Preparation method of ascorbyl tetraisopalmitate

Abstract

The invention discloses a preparation method of ascorbyl tetraisopalmitate, which is characterized in that L-ascorbic acid and 2-hexylcapraldehyde are used as raw materials, SO4 < 2-> / Fe3O4 (at) TiO2-ZrO2 is used as a main catalyst, GO-Cu-PMA is used as a cocatalyst, and an oxidative esterification reaction is carried out in the presence of an oxidant to prepare the ascorbyl tetraisopalmitate, the mass ratio of the main catalyst to the cocatalyst is (4.5-5.5): 1, and the oxidant is persulfate. The preparation method of ascorbyl tetraisopalmitate provided by the invention has the advantages of mild reaction conditions, high reaction efficiency, simple preparation process, easy recovery of the catalyst, high product yield and purity, easy realization of large-scale production, and very strong industrial application value.

Description

Technical Field

[0001] This invention relates to a method for preparing ascorbic acid tetraisopalmitate, belonging to the field of chemical synthesis technology. Background Technology

[0002] Tetraisopalmitate (TAP) is an oil-soluble vitamin C derivative with wide applications in various fields, primarily cosmetics and personal care products, but also in the food and pharmaceutical industries. In cosmetics, TAP is commonly used in serums, lotions, creams, sprays, and masks, exerting antioxidant, anti-aging, whitening, and moisturizing effects. For example, it can promote collagen synthesis, improve skin elasticity and firmness, reduce fine lines and wrinkles, and inhibit melanin production, helping to even out skin tone. In the food industry, TAP is used as an antioxidant to extend shelf life, commonly found in oily foods, edible oils, and baked goods. In the pharmaceutical industry, TAP is used as a nutritional fortifier or antioxidant additive in ointments, capsules, and other formulations.

[0003] Currently, ascorbic acid tetraisopalmitate is mainly prepared by chemical catalysis, and the choice of catalyst has a significant impact on the preparation method. The current preparation of ascorbic acid tetraisopalmitate typically uses concentrated sulfuric acid as a catalyst, which has drawbacks such as low production efficiency, strong corrosiveness, high equipment requirements, dangerous operation, intense exothermic reaction, and difficulty in temperature control. Summary of the Invention

[0004] In view of the above-mentioned problems in the prior art, the purpose of this invention is to provide a method for preparing ascorbic acid tetraisopalmitate.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing ascorbic acid tetraisopalmitate, using L-ascorbic acid and 2-hexyldecanal as raw materials, and SO42- as a solvent. 2- Ascorbic acid tetraisopalmitate is prepared by oxidative esterification reaction using Fe3O4@TiO2-ZrO2 as the main catalyst and GO-Cu-PMA (PMA is an abbreviation for phosphomolybdic acid) as the co-catalyst in the presence of an oxidant. The mass ratio of the main catalyst to the co-catalyst is (4.5-5.5):1, and the oxidant is persulfate.

[0006] In one embodiment, the main catalyst SO4 2- / Fe3O4@TiO2-ZrO2 is obtained by first coating a composite shell of TiO2 and ZrO2 onto the surface of Fe3O4 as a core, and then subjecting Fe3O4@TiO2-ZrO2 to sulfation treatment; the co-catalyst GO-Cu-PMA is obtained by first reacting graphene oxide GO with Cu 2+ Composite, yielding GO-Cu 2+ The complex was then subjected to a reducing agent to react with GO-Cu. 2+ Cu in the complex 2+ Partially reduced to Cu + The GO-Cu complex was obtained, and then phosphomolybdic acid was loaded onto the GO-Cu complex to obtain the final product.

[0007] In a preferred embodiment, the main catalyst SO4 2- The preparation of / Fe3O4@TiO2-ZrO2 includes the following steps: 1) Under nitrogen protection, ferric chloride hexahydrate and ferrous chloride tetrahydrate were dissolved in water, heated to 55-65℃, ammonia water was added, and the reaction was stirred for 1-2 hours. The reaction was then stopped, magnetically separated, washed and dried to obtain Fe3O4 powder. 2) Disperse Fe3O4 powder uniformly in anhydrous ethanol, add tetrabutyl titanate and zirconium oxychloride, stir for 25-45 minutes, then slowly add dilute nitric acid dropwise. After the addition is complete, stir and gel at 55-65℃ for 5-7 hours to stop the reaction, centrifuge to separate, wash, dry and calcine the obtained solid to obtain Fe3O4@TiO2-ZrO2; 3) Fe3O4@TiO2-ZrO2 was impregnated in an aqueous sulfuric acid solution for 5-7 hours, then filtered, dried, calcined, and magnetically separated to obtain SO4. 2- / Fe3O4@TiO2-ZrO2.

[0008] In a preferred embodiment, in step 1), the molar ratio of ferric chloride hexahydrate to ferrous chloride tetrahydrate is 2:1; in step 2), the molar ratio of Fe3O4: tetrabutyl titanate: zirconium oxychloride is 1:(2-2.5):(2-2.5).

[0009] In a preferred embodiment, in step 2), the roasting temperature is 540-560℃ and the roasting time is 3-5 hours; in step 3), the roasting temperature is 490-510℃ and the roasting time is 2-4 hours.

[0010] In a preferred embodiment, the preparation of the co-catalyst GO-Cu-PMA includes the following steps: a) Graphene oxide was dispersed in water to obtain a GO dispersion. Copper nitrate trihydrate was added, and the mixture was stirred at room temperature for 10-14 hours to obtain GO-Cu.2+ Mixture; b) Heat to 50-60℃, add acetic acid, adjust pH to 4.5±0.2, and then slowly add an aqueous solution of reducing agent. After the addition is complete, keep the reaction at the temperature for 1-2 hours. The solution color gradually changes from blue-green to dark brown or dark green to obtain a GO-Cu mixture. c) Add phosphomolybdic acid and continue the reaction at 50-60℃ for 5-7 hours. After the reaction is stopped, cool to room temperature, collect the solid product, wash and dry it to obtain GO-Cu-PMA.

[0011] In a preferred embodiment, in step a), the concentration of the GO dispersion is 1.5-2.5 mg / mL, and the mass ratio of GO to copper nitrate trihydrate is 1:(0.5-0.7); in step b), the reducing agent is L-ascorbic acid, and the amount of the reducing agent is 55-65% of the molar amount of copper nitrate trihydrate; in step c), the amount of phosphomolybdic acid is 35-45% of the molar amount of copper nitrate trihydrate.

[0012] In one embodiment, the oxidant is any one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0013] In one embodiment, the molar ratio of L-ascorbic acid to 2-hexyldecaldehyde is 1:(4-4.5), the molar ratio of oxidant to L-ascorbic acid is (2.5-3):1, and the total amount of the catalyst is 5.5-6.5% of the mass of L-ascorbic acid.

[0014] One embodiment of the preparation of the ascorbic acid tetraisopalmitate includes the following steps: L-ascorbic acid, 2-hexyldecaldehyde, the main catalyst and the co-catalyst were dispersed in ethyl acetate to form a suspension; the oxidant was dissolved in water to form an oxidant solution. The suspension was heated to 35-45℃, and the oxidant solution was slowly added dropwise. After the addition was complete, the mixture was kept warm and stirred for 2-4 hours. The reaction was then stopped, and sodium bicarbonate aqueous solution was added to adjust the pH of the reaction system to 6.0±0.2. The mixture was kept warm and stirred for 14-16 hours to obtain ascorbic acid tetraisopalmitate.

[0015] In a preferred embodiment, after the reaction is completed, the reaction solution is magnetically separated to separate the main catalyst, washed with ethyl acetate, the washing liquid is combined with the reaction solution, the reaction solution is filtered to recover the co-catalyst, the filtrate is transferred to a separatory funnel, allowed to stand for separation, the organic phase is collected, washed, dried, filtered, and distilled under reduced pressure to obtain the crude product, which is recrystallized with n-hexane to obtain pure ascorbic acid tetraisopalmitate.

[0016] Compared with the prior art, the present invention has the following significant advantages: This invention uses L-ascorbic acid and 2-hexyldecanal as raw materials, and SO4 as the raw material. 2- Using Fe3O4@TiO2-ZrO2 as the main catalyst, GO-Cu-PMA as the co-catalyst, and persulfate as the oxidant, a one-pot method for preparing ascorbic acid tetraisopalmitate was developed. Compared with traditional liquid catalytic reactions represented by concentrated sulfuric acid, this method offers milder reaction conditions, higher reaction efficiency, simpler preparation process, easier catalyst recovery, higher product yield and purity, and is easy to scale up for production, making it highly valuable for industrial applications. Detailed Implementation

[0017] The technical solution of the present invention will be further described in detail and completely below with reference to the embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Example 1

[0018] 1. Main catalyst SO4 2- Preparation of Fe3O4@TiO2-ZrO2 1) Under nitrogen protection, ferric chloride hexahydrate (5.4 g, 20 mmol) and ferrous chloride tetrahydrate (2.0 g, 10 mmol) were dissolved in 100 mL of water, heated to 60 °C, and 15 mL of 25 wt% ammonia solution was added. The mixture was kept at this temperature and stirred for 1.5 hours. The reaction was then stopped, and the mixture was magnetically separated. The separated product was first washed with deionized water until neutral, then washed twice with ethanol, and then vacuum dried at 60 °C for 12 hours to obtain Fe3O4 powder. 2) Add 1.0 g Fe3O4 powder (4.3 mmol) to 100 mL anhydrous ethanol and sonicate for 30 minutes to ensure uniform dispersion. Add tetrabutyl titanate (3.4 g, 10 mmol) and zirconium oxychloride (3.2 g, 10 mmol), stir for 30 minutes, and then slowly add dilute nitric acid (composed of 0.5 mL concentrated nitric acid and 10 mL deionized water). After the addition is complete, stir and gel at 60 °C for 6 hours to stop the reaction. Centrifuge to separate the solid. Wash the obtained solid with ethanol, dry at 80 °C for 12 hours, and then calcine it in a muffle furnace at 550 °C for 4 hours to obtain Fe3O4@TiO2-ZrO2. 3) Fe3O4@TiO2-ZrO2 was impregnated in a 1 mol / L sulfuric acid aqueous solution (10 mL of sulfuric acid aqueous solution per gram of Fe3O4@TiO2-ZrO2) for 6 hours, filtered, dried at 100℃ for 12 hours, calcined in a muffle furnace at 500℃ for 3 hours, and then magnetically separated after natural cooling to obtain SO4. 2- / Fe3O4@TiO2-ZrO2.

[0019] II. Preparation of the co-catalyst GO-Cu-PMA a) Disperse 200 mg of graphene oxide in 100 mL of water and sonicate for 1 hour to obtain a GO dispersion with a concentration of 2 mg / mL. Add copper nitrate trihydrate (121 mg, 0.5 mmol) and stir at room temperature for 12 hours to ensure Cu 2+ GO-Cu is fully adsorbed / coordinated on the GO surface to obtain GO-Cu. 2+ The mixture is uniformly blue-green in color. b) Heat to 55℃, add approximately 0.2 mL of acetic acid, adjust the pH to 4.5 ± 0.2, and then slowly add an aqueous solution of L-ascorbic acid (53 mg, 0.3 mmol of L-ascorbic acid dissolved in 5 mL of deionized water). After the addition is complete, maintain the temperature for 1.5 hours. The solution color gradually changes from blue-green to dark brown or dark green (indicating the formation of Cu). + / Cu 2+ (mixed valence state species) to obtain GO-Cu mixture; c) Add phosphomolybdic acid (360 mg, 0.2 mmol) and continue the reaction at 55 °C for 6 hours (the heteropoly anions of PMA can be firmly bound to the positively charged GO-Cu complex through electrostatic interaction). After the reaction is stopped, cool to room temperature, centrifuge, wash the separated solid product three times with deionized water, wash it once with ethanol, dry it under vacuum at 60 °C for 24 hours, grind it to obtain powdered GO-Cu-PMA.

[0020] III. Preparation of ascorbic acid tetraisopalmitate L-ascorbic acid (176 g, 1 mol), 2-hexyldecaldehyde (960 g, 4.0 mol), and the main catalyst SO4 were added. 2- / Fe3O4@TiO2-ZrO2 and the co-catalyst GO-Cu-PMA (8.80g main catalyst, 1.76g co-catalyst, total 10.56g, main catalyst:co-catalyst mass ratio 5:1, catalyst dosage 6% of L-ascorbic acid mass) were dispersed in 1.2L ethyl acetate to form a suspension; the oxidant (ammonium persulfate, 638g, 2.8mol) was dissolved in 400mL water to form an oxidant solution; Heat the suspension to 40°C, slowly add the oxidant solution dropwise, and control the addition to be completed within 2 hours. After the addition is completed, keep the temperature and stir the reaction for 3 hours to end the reaction. Add a 10wt% sodium bicarbonate aqueous solution to adjust the pH of the reaction system to 6.0±0.2, keep the temperature and stir the reaction for 15 hours to end the reaction. After the reaction was completed, the temperature was lowered to room temperature, and the reaction solution was magnetically separated. The separated main catalyst was washed three times with ethyl acetate, and the washings were combined with the reaction solution. The reaction solution was filtered, and the co-catalyst was recovered. The filtrate was transferred to a separatory funnel, allowed to stand for separation, and the organic phase was collected. The organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, filtered, and distilled under reduced pressure to obtain a pale yellow oily crude product. The crude product was recrystallized from n-hexane to obtain a white crystalline product, which was pure ascorbic acid tetraisopalmitate (1047 g, yield 92%, HPLC purity 99.6%). Example 2

[0021] L-ascorbic acid (176 g, 1 mol), 2-hexyldecaldehyde (1080 g, 4.5 mol), and the main catalyst SO4 prepared in Example 1 were used. 2- / Fe3O4@TiO2-ZrO2 and the co-catalyst GO-Cu-PMA prepared in Example 1 (7.92 g main catalyst, 1.76 g co-catalyst, total 9.68 g, main catalyst:co-catalyst mass ratio of 4.5:1, catalyst dosage of 5.5% of L-ascorbic acid mass) were dispersed in 1.2 L ethyl acetate to form a suspension; the oxidant (potassium persulfate, 676 g, 2.5 mol) was dissolved in 400 mL water to form an oxidant solution; Heat the suspension to 40°C, slowly add the oxidant solution dropwise, and control the addition to be completed within 2 hours. After the addition is completed, keep the temperature and stir the reaction for 3 hours to end the reaction. Add a 10wt% sodium bicarbonate aqueous solution to adjust the pH of the reaction system to 6.0±0.2, keep the temperature and stir the reaction for 15 hours to end the reaction. After the reaction was completed, the temperature was lowered to room temperature, and the reaction solution was magnetically separated. The separated main catalyst was washed three times with ethyl acetate, and the washings were combined with the reaction solution. The reaction solution was filtered, and the co-catalyst was recovered. The filtrate was transferred to a separatory funnel, allowed to stand for separation, and the organic phase was collected. The organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, filtered, and distilled under reduced pressure to obtain a pale yellow oily crude product. The crude product was recrystallized from n-hexane to obtain a white crystalline product, which was pure ascorbic acid tetraisopalmitate (1024 g, yield 90%, HPLC purity 99.4%). Example 3

[0022] L-ascorbic acid (176 g, 1 mol), 2-hexyldecaldehyde (1008 g, 4.2 mol), and the main catalyst SO4 prepared in Example 1 were used. 2- / Fe3O4@TiO2-ZrO2 and the co-catalyst GO-Cu-PMA prepared in Example 1 (9.68 g main catalyst, 1.76 g co-catalyst, total 11.44 g, mass ratio of main catalyst to co-catalyst 5.5:1, catalyst dosage 6.5% of L-ascorbic acid mass) were dispersed in 1.2 L ethyl acetate to form a suspension; the oxidant (sodium persulfate, 714 g, 3 mol) was dissolved in 400 mL water to form an oxidant solution; Heat the suspension to 40°C, slowly add the oxidant solution dropwise, and control the addition to be completed within 2 hours. After the addition is completed, keep the temperature and stir the reaction for 3 hours to end the reaction. Add a 10wt% sodium bicarbonate aqueous solution to adjust the pH of the reaction system to 6.0±0.2, keep the temperature and stir the reaction for 15 hours to end the reaction. After the reaction was completed, the temperature was lowered to room temperature, and the reaction solution was magnetically separated. The separated main catalyst was washed three times with ethyl acetate, and the washings were combined with the reaction solution. The reaction solution was filtered, and the co-catalyst was recovered. The filtrate was transferred to a separatory funnel, allowed to stand for separation, and the organic phase was collected. The organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, filtered, and distilled under reduced pressure to obtain a pale yellow oily crude product. The crude product was recrystallized from n-hexane to obtain a white crystalline product, which was pure ascorbic acid tetraisopalmitate (1036 g, yield 91%, HPLC purity 99.3%).

[0023] In summary, this invention uses L-ascorbic acid and 2-hexyldecanal as raw materials, and SO4 as the... 2- Ascorbic acid tetraisopalmitate was prepared in a one-pot process using Fe3O4@TiO2-ZrO2 as the main catalyst, GO-Cu-PMA as the co-catalyst, and persulfate as the oxidant. After the reaction, the catalyst could be recovered using conventional separation methods, making catalyst recovery easy and post-reaction processing simple. No column chromatography was required; the pure target product could be obtained through simple recrystallization. The persulfate oxidant used not only possesses excellent oxidizing properties and is environmentally friendly but also exhibits synergistic effects with the catalyst, enabling efficient and selective oxidation reactions and effectively ensuring high yield and high purity (yield > 90%, purity > 99%) of the final product. During the reaction, the main catalyst, co-catalyst, and oxidant showed synergistic effects. Specifically, the co-catalyst GO-Cu-PMA adsorbed the reactant 2-hexyldecanoate, accelerating its oxidation, while also activating the persulfate oxidant, promoting its oxidation, and supplementing the acid catalytic function of the main catalyst. The main catalyst SO4... 2- / Fe3O4@TiO2-ZrO2 possesses solid superacid sites containing both Lewis and Brønsted acids. While providing an acidic environment for esterification, it can adsorb and activate the hydroxyl groups of aldehydes and ascorbic acid, forming a hemiacetal intermediate, which is then oxidized to an ester. Furthermore, it exhibits synergistic oxidation capabilities, working in conjunction with oxidants to complete the oxidative esterification reaction. Due to the synergistic effect between the main catalyst, co-catalyst, and oxidant, L-ascorbic acid and 2-hexyldecanal can undergo continuous oxidative esterification under mild conditions of 35-45℃. This allows for the one-pot preparation of ascorbic acid tetraisopalmitate, with mild reaction conditions, high reaction efficiency, a simple preparation process, and ease of large-scale production, making it highly valuable for industrial applications.

[0024] Finally, it should be noted that the above are only some preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing ascorbate tetraisopalmitate, characterized in that, It uses L-ascorbic acid and 2-hexyldecaldehyde as raw materials, and SO4 2- Ascorbic acid tetraisopalmitate was prepared by oxidative esterification reaction using Fe3O4@TiO2-ZrO2 as the main catalyst and GO-Cu-PMA as the co-catalyst in the presence of an oxidant. The mass ratio of the main catalyst to the co-catalyst was (4.5-5.5):1, and the oxidant was persulfate.

2. The method for preparing ascorbic acid tetraisopalmitate according to claim 1, characterized in that, The main catalyst SO4 2- / Fe3O4@TiO2-ZrO2 is obtained by first coating a composite shell of TiO2 and ZrO2 onto the surface of Fe3O4 as a core, and then subjecting Fe3O4@TiO2-ZrO2 to sulfation treatment; the co-catalyst GO-Cu-PMA is obtained by first reacting graphene oxide GO with Cu 2+ Composite, yielding GO-Cu 2+ The complex was then subjected to a reducing agent to react with GO-Cu. 2+ Cu in the complex 2+ Partially reduced to Cu + The GO-Cu complex was obtained, and then phosphomolybdic acid was loaded onto the GO-Cu complex to obtain the final product.

3. The method for preparing ascorbic acid tetraisopalmitate according to claim 2, characterized in that, The main catalyst SO4 2- The preparation of / Fe3O4@TiO2-ZrO2 includes the following steps: 1) Under nitrogen protection, ferric chloride hexahydrate and ferrous chloride tetrahydrate were dissolved in water, heated to 55-65℃, ammonia water was added, and the reaction was stirred for 1-2 hours. The reaction was then stopped, magnetically separated, washed and dried to obtain Fe3O4 powder. 2) Disperse Fe3O4 powder uniformly in anhydrous ethanol, add tetrabutyl titanate and zirconium oxychloride, stir for 25-45 minutes, then slowly add dilute nitric acid dropwise. After the addition is complete, stir and gel at 55-65℃ for 5-7 hours to stop the reaction, centrifuge to separate, wash, dry and calcine the obtained solid to obtain Fe3O4@TiO2-ZrO2; 3) Fe3O4@TiO2-ZrO2 was impregnated in an aqueous sulfuric acid solution for 5-7 hours, then filtered, dried, calcined, and magnetically separated to obtain SO4. 2- / Fe3O4@TiO2-ZrO2.

4. The method for preparing ascorbic acid tetraisopalmitate according to claim 3, characterized in that, In step 1), the molar ratio of ferric chloride hexahydrate to ferrous chloride tetrahydrate is 2:1; in step 2), the molar ratio of Fe3O4, tetrabutyl titanate, and zirconium oxychloride is 1:(2-2.5):(2-2.5).

5. The method for preparing ascorbic acid tetraisopalmitate according to claim 2, characterized in that, The preparation of the co-catalyst GO-Cu-PMA includes the following steps: a) Graphene oxide was dispersed in water to obtain a GO dispersion. Copper nitrate trihydrate was added, and the mixture was stirred at room temperature for 10-14 hours to obtain GO-Cu. 2+ Mixture; b) Heat to 50-60℃, add acetic acid, adjust pH to 4.5±0.2, and then slowly add an aqueous solution of reducing agent. After the addition is complete, keep the reaction at the temperature for 1-2 hours. The solution color gradually changes from blue-green to dark brown or dark green to obtain a GO-Cu mixture. c) Add phosphomolybdic acid and continue the reaction at 50-60℃ for 5-7 hours. After the reaction is stopped, cool to room temperature, collect the solid product, wash and dry it to obtain GO-Cu-PMA.

6. The method for preparing ascorbic acid tetraisopalmitate according to claim 5, characterized in that, In step a), the concentration of the GO dispersion is 1.5-2.5 mg / mL, and the mass ratio of GO to copper nitrate trihydrate is 1:(0.5-0.7); in step b), the reducing agent is L-ascorbic acid, and the amount of the reducing agent is 55-65% of the molar amount of copper nitrate trihydrate; in step c), the amount of phosphomolybdic acid is 35-45% of the molar amount of copper nitrate trihydrate.

7. The method for preparing ascorbic acid tetraisopalmitate according to claim 1, characterized in that, The oxidant is any one of ammonium persulfate, potassium persulfate, and sodium persulfate.

8. The method for preparing ascorbic acid tetraisopalmitate according to claim 1, characterized in that, The molar ratio of L-ascorbic acid to 2-hexyldecaldehyde is 1:(4-4.5), the molar ratio of oxidant to L-ascorbic acid is (2.5-3):1, and the total amount of the catalyst is 5.5-6.5% of the mass of L-ascorbic acid.

9. The method for preparing ascorbic acid tetraisopalmitate according to claim 1, characterized in that, The preparation of the ascorbic acid tetraisopalmitate includes the following steps: L-ascorbic acid, 2-hexyldecaldehyde, the main catalyst and the co-catalyst were dispersed in ethyl acetate to form a suspension; the oxidant was dissolved in water to form an oxidant solution. The suspension was heated to 35-45℃, and the oxidant solution was slowly added dropwise. After the addition was complete, the mixture was kept warm and stirred for 2-4 hours. The reaction was then stopped, and sodium bicarbonate aqueous solution was added to adjust the pH of the reaction system to 6.0±0.

2. The mixture was kept warm and stirred for 14-16 hours to obtain ascorbic acid tetraisopalmitate.

10. The method for preparing ascorbic acid tetraisopalmitate according to claim 9, characterized in that, After the reaction was completed, the reaction solution was magnetically separated to separate the main catalyst. The catalyst was washed with ethyl acetate, and the washing liquid was combined with the reaction solution. The reaction solution was filtered to recover the co-catalyst. The filtrate was transferred to a separatory funnel, allowed to stand for separation, and the organic phase was collected. The organic phase was washed, dried, filtered, and distilled under reduced pressure to obtain the crude product. The crude product was recrystallized with n-hexane to obtain pure ascorbic acid tetraisopalmitate.