Catalyst, preparation method and application thereof

Abstract

The invention relates to a method for improving the yield of o-vanillin, and provides a novel metal ligand catalyst, the structural formula of which is as follows: # imgabs0 #, M represents a transition metal such as iron, manganese, copper and chromium, and R represents H or methyl. The catalyst is introduced into a condensation reaction, so that the ortho-position selectivity of mandelic acid can be greatly improved, and the yield of o-vanillin is further improved.

Description

Technical Field

[0001] The invention belongs to the field of catalysts, and specifically relates to a novel ligand catalyst and a preparation method thereof. The catalyst is used in the condensation reaction of glyoxylic acid and guaiacol to further improve the yield of o-vanillin. Background Art

[0002] Vanillin (vanillin) and o-vanillin (o-vanillin) are important chemical products that can be used as pharmaceutical and fine chemical intermediates. Vanillin is currently the world's largest spice with a strong milky flavor. It is widely used in food and daily chemical fields for flavor enhancement and fixation. Chemical methods are the main way to obtain vanillin. O-vanillin is a commonly used organic synthesis intermediate that can be used to synthesize 1,2,3-trimethoxybenzene, 1,2,3-trimethoxybenzene, brominated o-piperonal, phenolic epoxy resin, and 2,3-dimethoxybenzaldehyde. O-vanillin is also an important raw material for the production of berberine. The synthesis of industrial production of o-vanillin has not been reported. It is only obtained as a by-product of vanillin production after purification and separation. The global annual production of vanillin is about 20,000 to 30,000 tons, and the annual production of o-vanillin is only in the hundreds of tons level. The price of o-vanillin is higher than that of vanillin. How to improve the yield of o-vanillin has become the key to improving the competitiveness of vanillin projects.

[0003]

[0004] As can be seen from the above synthesis equation, the synthetic routes of vanillin and o-vanillin are basically the same. They both use guaiacol and glyoxylic acid as raw materials, and undergo condensation, oxidation and decarboxylation to obtain vanillin and o-vanillin respectively. The main difference between the two is the first step of condensation reaction. If the condensation product is an o-hydroxymandelic acid derivative (1-hydroxy-2-methoxymandelic acid), the final product is o-vanillin; if the condensation product is p-hydroxymandelic acid (3-methoxy-4-hydroxymandelic acid), the final product is vanillin. Therefore, if you want to increase the yield of vanillin reaction, you must first increase the yield of o-hydroxymandelic acid generated in the first step.

[0005] US Patent US535489 uses phenol and glyoxylic acid to synthesize o-hydroxymandelic acid, and uses metal salts and organic bases as catalysts to obtain o-hydroxymandelic acid with high selectivity. The process is an intermittent reaction, with large catalyst consumption and high production cost. Patent CN 1119312C discloses a method for industrial preparation of sodium o-hydroxymandelate, in which phenol and dihydroxyacetic acid solution are subjected to condensation reaction in two continuous reactors under the action of tertiary amine and trivalent metal cation catalysts at a temperature below 100°C and in an inert atmosphere, achieving an o-hydroxymandelic acid selectivity of about 84%, but the process is only applicable to o-hydroxymandelic acid and is not applied to 1-hydroxy-2-methoxymandelic acid. Patent CN102516045A discloses a method for preparing a mixture of o-vanillin and vanillin, using guaiacol and chloroform as raw materials, methanol as a medium, and dripping sodium hydroxide solution. The pH of the obtained product is adjusted to acidic with acid to obtain a mixture of o-vanillin and vanillin. However, the overall yield of this process is relatively low, making it a backward process for synthesizing vanillin. Summary of the invention

[0006] In order to improve the selectivity of 1-hydroxy-2-methoxymandelic acid in the condensation reaction product and further increase the proportion of o-vanillin in the final product, on the one hand, the present invention synthesizes a new type of metal ligand catalyst, and its structural formula is as follows:

[0007]

[0008] Wherein M represents a transition metal, such as iron, manganese, copper, chromium, etc., and R represents H or methyl.

[0009] On the other hand, the present invention also provides a method for preparing the above catalyst, comprising the following steps:

[0010] (1) 2-bromoquinoline reacts with 2-(trimethyltin chloride)quinoline to obtain a biquinoline derivative shown in compound 1;

[0011] (2) reacting the compound 1 obtained in step (1) with concentrated sulfuric acid to obtain a sulfonated derivative represented by compound 2;

[0012] (3) mixing the compound 2 obtained in step (2) with transition metal ions to obtain a metal ligand catalyst;

[0013] The structural formula of 2-(trimethyltin chloride)quinoline is Compound 1 is Compound 2 is

[0014] The following is a schematic diagram of the synthesis of this compound:

[0015]

[0016] The step (1) of the present invention is carried out under anhydrous and oxygen-free conditions.

[0017] The step (1) of the present invention can be carried out in solvent A, wherein the solvent A is selected from one or more of toluene, diethyl ether and tetrahydrofuran, preferably toluene and diethyl ether.

[0018] In step (1) of the present invention, the weight ratio of 2-bromoquinoline to solvent A is 1:(3-10), preferably 1:(5-8).

[0019] In step (1) of the present invention, the mass ratio of 2-bromoquinoline to 2-(trimethyltin chloride)quinoline is 1:(0.8-2.5), preferably 1:(1.2-1.8).

[0020] In step (1) of the present invention, the synthesis method of 2-(trimethyltin chloride)quinoline is as follows: under anhydrous and oxygen-free conditions, trimethyltin chloride and quinoline are reacted at 0-5°C to obtain the product.

[0021] The reaction temperature in step (1) of the present invention is 0-50°C, preferably 10-30°C.

[0022] The reaction time in step (1) of the present invention is 1-12 hours, and the preferred reaction temperature is 3-6 hours.

[0023] The concentrated sulfuric acid in step (2) of the present invention is fuming sulfuric acid or 98wt% concentrated sulfuric acid.

[0024] The reaction conditions of step (2) of the present invention are normal temperature and pressure.

[0025] The reaction time of step (2) of the present invention is 1 to 8 hours, preferably 3 to 5 hours.

[0026] The step (2) of the present invention is carried out in a solvent B, wherein the solvent B is selected from one or more of acetone, DMF, ethanol and methanol, preferably acetone or ethanol.

[0027] The mass ratio of compound 1 to solvent B in step (2) of the present invention is 1:(3-10), preferably 1:(5-8).

[0028] The mass ratio of sulfuric acid to compound 1 in step (2) of the present invention is (0.5-5):1, preferably (2-4):1.

[0029] In step (3) of the present invention, the metal ions are selected from aqueous solutions of ferric chloride, ferric nitrate, ferric sulfate, cupric chloride, cupric sulfate, cupric nitrate, cobalt chloride, cobalt sulfate and cobalt nitrate, and the preferred sources of metal ions are ferric sulfate and cobalt sulfate solutions.

[0030] The concentration of the metal ion solution in step (3) of the present invention is 5-15wt%.

[0031] In step (3) of the present invention, the mass ratio of the metal ion solution to the compound 2 is (5-20):1, preferably (10-15):1.

[0032] The reaction temperature of step (3) of the present invention is 10-60°C, preferably 30-50°C.

[0033] The reaction time of step (3) of the present invention is 0.1 to 3 hours, preferably 0.5 to 1.5 hours.

[0034] On the other hand, the present invention also provides a method for preparing o-vanillin, which comprises: according to the mass ratio of catalyst: guaiacol: glyoxylic acid being (0.001-0.01): (0.8-1.2): 1, guaiacol and glyoxylic acid are subjected to a condensation reaction, the reaction temperature is 20-40°C, the reaction pressure is normal pressure, the reaction liquid pH is 12-13, and the reaction time is 2-8h.

[0035] The reaction liquid after the condensation is oxidized, decarboxylated and refined to obtain o-vanillin and vanillin products, that is, sulfuric acid is added to the reaction liquid after the condensation to adjust the pH to 4-5, and toluene is added to extract and recover guaiacol, and the mass ratio of toluene to water phase is 1: (3-5). Then the reaction liquid is adjusted to alkaline, the pH is controlled to 12-13, and it is reacted with 10%-20% copper oxide at a mass ratio for 4-8h at normal pressure and 100°C to obtain an oxidation reaction liquid containing 3-methoxy-4-hydroxybenzoic acid, after filtering and separating the copper oxide, 3-5% sulfuric acid is added to carry out decarboxylation reaction to obtain crude vanillin, and the crude vanillin is further distilled, and the number of distillation plates is about 20-25, so that o-vanillin and pure vanillin can be obtained.

[0036] The above is a schematic diagram of the preparation scheme of o-vanillin. The specific method can refer to patent CN102010310A.

[0037] The beneficial effects of the present invention are:

[0038] A novel metal ion ligand catalyst is synthesized by the method of the present invention, and is applied to the reaction of condensing guaiacol and glyoxylic acid to prepare mandelic acid. The biquinoline ligand has a large specific surface area and steric hindrance. The large specific surface area can promote the dispersion effect of the bound metal ions and can have a larger contact area with the reactants; in addition, the biquinoline has a suitable conjugated structure and a certain acidic activation site, which can inhibit the selectivity of the para position, thereby improving the selectivity of the ortho position product. The introduction of sulfonic acid groups on the ligand can make the catalyst soluble in water, and the reaction is a homogeneous reaction, which can greatly improve the reaction activity and avoid the trouble of catalyst separation. Transition metal ions can improve the reaction activity of the condensation reaction, and the metal ligand catalyst obtained by combining with biquinoline can greatly improve the yield of 1-hydroxy-2-methoxymandelic acid in the condensation reaction. After oxidation, decarboxylation and purification processes, the proportion of o-vanillin in the final product can be further improved. DETAILED DESCRIPTION

[0039] The following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the rights claimed by the present invention.

[0040] Raw materials and sources;

[0041] 2-Bromoquinoline 98% J&K Technology Co., Ltd.

[0042] Toluene 99% Sinopharm Group Co., Ltd.

[0043] Concentrated sulfuric acid 98% Sinopharm Group Co., Ltd.

[0044] Copper Sulfate 99.5%Beijing Inokai Technology Co., Ltd.

[0045] Guaiacol 99% Aladdin Technology Co., Ltd.

[0046] Glyoxylic acid 50% Aladdin Technology Co., Ltd.

[0047] Test method: Agilent liquid chromatography instrument and external standard method were used to calibrate the content of glyoxylic acid, o- / p-mandelic acid and guaiacol in the system. The mobile phase of the liquid chromatography was acetonitrile and phosphoric acid aqueous solution, the chromatographic column was a benzene column, the column temperature was 40-45°C, and the detector was 230nm-250nm.

[0048] Synthesis of 2-(trimethyltin chloride)quinoline: Under anhydrous and oxygen-free conditions, at 5°C, trimethyltin chloride and quinoline are reacted in a molar ratio of 1:1 for 10 hours to obtain the product.

[0049] Example 1

[0050] In anhydrous, oxygen-free, 20°C conditions, 40g of 2-bromoquinoline and 200g of toluene were injected into a three-necked flask, and 40g of 2-(trimethyltin chloride)quinoline was slowly added to the reaction system. After the addition was completed, the reaction was continued for 3h, and water was added to quench. The upper oil phase was separated by rotary evaporation and column chromatography was performed. The eluent was petroleum ether and ethyl acetate, and the ratio of the two was 3:1. Compound 1 was separated and purified. At room temperature and pressure, 60g of compound 1 was dissolved in 300g of toluene, and 120g of 98% concentrated sulfuric acid was added to the reaction solution. The reaction was continued for 4h. After the reaction was completed, the reaction solution was freed of toluene and recrystallized with ethanol and water (1:8) solution. The mass ratio of the solvent to the crude product was 4:1. The recrystallization temperature was controlled at 17°C to obtain compound 2. 80g of compound 2 and 800g of copper sulfate solution (10%) were mixed and stirred at 40°C for 1h. After flocculent solids were precipitated, the metal ligand catalyst was obtained by filtering and washing. The catalyst was applied to the condensation reaction, wherein the mass ratio of catalyst: guaiacol: glyoxylic acid was 0.005:1.05:1, the reaction temperature was 30°C, the pH of the reaction solution was 12.7, the reaction time was 5h, the selectivity of 1-hydroxy-2-methoxymandelic acid (ortho-mandelic acid) was about 75.2%, and the selectivity of 3-methoxy-4-hydroxymandelic acid (para-mandelic acid) was about 18.78%. The condensation reaction solution was adjusted to pH = 4.2 by adding sulfuric acid, and toluene was added to extract and recover guaiacol, and the mass ratio of toluene to water phase was 1:3. The reaction solution is then adjusted to alkaline, the pH is controlled to be 12.5, and it is reacted with 15% copper oxide by mass for 6 hours at normal pressure and 100°C to obtain an oxidation reaction solution containing 3-methoxy-4-hydroxybenzoic acid. After filtering and separating the copper oxide, 4% sulfuric acid is added to cause a decarboxylation reaction to obtain a crude vanillin product. The crude vanillin product is further distilled with about 20 distillation plates to obtain pure o-vanillin and vanillin. The mass ratio of o-vanillin to vanillin in the product is 4.15.

[0051] Example 2

[0052] In anhydrous, oxygen-free, 5°C condition, 40g 2-bromoquinoline and 140g ether were injected into a three-necked flask, 88g 2-(trimethyltin chloride)-3-methylquinoline was slowly added dropwise to the reaction system, and the reaction was continued for 1.5h after the addition was completed, and water was added to quench the reaction. The upper oil phase was separated by rotary evaporation and column chromatography was performed. The eluent was petroleum ether and ethyl acetate, and the ratio of the two was 3:1. Compound 1 was obtained by separation and purification. At room temperature and pressure, 60g of compound 1 was dissolved in 240g DMF, 36g fuming sulfuric acid was added dropwise to the reaction solution, and the reaction was continued for 2h. After the reaction was completed, the reaction solution was desolventized and recrystallized with ethanol and water (1:8) solution. The mass ratio of solvent to crude product was 4:1, and the crystallization temperature was 16°C, and compound 2 was obtained. Take 80g of compound 2 and 480g of ferric chloride solution (6%) and mix them. Stir for 0.2h at 20℃. When flocculent solids are precipitated, filter and wash to obtain a metal ligand catalyst. The catalyst is applied to the condensation reaction, wherein the mass ratio of catalyst: guaiacol: glyoxylic acid is 0.002:0.85:1, the reaction temperature is 25℃, the pH of the reaction solution is 12.2, the reaction time is 3h, the selectivity of 1-hydroxy-2-methoxymandelic acid (ortho-mandelic acid) is about 68.4%, and the selectivity of 3-methoxy-4-hydroxymandelic acid (para-mandelic acid) is about 22.76%. The reaction solution after condensation is adjusted to pH=4.5 by adding sulfuric acid, and toluene is added to extract and recover guaiacol. The mass ratio of toluene to water phase is 1:3. The reaction solution is then adjusted to alkaline, the pH is controlled to be 12.3, and it is reacted with 16% copper oxide by mass at normal pressure and 100°C for 4.5 hours to obtain an oxidation reaction solution containing 3-methoxy-4-hydroxybenzoic acid. After filtering and separating the copper oxide, 3.7% sulfuric acid is added to cause a decarboxylation reaction to obtain a crude vanillin product. The crude vanillin product is further distilled with about 22 distillation plates to obtain pure o-vanillin and vanillin. The mass ratio of o-vanillin to vanillin in the product is 3.02.

[0053] Example 3

[0054] In anhydrous, oxygen-free, 45°C conditions, 40g of 2-bromoquinoline and 360g of tetrahydrofuran were injected into a three-necked flask, and 34g of 2-(trimethyltin chloride)quinoline was slowly added to the reaction system. After the addition was completed, the reaction was continued for 11h, and water was added to quench. The upper oil phase was separated by rotary evaporation and column chromatography was performed. The eluent was petroleum ether and ethyl acetate, and the ratio of the two was 3:1. Compound 1 was separated and purified. At room temperature and pressure, 60g of compound 1 was dissolved in 540g of ethanol, and 270g of 98% sulfuric acid was added to the reaction solution. The reaction was continued for 7h. After the reaction was completed, the reaction solution was desolvated and recrystallized with ethanol and water (1:8) solution. The mass ratio of solvent to crude product was 4:1, and the crystallization temperature was 18°C, and compound 2 was obtained. Take 80g of compound 2 and 1440g of cobalt sulfate solution (14%) and mix them. Stir at 55℃ for 2.8h. When flocculent solids are precipitated, filter and wash to obtain a metal ligand catalyst. The catalyst is applied to the condensation reaction, wherein the mass ratio of catalyst: guaiacol: glyoxylic acid is 0.01:1.2:1, the reaction temperature is 38℃, the pH of the reaction solution is 12.9, the reaction time is 7h, the selectivity of 1-hydroxy-2-methoxymandelic acid (ortho-mandelic acid) is about 72.5%, and the selectivity of 3-methoxy-4-hydroxymandelic acid (para-mandelic acid) is about 19.3%. The reaction solution after condensation is adjusted to pH=4.8 by adding sulfuric acid, and toluene is added to extract and recover guaiacol. The mass ratio of toluene to water phase is 1:3. The reaction solution is then adjusted to alkaline, the pH is controlled to be 12.7, and it is reacted with 17% copper oxide by mass for 6.5 hours at normal pressure and 100°C to obtain an oxidation reaction solution containing 3-methoxy-4-hydroxybenzoic acid. After filtering and separating the copper oxide, 4.4% sulfuric acid is added to cause a decarboxylation reaction to obtain a crude vanillin product. The crude vanillin product is further distilled with about 25 distillation plates to obtain pure o-vanillin and vanillin. The mass ratio of o-vanillin to vanillin in the product is 3.75.

[0055] Example 4

[0056] In anhydrous, oxygen-free, 30°C conditions, 40g of 2-bromoquinoline and 240g of toluene were injected into a three-necked flask, and 60g of 2-(trimethyltin chloride)quinoline was slowly added to the reaction system. After the addition was completed, the reaction was continued for 5h, and water was added to quench. The upper oil phase was separated by rotary evaporation and column chromatography was performed. The eluent was petroleum ether and ethyl acetate, and the ratio of the two was 3:1. Compound 1 was separated and purified. At room temperature and pressure, 60g of compound 1 was dissolved in 360g of methanol, and 180g of fuming sulfuric acid was added to the reaction solution. The reaction was continued for 3h. After the reaction was completed, the reaction solution was desolventized and recrystallized with ethanol and water (1:8) solution. The crystallization mass ratio was 4:1 and the crystallization temperature was 18°C ​​to obtain compound 2. 80g of compound 2 and 960g of copper chloride solution (8%) were mixed and stirred at 35°C for 1.2h. When flocculent solids were precipitated, the metal ligand catalyst was obtained by filtering and washing. The catalyst is applied to a condensation reaction, wherein the mass ratio of catalyst: guaiacol: glyoxylic acid is 0.003:1.1:1, the reaction temperature is 30°C, the pH of the reaction solution is 12.1, the reaction time is 6h, the selectivity of 1-hydroxy-2-methoxymandelic acid (ortho-mandelic acid) is about 60.8%, and the selectivity of 3-methoxy-4-hydroxymandelic acid (para-mandelic acid) is about 25.3%. The reaction solution after condensation is adjusted to pH=5 by adding sulfuric acid, and toluene is added to extract and recover guaiacol, and the mass ratio of toluene to water phase is 1:3. The reaction solution is then adjusted to alkaline, the pH is controlled to be 12.5, and it is reacted with 20% copper oxide by mass at normal pressure and 100°C for 4-8 hours to obtain an oxidation reaction solution containing 3-methoxy-4-hydroxybenzoic acid. After filtering and separating the copper oxide, 5% sulfuric acid is added to cause a decarboxylation reaction to obtain a crude vanillin product. The crude vanillin product is further distilled with about 20 distillation plates to obtain pure o-vanillin and vanillin. The mass ratio of o-vanillin to vanillin in the product is 2.59.

[0057] Comparative Example 1

[0058] The mass ratio of guaiacol to glyoxylic acid is 1.05:1, the reaction temperature is 30℃, the pH of the reaction solution is 12.7, the reaction time is 5h, the selectivity of 1-hydroxy-2-methoxymandelic acid (ortho-mandelic acid) is about 33.2%, and the selectivity of 3-methoxy-4-hydroxymandelic acid (para-mandelic acid) is about 59.6%. The condensation reaction solution is adjusted to acidity, and methyl isobutyl ketone is added to extract and recover the unreacted guaiacol. The remaining aqueous phase is adjusted to pH=13 with alkali solution, and the oxidation reaction is continued. The oxidation reaction temperature is 85℃, the residence time is 2h, and then sulfuric acid is added for decarboxylation. After decarboxylation, methyl isobutyl ketone is added to extract vanillin. The extract phase is subjected to distillation, crystallization and other processes to obtain vanillin and o-vanillin. The mass ratio of o-vanillin to vanillin in the product is 0.58.

Claims

1. A metal ligand catalyst, the structural formula of which is as follows: Wherein M represents a transition metal, such as iron, manganese, copper, chromium, and R represents H or methyl.

2. The method for preparing a metal ligand catalyst according to claim 1, characterized in that: The following steps are involved: (1) 2-bromoquinoline reacts with 2-(trimethyltin chloride)quinoline to obtain a biquinoline derivative shown in compound 1; (2) reacting the compound 1 obtained in step (1) with concentrated sulfuric acid to obtain a sulfonated derivative represented by compound 2; (3) mixing the compound 2 obtained in step (2) with transition metal ions to obtain a metal ligand catalyst; The structural formula of 2-(trimethyltin chloride)quinoline is Compound 1 is Compound 2 is 3. The preparation method according to claim 2, characterized in that: Step (1) is carried out in solvent A, wherein the solvent A is selected from one or more of toluene, ether and tetrahydrofuran, preferably toluene and ether; and / or the weight ratio of 2-bromoquinoline to solvent A is 1:(3-10), preferably 1:(5-8); and / or the mass ratio of 2-bromoquinoline to 2-(trimethyltin chloride)quinoline is 1:(0.8-2.5), preferably 1:(1.2-1.8).

4. The preparation method according to claim 2 or 3, characterized in that: The synthesis method of 2-(trimethyltin chloride)quinoline is as follows: under anhydrous and oxygen-free conditions, trimethyltin chloride and quinoline are reacted at 0-5°C to obtain the product; and / or, the reaction temperature in step (1) is 0-50°C, preferably 10-30°C; and / or, the reaction time in step (1) is 1-12h, preferably 3-6h.

5. The preparation method according to any one of claims 2 to 4, characterized in that: The reaction time of step (2) is 1 to 8 hours, preferably 3 to 5 hours; and / or step (2) is carried out in solvent B, and solvent B is selected from one or more of acetone, DMF, ethanol and methanol, preferably acetone or ethanol.

6. The preparation method according to any one of claims 2 to 5, characterized in that: The mass ratio of compound 1 to solvent B in step (2) is 1:(3-10), preferably 1:(5-8); and / or the mass ratio of sulfuric acid to compound 1 in step (2) is (0.5-5):1, preferably (2-4):

1.

7. The preparation method according to any one of claims 2 to 6, characterized in that: In step (3), the metal ion is selected from an aqueous solution of ferric chloride, ferric nitrate, ferric sulfate, cupric chloride, cupric sulfate, cupric nitrate, cobalt chloride, cobalt sulfate, and cobalt nitrate, and the preferred metal ion source is ferric sulfate and cobalt sulfate solution; and / or, the concentration of the metal ion solution in step (3) is 5-15wt%; and / or, the mass ratio of the metal ion solution to compound 2 in step (3) is (5-20):1, preferably (10-15):

1.

8. The preparation method according to any one of claims 2 to 7, characterized in that: The reaction temperature of step (3) is 10 to 60° C., preferably 30 to 50° C.; and / or the reaction time of step (3) is 0.1 to 3 h, preferably 0.5 to 1.5 h.

9. A method for preparing o-vanillin, comprising: allowing guaiacol and glyoxylic acid to undergo a condensation reaction according to a mass ratio of catalyst: guaiacol: glyoxylic acid of (0.001-0.01):(0.8-1.2):1, and subjecting the reaction solution after the condensation to oxidation, decarboxylation and purification to obtain o-vanillin and vanillin products, wherein the catalyst is selected from the metal ligand catalyst according to claim 1 or the metal ligand catalyst prepared by the preparation method according to any one of claims 2 to 8.

10. The preparation method according to claim 9, characterized in that: The condensation reaction temperature is 20-40°C, the reaction pressure is normal pressure, the reaction liquid pH is 12-13, and the reaction time is 2-8h; and / or, the oxidation, decarboxylation and refining process comprises the following steps: the reaction liquid after condensation is adjusted to pH=4-5 by adding sulfuric acid, and toluene is added to extract and recover guaiacol, and the mass ratio of toluene to water phase is 1:(3-5). Then the reaction liquid is adjusted to alkaline, the pH is controlled to 12-13, and at normal pressure and 100°C, it is reacted with 10%-20% copper oxide for 4-8h to obtain an oxidation reaction liquid containing 3-methoxy-4-hydroxybenzoic acid, after filtering and separating the copper oxide, 3-5% sulfuric acid is added to undergo decarboxylation reaction to obtain crude vanillin, and the crude vanillin is further distilled, and the number of distillation plates is about 20-25 to obtain pure o-vanillin and vanillin.

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