A method for preparing veratraldehyde

Abstract

The present application relates to the fine chemical preparation technical field, specifically to a kind of preparation method of veratraldehyde, comprising the following steps: step 1), in organic acid solvent, with veratrole and glyoxylic acid as raw material, preparation intermediate 3,4-dimethoxyphenyl glycolic acid;Step 2), oxidation reaction is carried out, and intermediate 3,4-dimethoxyphenyl glycolic acid is oxidized into veratraldehyde.The preparation method of veratraldehyde provided by the present application uses homogeneous reaction;Reduce catalyst consumption;Improve the yield and purity of veratraldehyde;Shorten reaction time;Avoid using high-pollution raw materials;Process environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of fine chemical preparation technology, specifically to a method for preparing veratral. Background Technology

[0002] Veratral, also known as methyl vanillin or methyl vanillin, has the chemical name 3,4-dimethoxybenzaldehyde. Its structural formula is as follows:

[0003]

[0004] Veratral is a compound that appears as white or pale yellow flaky crystals with unique physicochemical properties. Its melting point is between 40-43℃, and its boiling point is between 281-285℃. Veratral is readily soluble in ethanol and ethers, but only slightly soluble in hot water and insoluble in cold water. Furthermore, veratral is highly sensitive to air. Solutions of veratral can undergo oxidation under light to produce 3,4-dimethoxybenzoic acid. This substance is an important fragrance ingredient, possessing a distinctive aroma in natural vanilla beans and jasmine aldehydes. Therefore, veratral is widely used in the formulation of various fragrances and is also an important component of food and cosmetic additives. In addition, veratral can be used as a raw material for the synthesis of other fragrances, such as vanillin, isovillin, and veratric acid. It is also a very important pharmaceutical intermediate, playing a crucial role in the synthesis of dopamine-like drugs, the antihypertensive drug prazosin, the arthritis treatment tetrahydropalmatine, and the antihistamine tranicotinamide. Therefore, veratral holds an irreplaceable position in the field of pharmaceutical synthesis. Veratral has a wide range of applications and market demand. With the increasing demand for fragrances, food, cosmetics, and pharmaceutical products, the demand for veratral is also increasing year by year.

[0005] The current methods for synthesizing veratral are as follows:

[0006] ① Using vanillin as the starting material:

[0007] The main method for synthesizing veratral is the reaction of vanillin with a methylating agent under alkaline conditions via a phase transfer catalyst, yielding approximately 94% and achieving a purity of 97-99%. However, this method uses vanillin as a raw material, which is expensive, and the synthesis of veratral generates a large amount of wastewater, causing significant environmental pollution. The chemical reaction formula is as follows:

[0008]

[0009] ② Using 3,4-dimethoxytoluene as the starting material:

[0010] 3,4-Dimethoxytoluene is derived from coal chemical and petrochemical industries, making it widely available, but its purification is relatively difficult. This route can be further divided into oxidation and chlorination methods.

[0011] A. Oxidation method

[0012] The oxidation method involves oxidizing 3,4-dimethyltoluene to veratral in the presence of catalysts such as FeSO4-ZnAc2 or Pt-C, V-Ag-Cu, using K2S2O8 or air as the oxidant. The chemical reaction formula is as follows:

[0013]

[0014] B. Chlorination hydrolysis method

[0015] Chlorination of 3,4-dimethoxytoluene yields the intermediate 3,4-dimethoxybenzyl dichloro, which is then hydrolyzed in the presence of sodium bicarbonate to give veratral. The chemical reaction formula is as follows:

[0016]

[0017] The main drawbacks of these two methods are that the raw material price is high, sometimes even higher than the product price, and the chlorination hydrolysis method also has significant waste problems.

[0018] ③ Using veratrine as a starting material:

[0019] A. Gatterman's method

[0020] The Gatterman process first involves the cyanidation of veratroxylin and hydrogen cyanide and hydrogen chloride in the presence of zinc chloride, followed by hydrolysis under acidic conditions to produce veratraldehyde, with a yield of approximately 70%. However, hydrogen cyanide is highly toxic, and this synthetic method has been phased out. The chemical reaction formula is as follows:

[0021]

[0022] B. Sommelet method

[0023] The Sommelet method involves two steps: veratrine chloromethylation to generate 3,4-dimethoxybenzyl chloride, which then undergoes a Sommelet reaction with hexamethylenetetramine to produce veratrine, with a yield of 50-60%. The 3,4-dimethoxybenzyl chloride generated by this method is highly reactive and prone to polymerization, affecting the yield. Although this method avoids the use of highly toxic compounds, its low yield and complex operation make it difficult to scale up for industrial production. The chemical reaction formula is as follows:

[0024]

[0025] C. Vilsmeier method

[0026] The Vilsmeier process is an important method for synthesizing aromatic and heterocyclic aldehydes. This route uses veratrine as a starting material, undergoing an acylation reaction in the presence of Lewis acids to generate veratrine in one step. Although the yield can reach 93-96% and the purity 97-99%, it requires the use of highly polluting chemical raw materials, such as phosphorus oxychloride, aluminum trichloride, and sulfuryl chloride, resulting in significant environmental pollution. The chemical reaction formula is as follows:

[0027]

[0028] D. Glyoxylic acid method

[0029] CN110483264A discloses a two-step synthesis of veratral. This method uses dichloromethane, 1,2-dichloroethane, petroleum ether, toluene, etc., as solvents, and employs solid superacids SO2- / TiO2, SO2- / Fe2O3, and SO2- / ZrO2 as catalysts to prepare 3,4-dimethoxyphenylethanolic acid from veratral ether and glyoxylic acid. Then, 3,4-dimethoxyphenylethanolic acid is oxidized to obtain veratral under the action of a single oxidant or an oxidant combined with a catalyst. The first step of this method is a heterogeneous reaction, requiring solid superacid catalysis, which makes recovery difficult and costs high. The yield of the intermediate 3,4-dimethoxyphenylethanolic acid is 95-97%, the total yield of veratral is 94-97%, and the purity is 99.3-99.7%. The specific reaction formula is as follows:

[0030]

[0031] In summary, current methods for preparing veratral have the following shortcomings:

[0032] (1) Although the yield of veratral prepared from vanillin is about 94% and the purity is 97-99%, this synthesis method uses vanillin as raw material, which is expensive and generates a large amount of wastewater, causing significant environmental pollution.

[0033] (2) Using veratrine as a raw material to prepare veratrine, the one-step synthesis of veratrine described by the Vilsmeier method can achieve a yield of 93-96% and a purity of 97-99%, but it requires the use of highly polluting chemical raw materials, such as phosphorus oxychloride, aluminum trichloride, and sulfuryl chloride, which will cause significant environmental pollution.

[0034] (3) The two-step synthesis of veratraldehyde using veratraldehyde and glyoxylic acid can avoid the use of highly polluting raw materials. However, the first step reaction is a heterogeneous reaction, which requires a solid strong acid catalyst. The catalyst is used in large quantities and is not easy to recover, resulting in high cost. Summary of the Invention

[0035] This invention provides a method for preparing veratral, which solves the problems of requiring a large amount of phase transfer catalyst in the preparation process, the difficulty in recovering the phase transfer catalyst, and the high preparation cost.

[0036] This application provides the following technical solution:

[0037] A method for preparing veratral includes the following steps:

[0038] Step 1) In an organic acid solvent, using veratrine and glyoxylic acid as raw materials, the intermediate 3,4-dimethoxyphenylethanolic acid is prepared; the specific reaction formula is as follows:

[0039]

[0040] Step 2) An oxidation reaction is carried out to oxidize the intermediate 3,4-dimethoxyphenylethanolic acid to veratral. The specific reaction formula is as follows:

[0041]

[0042] The principle and advantages of this scheme are as follows: In reaction systems using toluene, dichloromethane, ethyl acetate, petroleum ether, etc., as solvents, veratril ether and glyoxylic acid form a two-phase system of water and oil, requiring a large amount of phase transfer catalyst, which is difficult to recover and costly. However, in reaction systems using organic acids as solvents, veratril ether and glyoxylic acid form a homogeneous system, eliminating the water-oil two-phase problem and thus eliminating the need for a phase transfer catalyst. Table 1 below shows a comparison of the reactions of veratril ether and glyoxylic acid in different solvents. In organic acid solvents, the intermediate 3,4-dimethoxyphenylethanolic acid can be prepared without a phase transfer catalyst. Furthermore, organic acid solvents are widely available, inexpensive, and readily available; they can be recovered and reused through filtration and distillation, eliminating waste and being environmentally friendly. The reaction of veratril ether and glyoxylic acid does not require a phase transfer catalyst, avoiding the need for catalyst recovery, improving production efficiency, and reducing production costs.

[0043] Table 1. Comparison of the reactions of veratrine ether and glyoxylic acid in different solvents

[0044]

[0045] Preferably, the organic acid solvent in step 1) is any one of formic acid, acetic acid, and propionic acid, with acetic acid being the most preferred.

[0046] In this technical solution, as shown in Table 1, the reaction time of veratrine ether and glyoxylic acid in acetic acid solvent is shorter than that in other organic acid solvents, thus improving the preparation efficiency.

[0047] Preferably, the glyoxylic acid in step 1) is an aqueous solution of glyoxylic acid with a mass fraction of 40% to 50%. More preferably, it is a 50% aqueous solution of glyoxylic acid.

[0048] In this technical solution, a 50% glyoxylic acid aqueous solution is inexpensive and readily available, and has a good reaction effect.

[0049] Preferably, the mass ratio of the organic acid solvent and veratrine ether in step 1) is 4 to 7:1, more preferably 5:1; the molar ratio of veratrine ether and glyoxylic acid is 1 to 1.4:1, more preferably 1.2:1.

[0050] In this technical solution, when the molar ratio of veratroxyethanol to glyoxylic acid is constant, the yield of intermediate 3,4-dimethoxyphenylethanolic acid is highest when the mass ratio of organic acid solvent to veratroxyethanol is 4 to 7:1; conversely, when the mass ratio exceeds this range, the yield of intermediate 3,4-dimethoxyphenylethanolic acid gradually decreases.

[0051] Preferably, in step 1), either veratrine or glyoxylic acid is mixed with an organic acid solvent to obtain a mixed solution. Under the condition of stirring speed of 60-70 r / min, another reagent is added dropwise to the mixed solution at a dropping rate of 5-6 g / min. More preferably, glyoxylic acid solution is added dropwise to the mixed solution of veratrine and organic acid solvent at a stirring speed of 60 r / min and a dropping rate of 5.3 g / min.

[0052] In this technical solution, the yield of intermediate 3,4-dimethoxyphenylethanolic acid is highest when glyoxylic acid solution is added dropwise to a mixed solution of veratrine ether and organic acid solvent, with a stirring speed of 60 r / min and a dropping rate of 5.3 g / min. This method is also easy to operate and has high preparation efficiency.

[0053] Preferably, the reaction temperature in step 1) is 20–50°C, more preferably 30°C; and the reaction time is 3–6 h, more preferably 4 h.

[0054] Compared with existing technologies that require phase transfer catalysts, this technical solution does not require phase transfer catalysts, produces fewer byproducts during the reaction process, does not require maintaining a low temperature, reduces energy consumption, and is both economical and environmentally friendly.

[0055] Preferably, the oxidant in the oxidation reaction in step 2) is air or oxygen; the molar ratio of oxygen to 3,4-dimethoxyphenylethanolic acid is 2 to 5:1, preferably 3:1.

[0056] In this technical solution, air is used as the oxidant, which is inexpensive, readily available, and exhibits good reaction performance. Under constant reaction conditions, the highest yield of veratral is achieved when the molar ratio of oxygen to 3,4-dimethoxyphenylethanolic acid is 2–5:1; conversely, outside this molar ratio range, the yield of veratral gradually decreases.

[0057] Preferably, the catalyst for the oxidation reaction in step 2) is any one of ferric chloride and ferric sulfate and a combination of cobalt chloride, and the mass ratio of the catalyst to 3,4-dimethoxyphenylethanolic acid is 0.01 to 0.05:1, preferably 0.03:1.

[0058] Preferably, the mass ratio of ferric chloride or ferric sulfate to cobalt chloride is 0.5 to 2:1; more preferably, it is ferric sulfate and cobalt chloride, with a mass ratio of ferric sulfate to cobalt chloride of 1:1.

[0059] Preferably, the reaction pressure in step 2) is 0.01-0.1 MPa, more preferably 0.04 MPa; the reaction temperature is 70-100°C, more preferably 80°C; and the reaction time is 1-2 h, more preferably 1.5 h.

[0060] In this technical solution, ferric chloride and ferric sulfate are strong oxidizing agents and inexpensive, but they are prone to over-oxidation when used alone. Cobalt chloride has weak oxidizing properties and cannot act as an oxidation catalyst when used alone. Combining these two catalysts, without requiring additional pressure and at a lower oxidation initiation temperature, yields 99.43–99.86% of veratraldehyde. Under constant reaction conditions, the purity and yield of veratraldehyde are highest when the mass ratio of catalyst to 3,4-dimethoxyphenylethanolic acid is 0.01–0.05:1; conversely, outside this range, the purity and yield of veratraldehyde gradually decrease. Under constant reaction conditions, the purity and yield of veratraldehyde are highest when the mass ratio of ferric chloride or ferric sulfate to cobalt chloride is 0.5–2:1; conversely, outside this range, the purity and yield of veratraldehyde gradually decrease.

[0061] Compared to commonly used catalysts on the market, such as copper salts and cuprous salts like copper sulfate and cuprous sulfate, which require pressure of 1–5 MPa during oxidation to achieve a veratraldehyde yield of 98.79–99.36%, this technical solution eliminates the need for additional pressure while still ensuring a veratraldehyde yield of 99.43–99.86%, while simultaneously reducing energy consumption and environmental pollution.

[0062] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0063] (1) The reaction yield is high. The yield of the intermediate 3,4-dimethoxyphenylethanolic acid prepared by using a homogeneous system without phase transfer catalyst is 98.17-99.87%. The yield of the oxidation reaction to prepare veratral is 99.43-99.86%; the overall yield of veratral in the two-step reaction is 97.61-99.73%.

[0064] (2) The product has high purity. It can be obtained by extraction followed by distillation. The purification is simple, and the purity of the prepared veratral is 99.5-99.8%.

[0065] (3) The reaction process is simple, avoids the use of highly polluting raw materials, has no waste problems, is environmentally friendly, and has low production costs. Detailed Implementation

[0066] The following detailed description provides further details on specific embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the materials and reagents used are all commercially available.

[0067] A method for preparing veratral includes the following steps:

[0068] Step 1) In a three-necked flask, add any one of the following reagents: veratrine, glyoxylic acid (40-50% by mass), and acetic acid solvent to obtain a mixed solution. While stirring at 60-70 r / min, add another reagent dropwise to the mixed solution at a rate of 5-6 g / min. The mass ratio of acetic acid solvent to veratrine is 4-7:1, and the molar ratio of veratrine to glyoxylic acid is 1-1.4:1. Control the reaction temperature at 20-50℃. After the glyoxylic acid aqueous solution is added, continue the reaction at this temperature for 3-6 hours. Monitor the reaction until the HPLC content of veratrine is below 0.5%, indicating the reaction endpoint has been reached, yielding the intermediate 3,4-dimethoxyphenylethanolic acid solution.

[0069] Step 2): In a three-necked flask, add the 3,4-dimethoxyphenylethanolic acid solution obtained in Step 1) and a catalyst. The mass ratio of catalyst to 3,4-dimethoxyphenylethanolic acid is 0.01–0.05:1. The catalyst is any one of ferric chloride or ferric sulfate and cobalt chloride, with a mass ratio of ferric chloride or ferric sulfate to cobalt chloride of 0.5–2:1. Control the reaction temperature at 70–100°C, introduce air, and maintain the molar ratio of oxygen in the air to 3,4-dimethoxyphenylethanolic acid at 2–5:1. Maintain the reaction pressure at 0.01–0.1 MPa, and monitor the reaction until the HPLC content of 3,4-dimethoxyphenylethanolic acid is below 0.5%, indicating the reaction endpoint has been reached. The reaction time is 1–2 hours. Then, perform vacuum distillation to recover the acetic acid solvent and unreacted veratrol ether. Finally, perform a second vacuum distillation to obtain the product veratrol aldehyde.

[0070] Example 1

[0071] In a 500 ml three-necked flask, 250.0 g of acetic acid and 50.0 g of veratroxyethanol were added to prepare a veratroxyethanol solution. Under stirring at 60 rpm, 53.6 g of a 50% glyoxylic acid aqueous solution was added dropwise to the veratroxyethanol solution at a dropping rate of 5.3 g / min, with the temperature controlled at 30 °C. The reaction continued at this temperature after the addition was complete, and samples were taken for monitoring until the veratroxyethanol HPLC content was below 0.5%, indicating the reaction endpoint. The reaction time was 3 h. The yield of 3,4-dimethoxyphenylethanolic acid, calculated as veratroxyethanol, was 98.53%.

[0072] Example 2

[0073] In a 500 ml three-necked flask, 250.0 g of acetic acid and 53.6 g of 50% glyoxylic acid were added to prepare a glyoxylic acid solution. Under stirring at 60 rpm, 50.0 g of veratrine was added dropwise to the glyoxylic acid solution at a dropping rate of 5.3 g / min, with the temperature controlled at 30 °C. The reaction continued at this temperature after the addition was complete, and samples were taken for monitoring until the veratrine content was below 0.5% according to HPLC, indicating the reaction endpoint was reached. The reaction time was 3 h. The yield of 3,4-dimethoxyphenylethanolic acid (based on veratrine) was 98.20%.

[0074] As can be seen from Examples 1 and 2, under the same reaction conditions, the yield of 3,4-dimethoxyphenylethanolic acid is higher when glyoxylic acid solution is added dropwise to a mixed solution of veratrine ether and organic acid solvent.

[0075] Examples 3-17 and Comparative Examples 1-7

[0076] Acetic acid and veratrol were added to a 500 ml three-necked flask to prepare a veratrol solution. Under stirring at 60 rpm, a 50% glyoxylic acid aqueous solution was added dropwise to the veratrol solution at a dropping rate of 5.3 g / min. The reaction continued at this temperature after the addition was complete, and samples were taken for monitoring until the veratrol content was below 0.5% by HPLC, indicating the reaction endpoint had been reached. The material ratios of acetic acid, veratrol, and glyoxylic acid, the reaction temperature, the reaction time, and the yield of the intermediates are shown in Table 2 below.

[0077] Table 2. Intermediate Yield Comparison Table

[0078]

[0079] As shown in Table 2, under the same reaction conditions, the yield of the intermediate 3,4-dimethoxyphenylethanolic acid was greater than 98.20% when the mass ratio of acetic acid solvent to veratroxyethanol was 4–7:1. The highest yield was achieved when the mass ratio of acetic acid solvent to veratroxyethanol was 5:1. Under the same reaction conditions, the highest yield of the intermediate 3,4-dimethoxyphenylethanolic acid was achieved when the molar ratio of veratroxyethanol to glyoxylic acid was 1.2:1. With the same material ratio, the highest yield of the intermediate 3,4-dimethoxyphenylethanolic acid was achieved at a reaction temperature of 30℃ and a reaction time of 4 h. As can be seen from Example 15, when the mass ratio of acetic acid solvent to veratrine ether is 5:1, the molar ratio of veratrine ether to glyoxylic acid is 1.2:1, the reaction temperature is 30°C, and the reaction time is 4h, the yield of the intermediate 3,4-dimethoxyphenylethanolic acid is the highest, reaching 99.87%.

[0080] Examples 18-20 and Comparative Examples 8-11

[0081] In a 500ml three-necked flask, the 3,4-dimethoxyphenylethanolic acid solution obtained in Example 15 and the catalyst were added, and the reaction temperature was controlled at 70°C. Air was introduced, and the molar ratio of oxygen in the air to 3,4-dimethoxyphenylethanolic acid was maintained at 2-3:1. The pressure was kept at 0.01MPa, and samples were taken for monitoring until the HPLC content of 3,4-dimethoxyphenylethanolic acid was lower than 0.5%, indicating that the reaction had reached its endpoint. The reaction time was 1 hour. Then, vacuum distillation was performed to recover the acetic acid solvent and unreacted veratril ether. Finally, a second vacuum distillation was performed to obtain the product veratrilaldehyde. Table 3 below shows the purity and yield of veratrilaldehyde under different catalysts.

[0082] Table 3. Comparison of Purity and Yield of Veratraldehyde under Different Catalysts

[0083]

[0084] As shown in Table 3, under the same reaction conditions, the combination of two catalysts effectively improves the purity and yield of veratraldehyde compared to a single catalyst. Under the same reaction conditions, the purity and yield of veratraldehyde are even higher when using a combination of ferric sulfate and cobalt chloride catalysts.

[0085] Examples 21-39 and Comparative Examples 12-15

[0086] In a 500ml three-necked flask, the 3,4-dimethoxyphenylethanolic acid solution obtained in Example 18 and the catalyst were added. Sampling was performed until the HPLC content of 3,4-dimethoxyphenylethanolic acid was below 0.5%, indicating the reaction endpoint had been reached. Then, vacuum distillation was performed to recover the acetic acid solvent and unreacted veratril ether. Finally, a second vacuum distillation was performed to obtain the product veratril aldehyde. The material ratios, reaction temperature, reaction pressure, reaction time, and the purity and yield of veratril aldehyde are shown in Table 4 below.

[0087] Table 4. Comparison of Purity and Yield of Veratralaldehyde

[0088]

[0089] As shown in Table 4, when the mass ratio of ferric sulfate to cobalt chloride in the catalyst is 0.5–2:1, the mass ratio of the catalyst to 3,4-dimethoxyphenylethanolic acid is 0.01–0.05:1, the molar ratio of oxygen in the air to 3,4-dimethoxyphenylethanolic acid is 2–5:1, the reaction temperature is 70℃–100℃, the reaction pressure is 0.01–0.1 MPa, and the reaction time is 1–2 h, the purity of veratral reaches 99.5%–99.8%, the yield of veratral based on 3,4-dimethoxyphenylethanolic acid is 99.43–99.86%, and the yield of veratral based on veratrine ether is 97.61–99.73%. As in Example 37, when the mass ratio of ferric sulfate to cobalt chloride in the catalyst was 1:1, the mass ratio of the catalyst to 3,4-dimethoxyphenylethanolic acid was 0.03:1, the molar ratio of oxygen in the air to 3,4-dimethoxyphenylethanolic acid was 3:1, the reaction temperature was 80°C, the reaction pressure was 0.04 MPa, and the reaction time was within 1.5 h, the purity of veratral reached 99.8%, the yield of veratral based on 3,4-dimethoxyphenylethanolic acid was 99.86%, and the yield of veratral based on veratral ether was 99.73%.

[0090] The above are merely embodiments of the present invention, and the invention is not limited to the fields covered by these embodiments. Commonly known structures and characteristics in the solutions are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solution of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing veratral, characterized in that, Includes the following steps: Step 1) In an organic acid solvent, using veratrine and glyoxylic acid as raw materials, the intermediate 3,4-dimethoxyphenylethanolic acid is prepared; the organic acid solvent is any one of formic acid, acetic acid, and propionic acid; the mass ratio of the organic acid solvent to veratrine is 4-7:1; the molar ratio of veratrine to glyoxylic acid is 1-1.4:

1. Step 2) An oxidation reaction is carried out to oxidize the intermediate 3,4-dimethoxyphenylethanolic acid to veratral; The catalyst for the oxidation reaction is any one of ferric chloride and ferric sulfate combined with cobalt chloride, and the mass ratio of the catalyst to 3,4-dimethoxyphenylethanolic acid is 0.01 to 0.05:1; the mass ratio of any one of ferric chloride and ferric sulfate to cobalt chloride is 0.5 to 2:

1.

2. The method for preparing veratral according to claim 1, characterized in that: Step 1) uses a glyoxylic acid aqueous solution with a mass fraction of 40% to 50%.

3. The method for preparing veratral according to claim 1, characterized in that: In step 1), either veratrine or glyoxylic acid is mixed with an organic acid solvent to obtain a mixed solution. Under the condition of stirring speed of 60-70 r / min, another reagent is added dropwise to the mixed solution at a dropping rate of 5-6 g / min.

4. The method for preparing veratral according to claim 1, characterized in that: The reaction temperature for step 1) is 20–50°C, and the reaction time is 3–6 h.

5. The method for preparing veratral according to claim 1, characterized in that: In step 2), the oxidant for the oxidation reaction is air or oxygen; the molar ratio of oxygen to 3,4-dimethoxyphenylethanolic acid is 2 to 5:

1.

6. The method for preparing veratral according to claim 1, characterized in that: The reaction pressure in step 2) is 0.01–0.1 MPa, the reaction temperature is 70–100 °C, and the reaction time is 1–2 h.

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