Method for preparing vitamin A intermediate through lipase catalysis

Abstract

The invention belongs to the field of compound synthesis, and particularly relates to a method for preparing a vitamin A intermediate through lipase catalysis, which comprises the following steps: mixing acetic acid and organic alkali in an organic solvent to obtain an acetic acid organic alkali salt solution; the method comprises the following steps: mixing a raw material containing vitamin A intermediate hydride, lipase and optional polyhydric alcohols and antioxidants in an organic solvent to obtain a base solution, dropwise adding an acetic acid organic alkali salt solution into the base solution to carry out acetylation reaction, and carrying out rectification dehydration on a reaction system before acetylation reaction and in the reaction process, the obtained reaction product is the vitamin A intermediate. The method not only can improve the conversion rate, the yield and the selectivity of the monoacyl compound, but also can avoid the problems of excessive diacyl compounds and complicated post-treatment caused by the traditional use of ester or anhydride acylating agents.

Description

Technical Field

[0001] The invention belongs to the field of compound synthesis, and particularly relates to a method for preparing a vitamin A intermediate by catalysis using lipase. Background Art

[0002] Vitamin A is an oil-soluble vitamin with extensive applications in additives and biopharmaceuticals. A key component of rhodopsin, a photoreceptor in the retina, vitamin A effectively prevents night blindness and vision loss. Vitamin A promotes bone and tooth development and cell differentiation, and is particularly crucial for children's height growth and bone health. As a nutritional supplement, it is widely added to infant formula, maternal nutrition, and dairy products to enhance nutritional value and improve taste. Vitamin A regulates the growth and differentiation of epithelial cells in the skin, respiratory tract, and digestive tract, preventing dryness and keratinization. It is used in anti-wrinkle and spot-lightening skincare products. As an animal feed additive, vitamin A can improve the growth rate and health of livestock and poultry.

[0003] Currently, chemical synthesis routes for vitamin A include the Hoffmann-La Roche method, which utilizes a C13+C1+C6 route, and the BASF method, which utilizes a C15+C5 route characterized by the Witting reaction. In the Hoffmann-La Roche method, the intermediate (hydride) undergoes acetylation to produce a monoacyl compound and a diacyl compound, which are then brominated and debrominated to produce vitamin A acetate. The vitamin A intermediate hydride has the structure shown in formula (1), the vitamin A intermediate monoacyl compound has the structure shown in formula (2), and the vitamin A intermediate diacyl compound has the structure shown in formula (3).

[0004]

[0005]

[0006] US3671575 reports a traditional acetylation method for preparing vitamin intermediates. Acylation is performed using acetyl chloride or acetic anhydride under the protection of an organic base such as pyridine. The main product is a mixture of monoacyl and diacyl compounds. However, since the diacyl compounds consume more hydrobromic acid in the subsequent debromination process, it is desirable to obtain a higher ratio of monoacyl compounds.

[0007] CN105154480A discloses a lipase-catalyzed hydride acetylation method, which includes using the cells obtained by fermentation culture of Aspergillus oryzae WZ007 as a catalyst and an organic solution of an acylating agent as a reaction medium for reaction. Wherein, the acylating agent is vinyl acetate, isopropyl acetate, acetic anhydride or ethyl acetate. The regional selectivity of this method can reach 99.5%, the reaction conversion rate can reach 100%, the catalyst can be reused, the downstream separation is simple, the energy consumption is low, the production cost is greatly reduced, the environmental pollution is small, and it is suitable for industrial production. However, since commonly used acylating agents generally use esters or anhydrides, for example, vinyl acetate, isopropyl acetate, ethyl acetate or acetic anhydride. Among them, esters will affect the debromination reaction, and special treatment is required before the subsequent reaction process. First, solvent replacement must be performed to remove the unreacted esters before continuing to the next step. Moreover, since esters and commonly used organic solvents are difficult to separate at boiling points, they must also be washed with saponification water before they can be applied. The use of anhydrides often results in higher diacyl compounds. In addition, due to the high cost of immobilized enzymes, the enzyme must be applied more than 20 times to achieve cost advantages. However, there are few reports at this stage, or even if the application frequency reaches more than 20 times, the raw materials and solvents must undergo special treatment. Summary of the Invention

[0008] The present invention aims to provide a novel method for preparing a vitamin A intermediate using lipase, which can not only improve the conversion rate and yield as well as the selectivity of monoacyl compounds, but also avoid the problem of complex post-processing caused by the traditional use of ester or anhydride acylating agents.

[0009] Specifically, the method for preparing a vitamin A intermediate catalyzed by lipase provided by the present invention comprises mixing acetic acid and an organic base in an organic solvent to obtain an acetic acid organic base salt solution, mixing a raw material containing a vitamin A intermediate hydride represented by formula (1), a lipase, and optionally a polyol and an antioxidant in the organic solvent to obtain a base liquid, dripping the acetic acid organic base salt solution into the base liquid to carry out an acetylation reaction, and performing distillation to remove water from the reaction system before and during the acetylation reaction. The obtained reaction product is the vitamin A intermediate;

[0010]

[0011] The key to the present invention is to use lipase as a catalyst, acetic acid as an acylating agent, and an organic base as a protective agent. A feeding method is adopted in which acetic acid and the organic base are first mixed to prepare an acetic acid organic base salt and then added dropwise to the reaction system. In addition, distillation is used to remove water before and during the acetylation reaction. In this way, not only can the conversion rate of vitamin A hydride and the yield of vitamin A intermediates be significantly improved, but also the selectivity of monoacyl compounds in vitamin A intermediates can be improved, thereby avoiding the problems of excessive diacyl compounds and complicated post-processing caused by using ester or anhydride acylating agents in traditional methods.

[0012] In a preferred embodiment, the method for preparing vitamin A intermediates by lipase catalysis further includes washing the raw material containing vitamin A intermediate hydride with water before mixing. At this time, the hexamethylenetetramine hydride in the raw material can be removed, reducing the attachment and poisoning of the hexamethylenetetramine hydride polymerization in the raw material to the immobilized lipase, thereby increasing the number of applications of the lipase.

[0013] In a preferred embodiment, the acetylation reaction uses a polyol as an active agent, which can improve the enzyme catalytic activity, thereby increasing the reaction rate and conversion rate.

[0014] In a preferred embodiment, the acetylation reaction uses dichloromethane as a solvent. Since dichloromethane is used as a solvent in both the upstream and downstream of the traditional industrial vitamin A preparation process, the acetylation reaction using dichloromethane as a solvent does not require solvent replacement. After a simple water wash, the subsequent reaction can be carried out, which can avoid the yield loss in the replacement process.

[0015] In a preferred embodiment, the method for preparing vitamin A intermediates catalyzed by lipase further comprises removing water from the bottom liquid by distillation to control the water content therein to below 0.05% before adding the organic base salt of acetic acid, which is more conducive to improving the reaction yield. DETAILED DESCRIPTION

[0016] The method for preparing a vitamin A intermediate by lipase catalysis provided by the present invention comprises mixing acetic acid and an organic base in an organic solvent to obtain an acetic acid organic base salt solution, mixing a raw material containing a vitamin A intermediate hydride, a lipase, and optionally a polyol and an antioxidant in an organic solvent to obtain a base liquid, dropping the acetic acid organic base salt solution into the base liquid to perform an acetylation reaction, and rectifying and removing water from the reaction system before and during the acetylation reaction. The resulting reaction product is the vitamin A intermediate. The method of first mixing acetic acid and an organic base to form an acetic acid organic base salt and then dropping it into the reaction system to feed the raw materials not only reduces the entrainment of the organic base during azeotropic dehydration during the reaction process, but also avoids the problem of excessively slow acylation rate when there is too much organic base and too little acetic acid in the early stage, resulting in the accumulation of a large amount of acetic acid organic base salt and the destruction of the hydride, thereby further improving the yield of the product and the selectivity of the monoacyl compound.

[0017] In the present invention, the vitamin A intermediate hydride has a structure as shown in formula (1). The acetylation reaction process is shown in reaction formula (1'). The acetylation reaction product is mainly composed of the vitamin A intermediate monoacyl compound (having the structure shown in formula (2)), and may contain a small amount of the vitamin A intermediate diacyl compound (having the structure shown in formula (3)).

[0018]

[0019]

[0020] In the present invention, the type of lipase is not particularly limited, as long as it can catalyze the esterification reaction of vitamin A intermediate hydride with acetic acid. It can be selected from at least one lipase obtained by fermentation of Candida antarctic, Thermomyces lanuginosus, Rhizomucor miehei, Aspergillus niger, Candida rugosa, and Pseudononas sp., and is particularly preferably Candida antarctic lipase, for example, Novozymes lipase novozym435. The inventors of the present invention have found that when the lipase is Candida antarctic lipase, it has higher catalytic efficiency and can further improve the yield of monoacyl compounds. In addition, the mass ratio of the lipase to the vitamin A intermediate hydride is preferably (0.05-0.2):1, such as 0.05:1, 0.08:1, 0.1:1, 0.12:1, 0.15:1, 0.18:1, 0.2:1 or any value therebetween.

[0021] In the present invention, the molar ratio of acetic acid to vitamin A intermediate hydride is preferably (1-1.2):1, such as 1:1, 1.02:1, 1.05:1, 1.08:1, 1.1:1, 1.12:1, 1.15:1, 1.18:1, 1.2:1, or any value therebetween. Furthermore, using acetic acid as the acylating agent can reduce post-processing steps, avoiding the problem of using ester acylating agents that require removal before proceeding to the next reaction.

[0022] In the present invention, the acetylation reaction preferably uses an organic base as a protective agent. The organic base may be, for example, at least one of an amine compound and a pyridine compound. Specific examples of the amine compound include, but are not limited to, at least one of diethylamine and triethylamine. Specific examples of the pyridine compound include, but are not limited to, at least one of pyridine, 2-methylpyridine, and 4-dimethylaminopyridine. The molar ratio of the organic base to acetic acid is preferably (1-1.5):1, such as 1:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.4:1, 1.45:1, 1.5:1, or any value therebetween. Furthermore, the time for adding the organic base salt solution of acetic acid to the base solution is preferably controlled to be between 1 and 6 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any value therebetween.

[0023] In the present invention, the acetylation reaction preferably uses a polyol as an active agent. The polyol is a compound containing two or more hydroxyl groups in the molecule, preferably a C1-C 10 The polyol includes, but is not limited to, at least one of ethylene glycol, propylene glycol, glycerol, butylene glycol, pentanediol, hexylene glycol, diethylene glycol, dipropylene glycol, and trimethylolpropane. The polyol is preferably used in an amount of 0.2% to 0.5% by weight of the lipase, such as 0.2%, 0.3%, 0.4%, 0.5%, or any value therebetween.

[0024] In the present invention, the acetylation reaction is preferably carried out in the presence of an antioxidant. The antioxidant may be at least one of butylated hydroxyanisole, 2,6-di-tert-butyl-4-methylphenol (BHT), pentaerythritol (Antioxidant 1010), octadecyl propionate (Antioxidant 1076), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane (Antioxidant CA), and tert-butylhydroquinone. The mass ratio of the antioxidant to the vitamin A intermediate hydride is preferably (0.5% to 1%):1, such as 0.5%:1, 0.6%:1, 0.7%:1, 0.8%:1, 0.9%:1, 1%:1, or any value therebetween.

[0025] In the present invention, the type of organic solvent used in the acetylation reaction is not particularly limited and can be any of the existing liquid inert media. Dichloromethane is particularly preferred as the organic solvent, which is the same as the upstream and downstream solvents for vitamin A synthesis. No solvent replacement or special treatment is required, thus simplifying the treatment process.

[0026] In the present invention, the lipase-catalyzed method for preparing a vitamin A intermediate preferably further comprises washing the raw material containing the vitamin A intermediate hydride with water before mixing. This effectively removes the hexanol hydride from the raw material, reduces the toxicity of the polymer obtained during the reaction to the lipase, and thereby effectively increases the number of enzyme applications. The number of water washes is not particularly limited, as long as the hexanol hydride is substantially removed, and generally can be 1 to 5 times.

[0027] In the present invention, the method for preparing vitamin A intermediates catalyzed by lipase preferably further includes removing water from the bottom liquid by distillation to control the water content therein to below 0.05% before adding the organic base salt of acetic acid. This can effectively avoid the adverse effects of water on the acetylation reaction process and further improve the reaction yield.

[0028] In the present invention, the acetylation reaction temperature is preferably 30-40° C., such as 30° C., 32° C., 34° C., 36° C., 38° C., 40° C., or any value therebetween. The acetylation reaction time is preferably such that the reaction is stopped when the water content in the system reaches below 0.05%.

[0029] The present invention will be described in detail below through examples.

[0030] Detection method of vitamin A intermediates:

[0031] Column: Dalian Elite Hypersil ODS2 5um×4.6mm×250mm;

[0032] Mobile phase: acetonitrile:isopropanol:water (volume ratio) = 75.0:12.5:12.5;

[0033] Detector: UV 210nm;

[0034] Column temperature: 30°C;

[0035] Flow rate: 1.0 mL / min;

[0036] Analysis time: 20 min;

[0037] Injection volume: 20 μL.

[0038] Example 1

[0039] To a 250 mL three-necked flask, add 200 g of dichloromethane and 14.62 g (0.145 mol) of triethylamine. Slowly add 8.28 g (0.138 mol) of acetic acid while stirring. Stir for 30 minutes to obtain an organic alkali salt solution of acetic acid. Transfer this solution to a dropping funnel and set aside. Take 200 g of a dichloromethane solution containing 20% (40 g, 0.13 mol) of the vitamin A intermediate hydride in 20% dichloromethane and wash twice with 50 mL of deionized water to obtain a hydride solution, which is set aside.

[0040] The above hydride solution was added to a 500 mL three-necked flask equipped with a distillation tower, and 0.20 g of 2,6-di-tert-butyl-4-methylphenol, 4 g of immobilized lipase novozym435 and 0.008 g of propylene glycol were added. The mixture was stirred under vacuum and heated to 30° C. After the water content of the dichloromethane extracted from the top of the distillation tower was less than 0.05%, the acetic acid organic base salt solution was added dropwise. The addition time was controlled to 4 h. After the addition was completed, the reaction was continued. After the water content of the extracted dichloromethane was less than 0.05%, the reaction was completed. The enzyme catalyst was filtered out, and the reaction solution was washed twice with water to obtain 195 g of vitamin A intermediate solution. Liquid chromatography detection showed that the monoacyl content was 23.18%, the yield was 99.3%, the conversion rate was 100%, and the mass ratio of monoacyl and diacyl was 99.8%:0.2%.

[0041] Example 2

[0042] To a 250 mL three-necked flask, add 200 g of dichloromethane and 12.47 g (0.158 mol) of pyridine. Slowly add 8.68 g (0.145 mol) of acetic acid while stirring. Stir for 30 minutes to obtain an organic alkali salt solution of acetic acid. Transfer this solution to a dropping funnel and set aside. Take 200 g of a dichloromethane solution containing 20% (40 g, 0.13 mol) of the vitamin A intermediate hydride in 20% dichloromethane and wash twice with 50 mL of deionized water to obtain a hydride solution, which is set aside.

[0043] In a 500 mL three-necked flask equipped with a distillation tower, the dichloromethane solution of the above hydride was added, 0.40 g of 2,6-di-tert-butyl-4-methylphenol, 8 g of immobilized lipase novozym435, and 0.04 g of glycerol were added, and the mixture was stirred under vacuum and heated to 40° C. After the water content of the dichloromethane extracted from the top of the distillation tower was less than 0.05%, the acetic acid organic base salt solution was added dropwise, and the addition time was controlled to 4 h. After the addition was completed, the reaction was continued. After the water content of the extracted dichloromethane was less than 0.05%, the reaction was completed, the enzyme catalyst was filtered out, and the reaction solution was washed twice with water to obtain 211 g of vitamin A intermediate solution. The monoacyl content was 21.34% by liquid chromatography, the yield was 98.9%, the conversion rate was 100%, and the mass ratio of monoacyl and diacyl was 99.7%:0.3%.

[0044] Example 3

[0045] To a 250 mL three-necked flask, add 200 g of dichloromethane and 18.35 g (0.197 mol) of 2-picoline. Slowly add 9.47 g (0.158 mol) of acetic acid while stirring. Stir for 30 minutes to obtain an organic alkali salt solution of acetic acid. Transfer this solution to a dropping funnel and set aside. Take 200 g of a dichloromethane solution containing 20% (40 g, 0.13 mol) of the vitamin A intermediate hydride in 200 g of water and wash it twice with 50 mL of deionized water to obtain a hydride solution, which is set aside.

[0046] The above hydride solution was added to a 500 mL three-necked flask equipped with a distillation tower, 0.20 g of butylated hydroxyanisole, 2 g of immobilized lipase novozym435 and 0.006 g of ethylene glycol were added, and the temperature was raised to 40° C. with slight vacuum stirring. After the water content of the dichloromethane extracted from the top of the distillation tower was less than 0.05%, the acetic acid organic base salt solution was added dropwise, and the addition time was controlled to 4 h. After the addition was completed, the reaction was continued. After the water content of the extracted dichloromethane was less than 0.05%, the reaction was completed, the enzyme catalyst was filtered out, and the reaction solution was washed twice with water to obtain 185 g of vitamin A intermediate solution. Liquid chromatography detection showed that the monoacyl content was 24.39%, the yield was 99.1%, the conversion rate was 100%, and the mass ratio of monoacyl and diacyl was 99.5%:0.5%.

[0047] Example 4

[0048] To a 250 mL three-necked flask, add 200 g of dichloromethane and 13.96 g (0.138 mol) of triethylamine. Slowly add 7.89 g (0.131 mol) of acetic acid while stirring. Stir for 30 minutes to obtain an organic alkali salt solution of acetic acid. Transfer this solution to a dropping funnel and set aside. Take 200 g of a dichloromethane solution containing 20% (40 g, 0.13 mol) of the vitamin A intermediate hydride in 200 g of water and wash twice with 50 mL of deionized water to obtain a hydride solution, which is set aside.

[0049] The above hydride solution was added to a 500 mL three-necked flask equipped with a distillation tower, and 0.28 g of tert-butylhydroquinone, 4 g of lipase novozym435 and 0.016 g of hexanediol were added. The temperature was raised to 40° C. with slight vacuum stirring. After the water content of the dichloromethane extracted from the top of the distillation tower was less than 0.05%, the acetic acid organic alkali salt solution was added dropwise. The addition time was controlled to 4 h. After the addition was completed, the reaction was continued. After the water content of the extracted dichloromethane was less than 0.05%, the reaction was completed. The enzyme catalyst was filtered out, and the reaction solution was washed twice with water to obtain 165 g of vitamin A intermediate solution. Liquid chromatography detection showed that the monoacyl content was 25.80%, the yield was 93.5%, the conversion rate was 95.0%, and the mass ratio of monoacyl and diacyl was 99.8%:0.2%.

[0050] Example 5: No polyol added

[0051] A vitamin A intermediate was prepared according to the method of Example 1, except that propylene glycol was replaced by the same weight portion of dichloromethane. The remaining conditions were the same as in Example 1, and 175 g of a vitamin A intermediate solution was obtained. Liquid chromatography analysis showed that the monoacyl content was 21.88%, the yield was 84.10%, the conversion rate was 85.40%, and the mass ratio of monoacyl and diacyl was 99.7%:0.3%.

[0052] Example 6: The raw material containing the vitamin A intermediate hydride was not washed with water.

[0053] The vitamin A intermediate was prepared according to the method of Example 1, except that the raw material containing the vitamin A intermediate hydride was not washed with water before the acetylation reaction. The specific steps are as follows:

[0054] Add 200 g of dichloromethane and 14.62 g (0.145 mol) of triethylamine to a 250 mL three-necked flask, and slowly add 8.28 g (0.138 mol) of acetic acid while stirring. After stirring for 30 min, obtain an acetic acid organic base salt solution, which is transferred to a dropping funnel and set aside.

[0055] In a 500mL three-necked flask equipped with a distillation tower, 200g of a dichloromethane solution containing 20% (40g, 0.13mol) of a vitamin A intermediate hydride was added, 0.20g of 2,6-di-tert-butyl-4-methylphenol, 4g of immobilized lipase novozym435 and 0.008g of propylene glycol were added, and the mixture was stirred under vacuum and heated to 30°C. After the water content of the dichloromethane extracted from the top of the distillation tower was less than 0.05%, the acetic acid organic base salt solution was added dropwise, and the addition time was controlled to 4h. After the addition was completed, the reaction was continued. After the water content of the extracted dichloromethane was less than 0.05%, the reaction was completed, the enzyme catalyst was filtered out, and the reaction solution was washed twice with water to obtain 208g of a vitamin A intermediate solution. Liquid chromatography detected the monoacyl content to be 21.71%, the yield was 99.2%, the conversion rate was 100%, and the mass ratio of monoacyl and diacyl was 99.8%:0.2%.

[0056] Example 7: Rectification and water removal did not control the water content within the preferred range

[0057] The vitamin A intermediate was prepared according to the method of Example 1, except that distillation was performed before and during the acetylation reaction to remove water, and the water content in the reaction system was controlled to be below 0.5%. The specific steps are as follows:

[0058] To a 250 mL three-necked flask, add 200 g of dichloromethane and 14.62 g (0.145 mol) of triethylamine. Slowly add 8.28 g (0.138 mol) of acetic acid while stirring. Stir for 30 minutes to obtain an organic alkali salt solution of acetic acid. Transfer this solution to a dropping funnel and set aside. Take 200 g of a dichloromethane solution containing 20% (40 g, 0.13 mol) of the vitamin A intermediate hydride in 20% dichloromethane and wash twice with 50 mL of deionized water to obtain a hydride solution, which is set aside.

[0059] The hydride solution was added to a 500 mL three-necked flask equipped with a distillation tower, and 0.20 g of 2,6-di-tert-butyl-4-methylphenol, 4 g of immobilized lipase novozym435 and 0.008 g of propylene glycol were added. The mixture was stirred under vacuum and heated to 30° C. After the water content of the dichloromethane extracted from the top of the distillation tower was less than 0.5%, the acetic acid organic base salt solution was added dropwise. The addition time was controlled to 4 h. After the addition was completed, the reaction was continued. After the water content of the extracted dichloromethane was less than 0.05%, the reaction was completed. The enzyme catalyst was filtered out, and the reaction solution was washed twice with water to obtain 165 g of vitamin A intermediate solution. Liquid chromatography detection showed that the monoacyl content was 18.05%, the yield was 65.43%, the conversion rate was 81.0%, and the mass ratio of monoacyl and diacyl was 99.6%:0.4%.

[0060] Example 8 Triethylamine molar dosage is less than acetic acid

[0061] To a 250 mL three-necked flask, add 200 g of dichloromethane and 13.29 g (0.131 mol) of triethylamine. Slowly add 8.28 g (0.138 mol) of acetic acid while stirring. Stir for 30 minutes to obtain an organic alkali salt solution of acetic acid. Transfer this solution to a dropping funnel and set aside. Take 200 g of a dichloromethane solution containing 20% (40 g, 0.13 mol) of the vitamin A intermediate hydride in 20% dichloromethane and wash twice with 50 mL of deionized water to obtain a hydride solution, which is set aside.

[0062] The above hydride solution was added to a 500 mL three-necked flask equipped with a distillation tower, and 0.20 g of 2,6-di-tert-butyl-4-methylphenol, 4 g of immobilized lipase novozym435 and 0.008 g of propylene glycol were added. The mixture was stirred under vacuum and heated to 30° C. After the water content of the dichloromethane extracted from the top of the distillation tower was less than 0.5%, the acylation solution was added dropwise. The addition time was controlled to 4 h. After the addition was completed, the reaction was continued. After the water content of the extracted dichloromethane was less than 0.05%, the reaction was completed. The enzyme catalyst was filtered out, and the reaction solution was washed twice with water to obtain 222 g of vitamin A intermediate solution. Liquid chromatography detection showed that the monoacyl content was 18.89%, the yield was 92.1%, the conversion rate was 100%, and the mass ratio of monoacyl and diacyl was 99.4%:0.6%.

[0063] Comparative Example 1 without distillation

[0064] To a 250 mL three-necked flask, add 200 g of dichloromethane and 14.62 g (0.145 mol) of triethylamine. Slowly add 8.28 g (0.138 mol) of acetic acid while stirring. Stir for 30 minutes to obtain an organic alkali salt solution of acetic acid. Transfer this solution to a dropping funnel and set aside. Take 200 g of a dichloromethane solution containing 20% (40 g, 0.13 mol) of the vitamin A intermediate hydride and wash it twice with 50 mL of deionized water to obtain a hydride solution, which is set aside.

[0065] The above hydride solution was added to a 500 mL three-necked flask equipped with a reflux water separator, and 0.20 g of 2,6-di-tert-butyl-4-methylphenol, 4 g of immobilized lipase novozym435 and 0.008 g of propylene glycol were added. The temperature was raised to 30° C. with slight vacuum stirring. The acetic acid organic base salt solution was added dropwise, and the addition time was controlled within 4 h. After the addition was completed, the reaction was continued until no obvious water layer was separated in the water separator. The reaction was completed, the enzyme catalyst was filtered out, and the reaction solution was washed twice with water to obtain 178 g of vitamin A intermediate solution. Liquid chromatography detection showed that the monoacyl content was 9.06%, the yield was 35.43%, the conversion rate was 35.5%, and the mass ratio of monoacyl and diacyl was 99.8%:0.2%.

[0066] Comparative Example 2: Add triethylamine first, then add acetic acid dropwise

[0067] Vitamin A intermediate was prepared according to the method of Example 1, except that acetic acid was added dropwise to the reaction system, and triethylamine was added to the base solution. The specific steps are as follows:

[0068] Add 200g of dichloromethane to a 250mL three-necked flask. Slowly add 8.28g (0.138mol) of acetic acid while stirring. Stir for 30 minutes to obtain an acetic acid solution, which is transferred to a dropping funnel and set aside. Take 200g of a dichloromethane solution containing 20% (40g, 0.13mol) of the vitamin A intermediate hydride in dichloromethane and wash twice with 50mL of deionized water to obtain a hydride solution, which is set aside.

[0069] The above hydride solution was added to a 500 mL three-necked flask equipped with a distillation tower, and 0.20 g of 2,6-di-tert-butyl-4-methylphenol, 4 g of immobilized lipase novozym435, 0.008 g of propylene glycol and 14.62 g (0.145 mol) of triethylamine were added. The mixture was stirred under vacuum and heated to 30° C. After the water content of the dichloromethane extracted from the top of the distillation tower was less than 0.05%, the acetic acid solution was added dropwise. The addition time was controlled to 4 h. After the addition was completed, the reaction was continued. After the water content of the extracted dichloromethane was less than 0.05%, the reaction was completed. The enzyme catalyst was filtered out, and the reaction solution was washed twice with water to obtain 247 g of vitamin A intermediate solution. Liquid chromatography detection showed that the monoacyl content was 7.38%, the yield was 40.05%, the conversion rate was 46.9%, and the mass ratio of monoacyl and diacyl was 85.4%:14.6%.

[0070] Comparative Example 3: No organic base was added

[0071] The vitamin A intermediate was prepared according to the method of Example 1, except that the organic base was replaced by acetic acid in the same molar amount. The specific steps are as follows:

[0072] Add 200g of dichloromethane to a 250mL three-necked flask. Slowly add 16.98g (0.283mol) of acetic acid while stirring. Stir for 30 minutes to obtain an acetic acid solution, which is transferred to a dropping funnel and set aside. Take 200g of a dichloromethane solution containing 20% (40g, 0.13mol) of the vitamin A intermediate hydride in dichloromethane and wash twice with 50mL of deionized water to obtain a hydride solution, which is set aside.

[0073] The above hydride solution was added to a 500 mL three-necked flask equipped with a distillation tower, and 0.20 g of 2,6-di-tert-butyl-4-methylphenol, 4 g of immobilized lipase novozym435 and 0.008 g of propylene glycol were added. The mixture was stirred under vacuum and heated to 30° C. After the water content of the dichloromethane extracted from the top of the distillation tower was less than 0.5%, the acetic acid solution was added dropwise. The addition time was controlled to 4 h. After the addition was completed, the reaction was continued. After the water content of the extracted dichloromethane was less than 0.05%, the reaction was completed. The enzyme catalyst was filtered out, and the reaction solution was washed twice with water to obtain 213 g of vitamin A intermediate solution. Liquid chromatography detection showed that the monoacyl content was 11.61%, the yield was 54.3%, the conversion rate was 100%, and the mass ratio of monoacyl and diacyl was 99.2%:0.8%.

[0074] Example 9 Enzyme Application

[0075] The enzyme catalyst filtered out after the reaction was completed according to the method of Example 1 was directly used in the next batch of reactions. The reaction process and conditions were the same as in Example 1. The number of enzyme applications and the results are shown in Table 1.

[0076] Table 1

[0077]

[0078]

[0079] Example 10 Enzyme application

[0080] After the reaction was completed according to the method of Example 6, the enzyme catalyst filtered out was directly used in the next batch of reactions. The reaction process and conditions were the same as in Example 6. The number of enzyme applications and the results are shown in Table 2.

[0081] Table 2

[0082]

[0083]

[0084] From the above results, it can be seen that the method provided by the present invention for preparing vitamin A intermediates can improve the conversion rate and yield as well as the selectivity of monoacyl compounds.

[0085] From the comparison between Example 1 and Example 5, it can be seen that when polyol is used as the active agent in the acetylation reaction, it is more conducive to improving the conversion rate and yield.

[0086] From the comparison between Example 1, Example 6 and Example 10, it can be seen that when the method for preparing vitamin A intermediate by lipase catalysis also includes washing the raw material containing vitamin A intermediate hydride with water before mixing, the attachment and poisoning of the hexamethylene alcohol hydride polymerization in the raw material to the immobilized lipase can be reduced, and the lipase can still exert good catalytic activity after multiple applications.

[0087] From the comparison between Example 1 and Example 7, it can be seen that when the method for preparing vitamin A intermediate by lipase catalysis also includes removing water from the bottom liquid by distillation to control the water content therein to below 0.05% before adding the organic base salt of acetic acid, it is more conducive to improving the conversion rate and yield.

[0088] From the comparison between Example 1 and Example 8, it can be seen that when the molar ratio of the organic base to the acetic acid is controlled at (1-1.5):1, it is more conducive to improving the yield.

[0089] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A method for preparing a vitamin A intermediate by lipase catalysis, characterized in that: The method comprises mixing acetic acid and an organic base in an organic solvent to obtain an acetic acid organic base salt solution, mixing a raw material containing a vitamin A intermediate hydride represented by formula (1), lipase, and optionally a polyol and an antioxidant in the organic solvent to obtain a base liquid, dripping the acetic acid organic base salt solution into the base liquid to perform an acetylation reaction, and rectifying and removing water from the reaction system before and during the acetylation reaction, to obtain a reaction product that is the vitamin A intermediate; 2. The method for preparing a vitamin A intermediate by lipase catalysis according to claim 1, characterized in that: The molar ratio of the acetic acid to the vitamin A intermediate hydride is (1-1.2):

1.

3. The method for preparing a vitamin A intermediate by lipase catalysis according to claim 1, characterized in that: The organic base is an amine compound and / or a pyridine compound; Preferably, the amine compound is diethylamine and / or triethylamine; Preferably, the pyridine compound is selected from at least one of pyridine, 2-methylpyridine and 4-dimethylaminopyridine; Preferably, the molar ratio of the organic base to acetic acid is (1-1.5):

1.

4. The method for preparing a vitamin A intermediate by lipase catalysis according to claim 1, characterized in that: The method also includes washing the raw material containing the vitamin A intermediate hydride with water before mixing.

5. The method for preparing a vitamin A intermediate by lipase catalysis according to claim 1, characterized in that: The mass ratio of the lipase to the vitamin A intermediate hydride is (0.05-0.2):

1.

6. The method for preparing a vitamin A intermediate by lipase catalysis according to claim 1, characterized in that: The polyol is selected from at least one of ethylene glycol, propylene glycol, glycerol, butylene glycol, pentanediol, hexylene glycol, diethylene glycol, dipropylene glycol and trimethylolpropane; Preferably, the amount of the polyol is 0.2% to 0.5% of the mass of the lipase.

7. The method for preparing a vitamin A intermediate by lipase catalysis according to claim 1, characterized in that: The mass ratio of the antioxidant to the vitamin A intermediate hydride is (0.5% to 1%):

1.

8. The method for preparing a vitamin A intermediate by lipase catalysis according to claim 1, characterized in that: The organic solvent is dichloromethane.

9. The method for preparing a vitamin A intermediate by lipase catalysis according to claim 1, characterized in that: The method further comprises the step of removing water from the bottom liquid by distillation before dropwise adding the organic alkali salt of acetic acid so as to control the water content of the bottom liquid to be below 0.05%.

10. The method for preparing a vitamin A intermediate by lipase catalysis according to claim 1, characterized in that: The conditions of the acetylation reaction include a temperature of 30-40° C., and stopping the reaction when the water content in the system reaches below 0.05%.

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