Method for confirming and controlling valproic acid ester as an impurity in valproic acid
By combining gas chromatography and nuclear magnetic resonance spectroscopy with column chromatography and pulping methods, the problem of detecting and controlling valproic acid ester impurities in valproic acid was solved, ensuring that the quality of valproic acid products meets pharmacopoeia requirements.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUNAN UNIV
- Filing Date
- 2026-03-02
- Publication Date
- 2026-06-12
AI Technical Summary
Existing technologies are insufficient to effectively detect and control valproate impurities in valproic acid, especially the presence of methyl valproate, ethyl valproate, and propyl valproate, which makes it difficult to guarantee product quality.
Gas chromatography combined with nuclear magnetic resonance spectroscopy was used to separate and identify valproate impurities through column chromatography and pulping. An Agilent 8890 gas chromatograph was used for detection to determine the types and contents of impurities, and product quality was controlled by pulping and blending methods.
This technology enables accurate detection and control of valproic acid ester impurities, ensuring that the quality of valproic acid products meets pharmacopoeia requirements.
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Figure CN122193441A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the identification and control of process impurities, including methyl valproate, ethyl valproate, and propyl valproate, in valproic acid prepared by the dimethyl malonate method and the diethyl malonate method. Background Technology
[0002] Valproic acid is a commonly used drug for treating epilepsy, bipolar disorder, and migraine. Since sodium valproate lacks a structure capable of producing ultraviolet (UV) absorption and its related impurities also lack characteristic UV absorption functional groups, direct determination by HPLC is generally difficult. Chen Shuang et al. used gas chromatography as an effective analytical method to separate potential impurities [Chen Shuang, Lou Yongjun. GC determination of related substances in sodium valproate sustained-release tablets. Chinese Journal of Modern Applied Pharmacy, 2018, 35(7): 998-1000]. Shen Guofang et al. used gas chromatography [Shen Guofang et al. Centrifugation-assisted liquid-liquid extraction-gas chromatography determination of 17 related substances in sodium valproate sustained-release tablets. Chinese Journal of Pharmaceutical Industry, 2025, 56(9): 1203-1210] to detect various impurities in sodium valproate sustained-release tablets, but there were no reports on the detection of methyl valproate, ethyl valproate, and propyl valproate.
[0003] Chengdu Betterdenuo Pharmaceutical Co., Ltd. used a similar method to the British Pharmacopoeia BP2020 to select gas chromatography [a method for the detection of related substances in sodium valproate oral solution, CN 114354803 B, authorized on 2023.11.14] to detect impurities 2-hexanone (impurity-O), 3-propyl-2-hexanone (impurity-P), methyl valproate (impurity-N), valeric acid (EP-A), 2-isopropylvaleric acid (EP-C) and 2-methyl-2-ethylvaleric acid (EP-K) in sodium valproate (prepared by methyl acetoacetate method) oral solution.
[0004]
[0005] The specification for the preparation of valproic acid using the diethyl malonate method [a method for preparing valproic acid using the diethyl malonate method, CN118184508 A, published on June 14, 2024] is paragraph 0088, and the specification is attached. Figures 3-6 In the above, it is speculated that the peak at RRT=0.28 is ethyl valproate; the peak at RRT=0.34 is not confirmed; the method for detecting impurities in the preparation of valproic acid by diethyl malonate method [Method for detecting impurities in the preparation of valproic acid by diethyl malonate method, CN118010875 A, published on 2024.5.10] is attached to the specification. Figure 1 , 3 In samples 5, 7, and 9, GC detection results showed impurity peaks at RRT = 0.27 and RRT = 0.34. Due to limitations (no control sample available), these peaks were not used for confirmation.
[0006] Summary of the Invention
[0007] The purpose of this invention is to provide a method for identifying and controlling valproic acid ester impurities, the operation process of which is as follows:
[0008] (1) Selective column chromatography was used to separate valproic acid crude product prepared by the malonic acid diester method to obtain valproic acid ester impurities;
[0009] (2) Select nuclear magnetic resonance spectroscopy to confirm the structure of the impurity;
[0010] (3) Select a reference standard and use gas chromatography to locate the impurities;
[0011] (4) Select products that have been pulped and controlled to have valproic acid ester impurities.
[0012] The purpose of this invention is to provide a gas chromatography method for detecting impurities in valproic acid: A gas chromatograph (Agilent 8890) is selected, and gas chromatography is used to confirm the process impurities of valproic acid ester in crude valproic acid prepared by the malondioxylate method. The detection conditions of the gas chromatography method are as follows: Column: DB-FFAP, specifications: 0.32 mm × 60 m, 0.5 μm; Carrier gas: Nitrogen; Detector: FID; Flow rate: 2 ml / min; Injection volume: 2 μl; Injector temperature: 220℃; Column temperature: 100℃; Temperature program: Initial temperature 100℃, hold for 5 min, then increase to 140℃ at a rate of 4℃ / min, hold for 5 min, then increase to 200℃ at a rate of 4℃ / min, hold for 15 min; Run time: 50 min; Detector temperature: 220℃; Injection method: Direct injection.
[0013] Weigh 10 mg of the test sample and transfer it to a 10 ml volumetric flask. Dilute to the mark with n-heptane and mix well to prepare the test sample stock solution. Accurately measure 1 ml of the test sample and place it in a 10 ml volumetric flask. Dilute to the mark with n-heptane and mix well to prepare the test sample solution. Accurately measure 10 mg of the reference standard and place it in a 100 ml volumetric flask. Dilute to the mark with n-heptane and mix well to prepare the reference solution. Take approximately 10 mg of 2-phenylethanol and place it in a 100 ml volumetric flask. Dissolve and dilute to the mark with n-heptane and mix well. Take 1 ml of this solution and place it in a 20 ml volumetric flask. Add 2 ml of the test sample stock solution and dilute to the mark with n-heptane and mix well to prepare the system suitability solution. Inject 2 μl each of the diluent n-heptane, the reference solution, and the test sample solution into the gas chromatograph and record the chromatogram. Based on the gas chromatographic detection results, determine the type and content of process impurities present in valproic acid using the reference sample.
[0014] Blank solution: n-Heptane.
[0015] The test sample was selected from crude valproic acid prepared by the dimethyl malonate method and the diethyl malonate method.
[0016] The reference standard for valproate impurities is selected from methyl valproate, ethyl valproate, or propyl valproate.
[0017]
[0018] A second aspect of the present invention provides a method for separating methyl valproate and propyl valproate impurities from valproic acid prepared by the dimethyl malonate method. Crude valproic acid prepared by the dimethyl malonate method is dissolved in an aqueous sodium hydroxide solution and extracted three times with ethyl acetate. The combined extracts are separated by petroleum ether-ethyl acetate column chromatography to obtain methyl valproate and propyl valproate; the relative elution times of methyl valproate and propyl valproate are RRT = 0.25 ± 0.01 and RRT = 0.34 ± 0.01, respectively.
[0019] A third aspect of the present invention provides a method for separating ethyl valproate and propyl valproate impurities from valproic acid prepared by the diethyl malonate method. Crude valproic acid prepared by the diethyl malonate method is dissolved in an aqueous sodium hydroxide solution and extracted three times with ethyl acetate. The combined extracts are separated by petroleum ether-ethyl acetate column chromatography to obtain ethyl valproate and propyl valproate. Methyl valproate, ethyl valproate, and propyl valproate are separated by column chromatography with petroleum ether, and the results are confirmed by nuclear magnetic resonance spectroscopy and gas chromatography. The relative elution times of ethyl valproate and propyl valproate are RRT = 0.28 ± 0.01 and RRT = 0.34 ± 0.01, respectively.
[0020] In the preparation of crude valproic acid using the dimethyl malonate method and the diethyl malonate method, gas chromatography analysis showed that it may contain methyl valproate, ethyl valproate, and propyl valproate.
[0021]
[0022] Methyl valproate, ethyl valproate, propyl valproate, and valproic acid are all liquids with similar boiling points. Although the content of methyl valproate, ethyl valproate, and propyl valproate is low, they are easier to distill off because of their lower boiling points. Therefore, methyl valproate, ethyl valproate, and propyl valproate are difficult to completely separate by distillation. Liquid compounds—methyl valproate, ethyl valproate, and propyl valproate—and the precursor compound of valproic acid—dipropylmalonic acid monomethyl ester (melting point 68-69°C); dipropylmalonic acid monoethyl ester (melting point 44-45°C) and dipropylmalonic acid (melting point 157-158°C) have significantly different melting points; dipropylmalonic acid monomethyl ester, dipropylmalonic acid monoethyl ester, and dipropylmalonic acid monopropyl ester have high solubility in thermally polar solvents, and dipropylmalonic acid monomethyl ester, dipropylmalonic acid monoethyl ester, and dipropylmalonic acid monopropyl ester can be separated from crude malondiic acid by slurry extraction. This invention separates dicarboxylic acids and dicarboxylic acid monoester solids based on the difference in solubility in thermally polar solvents, accurately removing difficult-to-separate liquid impurities.
[0023] The precursor compounds of methyl valproate, dipropylmalonate monomethyl ester, were identified using retrosynthetic analysis; the precursor compounds of ethyl valproate, dipropylmalonate monoethyl ester, and propyl valproate, dipropylmalonate monopropyl ester, were also identified.
[0024]
[0025] A fourth aspect of the present invention provides a method for controlling the content of methyl valproate, ethyl valproate, and propyl valproate through pulping and compounding to ensure the quality of valproic acid products. The operation process is as follows:
[0026] (1) Dipropylmalonic acid was prepared by dipropylation of malonate diester to crude dipropylmalonic acid by hydrolysis:
[0027] (2) Select a mixed solvent to pulp the crude dipropylmalonic acid obtained by hydrolysis, and then filter and dry it to obtain dipropylmalonic acid;
[0028] (3) The slurry recovery kit containing dipropylmalonic acid monoester is used for the hydrolysis reaction of dipropylmalonic acid diester;
[0029] (4) Valproic acid was prepared by heating and decarboxylating dipropylmalonic acid; the quality of the valproic acid product met the requirements of the pharmacopoeia.
[0030] The pulping temperature is selected from 30℃ to 80℃; the mixed solvent is selected from a mixture of water and alcohol; the volume ratio of alcohol to water is selected from 2 / 8 to 8 / 2.
[0031] The alcohol solvent is selected from methanol, ethanol, C3-C6 straight-chain or C3-C6 branched monohydric alcohols, ethylene glycol, C3-C5 straight-chain diols or C4-C5 branched diols.
[0032] Compared with the prior art, the present invention has the following advantages:
[0033] 1. Gas chromatography was used to detect crude valproic acid prepared by the dimethyl malonate method and the diethyl malonate method. The results showed that the RRT of valproic acid was 1.00, the RRT of methyl valproate was 0.26±0.01, the RRT of ethyl valproate was 0.28±0.01, and the RRT of propyl valproate was 0.34±0.01. The RRT of propyl valproate was confirmed by comparison with the detection methods of nuclear magnetic resonance spectroscopy and gas chromatography.
[0034] 2. The content of methyl valproate, ethyl valproate, and propyl valproate is controlled by pulping and overlaying methods to ensure that the quality of valproic acid products meets the pharmacopoeia requirements. Attached Figure Description
[0035] Appendix Figure 1 Gas chromatogram of valproic acid (dimethyl malonate method)
[0036] Appendix Figure 2 Gas chromatogram of valproic acid (diethyl malonate method)
[0037] Appendix Figure 3 Gas chromatogram of methyl valproate
[0038] Appendix Figure 4 Gas chromatogram of ethyl valproate
[0039] Appendix Figure 5 Gas chromatogram of propyl valproate
[0040] Appendix Figure 6 Gas chromatogram of a mixture of valproic acid (dimethyl malonate method) and methyl valproate.
[0041] Appendix Figure 7 Gas chromatogram of a mixture of valproic acid (dimethyl malonate method) and propyl valproate.
[0042] Appendix Figure 8 Gas chromatogram of a mixture of valproic acid (diethyl malonate method) and ethyl valproate.
[0043] Appendix Figure 9 Gas chromatogram of a mixture of valproic acid (diethyl malonate method) and propyl valproate.
[0044] Appendix Figure 10 Example 11 Gas chromatogram of valproic acid (dimethyl malonate method)
[0045] Appendix Figure 11Example 12 Gas chromatogram of valproic acid (diethyl malonate method) Detailed Implementation
[0046] The present invention will be further described in detail below with reference to the embodiments.
[0047] Example 1
[0048] Preparation of valproic acid (dimethyl malonate method)
[0049]
[0050] (1) Preparation of dimethyl dipropylmalonate
[0051] Add 3.0 mmol TBAB and 50 mL DMF (or 50 mL recovered DMF) to a three-necked flask and stir with an electric mixer. Then add 0.20 mol potassium carbonate (200 mesh), 13.2 g (0.10 mol) dimethyl malonate, and dropwise add 19.64 g (0.25 mol) 1-chloropropane. Stir at 75℃~85℃ for 4.0 h, 85℃~105℃ for 4.0 h, and 105℃~130℃ for 4.0 h to recover excess 1-chloropropane (for future use). After the reaction is complete, cool to room temperature, filter, and recover DMF from the filtrate under reduced pressure at 80~90℃ (for future use) to obtain a pale yellow liquid. Wash with 120 mL of water (40 mL × 3), and dry to obtain a pale yellow transparent liquid, dimethyl dipropyl malonate.
[0052] (2) Preparation of dipropylmalonic acid
[0053] In the pale yellow liquid of dipropylmalonic acid obtained in (1), potassium hydroxide aqueous solution (16 g KOH, 16 mL H2O) and 10 mL methanol were added, and the mixture was heated to 95 °C for 3 h for hydrolysis. The solid was obtained by rotary evaporation. 50 mL of water was added to dissolve the solid, and the pH was adjusted to 1~1.5 with concentrated hydrochloric acid. A solid precipitated out. The solid was filtered, and the filtrate was a mixture of KCl and HCl. The solid was recrystallized from the methanol aqueous solution to obtain dipropylmalonic acid.
[0054] (3) Preparation of valproic acid
[0055] The dipropylmalonic acid obtained in (2) was added to the reaction flask and decarboxylated at 160~180℃ for 2h to obtain yellow liquid valproic acid.
[0056] Example 2
[0057] Separation of valproate ester from valproic acid (dimethyl malonate method)
[0058] The valproic acid prepared in Example 1 was dissolved in an aqueous sodium hydroxide solution, and extracted three times with ethyl acetate. The combined extracts were separated by petroleum ether-ethyl acetate column chromatography to obtain propyl valproate.
[0059] Propyl valproate: 1 H NMR (400 MHz, CDCl3) δ: 4.02 (t, J = 6.6 Hz, 2H, OCH2), 2.38~2.33 (m, 1H, CH), 1.68~1.54 (m, 4H, CH2×2), 1.44~1.35 (m, 2H, CH2), 1.32~1.23 (m, 4H, CH2×2), 0.93 (t, J = 7.3 Hz, 3H, CH3), 0.88 (t, J = 7.3 Hz, 6H, CH3×2); 13 C NMR (101MHz, CDCl3) δ: 177.13, 66.06, 45.84, 35.17, 22.51, 21.09, 14.44, 10.87.
[0060] Example 3
[0061] Preparation of valproic acid (diethyl malonate method)
[0062]
[0063] (1) Preparation of diethyl dipropylmalonate
[0064] In a reaction vessel, 1.92 kg of diethyl malonate, 0.37 kg of tetrabutylammonium bromide, 2.99 kg of anhydrous potassium carbonate, 6.26 kg of DMF, and 3.30 kg of 1-chloropropane were added sequentially. The mixture was stirred at 75℃~85℃ for 4.0 h, 85℃~105℃ for 4.0 h, and 105℃~130℃ for 4.0 h. The mixture was then cooled to below 50℃, filtered, and the filter cake was washed with an appropriate amount of DMF. The filtrates were combined, and the DMF was distilled off under reduced pressure. In the pale yellow liquid obtained after removing the DMF by distillation, 6.40 kg of petroleum ether and 9.60 kg of water were added sequentially, and the mixture was stirred for 20 minutes and allowed to stand for 20 minutes. The organic phase was then distilled off under normal pressure to obtain 2.96 kg of diethyl dipropyl malonate.
[0065] (2) Preparation of dipropylmalonic acid
[0066] 2.96 kg of diethyl dipropylmalonate, 3.84 kg of potassium hydroxide solution (44%), and 0.96 kg of ethanol were added sequentially to a reaction vessel and refluxed for 3 h with stirring. The ethanol was recovered to dryness under normal pressure to obtain a white solid. 6.00 kg of water was added to dissolve the solid, and the temperature was lowered to below 40°C. Concentrated hydrochloric acid was added dropwise to adjust the pH of the solution to 1, causing the solid to precipitate. The solid was filtered, and the filter cake was washed with an appropriate amount of water to obtain 2.30 kg of dipropylmalonate.
[0067] (3) Preparation of valproic acid
[0068] 2.30 kg of dipropylmalonic acid was added to the reactor, the temperature was raised to 100°C to evaporate the water, and then the temperature was raised to 170°C~180°C and the decarboxylation reaction was maintained for 1 hour to obtain valproic acid.
[0069] Example 4
[0070] Separation of valproate ester from valproic acid (diethyl malonate method)
[0071] The valproic acid prepared in Example 3 was dissolved in an aqueous sodium hydroxide solution and extracted three times with ethyl acetate. The combined extracts were separated by petroleum ether-ethyl acetate column chromatography to obtain ethyl valproate and propyl valproate.
[0072] Ethyl valproate: 1 H NMR (400 MHz, DMSO-d6)δ: 4.12 (q, 2H, OCH2), 2.37~2.30 (m, 1H, CH), 1.63~1.52 (m, 2H, CH2), 1.45~1.35 (m, 2H, CH2), 1.32~1.23 (m, 7H, CH2×2, CH3), 0.88 (t, J = 7.3 Hz, 6H, CH3×2); 13 C NMR (101 MHz, DMSO-d6) δ: 177.06, 60.36, 45.76, 35.15, 21.08, 14.78, 14.45.
[0073] Example 5
[0074] Valproic acid gas chromatography
[0075] A gas chromatograph, model Agilent 8890, was selected to detect valproic acid ester process impurities in crude valproic acid prepared by the malonic acid diester method. The gas chromatographic detection conditions were as follows: column: DB-FFAP, 0.32 mm × 60 m, 0.5 μm; carrier gas: nitrogen; detector: FID; flow rate: 2 ml / min; injection volume: 2 μl; injection port temperature: 220℃; column temperature: 100℃; temperature program: initial temperature 100℃, hold for 5 min, then increase to 140℃ at a rate of 4℃ / min, hold for 5 min, then increase to 200℃ at a rate of 4℃ / min, hold for 15 min; run time: 50 min; detector temperature: 220℃; injection method: direct injection.
[0076] Weigh 10 mg of the test sample and transfer it to a 10 ml volumetric flask. Dilute to the mark with n-heptane and mix well to prepare the test sample stock solution. Accurately measure 1 ml of the test sample and place it in a 10 ml volumetric flask. Dilute to the mark with n-heptane and mix well to prepare the test sample solution. Accurately measure 10 mg of the reference standard and place it in a 100 ml volumetric flask. Dilute to the mark with n-heptane and mix well to prepare the reference solution. Take approximately 10 mg of 2-phenylethanol and place it in a 100 ml volumetric flask. Dissolve and dilute to the mark with n-heptane and mix well. Take 1 ml of this solution and place it in a 20 ml volumetric flask. Add 2 ml of the test sample stock solution and dilute to the mark with n-heptane and mix well to prepare the system suitability solution. Inject 2 μl each of the diluent n-heptane, the reference solution, and the test sample solution into the gas chromatograph and record the chromatogram. Based on the gas chromatographic detection results, determine the type and content of process impurities present in valproic acid using the reference sample.
[0077] Blank solution: n-Heptane.
[0078] The test sample was selected from crude valproic acid prepared by the dimethyl malonate method and the diethyl malonate method.
[0079] The reference standard for valproate impurities is selected from methyl valproate, ethyl valproate, or propyl valproate.
[0080] The gas chromatographic detection results of crude valproic acid prepared by the dimethyl malonate method (Example 1) are shown in the appendix. Figure 1 See Table 1.
[0081] Table 1. GC detection results of valproic acid (dimethyl malonate method)
[0082]
[0083] Figure 1The results in Table 1 show that peak 2, propyl valproate (RRT=0.35), 0.034%; peak 4, valeric acid (RRT=0.76), 0.032%; peak 5, 2-methylvaleric acid (RRT=0.80), 0.232%; and peak 7, valproic acid (RRT=1.00), 99.293%.
[0084] The gas chromatographic detection results of crude valproic acid prepared by the diethyl malonate method (Example 2) are shown in the appendix. Figure 2 And Table 2.
[0085] Table 2. GC detection results of valproic acid (diethyl malonate method)
[0086]
[0087] Figure 2 The results in Table 2 show that peak 2, ethyl valproate (RRT=0.27), 0.023%; peak 3, propyl valproate (RRT=0.34), 0.020%; peak 4, valeric acid (RRT=0.77), 0.188%; peak 5, 2-ethylvaleric acid (RRT=0.90), 0.031%; and peak 6, valproic acid (RRT=1.00), 99.716%.
[0088] Example 6
[0089] Gas chromatography of valproate
[0090] The detection method is the same as in Example 5. The gas chromatographic detection results of the reference standard methyl valproate are shown in the appendix. Figure 3 And Table 3.
[0091] Table 3. GC detection results of methyl valproate (reference standard)
[0092]
[0093] Figure 3 The results in Table 3 show that peak 1, methyl valproate (RT=7.397 min), 99.351%.
[0094] The gas chromatographic detection results of the reference standard ethyl valproate are shown in the appendix. Figure 4 And Table 4.
[0095] Table 4. GC detection results of ethyl valproate (reference standard)
[0096]
[0097] Figure 4 The results in Table 4 show that peak 2, ethyl valproate (RT=8.055 min), 99.408%.
[0098] The gas chromatographic detection results of the reference standard propyl valproate are shown in the appendix. Figure 5 See Table 5.
[0099] Table 5. GC detection results of propyl valproate (reference standard)
[0100]
[0101] Figure 5 The results in Table 5 show that peak 4, propyl valproate (RT=10.054 min), 99.457%.
[0102] Example 7
[0103] Gas chromatography of a mixture of valproic acid (dimethyl malonate method) and methyl valproate
[0104] Valproic acid prepared by the dimethyl malonate method was mixed with methyl valproate, and the mixture was analyzed according to the method in Example 5. The gas chromatographic results are shown in the appendix. Figure 6 See Table 6.
[0105] Table 6 GC detection results of the mixture of valproic acid and methyl valproate
[0106]
[0107] Figure 6 The results in Table 6 show that: peak 1, methyl valproate (RRT=0.25), 0.061%; peak 2, propyl valproate (RRT=0.34), 0.027%; peak 5, valeric acid (RRT=0.76), 0.032%; peak 6, 2-methylvaleric acid (RRT=0.80), 0.250%; and peak 8, valproic acid (RRT=1.00), 97.014%.
[0108] The gas chromatographic detection comparison results of crude valproic acid prepared by the dimethyl malonate method and a mixture of valproic acid and methyl valproate are shown in Table 7.
[0109] Table 7. Comparison results between crude valproic acid and a mixture of valproic acid and methyl valproate.
[0110]
[0111] ND: Not detected
[0112] In the gas chromatographic analysis of the mixture of valproic acid and methyl valproate, the contents of methyl valproate (RRT = 0.25) and 2-methylvaleric acid (RRT = 0.80) increased, while the contents of propyl valproate and valproic acid (RRT = 1.00) decreased.
[0113] Example 8
[0114] Gas chromatography of a mixture of valproic acid (dimethyl malonate method) and propyl valproate
[0115] Valproic acid prepared by the dimethyl malonate method was mixed with propyl valproate, and the mixture was analyzed according to the method in Example 5. The gas chromatographic results are shown below. Figure 7 See Table 8.
[0116] Table 8 GC detection results of a mixture of valproic acid and propyl valproate
[0117]
[0118] Figure 7 The results in Table 8 show that peak 1, propyl valproate (RRT=0.34), 0.073%; peak 5, valeric acid (RRT=0.76), 0.030%; peak 6, 2-methylvaleric acid (RRT=0.80), 0.250%; and peak 8, valproic acid (RRT=1.00), 98.943%.
[0119] The gas chromatographic detection comparison results of crude valproic acid prepared by the dimethyl malonate method and a mixture of valproic acid and propyl valproate are shown in Table 9.
[0120] Table 9. Comparison results between crude valproic acid and a mixture of valproic acid and propyl valproate.
[0121]
[0122] ND: Not detected
[0123] In the gas chromatographic analysis of the mixture of valproic acid and propyl valproate, the contents of propyl valproate (RRT = 0.34) and 2-methylvaleric acid (RRT = 0.80) increased, while the contents of valeric acid (RRT = 0.76) and valproic acid (RRT = 1.00) decreased.
[0124] Example 9
[0125] Gas chromatography of a mixture of valproic acid (diethyl malonate method) and ethyl valproate
[0126] Valproic acid prepared by the diethyl malonate method was mixed with ethyl valproate, and the mixture was analyzed according to the method in Example 5. The gas chromatographic results are shown below. Figure 8 See Table 10.
[0127] Table 10 GC detection results of the mixture of valproic acid and ethyl valproate
[0128]
[0129] Figure 8The results in Table 10 show that: Peak 2, ethyl valproate (RRT=0.27), 0.325%; Peak 3, propyl valproate (RRT=0.34), 0.154%; Peak 5, valeric acid (RRT=0.76), 0.080%; Peak 6, 2-methylvaleric acid (RRT=0.80), 0.066%; Peak 7, 2-ethylvaleric acid (RRT=0.90), 0.069%; and Peak 8, valproic acid (RRT=1.00), 99.181%.
[0130] The gas chromatographic detection comparison results of crude valproic acid prepared by the diethyl malonate method and a mixture of valproic acid and ethyl valproate are shown in Table 11.
[0131] Table 11 Comparison results of crude valproic acid and a mixture of valproic acid and ethyl valproate.
[0132]
[0133] Table 11 shows that the contents of ethyl valproate (RRT = 0.27), propyl valproate (RRT = 0.34), and 2-ethylvalerate (RRT = 0.9) increased, while the contents of valerate (RRT = 0.76) and valproate (RRT = 1.00) decreased.
[0134] Example 10 Gas chromatography of a mixture of valproic acid (diethyl malonate method) and propyl valproate.
[0135] Valproic acid prepared by the diethyl malonate method was mixed with propyl valproate, and the mixture was analyzed according to the method in Example 5. The gas chromatographic results are shown below. Figure 9 And Table 12.
[0136] Table 12 GC detection results of a mixture of valproic acid and propyl valproate
[0137]
[0138] Figure 9 The results in Table 12 show that peak 3, ethyl valproate (RRT=0.27), 0.101%; peak 4, propyl valproate (RRT=0.34), 0.165%; peak 6, valeric acid (RRT=0.76), 0.080%; peak 7, 2-methylvaleric acid (RRT=0.80), 0.067%; peak 8, 2-ethylvaleric acid (RRT=0.90), 0.070%; and peak 9, valproic acid (RRT=1.00), 99.079%.
[0139] Table 13 shows the gas chromatographic comparison results of crude valproic acid prepared by the diethyl malonate method with a mixture of valproic acid and propyl valproate.
[0140] Table 13 Comparison results of crude valproic acid and a mixture of valproic acid and propyl valproate.
[0141]
[0142] The comparison results in Table 13 show that the contents of ethyl valproate (RRT = 0.27), propyl valproate (RRT = 0.34), and 2-ethylvalerate (RRT = 0.90) increased, while the contents of valerate (RRT = 0.76) and valproate (RRT = 1.00) decreased.
[0143] Use methyl valproate, ethyl valproate, or propyl valproate reference standards respectively to confirm the location of impurities in methyl valproate, ethyl valproate, or propyl valproate:
[0144] The relative elution times of methyl valproate and propyl valproate were RRT=0.25±0.01 and RRT=0.34±0.01, respectively; the relative elution times of ethyl valproate and propyl valproate were RRT=0.28±0.01 and RRT=0.34±0.01, respectively.
[0145] Example 11
[0146] Preparation of valproic acid (dimethyl malonate method)
[0147] (1) Add 3.0 mmol TBAB and 50 mL DMF to a three-necked flask and stir with an electric stirrer. Then add 0.15 mol potassium carbonate (200 mesh), 13.2 g (0.10 mol) dimethyl malonate, and 19.64 g (0.25 mol) 1-chloropropane. Stir the reaction at 75℃~130℃ for 12.0 h and recover excess 1-chloropropane. After the reaction is complete, cool to room temperature and filter. The filter cake is an inorganic alkali salt. Filtrate 1 is a pale yellow liquid. Add 60 mL methanol to the filter cake and reflux to slurry the inorganic salt (1~2 times). Filter to obtain filtrate 2. Use the filter cake to recover potassium chloride. Combine filtrate 2 and filtrate 1, and recover methanol by atmospheric distillation. Then recover DMF under reduced pressure at 80℃~90℃ (for recycling). The residue (pale yellow liquid dipropyl malonate) is used for subsequent hydrolysis of dipropyl malonate.
[0148] (2) Add 16 g of potassium hydroxide and the slurry obtained from the previous batch (3) to the pale yellow liquid of dipropylmalonic acid. Hydrolyze at 90℃ for 3 h and obtain solid by rotary evaporation. Dissolve the solid in 50 mL of water and adjust the pH to 1~1.5 with concentrated hydrochloric acid. Solid precipitates out and is filtered. The solid is crude dipropylmalonic acid.
[0149] (3) Add 10 ml of methanol and 16 ml of water to crude dipropylmalonic acid and beat at 60 ℃±5℃ for 0.5 h; cool to 20±5℃ to crystallize, filter and dry to obtain dipropylmalonic acid; the filtrate is a slurry, and the slurry is used for the hydrolysis reaction of the pale yellow liquid of dipropylmalonic acid in the next batch of (2) step.
[0150] (4) Dipropylmalonic acid was added to the reaction flask and decarboxylated at 160-180°C for 2 hours to obtain yellow liquid valproic acid. Vacuum distillation under reduced pressure yielded colorless, transparent valproic acid, with a total yield of 92.6%. Valproic acid was detected according to the method in Example 5, and the gas chromatographic results are shown in the appendix. Figure 10 and Table 14. 1 H NMR (400 MHz, DMSO-d6) δ : 0.86 (t, J = 7.2 Hz, 6H, CH3×2), 1.32–1.22 (m, 4H, CH2×2), 1.39–1.34 (m, 2H, CH2), 1.53–1.44 (m, 2H, CH2), 2.24–2.18 (m, 1H, CH), 11.99 (bs, 1H, COOH).
[0151] Table 14. GC Detection Results of Valproic Acid
[0152]
[0153] Figure 10 and Table 14 show the following results: Peak 1, 2-methylvaleric acid (RRT=0.80), 0.004%; Peak 2, isopropylvaleric acid (RRT=0.96), 0.032%; Peak 3, valproic acid (RRT=1.00), 99.916%; Peak 4, 2-propylhexanoic acid (RRT=1.09), 0.047%. The quality of the valproic acid product meets the requirements of the European Pharmacopoeia.
[0154] Example 12
[0155] Preparation of valproic acid (diethyl malonate method)
[0156] (1) Add 3.0 mmol TBAB and 50 mL DMF to a three-necked flask and stir with an electric stirrer. Then add 0.15 mol potassium carbonate (200 mesh), 16.0 g (0.10 mol) diethyl malonate, and dropwise add 19.64 g (0.25 mol) 1-chloropropane. React at 85℃±10℃ (75℃~95℃) for 4 h; at 105℃±10℃ (95℃~115℃) for 4 h; and at 115℃~130℃ for 4 h. Recover excess 1-chloropropane (to be reused next time). After the reaction is complete, cool to room temperature and filter. The filter cake is an inorganic alkali salt. Filtrate 1 is a pale yellow liquid. Add 60 mL ethanol to the filter cake and reflux to remove inorganic salt (1~2 times). Filter to obtain filtrate 2. Use the filter cake to recover potassium chloride. Combine filtrate 2 and filtrate 1, and distill at atmospheric pressure to recover ethanol. Then, heat at 80℃~90℃. DMF was recovered under reduced pressure at ℃; the residue (diethyl dipropylmalonate, a pale yellow liquid) was then subjected to subsequent hydrolysis of diethyl dipropylmalonate.
[0157] (2) Add 16g of potassium hydroxide and the slurry from the previous batch (3) to the pale yellow liquid of dipropylmalonic acid, heat to 90℃ for 3 h for hydrolysis, and obtain solid by rotary evaporation. Add 50 mL of water to dissolve the solid, adjust the pH to 1~1.5 with concentrated hydrochloric acid, and solid precipitates out. Filter the solid; the solid is crude dipropylmalonic acid.
[0158] (3) Add 16 ml of ethanol and 10 ml of water to crude dipropylmalonic acid and beat at 60℃ ±5℃ for 1 h; cool to 20 ± 5℃, filter and dry to obtain dipropylmalonic acid, and use the slurry (filtrate) for the hydrolysis reaction of the next batch of diethyl dipropylmalonic acid in step (2).
[0159] (4) Dipropylmalonic acid was added to the reaction flask and decarboxylated at 160-180°C for 2 hours to obtain yellow liquid valproic acid. Vacuum distillation under reduced pressure yielded colorless, transparent valproic acid, with a total yield of 92.4%. Valproic acid was detected according to the method in Example 5, and the gas chromatographic results are shown in the appendix. Figure 11 See Table 15. 1 H NMR (400 MHz, DMSO-d6) δ : 0.86 (t, J = 7.2 Hz, 6H, CH3×2), 1.32–1.22 (m, 4H, CH2×2), 1.39–1.34 (m, 2H, CH2), 1.53–1.44 (m, 2H, CH2), 2.24–2.18 (m, 1H, CH), 11.99 (bs, 1H, COOH).
[0160] Table 15. GC Detection Results of Valproic Acid
[0161]
[0162] The results in Figure 11 and Table 15 show that peak 1, 2-ethylpentanoic acid (RRT=0.90), 0.036%; and peak 2, valproic acid (RRT=1.00), 99.964%. The quality of the valproic acid product meets the requirements of the European Pharmacopoeia.
[0163] In this specification, the invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the invention. Therefore, this specification should be considered illustrative rather than restrictive.
Claims
1. A method for identifying and controlling valproic acid ester impurities, characterized in that... The operation process is as follows: (1) Selective column chromatography was used to separate valproic acid crude product prepared by the malonic acid diester method to obtain valproic acid ester impurities; (2) Select nuclear magnetic resonance spectroscopy to confirm the structure of the impurity; (3) Select a reference standard and use gas chromatography to locate the impurities; (4) Select products that have been pulped and controlled to have valproic acid ester impurities.
2. The method for identifying and controlling impurities as described in claim 1, characterized in that... The gas chromatography detection method described above involves using an Agilent 8890 gas chromatograph to detect valproic acid ester process impurities in crude valproic acid prepared by the malonic acid diester method. The detection conditions for the gas chromatography method are as follows: chromatographic column: DB-FFAP, 0.32 mm × 60 m, 0.5 μm; carrier gas: nitrogen. Detector: FID; Flow rate: 2 ml / min; Injection volume: 2 μl; Injector temperature: 220℃; Column temperature: 100℃; Temperature program: Start at 100℃, hold for 5 min, then increase to 140℃ at a rate of 4℃ / min, hold for 5 min, then increase to 200℃ at a rate of 4℃ / min, hold for 15 min; Run time: 50 min; Detector temperature: 220℃; Injection method: Direct injection; Weigh 10 mg of the test sample and transfer it to a 10 ml volumetric flask. Dilute to the mark with n-heptane and mix well to prepare the test sample stock solution. Accurately measure 1 ml of the test sample and place it in a 10 ml volumetric flask. Dilute to the mark with n-heptane and mix well to prepare the test sample solution. Accurately measure 10 mg of the reference standard and place it in a 100 ml volumetric flask. Dilute to the mark with n-heptane and mix well to prepare the reference solution. Take approximately 10 mg of 2-phenylethanol and place it in a 100 ml volumetric flask. Dissolve and dilute to the mark with n-heptane and mix well. Take 1 ml of the solution and place it in a 20 ml volumetric flask. Add 2 ml of the test sample stock solution and dilute to the mark with n-heptane and mix well to prepare the system suitability solution. Inject 2 μl each of the diluent n-heptane, the reference solution, and the test sample solution into the gas chromatograph and record the chromatogram. Based on the gas chromatographic detection results, determine the type and content of process impurities present in valproic acid using the reference sample. Blank solution: n-heptane; The test sample was selected from crude valproic acid prepared by the malondialdehyde method; the malondialdehyde method was selected from either the dimethyl malonate method or the diethyl malonate method. The reference standard for valproate impurities is selected from: methyl valproate, ethyl valproate, or propyl valproate; 3. The method for identifying and controlling impurities as described in claim 1, characterized in that... Crude valproic acid, prepared by the dimethyl malonate method, was dissolved in an aqueous sodium hydroxide solution and extracted three times with ethyl acetate. The combined extracts were separated by petroleum ether-ethyl acetate column chromatography to obtain methyl valproate and propyl valproate. The methyl valproate and propyl valproate separated by petroleum ether column chromatography were identified and located by nuclear magnetic resonance spectroscopy and gas chromatography. The relative elution times of methyl valproate and propyl valproate were RRT=0.25±0.01 and RRT=0.34±0.01, respectively.
4. The method for identifying and controlling impurities as described in claim 1, characterized in that... Crude valproic acid, prepared by the diethyl malonate method, was dissolved in an aqueous sodium hydroxide solution and extracted three times with ethyl acetate. The combined extracts were separated by petroleum ether-ethyl acetate column chromatography to obtain ethyl valproate and propyl valproate. Methyl valproate and propyl valproate, separated by petroleum ether column chromatography, were identified and located by nuclear magnetic resonance spectroscopy and gas chromatography. The relative elution times of ethyl valproate and propyl valproate were RRT=0.28±0.01 and RRT=0.34±0.01, respectively.
5. The method for identifying and controlling impurities as described in claim 1, characterized in that... In the process of preparing valproic acid, the content of impurities such as methyl valproate, ethyl valproate, and propyl valproate is controlled by pulping and other methods.
6. The method for identifying and controlling impurities as described in claim 1, characterized in that... The pulping and application process is as follows: (1) Dipropylmalonic acid was prepared by dipropylation of malonate diester to crude dipropylmalonic acid by hydrolysis: (2) Select a mixed solvent to pulp the crude dipropylmalonic acid obtained by hydrolysis, and then filter and dry it to obtain dipropylmalonic acid; (3) The slurry recovery kit containing dipropylmalonic acid monoester is used for the hydrolysis reaction of dipropylmalonic acid diester; (4) Valproic acid was prepared by heating and decarboxylating dipropylmalonic acid; the quality of valproic acid prepared by the malondiester method met the requirements of the pharmacopoeia.
7. The method for identifying and controlling impurities as described in claim 6, characterized in that... The mixed solvent is a mixture of alcohol and water; the alcohol solvent is selected from methanol, ethanol, C3-C6 straight-chain or C3-C6 branched monohydric alcohols, ethylene glycol, C3-C5 straight-chain diols or C4-C5 branched diols.
8. The method for identifying and controlling impurities as described in claim 6, characterized in that... The pulping temperature is selected from 30℃ to 80℃.
9. The method for identifying and controlling impurities as described in claim 6, characterized in that... The method for preparing valproic acid is as follows: (1) Add 3.0 mmol TBAB and 50 mL DMF to a three-necked flask and stir with an electric stirrer. Then add 0.15 mol 200-mesh potassium carbonate and 0.10 mol dimethyl malonate, and add 0.25 mol 1-chloropropane dropwise. Stir the reaction at 75℃~130℃ for 12.0 h and recover excess 1-chloropropane. After the reaction is complete, cool to room temperature and filter. The filter cake is an inorganic alkali salt. Filtrate 1 is a pale yellow liquid. Add 60 mL methanol to the filter cake and reflux to slurry the inorganic salt 1~2 times. Filter to obtain filtrate 2. Use the filter cake to recover potassium chloride. Combine filtrate 2 with filtrate 1 and distill at atmospheric pressure to recover methanol. Then recover DMF under reduced pressure at 80℃~90℃ and reuse. The residue - dimethyl dipropyl malonate, a pale yellow liquid, is used for subsequent hydrolysis of dimethyl dipropyl malonate. (2) Add 16 g of potassium hydroxide and the slurry obtained from step (3) of the previous batch to the pale yellow liquid of dipropylmalonic acid. Heat to 90℃ and hydrolyze for 3 h. Obtain solid by rotary evaporation. Add 50 mL of water to dissolve the solid. Adjust the pH to 1~1.5 with concentrated hydrochloric acid. Solid precipitates out. Filter. The solid is crude dipropylmalonic acid. (3) Add 10 ml of methanol and 16 ml of water to crude dipropylmalonic acid and beat at 60 ℃±5℃ for 0.5 h; cool to 20 ±5℃ to crystallize, filter and dry to obtain dipropylmalonic acid; the filtrate is a slurry, and the slurry is used for the hydrolysis reaction of the next batch of dipropylmalonic acid dimethyl ester pale yellow liquid in step (2); (4) Dipropylmalonic acid was added to the reaction flask and decarboxylated at 160~180℃ for 2h to obtain yellow liquid valproic acid. The colorless transparent valproic acid was obtained by vacuum distillation. The purity of valproic acid was 99.92% as determined by gas chromatography.
10. The method for identifying and controlling impurities as described in claim 6, characterized in that... The method for preparing valproic acid is as follows: (1) Add 3.0 mmol TBAB and 50 mL DMF to a three-necked flask and stir with an electric stirrer. Then add 0.15 mol 200-mesh potassium carbonate and 0.10 mol diethyl malonate. Add 0.25 mol 1-chloropropane dropwise. React at 85℃±10℃ for 4 h; at 105℃±10℃ for 4 h; at 115℃~130℃ for 4 h. Recover excess 1-chloropropane and reuse it directly next time. After the reaction is complete, cool to room temperature and filter. The filter cake is an inorganic alkali salt. Filtrate 1 is a pale yellow liquid. Add 60 mL ethanol to the filter cake and reflux to slurry the inorganic salt 1~2 times. Filter to obtain filtrate 2. Use the filter cake to recover potassium chloride. Combine filtrate 2 and filtrate 1. Distill at atmospheric pressure to recover ethanol. Then recover DMF under reduced pressure at 80℃~90℃. The residue - diethyl dipropyl malonate, a pale yellow liquid, is used for subsequent hydrolysis of diethyl dipropyl malonate. (2) Add 16g of potassium hydroxide and the slurry from step (3) of the previous batch to the pale yellow liquid of dipropylmalonic acid, heat to 90℃ for 3 h for hydrolysis, and obtain solid by rotary evaporation; add 50 mL of water to dissolve the solid, adjust the pH to 1~1.5 with concentrated hydrochloric acid, and solid precipitates out; filter; the solid is crude dipropylmalonic acid. (3) Add 16 ml of ethanol and 10 ml of water to crude dipropylmalonic acid and beat at 60℃ ±5℃ for 1 h; cool to 20 ±5℃, filter and dry to obtain dipropylmalonic acid, and use the slurry for the hydrolysis reaction of the next batch of diethyl dipropylmalonic acid in step (2). (4) Dipropylmalonic acid was added to the reaction flask and decarboxylated at 160~180℃ for 2h to obtain yellow liquid valproic acid. The colorless transparent valproic acid was obtained by vacuum distillation. The purity of valproic acid was 99.96% as determined by gas chromatography.