Method for detecting valproic acid key intermediate and impurities thereof

Abstract

The invention belongs to the technical field of medicine detection, and particularly relates to a high performance liquid chromatography detection method for dipropylmalonic acid and impurities thereof. The method comprises the following steps: preparing a to-be-detected sample into a test solution; the to-be-detected sample is dipropyl malonic acid prepared by adopting a diethyl malonate method and impurities of the dipropyl malonic acid; and detecting the test solution by adopting a high performance liquid chromatography method to obtain a detection result of dipropylmalonic acid and impurities thereof in the sample to be detected. According to the detection method provided by the invention, the detection of dipropylmalonic acid prepared by adopting a diethyl malonate method and impurities thereof is realized through high performance liquid chromatography (HPLC) for the first time, and the problems of quality control and process evaluation of the dipropylmalonic acid prepared by adopting the diethyl malonate method, which is an intermediate of a sodium valproate raw material medicine, are solved; therefore, detection and control of impurities (including 2-ethyl valeric acid) in the sodium valproate raw material medicine are realized.

Description

Technical Field

[0001] This invention belongs to the field of drug detection technology, specifically relating to a method for detecting dipropylmalonic acid and its impurities—propylmalonic acid, monoethyl propylmalonic acid, diethyl propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, monoethyl dipropylmalonic acid, monopropyl dipropylmalonic acid, or diethyl dipropylmalonic acid—prepared by the diethyl malonate method. Background Technology

[0002] Sichuan Keruide Pharmaceutical Co., Ltd. [A method for preparing dipropylmalonate, an intermediate of valproic acid, CN 202111473302.7, 2023.06.06] disclosed a method for preparing dipropylmalonate by reacting diethyl malonate and 1-bromopropane in an amide solvent under the action of a base and a phase transfer catalyst; controlling the impurity content of dipropylmalonate to ≤0.17% (GC); the purity of dipropylmalonate to ≥98.16% (GC); and the yield to ≥85%.

[0003]

[0004] Sichuan Keruide Pharmaceutical Co., Ltd. [A method for detecting impurities related to dipropylmalonic acid, ZL201911229436.7, 2022.10.28] used high performance liquid chromatography (HPLC) to detect propylmalonic acid and four monoester impurities in the dipropylmalonic acid reaction solution: monomethyl propylmalonic acid, monoethyl propylmalonic acid, monomethyl dipropylmalonic acid, and monoethyl dipropylmalonic acid. Their structural formulas are as follows:

[0005]

[0006] Appendix to its patent specification Figure 1 The results indicate the presence of some unknown impurities that have not been confirmed. It is unclear whether 2-ethyl-2-propylmalonic acid is present. 2-ethyl-2-propylmalonic acid is a key intermediate in the production of the valproic acid impurity 2-ethylpentanoic acid.

[0007] Chinese invention patent [A method for the preparation and hydrolysis of 2-alkyl-2-propylmalonic acid diester, CN117430509A, 2024.1.23] speculates that the product for preparing dipropylmalonic acid diethyl ester may contain propyl 2-dipropylmalonic acid ethyl ester, diethyl 2-ethyl-2-propylmalonic acid diethyl ester (II), diethyl 2-propyl-2-butylmalonic acid diethyl ester and diethyl 2-propyl-2-isopropylmalonic acid diethyl ester; wherein II is hydrolyzed in subsequent processes to produce 2-ethyl-2-propylmalonic acid (I) as a byproduct; the presence of impurity I will seriously affect the quality of dipropylmalonic acid; this impurity is transferred to the target product in subsequent reactions, forming impurity 2-ethylpentanoic acid (B) in the production of sodium valproate:

[0008]

[0009] Xi'an Yuanda Detian Pharmaceutical Co., Ltd. [A method for detecting sodium valproate and related substances in sodium valproate injection, ZL202011522863.7, 2023.9.22] describes that the impurities in sodium valproate products are valeric acid and 2-ethylvaleric acid (B). Beijing Yuekang Kechuang Pharmaceutical Technology Co., Ltd. [A method for preparing sodium valproate, CN202310028759.X, 2023.5.9] uses gas chromatography to detect impurities in sodium valproate products prepared by the diethyl malonate method. The main impurity detected in the optimal example 1 is 2-ethylvaleric acid (B).

[0010] Regarding the detection of 2-ethylpentanoic acid in sodium valproate raw material, there are currently no reports of highly accurate detection methods. Furthermore, there are no publicly available reports on the detection methods and results for 2-ethyl-2-propylmalonic acid, an impurity in dipropylmalonic acid prepared by the diethyl malonate method. Summary of the Invention

[0011] The purpose of this invention is to provide a high-performance liquid chromatography (HPLC) method for the detection of dipropylmalonic acid and its impurities. The detection method provided by this invention can detect dipropylmalonic acid and its impurities (including 2-ethyl-2-propylmalonic acid), thereby enabling the detection and control of impurities (including 2-ethylvalerate) in sodium valproate raw material.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] This invention provides a high-performance liquid chromatography (HPLC) method for the detection of dipropylmalonic acid and its impurities, comprising the following steps:

[0014] The sample to be tested is prepared into a test solution; the sample to be tested is dipropylmalonic acid and its impurities prepared by the diethyl malonate method; the impurities include 2-ethyl-2-propylmalonic acid, and also include one or more of propylmalonic acid, 2-propyl-2-butylmalonic acid, monoethyl propylmalonic acid, 2-ethyl-2-propylmalonic acid monoethyl ester, diethyl propylmalonic acid monoethyl ester, 2-propyl-2-butylmalonic acid monoethyl ester, diethyl propylmalonic acid monopropyl ester, diethyl propylmalonic acid monoethyl ester, diethyl propyl propylmalonic acid monoethyl ester, diethyl propyl propylmalonic acid monoethyl ester, diethyl propyl propyl propylmalonic acid monoethyl ester, and diethyl propyl propyl propyl 2-propyl-2-butylmalonic acid diethyl ester; its structural formula is as follows:

[0015]

[0016] The test solution was analyzed by high performance liquid chromatography to obtain the detection results of dipropylmalonic acid and its impurities in the sample.

[0017] The detection conditions of the high-performance liquid chromatography method include: a detection wavelength of 200–215 nm, a mobile phase comprising mobile phase A and mobile phase B, wherein mobile phase A is an aqueous solution of trifluoroacetic acid with a volume fraction of 0.1% of trifluoroacetic acid, mobile phase B is acetonitrile, the elution program is isocratic elution, and the volume ratio of mobile phase A to mobile phase B is 20–50:80–50.

[0018] Preferably, the flow rate of the mobile phase is 0.6 to 1.2 mL / min.

[0019] Preferably, the column temperature is 32℃.

[0020] Preferably, the chromatographic column used in the high performance liquid chromatography method is the Ultimate ODS-3, with the following specifications: column length of 250 mm, inner diameter of 4.6 mm, and packing particle size of 5 μm.

[0021] Preferably, the method for preparing the test solution includes: mixing the sample to be tested, acetonitrile, and water to obtain the test solution; the volume ratio of acetonitrile to water in the test solution is 1:1; and the concentration of the sample to be tested in the test solution is 3-4 mg / mL.

[0022] Preferably, the impurity is propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, propylmalonic acid monoethyl ester, dipropylmalonic acid monoethyl ester, and propylmalonic acid diethyl ester.

[0023] Preferably, the impurity is propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, propylmalonic acid monoethyl ester, dipropylmalonic acid monoethyl ester, propylmalonic acid diethyl ester, and dipropylmalonic acid diethyl ester.

[0024] Preferably, the impurity is propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, monoethyl dipropylmalonic acid, diethyl propyl propyl dipropylmalonic acid, and diethyl 2-propyl-2-butylmalonic acid.

[0025] Preferably, the detection of chromatographic data further includes: using an area normalization method to obtain the content of dipropylmalonic acid and its impurities in the sample to be tested based on the chromatographic data.

[0026] This invention provides a method for detecting dipropylmalonic acid and its impurities prepared by the diethyl malonate method. The detection method provided by this invention is the first to achieve the detection of dipropylmalonic acid and its impurities prepared by the diethyl malonate method using high performance liquid chromatography (HPLC). The impurities include one or more of the following: propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, propylmalonic acid monoethyl ester, 2-ethyl-2-propylmalonic acid monoethyl ester, dipropylmalonic acid monoethyl ester, 2-propyl-2-butylmalonic acid monoethyl ester, diethyl propyl malonate, dipropylmalonic acid monopropyl ester, 2-ethyl-2-propylmalonic acid diethyl ester, dipropylmalonic acid diethyl ester, dipropylmalonic acid ethyl ester propyl ester, and 2-propyl-2-butylmalonic acid diethyl ester. This method solves the quality control and process evaluation problems of dipropylmalonic acid prepared by the diethyl malonate method, an intermediate of sodium valproate.

[0027] For the first time, HPLC was used to detect and confirm the RRT values ​​of dipropylmalonic acid and its impurities prepared by the diethyl malonate method: propylmalonic acid RRT = 0.68–0.71, 2-ethyl-2-propylmalonic acid RRT = 0.87–0.88, dipropylmalonic acid RRT = 1.00, 2-propyl-2-butylmalonic acid RRT = 1.12–1.13, propylmalonic acid monoethyl ester RRT = 1.27, dipropylmalonic acid monoethyl ester RRT = 1.35–1.37, propylmalonic acid diethyl ester RRT = 1.45–1.46, and dipropylmalonic acid diethyl ester RRT = 1.68–1.73.

[0028] To locate the impurity 2-ethyl-2-propylmalonic acid in the preparation of dipropylmalonic acid via the diethyl malonate method, this invention also provides a method for preparing 2-ethyl-2-propylmalonic acid as shown in chemical formula I. The method is characterized by the propylation of diethyl ethyl malonate with 1-chloropropane to prepare diethyl 2-ethyl-2-propylmalonic acid as shown in formula II; formula II is then hydrolyzed to prepare 2-ethyl-2-propylmalonic acid as shown in formula I. The preparation reactions are as follows:

[0029]

[0030] The propylated PTC is selected from quaternary ammonium salts; the propylation reaction temperature is selected from 80℃±10℃, reaction time 2~4h; 100℃±10℃, reaction time 2~4h; 120±10℃, reaction time 2~4h; the potassium hydroxide concentration for hydrolysis is selected from 40%~50%; the hydrolysis temperature is selected from 70℃~100℃; the hydrolysis reaction time is selected from 2.0h~4.0h; the propylation feed amount is selected from a molar ratio of diethyl malonate to 1-chloropropane = 1:1.0~1.7; the propylation potassium carbonate amount is selected from a molar ratio of diethyl malonate to potassium carbonate = 1:0.80~1.70.

[0031] To locate the impurity dipropylmalonic acid monoethyl ester in the preparation of dipropylmalonic acid via the diethyl malonate method, this invention also provides a method for preparing dipropylmalonic acid monoethyl ester with chemical structural formula IV. The method is characterized by selecting diethyl malonate and reacting it with a hydrolysis reaction to prepare dipropylmalonic acid monoethyl ester with formula IV. The preparation reaction is as follows:

[0032]

[0033] The concentration of sodium hydroxide in the hydrolysis reaction is selected from 20% to 30%; the hydrolysis temperature is selected from 30℃ to 50℃; and the hydrolysis reaction time is selected from 8.0h to 12.0h.

[0034] To locate the impurity dipropylmalonate monopropyl ester in the preparation of dipropylmalonic acid via the diethyl malonate method, this invention also provides a method for preparing dipropylmalonate monopropyl ester with chemical structural formula V. The method is characterized by selecting dipropylmalonate monopropyl ester and preparing it via hydrolysis; the preparation reaction is as follows:

[0035]

[0036] Among them, the propylated PTC is selected from quaternary ammonium salts; the propylation reaction temperature is selected from 80℃±10℃, reaction time 2~4h; 100℃±10℃, reaction time 2~4h; 120±10℃, reaction time 2~4h; the sodium hydroxide concentration in the hydrolysis reaction is selected from 20%~30%; the hydrolysis temperature is selected from 30℃~50℃; and the hydrolysis reaction time is selected from 8.0h~12.0h.

[0037] Impurities in the dipropylmalonic acid product or reaction solution prepared by the diethyl malonate method are selected from one or more of propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, monoethyl propylmalonic acid, monoethyl 2-ethyl-2-propylmalonic acid, monoethyl dipropylmalonic acid, monoethyl 2-propyl-2-butylmalonic acid, diethyl propylmalonic acid, monopropyl dipropylmalonic acid, diethyl 2-ethyl-2-propylmalonic acid, diethyl dipropylmalonic acid, propyl ethyl dipropylmalonic acid, and diethyl 2-propyl-2-butylmalonic acid.

[0038] The impurities in the dipropylmalonic acid monoethyl ester product or reaction solution prepared by the diethyl malonate method are selected from one or more of propylmalonic acid, 2-ethyl-2-propylmalonic acid, dipropylmalonic acid, 2-propyl-2-butylmalonic acid, propylmalonic acid monoethyl ester, 2-ethyl-2-propylmalonic acid monoethyl ester, 2-propyl-2-butylmalonic acid monoethyl ester, diethyl propyl malonate, dipropylmalonic acid monopropyl ester, 2-ethyl-2-propylmalonic acid diethyl ester, dipropylmalonic acid diethyl ester, propyl dipropylmalonic acid ethyl ester, and 2-propyl-2-butylmalonic acid diethyl ester.

[0039] Impurities in the dipropylmalonic acid monoethyl ester product or reaction solution prepared by the diethyl malonate method are selected from one or more of propylmalonic acid monoethyl ester, 2-ethyl-2-propylmalonic acid monoethyl ester, 2-propyl-2-butylmalonic acid monoethyl ester, and dipropylmalonic acid monopropyl ester.

[0040] Impurities in the dipropylmalonic acid product or reaction solution prepared by the diethyl malonate method are selected from one or more of propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-isopropyl-2-propylmalonic acid, and 2-propyl-2-butylmalonic acid.

[0041] 2-Methyl-2-propylmalonic acid, monomethyl dipropylmalonic acid, and dimethyl dipropylmalonic acid were not detected in the dipropylmalonic acid product prepared by the diethyl malonate method.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] (1) 2-Ethyl-2-propylmalonic acid was prepared for the first time using diethyl ethylmalonic acid via a phase transfer catalyst. The preparation reaction is as follows:

[0044]

[0045] (2) For the first time, HPLC detection was used to identify new impurities in dipropylmalonic acid prepared by the diethyl malonate method, namely 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, monoethyl 2-ethyl-2-propylmalonic acid, monoethyl 2-propyl-2-butylmalonic acid, monopropyl dipropyl malonate, diethyl 2-ethyl-2-propylmalonic acid, propyl dipropyl ethyl malonate, and diethyl 2-propyl-2-butylmalonic acid.

[0046] (3) No 2-methyl-2-propylmalonic acid, monomethyl dipropylmalonic acid and dimethyl dipropylmalonic acid were detected in dipropylmalonic acid prepared by the diethyl malonate method.

[0047] This invention is the first to select HPLC detection and confirm the relative peak times of dipropylmalonic acid and its impurities prepared by the diethyl malonate method. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 Example 1: High-performance liquid chromatogram of dipropylmalonic acid product;

[0050] Figure 2 Example 2: High performance liquid chromatogram of diethyl dipropylmalonate reference standard;

[0051] Figure 3 Example 32: High-performance liquid chromatogram of 2-ethyl-2-propylmalonic acid reference standard;

[0052] Figure 4 Example 52: High-performance liquid chromatogram of propyl-2-butylmalonic acid reference standard;

[0053] Figure 5 Example 6: High-performance liquid chromatogram of diethyl propyl malonate reference standard;

[0054] Figure 6 Example 7: High-performance liquid chromatogram of propylmalonic acid reference standard;

[0055] Figure 7 Example 8: High-performance liquid chromatogram of dipropylmalonic acid monoethyl ester reference standard;

[0056] Figure 8 Example 2: High-performance liquid chromatogram of the diethyl dipropylmalonic acid hydrolysis reaction solution;

[0057] Figure 9 Example 2: High performance liquid chromatogram of the diethyl dipropylmalonic acid semi-hydrolysis reaction solution. Detailed Implementation

[0058] This invention provides a method for detecting dipropylmalonic acid and its impurities, utilizing high-performance liquid chromatography (HPLC), comprising the following steps:

[0059] Main experimental instruments:

[0060] HPLC: Tsushima High Performance Liquid Chromatography System

[0061] Infusion pump: LC-20AT; Detector: SPD-20A; Chromatographic analysis and processing system: LCsolution;

[0062] Mix the test sample, acetonitrile, and water to obtain the test sample solution;

[0063] The blank solution and the test solution were injected into a high-performance liquid chromatograph (HPLC) and the chromatograms were recorded. The HPLC column was Ultimate ODS-3 (4.6 mm × 250 mm, 5 μm), the detection wavelength was 200–215 nm, the flow rate was 0.6–1.2 mL / min, the mobile phase A was trifluoroacetic acid solution, and the mobile phase B was acetonitrile. The volume ratio of the mobile phase A to the mobile phase B was 20–50:80–50.

[0064] In this invention, a test sample, acetonitrile, and water are mixed (denoted as Mixture A) to obtain a test sample solution. In this invention, the test sample may include dipropylmalonic acid and its impurities; the impurities include one or more of the following: propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, monoethyl propylmalonic acid, 2-ethyl-2-propylmalonic acid, diethyl dipropylmalonic acid, 2-propyl-2-butylmalonic acid, diethyl propylmalonic acid, dipropylmalonic acid monopropyl, 2-ethyl-2-propylmalonic acid diethyl ester, diethyl dipropylmalonic acid, propyl dipropylmalonic acid, and diethyl 2-propyl-2-butylmalonic acid, with the following structural formula:

[0065]

[0066] In this invention, the concentration of the test sample in the test sample solution can be 3 to 4 mg / mL.

[0067] In this invention, the water can be purified water; the volume ratio of acetonitrile to water can be 1:1.

[0068] In this invention, the mixture A may include the following steps: placing the test sample in a volumetric flask, adding water and acetonitrile to dissolve and dilute to the mark, and shaking well.

[0069] After obtaining the test solution, the present invention injects the blank solution and the test solution into a high-performance liquid chromatograph and records the chromatogram. In the present invention, the injection volume of the test solution can be 20 μL.

[0070] In this invention, the column of the high performance liquid chromatograph can have a column length of 250 mm, an inner diameter of 4.6 mm, and a packing particle size of 5 μm.

[0071] In this invention, when the test solution is injected into the high-performance liquid chromatograph, the column temperature of the high-performance liquid chromatograph column can be 32°C.

[0072] In this invention, the volume concentration of the trifluoroacetic acid solution can be 0.1%; the solvent of the trifluoroacetic acid solution can be water; and the water can be purified water.

[0073] In this invention, the recording of the chromatogram may further include: calculating the content of the compound by area normalization.

[0074] One or more of the following are selected as impurity reference standards in the quality analysis and testing of sodium valproate or dipropylmalonic acid: propylmalonic acid, diethyl propylmalonic acid, 2-ethyl-2-propylmalonic acid (Ⅰ), 2-propyl-2-butylmalonic acid (Ⅲ), monoethyl dipropylmalonic acid (Ⅳ), monopropyl dipropylmalonic acid (Ⅴ), and diethyl dipropylmalonic acid.

[0075]

[0076] 2-Methyl-2-propylmalonic acid, monomethyl dipropylmalonic acid and dimethyl dipropylmalonic acid were also selected as impurity reference standards.

[0077] To further illustrate the present invention, the following detailed description of the invention's solutions, in conjunction with the accompanying drawings and embodiments, is provided, but should not be construed as limiting the scope of protection of the present invention.

[0078] This invention provides a high-performance liquid chromatography (HPLC) method for the detection of dipropylmalonic acid and its impurities, comprising the following steps:

[0079] The sample to be tested is prepared into a test solution; the sample to be tested is dipropylmalonic acid and its impurities prepared by the diethyl malonate method; the impurities include 2-ethyl-2-propylmalonic acid, and the impurities also include one or more of propylmalonic acid, 2-propyl-2-butylmalonic acid, propylmalonic acid monoethyl ester, 2-ethyl-2-propylmalonic acid monoethyl ester, dipropylmalonic acid monoethyl ester, 2-propyl-2-butylmalonic acid monoethyl ester, diethyl propyl malonate, dipropylmalonic acid monopropyl ester, 2-ethyl-2-propylmalonic acid diethyl ester, diethyl propyl dipropyl malonate, propyl dipropylmalonic acid, and 2-propyl-2-butylmalonic acid diethyl ester;

[0080] The test solution was analyzed by high performance liquid chromatography to obtain the detection results of dipropylmalonic acid and its impurities in the sample.

[0081] The detection conditions of the high-performance liquid chromatography method include: a detection wavelength of 200–215 nm, a mobile phase comprising mobile phase A and mobile phase B, wherein mobile phase A is an aqueous solution of trifluoroacetic acid with a volume fraction of 0.1% of trifluoroacetic acid, mobile phase B is acetonitrile, the elution program is isocratic elution, and the volume ratio of mobile phase A to mobile phase B is 20–50:80–50.

[0082] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0083] This invention prepares a test solution from the sample to be tested; the sample to be tested is dipropylmalonic acid and its impurities prepared by the diethyl malonate method; the impurities include 2-ethyl-2-propylmalonic acid, and also include one or more of propylmalonic acid, 2-propyl-2-butylmalonic acid, ethyl propylmalonic acid, 2-ethyl-2-propylmalonic acid, diethyl dipropylmalonic acid, 2-propyl-2-butylmalonic acid, diethyl propylmalonic acid, dipropylmalonic acid, dipropyl dipropylmalonic acid, diethyl 2-ethyl-2-propylmalonic acid, diethyl dipropylmalonic acid, propyl ethyl dipropyl dipropylmalonic acid, and diethyl 2-propyl-2-butylmalonic acid.

[0084] In this invention, the sample to be tested is the test specimen. The raw material for preparing the sample to be tested is diethyl malonate.

[0085] In this invention, the structural formulas of propylmalonic acid, propylmalonic acid monoethyl ester, 2-ethyl-2-propylmalonic acid (the compound shown in Formula I), 2-propyl-2-butylmalonic acid (the compound shown in Formula III), dipropylmalonic acid monoethyl ester (the compound shown in Formula IV), dipropylmalonic acid monopropyl ester (the compound shown in Formula V), and dipropylmalonic acid diethyl ester are as follows:

[0086]

[0087] To locate the impurity 2-ethyl-2-propylmalonic acid in dipropylmalonic acid and its impurities (samples to be tested) prepared by the diethyl malonate method, this invention also provides a method for preparing 2-ethyl-2-propylmalonic acid (the compound shown in Formula I), preferably comprising: reacting diethyl ethyl malonate with 1-chloropropane in a propylation reaction to prepare diethyl 2-ethyl-2-propylmalonic acid as shown in Formula II; and hydrolyzing the diethyl 2-ethyl-2-propylmalonic acid as shown in Formula II to prepare 2-ethyl-2-propylmalonic acid as shown in Formula I; the preparation reaction is as follows:

[0088]

[0089] This invention is the first to use diethyl ethyl malonate to prepare 2-ethyl-2-propylmalonic acid via a phase transfer catalyst.

[0090] In this invention, the preferred amount of raw materials used in the propylation reaction is: the molar ratio of diethyl ethyl malonate to 1-chloropropane is preferably 1:1.0-1.7. The preferred amount of potassium carbonate used in the propylation reaction is: the molar ratio of diethyl ethyl malonate to potassium carbonate is preferably 1:0.80-1.70. The phase transfer catalyst (PTC) for the propylation reaction is preferably selected from quaternary ammonium salts. The preferred temperature control sequence for the propylation reaction is as follows: reaction temperature preferably 70℃-90℃, reaction time preferably 2-4h; reaction temperature preferably 90℃-110℃, reaction time preferably 2-4h; reaction temperature preferably 110℃-130℃, reaction time preferably 2-4h. In this invention, the mass fraction of potassium hydroxide in the hydrolysis reaction system is preferably 40%-50%. The preferred temperature for the hydrolysis reaction is 70℃-100℃. The preferred time for the hydrolysis reaction is 2.0h-4.0h.

[0091] To locate the impurity dipropylmalonic acid monoethyl ester in dipropylmalonic acid and its impurities (samples to be tested) prepared by the diethyl malonate method, this invention also provides a method for preparing dipropylmalonic acid monoethyl ester (compound shown in Formula IV), preferably comprising: preparing dipropylmalonic acid monoethyl ester shown in Formula IV by hydrolysis of diethyl malonate; the preparation reaction is as follows:

[0092]

[0093] In this invention, the mass fraction of sodium hydroxide in the hydrolysis reaction system is preferably 20% to 30%. The temperature of the hydrolysis reaction is preferably 30°C to 50°C. The time of the hydrolysis reaction is preferably 8.0 h to 12.0 h.

[0094] To locate the impurity dipropylmalonic acid monopropyl ester in dipropylmalonic acid and its impurities (samples to be tested) prepared by the diethyl malonate method, this invention also provides a method for preparing dipropylmalonic acid monopropyl ester (the compound shown in Formula V), preferably comprising: hydrolyzing dipropylmalonic acid to prepare dipropylmalonic acid monopropyl ester shown in Formula V; the preparation reaction is as follows:

[0095]

[0096] In this invention, when preparing dipropylmalonic acid monopropyl ester of formula V: the phase transfer catalyst (PTC) for the propylation reaction in the above reaction is preferably selected from quaternary ammonium salts. The preferred temperature control sequence for the propylation reaction is as follows: reaction temperature preferably 70℃~90℃, reaction time preferably 2~4h; reaction temperature preferably 90℃~110℃, reaction time preferably 2~4h; reaction temperature preferably 110℃~130℃, reaction time preferably 2~4h. In this invention, the mass fraction of potassium hydroxide in the hydrolysis reaction system is preferably 40%~50%. The temperature of the hydrolysis reaction is preferably 70℃~100℃. The time of the hydrolysis reaction is preferably 2.0h~4.0h. In this invention, the mass fraction of sodium hydroxide in the hydrolysis reaction system is preferably 20%~30%. The temperature of the hydrolysis reaction is preferably 30℃~50℃. The time of the hydrolysis reaction is preferably 8.0h~12.0h.

[0097] In this invention, the preparation method of the test solution preferably includes: mixing the sample to be tested, acetonitrile, and water to obtain the test solution. The water in the test solution is preferably purified water, and the volume ratio of acetonitrile to water in the test solution is preferably 1:1. The concentration of the sample to be tested in the test solution is preferably 3-4 mg / mL.

[0098] After obtaining the test solution, the present invention uses high performance liquid chromatography to detect the test solution and obtain the detection results of dipropylmalonic acid and its impurities in the sample to be tested.

[0099] In this invention, the detection conditions of the high-performance liquid chromatography (HPLC) method include: a detection wavelength of 200–215 nm. The mobile phase includes mobile phase A and mobile phase B. Mobile phase A is an aqueous solution of trifluoroacetic acid. The volume fraction of trifluoroacetic acid in the aqueous solution is 0.1%. The water in the aqueous solution of trifluoroacetic acid is preferably purified water. Mobile phase B is acetonitrile. The elution program is isocratic elution. The volume ratio of mobile phase A to mobile phase B is 20–50:80–50, preferably 25–45:75–55, more preferably 30–40:70–60, and in the examples, it can be 35:65. The flow rate of the mobile phase is preferably 0.6–1.2 mL / min, more preferably 0.8–1.1 mL / min, and in the examples, it can be 1.0 mL / min. The column temperature of the chromatographic column used in the HPLC method is preferably 32 °C. In the embodiments of this invention, the injection volume of the test solution can be 20 μL.

[0100] In this invention, the chromatographic column used in the high-performance liquid chromatography (HPLC) method is an Ultimate ODS-3 column with the following specifications: column length 250 mm, inner diameter 4.6 mm, and packing particle size 5 μm. The chromatograph used in the HPLC method is preferably a Tsushima HPLC system, with an LC-20AT pump, an SPD-20A detector, and an LCsolution chromatographic analysis and processing system.

[0101] In this invention, the detection further includes: detecting the blank solution using high-performance liquid chromatography to obtain chromatographic data of the blank solution.

[0102] In this invention, the detection further includes: detecting the reference solution using high performance liquid chromatography to obtain chromatographic data of the reference solution.

[0103] In this invention, the reference standard preferably includes one or more of 2-ethyl-2-propylmalonic acid (the compound shown in Formula I), 2-propyl-2-butylmalonic acid (the compound shown in Formula III), dipropylmalonic acid monoethyl ester (the compound shown in Formula IV), dipropylmalonic acid monopropyl ester (the compound shown in Formula V), and dipropylmalonic acid diethyl ester.

[0104] In this invention, the reference standard is preferably 2-methyl-2-propylmalonic acid, monomethyl dipropylmalonic acid, and dimethyl dipropylmalonic acid.

[0105] In this invention, the detection of chromatographic data is preferred to further include: using an area normalization method to obtain the content of dipropylmalonic acid and its impurities in the sample to be tested based on the chromatographic data.

[0106] As one or more embodiments of the present invention, the detection result is: the impurity is propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, propylmalonic acid monoethyl ester, dipropylmalonic acid monoethyl ester and propylmalonic acid diethyl ester.

[0107] As one or more embodiments of the present invention, the detection result is: the impurity is propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, propylmalonic acid monoethyl ester, dipropylmalonic acid monoethyl ester, propylmalonic acid diethyl ester and dipropylmalonic acid diethyl ester.

[0108] As one or more embodiments of the present invention, the detection result is: the impurity is propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, dipropylmalonic acid monoethyl ester, diethyl propylmalonic acid, propyl ethyl dipropylmalonic acid and diethyl 2-propyl-2-butylmalonic acid.

[0109] As one or more embodiments of the present invention, the detection result is: 2-methyl-2-propylmalonic acid, dipropylmalonic acid monomethyl ester and dipropylmalonic acid dimethyl ester were not detected in the sample to be tested.

[0110] The detection method provided by this invention uses high-performance liquid chromatography (HPLC) to detect dipropylmalonic acid and its impurities prepared by the diethyl malonate method (e.g., Figure 1 The impurities include one or more of these. This invention solves the problems of quality control of dipropylmalonic acid, an intermediate in the preparation of sodium valproate via the diethyl malonate method, and quality evaluation of sodium valproate.

[0111] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0112] The following examples use high-performance liquid chromatography (HPLC) for detection, and the experimental instruments used include:

[0113] Main experimental instruments:

[0114] HPLC: Tsushima high-performance liquid chromatograph;

[0115] Infusion pump: LC-20AT; Detector: SPD-20A; Chromatographic analysis and processing system: LCsolution;

[0116] Mix the test sample, acetonitrile, and water to obtain the test sample solution;

[0117] The blank solution and the test solution were injected into a high-performance liquid chromatograph (HPLC) and the chromatograms were recorded. The HPLC column was Ultimate ODS-3 (4.6 mm × 250 mm, 5 μm), the detection wavelength was 200–215 nm, the flow rate was 0.6–1.2 mL / min, the mobile phase A was trifluoroacetic acid solution, and the mobile phase B was acetonitrile. The volume ratio of the mobile phase A to the mobile phase B was 20–50:80–50.

[0118] Example 1

[0119] Preparation of dipropylmalonic acid

[0120] Dipropylmalonic acid was prepared by means of the method described in Example 1 of the Chinese Invention Patent [A method and application for preparing dipropylmalonic acid using chloropropane as an alkylating agent, CN116768697A, published on 2023.9.19], with a yield of 90.4% and an HPLC yield of 99.288%. The high-performance liquid chromatography (HPLC) of dipropylmalonic acid in this example is as follows: Figure 1 As shown.

[0121] Example 2

[0122] Preparation of diethyl dipropylmalonate

[0123] Diethyl malonate was prepared according to the method in Example 2 of the Chinese Invention Patent [A method and application for preparing dipropylmalonic acid using chloropropane as an alkylating agent, CN116768697A, published on 2023.9.19]. The high-performance liquid chromatography (HPLC) result of diethyl malonate in this example is as follows: Figure 2 As shown.

[0124] Following the method in Example 1, the high-performance liquid chromatography (HPLC) of the dipropylmalonic acid diethyl ester hydrolysis reaction solution (dipropylmalonic acid) is as follows: Figure 8 As shown.

[0125] Following the method in Example 8, the semi-hydrolyzed reaction solution of dipropylmalonate (monoethyl dipropylmalonate) was subjected to high-performance liquid chromatography as follows: Figure 9 As shown.

[0126] Example 3

[0127] Preparation of 2-ethyl-2-propylmalonic acid

[0128]

[0129] (1) Add 0.2 mol diethyl malonate, 0.01 mol tetraethylammonium bromide, 0.03 mol KBr, 0.3 mol K2CO3, 120 mL DMF, and 0.32 mol 1-chloropropane sequentially. React at 70℃~90℃ for 2~4 h; at 90℃~110℃ for 2~4 h; and at 110℃~130℃ for 2~4 h. After the reaction is complete, cool to room temperature and filter. Filter cake 1 is an inorganic base salt (KCl and KHCO3). Filtrate 1 is a pale yellow liquid. Add 60 mL of ethanol to the filter cake and reflux to remove inorganic salts. Filter the mixture to obtain filtrate 2. Filter cake 2 (inorganic salts) is used to recover potassium chloride. Filtrate 2 and filtrate 1 are combined and distilled at atmospheric pressure to recover ethanol. Then, DMF is recovered under reduced pressure at 80℃~90℃ (for recycling). The residue is then subjected to hydrolysis of diethyl 2-ethyl-2-propylmalonate.

[0130] (2) In the pale yellow liquid of diethyl 2-ethyl-2-propylmalonic acid, potassium hydroxide aqueous solution (KOH 32g, H2O 32mL) and 20mL ethanol were added, and the mixture was heated to 90℃ for 3h to hydrolyze. The solid was obtained by rotary evaporation. The solid was dissolved in 50mL of water, and the pH was adjusted to 1-1.5 with concentrated hydrochloric acid. A solid precipitated out. The solid was filtered to obtain filtrate 3 and filter cake 3. Filtrate 3 and filter cake 2 (inorganic salt) were concentrated, crystallized and dried to recover KCl. Filter cake 3 was recrystallized in methanol aqueous solution to obtain 28.3g of white solid 2-ethyl-2-propylmalonic acid, mp. 117-118℃, yield 81.4%, HPLC purity 98.86%. The high performance liquid chromatography of 2-ethyl-2-propylmalonic acid in this example is as follows: Figure 3 As shown.

[0131] 2-Ethyl-2-propylmalonic acid: 1 H NMR (400MHz, DMSO-d6) δ: 12.65 (bs, 2H, 2×COOH), 1.77 (q, J=7.6Hz, 2H, CH2), 1.72~1.67 (m , 2H, CH2), 1.16~1.08 (m, 2H, CH2), 0.89 (t, J=7.2Hz, 3H, CH3), 0.76 (t, J=7.6Hz, 3H, CH3).

[0132] Example 4

[0133] Preparation of 2-ethylpentanoic acid (B) (decarboxylation of 2-ethyl-2-propylmalonic acid)

[0134]

[0135] 20.0 g of 2-ethyl-2-propylmalonic acid was placed in a single-necked round-bottom flask and decarboxylated at 180–190 °C for 2 h to obtain a yellow liquid. The liquid was then distilled, and 11.5 g of the fraction distilled at 102 °C / 16 mmHg was collected, yielding 77.1% and a GC purity of 98.50%.

[0136] 2-Ethylpentanoic acid: 1 H NMR (400MHz, DMSO-d6) δ: 12.02 (s, 1H, COOH), 2.15~2.12 (m, 1H, CH), 1.53~1.19 (m, 6H, CH2CH2+CH2), 0.85 (t, J=7.6Hz, 3H, CH3), 0.83 (t, J=7.6Hz, 3H, CH3); 13 C NMR (101MHz, DMSO-d6) δ: 176.94, 46.31, 33.76, 24.93, 20.15, 13.94, 11.72.

[0137] Example 5

[0138] Preparation of 2-propyl-2-butylmalonic acid

[0139]

[0140] 2-Propyl-2-butylmalonic acid was prepared according to the method in Example 1 of the Chinese Invention Patent [A Method for Preparing 2-Propylhexanoic Acid, CN116730832A], with an HPLC resolution of 93.277%. The high-performance liquid chromatography (HPLC) of 2-propyl-2-butylmalonic acid in this example is as follows: Figure 4 As shown.

[0141] 1 H NMR (DMSO-d6, 400MHz) δ: 0.88 (t, J=6.8Hz, 3H, CH3), 0.89 (t, J=6.8Hz, 3H, CH3), 1.08~1. 17(m, 4H, CH2CH2), 1.26~1.32(m, 2H, CH2), 1.69~1.75(m, 4H, CH2×2), 12.61(s, 2H, CO2H).

[0142] Example 6

[0143] Preparation of diethyl propyl malonate

[0144] Diethyl propylmalonic acid was prepared according to the method in Example 1 of the specification of Chinese Invention Patent [A method for preparing propylmalonic acid and its homologues, CN 116023232A]. The high-performance liquid chromatography (HPLC) of diethyl propylmalonic acid in this example is as follows: Figure 5 As shown.

[0145] Example 7

[0146] Preparation of propylmalonic acid

[0147] Propylmalonic acid was prepared according to the method in Example 1 of the specification of Chinese Invention Patent [A method for preparing propylmalonic acid and its homologues, CN 116023232A]. The high-performance liquid chromatography (HPLC) of propylmalonic acid in this example is as follows: Figure 6 As shown.

[0148] Example 8

[0149] Preparation of dipropylmalonic acid monoethyl ester

[0150]

[0151] Under ice bath conditions, 20 g of 25 wt% sodium hydroxide solution was added dropwise to 15 mL of ethanol solution containing 20 g (0.08 mol) of dipropylmalonide. After the addition was complete, the mixture was stirred at 45 °C for 12 h. The ethanol was removed by rotary evaporation, and 10 wt% sodium hydroxide aqueous solution was added to adjust the pH to 12. Ethyl acetate was added for extraction (30 mL × 3 times), and the lower aqueous layer was collected. The organic layer was then back-extracted with 10 wt% sodium hydroxide aqueous solution, and the aqueous layers were combined. The aqueous layer was acidified with hydrochloric acid to a pH of 1–2, and extracted with ethyl acetate (30 mL × 3 times). The organic layers were combined, dried with anhydrous sodium sulfate, filtered, and the ethyl acetate was removed by rotary evaporation to obtain 8.45 g of dipropylmalonide monoethyl ester, mp. 59–60 °C, yield 48.8%, HPLC 94.84%. The high-performance liquid chromatography of dipropylmalonide monoethyl ester in this example is as follows: Figure 7 As shown.

[0152] Dipropylmalonyl monoethyl ester: 1 H NMR (400MHz, DMSO-d6) δ: 0.86 (t, J=7.2Hz, 6H, CH3×2), 1.06-1.13 (m, 4H, CH2×2), 1.14 (t, J=7.2Hz, 3H, CH3), 1.69-1.74 (m, 4H, CH2×2), 4.06 (q, J=7.2Hz, 2H, OCH2); 13 C NMR (101MHz, DMSO-d6) δ: 13.8, 14.2, 16.9, 33.5, 56.7, 60.3, 171.4 and 172.6.

[0153] Example 9

[0154] Preparation of dipropylmalonic acid monopropyl ester

[0155]

[0156] Dipropyl malonate was prepared according to the method described in Chinese Invention Patent [A method and application for preparing dipropylmalonic acid using chloropropane as an alkylating agent, CN116768697A, published on 2023.9.19]. The latter was then hydrolyzed according to the method in Example 8 to obtain dipropylmalonic acid monopropyl ester.

[0157] The diethyl propyl malonate obtained in Example 6 was hydrolyzed according to the method in Example 8 to prepare monoethyl propyl malonate.

[0158] Example 10 HPLC Detection

[0159] (1) Solution preparation: Trifluoroacetic acid solution: Dissolve 1 mL of trifluoroacetic acid in 1000 mL of purified water and mix well to obtain a trifluoroacetic acid solution with a volume concentration of 0.1%; Diluent: a mixture of purified water and acetonitrile (volume ratio 50:50); Test solution: Weigh 30-40 mg of test sample, place it in a 10 mL volumetric flask, add diluent to dissolve and dilute to the mark, shake well to obtain the test solution.

[0160] (2) The liquid chromatography conditions are as follows: Column: Ultimate ODS-3 (4.6 mm × 250 mm, 5 μm); Detection wavelength: 200~215 nm; Mobile phase A: 0.1% trifluoroacetic acid solution, 35%; Mobile phase B: acetonitrile, 65%; Flow rate: 1.0 mL / min; Column temperature: 32℃.

[0161] (3) Perform the test according to the high performance liquid chromatography (HPLC) conditions in step (2). Inject blank solution and test solution separately, and record the chromatograms. The HPLC chromatograms of the test solutions prepared in Examples 1-3 and Examples 5-7 as test samples are shown below. Figures 1-6 As shown, the content of the compound is calculated using the area normalization method.

[0162] A sample of dipropylmalonic acid prepared in Example 1 was analyzed by HPLC, and the results are as follows: Figure 1 As shown in Table 1.

[0163] Table 1. HPLC detection data from Example 1

[0164]

[0165] according to Figure 1As shown in Table 1, peak 1 (retention time 13.873 min, RRT = 0.71): propylmalonic acid, 0.086%; peak 2 (retention time 17.197 min, RRT = 0.88): 2-ethyl-2-propylmalonic acid, 0.022%; peak 4 (retention time 19.617 min, RRT = 1.00): dipropylmalonic acid, 99.288%; peak 5 (retention time 22.237 min, RRT = 1.13): 2-propyl-2-butylmalonic acid, 0. 0.036%; Peak 6 (retention time 25.043 min, RRT = 1.28): Diethyl propylmalonate, 0.056%; Peak 7 (retention time 26.858 min, RRT = 1.37): Diethyl dipropylmalonate, 0.046%; Peak 8 (retention time 28.566 min, RRT = 1.46): Diethyl propylmalonate, 0.041%; Peak 9 (retention time 33.984 min, RRT = 1.73): Diethyl dipropylmalonate, 0.192%.

[0166] The results showed that 2-methyl-2-propylmalonic acid, monomethyl dipropylmalonic acid, and dimethyl dipropylmalonic acid were not detected in dipropylmalonic acid prepared by the diethyl malonate method.

[0167] The diethyl dipropylmalonate prepared in Example 2 was sampled and analyzed by HPLC. The results are as follows: Figure 2 As shown in Table 2.

[0168] Table 2 HPLC detection data from Example 2

[0169]

[0170] according to Figure 2 As shown in Table 2, peak 2 (retention time 28.227 min, RRT = 1.45): diethyl propyl malonate, 0.117%; peak 4 (retention time 32.844 min, RRT = 1.72): diethyl dipropyl malonate, 99.545%.

[0171] The 2-ethyl-2-propylmalonic acid prepared in Example 3 was sampled and analyzed by HPLC. The results are as follows: Figure 3 As shown in Table 3.

[0172] Table 3. HPLC detection data from Example 3

[0173]

[0174] according to Figure 3As shown in Table 3, peak 3 (retention time 17.031 min): 2-ethyl-2-propylmalonic acid, 98.857%; peak 6 (retention time 19.536 min): dipropylmalonic acid, 0.051%.

[0175] The 2-propyl-2-butylmalonic acid prepared in Example 5 was sampled and analyzed by HPLC. The results are as follows: Figure 4 As shown in Table 4.

[0176] Table 4. HPLC detection data from Example 5

[0177]

[0178] according to Figure 4 As shown in Table 4, peak 4 (retention time 19.280 min, RRT = 1.00): dipropylmalonic acid, 2.621%; peak 5 (retention time 21.506 min, RRT = 1.12): 2-propyl-2-butylmalonic acid, 93.462%; peak 8 (retention time 28.165 min, RRT = 1.46): diethyl propylmalonic acid, 0.176%.

[0179] The diethyl propyl malonate prepared in Example 6 was sampled and analyzed by HPLC. The results are as follows: Figure 5 As shown in Table 5.

[0180] Table 5 HPLC detection data from Example 6

[0181]

[0182] Peak 3 (retention time 24.217 min, RRT = 1.27): ethyl propyl malonate, 0.865%; Peak 4 (retention time 25.906 min, RRT = 1.36): ethyl dipropyl malonate, 0.019%; Peak 7 (retention time 27.706 min, RRT = 1.45): diethyl propyl malonate, 98.902%; Peak 9 (retention time 33.191 min, RRT = 1.73): diethyl dipropyl malonate, 0.019%.

[0183] The propylmalonic acid prepared in Example 7 was sampled and analyzed by HPLC. The results are as follows: Figure 6 As shown in Table 6.

[0184] Table 6. HPLC Detection Data from Example 7

[0185]

[0186] according to Figure 6As shown in Table 6, peak 6 (retention time 12.823 min, RRT = 0.68): propylmalonic acid, 98.710%; peak 11 (retention time 19.236 min, RRT = 1.00): dipropylmalonic acid, 0.417%; peak 12 (retention time 26.321 min, RRT = 1.37): monoethyl dipropylmalonic acid, 0.016%; peak 13 (retention time 33.352 min, RRT = 1.73): diethyl dipropylmalonic acid, 0.006%.

[0187] The dipropylmalonic acid monoethyl ester prepared in Example 8 was sampled and analyzed by HPLC. The results are as follows: Figure 7 As shown in Table 7.

[0188] Table 7 HPLC Detection Data of Example 8

[0189]

[0190] according to Figure 7 As shown in Table 7, peak 1 (retention time 13.893 min, RRT = 0.71): propylmalonic acid, 0.075%; peak 2 (retention time 19.532 min, RRT = 1.00): dipropylmalonic acid, 4.937%; peak 4 (retention time 26.402 min, RRT = 1.35): monoethyl dipropylmalonic acid, 94.839%; peak 6 (retention time 28.238 min, RRT = 1.45): diethyl dipropylmalonic acid, 0.028%; peak 7 (retention time 32.888 min, RRT = 1.68): diethyl dipropylmalonic acid, 0.024%.

[0191] The reaction solution (dipropylmalonic acid) from the hydrolysis of diethyl dipropylmalonic acid prepared in Example 2 was sampled and analyzed by HPLC. The results are as follows: Figure 8 As shown in Table 8.

[0192] Table 8. HPLC detection data of dipropylmalonic acid diethyl ester hydrolysis reaction solution (dipropylmalonic acid) in Example 2.

[0193]

[0194]

[0195] according to Figure 8As shown in Table 8, peak 1 (retention time 13.885 min, RRT = 0.71): propylmalonic acid, 0.116%; peak 4 (retention time 17.125 min, RRT = 0.87): 2-ethyl-2-propylmalonic acid, 0.042%; peak 6 (retention time 19.573 min, RRT = 1.00): dipropylmalonic acid, 92.019%; peak 8 (retention time 22.126 min, RRT = 1.13): 2-propyl-2-butylmalonic acid, 0.05%. 2%; Peak 12 (retention time 24.811 min, RRT = 1.27): Diethyl propyl malonate, 0.660%; Peak 14 (retention time 26.572 min, RRT = 1.36): Diethyl dipropyl malonate, 6.328%; Peak 15 (retention time 28.227 min, RRT = 1.44): Diethyl propyl malonate, 0.271%; Peak 16 (retention time 33.485 min, RRT = 1.71): Diethyl dipropyl malonate, 0.029%.

[0196] The dipropylmalonide diethyl malonate hemihydrolysis reaction solution (dipropylmalonide monoethyl ester) prepared in Example 2 was sampled and analyzed by HPLC. The results are as follows: Figure 9 As shown in Table 9.

[0197] Table 9. HPLC detection data of the dipropylmalonate diethyl hemihydrolysis reaction solution (dipropylmalonate monoethyl ester) in Example 2.

[0198]

[0199] according to Figure 9 As shown in Table 9, peak 1 (retention time 13.799 min, RRT = 0.71): 2-propylmalonic acid, 2.342%; peak 3 (retention time 17.194 min, RRT = 0.88): 2-ethyl-2-propylmalonic acid, 0.019%; peak 4 (retention time 19.556 min, RRT = 1.00): dipropylmalonic acid, 5.929%; peak 7 (retention time 26.432 min, RRT = 1.35): monoethyl dipropylmalonic acid, 89.599%; peak 8 (retention time 28.202 min, RRT = 1.44): diethyl propylmalonic acid, 0.034%; peak 12 (retention time 33.464 min, RRT = 1.71): diethyl dipropylmalonic acid, 0.041%.

[0200] The peak times and relative time (RRT) data of dipropylmalonic acid and its impurities from the HPLC detection and analysis reports of Examples 1-3 and Examples 5-8 are summarized in Table 10:

[0201] Table 10 Key data from HPLC detection in Examples 1-3 and Examples 5-8

[0202]

[0203] ND: Not detected.

[0204] The HPLC data of the reaction solutions of Examples 1 and 8 with diethyl dipropylmalonate hydrolyzed and semi-hydrolyzed are summarized in Table 11.

[0205] Table 11 Comparison of HPLC detection data

[0206]

[0207] ND: Not detected.

[0208] As can be seen from Examples 1 to 8 and Tables 10 and 11, the impurities in the dipropylmalonic acid product or reaction solution prepared by the diethyl malonate method are selected from one or more of propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, monoethyl propylmalonic acid, 2-ethyl-2-propylmalonic acid monoethyl ester, diethylmalonic acid monoethyl ester, 2-propyl-2-butylmalonic acid monoethyl ester, diethyl propylmalonic acid, dipropylmalonic acid monopropyl ester, diethyl-2-propylmalonic acid diethyl ester, diethylmalonic acid diethyl ester, propyl propylmalonic acid diethyl ester, and 2-propyl-2-butylmalonic acid diethyl ester, and their chemical structures are as follows:

[0209]

[0210] The impurities in the dipropylmalonic acid monoethyl ester product or reaction solution prepared by the diethyl malonate method are selected from one or more of propylmalonic acid, 2-ethyl-2-propylmalonic acid, dipropylmalonic acid, 2-propyl-2-butylmalonic acid, propylmalonic acid monoethyl ester, 2-ethyl-2-propylmalonic acid monoethyl ester, 2-propyl-2-butylmalonic acid monoethyl ester, diethyl propyl malonate, dipropylmalonic acid monopropyl ester, diethyl-2-propylmalonic acid diethyl ester, dipropylmalonic acid diethyl ester, and 2-propyl-2-butylmalonic acid diethyl ester, with the following chemical structures:

[0211]

[0212] The results showed that 2-methyl-2-propylmalonic acid, monomethyl dipropylmalonic acid, and dimethyl dipropylmalonic acid were not detected in the dipropylmalonic acid product prepared by the diethyl malonate method.

[0213] HPLC analysis confirmed the relative elution times of dipropylmalonic acid and its impurities prepared by the diethyl malonate method: propylmalonic acid RRT = 0.68–0.71, 2-ethyl-2-propylmalonic acid RRT = 0.87–0.88, dipropylmalonic acid RRT = 1.00, 2-propyl-2-butylmalonic acid RRT = 1.12–1.13, propylmalonic acid monoethyl ester RRT = 1.27, dipropylmalonic acid monoethyl ester RRT = 1.35–1.37, propylmalonic acid diethyl ester RRT = 1.45–1.46, and dipropylmalonic acid diethyl ester RRT = 1.68–1.73.

[0214] As can be seen from the above embodiments, the detection method provided by the present invention is the first to achieve the detection of dipropylmalonic acid and its impurities prepared by the diethyl malonate method through high performance liquid chromatography, thus solving the quality control and process evaluation problems of dipropylmalonic acid, an intermediate of sodium valproate.

[0215] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A high-performance liquid chromatography (HPLC) method for the detection of dipropylmalonic acid and its impurities, characterized in that, Includes the following steps: The sample to be tested is prepared into a test solution; the sample to be tested is dipropylmalonic acid and its impurities prepared by the diethyl malonate method; the impurities include 2-ethyl-2-propylmalonic acid, and the impurities also include one or more of propylmalonic acid, 2-propyl-2-butylmalonic acid, propylmalonic acid monoethyl ester, 2-ethyl-2-propylmalonic acid monoethyl ester, dipropylmalonic acid monoethyl ester, 2-propyl-2-butylmalonic acid monoethyl ester, diethyl propyl malonate, dipropylmalonic acid monopropyl ester, 2-ethyl-2-propylmalonic acid diethyl ester, diethyl propyl dipropyl malonate, and 2-propyl-2-butylmalonic acid diethyl ester; The test solution was analyzed by high performance liquid chromatography to obtain the detection results of dipropylmalonic acid and its impurities in the sample. The detection conditions of the high performance liquid chromatography method include: a detection wavelength of 200-215 nm, a mobile phase comprising mobile phase A and mobile phase B, wherein mobile phase A is an aqueous solution of trifluoroacetic acid with a volume fraction of 0.1% of trifluoroacetic acid, mobile phase B is acetonitrile, the elution program is isocratic elution, and the volume ratio of mobile phase A to mobile phase B is 20-50:80-50. The flow rate of the mobile phase is 0.6–1.2 mL / min; when the test solution is injected into the high-performance liquid chromatograph, the column temperature of the high-performance liquid chromatograph column is 32 °C. The high-performance liquid chromatography method uses an Ultimate ODS-3 column with the following specifications: column length 250 mm, inner diameter 4.6 mm, and packing particle size 5 μm. The preparation method of the test solution includes: mixing the sample to be tested, acetonitrile and water to obtain the test solution; the volume ratio of acetonitrile and water in the test solution is 1:1; the concentration of the sample to be tested in the test solution is 3-4 mg / mL.

2. The detection method according to claim 1, characterized in that, The impurities include one or more of the following: propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, ethyl propylmalonic acid, 2-ethyl-2-propylmalonic acid, diethyl propylmalonic acid, 2-propyl-2-butylmalonic acid, diethyl propylmalonic acid, dipropylmalonic acid, dipropyl propylmalonic acid, diethyl 2-ethyl-2-propylmalonic acid, diethyl propyl dipropylmalonic acid, propyl dipropylmalonic acid, and diethyl 2-propyl-2-butylmalonic acid, with the following structural formulas in sequence:

3. The detection method according to claim 1, characterized in that, Dipropylmalonic acid and its impurities prepared by the diethyl malonate method, wherein the impurities do not include 2-methyl-2-propylmalonic acid, monomethyl dipropylmalonic acid, and dimethyl dipropylmalonic acid.

4. The detection method according to claim 2, characterized in that, The preparation method of 2-ethyl-2-propylmalonic acid shown in Formula I includes: reacting diethyl ethyl malonate with 1-chloropropane via a propylation reaction to prepare diethyl 2-ethyl-2-propylmalonic acid shown in Formula II; and hydrolyzing diethyl 2-ethyl-2-propylmalonic acid shown in Formula II to prepare 2-ethyl-2-propylmalonic acid shown in Formula I; the preparation reactions are as follows: The phase transfer catalyst for the propylation reaction is selected from quaternary ammonium salts; the temperature control program for the propylation reaction includes: a temperature selected from 70℃~90℃, reaction time 2~4h; 90℃~110℃, reaction time 2~4h; 110℃~130℃, reaction time 2~4h; the mass concentration of the potassium hydroxide solution used in the hydrolysis reaction is selected from 40%~50%; the temperature of the hydrolysis reaction is selected from 70℃~100℃; the time of the hydrolysis reaction is selected from 2.0h~4.0h; the feed amount for the propylation reaction is selected from a molar ratio of diethyl malonate to 1-chloropropane of 1:1.0~1.7; the amount of potassium carbonate used in the propylation reaction is selected from a molar ratio of diethyl malonate to potassium carbonate of 1:0.80~1.

70.

5. The detection method according to claim 2, characterized in that, The preparation method of dipropylmalonic acid monoethyl ester as shown in Formula IV includes: preparing dipropylmalonic acid monoethyl ester as shown in Formula IV by hydrolysis of dipropylmalonic acid; the preparation reaction is as follows: The mass concentration of sodium hydroxide used in the hydrolysis reaction is selected from 20% to 30%; the temperature of the hydrolysis reaction is selected from 30℃ to 50℃; and the time of the hydrolysis reaction is selected from 8.0h to 12.0h.

6. The detection method according to claim 2, characterized in that, The preparation method of dipropylmalonate monopropyltrimonium shown in Formula V includes: selecting dipropylmalonate dipropyltrimonium ester and preparing dipropylmalonate monopropyltrimonium ester shown in Formula V by hydrolysis reaction; the preparation reaction is as follows: Wherein, the propylated PTC is selected from quaternary ammonium salts; the propylation reaction temperature is selected from 70℃~90℃, reaction time 2~4h; 90℃~110℃, reaction time 2~4h; 110℃~130℃, reaction time 2~4h; the mass concentration of sodium hydroxide used in the hydrolysis reaction is selected from 20%~30%; the hydrolysis reaction temperature is selected from 30℃~50℃; and the hydrolysis reaction time is selected from 8.0h~12.0h.

7. The detection method according to claim 1, characterized in that, Impurities in the dipropylmalonic acid product or reaction solution prepared by the diethyl malonate method are selected from one or more of propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-propyl-2-butylmalonic acid, monoethyl propylmalonic acid, monoethyl 2-ethyl-2-propylmalonic acid, monoethyl dipropylmalonic acid, monoethyl 2-propyl-2-butylmalonic acid, diethyl propylmalonic acid, monopropyl dipropylmalonic acid, diethyl 2-ethyl-2-propylmalonic acid, diethyl dipropylmalonic acid, propyl ethyl dipropylmalonic acid, and diethyl 2-propyl-2-butylmalonic acid.

8. The detection method according to claim 1, characterized in that, The impurities in the dipropylmalonic acid monoethyl ester product or reaction solution prepared by the diethyl malonate method are selected from one or more of propylmalonic acid, 2-ethyl-2-propylmalonic acid, dipropylmalonic acid, 2-propyl-2-butylmalonic acid, propylmalonic acid monoethyl ester, 2-ethyl-2-propylmalonic acid monoethyl ester, 2-propyl-2-butylmalonic acid monoethyl ester, diethyl propyl malonate, dipropylmalonic acid monopropyl ester, 2-ethyl-2-propylmalonic acid diethyl ester, dipropylmalonic acid diethyl ester, propyl dipropylmalonic acid ethyl ester, and 2-propyl-2-butylmalonic acid diethyl ester.

9. The detection method according to claim 1, characterized in that, Impurities in the dipropylmalonate monoethyl ester product or reaction solution prepared by the diethyl malonate method are selected from one or more of propylmalonate monoethyl ester, 2-ethyl-2-propylmalonate monoethyl ester, 2-propyl-2-butylmalonate monoethyl ester, and dipropylmalonate monopropyl ester.

10. The detection method according to claim 1, characterized in that, Impurities in the dipropylmalonic acid product or reaction solution prepared by the diethyl malonate method are selected from one or more of propylmalonic acid, 2-ethyl-2-propylmalonic acid, 2-isopropyl-2-propylmalonic acid, and 2-propyl-2-butylmalonic acid.

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