Efficient catalytic synthesis method of nipagin ester

Abstract

The invention relates to the technical field of chemical catalysis, in particular to an efficient catalytic synthesis method of nipagin ester. According to the method, a supported heteropolyacid ionic liquid catalyst with UiO-66-NH2 as a carrier is adopted, ionic liquid and metal heteropolyacid salt are supported on the surface of epoxy group modified UiO-66-NH2 through specific steps, p-hydroxybenzoic acid and corresponding alcohol are used as raw materials, the catalyst accounting for 3%-5% of the mass of p-hydroxybenzoic acid is added under the specific substance amount ratio, and the reaction is carried out for 1-2 hours at the temperature of 50-60 DEG C to obtain the UiO-66-NH2 supported heteropolyacid ionic liquid catalyst. And the nipagin ester is synthesized, so that the yield is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical catalysis, and in particular to a high-efficiency catalytic synthesis method of paraben. Background Art

[0002] Parabens have excellent antibacterial properties and are widely used as preservatives in food, cosmetics, and pharmaceuticals. Common parabens include methyl, ethyl, propyl, and butyl parabens, and their antibacterial activity increases with increasing alkyl carbon chain length. Due to their low toxicity, lack of irritation, and wide range of applications, they offer significant advantages in replacing traditional benzoic acid preservatives, and market demand continues to grow. Traditional paraben synthesis methods primarily use p-hydroxybenzoic acid and the corresponding alcohol as raw materials, followed by an esterification reaction in the presence of a catalyst. Common catalysts include protic acids such as concentrated sulfuric acid and p-toluenesulfonic acid. However, concentrated sulfuric acid has strong oxidizing and dehydrating properties, which easily triggers side reactions during the reaction, such as dehydration and oxidation of alcohols and carbonization of p-hydroxybenzoic acid, resulting in a darker product color and reduced purity. p-Toluenesulfonic acid is a solid organic acid that is less corrosive than concentrated sulfuric acid and has relatively fewer side reactions. It also plays a catalytic role in the esterification reaction by providing protons. However, p-Toluenesulfonic acid has limited solubility in the reaction system, and its catalytic efficiency needs to be improved. Moreover, the separation and recovery of the catalyst after the reaction is relatively difficult, making it difficult to reuse, resulting in increased production costs. With the increasing market demand for parabens and increasingly stringent environmental protection requirements, the development of an efficient, green, and economical catalytic synthesis method for parabens has important practical significance. Various existing catalytic synthesis methods all have defects to varying degrees and cannot simultaneously meet the requirements of improving product quality, reducing production costs, and reducing environmental pollution. Therefore, there is an urgent need for a new catalytic synthesis method that can overcome the shortcomings of the existing technology and achieve efficient and clean production of parabens to meet market demand and promote the sustainable development of the industry. Summary of the Invention

[0003] In view of the deficiencies in the prior art, the present invention provides a highly efficient catalytic synthesis method for parabens.

[0004] The present invention is achieved through the following technical solutions: A highly efficient catalytic synthesis method for parabens comprises the following steps: (1) Preparation of catalyst: (11) Molybdenum trioxide and vanadium pentoxide were added to deionized water, heated to 100°C, stirred for 20-30 min, 85 wt% phosphoric acid solution was added dropwise, stirred for 6-8 h, filtered, and the filtrate was dried at 80°C and ground to obtain phosphomolybdovanadium heteropoly acid; (12) preparing a cobalt nitrate solution with a concentration of 0.1 mol / L, adding the phosphomolybdovanadium heteropoly acid obtained in step (11) into deionized water and mixing evenly, adding the cobalt nitrate solution dropwise at a rate of 1 mL / min with continuous stirring, and stirring at 70°C for 4 h after the addition is complete, drying at 120°C, grinding, and calcining at 250°C for 2 h to obtain a metal heteropoly acid salt; (13) Zirconium tetrachloride and 2-aminoterephthalic acid were dissolved in DMF, glacial acetic acid was added under stirring, the mixture was evenly mixed, and the mixture was transferred to a polytetrafluoroethylene-lined autoclave. The mixture was reacted at 120 °C for 24 h, cooled to room temperature, and centrifuged at 10,000 rpm for 15 min. The precipitate was washed with DMF and ethanol, and dried in vacuo to obtain UiO-66-NH2. (14) Under N2 atmosphere, the UiO-66-NH2 obtained in step (13) was dispersed in DMF, and after adding NaH, hydrogen was removed at 40°C for 6 hours. Epibromopropane was added and reacted at 40°C for 12 hours. The mixture was cooled to room temperature, deionized water was added, and the mixture was centrifuged at 10,000 rpm for 15 minutes. The precipitate was washed with water and ethanol, and dried in vacuo to obtain epoxy UiO-66-NH2. (15) 2,4-dihydroxybenzaldehyde and K2CO3 were added to DMF, stirred at 100 °C for 1 h, and then the epoxy UiO-66-NH2 obtained in step (14) was added. The reaction was continued for 12 h, cooled to room temperature, centrifuged at 8000 rpm for 10-15 min, the precipitate was washed with DMF and anhydrous ethanol, vacuum dried, added to anhydrous ethanol at a ratio of 10 mg / mL, ultrasonicated at 300W for 10 min, and slowly added to 8-12 mg / mL 2-amino-4-chlorophenol ethanol solution. After stirring at room temperature for 4-6 h, the filter was filtered, the filter cake was washed with ethanol, and vacuum dried; (16) Under nitrogen conditions, 2-methyl-4-aminopyridine was added to anhydrous ethanol at a ratio of 20 mg / mL to obtain a mixed solution, terephthalaldehyde was added to ethanol at a ratio of 20 mg / mL, the mixed solution was added dropwise, heated under reflux for 3-4 h, recrystallized in ethanol, vacuum dried, and mixed with the vacuum-dried product obtained in step (15) at a ratio of 1:2-3, 20 times the weight volume of DMF and anhydrous ethanol were added in sequence, heated under reflux at 110-120 ° C for 24 h, centrifuged at 8000 rpm for 8-12 min, and the precipitate was washed with DMF and anhydrous ethanol, and dried to obtain modified UiO-66-NH2; (17) The metal heteropolyacid obtained in step (12) was added to ethanol at a ratio of 3-5 mg / mL, and the modified UiO-66-NH2 obtained in step (16) was added, stirred at room temperature for 12-14 h, centrifuged at 8000 rpm for 8-12 min, washed with ethanol, and dried to obtain a catalyst; (2) Mix p-hydroxybenzoic acid, alcohol, catalyst, and toluene, and heat under reflux for 3-5 hours; (3) After the reaction in step (2) is completed, the product is filtered, the filtrate is evaporated under reduced pressure to remove the solvent, recrystallized from ethanol, and dried in vacuum to obtain paraben. Furthermore, in step (11), the molar ratio of molybdenum trioxide, vanadium pentoxide and phosphoric acid is 10:1:1.

[0005] Furthermore, in step (11), the mass concentration of molybdenum trioxide in deionized water is 40-50 mg / mL.

[0006] Furthermore, in step (12), the mass concentration of the phosphomolybdovanadium heteropoly acid in deionized water is 0.1 g / mL.

[0007] Furthermore, in step (12), the mass ratio of the cobalt nitrate to the phosphomolybdovanadium heteropoly acid is 1:5.

[0008] Furthermore, in step (13), the ratio of zirconium tetrachloride, 2-aminoterephthalic acid, DMF and glacial acetic acid is 1 mmol:1 mmol:100 mL:10 mL.

[0009] Furthermore, in step (14), the dispersion concentration of UiO-66-NH2 in DMF is 20 mg / mL.

[0010] Furthermore, in step (14), the mass ratio of UiO-66-NH2, NaH and epibromopropane is 25:4:40.

[0011] Furthermore, in step (14), the volume ratio of deionized water to DMF is 1:5-10.

[0012] Furthermore, in step (15), the mass ratio of the 2,4-dihydroxybenzaldehyde to the epoxy UiO-66-NH2 is 1:1.2.

[0013] Furthermore, in step (15), the usage ratio of 2,4-dihydroxybenzaldehyde, K2CO3, DMF and 2-amino-4-chlorophenol is 1 g:3 g:50 mL:1-1.2 g.

[0014] Furthermore, in step (16), the mass ratio of terephthalaldehyde to 2-methyl-4-aminopyridine is 1:1.6-2.

[0015] Furthermore, in step (17), the mass ratio of the metal heteropoly acid salt to the modified UiO-66-NH2 is 1:3-5.

[0016] Furthermore, in step (2), the alcohol is at least one of methanol, ethanol, propanol, and butanol.

[0017] Furthermore, in step (2), the molar ratio of p-hydroxybenzoic acid to alcohol is 1:3-5.

[0018] Furthermore, in step (2), the amount of the catalyst added is 3%-5% of the mass of the hydroxybenzoic acid.

[0019] Furthermore, in step (2), the amount of toluene is 15%-25% of the total volume of the reaction system.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a highly efficient catalytic method for the production of parabens, wherein a supported heteropolyacid ionic liquid catalyst is prepared. The catalyst combines the advantages of ionic liquids, heteropolyacids, and porous materials, has high catalytic activity, can significantly improve the yield of parabens, reduce the occurrence of side reactions, and reduce the generation of wastewater during product post-processing. Furthermore, the catalyst is reusable, reducing catalyst waste and environmental pollution. The catalyst has good reusability, reducing production costs. Furthermore, the reaction conditions are mild, and the equipment requirements are not high, further saving equipment investment and operating costs. The present invention prepares a phosphomolybdenumvanadium heteropolyacid, adopts an ion exchange method to prepare a metal heteropolyacid, and introduces metal cobalt, which can effectively enhance the catalytic activity and facilitate subsequent coordination. The present invention prepares UiO-66-NH2, which is epoxy-modified using epibromohydrin to connect epoxy groups to the surface. The epoxy groups are covalently bonded to the phenolic hydroxyl groups of 2,4-dihydroxybenzaldehyde, successfully grafting 2,4-dihydroxybenzaldehyde. The aldehyde group reacts with 2-amino-4-chlorophenol to form a Schiff base, introducing Schiff base bonds and chlorine atom groups, providing a basis for subsequent reactions. The present invention causes the amino group of 2-methyl-4-aminopyridine to react with the two aldehyde groups of terephthalaldehyde to undergo a Schiff base reaction, introduces multiple Schiff base bonds, provides sufficient sites for subsequent coordination, and the amino group at the 4th position of 2-methyl-4-aminopyridine participates in the Schiff base reaction. The amino group on the pyridine ring and the chlorine atom in the 2-amino-4-chlorophenol group can react with the amino group of the pyridine ring to form an ionic liquid, thereby realizing the UiO-66-NH2 porous material loaded with the ionic liquid. The introduced Schiff base bond forms a coordination bond with the metal heteropolyacid salt, effectively loads the heteropolyacid, increases the loading amount, and enhances the catalytic activity. The present invention loads the metal heteropolyacid salt and the ionic liquid on UiO-66-NH2. UiO-66-NH2 has a large specific surface area and a regular pore structure, can highly disperse the metal heteropolyacid salt, increase the exposure degree of the active site, further improve the catalytic efficiency of the catalyst, promote the more complete reaction of p-hydroxybenzoic acid and alcohol to form paraben, and improve the yield. Compared with traditional concentrated sulfuric acid catalysis, the catalyst of the present invention avoids many side reactions caused by the strong oxidizing and dehydrating properties of concentrated sulfuric acid, such as the dehydration and oxidation of alcohol and the carbonization of p-hydroxybenzoic acid, thereby effectively reducing the generation of impurities and improving the purity of the paraben product. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1This is the preparation principle of the modified UiO-66-NH2 described in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of the metal heteropoly acid salt described in Example 2 of the present invention; Figure 3 This is a cyclic performance test of the catalyst described in Example 3 of the present invention; Figure 4 The yields of parabens prepared by the methods described in Examples 1-3 and Comparative Examples 1-3 of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with specific examples, but the present invention is not limited to the following examples. It should be noted that, unless otherwise specified, the chemical reagents involved in the present invention were purchased through commercial channels.

[0024] Example 1: A highly efficient catalytic synthesis method of parabens, comprising the following steps: (1) Preparation of catalyst: (11) 10 g of molybdenum trioxide and vanadium pentoxide were added to 200 mL of deionized water, heated to 100 °C, stirred for 30 min, and 85 wt% phosphoric acid solution was added dropwise. The molar ratio of molybdenum trioxide, vanadium pentoxide, and phosphoric acid was 10:1:1. The mixture was stirred for 8 h, filtered, and the filtrate was dried at 80 °C and ground to obtain phosphomolybdovanadium heteropoly acid. (12) Take 1 g of cobalt nitrate to prepare a cobalt nitrate solution with a concentration of 0.1 mol / L, add 5 g of the phosphomolybdovanadium heteropoly acid obtained in step (11) into 50 mL of deionized water and mix well, add the cobalt nitrate solution dropwise at a rate of 1 mL / min and stir continuously, after the addition is complete, continue stirring at 70°C for 4 h, dry at 120°C, grind, and calcine at 250°C for 2 h to obtain a metal heteropoly acid salt; (13) 1 mmol of zirconium tetrachloride and 1 mmol of 2-aminoterephthalic acid were dissolved in 100 mL of DMF. 10 mL of glacial acetic acid was added under stirring, mixed evenly, and transferred to a polytetrafluoroethylene-lined autoclave. The mixture was reacted at 120 °C for 24 h, cooled to room temperature, and centrifuged at 10,000 rpm for 15 min. The precipitate was washed with DMF and ethanol and dried in vacuum to obtain UiO-66-NH2. (14) Under N2 atmosphere, 2 g of UiO-66-NH2 obtained in step (13) was dispersed in 100 mL of DMF, 0.32 g of NaH was added, and hydrogen was removed at 40 °C for 6 h. 3.2 g of epibromopropane was added, and the reaction was carried out at 40 °C for 12 h. The reaction was cooled to room temperature, 10 mL of deionized water was added, and the reaction was centrifuged at 10,000 rpm for 15 min. The precipitate was washed with water and ethanol, and dried in vacuo to obtain epoxy UiO-66-NH2. (15) 1 g of 2,4-dihydroxybenzaldehyde and 3 g of K2CO3 were added to 50 mL of DMF, stirred at 100 °C for 1 h, and then 1.2 g of the epoxy UiO-66-NH2 obtained in step (14) was added. The reaction was continued for 12 h, cooled to room temperature, centrifuged at 8000 rpm for 15 min, and the precipitate was washed with DMF and anhydrous ethanol, dried in vacuo, added to anhydrous ethanol at a ratio of 10 mg / mL, ultrasonicated at 300 W for 10 min, and slowly added to a 12 mg / mL ethanol solution of 2-amino-4-chlorophenol. The mass ratio of 2,4-dihydroxybenzaldehyde to 2-amino-4-chlorophenol was 1:1.2. After stirring at room temperature for 6 h, the mixture was filtered, the filter cake was washed with ethanol, and dried in vacuo. (16) Under nitrogen conditions, 2 g of 2-methyl-4-aminopyridine was added to anhydrous ethanol at a ratio of 20 mg / mL to obtain a mixed solution. 1 g of terephthalaldehyde was added to ethanol at a ratio of 20 mg / mL. The mixed solution was added dropwise, heated under reflux for 4 h, recrystallized in ethanol, and vacuum-dried. The mixture was mixed with the vacuum-dried product obtained in step (15) at a ratio of 1:3. 20 times the weight volume of DMF and anhydrous ethanol were added in sequence. The mixture was heated under reflux at 120 °C for 24 h, centrifuged at 8000 rpm for 12 min, and the precipitate was washed with DMF and anhydrous ethanol and dried to obtain modified UiO-66-NH2. The preparation principle is as follows: Figure 1 As shown; (17) 1 g of the metal heteropolyacid obtained in step (12) was added to ethanol at a ratio of 5 mg / mL, and 5 g of the modified UiO-66-NH2 obtained in step (16) was added, stirred at room temperature for 14 h, centrifuged at 8000 rpm for 12 min, washed with ethanol, and dried to obtain a catalyst; (2) 10 g of p-hydroxybenzoic acid, ethanol, 0.5 g of catalyst, and toluene were mixed, with the molar ratio of p-hydroxybenzoic acid to alcohol being 1:5; the amount of toluene was 25% of the total volume of the reaction system, and the mixture was heated under reflux for 3 h. (3) After the reaction in step (2) is completed, the product is filtered, the filtrate is evaporated under reduced pressure to remove the solvent, recrystallized from ethanol, and dried in vacuum to obtain paraben. Example 2: A highly efficient catalytic synthesis method of parabens, comprising the following steps: (1) Preparation of catalyst: (11) 10 g of molybdenum trioxide and vanadium pentoxide were added to 250 mL of deionized water, heated to 100 °C, stirred for 20 min, and 85 wt% phosphoric acid solution was added dropwise. The molar ratio of molybdenum trioxide, vanadium pentoxide, and phosphoric acid was 10:1:1. The mixture was stirred for 6 h, filtered, and the filtrate was dried at 80 °C and ground to obtain phosphomolybdovanadium heteropoly acid. (12) Take 1 g of cobalt nitrate to prepare a cobalt nitrate solution with a concentration of 0.1 mol / L, add 5 g of the phosphomolybdovanadium heteropoly acid obtained in step (11) into 50 mL of deionized water and mix well, add the cobalt nitrate solution dropwise at a rate of 1 mL / min and stir continuously. After the addition is complete, continue stirring at 70°C for 4 h, dry at 120°C, grind, and calcine at 250°C for 2 h to obtain a metal heteropoly acid salt. The scanning electron microscope image is as shown below. Figure 2 As shown; (13) 1 mmol of zirconium tetrachloride and 1 mmol of 2-aminoterephthalic acid were dissolved in 100 mL of DMF. 10 mL of glacial acetic acid was added under stirring, mixed evenly, and transferred to a polytetrafluoroethylene-lined autoclave. The mixture was reacted at 120 °C for 24 h, cooled to room temperature, and centrifuged at 10,000 rpm for 15 min. The precipitate was washed with DMF and ethanol and dried in vacuum to obtain UiO-66-NH2. (14) Under N2 atmosphere, 2 g of UiO-66-NH2 obtained in step (13) was dispersed in 100 mL of DMF, 0.32 g of NaH was added, and hydrogen was removed at 40 °C for 6 h. 3.2 g of epibromopropane was added, and the reaction was carried out at 40 °C for 12 h. The reaction was cooled to room temperature, 20 mL of deionized water was added, and the reaction was centrifuged at 10,000 rpm for 15 min. The precipitate was washed with water and ethanol, and dried in vacuo to obtain epoxy UiO-66-NH2. (15) 1 g of 2,4-dihydroxybenzaldehyde and 3 g of K2CO3 were added to 50 mL of DMF, stirred at 100 °C for 1 h, and then 1.2 g of the epoxy UiO-66-NH2 obtained in step (14) was added. The reaction was continued for 12 h, cooled to room temperature, centrifuged at 8000 rpm for 10 min, and the precipitate was washed with DMF and anhydrous ethanol, dried in vacuo, added to anhydrous ethanol at a ratio of 10 mg / mL, ultrasonicated at 300 W for 10 min, and slowly added to an 8 mg / mL ethanol solution of 2-amino-4-chlorophenol. The mass ratio of 2,4-dihydroxybenzaldehyde to 2-amino-4-chlorophenol was 1:1. After stirring at room temperature for 4 h, the mixture was filtered, and the filter cake was washed with ethanol and dried in vacuo. (16) Under nitrogen conditions, 1.6 g of 2-methyl-4-aminopyridine was added to anhydrous ethanol at a ratio of 20 mg / mL to obtain a mixed solution, 1 g of terephthalaldehyde was added to ethanol at a ratio of 20 mg / mL, the mixed solution was added dropwise, heated under reflux for 3 h, recrystallized in ethanol, vacuum dried, and mixed with the vacuum-dried product obtained in step (15) at a ratio of 1:2. 20 times the weight volume of DMF and anhydrous ethanol were added in sequence, and the mixture was heated under reflux at 110°C for 24 h. The mixture was centrifuged at 8000 rpm for 8 min, and the precipitate was washed with DMF and anhydrous ethanol, and dried to obtain modified UiO-66-NH2; (17) 1 g of the metal heteropolyacid obtained in step (12) was added to ethanol at a ratio of 3 mg / mL, and 3 g of the modified UiO-66-NH2 obtained in step (16) was added, stirred at room temperature for 12 h, centrifuged at 8000 rpm for 8 min, washed with ethanol, and dried to obtain a catalyst; (2) 10 g of p-hydroxybenzoic acid, ethanol, 0.3 g of catalyst, and toluene were mixed, with the molar ratio of p-hydroxybenzoic acid to alcohol being 1:3; the amount of toluene was 15% of the total volume of the reaction system, and the mixture was heated under reflux for 5 h. (3) After the reaction in step (2) is completed, the product is filtered, the filtrate is evaporated under reduced pressure to remove the solvent, recrystallized from ethanol, and dried in vacuum to obtain paraben. Example 3: A highly efficient catalytic synthesis method of parabens, comprising the following steps: (1) Preparation of catalyst: (11) 10 g of molybdenum trioxide and vanadium pentoxide were added to 220 mL of deionized water, heated to 100 °C, stirred for 25 min, and 85 wt% phosphoric acid solution was added dropwise. The molar ratio of molybdenum trioxide, vanadium pentoxide, and phosphoric acid was 10:1:1. The mixture was stirred for 7 h, filtered, and the filtrate was dried at 80 °C and ground to obtain phosphomolybdovanadium heteropoly acid. (12) Take 1 g of cobalt nitrate to prepare a cobalt nitrate solution with a concentration of 0.1 mol / L, add 5 g of the phosphomolybdovanadium heteropoly acid obtained in step (11) into 50 mL of deionized water and mix well, add the cobalt nitrate solution dropwise at a rate of 1 mL / min and stir continuously, after the addition is complete, continue stirring at 70°C for 4 h, dry at 120°C, grind, and calcine at 250°C for 2 h to obtain a metal heteropoly acid salt; (13) 1 mmol of zirconium tetrachloride and 1 mmol of 2-aminoterephthalic acid were dissolved in 100 mL of DMF. 10 mL of glacial acetic acid was added under stirring, mixed evenly, and transferred to a polytetrafluoroethylene-lined autoclave. The mixture was reacted at 120 °C for 24 h, cooled to room temperature, and centrifuged at 10,000 rpm for 15 min. The precipitate was washed with DMF and ethanol and dried in vacuum to obtain UiO-66-NH2. (14) Under N2 atmosphere, 2 g of UiO-66-NH2 obtained in step (13) was dispersed in 100 mL of DMF, 0.32 g of NaH was added, and hydrogen was removed at 40 °C for 6 h. 3.2 g of epibromopropane was added, and the reaction was carried out at 40 °C for 12 h. The reaction was cooled to room temperature, 15 mL of deionized water was added, and the reaction was centrifuged at 10,000 rpm for 15 min. The precipitate was washed with water and ethanol, and dried in vacuo to obtain epoxy UiO-66-NH2. (15) 1 g of 2,4-dihydroxybenzaldehyde and 3 g of K2CO3 were added to 50 mL of DMF, stirred at 100 °C for 1 h, and then 1.2 g of the epoxy UiO-66-NH2 obtained in step (14) was added. The reaction was continued for 12 h, cooled to room temperature, centrifuged at 8000 rpm for 12 min, and the precipitate was washed with DMF and anhydrous ethanol, dried in vacuo, added to anhydrous ethanol at a ratio of 10 mg / mL, ultrasonicated at 300 W for 10 min, and slowly added to a 10 mg / mL ethanol solution of 2-amino-4-chlorophenol. The mass ratio of 2,4-dihydroxybenzaldehyde to 2-amino-4-chlorophenol was 1:1.1. After stirring at room temperature for 5 h, the mixture was filtered, the filter cake was washed with ethanol, and dried in vacuo. (16) Under nitrogen conditions, 1.8 g of 2-methyl-4-aminopyridine was added to anhydrous ethanol at a ratio of 20 mg / mL to obtain a mixed solution, 1 g of terephthalaldehyde was added to ethanol at a ratio of 20 mg / mL, the mixed solution was added dropwise, heated under reflux for 3.5 h, recrystallized in ethanol, vacuum dried, and mixed with the vacuum-dried product obtained in step (15) at a ratio of 1:2.5. 20 times the weight volume of DMF and anhydrous ethanol were added in sequence, heated under reflux at 115 ° C for 24 h, centrifuged at 8000 rpm for 10 min, and the precipitate was washed with DMF and anhydrous ethanol, and dried to obtain modified UiO-66-NH2; (17) 1 g of the metal heteropolyacid obtained in step (12) was added to ethanol at a ratio of 4 mg / mL, and 4 g of the modified UiO-66-NH2 obtained in step (16) was added, stirred at room temperature for 13 h, centrifuged at 8000 rpm for 10 min, washed with ethanol, and dried to obtain a catalyst; (2) 10 g of p-hydroxybenzoic acid, ethanol, 0.4 g of catalyst, and toluene were mixed, with the molar ratio of p-hydroxybenzoic acid to alcohol being 1:4; the amount of toluene was 20% of the total volume of the reaction system, and the mixture was heated under reflux for 4 h. (3) After the reaction in step (2) is completed, the product is filtered, the filtrate is evaporated under reduced pressure to remove the solvent, recrystallized from ethanol, and dried in vacuum to obtain paraben. The only difference between Comparative Example 1 and Example 1 is that the vacuum-dried product obtained in step (15) is used instead of the modified UiO-66-NH2.

[0025] The only difference between Comparative Example 2 and Example 1 is that the catalyst is replaced by modified UiO-66-NH2.

[0026] The only difference between Comparative Example 3 and Example 1 is that the catalyst is replaced by a metal heteropolyacid salt.

[0027] Experimental Example 1: After preparing paraben according to the method of Example 3, the filter cake obtained by filtration was used as the catalyst, which was washed with ethanol several times and then vacuum-dried at 80°C and reused. This was repeated 5 times, and the yield of paraben was measured each time. The results are shown in FIG. Figure 3 shown.

[0028] Figure 3 The results showed that after five cycles, the activity of the catalyst still maintained a yield of more than 85%, indicating that the efficient catalytic method for producing parabens of the present invention can achieve a high yield of parabens with high purity and a fast synthesis speed. The obtained catalyst has good recycling performance, effectively reduces costs, and overcomes the shortcomings of traditional catalysts that are difficult to recycle and pollute the environment.

[0029] Experimental Example 2: Paraben was prepared according to the method of Examples 1-3 and Comparative Examples 1-3, and the yield of paraben was calculated. The results are as follows: Figure 4 shown.

[0030] Figure 4 The results showed that the yields of Examples 1-3 were significantly higher than those of Comparative Examples 1-3. Comparative Example 1, which did not support an ionic liquid, exhibited decreased catalytic activity; Comparative Example 2, which did not support a heteropolyacid, exhibited decreased catalytic activity; and Comparative Example 3, which used only a metal heteropolyacid salt as a catalyst, exhibited relatively low catalytic activity. The efficient catalytic synthesis method for parabens of the present invention can efficiently prepare parabens.

[0031] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A highly efficient catalytic synthesis method for parabens, characterized in that: The following steps are involved: (1) Preparation of catalyst: (11) preparing phosphomolybdovanadium heteropoly acid by using molybdenum trioxide and vanadium pentoxide; (12) adding cobalt nitrate solution dropwise to phosphomolybdovanadium heteropoly acid to prepare metal heteropoly acid salt; (13) Preparation of UiO-66-NH2 using zirconium tetrachloride and 2-aminoterephthalic acid; (14) UiO-66-NH2 is reacted with epibromopropane to obtain epoxy UiO-66-NH2; (15) Dihydroxybenzaldehyde reacts with epoxy UiO-66-NH2 under alkaline conditions and then reacts with aminochlorophenol; (16) adding aminopyridine dropwise to phthalaldehyde, and mixing with the product obtained in step (15) to react, thereby obtaining modified UiO-66-NH2; (17) mixing the metal heteropolyacid salt obtained in step (12) and the modified UiO-66-NH2 obtained in step (16) to obtain a catalyst; (2) mixing p-hydroxybenzoic acid, alcohol, catalyst and toluene and refluxing; (3) After the reaction in step (2) is completed, the product is separated and purified to obtain paraben.

2. The high-efficiency catalytic synthesis method of parabens according to claim 1, characterized in that: In step (11), the molar ratio of molybdenum trioxide, vanadium pentoxide and phosphoric acid is 10:1:

1.

3. The high-efficiency catalytic synthesis method of parabens according to claim 2, characterized in that: In step (12), the mass ratio of the cobalt nitrate to the phosphomolybdovanadium heteropoly acid is 1:

5.

4. The high-efficiency catalytic synthesis method of parabens according to claim 4, characterized in that: In step (14), the mass ratio of UiO-66-NH2 and epibromopropane is 25:

40.

5. The high-efficiency catalytic synthesis method of parabens according to claim 5, characterized in that: In step (15), the mass ratio of dihydroxybenzaldehyde, epoxy UiO-66-NH2 and aminochlorophenol is 1:1.2:1-1.

2.

6. The high-efficiency catalytic synthesis method of parabens according to claim 6, characterized in that: In step (16), the mass ratio of the phthalaldehyde to the aminopyridine is 1:1.6-2.

7. The high-efficiency catalytic synthesis method of parabens according to claim 7, characterized in that: In step (17), the mass ratio of the metal heteropoly acid salt to the modified UiO-66-NH2 is 1:3-5.

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