Magnetic solid acid catalyst as well as preparation method and application thereof

Abstract

The invention discloses a magnetic solid acid catalyst as well as a preparation method and application thereof. The magnetic solid acid catalyst takes Fe3O4 as a magnetic core and SiO2 and ethylene glycol as a shell group, and the surface of the magnetic solid acid catalyst is connected with a sulfonic acid group or a benzenesulfonic acid group. The method also comprises the step of preparing methyl cinnamate and derivatives thereof through esterification reaction by taking magnetic solid acid as a catalyst and taking substituted cinnamic acid and methanol as reaction raw materials. Compared with a traditional protonic acid catalysis process, the method has the advantages that reaction conditions are milder, corrosion to equipment is avoided, the catalyst can be recycled for multiple times, excessive methanol can be recycled, and the resource utilization rate is greatly increased. The yield of methyl cinnamate prepared through the method can reach 90% or above, the requirement of a green catalysis process is met, and the method has good popularization value.

Description

Technical Field

[0001] The present invention relates to a magnetic solid acid catalyst and a preparation method and application thereof, in particular to a magnetic solid acid catalyst and a preparation method thereof and application thereof in synthesizing methyl cinnamate and derivatives thereof, belonging to the technical field of chemical synthesis. Background Art

[0002] Methyl cinnamate and its derivatives are important flavoring and chemical intermediates, widely used in food, cosmetics, pharmaceuticals, and other fields. They possess unique aromatic properties (similar to strawberry and cherry aromas) and show potential in the development of UV absorbers and antimicrobial agents, with market demand continuing to grow. Currently, methyl cinnamate and its derivatives are primarily prepared industrially through the esterification reaction of substituted cinnamic acid with methanol. The general reaction formula is as follows:

[0003]

[0004] Traditional methods for preparing methyl cinnamate and its derivatives mainly use strong acids such as concentrated sulfuric acid and p-toluenesulfonic acid as catalysts. These methods have many disadvantages, such as the generation of acidic wastewater, severe equipment corrosion, complex post-processing, and environmental pollution.

[0005] In recent years, as the concepts of green chemistry and sustainable development have become increasingly popular, the development of efficient, environmentally friendly, and reusable catalysts has become a research hotspot. Magnetic solid acid catalysts have gained increasing attention due to their unique magnetic separation properties and excellent catalytic activity. For example, the Fe3O4@SBA-15@SO3H material has been successfully applied in the esterification of lactic acid with n-butanol, and Fe3O4@SiO2@SO3H has been used in the hydrolysis of wood cellulose, demonstrating its potential in catalysis. However, the synthesis process for methyl cinnamate and its derivatives suffers from high costs and unsafe and environmentally friendly conditions. Therefore, the development of a safe and environmentally friendly process with low-cost catalysts is particularly important. Summary of the Invention

[0006] Objectives of the invention: In response to the problems existing in the prior art, the first objective of the present invention is to provide a magnetic solid acid catalyst, the second objective of the present invention is to provide a method for preparing the magnetic solid acid catalyst, and the third objective of the present invention is to provide the use of the magnetic solid acid catalyst in the catalytic synthesis of methyl cinnamate and its derivatives.

[0007] Technical solution: The magnetic solid acid catalyst described in the present invention includes Fe3O4 as a magnetic core, SiO2 and ethylene glycol as a shell, and a sulfonic acid group or a benzenesulfonic acid group connected to the surface.

[0008] The magnetic solid acid catalyst of the present invention comprises Fe3O4@SiO2 nanoparticles as magnetic cores, which are obtained by etherification reaction with ethylene glycol.

[0009] The preparation method of the magnetic solid acid catalyst of the present invention comprises the following steps:

[0010] (1) Fe3O4@SiO2 nanoparticles were added to water, ethylene glycol and dicyclohexylcarbodiimide were added, stirred for reaction, and magnetic separation was performed to obtain Fe3O4@SiO2@OCH2CH2OH;

[0011] (2) dissolving aminosulfonic acid or p-aminobenzenesulfonic acid in water and sodium hydroxide aqueous solution, stirring to react, cooling, and adding hydrochloric acid solution dropwise while stirring to prepare a diazonium salt solution;

[0012] (3) Add the diazonium salt solution dropwise to the aqueous solution of Fe3O4@SiO2@OCH2CH2OH, stir to react, and perform magnetic separation to obtain a magnetic solid acid catalyst.

[0013] Furthermore, in step (1), the solid-to-liquid ratio of Fe3O4@SiO2 nanoparticles, water, ethylene glycol and dicyclohexylcarbodiimide is 4:(30-60):(1-3):(1-3) g / mL / mL / g, preferably 4:60:2:3 g / mL / mL / g.

[0014] Furthermore, in step (1), the stirring reaction time is more than 4 hours.

[0015] Furthermore, in step (2), the concentration of the sodium hydroxide aqueous solution is 1 to 4 mol / L, preferably 2 mol / L.

[0016] Furthermore, in step (2), the solid-to-liquid ratio of p-aminobenzenesulfonic acid or aminosulfonic acid, water and sodium hydroxide aqueous solution is (1-3):(10-20):(1-5) g / mL / mL, preferably 2:10:2 g / mL / mL.

[0017] Furthermore, in step (2), the stirring reaction time is 20 to 40 minutes, preferably 30 minutes.

[0018] Furthermore, in step (2), the temperature is lowered to 5-12°C, preferably 10°C.

[0019] Furthermore, in step (3), the weight ratio of the diazonium salt to Fe3O4@SiO2@OCH2CH2OH is (0.3-0.8):1.

[0020] Furthermore, in step (3), the stirring reaction time is more than 3 hours.

[0021] The invention discloses an application of the magnetic solid acid catalyst in catalytic synthesis of methyl cinnamate and its derivatives.

[0022] The present invention also includes a method for catalytically synthesizing methyl cinnamate and its derivatives using the magnetic solid acid catalyst of the present invention, comprising the following steps:

[0023] Substituted cinnamic acid and the magnetic solid acid catalyst of the present invention are added to methanol, heated for reaction, cooled, magnetically separated, distilled, and recrystallized for purification.

[0024] Furthermore, the structural formula of the substituted cinnamic acid is shown in Formula I below:

[0025]

[0026] wherein X1, X2, X3, X4 and X5 are the same as or different from each other and each represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms.

[0027] Furthermore, the weight ratio of the substituted cinnamic acid to the magnetic solid acid catalyst is 1:(0.002-0.05), and the molar ratio of the substituted cinnamic acid to methanol is 1:(20-50).

[0028] Furthermore, the heating reaction temperature is 60-80° C., and the heating reaction time is 2-6 hours.

[0029] Furthermore, the reaction process was monitored by TLC plate, and the disappearance of the raw material spot of substituted cinnamic acid indicated that the reaction was complete.

[0030] Furthermore, the structure of methyl cinnamate and its derivatives is shown in the following formula II:

[0031]

[0032] wherein X1, X2, X3, X4 and X5 are the same as or different from each other and each represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms.

[0033] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0034] (1) The magnetic solid acid catalyst of the present invention comprises Fe₃O₄ as a magnetic core, SiO₂ and ethylene glycol as a shell, and surface-attached sulfonic acid groups or benzenesulfonic acid groups. It exhibits excellent catalytic activity and is easily recyclable and can be reused multiple times. The preparation process is gentle and easy to operate.

[0035] (2) The present invention uses a magnetic solid acid as a catalyst, replacing cinnamic acid and methanol as reaction raw materials, to prepare methyl cinnamate and its derivatives through an esterification reaction. Compared with traditional protonic acid catalytic processes, the present invention has milder reaction conditions, avoids corrosion to equipment, and the catalyst can be recycled multiple times. Excess methanol can be recovered and reused, greatly improving resource utilization. The yield of methyl cinnamate prepared by the method of the present invention can reach over 90%, meeting the requirements of a green catalytic process and having good promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 HNMR spectrum of methyl cinnamate prepared in Example 3;

[0037] Figure 2 IR spectrum of methyl cinnamate prepared in Example 3;

[0038] Figure 3 This figure shows the effect of the number of times the carbon-based solid acid catalyst is reused on the yield of methyl cinnamate. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0040] Preparation of Fe3O4@SiO2 nanoparticles: refer to "Meng Yan. Preparation and characterization of carboxyl surface modified magnetic Fe3O4@SiO2 nanoparticles[J]. Applied Chemical Industry, 2019, 48(09): 2134-2136.DOI:10.16581 / j.cnki.issn1671-3206.2019.09.007".

[0041] Example 1

[0042] 4 g of Fe3O4@SiO2 nanoparticles were added to 60 mL of water, followed by 2.0 mL of ethylene glycol and 3.0 g of dicyclohexylcarbodiimide. After stirring at room temperature for 4 h, Fe3O4@SiO2@OCH2CH2OH composite material was obtained by magnetic separation.

[0043] Add 2 g of p-aminobenzenesulfonic acid to a mixture consisting of 10 mL of water and 2 mL of 2 mol / L sodium hydroxide solution. Stir at room temperature for 30 minutes, then cool the solution to approximately 10°C. While stirring, add 1.6 mL of concentrated hydrochloric acid in 10 mL of water dropwise to the solution to prepare a diazonium salt solution.

[0044] The prepared diazonium salt solution was added dropwise to a 50 mL aqueous solution of Fe3O4@SiO2@OCH2CH2OH, stirred at room temperature for 3 h, and then subjected to magnetic separation to obtain the magnetic solid acid Fe3O4@SiO2@OCH2CH2OPhSO3H.

[0045] Example 2

[0046] 4 g of Fe3O4@SiO2 nanoparticles were added to 30 mL of water, followed by 3.0 mL of ethylene glycol and 1.0 g of dicyclohexylcarbodiimide. After stirring at room temperature for 4 h, the Fe3O4@SiO2@OCH2CH2OH composite material was obtained by magnetic separation.

[0047] Add 2g of aminosulfonic acid to a mixture consisting of 10mL of water and 1mL of 1mol / L sodium hydroxide solution. Stir at room temperature for 30 minutes, then cool the solution to approximately 10°C. While stirring, add 10mL of an aqueous solution containing 2mL of concentrated hydrochloric acid dropwise to the solution to prepare a diazonium salt solution.

[0048] The prepared diazonium salt solution was added dropwise to 50 mL of an aqueous solution of Fe3O4@SiO2@OCH2CH2OH, stirred at room temperature for 3 h, and then subjected to magnetic separation to obtain the magnetic solid acid Fe3O4@SiO2@OCH2CH2OSO3H.

[0049] Example 3

[0050] To a reaction vessel, 14.82g of cinnamic acid, 0.74g of the magnetic solid acid Fe3O4@SiO2@OCH2CH2OPhSO3H prepared in Example 1, and 96.00g of methanol were added. The reaction was heated to reflux and continued until completion (TLC monitoring). The reaction solution was cooled to room temperature and the catalyst was recovered using a magnet. The reaction solution was distilled under atmospheric pressure, and the unreacted methanol was collected and recycled. The crude methyl cinnamate obtained after distillation was recrystallized from a mixture of ethanol and water (volume ratio = 1:5) to obtain 15.15g of the product, with a yield of 93.4%.

[0051] The methyl cinnamate prepared in this embodiment was subjected to HNMR analysis, and the results were as follows: Figure 1 shown.

[0052] The methyl cinnamate prepared in this embodiment was subjected to IR analysis, and the results were as follows: Figure 2 shown.

[0053] Example 4

[0054] To a reaction vessel, 148.20 g of cinnamic acid, 0.30 g of the magnetic solid acid Fe₃O₄@SiO₂@OCH₂CH₂OPhSO₃H prepared in Example 1, and 640.00 g of methanol were added. The reaction was heated to reflux and allowed to react until completion (TLC monitoring). The reaction solution was cooled to room temperature and the catalyst was recovered using a magnet. The reaction solution was distilled under atmospheric pressure, and the unreacted methanol was collected and recycled. The crude methyl cinnamate obtained after distillation was recrystallized from a mixture of ethanol and water (volume ratio = 1:5) to obtain 151.98 g of the product, with a yield of 93.7%.

[0055] Example 5

[0056] To a reaction vessel, 148.20 g of cinnamic acid, 0.60 g of the magnetic solid acid Fe₃O₄@SiO₂@OCH₂CH₂OPhSO₃H prepared in Example 1, and 1600.00 g of methanol were added. The reaction was heated and refluxed until completion (TLC monitoring). The reaction solution was cooled to room temperature and the catalyst was recovered using a magnet. The reaction solution was distilled under atmospheric pressure, and the unreacted methanol was collected and recycled. The crude methyl cinnamate obtained after distillation was recrystallized from a mixture of ethanol and water (volume ratio = 1:5) to obtain 152.63 g of the product, with a yield of 94.1%.

[0057] Example 6

[0058] To a reaction vessel, add 227.06g of 4-bromocinnamic acid, 2.27g of the magnetic solid acid Fe3O4@SiO2@OCH2CH2OPhSO3H prepared in Example 1, and 1200.00g of methanol. The reaction was heated and refluxed until completion (TLC monitoring). The reaction solution was cooled to room temperature and the catalyst was recovered using a magnet. The reaction solution was distilled under atmospheric pressure, and the unreacted methanol was collected and recycled. The crude methyl 4-bromocinnamate obtained after distillation was recrystallized from a mixture of ethanol and water (volume ratio = 1:5) to obtain 222.28g of the product, with a yield of 92.2%.

[0059] Example 7

[0060] To a reaction vessel, 227.06g of 4-bromocinnamic acid, 6.81g of the magnetic solid acid Fe3O4@SiO2@OCH2CH2OSO3H, and 900.00g of methanol were added. The reaction was heated to reflux and continued until completion (TLC monitoring). The reaction solution was cooled to room temperature and the catalyst was recovered using a magnet. The reaction solution was distilled under atmospheric pressure, and the unreacted methanol was collected and recycled. The crude methyl 4-bromocinnamate obtained after distillation was recrystallized from a mixture of ethanol and water (volume ratio = 1:5) to obtain 226.37g of the product, with a yield of 93.9%.

[0061] Example 8

[0062] To a reaction vessel, 178.19 g of 4-methoxycinnamic acid, 8.90 g of the magnetic solid acid Fe₃O₄@SiO₂@OCH₂CH₂OSO₃H prepared in Example 1, and 640.00 g of methanol were added. The reaction was heated and refluxed until completion (TLC monitoring). The reaction solution was cooled to room temperature and the catalyst was recovered using a magnet. The reaction solution was distilled under atmospheric pressure, and the unreacted methanol was collected and recycled. The crude methyl 4-methoxycinnamate obtained after distillation was recrystallized from a mixture of ethanol and water (volume ratio = 1:5) to obtain 178.95 g of the product, with a yield of 93.1%.

[0063] Example 9

[0064] The experimental process is the same as in Example 3. The magnetic solid acid is recovered by magnet and methyl cinnamate is synthesized. The process is repeated 5 times. The target compound is purified as shown in FIG. Figure 3 As shown. Figure 3 It can be seen that the catalytic effect of the magnetic solid acid catalyst of the present invention is not significantly reduced after being recycled and reused 5 times.

Claims

1. A magnetic solid acid catalyst, characterized in that The magnetic solid acid catalyst has Fe3O4 as a magnetic core, SiO2 and ethylene glycol as a shell, and a sulfonic acid group or a benzenesulfonic acid group connected to the surface.

2. The method for preparing the magnetic solid acid catalyst according to claim 1, wherein: The Fe3O4@SiO2 nanoparticles are used as magnetic cores and are etherified with ethylene glycol, comprising the following steps: (1) Fe3O4@SiO2 nanoparticles were added to water, ethylene glycol and dicyclohexylcarbodiimide were added, stirred for reaction, and magnetic separation was performed to obtain Fe3O4@SiO2@OCH2CH2OH; (2) dissolving sulfamic acid or p-aminobenzenesulfonic acid in water and sodium hydroxide aqueous solution, stirring to react, cooling, and adding hydrochloric acid solution dropwise while stirring to prepare a diazonium salt solution; (3) Add the diazonium salt solution dropwise to the aqueous solution of Fe3O4@SiO2@OCH2CH2OH, stir to react, and perform magnetic separation to obtain a magnetic solid acid catalyst.

3. The preparation method according to claim 2, characterized in that In step (1), the solid-liquid ratio of Fe3O4@SiO2 nanoparticles, water, ethylene glycol and dicyclohexylcarbodiimide is 4:(30-60):(1-3):(1-3) g / mL / mL / g, and the stirring reaction time is more than 4 hours.

4. The preparation method according to claim 2, characterized in that In step (2), the concentration of the sodium hydroxide aqueous solution is 1-4 mol / L, and the solid-to-liquid ratio of sulfamic acid or p-aminobenzenesulfonic acid, water and the sodium hydroxide aqueous solution is (1-3):(10-20):(1-5) g / mL / mL.

5. The preparation method according to claim 2, characterized in that In step (2), the stirring reaction time is 20 to 40 minutes, and the temperature is lowered to 5 to 12°C.

6. The preparation method according to claim 2, characterized in that In step (3), the weight ratio of diazonium salt to Fe3O4@SiO2@OCH2CH2OH is (0.3-0.8):1, and the stirring reaction time is more than 3 hours.

7. Use of the magnetic solid acid catalyst according to claim 1 in the catalytic synthesis of methyl cinnamate and its derivatives.

8. A method for synthesizing methyl cinnamate and its derivatives using the magnetic solid acid catalyst according to claim 1, comprising the steps of: Substituted cinnamic acid and the magnetic solid acid catalyst according to claim 1 are added to methanol, heated for reaction, cooled, subjected to magnetic separation, distilled, and recrystallized for purification.

9. The synthesis method according to claim 8, characterized in that The structural formula of substituted cinnamic acid is shown in Formula I below: wherein X1, X2, X3, X4 and X5 are the same as or different from each other and each represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms.

10. The synthesis method according to claim 8, characterized in that The weight ratio of the substituted cinnamic acid to the magnetic solid acid catalyst is 1:(0.002-0.05), the molar ratio of the substituted cinnamic acid to methanol is 1:(20-50), the heating reaction temperature is 60-80°C, and the heating reaction time is 2-6 hours.

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