Preparation method and application of vanillin

Abstract

The invention provides a preparation method and application of vanillin. The vanillin preparation method provided by the invention comprises the following steps: mixing guaiacol, methanol, an alkaline substance, a catalyst and water for reaction to obtain a reaction solution containing a vanillin crude product; and carrying out purification treatment on the reaction liquid containing the vanillin crude product to obtain vanillin and ortho-vanillin. According to the vanillin preparation method provided by the invention, the guaiacol, the methanol, the alkaline substance, the catalyst and the water are mixed for reaction, the vanillin is prepared by adopting a one-pot method, and the methanol is used as a reactant and a reaction solvent, so that the production cost can be reduced, the process route is shortened, the energy consumption is reduced, and the environmental pollution is reduced; meanwhile, the selectivity of vanillin can be improved, and industrial production is easy to realize.

Description

Technical Field

[0001] The present application relates to the technical field of organic synthesis, and more particularly, to a method for preparing vanillin and its application. Background Art

[0002] Vanillin is one of the largest volume flavor and fragrance products and also the first synthetic fragrance in human history. The production routes of vanillin mainly include natural extraction, biological fermentation, and chemical synthesis.

[0003] The chemical synthesis methods mainly include the lignin method, guaiacol method, eugenol method, p-cresol method, p-hydroxybenzaldehyde method, etc. Currently, the guaiacol method is the mainstream process route, in which guaiacol reacts with glyoxylic acid through condensation, oxidation, and decarboxylation reactions, and then high-purity vanillin is obtained through rectification and crystallization. The biggest drawback of this process is the long reaction route, and the whole reaction process requires three acid-base neutralizations. Moreover, the amount of alkali used in the condensation step is as much as 3 times the molar amount of the raw materials, resulting in a large amount of resource waste and generating a large amount of waste salts and wastewater, with relatively high environmental protection costs.

[0004] In view of this, the present application is specifically proposed. Summary of the Invention

[0005] The main object of the present application is to provide a method for preparing vanillin, so as to solve the technical problems in the prior art that the reaction route for preparing vanillin from guaiacol and glyoxylic acid through condensation, oxidation, and decarboxylation reactions is long, resulting in resource waste, environmental pollution, and low selectivity of vanillin.

[0006] To achieve the above object, according to one aspect of the present application, a method for preparing vanillin is provided. The preparation method includes: Step S1, mixing guaiacol, methanol, an alkaline substance, a catalyst, and water for reaction to obtain a reaction solution containing crude vanillin; Step S2, purifying the reaction solution containing crude vanillin to obtain the vanillin and o-vanillin.

[0007] Further, in the above Step S1, the molar ratio of methanol to guaiacol is 3 - 10:1, preferably 4 - 6:1.

[0008] Further, in the above Step S1, the mass ratio of water to guaiacol is 0.1 - 0.5:1, preferably 0.3 - 0.4:1.

[0009] Further, in the above Step S1, the alkaline substance includes one or more of sodium hydroxide, potassium hydroxide, and sodium carbonate, preferably sodium hydroxide, and its molar ratio to guaiacol is 1 - 3:1, preferably 1.5 - 2:1.

[0010] Further, in the above step S1, the catalyst is a mixture of a first catalyst and a second catalyst; the first catalyst is at least one of copper chloride, copper acetate, copper nitrate, copper sulfate, copper acetylacetonate, iron acetate, iron chloride, and iron acetylacetonate, preferably at least one of copper chloride, copper acetate, and iron acetate; the second catalyst is at least one of cobalt chloride, cobalt acetate, cobalt acetylacetonate, molybdenum chloride, molybdenum acetate, and molybdenum acetylacetonate, preferably at least one of cobalt chloride and cobalt acetate;

[0011] Further, the mass ratio of the first catalyst to guaiacol is 0.02 - 0.05:100; the mass ratio of the second catalyst to guaiacol is 0.04 - 0.1:100.

[0012] Further, in the above step S1, the reaction temperature is 90 - 120 °C, preferably 95 - 110 °C.

[0013] Further, in the above step S1, at least one of air or oxygen is continuously introduced during the reaction, and the reaction pressure is 2.5 - 3.5 MPa.

[0014] Further, in the above step S2, the purification treatment includes: first performing solid-liquid separation on the reaction solution containing the crude vanillin to remove the catalyst, then performing acidification treatment, and then performing rectification treatment to obtain vanillin and o-vanillin;

[0015] Further, the pH value of the solution to be rectified is made 4 - 5 through acidification treatment.

[0016] Further, in the above step S2, the vacuum degree of the rectification treatment is 5 - 20 Pa, preferably 5 - 10 Pa.

[0017] Further, the preparation method further includes step S3, in which vanillin is sequentially subjected to crystallization, solid-liquid separation, and drying treatment to obtain vanillin crystals;

[0018] Further, the crystallization temperature is 2 - 10 °C, preferably 3 - 6 °C;

[0019] Further, the drying temperature is 30 - 70 °C, preferably 40 - 60 °C, and more preferably 55 - 60 °C.

[0020] Further, in the above step S3, vanillin is first dispersed in a solvent and then crystallized.

[0021] Further, the solvent is a mixed solution of ethanol and water, and the mass ratio of the two is 95:5. The mass ratio of the solvent to vanillin is 1 - 3:1, preferably 2 - 2.5:1.

[0022] According to another aspect of the present application, there is provided the use of vanillin prepared by the above-mentioned method for preparing vanillin in industries such as food, medicine, and rubber.

[0023] Applying the technical solution of the present application, the present application provides a method for preparing vanillin. By mixing guaiacol, methanol, an alkaline substance, a catalyst, and water for reaction, vanillin is prepared by a one-pot method. Among them, methanol serves as both a reactant and a reaction solvent, which can not only reduce production costs, shorten the process route, reduce energy consumption, and reduce environmental pollution, but also improve the selectivity of vanillin and is easy to realize industrial production. Detailed implementation manners

[0024] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0025] As analyzed in the background art of the present application, the prior art synthesizes by reacting guaiacol with glyoxylic acid through condensation, oxidation, and decarboxylation reactions. This preparation method has a long reaction route. The entire reaction process requires three acid-base neutralizations, resulting in a large amount of resource waste, generating a large amount of waste salts and waste water, with a high environmental protection cost, and a low selectivity of vanillin. To solve this problem, the present application provides a method for preparing vanillin and its use.

[0026] In a typical implementation manner of the present application, there is provided a method for preparing vanillin, which includes the following steps: Step S1, mixing guaiacol, methanol, an alkaline substance, a catalyst, and water for reaction to obtain a reaction solution containing crude vanillin; Step S2, purifying the reaction solution containing crude vanillin to obtain vanillin and o-vanillin.

[0027] Applying the technical solution of the present application, the present application provides a method for preparing vanillin. By mixing guaiacol, methanol, an alkaline substance, a catalyst, and water for reaction, vanillin is prepared by a one-pot method. Among them, methanol serves as both a reactant and a reaction solvent, which can not only reduce production costs, shorten the process route, reduce energy consumption, and reduce environmental pollution, but also improve the selectivity of vanillin and is easy to realize industrial production.

[0028] Guaiacol, as a common fine chemical intermediate in the art, can be prepared by chemical synthesis methods or by natural extraction. Guaiacol is easily obtained and has a low price. As the main raw material for preparing vanillin, it is easy to realize large-scale production.

[0029] In this application, the entire reaction process includes two parts. The chemical reaction process is shown in Equation (1). First, methanol acts as a methylation reagent and reacts with guaiacol under the action of a catalyst to form the intermediate 4-methylguaiacol. Then, the prepared 4-methylguaiacol is oxidized in one step to form vanillin. Among them, when methanol and guaiacol react to form 4-methylguaiacol under the action of a catalyst, a small amount of by-product 6-methylguaiacol is also generated. By selecting a suitable catalyst and controlling the reaction conditions, the selectivity of generating 4-methylguaiacol is improved. The whole process adopts a one-pot method, which not only simplifies the preparation process, reduces the preparation cost, but also avoids the loss of 4-methylguaiacol during the post-treatment process of 4-methylguaiacol, thereby increasing the yield of vanillin.

[0030]

[0031] In the above Equation (1), CAT refers to the catalyst.

[0032] In some embodiments, the catalyst used for the reaction of methanol and guaiacol to form 4-methylguaiacol is the same as the catalyst used for the further oxidation reaction of 4-methylguaiacol to form vanillin. By generating vanillin from guaiacol and methanol in one pot under the action of a catalyst, the utilization rate of the catalyst can be increased, the waste of the catalyst can be avoided, the cost of preparing vanillin can be reduced, and it is beneficial to large-scale production.

[0033] In the above step S1, in order to further increase the yield of vanillin, the molar ratio of methanol to guaiacol is preferably 3 - 10:1, and more preferably 4 - 6:1. Methanol not only reacts with guaiacol as a reactant to form the intermediate 4-methylguaiacol, but also serves as the reaction solvent for preparing vanillin. If the addition amount of methanol is too high, the cost of vanillin increases and it is difficult to recover methanol. If the addition amount of methanol is too low, on the one hand, the reaction between methanol and guaiacol is insufficient, the yield of 4-methylguaiacol is low, resulting in a decrease in the yield of vanillin. On the other hand, with less methanol, the raw materials are not dissolved sufficiently, resulting in uneven material contact and easy generation of by-products. Within the above range, the yield and selectivity of vanillin can be effectively increased.

[0034] In order to further improve the yield of vanillin, it is preferred that the basic substance includes at least one of sodium hydroxide, potassium hydroxide, and sodium carbonate, and more preferably sodium hydroxide. The role of the basic substance is to form inorganic salts with 4-methylguaiacol and vanillin to form a protection, and it plays an activating role in the oxidation of 4-methylguaiacol to prepare vanillin. Among them, the molar ratio of sodium hydroxide to guaiacol is 1-3:1, preferably 1.5-2:1. If the addition amount of sodium hydroxide is too small, there are more by-products generated during the oxidation process, and more tar is generated, resulting in a lower yield of vanillin. When the addition amount of sodium hydroxide is too large, when the addition amount of sodium hydroxide increases to a certain extent, the yield of vanillin no longer increases significantly. Continuing to increase the addition amount of sodium hydroxide will not improve the yield of vanillin, resulting in an increase in production costs and an increase in the difficulty of post-treatment. Within the above range, the yield of vanillin can be effectively improved, and the waste of sodium hydroxide can be avoided.

[0035] In some embodiments, since the basic substance is an inorganic substance and has a low solubility in methanol, in order to ensure that the basic substance can be fully dissolved, the basic substance is first dissolved in water, where the mass ratio of water to guaiacol is 0.1-0.5:1, preferably 0.3-0.4:1. If the addition amount of water is too small, the basic substance cannot be completely dissolved, resulting in a smaller amount of the basic substance actually participating in the reaction and a lower yield of vanillin. Within the above range, the basic substance can be completely dissolved, further improving the yield of vanillin.

[0036] In order to further improve the selectivity of vanillin, it is preferred that the catalyst is a mixture of a first catalyst and a second catalyst. The first catalyst is at least one of copper chloride, copper acetate, copper nitrate, copper sulfate, copper acetylacetonate, iron acetate, iron chloride, and iron acetylacetonate, preferably at least one of copper chloride, copper acetate, and iron acetate; the second catalyst is at least one of cobalt chloride, cobalt acetate, cobalt acetylacetonate, molybdenum chloride, molybdenum acetate, and molybdenum acetylacetonate, preferably at least one of cobalt chloride and cobalt acetate. Under the action of the above catalyst, on the one hand, during the reaction of methanol and guaiacol to generate the intermediate 4-methylguaiacol, the selectivity of 4-methylguaiacol is improved, the generation of by-products is avoided, and thus the selectivity of vanillin is improved. On the other hand, the conversion rate of 4-methylguaiacol is increased, and the yield of vanillin is increased.

[0037] In order to further improve the selectivity of vanillin, the mass ratio of the first catalyst to guaiacol is 0.02 - 0.05:100; the mass ratio of the second catalyst to guaiacol is 0.04 - 0.1:100. Among them, if the addition amount of the catalyst is too small or a single catalyst is used, during the reaction of methanol and guaiacol, the reaction selectivity is low, side reactions increase, resulting in a low yield of vanillin and a large amount of o-vanillin being generated. In addition, during the oxidation of 4-methylguaiacol, the reaction rate is low, the conversion rate of 4-methylguaiacol is low, and the yield of vanillin is low. If the catalyst dosage is too large, the price of the catalyst is high. Increasing the amount of the catalyst will, on the one hand, lead to an increase in reaction by-products, and on the other hand, increase the preparation cost. Within the above range, the yield of vanillin can be effectively improved.

[0038] In some embodiments, in the above step S1, at least one of air or oxygen is continuously introduced to provide oxygen for the oxidation of 4-methylguaiacol to vanillin, and the reaction pressure is 2.5 - 3.5 MPa. The higher the pressure, the shorter the reaction time, but it will promote the occurrence of side reactions. If the pressure is too small, the conversion rate of guaiacol is low. Within the above range of reaction pressure, not only can the reaction rate be increased, but also the explosion limit of methanol can be avoided, reducing the safety hazards existing in the reaction process.

[0039] There is no limitation on the reaction equipment used in the above step S1, which is a common reaction equipment in the art. In this application, a high-pressure reaction kettle is used, and the rotation speed set in the high-pressure reaction kettle is 400 - 700 revolutions per minute. If the stirring rate is too low, the reactants do not contact sufficiently, resulting in incomplete reaction and being unfavorable for mass transfer between gas and liquid. As the stirring rate increases, the mass transfer ability of oxygen improves, the contact area between gas and liquid phases increases, the reaction time is shortened, and the yield of vanillin is increased. When the rotation speed exceeds 1000 revolutions per minute, the mass transfer of oxygen reaches saturation, and if the rotation speed is further increased, by-products increase, resulting in a decrease in the yield of vanillin.

[0040] In some embodiments, the reaction temperature is 90 - 120 °C, preferably 95 - 110 °C. If the temperature is too low, 4-methylguaiacol is partially converted into alcohol substances, and the selectivity is low. As the reaction temperature increases, the yield and purity of the product continuously increase. If the temperature is too high, 4-methylguaiacol is easily deeply oxidized to acid, and tar will be generated, causing overreaction. It has been found through experiments that within the above range of reaction temperature, a high yield can be obtained.

[0041] In some embodiments, the reaction progress is tracked and detected by high-performance liquid chromatography, and when the purity of the product reaches the maximum value, the reaction is stopped to avoid continued reaction to generate by-products, resulting in a decrease in the yield of vanillin.

[0042] In this application, after the reaction is completed, a reaction solution containing crude vanillin is obtained. To further improve the purification efficiency, step S2 is preferably adopted. First, the catalyst in the reaction solution is removed by solid-liquid separation, and then an acid is added to neutralize the alkaline substances in the reaction solution. The type of acid in this application is not restricted. Hydrochloric acid is used to adjust the pH value of the reaction solution to 4-5. The reaction solution with a pH value of 4-5 obtained is subjected to rectification. According to the different volatilities of the components in the reaction solution, each component is separated. First, methanol is recovered, then water is separated by rectification, and finally the target product vanillin and the by-product o-vanillin are separated. Through the rectification process, not only vanillin with a higher purity is obtained, but also the by-product o-vanillin with a higher purity is obtained, which can be used for other production. In addition, the remaining methanol in the reaction is recovered, reducing resource waste and lowering the production cost, which is beneficial to large-scale production.

[0043] To further improve the purity of vanillin, it is preferred that the vacuum degree is 5-20 Pa, preferably 5-10 Pa, when separating vanillin and o-vanillin in the rectification process.

[0044] In some embodiments, to obtain vanillin with better crystal form, the preparation method further includes step S3, in which vanillin is successively subjected to crystallization solid-liquid separation and drying treatment to obtain vanillin crystals. To further improve the crystallization efficiency, it is preferred to first disperse vanillin in a solvent. The solvent generally used is at least one of ethanol and water. In this application, a mixed solution of ethanol and water is used, in which the mass ratio of ethanol to water is 95:5. Using the above solvent makes the vanillin crystals obtained after crystallization have a higher purity.

[0045] To further improve the yield of vanillin, it is preferred that the mass ratio of the mixed solution of ethanol and water to vanillin is 1-3:1, and more preferably 2-2.5:1. If the addition amount of the mixed solution of ethanol and water is too small, the crystallization process is easily saturated and crystals are precipitated, resulting in the agglomeration of the vanillin crystals obtained. If the addition amount of the mixed solution of ethanol and water is too large, not only the solvent is wasted and the production cost is increased, but on the other hand, the crystallization time is longer, the crystals are not easily precipitated, and part of the vanillin crystals are dissolved in the solvent, resulting in a decrease in the yield of vanillin. Within the above range, the yield of vanillin can be effectively improved.

[0046] In some embodiments, the crystallization temperature is 2-10 °C, preferably 3-6 °C. If the crystallization temperature is too high, the product has a higher solubility and is not easily precipitated as crystals. If the crystallization temperature is too low, it causes energy waste and increases the difficulty of preparation, which is not conducive to large-scale production. Within the above range, the yield of vanillin can be effectively improved.

[0047] In this application, the crystals obtained after crystallization are dried. The vacuum drying method is adopted in this application for drying. The temperature of vacuum drying is 30 - 70°C, preferably 40 - 60°C, and further preferably 55 - 60°C. If the temperature is too low, it is difficult to completely remove the mixed solution of ethanol and water in the crystals, resulting in a longer drying time. If the temperature is too high, since the melting point of vanillin is relatively low, at 81 - 83°C, when the drying temperature reaches the melting point of vanillin, vanillin changes from a crystal state to a liquid state, and vanillin crystals with good crystal form cannot be obtained.

[0048] As described above, in order to obtain ortho-vanillin crystals, the same method as that for vanillin can also be used to treat ortho-vanillin.

[0049] In the second typical embodiment of this application, the application of vanillin prepared in the first typical embodiment in industries such as food, medicine, and rubber.

[0050] The beneficial effects of this application will be further described below in conjunction with examples and comparative examples.

[0051] Example 1

[0052] This example provides a vanillin product, and its preparation method includes the following steps:

[0053] (1) Add 24.8 g of guaiacol, 25.6 g of methanol, 7.44 g of water, 12 g of sodium hydroxide, 74.4 mg of copper acetate, and 148.8 mg of cobalt acetate into a 250 mL high-pressure reactor, and stir until fully dissolved. Seal the reactor, set the rotation speed to 600 revolutions per minute, and set the reaction temperature to 95°C; open the main valve of the high-purity air cylinder, adjust its pressure reducing valve so that the pressure gauge shows 3 MPa, continuously introduce air for reaction, and use HPLC to track and detect the reaction progress. After the reaction is completed, unload the material to obtain a reaction solution containing crude vanillin.

[0054] (2) Filter the reaction solution containing crude vanillin to remove the catalyst, then acidify the product solution with concentrated hydrochloric acid to make the pH of the acidified product solution 4 - 5, then recover methanol, rectify to remove water and separate the target product vanillin 26.1 g and the by-product ortho-vanillin 2.85 g. The pressure during the rectification process is 5 Pa. The vanillin separated by rectification is added to a 95% ethanol aqueous solution and slowly cooled for crystallization. Keep it at 5°C for 1 h, filter and then vacuum dry to obtain the finished vanillin product. The drying temperature is 55°C and the drying time is 240 min.

[0055] Example 2

[0056] This example provides a vanillin product, and its preparation method includes the following steps:

[0057] (1) Add 24.8 g of guaiacol, 38.4 g of methanol, 7.44 g of water, 12 g of sodium hydroxide, 74.4 mg of copper acetate, and 148.8 mg of cobalt acetate into a 250 mL high-pressure reactor, and stir until fully dissolved. Seal the reactor, set the rotation speed to 600 revolutions per minute, and set the reaction temperature to 95 °C; open the main valve of the high-purity air cylinder, adjust its pressure reducing valve so that the pressure gauge shows 3 MPa, continuously introduce air for reaction, and use HPLC to track and detect the reaction progress. After the reaction is completed, unload the material to obtain a reaction solution containing crude vanillin.

[0058] (2) Filter the reaction solution containing crude vanillin to remove the catalyst, then acidify the product solution with concentrated hydrochloric acid to make the pH of the acidified product solution 4 - 5. Then recover methanol, rectify to remove water and separate the target product vanillin (26.5 g) and the by-product o-vanillin (2.85 g). The pressure during the rectification process is 5 Pa. The vanillin separated by rectification is added to an aqueous solution of 95% ethanol and slowly cooled for crystallization, maintained at 5 °C for 1 h, filtered, and then vacuum dried to obtain the finished vanillin product. The drying temperature is 55 °C and the drying time is 240 min.

[0059] Example 3

[0060] This example provides a vanillin product, and its preparation method includes the following steps:

[0061] (1) Add 24.8 g of guaiacol, 25.6 g of methanol, 7.44 g of water, 12 g of sodium hydroxide, 74.4 mg of copper chloride, and 148.8 mg of cobalt chloride into a 250 mL high-pressure reactor, and stir until fully dissolved. Seal the reactor, set the rotation speed to 600 revolutions per minute, and set the reaction temperature to 95 °C; open the main valve of the high-purity air cylinder, adjust its pressure reducing valve so that the pressure gauge shows 3 MPa, continuously introduce air for reaction, and use HPLC to track and detect the reaction progress. After the reaction is completed, unload the material to obtain a reaction solution containing crude vanillin.

[0062] (2) Filter the reaction solution containing crude vanillin to remove the catalyst, then acidify the product solution with concentrated hydrochloric acid to make the pH of the acidified product solution 4 - 5. Then recover methanol, rectify to remove water and separate the target product vanillin (26.4 g) and the by-product o-vanillin (2.87 g). The pressure during the rectification process is 5 Pa. The vanillin separated by rectification is added to an aqueous solution of 95% ethanol and slowly cooled for crystallization, maintained at 5 °C for 1 h, filtered, and then vacuum dried to obtain the finished vanillin product. The drying temperature is 55 °C and the drying time is 240 min.

[0063] Example 4

[0064] This example provides a vanillin product, and its preparation method includes the following steps:

[0065] (1) Add 24.8 g of guaiacol, 38.4 g of methanol, 9.92 g of water, 12 g of sodium hydroxide, 74.4 mg of copper acetate, and 148.8 mg of cobalt acetate into a 250 mL high-pressure reactor, and stir until fully dissolved. Seal the reactor, set the rotation speed to 600 revolutions per minute, and set the reaction temperature to 95 °C; open the main valve of the high-purity air cylinder, adjust its pressure reducing valve so that the pressure gauge shows 3 MPa, continuously introduce air for reaction, and use HPLC to track and detect the reaction progress. After the reaction is completed, unload the material to obtain a reaction solution containing crude vanillin.

[0066] (2) Filter the reaction solution containing crude vanillin to remove the catalyst, then acidify the product solution with concentrated hydrochloric acid to make the pH of the acidified product solution 4 - 5, then recover methanol, rectify to remove water and separate the target product vanillin 26.2 g and the by-product o-vanillin 2.85 g. The pressure during the rectification process is 5 Pa. The vanillin separated by rectification is added to a 95% ethanol aqueous solution and slowly cooled for crystallization, maintained at 5 °C for 1 h, filtered and then vacuum dried to obtain the finished vanillin product. The drying temperature is 55 °C and the drying time is 240 min.

[0067] Example 5

[0068] This example provides a vanillin product, and its preparation method includes the following steps:

[0069] (1) Add 24.8 g of guaiacol, 25.6 g of methanol, 7.44 g of water, 16 g of sodium hydroxide, 74.4 mg of copper acetate, and 148.8 mg of cobalt acetate into a 250 mL high-pressure reactor, and stir until fully dissolved. Seal the reactor, set the rotation speed to 600 revolutions per minute, and set the reaction temperature to 95 °C; open the main valve of the high-purity air cylinder, adjust its pressure reducing valve so that the pressure gauge shows 3 MPa, continuously introduce air for reaction, and use HPLC to track and detect the reaction progress. After the reaction is completed, unload the material to obtain a reaction solution containing crude vanillin.

[0070] (2) Filter the reaction solution containing crude vanillin to remove the catalyst, then acidify the product solution with concentrated hydrochloric acid to make the pH of the acidified product solution 4 - 5, then recover methanol, rectify to remove water and separate the target product vanillin 25.9 g and the by-product o-vanillin 2.81 g. The pressure during the rectification process is 5 Pa. The vanillin separated by rectification is added to a 95% ethanol aqueous solution and slowly cooled for crystallization, maintained at 5 °C for 1 h, filtered and then vacuum dried to obtain the vanillin product. The drying temperature is 55 °C and the drying time is 240 min.

[0071] Example 6

[0072] The difference between this example and Example 1 is 19.2 g of methanol.

[0073] Example 7

[0074] In this example, which is different from Example 1, the amount of methanol is 64 g.

[0075] Example 8

[0076] In this example, which is different from Example 1, the amount of methanol is 10 g.

[0077] Example 9

[0078] In this example, which is different from Example 1, the amount of methanol is 80 g.

[0079] Example 10

[0080] In this example, which is different from Example 1, the amount of water is 2.48 g.

[0081] Example 11

[0082] In this example, which is different from Example 1, the amount of water is 12.4 g.

[0083] Example 12

[0084] In this example, which is different from Example 1, the amount of water is 1 g.

[0085] Example 13

[0086] In this example, which is different from Example 1, the amount of water is 20 g.

[0087] Example 14

[0088] In this example, which is different from Example 1, the amount of sodium hydroxide is 8 g.

[0089] Example 15

[0090] In this example, which is different from Example 1, the amount of sodium hydroxide is 24 g.

[0091] Example 16

[0092] In this example, which is different from Example 1, the amount of sodium hydroxide is 2 g.

[0093] Example 17

[0094] In this example, which is different from Example 1, the amount of sodium hydroxide is 40 g.

[0095] Example 18

[0096] In this example, which is different from Example 1, the amount of copper acetate is 4.96 mg and the amount of cobalt acetate is 9.92 mg.

[0097] Example 19

[0098] In this example, which is different from Example 1, the amount of copper acetate is 12.4 mg and the amount of cobalt acetate is 24.8 mg.

[0099] Example 20

[0100] The difference between this example and Example 1 is that copper acetate is not added.

[0101] Example 21

[0102] The difference between this example and Example 1 is that cobalt acetate is not added.

[0103] Comparative Example 1

[0104] This comparative example provides a vanillin, and its preparation method includes the following steps:

[0105] Catalyst preparation: Weigh 7.5 g (0.03 mol) of reagent copper sulfate, 3.4 g (0.02 mol) of reagent manganese sulfate, and 2.4 g (0.01 mol) of reagent cobalt sulfate, and dissolve them in 100 m of deionized water to make a metal salt solution. Add 100 g of Y-type molecular sieve (benzene absorption capacity ≥ 230 mg / g; mechanical strength ≥ 80%; SiO 2 / Al 2 O 3 ≥ 4.5) to the above metal salt solution, impregnate for 30 minutes, add 5% sodium hydroxide solution to pH 11, vacuum filter to separate the molecular sieve, wash with a small amount of deionized water, dry at 105 °C, and oxidize and roast in a high-temperature furnace at 550 °C for 60 minutes for standby.

[0106] Vanillin synthesis: Install a 1000 mL four-neck reaction flask equipped with an air distributor, a reflux condenser, a stirrer, and three constant-pressure dropping funnels on a constant-temperature water bath. Add 74.1 g (0.4 mol) of 40% glyoxylic acid, 59.5 g (0.48 mol) of guaiacol, and 100 mL of 30% liquid alkali to the three constant-pressure dropping funnels respectively. Add 500 mL of deionized water, 106.6 g (0.8 mol) of 30% liquid alkali, and 5.0 g of catalyst to the four-neck reaction flask, stir and blow air, and the air pressure is 0.05 Mpa. After heating the solution to 60 °C, simultaneously drop glyoxylic acid, guaiacol, and the alkali solution into the reaction flask. The dropping rates of glyoxylic acid and guaiacol are both controlled at 10 mL / h. Sample and detect that the concentration of the 3-methoxy-4-hydroxyphenylglycolic acid intermediate in the solution is less than 2.0%, and control the dropping rate of the alkali solution to make the solution pH 11 - 13. It takes about 6 hours to drop the raw material liquid, then raise the temperature to 100 °C, continue to stir and blow air for 2.0 hours, and end the reaction when sampling and detecting that the aldehyde group content no longer increases.

[0107] Vanillin separation and purification: The reaction solution was clarified and filtered to separate the catalyst. Approximately 157.0 g (0.4 mol) of 50% sulfuric acid was added to the filtrate to neutralize it to pH 4 - 5, so that the unreacted guaiacol was liberated. After cooling to 30 - 40 °C, the liberated guaiacol was extracted twice with 100 mL of toluene, and 9.9 g of guaiacol was recovered by distillation. Approximately 157.0 g (0.4 mol) of 50% sulfuric acid was continuously added to the aqueous phase until the pH reached 0.5 - 2, and then heated to 100 °C and held at this temperature until no more carbon dioxide gas was evolved, completing the decarboxylation reaction. The decarboxylation reaction solution was cooled to 50 - 60 °C, and the precipitated vanillin was extracted three times with 200 mL of toluene. The organic phases were combined, washed twice with 20 mL of water, and the toluene solvent was recovered by vacuum distillation of the organic phase. The residual solvent was crystallized to obtain yellow vanillin crystals, and the crystals were transferred to a high-vacuum distillation apparatus to obtain vanillin products.

[0108] Test Example 1

[0109] The masses of the vanillin products prepared in the examples and comparative examples were weighed respectively, and the conversion rate of guaiacol and the yield of vanillin were calculated. The results are shown in Table 1 below. Among them:

[0110] (1) The calculation method for the yield of the vanillin product is: (the molar amount of the vanillin product obtained after crystallization / the molar amount of the guaiacol charged)

[0111] (2) The measurement method for the mass of the vanillin product is: HPLC detection, mobile phase: methanol: water = 65:35, flow rate: 1.0 mL / min, detection wavelength: 280 nm, column temperature: 30 °C, injection volume: 10 μL. Column model: Shiseido MGⅡ, 250 * 4.6 mm, 5 μm.

[0112] Table 1

[0113]

[0114]

[0115] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0116] The present application provides a method for preparing vanillin. By mixing guaiacol, methanol, an alkaline substance, a catalyst, and water for reaction, vanillin is prepared by a one-pot method. Methanol serves as both a reactant and a reaction solvent, which can not only reduce production costs, shorten the process route, reduce energy consumption, and reduce environmental pollution, but also improve the selectivity of vanillin and is easy to realize industrial production.

[0117] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of vanillin, characterized in that, the preparation method comprises the following steps: Step S1, mixing guaiacol, methanol, an alkaline substance, a catalyst and water for reaction to obtain a reaction solution containing crude vanillin; Step S2, purifying the reaction solution containing crude vanillin to obtain the vanillin and o-vanillin.

2. The preparation method of vanillin according to claim 1, characterized in that, in Step S1, the molar ratio of the methanol to the guaiacol is 3 - 10:1, preferably 4 - 6:1; and / or, the mass ratio of the water to the guaiacol is 0.1 - 0.5:1, preferably 0.3 - 0.4:

1.

3. The preparation method of vanillin according to claim 1, characterized in that, in Step S1, the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, and sodium carbonate, preferably sodium hydroxide, and the molar ratio of it to the guaiacol is 1 - 3:1, preferably 1.5 - 2:

1.

4. The preparation method of vanillin according to claim 1, characterized in that, in Step S1, the catalyst is a mixture of a first catalyst and a second catalyst; wherein, the first catalyst is at least one of copper chloride, copper acetate, copper nitrate, copper sulfate, copper acetylacetonate, iron acetate, iron chloride, and iron acetylacetonate, preferably at least one of copper chloride, copper acetate, and iron acetate; the second catalyst is at least one of cobalt chloride, cobalt acetate, cobalt acetylacetonate, molybdenum chloride, molybdenum acetate, and molybdenum acetylacetonate, preferably at least one of cobalt chloride and cobalt acetate; preferably, the mass ratio of the first catalyst to the guaiacol is 0.02 - 0.05:100; the mass ratio of the second catalyst to the guaiacol is 0.04 - 0.1:

100.

5. The preparation method of vanillin according to claim 1, characterized in that, in Step S1, the reaction temperature is 90 - 120 °C, preferably 95 - 110 °C; and / or, at least one of air or oxygen is continuously introduced during the reaction, and the reaction pressure is 2.5 - 3.5 MPa.

6. The preparation method of vanillin according to claim 1, characterized in that, in Step S2, the purification treatment includes: first performing solid-liquid separation on the reaction solution containing crude vanillin to remove the catalyst, then performing acidification treatment, and then performing rectification treatment to obtain the vanillin and the o-vanillin; preferably, the pH value of the solution to be rectified is 4 - 5 through the acidification treatment.

7. The preparation method of vanillin according to claim 6, characterized in that, in Step S2, the vacuum degree of the rectification treatment is 5 - 20 Pa, preferably 5 - 10 Pa.

8. The preparation method of vanillin according to any one of claims 1 to 7, characterized in that, the preparation method further includes Step S3, crystallizing, performing solid-liquid separation and drying on the vanillin in sequence to obtain vanillin crystals; preferably, the temperature of the crystallization is 2 - 10 °C, preferably 3 - 6 °C; Preferably, the drying temperature is 30 - 70°C, more preferably 40 - 60°C, and even more preferably 55 - 60°C.

9. The method for preparing vanillin according to claim 8, wherein, in step S3, the vanillin is first dispersed in a solvent and then the crystallization is carried out; Preferably, the solvent is a mixed solution of ethanol and water, and the mass ratio of the two is 95:

5. The mass ratio of the solvent to the vanillin is 1 - 3:1, preferably 2 - 2.5:

1.

10. Application of vanillin prepared by the method for preparing vanillin according to any one of claims 1 to 9 in industries such as food, medicine, and rubber.

Images