Preparation method of 3-o-ethyl ascorbic acid

Abstract

The invention relates to the technical field of organic synthesis and biochemical engineering, and discloses a preparation method of 3-o-ethyl ascorbic acid, which comprises the following steps: (1) carrying out pre-acetylation reaction on ascorbic acid and vinyl acetate under the catalysis of lipase to obtain 6-acetyl ascorbic acid; (2) carrying out ethylation reaction on the product in the step (1) and diethyl carbonate by taking ionic liquid as a catalyst; (3) purifying the product by combining supercritical COextraction with membrane filtration; according to the preparation method of the 3-o-ethyl ascorbic acid provided by the invention, the purity and the yield of the product are remarkably improved through a synergistic process of lipase pre-acetylation, ionic liquid catalytic ethylation and supercritical COextraction combined with membrane filtration and purification; 6-hydroxyl of ascorbic acid can be selectively protected. The step utilizes the specific catalysis function of the enzyme to avoid the non-selective reaction of other hydroxyl groups.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis and biochemical engineering, in particular to a method for preparing 3-o-ethyl ascorbic acid. Background Art

[0002] 3-o-ethyl ascorbic acid, as an important vitamin C derivative, combines the antioxidant properties of ascorbic acid with good chemical stability, and has broad application prospects in cosmetics, food additives, and medicine.

[0003] In the cosmetics field, the antioxidant capacity of 3-o-ethyl ascorbic acid can effectively inhibit the production of skin melanin, promote collagen synthesis, and achieve the effects of whitening and anti-wrinkle; in the food industry, 3-o-ethyl ascorbic acid can be used as a high-efficiency antioxidant to extend the shelf life of food and prevent oil oxidation and rancidity; in the pharmaceutical field, due to the good biocompatibility and antioxidant activity of 3-o-ethyl ascorbic acid, it can be used to develop drugs to prevent and treat oxidative stress-related diseases.

[0004] At present, the traditional preparation methods of 3-o-ethyl ascorbic acid mainly have problems such as low reaction efficiency, unsatisfactory product purity and yield. Some processes not only have poor reaction selectivity and are prone to produce a large number of by-products, making subsequent separation and purification difficult, but also have harsh reaction conditions, requiring high temperature, high pressure or strong acid-base environments, which increases energy consumption and equipment requirements. At the same time, traditional purification methods such as recrystallization and column chromatography are difficult to effectively remove trace impurities, making the final product purity generally low and the yield generally low. The current situation of this low purity and low yield has limited the large-scale industrial production and high-end applications of 3-o-ethyl ascorbic acid. Summary of the Invention

[0005] In view of the problems in the prior art, the present invention provides a method for preparing 3-o-ethyl ascorbic acid.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing 3-o-ethyl ascorbic acid, comprising the following steps: (1) Pre-acetylation of ascorbic acid with vinyl acetate under lipase catalysis to obtain 6-acetyl ascorbic acid; (2) using an ionic liquid as a catalyst to carry out an ethylation reaction between the product of step (1) and diethyl carbonate; (3) The product was purified by supercritical CO2 extraction combined with membrane filtration.

[0007] As a further technical solution, the pre-acetylation reaction in step (1) is specifically as follows: Ascorbic acid and vinyl acetate are added to an organic solvent at a molar ratio of 1:(2-4) and mixed. The amount of the organic solvent used is determined to be sufficient to completely dissolve the ascorbic acid and vinyl acetate and ensure good fluidity of the reaction system. Immobilized lipase is then added at a ratio of 0.1-0.15 grams of immobilized lipase per gram of ascorbic acid. The reaction is continued for 3-4 hours at a temperature controlled at 30-45°C to allow the ascorbic acid to react with the vinyl acetate to form an acetylated ascorbic acid intermediate.

[0008] As a further technical solution, the amount of the organic solvent used is specifically: 1-2 liters of organic solvent is used for every mol of ascorbic acid.

[0009] As a further technical solution, the organic solvent is tetrahydrofuran.

[0010] As a further technical solution, the immobilized lipase is Candida antarctica LipaseB.

[0011] As a further technical solution, the ethylation reaction in step (2) is specifically as follows: The pre-acetylated product is mixed with diethyl carbonate in a molar ratio of 1:3-5, and 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid is added as a catalyst. The amount of the ionic liquid is 8-10% of the substrate mass. The reaction is carried out at 70-78°C for 6-8 hours.

[0012] As a further technical solution, the ionic liquid has both solvent and catalyst functions.

[0013] As a further technical solution, the specific operation of supercritical CO2 extraction in step (3) is as follows: The reaction liquid obtained in step (2) is placed in a vacuum distillation apparatus and subjected to vacuum distillation at a pressure of 1-2 kPa and a temperature of 55-60° C. to remove the organic solvent therein. The remaining material after distillation is transferred to a supercritical CO2 extraction device, and the CO2 flow rate is controlled to be 15-18 kg / h, the extraction pressure is controlled to be 20-22 MPa, the extraction temperature is controlled to be 40-50° C., and the extraction time is controlled to be 1-2 hours, thereby separating the unreacted ethylating agent and low-polarity by-products.

[0014] As a further technical solution, the membrane filtration described in step (3) is specifically as follows: the product after supercritical CO2 extraction is dissolved in an ethanol aqueous solution with a volume fraction of 70%-80% to form a solution with a mass concentration of 10%-12%, and the solution is passed through a nanofiltration membrane with a molecular weight cutoff of 500Da and an organic phase microfiltration membrane with a pore size of 0.22μm at a flow rate of 1.5-2m³ / h, and the operating pressure is controlled at 1-2MPa. The large molecular by-products and particulate impurities are removed by the filtration action of these two membranes.

[0015] As a further technical solution, step (3) is finally concentrated under reduced pressure and freeze-dried to obtain white crystalline 3-o-ethyl ascorbic acid with a purity of ≥99.5%.

[0016] Beneficial effects of the present invention: The present invention provides a method for preparing 3-o-ethyl ascorbic acid, which significantly improves the purity and yield of the product through a collaborative process of lipase pre-acetylation, ionic liquid-catalyzed ethylation, and supercritical CO2 extraction combined with membrane filtration purification: By using immobilized lipase to catalyze the pre-acetylation reaction of ascorbic acid with vinyl acetate, the 6-hydroxyl group of ascorbic acid can be selectively protected. This step utilizes the enzyme's specific catalytic function to avoid non-selective reactions of other hydroxyl groups, effectively reducing side reactions during the subsequent ethylation process and laying the foundation for improving product purity. Furthermore, the mild reaction conditions reduce energy consumption and equipment requirements, in line with the concept of green chemistry.

[0017] The ethylation reaction was carried out using the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate as a catalyst. The ionic liquid acts as both a solvent and a catalyst. Through hydrogen bonding with the reactant molecules, it promotes the targeted introduction of the ethyl group adjacent to the 3-hydroxyl group, achieving a regioselectivity exceeding 95%. Compared to traditional chemical catalysts, this method significantly improves the selectivity and efficiency of the reaction, significantly reduces the formation of byproducts, and thus increases the product yield and purity.

[0018] Supercritical CO2 extraction technology leverages the unique solubility properties of CO2 in a supercritical state to efficiently separate unreacted ethylating agents and low-polarity byproducts, avoiding the residue problems associated with traditional organic solvent extraction. Combined with graded filtration using nanofiltration and microfiltration membranes, it further removes macromolecular byproducts and particulate impurities. This combined purification method achieves comprehensive removal of impurities from low-polarity to macromolecular impurities, ultimately achieving a product purity of ≥99.5%, far exceeding the level of traditional processes. DETAILED DESCRIPTION

[0019] In order to help those skilled in the art better understand the present invention, the following clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0020] The present invention's method for preparing 3-o-ethyl ascorbic acid utilizes lipase-catalyzed preacetylation, ionic liquid-catalyzed ethylation, and combines supercritical CO extraction with membrane filtration purification technology to efficiently and efficiently produce 3-o-ethyl ascorbic acid with high purity. The lipase selectively catalyzes the preacetylation of ascorbic acid, protecting specific hydroxyl groups; the ionic liquid acts as both a solvent and a catalyst, promoting the ethylation reaction; and the supercritical CO extraction and membrane filtration effectively remove impurities, improving product purity.

[0021] Raw material preparation The raw materials used in this method, such as ascorbic acid, vinyl acetate, diethyl carbonate, immobilized lipase (Candida antarctica Lipase B), 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid, tetrahydrofuran, and ethanol, were all commercially available chemically pure or analytically pure reagents.

[0022] Immobilized lipase was purchased from Guangdong Maike Baisheng Biotechnology Co., Ltd., product model: CALB-A168; Preparation steps (1) Pre-acetylation reaction In a suitable reaction vessel, add ascorbic acid to vinyl acetate at a molar ratio of 1:(2-4). Simultaneously, add the organic solvent tetrahydrofuran (TEF). Use 1-2 liters of organic solvent per mole of ascorbic acid to ensure complete solubility of the ascorbic acid and vinyl acetate and good fluidity of the reaction system. Next, add immobilized lipase (Candida antarctica Lipase B) at a ratio of 0.1-0.15 grams per gram of ascorbic acid. Maintain the reaction temperature at 30-45°C for 3-4 hours to allow the ascorbic acid to react with vinyl acetate to form the acetylated ascorbic acid intermediate, 6-acetyl ascorbic acid.

[0023] (2) Ethylation reaction The product from the pre-acetylation reaction is mixed with diethyl carbonate in a molar ratio of 1:(3-5). 1-Butyl-3-methylimidazolium tetrafluoroborate ionic liquid is added as a catalyst, with the amount of 1-butyl-3-methylimidazolium tetrafluoroborate being 8-10% of the mass of the substrates (pre-acetylated product and diethyl carbonate). Because this ionic liquid functions as both a solvent and a catalyst, it effectively promotes the reaction. The reaction system is then kept at 70-78°C for 6-8 hours to allow the ethylation of 6-acetyl ascorbic acid with diethyl carbonate.

[0024] (3) Purification of products Supercritical CO2 extraction: The reaction solution obtained in step (2) is transferred to a vacuum distillation apparatus and subjected to vacuum distillation at a pressure of 1-2 kPa and a temperature of 55-60°C to remove the organic solvent. The remaining material after distillation is transferred to a supercritical CO2 extraction device, with the CO2 flow rate controlled at 15-18 kg / h, the extraction pressure at 20-22 MPa, the extraction temperature at 40-50°C, and the extraction time at 1-2 hours, thereby separating the unreacted ethylating agent and low-polarity by-products.

[0025] Membrane filtration: The product after supercritical CO2 extraction is dissolved in a 70%-80% ethanol-water solution to form a solution with a mass concentration of 10%-12%. This solution is passed through a nanofiltration membrane with a molecular weight cutoff of 500 Da and an organic phase microfiltration membrane with a pore size of 0.22 μm at a flow rate of 1.5-2 m³ / h. The operating pressure is controlled at 1-2 MPa. The filtration action of these two membranes removes large molecular byproducts and particulate impurities.

[0026] Concentration under reduced pressure and freeze drying: The solution after membrane filtration is concentrated under reduced pressure to remove most of the solvent, and then freeze-dried to finally obtain white crystalline 3-o-ethyl ascorbic acid with a purity of ≥99.5%. Specific embodiments Example 1 Preacetylation: Add 1 mol of ascorbic acid and 2 mol of vinyl acetate to a reaction vessel, followed by 1 L of tetrahydrofuran. Next, add 0.1 g of immobilized lipase (Candida antarctica Lipase B) per gram of ascorbic acid and react at 30°C for 3 hours to produce 6-acetyl ascorbic acid.

[0028] Ethylation reaction: The above pre-acetylated product was mixed with 3 mol of diethyl carbonate, and 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid (8% by weight of the substrate) was added, and the mixture was reacted at 70°C for 6 hours.

[0029] Purified product: Supercritical CO2 extraction: The reaction solution was distilled under reduced pressure at 1 kPa and 55°C to remove the organic solvent. The remaining material was transferred to a supercritical CO2 extraction device with a CO2 flow rate of 15 kg / h and extraction at 20 MPa and 40°C for 1 hour.

[0030] Membrane filtration: The extracted product was dissolved in a 70% volume fraction ethanol aqueous solution to form a solution with a mass concentration of 10%, which was passed through the nanofiltration membrane and microfiltration membrane in sequence at a flow rate of 1.5 m³ / h and an operating pressure of 1 MPa.

[0031] Concentration under reduced pressure and freeze drying: The solution after membrane filtration was concentrated under reduced pressure and freeze dried to obtain white crystalline 3-o-ethyl ascorbic acid with a purity of 99.6% after testing.

[0032] Example 2 Preacetylation: Add 1 mol of ascorbic acid and 3 mol of vinyl acetate to a reaction vessel, along with 1.5 L of tetrahydrofuran. Add 0.12 g of immobilized lipase (Candida antarctica Lipase B) per gram of ascorbic acid and react at 38°C for 3.5 hours to produce 6-acetyl ascorbic acid.

[0033] Ethylation reaction: The pre-acetylated product was mixed with 4 mol of diethyl carbonate, and 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid (9% by weight of the substrate) was added and reacted at 74°C for 7 hours.

[0034] Purified product: Supercritical CO2 extraction: The reaction solution was distilled under reduced pressure at 1.5 kPa and 58°C to remove the organic solvent. The remaining material was transferred to a supercritical CO2 extraction device with a controlled CO2 flow rate of 16 kg / h and extraction at 21 MPa and 45°C for 1.5 hours.

[0035] Membrane filtration: The extracted product was dissolved in an ethanol aqueous solution with a volume fraction of 75% to form a solution with a mass concentration of 11%. The solution was passed through the nanofiltration membrane and the microfiltration membrane in sequence at a flow rate of 1.8 m³ / h and an operating pressure of 1.5 MPa.

[0036] Concentration under reduced pressure and freeze drying: The solution after membrane filtration was concentrated under reduced pressure and freeze dried to obtain white crystalline 3-o-ethyl ascorbic acid with a purity of 99.7%.

[0037] Example 3 Preacetylation: Add 1 mol of ascorbic acid and 4 mol of vinyl acetate to a reaction vessel, followed by 2 L of tetrahydrofuran. Add 0.15 g of immobilized lipase (Candida antarctica Lipase B) per gram of ascorbic acid and react at 45°C for 4 hours to produce 6-acetyl ascorbic acid.

[0038] Ethylation reaction: The pre-acetylated product was mixed with 5 mol of diethyl carbonate, and 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid (10% by weight of the substrate) was added and reacted at 78°C for 8 hours.

[0039] Purified product: Supercritical CO2 extraction: The reaction solution was distilled under reduced pressure at 2 kPa and 60°C to remove the organic solvent. The remaining material was transferred to a supercritical CO2 extraction device with a CO2 flow rate of 18 kg / h. Extraction was performed at 22 MPa and 50°C for 2 hours.

[0040] Membrane filtration: The extracted product was dissolved in an 80% ethanol aqueous solution to form a 12% mass concentration solution, which was passed through the nanofiltration membrane and microfiltration membrane in sequence at a flow rate of 2 m³ / h and an operating pressure of 2 MPa.

[0041] Concentration under reduced pressure and freeze drying: The solution after membrane filtration was concentrated under reduced pressure and freeze dried to obtain white crystalline 3-o-ethyl ascorbic acid with a purity of 99.8% after testing.

[0042] Comparative Example 1 The difference from Example 1 was that immobilized lipase (Candida antarctica Lipase B) was not used in the preacetylation reaction. The remaining operations were identical. The final product had a purity of only 93.1% and a low yield, indicating that the immobilized lipase played a key catalytic role in the preacetylation reaction.

[0043] Comparative Example 2 The difference from Example 1 was that 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid was not used in the ethylation reaction; the remaining operations were identical. The reaction proceeded slowly, and the product yield and purity were significantly lower than those in Example 1, demonstrating that the ionic liquid plays the important role of both solvent and catalyst in the ethylation reaction.

[0044] Comparative Example 3 The difference from Example 1 was that supercritical CO extraction was not performed during the purification process; only membrane filtration was used, with all other operations remaining the same. The resulting product had a purity of 95.2%, lower than that of Example 1, demonstrating that supercritical CO extraction effectively removed unreacted ethylating agent and low-polarity byproducts, thereby improving product purity.

[0045] test Purity detection experiment Test method: Referring to the high performance liquid chromatography (HPLC) detection principle in "GB / T22388-2008 Detection Method for Melamine in Raw Milk and Dairy Products" and combining the instrument operation specifications of "GB / T37109-2018 General Rules for High Performance Liquid Chromatographic Analysis of Chemical Reagents", the products of Examples 1-3 and Comparative Examples 1-3 were tested for purity. A C18 reverse phase chromatography column (4.6×250mm, 5μm) was used, the mobile phase was acetonitrile-water (volume ratio 15:85), the flow rate was 1.0mL / min, the column temperature was 30°C, the detection wavelength was 243nm, and the injection volume was 10μL. A standard curve was drawn with 3-o-ethyl ascorbic acid standard, and the sample purity was calculated by the peak area external standard method; Data comparison: Table 1

[0046] It can be seen from Table 1 that the product obtained by the present invention has higher purity.

[0047] 2. Yield comparison experiment Experimental Method: The theoretical yield of 3-o-ethyl ascorbic acid was calculated based on the raw material input. The actual product mass was weighed using a precision balance (accuracy 0.0001g). The yield was calculated using the formula "Yield (%) = (Actual Yield / Theoretical Yield) × 100%." Each experiment was repeated three times, and the average value was calculated.

[0048] Table 2

[0049] As can be seen from Table 2, the product yield obtained by the method of the present invention is higher.

[0050] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing 3-o-ethyl ascorbic acid, characterized in that: The following steps are involved: (1) Pre-acetylation of ascorbic acid with vinyl acetate under lipase catalysis to obtain 6-acetyl ascorbic acid; (2) using an ionic liquid as a catalyst to carry out an ethylation reaction between the product of step (1) and diethyl carbonate; (3) The product was purified by supercritical CO2 extraction combined with membrane filtration.

2. The method for preparing 3-o-ethyl ascorbic acid according to claim 1, wherein The pre-acetylation reaction described in step (1) is specifically as follows: Ascorbic acid and vinyl acetate are added to an organic solvent at a molar ratio of 1:(2-4) and mixed. The amount of the organic solvent used is determined to be sufficient to completely dissolve the ascorbic acid and vinyl acetate and ensure good fluidity of the reaction system. Immobilized lipase is then added at a ratio of 0.1-0.15 grams of immobilized lipase per gram of ascorbic acid. The reaction is continued for 3-4 hours at a temperature controlled at 30-45°C to allow the ascorbic acid to react with the vinyl acetate to form an acetylated ascorbic acid intermediate.

3. The method for preparing 3-o-ethyl ascorbic acid according to claim 2, wherein The specific amount of the organic solvent is as follows: 1-2 liters of organic solvent is used for each mole of ascorbic acid.

4. The method for preparing 3-o-ethyl ascorbic acid according to claim 2, wherein The organic solvent is tetrahydrofuran.

5. The method for preparing 3-o-ethyl ascorbic acid according to claim 1, wherein The immobilized lipase was Candida antarctica Lipase B.

6. The method for preparing 3-o-ethyl ascorbic acid according to claim 1, wherein The ethylation reaction in step (2) is specifically as follows: The pre-acetylated product is mixed with diethyl carbonate in a molar ratio of 1:3-5, and 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid is added as a catalyst. The amount of the ionic liquid is 8-10% of the substrate mass. The reaction is carried out at 70-78°C for 6-8 hours.

7. The method for preparing 3-o-ethyl ascorbic acid according to claim 6, wherein The ionic liquid has both solvent and catalyst functions.

8. The method for preparing 3-o-ethyl ascorbic acid according to claim 1, wherein The specific operation of supercritical CO2 extraction in step (3) is as follows: The reaction liquid obtained in step (2) is placed in a vacuum distillation apparatus and subjected to vacuum distillation at a pressure of 1-2 kPa and a temperature of 55-60° C. to remove the organic solvent therein. The remaining material after distillation is transferred to a supercritical CO2 extraction device, and the CO2 flow rate is controlled to be 15-18 kg / h, the extraction pressure is controlled to be 20-22 MPa, the extraction temperature is controlled to be 40-50° C., and the extraction time is controlled to be 1-2 hours, thereby separating the unreacted ethylating agent and low-polarity by-products.

9. The method for preparing 3-o-ethyl ascorbic acid according to claim 1, wherein The membrane filtration described in step (3) is specifically as follows: the product after supercritical CO2 extraction is dissolved in an ethanol aqueous solution with a volume fraction of 70%-80% to form a solution with a mass concentration of 10%-12%, and the solution is passed through a nanofiltration membrane with a molecular weight cutoff of 500Da and an organic phase microfiltration membrane with a pore size of 0.22μm at a flow rate of 1.5-2m³ / h. The operating pressure is controlled at 1-2MPa, and the large molecular by-products and particulate impurities are removed through the filtration action of these two membranes.

10. The method for preparing 3-o-ethyl ascorbic acid according to claim 1, wherein Step (3) is finally concentrated under reduced pressure and freeze-dried to obtain white crystalline 3-o-ethyl ascorbic acid with a purity of ≥99.5%.

Images