Synthesis method of 3, 4-dihydroxy-5-nitrobenzaldehyde

Abstract

The invention provides a synthetic method of 3, 4-dihydroxy-5-nitrobenzaldehyde, which comprises the following steps: (a) carrying out nitration reaction on methyl vanillin dissolved in glacial acetic acid and a nitric acid solution in a microchannel reactor to obtain 5-nitrovanillin; and (b) reacting the 5-nitrovanillin with pyridine in the presence of aluminum chloride to generate the 3, 4-dihydroxy-5-nitrobenzaldehyde. The micro-channel reactor is used as equipment for the first-step reaction and ethyl acetate is used as a solvent, so that the product does not need to be purified through multiple post-treatments, the solvent residue is reduced, the material loss is avoided, the production efficiency is improved, the production period is shortened, and the product is stable in yield and high in purity; a single solvent is selected in the demethylation section, multiple solvents are not needed, multiple solvent residues are avoided, multiple recrystallization is not needed, and the purity of the product can reach 99.9%.

Description

Technical Field

[0001] The invention belongs to the technical field of fine chemical products, and specifically relates to a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde. Background Art

[0002] Patent application number WO9300323 discloses a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde, which is dealkylated in a polar aprotic solvent using a mixture of lithium hydroxide and thiophenol or 2-mercaptobenzothiazole. This method does not have the problem of product decomposition in the reaction medium, so the reaction can be carried out completely. In this way, pure 3,4-dihydroxy-5-nitrobenzaldehyde can be produced, but there are still many problems that make it difficult to apply it on a large scale in industry. First, organic reagents and expensive lithium hydroxide are consumed during the reaction process, and these compounds cannot be recycled; second, this method requires the use of a polar aprotic solvent and another organic solvent and water. In the recycling of these solvents, a method is required to separate the two organic solvents from each other and to dry the polar aprotic solvent sufficiently for further use.

[0003] In addition, in the prior art, 3,4-dihydroxy-5-nitrobenzaldehyde is usually nitrated using conventional reaction equipment during the nitration stage of production, resulting in poor product quality and the generation of isomer impurities, which requires multiple recrystallizations and purifications before the next step of reaction. Multiple recrystallizations lead to material loss and high costs; in the subsequent synthesis stage, conventional solvents are used as solvents for reaction, followed by post-treatment, extraction and purification, with multiple solvent residues. Summary of the invention

[0004] In order to solve the above technical problems, the object of the present invention is to provide a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde.

[0005] In order to achieve the above technical problem, the present invention provides a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde, comprising the following steps: (a) methyl vanillin dissolved in glacial acetic acid is subjected to nitration reaction with nitric acid solution in a microchannel reactor to obtain 5-nitro vanillin; (b) reacting the 5-nitrovanillin with pyridine in the presence of aluminum chloride to generate 3,4-dihydroxy-5-nitrobenzaldehyde.

[0006] Optimally, in step (a), the molar ratio of the methyl vanillin to the nitric acid in the nitric acid solution is 1:0.9-2.1.

[0007] Furthermore, the molar ratio of mono-nitrovanillin, aluminum chloride and pyridine is 1:0.9~2.5:2~6.

[0008] Furthermore, the microchannel reactor includes a reaction unit and two groups of heat exchange units formed on both sides of the reaction unit for exchanging heat with the reaction unit, the reaction unit includes a lower cover plate, an upper cover plate matching the lower cover plate, a first sealing baffle formed between the lower cover plate and the upper cover plate to form a accommodating chamber, a methyl vanillin material pipe and a nitric acid solution material pipe respectively connected to the accommodating chamber, and a discharge pipe connected to the accommodating chamber, the inner surface of the lower cover plate is formed with a plurality of first convex strips arranged at intervals, the inner surface of the upper cover plate is formed with a plurality of second convex strips staggered with the first convex strips, and a reaction microchannel is formed between the plurality of first convex strips and the plurality of second convex strips.

[0009] In one embodiment of the present invention, each group of the heat exchange units includes a heat exchange jacket installed on the outer surface of the lower cover plate or the upper cover plate through a second sealing baffle, and a heat exchange medium cavity is formed between the heat exchange jacket and the lower cover plate or the upper cover plate; each group of the heat exchange units also includes a heat exchange medium inlet pipe and a heat exchange medium outlet pipe connected to the heat exchange medium cavity.

[0010] Furthermore, in step (a), the temperature of the nitration reaction is 0-35°C, preferably 2-30°C, and more preferably 10-15°C.

[0011] Furthermore, in step (a), ice water is added dropwise to the reaction solution after the nitration reaction is completed, stirred at 0-5°C, filtered, washed with ice water, and dried to obtain 5-nitrovanillin.

[0012] Furthermore, in step (b), after the reaction, hydrochloric acid is used to quench the reaction, the ethyl acetate phase is separated and collected, anhydrous sodium sulfate and activated carbon are added, stirred and filtered, and the filtrate is concentrated and then cooled for crystallization; then filtered, washed and dried.

[0013] Furthermore, in step (b), anhydrous aluminum chloride is added in batches and the temperature is controlled not to exceed 30°C; pyridine is then added dropwise and the temperature is controlled to be 10-15°C; after the addition is completed, the temperature is raised to 60°C for reaction.

[0014] The method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde adopts a microchannel reactor as equipment for the first step reaction and uses ethyl acetate as a solvent, and does not need to purify the product through multiple post-treatments, thereby reducing solvent residues, avoiding material loss, improving production efficiency, and shortening the production cycle. The product yield is stable and the purity is high. A single solvent is selected in the demethylation section, and multiple solvents are not needed to avoid the generation of multiple solvent residues. The product purity can reach 99.9% without multiple recrystallizations. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1is the chemical reaction formula of the synthesis method of 3,4-dihydroxy-5-nitrobenzaldehyde of the present invention; Figure 2 The process flow chart of the synthesis method of 3,4-dihydroxy-5-nitrobenzaldehyde of the present invention; Figure 3 The structure diagram of the microchannel reactor used in the synthesis method of 3,4-dihydroxy-5-nitrobenzaldehyde of the present invention; Figure 4 It is a liquid chromatogram of the product in the synthesis method of 3,4-dihydroxy-5-nitrobenzaldehyde of the present invention. DETAILED DESCRIPTION

[0016] The synthesis method of 3,4-dihydroxy-5-nitrobenzaldehyde of the present invention is characterized by comprising the following steps: (a) nitrating methyl vanillin dissolved in glacial acetic acid with a nitric acid solution in a microchannel reactor to obtain 5-nitro vanillin; (b) reacting the 5-nitro vanillin with pyridine in the presence of aluminum chloride to generate 3,4-dihydroxy-5-nitrobenzaldehyde. The microchannel reactor is used as the equipment for the first step reaction and ethyl acetate is used as the solvent, so that the product does not need to be purified through multiple post-treatments, the solvent residue is reduced, the material loss is avoided, the production efficiency is improved, the production cycle is shortened, the product yield is stable, and the purity is high; and the demethylation section uses a single solvent, and does not need to use multiple solvents, so as to avoid the generation of multiple solvent residues, and the product purity can reach 99.9% without multiple recrystallizations.

[0017] In step (a), the molar ratio of the methyl vanillin to the nitric acid in the nitric acid solution is 1:0.9-2.1. In step (b), the molar ratio of the mono-nitro vanillin, aluminum chloride and pyridine is 1:0.9-2.5:2-6.

[0018] The microchannel reactor is Figure 3As shown, it includes a reaction unit 1 and two groups of heat exchange units 2 formed on both sides of the reaction unit 1 for exchanging heat therewith, the reaction unit 1 includes a lower cover plate 11, an upper cover plate 12 matched with the lower cover plate 11, a first sealing baffle 13 formed between the lower cover plate 11 and the upper cover plate 12 to form a accommodating chamber, a methyl vanillin material pipe 15 and a nitric acid solution material pipe 16 respectively connected to the accommodating chamber, and a discharge pipe 17 connected to the accommodating chamber, the inner surface of the lower cover plate 11 is formed with a plurality of first ridges 111 arranged at intervals, the inner surface of the upper cover plate 12 is formed with a plurality of second ridges 121 staggered from the first ridges 111, and a reaction microchannel 14 is formed between the plurality of first ridges 111 and the plurality of second ridges 121. Each group of the heat exchange units 2 includes a heat exchange jacket 21 installed on the outer surface of the lower cover plate 11 or the upper cover plate 12 through a second sealing baffle 22, and a heat exchange medium cavity is formed between the heat exchange jacket 21 and the lower cover plate 11 or the upper cover plate 12; each group of the heat exchange units 2 also includes a heat exchange medium inlet pipe 23 and a heat exchange medium outlet pipe 24 connected to the heat exchange medium cavity.

[0019] In step (a), the temperature of the nitration reaction is 0-35°C, preferably 2-30°C, and more preferably 10-15°C. In step (a), ice water is added dropwise to the reaction solution after the nitration reaction is completed, stirred and filtered at 0-5°C, then washed with ice water and dried to obtain 5-nitrovanillin. In step (b), after the reaction, hydrochloric acid is used to quench, the ethyl acetate phase is collected by liquid separation, anhydrous sodium sulfate and activated carbon are added, stirred and filtered, and the filtrate is concentrated and then cooled and crystallized; then filtered, washed and dried. In step (b), anhydrous aluminum chloride is added in batches and the temperature is controlled not to exceed 30°C; pyridine is then added dropwise to control the temperature to 10-15°C; after the addition is completed, the temperature is raised to 60°C for reaction.

[0020] The present invention will be further described below in conjunction with the embodiments shown in the accompanying drawings. Example 1

[0021] This embodiment provides a microchannel reactor, such as Figure 3 As shown, it mainly includes a reaction unit 1 and two groups of heat exchange units 2.

[0022] The reaction unit 1 includes a lower cover plate 11 , an upper cover plate 12 , a first sealing baffle 13 , a reaction microchannel 14 , a methyl vanillin material pipe 15 , a nitric acid solution material pipe 16 , a discharge pipe 17 and other structures.

[0023] The upper cover plate 12 and the lower cover plate 11 are arranged opposite to each other and cooperate with each other; the first sealing baffle 13 is formed between the lower cover plate 11 and the upper cover plate 12 to form a accommodating chamber; the methyl vanillin material pipe 15 is connected to the accommodating chamber, and is used to transport the glacial acetic acid solution of methyl vanillin into the accommodating chamber; the nitric acid solution material pipe 16 is also connected to the accommodating chamber, and is used to transport the nitric acid solution into the accommodating chamber; the discharge pipe 17 is also connected to the accommodating chamber, and is used to output the reaction product of methyl vanillin and nitric acid.

[0024] In this embodiment, the inner surface of the lower cover plate 11 is formed with a plurality of first ridges 111 arranged at intervals, and the inner surface of the upper cover plate 12 (i.e., the inner surface of the upper cover plate 12 is arranged opposite to the inner surface of the lower cover plate 11) is formed with a plurality of second ridges 121 staggered and matched with the first ridges 111, so that a reaction microchannel 14 (i.e., a reaction zone) is formed between the plurality of first ridges 111 and the plurality of second ridges 121. It is also preferred to provide a first stopper located on both sides of the plurality of first ridges 111 on the inner surface of the lower cover plate 11, and a second stopper located on both sides of the plurality of second ridges 121 on the inner surface of the upper cover plate 12 (the first stopper and the second stopper cooperate with each other to achieve sealing), so as to prevent the reaction raw materials from leaking from both sides of the reaction unit 1, thereby improving the efficiency of the reaction. In addition, the first sealing baffle 13 can cooperate with the aforementioned first stopper and second stopper to seal, so as to limit the flow direction of the reaction raw materials (the raw materials can only be passed by Figure 3 from the left side to the right side).

[0025] In this embodiment, the orifice of the methyl vanillin feed pipe 15 is sealed and connected to the orifice of the nitric acid solution feed pipe 16, and the orifice of the nitric acid solution feed pipe 16 is also close to the inlet of the reaction microchannel 14, so that the acetic acid solution of methyl vanillin and the nitric acid solution are mixed and enter the reaction microchannel 14 for chemical reaction. The orifice of the discharge pipe 17 is located on the other side of the reaction microchannel 14 to output the reaction product of methyl vanillin and nitric acid.

[0026] Each set of heat exchange units 2 includes a heat exchange jacket 21 installed on the outer surface of the lower cover plate 11 or the upper cover plate 12 through a second sealing baffle 22, and a heat exchange medium cavity is formed between the heat exchange jacket 21 and the lower cover plate 11 (or the upper cover plate 12); each set of heat exchange units 2 also includes a heat exchange medium inlet pipe 23 and a heat exchange medium outlet pipe 24 connected to the heat exchange medium cavity. In this embodiment, the two sets of heat exchange units 2 can be combined to communicate with each other, so that the circulation of the heat exchange medium can be achieved. Example 2

[0027] This embodiment provides a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde, such as Figure 1 and Figure 2 As shown, the following steps are included: (a) methyl vanillin dissolved in glacial acetic acid is subjected to nitration reaction with nitric acid solution in a microchannel reactor (using the reactor in Example 1) to obtain 5-nitro vanillin; The details are as follows: dissolve 200g (1.31mol) of methyl vanillin in 640g of glacial acetic acid (10.66mol) and add to the first raw material tank; add 140.1g of 65% nitric acid (1.32mol) to the second raw material tank, set the flow rate of the pump group: the flow setting value of the first pump: 3.39mL / min, the upper limit alarm value of the first pump 6.78mL / min, the lower limit alarm value of the first pump 2.03mL / min (the first pump is connected to the methyl vanillin material pipe 15); the flow rate of the second pump Set value: 0.55mL / min, upper limit alarm value of the second pump 1.10mL / min, lower limit alarm value of the second pump 0.33mL / min (the second pump is connected to the nitric acid solution pipe 16); pressure setting (pressure in the microchannel reactor): upper limit alarm value of pressure 1Bar, upper limit shutdown value of pressure 1.5Bar; reaction zone temperature setting: temperature setting value: 10℃, upper limit alarm value of temperature: 30℃, lower limit alarm value of temperature: 2℃, upper limit shutdown value of temperature: 35℃, lower limit shutdown value of temperature: 0℃. After completing the parameter setting and pre-start preparation work, open the material feed valve (according to the existing conventional settings). Click "Start" to run the equipment. After the reaction is completed, add 3000g (166.67mol) of ice water to the reaction solution (i.e., the reaction solution after the nitration reaction is completed), stir at 0~5℃ for 30 minutes, filter, wash with ice water and dry to obtain 221g (1.12mol, yield 85.3%, purity 98.7%) of light yellow solid 5-nitro vanillin.

[0028] (b) reacting the 5-nitrovanillin and pyridine in the presence of aluminum chloride to generate 3,4-dihydroxy-5-nitrobenzaldehyde; The details are as follows: add 736g (8.35mol) of ethyl acetate to a 5L reactor, add 221g of the above-mentioned 5-nitrovanillin, cool to 10°C in an ice bath, then start adding 186.8g (1.40mol) of anhydrous aluminum chloride in batches, and control the temperature not to exceed 30°C during the process; after the addition is completed, add 369g (4.19mol) of ethyl acetate, start nitrogen protection, and continue to cool to 10°C; start to drop 443g (5.60mol) of pyridine, and control the temperature during the addition process at 10-15°C; after the addition is completed, heat to 60°C, keep warm for 3.5h, then take a sample of the reaction liquid for detection (the reaction liquid is quenched with hydrochloric acid), and the ethyl acetate phase enters the liquid phase (5-nitrovanillin ≤0.1% is qualified): if it fails to meet the requirements, continue to keep warm for 30 minutes before detection. After the reaction is completed, the temperature is lowered to 50°C, and 2273.1g (5.61mol) of 9% hydrochloric acid (mass concentration) is slowly added dropwise, and the temperature of the dropwise addition process is ≤65°C. After the dropwise addition is completed, the mixture is kept at 50°C and stirred for 30 minutes. After the stirring is completed, liquid separation begins. After adding 331.5g (3.76mol) of ethyl acetate to the lower aqueous phase, the mixture is stirred for 30 minutes and then separated. The lower aqueous phase is washed once with 331.5g (3.76mol) of ethyl acetate. The ethyl acetate phase obtained by the two washes is combined with the upper liquid of the liquid separation. After the combined ethyl acetate phase is added with 331.5g (18.42mol) of drinking water, the mixture is stirred for 30 minutes and then separated. The upper ethyl acetate phase is washed once with 331.5g (18.42mol) of drinking water. After washing, the content of 3,4-dihydroxy-5-nitrobenzaldehyde is detected by HPLC (≥99.5% qualified) (if unqualified, it is washed once with 331.5g (18.42mol) of drinking water and then re-tested) After the test is qualified, 590g (4.15mol) of anhydrous sodium sulfate and 35.4g (2.95mol) of activated carbon are added, stirred for 30 minutes and then filtered; the obtained filtrate is transferred to a 2L reactor and concentrated under negative pressure at 60℃, and the vacuum degree is ≤-0.07MPa (displayed value). The filtrate is concentrated until a small amount of solid precipitates, and the volume is about 1 / 3 of the original volume. Stop heating, fill with nitrogen to normal pressure and start cooling. After cooling to 0~5℃, filter while it is cold. The filter cake is washed with 110.5g (2.01mol) of glacial ethyl acetate and then dried at 60℃ in vacuum to obtain 190.3g (1.04mol) of yellow solid 3,4-dihydroxy-5-nitrobenzaldehyde, the stage yield is 92.7%, the total yield is 79.1%, and the purity is 99.9%. Figure 4 as shown). Example 3

[0029] This embodiment provides a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde, which is basically the same as that in Embodiment 2, except that in step (a), 126.1 g of 65% nitric acid (1.19 mol) is added to the second raw material tank to obtain 198.2 g of light yellow solid 5-nitrovanillin (1.01 mol, yield 76.4%, purity 98.4%). Example 4

[0030] This embodiment provides a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde, which is basically the same as that in Example 2, except that in step (a), 294.2 g of 65% nitric acid (2.77 mol) is added to the second raw material tank to obtain 229 g of light yellow solid 5-nitrovanillin (1.16 mol, yield 88.3%, purity 99.0%). Example 5

[0031] This embodiment provides a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde, which is basically the same as that in Embodiment 2, except that: in step (b), 736 g (8.35 mol) of ethyl acetate is added to a 5 L reactor, 221 g of the above-mentioned 5-nitrovanillin is added, and after cooling to 10° C. in an ice bath, 133.4 g (1.0 mol) of anhydrous aluminum chloride is added in batches, and the process temperature is controlled not to exceed 30° C.; after the addition is completed, 369 g (4.19 mol) of ethyl acetate is added, nitrogen protection is turned on, and the temperature is continued to be lowered to 10° C.; 443 g (5.60 mol) of pyridine is added dropwise; The final yellow solid 3,4-dihydroxy-5-nitrobenzaldehyde was 152.6 g (stage yield 74.4%, total yield 63.5%, purity 99.9%). Example 6

[0032] This embodiment provides a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde, which is basically the same as that in Embodiment 2, except that: in step (b), 736 g (8.35 mol) of ethyl acetate is added to a 5 L reactor, 221 g of the above-mentioned 5-nitrovanillin is added, and after cooling to 10° C. in an ice bath, 266.68 g (2.0 mol) of anhydrous aluminum chloride is added in batches, and the process temperature is controlled not to exceed 30° C.; after the addition is completed, 369 g (4.19 mol) of ethyl acetate is added, nitrogen protection is turned on, and the temperature is continued to be cooled to 10° C.; 443 g (5.60 mol) of pyridine is added dropwise; The final yellow solid 3,4-dihydroxy-5-nitrobenzaldehyde was 194.8 g (1.06 mol, step yield 95.0%, total yield 81.0%, purity 99.9%).

[0033] Comparative Example 1 This example provides a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde, which is basically the same as that in Example 2, except that a conventional reaction kettle is used instead of the microchannel reactor in Example 1; 188.1 g of light yellow solid 5-nitrovanillin is obtained (yield 72.5%, purity 96.7%).

[0034] Comparative Example 2 This example provides a method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde, which is basically the same as that in Example 2, except that: the temperature setting of the reaction zone: temperature setting value: 40~50°C; 196.3g of light yellow solid 5-nitrovanillin is obtained (yield 75.6%, purity 82.4%).

[0035] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde, characterized in that: The following steps are involved: (a) methyl vanillin dissolved in glacial acetic acid is subjected to nitration reaction with nitric acid solution in a microchannel reactor to obtain 5-nitro vanillin; (b) reacting the 5-nitrovanillin with pyridine in the presence of aluminum chloride to generate 3,4-dihydroxy-5-nitrobenzaldehyde.

2. The method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde according to claim 1, characterized in that: In step (a), the molar ratio of the methyl vanillin to the nitric acid in the nitric acid solution is 1:0.9-2.

1.

3. The method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde according to claim 2, characterized in that: In step (b), the molar ratio of mono-nitrovanillin, aluminum chloride and pyridine is 1:0.9-2.5:2-6.

4. The method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde according to claim 1 or 2, characterized in that: The microchannel reactor comprises a reaction unit (1) and two groups of heat exchange units (2) formed on both sides of the reaction unit (1) for exchanging heat with the reaction unit. The reaction unit (1) comprises a lower cover plate (11), an upper cover plate (12) matched with the lower cover plate (11), a first sealing baffle plate (13) formed between the lower cover plate (11) and the upper cover plate (12) to form a receiving chamber, a methyl vanillin material pipe (15) and a nitric acid solution material pipe (16) respectively connected to the receiving chamber, and a discharge pipe (17) connected to the receiving chamber. The inner surface of the lower cover plate (11) is formed with a plurality of first convex strips (111) arranged at intervals, and the inner surface of the upper cover plate (12) is formed with a plurality of second convex strips (121) staggered with the first convex strips (111), and a reaction microchannel (14) is formed between the plurality of first convex strips (111) and the plurality of second convex strips (121).

5. The method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde according to claim 4, characterized in that: Each group of the heat exchange units (2) comprises a heat exchange jacket (21) mounted on the outer surface of the lower cover plate (11) or the upper cover plate (12) via a second sealing baffle (22), wherein a heat exchange medium cavity is formed between the heat exchange jacket (21) and the lower cover plate (11) or the upper cover plate (12); each group of the heat exchange units (2) further comprises a heat exchange medium inlet pipe (23) and a heat exchange medium outlet pipe (24) connected to the heat exchange medium cavity.

6. The method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde according to claim 2, characterized in that: In step (a), the temperature of the nitration reaction is 0-35°C, preferably 2-30°C, and more preferably 10-15°C.

7. The method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde according to claim 6, characterized in that: In step (a), ice water is added dropwise to the reaction solution after the nitration reaction is completed, stirred at 0-5° C., filtered, washed with ice water, and dried to obtain 5-nitrovanillin.

8. The method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde according to claim 3, characterized in that: In step (b), after the reaction, the reaction is quenched with hydrochloric acid, the ethyl acetate phase is separated and collected, anhydrous sodium sulfate and activated carbon are added, stirred and filtered, the filtrate is concentrated, cooled and crystallized; and then filtered, washed and dried.

9. The method for synthesizing 3,4-dihydroxy-5-nitrobenzaldehyde according to claim 8, characterized in that: In step (b), anhydrous aluminum chloride is added in batches and the temperature is controlled not to exceed 30° C.; pyridine is then added dropwise and the temperature is controlled at 10-15° C.; after the addition is completed, the temperature is raised to 60° C. for reaction.

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