Preparation method of (R)-3-hydroxybutyric acid

Abstract

The invention belongs to the technical field of biochemistry, and provides a preparation method of (R)-3-hydroxybutyric acid. According to the method, poly (R)-3-hydroxybutyric acid is adopted as a raw material, an acid solution with the mass concentration of 25-35% is adopted as a catalyst, hydrolysis reaction is conducted in a polar solvent through microwave heating, after hydrolysis reaction is completed, the pH value is adjusted to 2-3.5, and (R)-3-hydroxybutyric acid is prepared. Compared with the prior art, the method has the advantages that the hydrolysis reaction time is shortened, the energy consumption is reduced, and the pH regulator required for subsequently regulating the pH value is reduced due to low acid consumption, so that the salt content in the product is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of biochemical engineering, and more specifically, to a method for preparing (R)-3-hydroxybutyric acid. Background Art

[0002] 3-Hydroxybutyric acid (abbreviated as 3-HB) is the monomer form of the natural polymer poly (R)-3-hydroxybutyric acid (hereinafter referred to as PHB), and exists in a pure R configuration in the natural state. As an important ketone body in the body, 3-hydroxybutyric acid is produced by the degradation of long-chain fatty acids in the liver, transported to peripheral tissues through the blood and regulates the body's functions. It has been reported in the literature that 3-hydroxybutyric acid has great application value and prospects in the health care products, food and pharmaceutical industries, including: accelerating weight loss, stimulating the expression of various health-promoting genes, reducing the occurrence of inflammatory complications, improving exercise performance and training efficiency, enhancing metabolic efficiency, providing optimal energy for the heart, reducing the incidence of cardiovascular diseases, improving insulin sensitivity, preventing cancer and related diseases caused by glucose metabolism disorders, increasing cognitive ability, preventing Alzheimer's disease, and prolonging life.

[0003] At present, there are three main methods for preparing (R)-3-hydroxybutyric acid using PHB, but each has some disadvantages:

[0004] (1) Alkaline degradation method: First, use strong alkali to hydrolyze PHB to prepare 3-hydroxybutyrate, and then use acid to neutralize it to obtain (R)-3-hydroxybutyric acid.

[0005] (2) Acid-catalyzed hydrolysis: Acid is used to hydrolyze PHB. However, if the acid concentration is low during this process, the hydrolysis time will inevitably be too long. Therefore, in order to accelerate the hydrolysis of PHB, the acid concentration is often increased (generally, the hydrogen ion concentration in the system is required to reach 3.0 mol / L to accelerate the hydrolysis of PHB in the system). On the one hand, the probability of hydrogen ions contacting the ester bonds in the PHB molecular chain can be increased; on the other hand, the acid can act as a catalyst in the ester bond hydrolysis reaction process. The greater the amount of catalyst used, the faster the reaction rate. However, after the hydrolysis reaction is completed, inorganic salts such as sodium bicarbonate need to be used to neutralize the reaction solution and adjust the pH to a certain range before it can be drunk. Therefore, although increasing the acid concentration can greatly promote the hydrolysis rate of PHB, if the acid concentration is too high, the corresponding amount of inorganic salts such as sodium bicarbonate will also increase, and more excess anions will also be brought in (for example, hydrochloric acid brings chloride ions, and sulfuric acid brings sulfate ions).

[0006] The above traditional alkaline degradation method and acid-catalyzed hydrolysis method will inevitably lead to the final product containing more cations such as sodium ions or other anions. The increase in inorganic salts will not only affect the taste of 3-hydroxybutyric acid, but also increase the user's salt intake, bringing negative effects to the body.

[0007] (3) PHB is first alcoholyzed to produce 3-hydroxybutyrate, which is then hydrolyzed to produce 3-hydroxybutyric acid. This method is relatively complicated and costly.

[0008] Therefore, there is an urgent need to develop a simple and low-cost method for preparing (R)-3-hydroxybutyric acid using PHB, and the content of inorganic salts in the prepared (R)-3-hydroxybutyric acid is low. Summary of the invention

[0009] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a method for preparing (R)-3-hydroxybutyric acid. The present invention uses PHB as a raw material, assisted by microwave heating for acid hydrolysis, and obtains high-purity 3-hydroxybutyric acid in a relatively short time (only 42-56 hours). The method is simple and easy to operate, and the hydrolysis can be completed using a relatively low concentration of acid catalyst (mass concentration of 25-35%), so that the pH value of the product is not too low, so there is no need to use too much pH regulator (such as sodium bicarbonate), thereby reducing the inorganic salt content in the product, reducing cost and energy consumption, and improving the yield and optical purity of (R)-3-hydroxybutyric acid (the yield of (R)-3-hydroxybutyric acid can reach 83.46-84.03%, and the optical purity is as high as 94.58-95.18%).

[0010] A first aspect of the present invention provides a method for preparing (R)-3-hydroxybutyric acid.

[0011] Specifically, a method for preparing (R)-3-hydroxybutyric acid comprises the following steps:

[0012] First, poly (R)-3-hydroxybutyric acid, a polar solvent, and an acid solution are mixed, and then heated by microwave to perform a hydrolysis reaction. After the hydrolysis reaction is completed, the pH value of the reaction system is controlled to 2-3.5 to obtain the (R)-3-hydroxybutyric acid;

[0013] The mass concentration of acid in the acid solution is 25-37%.

[0014] Because PHB is a polyester with high crystallinity, in the acidic hydrolysis process, water molecules and hydrogen ions are difficult to penetrate into the inside of PHB, reducing the contact probability of water molecules with hydrogen ions and the ester bonds on the PHB molecular chain, affecting the speed of preparing (R)-3-hydroxybutyric acid by acid hydrolysis of PHB. Therefore, the present invention adopts PHB as raw material, with acid solution as catalyst, and by using microwave heating, polar solvents are used to have the characteristics of microwave energy absorption, so that the movement of polar solvent molecules in the system is more rapid (especially water molecules). Therefore, under microwave heating conditions, water molecules can better improve the movement speed of water molecules and hydrogen ions relative to traditional heating methods, more easily penetrate into the inside of PHB, increase the contact probability of the ester bonds in the PHB molecular chain, and promote the occurrence of hydrolysis reaction. Moreover, microwave heating can also destroy the force between the PHB molecular chains, promote loosening between the PHB molecular chains, destroy its internal structure, help to reduce crystallinity, make water molecules and hydrogen ions more easily penetrate into the inside of PHB, thereby further accelerating the hydrolysis of PHB. Therefore, through microwave-assisted hydrolysis reaction, even if the raw material PHB has high crystallinity, it can be hydrolyzed under the catalysis of a relatively low concentration of acid solution, thereby shortening the time required for the hydrolysis reaction and reducing energy consumption. Moreover, since the concentration of the acid solution is relatively low, the amount of pH regulator required for subsequent pH adjustment is reduced, thereby reducing the salt content in the product.

[0015] Preferably, the mass concentration of the acid in the acid solution is 25-35%.

[0016] More preferably, the mass concentration of the acid solution is 28-31%.

[0017] Preferably, when the amount of the poly (R) -3-hydroxybutyric acid added is 40 g, the amount of the acid solution added is 0.1-5 mL.

[0018] Further preferably, when the amount of the poly (R) -3-hydroxybutyric acid added is 40 g, the amount of the acid solution added is 1-2 mL.

[0019] Preferably, the number average molecular weight of the poly(R)-3-hydroxybutyric acid is 300,000-500,000 Daltons, and / or the molecular weight dispersity of the poly(R)-3-hydroxybutyric acid is 1.0-3.0, and / or the crystallinity of the poly(R)-3-hydroxybutyric acid is 65.0-70.0%.

[0020] Further preferably, the number average molecular weight of the poly (R) -3-hydroxybutyric acid is 400,000-500,000 Daltons, and / or the molecular weight dispersity of the poly (R) -3-hydroxybutyric acid is 2.0-3.0, and / or the crystallinity of the poly (R) -3-hydroxybutyric acid is 68.0-69.0%.

[0021] Preferably, the microwave heating is heating using a microwave oven, and / or the temperature of the microwave heating is 85-105° C., and / or the time of the microwave heating is 35-65 h.

[0022] Further preferably, the microwave heating is heating using a microwave oven, and / or the temperature of the microwave heating is 90-100° C., and / or the time of the microwave heating is 40-60 h.

[0023] Preferably, the power of the microwave oven is ≥1000W.

[0024] Further preferably, the power of the microwave oven is ≥2000W.

[0025] More preferably, the power of the microwave oven is 2000-3000W.

[0026] Preferably, the microwave heating step comprises: heating in a microwave oven to 85-105° C., sealing, keeping warm for 0.5-1h, and cooling to 20-30° C., wherein the microwave oven is used for temperature control during the heating and keeping warm periods.

[0027] Preferably, the hydrolysis reaction is completed when the system becomes a clear transparent liquid.

[0028] Preferably, the polar solvent is water.

[0029] Preferably, the pH value is adjusted to 2-3.

[0030] Preferably, the pH value is adjusted by using a pH adjusting agent, and the pH adjusting agent is at least one of sodium bicarbonate, sodium carbonate, potassium carbonate, calcium carbonate, potassium bicarbonate, and calcium bicarbonate. Since the amount of acid used in the hydrolysis reaction of the present invention is relatively low, the pH value of the system is not too low, and a large amount of pH adjusting agent does not need to be added to make the product meet the drinking standard, thereby reducing the salt content in the product.

[0031] Preferably, after adjusting the pH value to 2-3, filtering is performed, the filtrate is collected for decolorization, filtering is performed again, and the filtrate is collected for reduced pressure distillation to obtain the (R)-3-hydroxybutyric acid.

[0032] Preferably, the decolorization is performed by adding activated carbon.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] The invention adopts poly (R) -3-hydroxybutyric acid as a raw material, uses an acid solution with a mass concentration of 25-35% as a catalyst, and performs a hydrolysis reaction in a polar solvent by microwave heating, and then adjusts the pH value to 2-3.5 to obtain (R) -3-hydroxybutyric acid. The invention utilizes microwave heating to assist in hydrolysis, significantly reduces the crystallinity of PHB (the initial crystallinity of PHB is as high as 68.0-68.8%, and the crystallinity after microwave-assisted hydrolysis reaction for 0.5h has dropped to 10.8-16.5%), promotes the acid hydrolysis of PHB, and shortens the hydrolysis reaction time. The time required for the preparation of the present invention is shortened (only 42-56 hours are required), energy consumption is reduced, and since the amount of acid required for the preparation method of the present invention is relatively low, the pH regulator required for subsequent pH adjustment is reduced, thereby reducing the salt content in the product. The (R)-3-hydroxybutyric acid content in the product can reach 41.06-41.29%, the yield of (R)-3-hydroxybutyric acid can reach 83.46-84.03%, the content of crotonic acid is only 0.10-0.16%, and the optical purity of (R)-3-hydroxybutyric acid is as high as 94.58-95.18%. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a high performance liquid chromatogram of (R)-3-hydroxybutyric acid obtained in Example 1 of the present invention;

[0036] Figure 2 This is a high performance liquid chromatogram of (R)-3-hydroxybutyric acid obtained in Example 2 of the present invention;

[0037] Figure 3 This is a high performance liquid chromatogram of (R)-3-hydroxybutyric acid obtained in Example 3 of the present invention;

[0038] Figure 4 This is a high performance liquid chromatogram of (R)-3-hydroxybutyric acid obtained in Example 4 of the present invention;

[0039] Figure 5 is a high performance liquid chromatogram of (R)-3-hydroxybutyric acid prepared in Comparative Example 1;

[0040] Figure 6 This is a high performance liquid chromatogram of (R)-3-hydroxybutyric acid obtained in Comparative Example 2;

[0041] Figure 7 This is the high performance liquid chromatogram of (R)-3-hydroxybutyric acid prepared in Comparative Example 3. DETAILED DESCRIPTION

[0042] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0043] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0044] Example 1

[0045] A method for preparing (R)-3-hydroxybutyric acid comprises the following steps:

[0046] (1) 40 g of PHB powder (content 99.98%, number average molecular weight Mn about 400,000 Daltons, molecular weight dispersion 2.0, crystallinity 68.0%, Zhuhai Maidefa Biotechnology Co., Ltd.) was added to a 500 mL three-necked flask, 120 mL of purified water and 1 mL of 31% hydrochloric acid (food grade) were added, the hydrogen ion concentration in the system was 0.08 mol / L, stirred, heated in a microwave oven (power 2000 W), raised to 90° C., kept at 90° C. for 0.5 h, sampled and tested for crystallinity of about 16.5%; then sealed, kept warm for hydrolysis reaction until hydrolysis was completed (the system was clear and transparent liquid when hydrolysis was completed), which took about 56 h, and cooled to room temperature.

[0047] (2) Using sodium bicarbonate, the pH value of the system was adjusted to 2-3, and the system was filtered to remove the insoluble matter; 4 g of activated carbon (medical grade) was added to the filtrate, and the mixture was stirred for 1 h; the filtrate was filtered, and the collected filtrate was distilled under reduced pressure at 60° C. for about 1 h to obtain a colorless transparent liquid to obtain (R)-3-hydroxybutyric acid; the system was then tested by high performance liquid chromatography, and the test results were as follows: Figure 1 As shown, the mass percentage of (R)-3-hydroxybutyric acid is 41.06%, the mass percentage of crotonic acid is 0.11%, and the yield is calculated. The yield of (R)-3-hydroxybutyric acid can reach 84.44%. The optical purity is detected by using a specific polarimeter, and the optical purity of (R)-3-hydroxybutyric acid is 95.02%.

[0048] Example 2

[0049] A method for preparing (R)-3-hydroxybutyric acid comprises the following steps:

[0050] (1) 40 g of PHB powder (content 99.98%, number average molecular weight Mn about 400,000 Daltons, molecular weight dispersion 2.0, crystallinity 68.8%, Zhuhai Maidefa Biotechnology Co., Ltd.) was added to a 500 mL three-necked flask, 120 mL of purified water and 1 mL of 31% hydrochloric acid (food grade) were added, the hydrogen ion concentration in the system was 0.08 mol / L, and the mixture was stirred and heated in a microwave oven (power 2000 W) to 95° C. and kept at 95° C. for 0.5 h. The crystallinity was detected by sampling and was about 14.5%; the mixture was then sealed and kept warm for hydrolysis reaction until the hydrolysis was completed (the hydrolysis was completed when the system was a clear transparent liquid), which took about 50 h; and the mixture was cooled to room temperature.

[0051] (2) Using sodium bicarbonate, the pH value of the system was adjusted to 2-3, and the system was filtered to remove the insoluble matter in the system; 4 g of activated carbon (medical grade) was added to the filtrate, and the mixture was stirred for 1 h; the filtrate was filtered, and the collected filtrate was distilled under reduced pressure at 60° C. for about 1 h to obtain a colorless transparent liquid to obtain (R)-3-hydroxybutyric acid; the system was then tested by high performance liquid chromatography, and the test results were as follows: Figure 2 As shown, the mass percentage of (R)-3-hydroxybutyric acid is 41.15%, the mass percentage of crotonic acid is 0.16%, and the yield is calculated. The yield of (R)-3-hydroxybutyric acid can reach 83.46%. The optical purity is detected by using a specific polarimeter, and the optical purity of (R)-3-hydroxybutyric acid is 94.58%.

[0052] Example 3

[0053] A method for preparing (R)-3-hydroxybutyric acid comprises the following steps:

[0054] (1) 40 g of PHB powder (content 99.98%, number average molecular weight Mn about 400,000 Daltons, molecular weight dispersion 2.0, crystallinity 68.8%, Zhuhai Maidefa Biotechnology Co., Ltd.) was added to a 500 mL three-necked flask, 120 mL of purified water and 2 mL of 31% hydrochloric acid (food grade) were added, the hydrogen ion concentration in the system was 0.16 mol / L, and the mixture was stirred and heated in a microwave oven (2000 W) to 100° C. (maintained at 100° C. for 0.5 h, and the crystallinity was detected by sampling and was about 10.8%); the mixture was sealed and kept warm for hydrolysis reaction until the hydrolysis was completed (the system was a clear transparent liquid), which took about 43 h; and the mixture was cooled to room temperature.

[0055] (2) Using sodium bicarbonate, the pH value of the system was adjusted to 2-3, and the system was filtered to remove the insoluble matter in the system; 4 g of activated carbon (medical grade) was added to the filtrate, and the mixture was stirred for 1 h; the filtrate was filtered, and the collected filtrate was subjected to reduced pressure distillation at 60° C. for about 1 h to obtain a colorless transparent liquid, thereby obtaining (R)-3-hydroxybutyric acid; the system was then tested by high performance liquid chromatography, and the test results were as follows: Figure 3 As shown, the mass percentage of (R)-3-hydroxybutyric acid is 41.29%, the mass percentage of crotonic acid is 0.15%, and the yield is calculated. The yield of (R)-3-hydroxybutyric acid can reach 84.03%. The optical purity is detected by using a specific polarimeter, and the optical purity of (R)-3-hydroxybutyric acid is 94.93%.

[0056] Example 4

[0057] A method for preparing (R)-3-hydroxybutyric acid comprises the following steps:

[0058] (1) Take 40 g of PHB powder (content 99.98%, number average molecular weight Mn about 400,000 Daltons, molecular weight dispersion 2.0, crystallinity 68.8%, Zhuhai Maidefa Biotechnology Co., Ltd.) and add it to a 500 mL three-necked flask, add 120 mL of purified water and 5 mL of 31% hydrochloric acid (food grade), the hydrogen ion concentration in the system is 0.39 mol / L, stir, use a microwave oven (2000 W), heat to 95° C. (95° C. for 0.5 h, sample and detect the crystallinity of about 14.7%); seal, keep warm and carry out hydrolysis reaction until the hydrolysis is completed (the system is a clear transparent liquid), which takes about 42 h; cool to room temperature (25° C.).

[0059] (2) Using sodium bicarbonate, the pH value of the system was adjusted to 2-3, and the system was filtered to remove the insoluble matter in the system; 4 g of activated carbon (medical grade) was added to the filtrate, and the mixture was stirred for 1 h; the filtrate was filtered, and the collected filtrate was subjected to reduced pressure distillation at 60° C. for about 1 h to obtain a colorless transparent liquid, thereby obtaining (R)-3-hydroxybutyric acid; the system was then tested by high performance liquid chromatography, and the test results were as follows: Figure 4 As shown, the mass percentage of (R)-3-hydroxybutyric acid is 41.06%, the mass percentage of crotonic acid is 0.10%, and the yield is calculated. The yield of (R)-3-hydroxybutyric acid can reach 84.85%. The optical purity is detected by using a specific polarimeter, and the optical purity of (R)-3-hydroxybutyric acid is 95.18%.

[0060] Comparative Example 1

[0061] A method for preparing (R)-3-hydroxybutyric acid comprises the following steps:

[0062] (1) Take 40 g of PHB powder (content 99.98%, number average molecular weight Mn about 400,000 Daltons, molecular weight dispersion 2.0, crystallinity 68.8%, Zhuhai Maidefa Biotechnology Co., Ltd.) and add it to a 500 mL three-necked flask, add 120 mL of purified water and 1 mL of 31% hydrochloric acid (food grade), the hydrogen ion concentration in the system is 0.08 mol / L, stir, use a water bath to heat, raise the temperature to 95°C, keep it at 95°C for 0.5 h, take a sample to detect the crystallinity of about 64.7%, then seal and keep it warm for hydrolysis reaction until the hydrolysis is completed (the system is a clear and transparent liquid when the hydrolysis is completed), which takes about 128 h; cool to room temperature.

[0063] (2) Using sodium bicarbonate, the pH value of the system was adjusted to 2-3, and the system was filtered to remove the insoluble matter in the system; 4 g of activated carbon (medical grade) was added to the filtrate, and the mixture was stirred for 1 h; the filtrate was filtered, and the collected filtrate was subjected to reduced pressure distillation at 60° C. for about 1 h to obtain a colorless transparent liquid, thereby obtaining (R)-3-hydroxybutyric acid; the system was then tested by high performance liquid chromatography, and the test results were as follows: Figure 5 As shown, the mass percentage of (R)-3-hydroxybutyric acid is 40.03%, the mass percentage of crotonic acid is 0.60%, and the yield is calculated. The yield of (R)-3-hydroxybutyric acid is 80.05%. The optical purity is detected by using a specific polarimeter, and the optical purity of (R)-3-hydroxybutyric acid is 90.18%.

[0064] Comparative Example 2

[0065] A method for preparing (R)-3-hydroxybutyric acid comprises the following steps:

[0066] (1) 40 g of PHB powder (content 99.98%, number average molecular weight Mn about 400,000 Daltons, molecular weight dispersion 2.0, crystallinity 68.8%, Zhuhai Maidefa Biotechnology Co., Ltd.) was added to a 500 mL three-necked flask, 120 mL of purified water and 60 mL of 31% hydrochloric acid (food grade) were added, the hydrogen ion concentration in the system was 3.28 mol / L, and the mixture was stirred and heated in a water bath to 95° C., kept at 95° C. for 0.5 h, and the crystallinity was detected by sampling, which was about 64.0%; then the mixture was sealed and kept warm for hydrolysis reaction until the hydrolysis was completed (the system was a clear transparent liquid), which took about 86 h; and the mixture was cooled to room temperature.

[0067] (2) Using sodium bicarbonate, the pH value of the system was adjusted to 2-3, and the system was filtered to remove the insoluble matter in the system; 4 g of activated carbon (medical grade) was added to the filtrate, and the mixture was stirred for 1 h; the filtrate was filtered, and the collected filtrate was subjected to reduced pressure distillation at 60° C. for about 1 h to obtain a colorless transparent liquid, thereby obtaining (R)-3-hydroxybutyric acid; the system was then tested by high performance liquid chromatography, and the test results were as follows: Figure 6As shown, the mass percentage of (R)-3-hydroxybutyric acid is 39.16%, the mass percentage of crotonic acid is 0.75%, and the yield is calculated. The yield of (R)-3-hydroxybutyric acid is 79.15%. The optical purity is detected by using a specific polarimeter, and the optical purity of (R)-3-hydroxybutyric acid is 90.08%.

[0068] Comparative Example 3

[0069] A method for preparing (R)-3-hydroxybutyric acid comprises the following steps:

[0070] (1) Take 40 g of PHB powder (content 99.98%, number average molecular weight Mn about 400,000 Daltons, molecular weight dispersion 2.0, crystallinity 68.8%, Zhuhai Maidefa Biotechnology Co., Ltd.) and add it to a 500 mL three-necked flask, add 120 mL of purified water and 1 mL of 31% hydrochloric acid (food grade), the hydrogen ion concentration in the system is 0.08 mol / L, stir, use a microwave oven (power 800 W), heat to 95° C. (95° C. for 0.5 h, sample and detect the crystallinity of about 64.5%); seal, keep warm and carry out hydrolysis reaction until the hydrolysis is completed (the system is a clear transparent liquid), which takes about 98 h; cool to room temperature.

[0071] (2) Using sodium bicarbonate, the pH value of the system was adjusted to 2-3, and the system was filtered to remove the insoluble matter in the system; 4 g of activated carbon (medical grade) was added to the filtrate, and the mixture was stirred for 1 h; the filtrate was filtered, and the collected filtrate was subjected to reduced pressure distillation at 60° C. for about 1 h to obtain a colorless transparent liquid, thereby obtaining (R)-3-hydroxybutyric acid; the system was then tested by high performance liquid chromatography, and the test results were as follows: Figure 7 As shown, the mass percentage of (R)-3-hydroxybutyric acid is 41.15%, the mass percentage of crotonic acid is 0.16%, and the yield is calculated. The yield of (R)-3-hydroxybutyric acid can reach 83.46%. The optical purity is detected by using a specific polarimeter, and the optical purity of (R)-3-hydroxybutyric acid is 91.18%.

[0072] Figure 1-Figure 7 In the figure, the blue curve indicates that the wavelength of the detection light source is 210nm, which is used to detect R-3-hydroxybutyric acid. The red curve indicates that the wavelength of the detection light source is 230nm, which is used to detect crotonic acid.

[0073] Product effect testing

[0074] The optical purity of (R)-3-hydroxybutyric acid obtained in Example 1-4 and Comparative Example 1-3 was determined according to GB / T 613-2007, and the crystallinity was determined by X-ray diffraction. The results are summarized in Table 1.

[0075] Table 1 Hydrolysis reaction parameters and hydrolysis products of various embodiments and comparative examples

[0076]

[0077]

[0078] As can be seen from the above table, the hydrolysis reaction of Examples 1-4 of the present invention only takes 42-56 hours, and the crystallinity of PHB (initial crystallinity is as high as 68.0-68.8%) has dropped to 10.8-16.5% after 0.5 hours of microwave-assisted hydrolysis reaction, the (R)-3-hydroxybutyric acid content can reach 41.06-41.29%, the (R)-3-hydroxybutyric acid yield can reach 83.46-84.03%, while the crotonic acid content is only 0.10-0.16%, and the optical purity of (R)-3-hydroxybutyric acid is as high as 94.58-95.18%.

[0079] Compared with Example 2, in Comparative Example 1, microwave heating was replaced by water bath heating, resulting in that after 0.5 h of hydrolysis reaction, the PHB crystallinity was still as high as 64.7%, the hydrolysis time was as long as 128 h, and the (R)-3-hydroxybutyric acid content decreased and the crotonic acid content increased, resulting in a significant decrease in the yield and optical purity of (R)-3-hydroxybutyric acid.

[0080] Compared with Example 2, Comparative Example 2 uses a water bath to heat the hydrolysis reaction. Although the amount of hydrochloric acid catalyst is greatly increased, the crystallinity after 0.5 h of the hydrolysis reaction is still as high as 64.0%, the hydrolysis time is as long as 86 h, and the (R)-3-hydroxybutyric acid content decreases and the crotonic acid content increases, resulting in a significant decrease in the yield and optical purity of (R)-3-hydroxybutyric acid.

[0081] It can be seen from Comparative Examples 1 and 2 that due to conventional water bath heating, the movement rate of polar molecules such as water molecules is much lower than that of microwave heating, making it difficult for polar molecules such as water molecules to penetrate into the internal structure of PHB and destroy its crystalline state.

[0082] Compared with Example 2, Comparative Example 3 reduces the power of the microwave oven. Due to the low power of the microwave oven, the movement speed of polar molecules such as water molecules is low, which makes it difficult for them to penetrate into the interior of PHB and destroy the crystalline state of PHB. In addition, the power is low, and the microwave radiation intensity becomes low, which makes it difficult to loosen the molecular chain of PHB and destroy the crystalline state of PHB, resulting in the crystallinity of PHB still as high as 64.5% after 0.5h of hydrolysis reaction, and the hydrolysis time is as long as 98h. In addition, the content of (R)-3-hydroxybutyric acid decreases, and the content of crotonic acid increases, resulting in a significant decrease in the yield and optical purity of (R)-3-hydroxybutyric acid.

Claims

1. A method for preparing (R)-3-hydroxybutyric acid, characterized in that: The steps include: First, poly (R)-3-hydroxybutyric acid, a polar solvent, and an acid solution are mixed, and then heated by microwave to perform a hydrolysis reaction. After the hydrolysis reaction is completed, the pH value of the reaction system is controlled to 2-3.5 to obtain the (R)-3-hydroxybutyric acid; The mass concentration of acid in the acid solution is 25-37%.

2. The preparation method according to claim 1, characterized in that: The mass concentration of acid in the acid solution is 28-31%.

3. The preparation method according to claim 1, characterized in that: When the amount of the poly (R) -3-hydroxybutyric acid added is 40 g, the amount of the acid solution added is 0.1-5 mL.

4. The preparation method according to claim 1, characterized in that: The number average molecular weight of the poly(R)-3-hydroxybutyric acid is 300,000-500,000 Daltons, and / or the molecular weight dispersity of the poly(R)-3-hydroxybutyric acid is 1.0-3.0, and / or the crystallinity of the poly(R)-3-hydroxybutyric acid is 65.0-70.0%.

5. The preparation method according to claim 1, characterized in that: The microwave heating is heating using a microwave oven, and / or the microwave heating temperature is 85-105° C., and / or the microwave heating time is 35-65 h.

6. The preparation method according to claim 5, characterized in that: The power of the microwave oven is ≥1000W.

7. The preparation method according to claim 5, characterized in that: The microwave heating step comprises: heating in a microwave oven to 85-105° C., sealing, keeping warm for 0.5-1h, and cooling to 20-30° C., wherein the microwave oven is used for temperature control during the heating and keeping warm periods.

8. The preparation method according to claim 1, characterized in that: The polar solvent is water.

9. The preparation method according to claim 1, characterized in that: The pH value is adjusted by using a pH adjusting agent, and the pH adjusting agent is at least one of sodium bicarbonate, sodium carbonate, potassium carbonate, calcium carbonate, potassium bicarbonate, and calcium bicarbonate.

10. Use of the method for preparing (R)-3-hydroxybutyric acid according to any one of claims 1 to 9 in preparing food and medicine.

Images