentrated, and separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2a and 3a. Product 2a (yield: 77%); Product 3a (yield: 63%).

[0053] Example 7

[0054]

[0055] A suitable stir bar was placed in a dry quartz reaction tube (10 mL), and 0.1 mmol of 1-(3,4-dimethoxyphenyl)-2-(3-methoxyphenoxy)ethane-1-one was added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, 3 mL of isopropanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and stirred for 48 hours. The reaction was then stopped, and the reaction tube was removed from the reactor. After concentration, the product was separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2a and 3c. Product 2a (yield: 66%); Product 3b (yield: 57%).

[0056] Example 8

[0057]

[0058] A suitable stir bar was placed in a dry quartz reaction tube (10 mL), and 0.1 mmol of 1-(3,4-dimethoxyphenyl)-2-(4-methoxyphenoxy)ethane-1-one and 0.15 mmol of chloroacetic acid were added. The reaction tube was then evacuated and purged with argon gas, and the purging was repeated three times. Isopropanol (3 mL) was slowly added to the reaction tube using a syringe under an argon atmosphere. The reaction tube was placed in a 254 nm UV reactor and stirred for 12 hours. The reaction was then stopped, and the reaction tube was removed from the reactor. After concentration, the product was separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2a and 3c. Product 2a (yield: 73%); Product 3c (yield: 62%).

[0059] Example 9

[0060]

[0061] A suitable stir bar was placed in a dry quartz reaction tube (10 mL), and 0.1 mmol of 1-(3,4-dimethoxyphenyl)-2-(2,6-dimethoxyphenoxy)ethane-1-one and 0.15 mmol of chloroacetic acid were added. The reaction tube was then evacuated and purged with argon gas, and the purging was repeated three times. Isopropanol (3 mL) was slowly added to the reaction tube using a syringe under an argon atmosphere. The reaction tube was placed in a 254 nm UV reactor and stirred for 12 hours. The reaction was then stopped, and the reaction tube was removed from the reactor. After concentration, the product was separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2a and 3d. Product 2a (yield: 70%); Product 3d (yield: 59%).

[0062] Example 10

[0063]

[0064] A suitable stir bar was placed in a dry quartz reaction tube (10 mL), and 0.1 mmol of 1-(3,4-dimethoxyphenyl)-2-(2-methoxy-4-methylphenoxy)ethane-1-one and 0.15 mmol of chloroacetic acid were added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, 3 mL of isopropanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and the reaction was stirred. After 12 hours, the reaction was stopped, the reaction tube was removed from the reactor, concentrated, and separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2a and 3e. Product 2a (yield: 73%); Product 3e (yield: 62%).

[0065] Example 11

[0066]

[0067] A suitable stir bar was placed in a dry quartz reaction tube (10 mL), and 0.1 mmol of 1-(3,4,5-trimethoxyphenyl)-2-(2-methoxyphenoxy)ethane-1-one and 0.15 mmol of chloroacetic acid were added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, 3 mL of isopropanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and the reaction was stirred. After 12 hours, the reaction was stopped, the reaction tube was removed from the reactor, concentrated, and separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2b and 3a. Product 2b (yield: 94%); Product 3a (yield: 57%).

[0068] Example 12

[0069]

[0070] A suitable stir bar was placed in a dry quartz reaction tube (10 mL), and 0.1 mmol of 2-(4-phenoxyphenoxy)-1-(3,4,5-trimethoxyphenyl)ethane-1-one and 0.15 mmol of chloroacetic acid were added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, 3 mL of isopropanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and the reaction was stirred. After 12 hours, the reaction was stopped, the reaction tube was removed from the reactor, concentrated, and separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2b and 3f. Product 2b (yield: 86%); Product 3f (yield: 45%).

[0071] Example 13

[0072]

[0073] A suitable stir bar was placed in a dry quartz reaction tube (10 mL), and 0.1 mmol of 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethane-1-one and 0.15 mmol of chloroacetic acid were added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, 3 mL of isopropanol was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and the reaction was stirred. After 12 hours, the reaction was stopped, the reaction tube was removed from the reactor, concentrated, and separated by thin-layer chromatography (eluent: n-hexane / ethyl acetate = 10 / 1) to obtain the target products 2c and 3b. Product 2c (yield: 76%); Product 3f (yield: 54%).

[0074] Example 14

[0075] A suitable magnetic stir bar was placed in a dry quartz reaction flask (10 mL), and oxidized pine lignin (25 mg) and chloroacetic acid (0.15 mmol) were added. The reaction tube was then evacuated and purged with argon gas, repeating this process three times. Under an argon atmosphere, isopropanol (3 mL) was slowly added to the reaction tube using a syringe. The reaction tube was placed in a 254 nm UV reactor and stirred for 24 hours. After the reaction was stopped, the reaction tube was removed from the reactor and concentrated to obtain 13.5 mg of an oily mixture rich in monomers. GC-MS analysis of the obtained oily mixture revealed a large amount of G-type and a small amount of H-type monomer products. Examples include: 4-hydroxy-3-methoxybenzaldehyde, 1-(4-hydroxy-3-methoxyphenyl)ethane-1-one, 4-hydroxy-3-methoxybenzoic acid, 1-(4-hydroxy-3-methoxyphenyl)prop-2-en-1-one, isopropyl 4-hydroxy-3-methoxybenzoate, 3-hydroxy-1-(4-hydroxy-3-methoxyphenyl)prop-1-one, and 4-hydroxybenzoic acid.

[0076] Example 15

[0077] Place a suitable stir bar in a dry quartz reaction flask (10 mL), add oxidized birch lignin (25 mg) and chloroacetic acid (0.15 mmol), then evacuate the reaction tube and purge it with argon gas. Repeat this process three times. Under an argon atmosphere, slowly add isopropanol (3 mL) to the reaction tube using a syringe. Place the reaction tube in a 254 nm UV reactor and stir the reaction for 24 hours. Stop the reaction, remove the reaction tube from the reactor, and concentrate it to obtain 10.0 mg of an oily mixture rich in monomers.

[0078] Example 16

[0079] Place a suitable stir bar in a dry quartz reaction flask (10 mL), add oxidized wheat straw lignin (25 mg) and chloroacetic acid (0.15 mmol), then evacuate the reaction tube and purge it with argon gas. Repeat this process three times. Under an argon atmosphere, slowly add isopropanol (3 mL) to the reaction tube using a syringe. Place the reaction tube in a 254 nm UV reactor and stir the reaction for 24 hours. Stop the reaction, remove the reaction tube from the reactor, and concentrate it to obtain 13.5 mg of an oily mixture rich in monomers.

[0080] Example 17

[0081] Place a suitable stir bar in a dry quartz reaction flask (10 mL), add oxidized camphor wood lignin (25 mg) and chloroacetic acid (0.15 mmol), then evacuate the reaction tube and purge it with argon gas. Repeat this process three times. Under an argon atmosphere, slowly add isopropanol (3 mL) to the reaction tube using a syringe. Place the reaction tube in a 254 nm ultraviolet reactor and stir the reaction for 24 hours. Stop the reaction, remove the reaction tube from the reactor, and concentrate it to obtain 16.0 mg of an oily mixture rich in monomers.

[0082] Example 18

[0083] Place a suitable stir bar in a dry quartz reaction flask (250 mL), add oxidized pine lignin (1 g) and chloroacetic acid (6 mmol), then evacuate the reaction tube and purge it with argon gas. Repeat this process three times. Under an argon atmosphere, slowly add isopropanol (120 mL) to the reaction tube using a syringe. Place the reaction tube in a 254 nm UV reactor and stir for 24 hours. Stop the reaction, remove the reaction tube from the reactor, and concentrate to obtain 0.36 g of an oily mixture rich in monomers.

[0084] Example 19

[0085] Place a suitable stir bar in a dry quartz reaction flask (1 L), add oxidized pine lignin (10 g) and chloroacetic acid (60 mmol), then evacuate the reaction tube and purge it with argon gas. Repeat this process three times. Under an argon atmosphere, slowly add isopropanol (500 mL) to the reaction tube using a syringe. Place the reaction tube in a 254 nm ultraviolet reactor and stir the reaction for 24 hours. Stop the reaction, remove the reaction tube from the reactor, and concentrate it to obtain 3.4 g of an oily mixture rich in monomers.

[0086] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for converting oxidized lignin and its model compounds into high-value-added small-molecule organic compounds, characterized in that, Includes the following steps: Adding 0-5.0 equivalents of additives and alcohol solvents to oxidized lignin model compounds, followed by deoxygenation and ultraviolet irradiation degradation, yields small organic molecule compounds; among which, The structural formula of the oxidized lignin model compound is: ; The organic small molecule compound is: aryl ketone compound. phenolic compounds ; Wherein, R and R' are each independently a substituent group of aryl, aryl ether, alkyl, alkoxy, or halogen; the aryl group is phenyl, p-methylphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 3,5-dimethoxyphenyl, or phenoxy; the aryl ether is phenyl ether, p-methylphenyl ether, 2-methoxyphenyl ether, 3-methoxyphenyl ether, 3,5-dimethoxyphenyl ether, or phenoxy ether; the alkyl group is methyl, ethyl, or tert-butyl; the alkoxy group is methoxy or ethoxy; and the halogen is fluorine, chlorine, bromine, or iodine. The light is irradiated with ultraviolet light at a wavelength of 254 nm, and the additive is hydrochloric acid, nitric acid, sulfuric acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, formic acid, acetic acid, propionic acid, or trifluoroacetic acid.

2. The method according to claim 1, characterized in that, The alcohol solvent is methanol, ethanol, isopropanol, ethylene glycol methyl ether, cyclohexanol, or tert-butanol.

3. The method according to claim 1 or 2, characterized in that, The amount of alcohol solvent used is such that the concentration range of the oxidized lignin model compound is 1-50 mg / mL and 0.005-0.2 mmol / mL, respectively.

4. The method according to claim 1, characterized in that, The reaction is carried out under the protection of an inert gas at a temperature of 20-30°C for a time of 4-48 hours.

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