Preparation method of high-purity magnesium octoate

Abstract

The invention discloses a preparation method of high-purity magnesium octoate, which comprises the following steps: by taking an ionic liquid-ethanol mixed system as a reaction medium, firstly, carrying out reduced pressure distillation on octanoic acid until the purity is greater than or equal to 99%, taking ethanol as a cosolvent, adding ionic liquid, octanoic acid and a magnesium source into the system, constructing a homogeneous system, and reacting under certain conditions to obtain the high-purity magnesium octoate. The preparation method comprises the following steps: monitoring in real time through an online infrared spectrum until the characteristic peak of caprylic acid disappears, then carrying out two-stage gradient cooling on a reaction solution to induce the growth of regular flaky crystals, and finally carrying out centrifugation, ethanol washing and vacuum drying. A sustainable preparation scheme is provided for application of magnesium octoate in the fields of high-end drug carriers, cosmetic emulsifiers and food-grade heat stabilizers, and the magnesium octoate has remarkable industrial application value.

Description

Technical Field

[0001] This invention relates to the field of magnesium salt preparation technology, and specifically to a method for preparing high-purity magnesium octoate. Background Technology

[0002] Magnesium octoate, an important organomagnesium compound, has wide applications in pharmaceuticals, cosmetics, and plastics processing. For example, in pharmaceuticals, it can serve as a drug carrier, improving drug stability and bioavailability; in cosmetics, it acts as an emulsifier and thickener; and in the plastics processing industry, it can be used as a heat stabilizer. However, current methods for preparing magnesium octoate have many problems. Traditional methods often involve the direct reaction of octanoic acid with magnesium oxide or magnesium hydroxide in organic solvents. This method has a slow reaction rate, typically lasting 6-8 hours, and the reaction is incomplete, often leaving unreacted octanoic acid and magnesium source impurities in the product, resulting in low purity, generally only around 85%-90%. Furthermore, the use of organic solvents not only increases production costs but also causes environmental pollution, and subsequent solvent recovery is complex and energy-intensive. In addition, magnesium octoate products obtained by traditional methods have irregular crystal structures and uneven particle size distribution, affecting their application in high-end fields. Therefore, there is an urgent need to develop a new, efficient, environmentally friendly method for preparing high-purity magnesium octoate. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing high-purity magnesium octoate, which solves the problems of slow reaction rate, low product purity, large environmental pollution and unsatisfactory crystal form and particle size in existing preparation methods.

[0004] The technical solution adopted by this invention to solve its technical problem is as follows: A method for preparing high-purity magnesium octoate, comprising the following steps:

[0005] Step (1) Raw material pretreatment: Confirm the purity of the raw materials to ensure that the purity of octanoic acid is ≥99%, wherein the octanoic acid is the octanoic acid with the longest main chain;

[0006] Step (2) Construction of the ionic liquid system: Select an ionic liquid and add it to the reaction vessel at 10%-15% of the mass of octanoic acid. Then add an appropriate amount of anhydrous ethanol as a co-solvent to form a homogeneous reaction medium system. The volume ratio of ethanol to ionic liquid is 1:1-1.5. The volume ratio of ethanol to octanoic acid is 0.5-0.8:1.

[0007] Step (3) Reaction process: The pretreated octanoic acid and magnesium source are added sequentially to the constructed ionic liquid system. The reaction is carried out at a temperature of 70-90℃ and a stirring speed of 300-400 r / min for 1-1.5 hours. The magnesium source is selected from any one of magnesium oxide, magnesium hydroxide, magnesium laurate, and magnesium carbonate. During the reaction, the reaction progress is monitored in real time by online infrared spectroscopy. When the characteristic absorption peak of octanoic acid disappears, the reaction is considered to be basically completed.

[0008] Step (4) Dynamic gradient solvent crystallization: The crystal form is controlled by a gradient crystallization program, which includes a first stage and a second stage in sequence: the first stage is to cool down from 90°C to 50°C and keep it at that temperature for 1 to 1.5 hours; the second stage is to cool down from 50°C to 25°C and keep it at that temperature for 1 to 1.5 hours.

[0009] Step (5) Product Separation and Purification: Crude magnesium octoate is obtained by centrifugation. The crude product is washed 2-3 times with anhydrous ethanol, with a mass ratio of ethanol to crude product of 5-6:1 each time, to remove surface-adsorbed ionic liquids and other impurities. Finally, the washed magnesium octoate is vacuum dried at a temperature of 50-60℃, a vacuum degree of -0.08-0.09MPa, and a drying time of 3-4 hours to obtain high-purity magnesium octoate.

[0010] In the above technical solution, in step (2), the ionic liquid has good solubility and designability, which can effectively promote the contact and reaction between reactants. At the same time, its low volatility and reusability reduce environmental pollution and production costs.

[0011] In step (4), a gradient crystallization procedure is used to precisely control the crystal form and suppress impurity embedding. This gradient crystallization procedure includes two stages: the first stage involves cooling from 90°C to 50°C and holding for 1–1.5 hours; the second stage involves cooling from 50°C to 25°C and holding for 1–1.5 hours. Through this stepwise cooling and holding operation, the differences in solute crystallization characteristics at different temperatures are utilized to precisely intervene in the crystal nucleation and growth kinetics—avoiding the disordered growth of polycrystalline nuclei caused by rapid cooling, and providing stable conditions for ordered crystal growth through staged holding, effectively improving the crystal's particle size distribution, surface morphology, and internal structure, achieving a controllable transformation of the crystal form from disorder to order and from polymorphism to single-state, breaking through the traditional controllable crystal form preparation technology, thereby obtaining the desired crystal structure.

[0012] Furthermore, in step (1), if the purity of octanoic acid is less than 99%, the octanoic acid is purified by vacuum distillation, and the fraction at 2.13 kPa and 120-130°C is collected to remove impurities and low-boiling-point substances, so that the purity of octanoic acid reaches more than 99%.

[0013] Preferably, in step (2), the ionic liquid is 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, N-butylpyridine tetrafluoroborate, or tetrabutylammonium bromide, etc.

[0014] Preferably, in step (3), the molar ratio of the octanoic acid to the magnesium salt is 2.1-2.3:1.

[0015] Preferably, in step (3), the temperature of the reaction zone is controlled at 70-90℃. This temperature range is set based on a comprehensive consideration of factors such as the chemical equilibrium and reaction rate of the magnesium octoate preparation reaction, aiming to ensure that the reaction can proceed efficiently under suitable temperature conditions, while avoiding problems such as abnormal reaction or product quality decline caused by excessively high or low temperatures.

[0016] Preferably, in step (4), the gradient cooling process consists of a first stage of 90℃→50℃, slow cooling to allow uniform crystal nuclei to form; and a second stage of 50℃→25℃, further cooling to accelerate crystal growth and stabilizing the crystal form by heat preservation, with each stage lasting 1-1.5 hours. Furthermore, in step (4), the gradient crystallization procedure involves a first stage of cooling from 90℃ to 50℃ at a rate of 2℃ / min, with the first stage held for 1 hour; and a second stage of cooling from 50℃ to 25℃ at a rate of 1℃ / min, with the second stage held for 1.5 hours. The holding time for each stage is the total time consumed for each stage. Furthermore, in step (5), after the reaction is complete, the centrifugal filtration speed is 3000-4000 r / min, and the time is 5-10 minutes.

[0017] Basic principle of this invention:

[0018] Ionic liquids, with their "amphiphilic solubility" properties, can dissolve polar magnesium sources through their polar frameworks and are compatible with hydrophobic octanoic acid through their hydrophobic side chains. When combined with ethanol, they can solve the problem of uneven reaction caused by differences in the polarity of raw materials, build a homogeneous system, and improve the utilization rate of raw materials.

[0019] Magnesium octoate, with its amphiphilic structure of a "polar carboxyl magnesium salt end and a nonpolar long-chain alkyl end," leverages the synergistic effect of ionic liquids and gradient crystallization to precisely control crystal form and suppress impurity embedding. Ionic liquids can form a directional interaction with the polar carboxyl magnesium salt end of magnesium octoate through their polar framework. Simultaneously, their hydrophobic side chains are compatible with the long-chain alkyl groups, pre-guiding the orderly arrangement of magnesium octoate molecules, reducing disordered aggregation, and laying a regular foundation for crystal growth.

[0020] During the gradient crystallization process, the ionic liquid and gradient crystallization form a precise match for the magnesium octoate structure. In the first stage of cooling, the ionic liquid anchors the polar end of the magnesium carboxyl salt. With the slow cooling in this temperature range, the crystal nuclei are prevented from being randomly generated due to sudden temperature changes, ensuring that the nucleation direction is consistent with the pre-arrangement of molecules. In the second stage of low-temperature holding, its compatibility with long-chain alkyl groups becomes more stable as the temperature decreases, which helps the crystal grow along the ordered direction of the alkyl chain. At the same time, because the cooling rate is controllable, the crystal growth rhythm is slow, which can prevent impurities from being buried with the rapidly growing crystal.

[0021] It is the directional guidance of the ionic liquid on the amphiphilic structure of magnesium octoate, combined with the phased temperature control of gradient crystallization, that precisely intervenes in the crystal nucleation and growth kinetics, effectively improving the crystal's particle size distribution, surface morphology, and internal structure. This enables a controllable transformation of the crystal form from disorder to order and from polymorphism to single state, breaking through the traditional controllable crystal form preparation technology, thereby obtaining the desired crystal structure.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The present invention uses an ionic liquid-ethanol mixture system as a reaction medium, which significantly improves the reaction rate and shortens the reaction time from 6-8 hours in the traditional method to 1-1.5 hours, greatly improving production efficiency.

[0024] (2) Through raw material pretreatment, optimized reaction conditions and a fine separation and purification process, the generation and residue of impurities are effectively reduced, and the purity of the prepared magnesium octoate can reach more than 99.5%, which meets the application needs of high-end fields.

[0025] (3) Ionic liquids can be reused, which reduces the use and waste of organic solvents and reduces environmental pollution. At the same time, optimized reaction conditions and separation processes reduce energy consumption and meet the requirements of green chemistry development.

[0026] (4) Through crystal form control technology, magnesium octoate is formed into regular plate-like crystals with uniform particle size distribution, which improves the stability and application performance of the product and expands the application range of the product.

[0027] (5) This invention produces magnesium octoate with a purity of ≥99.5%, a magnesium content reaching the theoretical value, and regular flake-shaped crystals with uniform particle size distribution. This method optimizes reaction kinetics with ionic liquids and combines gradient crystallization control technology, which shortens the reaction time to 1 / 5 of the traditional method. The ionic liquid can be reused ≥5 times, the ethanol recovery rate is over 90%, the organic solvent consumption is reduced by more than 80%, and the impurity content is <0.3%, meeting the pharmaceutical grade standard. This provides a sustainable preparation solution for the application of magnesium octoate in high-end drug carriers, cosmetic emulsifiers, and food-grade heat stabilizers, and has significant industrial application value. Attached Figure Description

[0028] Figure 1 It is the infrared spectrum of caprylic acid;

[0029] Figure 2 This is a schematic diagram of the near-infrared spectrum collected from the magnesium octanoate sample in Example 1;

[0030] Figure 3 This is a comparison of the crystal forms of magnesium octoate prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0031] To better understand the content of this invention, specific embodiments are described below. It should be understood that these embodiments are for further illustration only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art may make non-essential modifications or adjustments to the invention, which still fall within the protection scope of this invention.

[0032] Example 1

[0033] First, 300g of octanoic acid (octanoic acid with the longest main chain; Hangzhou Jiangding Chemical Co., Ltd.) was purified by vacuum distillation, and the fraction collected at 2.13kPa and 120-130℃ was collected to make the purity of octanoic acid ≥99%. It was added to 30g of ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate), 150ml of ethanol was added, and 21.53g of magnesium hydroxide was added at room temperature. The reaction was carried out in a 90°C water bath for 1.5h until the solution became clear. At the same time, the characteristic peak of octanoic acid disappeared by online infrared spectroscopy. Then the reaction solution was transferred to a temperature-controlled cooling tank and a gradient crystallization program was started: in the first stage, the temperature was reduced from 90°C to 50°C at a rate of 2°C / min and held for 1h to promote uniform nucleation of crystal nuclei; in the second stage, the temperature was reduced from 50°C to 25°C (room temperature) at a rate of 1°C / min and held for 1.5h to guide the directional growth of crystals. After crystallization, the system was centrifuged at 3000 r / min for 10 min to collect the magnesium octoate crystals. The mother liquor was reused, and the crude product was washed 2-3 times with anhydrous ethanol at a mass ratio of 5-6:1 to remove adsorbed ionic liquids and other impurities. Finally, the washed magnesium octoate was vacuum dried at 50℃, under a vacuum of -0.08 to 0.09 MPa for 3 hours to obtain high-purity magnesium octoate.

[0034] Example 2

[0035] First, 300g of octanoic acid (octanoic acid with the longest main chain; Hangzhou Jiangding Chemical Co., Ltd.) was purified by vacuum distillation, and the fraction collected at 2.13kPa and 120-130℃ was collected to make the purity of octanoic acid ≥99%. This fraction was added to the mother liquor in Example 1, followed by 5g of ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate), 100ml of ethanol, and 21.53g of magnesium hydroxide at room temperature. The mixture was then reacted in a 90°C water bath for 1.5h until the solution became clear. Simultaneously, the characteristic peak of octanoic acid was monitored by online infrared spectroscopy until it disappeared. The reaction solution was then transferred to a temperature-controlled cooling tank, and a gradient crystallization program was started: in the first stage, the temperature was lowered from 90°C to 50°C at a rate of 2°C / min and held for 1h to promote uniform nucleation of crystal nuclei; in the second stage, the temperature was lowered from 50°C to 25°C (room temperature) at a rate of 1°C / min and held for 1.5h to guide the directional growth of crystals. After crystallization, the system was centrifuged at 3000 r / min for 10 min to collect the magnesium octoate crystals. The mother liquor was reused, and the crude product was washed 2-3 times with anhydrous ethanol at a mass ratio of 5-6:1 to remove adsorbed ionic liquids and other impurities. Finally, the washed magnesium octoate was vacuum dried at 50℃, under a vacuum of -0.08 to 0.09 MPa for 3 hours to obtain high-purity magnesium octoate.

[0036] Example 3

[0037] First, 300g of octanoic acid (octanoic acid with the longest main chain; Hangzhou Jiangding Chemical Co., Ltd.) was purified by vacuum distillation, and the fraction collected at 2.13kPa and 120-130℃ was collected to make the purity of octanoic acid ≥99%. This fraction was added to the mother liquor in Example 2, and then 6g of the ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) was added. 80ml of ethanol was added, and 21.53g of magnesium hydroxide was added at room temperature. The mixture was reacted in a 90°C water bath for 1.5h until the solution became clear. At the same time, the characteristic peak of octanoic acid was monitored by online infrared spectroscopy until it disappeared. Then, the reaction solution was transferred to a temperature-controlled cooling tank and a gradient crystallization program was started: in the first stage, the temperature was reduced from 90°C to 50°C at a rate of 2°C / min and held for 1h to promote uniform nucleation of crystal nuclei; in the second stage, the temperature was reduced from 50°C to 25°C (room temperature) at a rate of 1°C / min and held for 1.5h to guide the directional growth of crystals. After crystallization, the system was centrifuged at 3000 r / min for 10 min to collect the magnesium octoate crystals. The mother liquor was reused, and the crude product was washed 2-3 times with anhydrous ethanol at a mass ratio of 5-6:1 to remove adsorbed ionic liquids and other impurities. Finally, the washed magnesium octoate was vacuum dried at 50℃, under a vacuum of -0.08 to 0.09 MPa for 3 hours to obtain high-purity magnesium octoate.

[0038] Example 4

[0039] First, 300g of octanoic acid (octanoic acid with the longest main chain; Hangzhou Jiangding Chemical Co., Ltd.) was purified by vacuum distillation, and the fraction collected at 2.13kPa and 120-130℃ was collected to make the purity of octanoic acid ≥99%. It was added to 30g of ionic liquid (N-butylpyridine tetrafluoroborate), 150ml of ethanol was added, and 14.88g of magnesium oxide was added at room temperature. The reaction was carried out in a 90°C water bath for 1.5h until the solution became clear. At the same time, the characteristic peak of octanoic acid disappeared by online infrared spectroscopy. Then the reaction solution was transferred to a temperature-controlled cooling tank and a gradient crystallization program was started: in the first stage, the temperature was reduced from 90°C to 50°C at a rate of 2°C / min and held for 1h to promote uniform nucleation of crystal nuclei; in the second stage, the temperature was reduced from 50°C to 25°C (room temperature) at a rate of 1°C / min and held for 1.5h to guide the directional growth of crystals. After crystallization, the system was centrifuged at 3000 r / min for 10 min to collect the magnesium octoate crystals. The mother liquor was reused, and the crude product was washed 2-3 times with anhydrous ethanol at a mass ratio of 5-6:1 to remove adsorbed ionic liquids and other impurities. Finally, the washed magnesium octoate was vacuum dried at 50℃, under a vacuum of -0.08 to 0.09 MPa for 3 hours to obtain high-purity magnesium octoate.

[0040] Example 5

[0041] First, 300g of octanoic acid (octanoic acid with the longest main chain; Hangzhou Jiangding Chemical Co., Ltd.) was purified by vacuum distillation, and the fraction collected at 2.13kPa and 120-130℃ was collected to make the purity of octanoic acid ≥99%. It was added to 30g of ionic liquid (tetrabutylammonium bromide), 150ml of ethanol was added, and 14.88g of magnesium oxide was added at room temperature. The reaction was carried out in a 90°C water bath for 1.5h until the solution became clear. At the same time, the characteristic peak of octanoic acid disappeared by online infrared spectroscopy. Then the reaction solution was transferred to a temperature-controlled cooling tank and a gradient crystallization program was started: in the first stage, the temperature was reduced from 90°C to 50°C at a rate of 2°C / min and held for 1h to promote uniform nucleation of crystal nuclei; in the second stage, the temperature was reduced from 50°C to 25°C (room temperature) at a rate of 1°C / min and held for 1.5h to guide the directional growth of crystals. After crystallization, the system was centrifuged at 3000 r / min for 10 min to collect the magnesium octoate crystals. The mother liquor was reused, and the crude product was washed 2-3 times with anhydrous ethanol at a mass ratio of 5-6:1 to remove adsorbed ionic liquids and other impurities. Finally, the washed magnesium octoate was vacuum dried at 50℃, under a vacuum of -0.08 to 0.09 MPa for 3 hours to obtain high-purity magnesium octoate.

[0042] Comparative Example 1: Preparation of Magnesium Octanoate by Traditional Method

[0043] Take 300g of octanoic acid purified by vacuum distillation (purity ≥99%), add it to 150mL of ethanol, add 21.53g of magnesium hydroxide at room temperature, react for several minutes, then place it in a 90℃ water bath and react for 1.5h until the solution is clear. Directly cool to room temperature, centrifuge the crystallized product at 3000r / min, wash the crude product 2-3 times with anhydrous ethanol (ethanol to crude product mass ratio 5-6:1), and dry it with hot air at 40℃ for 18h. Collect the product to obtain magnesium octanoate.

[0044] Comparative Example 2: Gradient cooling-assisted preparation (ionless liquid system)

[0045] First, 300g of octanoic acid (octanoic acid with the longest main chain; Hangzhou Jiangding Chemical Co., Ltd. / Jiangxi Zhongding Biotechnology Co., Ltd.) was purified by vacuum distillation, and the fraction collected at 2.13kPa and 120-130℃ was collected to make the purity of octanoic acid ≥99%. 150ml of ethanol was added to the fraction, and 21.53g of magnesium hydroxide was added at room temperature. After reacting for several minutes, the fraction was transferred to a 90℃ water bath and reacted at a constant temperature for 1.5h until the solution was completely clear. Then, the reaction solution was transferred to a temperature-controlled cooling tank and a gradient crystallization program was started: in the first stage, the temperature was reduced from 90℃ to 50℃ at a rate of 2℃ / min and held for 1h to promote uniform nucleation of crystal nuclei; in the second stage, the temperature was reduced from 50℃ to 25℃ (room temperature) at a rate of 1℃ / min and held for 1.5h to guide the directional growth of crystals. After crystallization, the system was centrifuged at 3000 r / min for 10 min to collect the magnesium octoate crystals. The mother liquor was reused, and the crude product was washed 2-3 times with anhydrous ethanol at a mass ratio of 5-6:1 to remove adsorbed ionic liquids and other impurities. Finally, the washed magnesium octoate was vacuum dried at 50℃, under a vacuum of -0.08 to 0.09 MPa for 3 hours to obtain high-purity magnesium octoate.

[0046] Comparative Example 3: Ionic Liquid-Mediated Preparation (Gradient-Free Cooling Process)

[0047] Take 300g of octanoic acid purified by vacuum distillation (purity ≥99%), add it to 30g of ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) and 150mL of ethanol, add 21.53g of magnesium hydroxide at room temperature, react for several minutes, and then place it in a 90℃ water bath for 1.5h until the solution is clear. Directly cool to room temperature naturally (without gradient control), centrifuge the crystallized product at 3000r / min, wash the crude product 2-3 times with anhydrous ethanol (ethanol to crude product mass ratio 5-6:1), and vacuum dry at 50℃ (-0.08 to -0.09MPa) for 3 hours to obtain magnesium octanoate product.

[0048] Test case

[0049] Experimental Example 1

[0050] This experimental example illustrates the infrared spectrum of magnesium octanoate in Example 1.

[0051] The magnesium octanoate prepared in Example 1 was analyzed using a Bruker ALPHA Fourier transform infrared spectrometer (Germany). Figure 1 , Figure 2 The infrared spectrum is shown. As can be seen from the figure, after octanoic acid undergoes a chelation reaction with magnesium ions, the corresponding characteristic peak positions shift significantly. Octanoic acid is a carboxylic acid, and its peak position is between 3200-3600 cm⁻¹. -1 The peak exhibits an OH stretching vibration within the range of 1700-1750 cm⁻¹. Due to the presence of the hydroxyl group in the carboxyl group and the formation of intermolecular hydrogen bonds, this peak appears broad; it is located in the 1700-1750 cm⁻¹ range. -1 The presence of a strong absorption peak is due to the C=O stretching vibration of the carboxyl group. In magnesium octoate, this peak may be due to the anhydrous state and the involvement of the carboxyl group in coordination, resulting in a peak at 3200-3600 cm⁻¹. -1 The absorption peaks weaken or disappear within the specified range. In magnesium octanoate, the carboxyl group participates in a coordination reaction, causing a red shift in the C=O stretching vibration. This results in a shift of the absorption peak position towards lower wavenumbers, and the peak intensity may also change. Furthermore, the CH stretching vibrations of the methyl and methylene groups in octanoate occur at 2800-3000 cm⁻¹. -1 There is an absorption peak, but in magnesium octoate, this absorption peak may vary due to changes in molecular structure, such as changes in peak intensity or slight shifts in position.

[0052] Experimental Example 2

[0053] This experimental example illustrates the yield and purity of magnesium octoate in the examples and comparative examples.

[0054] The crystal structure of magnesium octoate was determined by X-ray diffractometer model D8 Advance. The experimental results were compared with the standard magnesium octoate crystal structure by MDI Jade 6 software to evaluate the purity of the product. The results are shown in Table 1.

[0055] First, the theoretically achievable mass of magnesium octoate needs to be calculated based on the equilibrium reaction equation and molar ratio. After synthesizing magnesium octoate, the actual mass of the obtained magnesium octoate product is measured using a balance.

[0056] The percentage yield can be obtained by dividing the actual mass of magnesium octoate produced by the theoretical mass and multiplying by 100%.

[0057] Yield (%) = (Actual product mass / Theoretical product mass) × 100%

[0058] When calculating yield, if the product is not 100% pure, a correction is needed based on purity. The correction formula is: Actual Yield (%) = (Actual Product Mass / Theoretical Product Mass) × Purity × 100% (Example 3)

[0059] This experimental example illustrates the determination of Mg content in magnesium octoate in the examples and comparative examples.

[0060] Weigh approximately 200 mg of the dried sample to constant weight, accurate to 0.0001 g, and place it in a 250 mL Erlenmeyer flask. Add 25 mL of water to dissolve the sample, add 10 mL of ammonia-ammonium chloride buffer solution, add 2 drops of Eriochrome Black T indicator solution, and titrate with disodium ethylenediaminetetraacetate standard titration solution until the solution changes from purple-red to pure blue as the endpoint.

[0061] Simultaneously prepare a blank solution. The blank sample solution should contain the same types and amounts of reagents as the sample solution, except for the absence of the sample solution (excluding standard titration solutions). Prepare two parallel determinations and take the average result. The absolute difference between the two parallel determinations should not exceed 0.3%.

[0062] Calculation formula: Magnesium (calculated as Mg) content X1 is expressed as mass fraction % and is calculated according to the following formula.

[0063]

[0064] In the formula: V: the numerical value of the volume of EDTA standard titration solution consumed by the sample, in milliliters (mL);

[0065] V0: The numerical value of the volume of EDTA standard titration solution consumed in the blank test, in milliliters (mL);

[0066] c: Concentration of EDTA standard solution, in moles per liter (mol / L);

[0067] M: The numerical value of the molar mass of magnesium, in grams per mole (g / mol) [M(magnesium) = 24];

[0068] m: The numerical value of the sample mass, in mg;

[0069] Test Example 4

[0070] This experimental example illustrates the determination of the Mg chelation rate of magnesium octoate in the examples and comparative examples.

[0071] Method for determining magnesium content: EDTA titration. Take the test solution, add 5 mL of ammonia-ammonium chloride buffer (pH = 10.0) and 5 drops of 0.5% Eriochrome Black T solution, and immediately titrate with 0.05 mol / L EDTA-Na2 until the solution changes from purple-red to sky blue. Perform three parallel titrations and record the volume of titrant used.

[0072] The formula for calculating the chelation rate is as follows:

[0073] Chelation rate (%) = (Mm) / M × 100%

[0074] In the formula, M represents the total amount of magnesium, and m represents the amount of free magnesium.

[0075] The results showed that, compared with the traditional method for extracting magnesium octanoate, this method not only greatly shortened the reaction time but also improved the magnesium chelation rate and reaction efficiency.

[0076] Table 1 Comparison of magnesium octanoate yield, purity, magnesium content, and chelation rate

[0077] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Yield 97.8％ 98.7％ 98.9％ 87.9％ 97.9％ 75.4％ 80.1％ 79.3％ purity 98.5％ 98.8％ 98.8％ 88.3％ 98.3％ 67.3％ 65.3％ 68.0％ magnesium content 7.78％ 7.80％ 7.79％ 7.77％ 7.79％ 7.35％ 7.24％ 7.31％ Magnesium chelation rate 74.4％ 74.9％ 74.1％ 63.9％ 73.9％ 42.7％ 44.7％ 43.9％

[0078] As shown in Table 1, the magnesium octoate prepared in the examples is significantly superior to the comparative example in terms of yield, purity, magnesium content, and magnesium chelation rate. This fully demonstrates that using an ionic liquid-ethanol mixture as the reaction medium for preparing magnesium octoate is highly effective. The unique properties of ionic liquids, such as high solubility, low volatility, and designability, greatly promote the contact between reactants, accelerate the reaction rate, and significantly improve the yield and purity of magnesium octoate, while also increasing the magnesium content and magnesium chelation rate. In contrast, magnesium octoate prepared by traditional methods shows significant differences in all indicators.

[0079] Experimental Example 5

[0080] This experimental example illustrates the comparison of particle size distribution and crystal form between the examples and comparative examples.

[0081] Particle size distribution: Laser particle size analyzer (Malvern Mastersizer 3000), test range 0.1-2000μm, each sample was measured 3 times and the average value was taken. The results are shown in Table 2.

[0082] Crystal form observation: Scanning electron microscope (SEM, JEOL JSM-7610F), accelerating voltage 5kV, surface morphology of the sample after gold sputtering was observed, results are as follows. Figure 3 As shown, Figure (a) is the crystal form of Comparative Example 1, and Figure (b) is the crystal form of Example 1;

[0083] Table 2 Comparison of Magnesium Octanoate Particle Size Distribution

[0084]

[0085] D10, D50, and D90 represent the particle size of 10%, 50%, and 90% of the particles, respectively, reflecting the degree of dispersion in particle size distribution.

[0086] As shown in Table 2, the D10 of Examples 1-5 is between 2.0-2.5 μm, the D50 is between 5.5-5.8 μm, and the D90 is between 8.5-9.0 μm, with a range of only 6.0-6.9 μm. This indicates that the magnesium octoate particles in these examples are concentrated in the 2-9 μm range, with uniform overall size and no obvious agglomeration or coarse particles. In contrast, the D10 of Comparative Examples 1-3 is 1.3-1.5 μm, the D50 reaches 12.5-13.5 μm, and the D90 is even higher at 44.2-45.2 μm, with a range of 42.9-43.7 μm. Their particle size distribution is extremely wide, ranging from 1.3-45.2 μm, and the D50 is significantly larger than that of the examples, with a very large range. This indicates that the crystals generated by the traditional method are uneven in size and may have problems with secondary aggregation or uncontrolled growth.

[0087] In summary, traditional methods often result in excessively high supersaturation due to abrupt changes in solvent polarity, leading to rapid and disordered crystal growth. Furthermore, residual solvent can easily cause agglomeration. Ionic liquids, on the other hand, can suppress abnormal crystal growth by regulating interfacial tension, while gradient cooling can achieve uniform particle size through precise control of nucleation and growth rates. The synergistic effect of these two methods effectively controls the particle size and uniformity of magnesium octoate, making it a key process combination for preparing high-quality magnesium octoate.

[0088] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Such modifications or substitutions also fall within the protection scope defined by the appended claims.

Claims

1. A method for preparing high-purity magnesium octanoate, characterized in that, Includes the following steps: (1) Raw material pretreatment: Confirm the purity of the raw materials to ensure that the purity of octanoic acid is ≥99%, wherein the octanoic acid is the octanoic acid with the longest main chain. (2) Construction of ionic liquid system: Add ionic liquid at 10%-15% of the mass of octanoic acid, and then add anhydrous ethanol as a co-solvent to form a homogeneous reaction medium, wherein the volume ratio of ethanol to ionic liquid is 1:1-1.5:1, and the volume ratio of ethanol to octanoic acid is 0.5-0.8:

1. (3) Reaction process: Add the pretreated octanoic acid and magnesium source to the system of step (2) and react for 1-1.5 hours at 70-90℃ and 300-400r / min; the magnesium source is selected from any one of magnesium oxide, magnesium hydroxide, magnesium laurate and magnesium carbonate; (4) Dynamic gradient solvent crystallization: The crystal form is controlled by a gradient crystallization program, which includes a first stage and a second stage in sequence: the first stage is to cool down from 90°C to 50°C and hold for 1 to 1.5 hours; the second stage is to cool down from 50°C to 25°C and hold for 1 to 1.5 hours. (5) Product separation and purification: Centrifuge to obtain crude magnesium octoate. Wash the crude product with anhydrous ethanol 2-3 times, with the mass ratio of ethanol to crude product being 5-6:1 each time. Vacuum dry the washed magnesium octoate at a temperature of 50-60℃, a vacuum degree of -0.08--0.09MPa, and a drying time of 3-4 hours to obtain high-purity magnesium octoate.

2. The method for preparing high-purity magnesium octanoate according to claim 1, characterized in that, In step (1), if the purity of octanoic acid is less than 99%, the octanoic acid is purified by vacuum distillation, and the fraction at 2.13 kPa and 120-130℃ is collected to make the purity of octanoic acid ≥ 99%.

3. The preparation method according to claim 1, characterized in that, In step (3), the reaction process is monitored in real time by online infrared spectroscopy. When the characteristic absorption peak of octanoic acid disappears, the reaction is considered to be basically completed.

4. The preparation method according to claim 1, characterized in that, In the gradient crystallization process, the first stage involves cooling from 90°C to 50°C at a rate of 2°C / min and holding at that temperature for 1 hour. The second stage involves cooling from 50°C to 25°C at a rate of 1°C / min and holding at that temperature for 1.5 hours.

5. The method for preparing high-purity magnesium octanoate according to claim 1, characterized in that, The ionic liquid in step (2) is 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, N-butylpyridine tetrafluoroborate or tetrabutylammonium bromide.

6. The method for preparing high-purity magnesium octanoate according to claim 1, characterized in that, In step (3), the molar ratio of octanoic acid to magnesium source is 2.1-2.3:

1.

7. The method for preparing high-purity magnesium octanoate according to claim 1, characterized in that, In step (5), after the reaction is complete, the centrifugal filtration speed is 3000-4000 r / min and the time is 5-10 minutes.

8. The method for preparing high-purity magnesium octanoate according to claim 1, characterized in that, The obtained magnesium octoate is a regular plate-shaped crystal with a purity of ≥99.5% and a uniform particle size distribution.

9. The method for preparing high-purity magnesium octanoate according to claim 1, characterized in that, The resulting magnesium octoate particles had a particle size of 2-9 μm.

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