A method for electrochemical oxidative cleavage of a lignin model compound

Abstract

The application discloses a method for electrochemically oxidizing and cracking a lignin model compound, which comprises the following steps: preparing a solution of the lignin model compound in acetonitrile with a concentration of 10-20 mM, adding 10-20 mM electrolyte n-Bu4NOAc, and performing a constant potential electrolysis reaction for 4-8 h under an anode potential of 1.8-3.0 V in a three-electrode system to obtain benzaldehyde. The C alpha-C beta bond in the beta-O-4 lignin model compound can be efficiently cracked under specific reaction conditions, and the selectivity is relatively high, so that the breaking of other bonds is avoided, and thus the yield of the target product benzaldehyde is significantly improved. In addition, the method only needs to use a simple supporting electrolyte, and does not need an expensive catalyst or a complex reaction condition, so that the reaction cost is greatly reduced. Meanwhile, the operation steps are simple, and the method is easy to implement in industrial production, and has relatively high practicability and popularization value.

Description

TECHNICAL FIELD

[0001] The present application relates to biomass resource utilization, and in particular to a method for electrochemical oxidative cleavage of a lignin model compound. BACKGROUND

[0002] Lignin is a complex polymer with phenylpropane structural units randomly connected by various chemical bonds. The content of β-O-4 bond is the most abundant, accounting for about 50% of the total bond type of lignin. Selective cleavage of β-O-4 bond to realize depolymerization of lignin macromolecules is a key way to obtain high value-added small molecule products. Therefore, precise selective cleavage of β-O-4 bond has important scientific significance and application value for improving the monomer yield of lignin conversion. From the mechanism of chemical bond cleavage, the cleavage of β-O-4 bond is mainly realized by cleavage of C β -O bond or C α -C β bond. Traditional cleavage methods mainly rely on heterogeneous or homogeneous catalytic conversion under high temperature conditions. However, compared with the cleavage of C β -O bond, the cleavage of C α -C β bond in β-O-4 bond faces greater challenges, which is mainly due to its inherent chemical stability.

[0003] In recent years, the rise of indirect electrochemical conversion technology provides a new way to solve this problem. This method can effectively reduce the reaction potential and improve the reaction selectivity. It has been reported that by introducing oxidizing medium tert-butyl hydroperoxide, electrochemical indirect oxidative depolymerization of model compounds can be realized. However, the introduction of peroxide in the electrochemical reaction system may weaken the inherent safety advantage of electrochemical method. Therefore, developing a safer and more convenient method for indirect electrochemical oxidation of lignin, and further improving the depolymerization efficiency of lignin, has become a key technical problem to be broken through in this field. SUMMARY

[0004] To solve the above technical problems, the present application provides a method for electrochemical oxidative cleavage of a lignin model compound.

[0005] The present inventors have found through systematic research that by using n-Bu4NOAc as a supporting electrolyte, the efficiency of electrochemical oxidative cleavage of β-O-4 lignin model compound can be improved, and the C α -C β bond cleavage selectivity is extremely high, thereby completing the present application.

[0006] The technical scheme of the present application is as follows:

[0007] A method for electrochemical oxidative cleavage of a lignin model compound, characterized in that the lignin model compound is prepared into a 10-20 mM solution using acetonitrile as a solvent, 10-20 mM electrolyte n-Bu4NOAc is added, and a three-electrode system is used to perform a constant potential electrolysis reaction at an anolyte potential of 1.8-3.0 V for 4-8 h to obtain benzaldehyde; the structural formula of the lignin model compound is:

[0008]

[0009] R1 and R2 are selected from hydrogen, halogen, or nitro, either the same or different.

[0010] Preferably, the anode potential is 2.3 to 2.8 V.

[0011] Preferably, the reaction time is 6 to 8 hours.

[0012] Preferably, the reaction temperature is 10–40°C.

[0013] Preferably, the lignin model compound is 2-phenoxy-1-phenylethanol.

[0014] There are no particular limitations on the cathode and anode used in the electrochemical reaction of the electrochemical depolymerization method of the present invention. Those skilled in the art can select suitable cathodes and anodes as needed. For example, commonly used corrosion-resistant electrodes (DSA) such as platinum electrodes, ruthenium electrodes, and ruthenium-titanium alloy electrodes can be used.

[0015] In the electrochemical depolymerization method of the present invention, the electrochemical reaction can be carried out using, for example, a three-electrode reaction system. When using a three-electrode system, there are no particular limitations on the reference electrode used in the electrochemical reaction of the electrochemical depolymerization method of the present invention. Those skilled in the art can select a suitable reference electrode as needed; for example, Ag / Ag can be used. + Electrodes, etc., are used as reference electrodes.

[0016] In the electrochemical depolymerization method of lignin of the present invention, after the electrochemical reaction, the depolymerization product can be separated from the acetonitrile solvent by a suitable separation technique to obtain a high-value small-molecule aromatic compound. For example, the depolymerization product can be extracted from the reaction system by means of extraction, taking advantage of the difference in molecular weight and polarity between the depolymerization product and the raw material; or the product can be separated by distillation, taking advantage of the difference in boiling points between the product and the raw material.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1)High selectivity of cleavage: the present application can efficiently cleave the Cα-Cβ bond in the β-O-4 lignin model compound by specific reaction conditions, and has high selectivity, avoiding the cleavage of other bonds, thereby significantly improving the yield of the target product benzaldehyde.

[0019] (2)Low cost and simple operation: the present application only needs to use a simple supporting electrolyte, without the need for expensive catalysts or complex reaction conditions, greatly reducing the reaction cost. At the same time, the operation steps are simple, easy to implement in industrial production, and have high practicability and popularization value. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the reaction process of Example 8 of the present application.

[0021] Figure 2 (a) is an electrolysis experiment effect diagram under different electrolyte concentrations, Figure 2 (b) is an electrolysis experiment effect diagram under different electrolysis times.

[0022] Figure 3 is the GC-FID diagram of Example 1.

[0023] Figure 4 is the GC-FID diagram of Comparative Example 3.

[0024] Figure 5 is the GC-FID diagram of Comparative Example 4.

[0025] Figure 6 is the GC-FID diagram of Comparative Example 6.

[0026] Figure 7 is the GC-FID diagram of Comparative Example 7. DETAILED DESCRIPTION

[0027] The present application will be further specifically and in detail described below in combination with specific examples, but the embodiments of the present application are not limited thereto. For the process parameters not specifically mentioned, conventional techniques can be referred to.

[0028] Example 1

[0029] In a diaphragm-free electrolytic cell, platinum sheet electrodes (20mm x 20mm x 0.1mm) were used as cathode and anode, Ag / Ag + electrode to establish a three-electrode system. 20mL of acetonitrile was measured, 2-phenoxy-1-phenyl ethanol (PP-ol) was used as a lignin model compound, a 10mM solution was prepared and transferred to the electrolytic cell, and 20mM electrolyte n-Bu4NOAc was added. Constant potential electrolysis was carried out at 20℃ with an anode potential of 2.5V for 8h. Gas chromatography-mass spectrometry (GC-MS) was used for product analysis, and the yield of benzaldehyde was 69%.

[0030] Example 2

[0031] In a diaphragm-free electrolytic cell, platinum sheet electrodes (20mm×20mm×0.1mm) are used as both the cathode and anode, with Ag / Ag ratios... + A three-electrode system was established using acetonitrile as the reference electrode. 20 mL of acetonitrile was measured, and a 10 mM solution was prepared using 2-phenoxy-1-phenylethanol (PP-ol) as the lignin model compound. This solution was transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NNO2 was added. Electrolysis was performed at a constant potential of 2.5 V at 20 °C for 8 h. Product analysis was performed using gas chromatography-mass spectrometry (GC-MS), revealing a benzaldehyde yield of 49%.

[0032] Example 3

[0033] In a diaphragm-free electrolytic cell, platinum sheet electrodes (20mm×20mm×0.1mm) are used as both the cathode and anode, with Ag / Ag ratios... + A three-electrode system was established using the reference electrode. 20 mL of acetonitrile was measured, and a 10 mM solution of 2-phenoxy-1-phenylethanol (PP-ol) was prepared as the lignin model compound. This solution was transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. Electrolysis was performed at a constant potential of 1.5 V at 20 °C for 8 h. Product analysis was performed using gas chromatography-mass spectrometry (GC-MS), revealing a benzaldehyde yield of 35%.

[0034] Example 4

[0035] In a diaphragm-free electrolytic cell, platinum sheet electrodes (20mm×20mm×0.1mm) are used as both the cathode and anode, with Ag / Ag ratios... + A three-electrode system was established using acetonitrile as the reference electrode. 20 mL of acetonitrile was measured, and a 10 mM solution was prepared using 2-phenoxy-1-phenylethanol (PP-ol) as the lignin model compound. This solution was transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. Electrolysis was performed at a constant potential of 1.8 V at 20 °C for 8 h. Product analysis was performed using gas chromatography-mass spectrometry (GC-MS), revealing a benzaldehyde yield of 63%.

[0036] Example 5

[0037] In a diaphragm-free electrolytic cell, platinum sheet electrodes (20mm×20mm×0.1mm) are used as both the cathode and anode, with Ag / Ag ratios... +A three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, 2-phenoxy-1-phenylethanol (PP-ol) was used as a lignin model compound, a 10 mM solution was prepared and transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. The constant potential electrolysis was carried out at 2.0 V of anode potential at 20°C for 8 h. Gas chromatography-mass spectrometry (GC-MS) was used for product analysis, and the yield of benzaldehyde was 65%.

[0038] Example 6

[0039] In a diaphragmless electrolytic cell, a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) was used as the cathode and anode, and Ag / Ag + A three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, 2-phenoxy-1-phenylethanol (PP-ol) was used as a lignin model compound, a 10 mM solution was prepared and transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. The constant potential electrolysis was carried out at 2.3 V of anode potential at 20°C for 8 h. Gas chromatography-mass spectrometry (GC-MS) was used for product analysis, and the yield of benzaldehyde was 75%.

[0040] Example 7

[0041] In a diaphragmless electrolytic cell, a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) was used as the cathode and anode, and Ag / Ag + A three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, 2-phenoxy-1-phenylethanol (PP-ol) was used as a lignin model compound, a 10 mM solution was prepared and transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. The constant potential electrolysis was carried out at 2.8 V of anode potential at 20°C for 8 h. Gas chromatography-mass spectrometry (GC-MS) was used for product analysis, and the yield of benzaldehyde was 76%.

[0042] Example 8

[0043] In a diaphragmless electrolytic cell, a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) was used as the cathode and anode, and Ag / Ag + A three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, 2-phenoxy-1-phenylethanol (PP-ol) was used as a lignin model compound, a 10 mM solution was prepared and transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. The constant potential electrolysis was carried out at 3.0 V of anode potential at 20°C for 8 h. Gas chromatography-mass spectrometry (GC-MS) was used for product analysis, and the yield of benzaldehyde was 68%.

[0044] Example 9

[0045] A three-electrode system was established with a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) as the cathode and anode, Ag / Ag + A three-electrode system was established with a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) as the cathode and anode, Ag / Ag

[0046] Example 10

[0047] A three-electrode system was established with a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) as the cathode and anode, Ag / Ag + A three-electrode system was established with a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) as the cathode and anode, Ag / Ag

[0048] Example 11

[0049] A three-electrode system was established with a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) as the cathode and anode, Ag / Ag + A three-electrode system was established with a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) as the cathode and anode, Ag / Ag

[0050] Example 12

[0051] A three-electrode system was established with a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) as the cathode and anode, Ag / Ag + A three-electrode system was established with a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) as the cathode and anode, Ag / Ag

[0052] Example 13

[0053] In a diaphragm-free electrolytic cell, platinum sheet electrodes (20mm×20mm×0.1mm) are used as both the cathode and anode, with Ag / Ag ratios... + A three-electrode system was established using acetonitrile as the reference electrode. 20 mL of acetonitrile was measured, and a 10 mM solution was prepared using 2-phenoxy-1-phenylethanol (PP-ol) as the lignin model compound. This solution was transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. Electrolysis was performed at a constant potential of 2.8 V at 20 °C for 2 h. Product analysis was performed using gas chromatography-mass spectrometry (GC-MS), revealing a benzaldehyde yield of 37%.

[0054] Example 14

[0055] In a diaphragm-free electrolytic cell, platinum sheet electrodes (20mm×20mm×0.1mm) are used as both the cathode and anode, with Ag / Ag ratios... + A three-electrode system was established using the reference electrode. 20 mL of acetonitrile was measured, and a 10 mM solution of 2-phenoxy-1-phenylethanol (PP-ol) was prepared as the lignin model compound. This solution was transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. Electrolysis was performed at a constant potential of 2.8 V at 20 °C for 4 h. Product analysis was performed using gas chromatography-mass spectrometry (GC-MS), revealing a benzaldehyde yield of 60%.

[0056] Example 15

[0057] In a diaphragm-free electrolytic cell, platinum sheet electrodes (20mm×20mm×0.1mm) are used as both the cathode and anode, with Ag / Ag ratios... + A three-electrode system was established using acetonitrile as the reference electrode. 20 mL of acetonitrile was measured, and a 10 mM solution was prepared using 2-phenoxy-1-phenylethanol (PP-ol) as the lignin model compound. This solution was transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. Electrolysis was performed at a constant potential of 2.8 V at 20 °C for 6 h. Product analysis was performed using gas chromatography-mass spectrometry (GC-MS), revealing a benzaldehyde yield of 75%.

[0058] Example 16

[0059] In a diaphragm-free electrolytic cell, platinum sheet electrodes (20mm×20mm×0.1mm) are used as both the cathode and anode, with Ag / Ag ratios... +A three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, 2-phenoxy-1-phenyl ethanol (PP-ol) was used as a lignin model compound, a 10 mM solution was prepared and transferred into an electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. Constant potential electrolysis was carried out at 2.8 V of anode potential at 20°C for 10 h. Product analysis was performed using gas chromatography-mass spectrometry (GC-MS), and the yield of benzaldehyde was 12%.

[0060] The reaction process of the present application is as follows:

[0061]

[0062] Table 1: Electrolysis experimental results at different voltages

[0063]

[0064] Comparative Example 1

[0065] The difference between this example and Example 1 is that the electrolyte is replaced by n-Bu4NClO4

[0066] In a diaphragm-free electrolytic cell, a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) was used as the cathode and anode, and Ag / Ag + A three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, 2-phenoxy-1-phenyl ethanol (PP-ol) was used as a lignin model compound, a 10 mM solution was prepared and transferred into an electrolytic cell, and 20 mM electrolyte n-Bu4NClO4 was added. Constant potential electrolysis was carried out at 2.5 V of anode potential at 20°C for 8 h. Product analysis was performed using gas chromatography-mass spectrometry (GC-MS), and the yield of benzaldehyde was 12%.

[0067] Comparative Example 2

[0068] The difference between this example and Example 1 is that the electrolyte is replaced by LiClO4

[0069] In a diaphragm-free electrolytic cell, a platinum sheet electrode (20 mm x 20 mm x 0.1 mm) was used as the cathode and anode, and Ag / Ag + A three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, 2-phenoxy-1-phenyl ethanol (PP-ol) was used as a lignin model compound, a 10 mM solution was prepared and transferred into an electrolytic cell, and 20 mM electrolyte LiClO4 was added. Constant potential electrolysis was carried out at 2.5 V of anode potential at 20°C for 8 h. Product analysis was performed using gas chromatography-mass spectrometry (GC-MS), and the yield of benzaldehyde was 4% and the yield of acetophenone was 5%.

[0070] Comparative Example 3

[0071] The difference between this example and Example 1 is that the substrate is changed to phenoxyethylbenzene

[0072] In a diaphragmless electrolytic cell, platinum plate electrode (20 mm x 20 mm x 0.1 mm) was used as cathode and anode, Ag / Ag + A three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, and a 10 mM solution of phenoxyethylbenzene as a lignin model compound was transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. Constant potential electrolysis was carried out at 2.5 V of anode potential at 20°C for 8 h. Gas chromatography-mass spectrometry (GC-MS) was used for product analysis, and the yield of phenethyl alcohol was 15%.

[0073] Comparative Example 4

[0074] The difference between this example and Example 1 is that the substrate is changed to 2-phenoxy-1-phenylethanone

[0075] In a diaphragmless electrolytic cell, platinum plate electrode (20 mm x 20 mm x 0.1 mm) was used as cathode and anode, Ag / Ag + A three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, and a 10 mM solution of 2-phenoxy-1-phenylethanone as a lignin model compound was transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. Constant potential electrolysis was carried out at 2.5 V of anode potential at 20°C for 8 h. Gas chromatography-mass spectrometry (GC-MS) was used for product analysis, and the yield of butyl benzoate was 10%.

[0076] Comparative Example 5

[0077] The difference between this example and Example 1 is that the substrate is changed to benzyl phenyl ether

[0078] In a diaphragmless electrolytic cell, platinum plate electrode (20 mm x 20 mm x 0.1 mm) was used as cathode and anode, Ag / Ag + A three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, and a 10 mM solution of benzyl phenyl ether as a lignin model compound was transferred to the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. Constant potential electrolysis was carried out at 2.5 V of anode potential at 20°C for 8 h. Gas chromatography-mass spectrometry (GC-MS) was used for product analysis, and the yield of benzyl alcohol was 13%.

[0079] Comparative Example 6

[0080] In a diaphragmless electrolytic cell, platinum plate electrode (20 mm x 20 mm x 0.1 mm) was used as cathode and anode, Ag / Ag +The three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, 2-(2-methoxyphenoxy)-1-phenyl ethanol was used as a lignin model compound, a 10 mM solution was prepared and transferred into the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. The constant potential electrolysis was carried out at 20°C with an anode potential of 2.5V for 8h. The product was analyzed by gas chromatography-mass spectrometry (GC-MS), and the yield of benzaldehyde was 7%.

[0081] Comparative Example 7

[0082] In a diaphragm-free electrolytic cell, a platinum sheet electrode (20mm x 20mm x 0.1mm) was used as the cathode and anode, Ag / Ag + The three-electrode system was established with the electrode as the reference electrode. 20 mL of acetonitrile was measured, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl) ethanol was used as a lignin model compound, a 10 mM solution was prepared and transferred into the electrolytic cell, and 20 mM electrolyte n-Bu4NOAc was added. The constant potential electrolysis was carried out at 20°C with an anode potential of 2.5V for 8h. The product was analyzed by gas chromatography-mass spectrometry (GC-MS), and the yield of p-methoxybenzaldehyde was 11%.

[0083] From the comparison of the examples and the comparative examples, it can be seen that, in the examples of the present application, n-Bu4NOAc is used as the supporting electrolyte, and 2-phenoxy-1 phenyl ethanol (PP-ol) is used as a chemical oxidative cleavage lignin model compound, and the yield of benzaldehyde and C α -C β The bond cleavage selectivity is improved.

[0084] The above examples are preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A method for electrochemically oxidatively cleaving lignin model compounds, characterized in that, A lignin model compound was prepared into a 10-20 mM solution using acetonitrile as the solvent. Then, 10-20 mM of electrolyte n-Bu4NOAc was added. A three-electrode system was used, and a constant-potential electrolysis reaction was carried out at an anode potential of 1.8-3.0 V for 4-8 hours to obtain benzaldehyde. The structural formula of the lignin model compound is as follows: R1 and R2 are selected from hydrogen, halogen, or nitro, either the same or different.

2. The method according to claim 1, characterized in that, The anode potential is 2.3–2.8V.

3. The method according to claim 2, characterized in that, The reaction time is 6 to 8 hours.

4. The method according to claim 1, 2, or 3, characterized in that, The reaction temperature is 10–40℃.

5. The method according to claim 4, characterized in that, The lignin model compound is 2-phenoxy-1-phenylethanol.

6. The method according to claim 1, 2, or 3, characterized in that, The three-electrode system uses a platinum electrode, a ruthenium electrode, or a ruthenium-titanium alloy electrode as the cathode and anode, Ag / Ag + The electrode is a reference electrode.

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