Rel-(2S, 3S)-2, 3-diisopropyl-2-cyano diethyl succinate compound as well as preparation method and application thereof

Abstract

The invention belongs to the field of catalyst preparation, and relates to a rel-(2S, 3S)-2, 3-diisopropyl-2-cyanosuccinic acid diethyl ester compound as well as a preparation method and application of the rel-(2S, 3S)-2, 3-diisopropyl-2-cyanosuccinic acid diethyl ester compound. The compound has a structure as shown in a formula (I), is a pure raceme, has an impurity content of less than 0.1%, and has a nuclear magnetic hydrogen spectrogram basically consistent with a figure 5. The invention provides a pure rel-(2S, 3S)-2, 3-diisopropyl-2-cyanosuccinic acid diethyl ester compound and a preparation method thereof, and completes the identification of the relative configuration of the rel-(2S, 3S)-2, 3-diisopropyl-2-cyanosuccinic acid diethyl ester compound. The preparation method is suitable for industrial large-scale production of pure (2S, 3S)-2, 3-diisopropyl-2-cyanosuccinic acid diethyl ester, and the pure (2S, 3S)-2, 3-diisopropyl-2-cyanosuccinic acid diethyl ester is used as an internal electron donor for preparation of a Ziegler-Natta polypropylene catalyst.

Description

Technical Field

[0001] The present invention belongs to the field of catalyst preparation, and specifically relates to a rel-(2S,3S)-2,3-diisopropyl-2-cyanobutanedioic acid diethyl ester compound, a preparation method thereof, and an application thereof. Background Art

[0002] As is well known, internal electron donors are the core components of Ziegler-Natta polypropylene catalysts, and are metaphorically called the DNA of polypropylene catalysts by international scholars. To a great extent, they determine the activity, hydrogen regulation performance, and stereospecific ability of the catalysts, and thus determine the microstructure, mechanical properties, and processing properties of the resins. The exploration and research of new internal electron donors have always been the basis and important direction for the development of polypropylene catalyst technology. 2,3-Diisopropyl-2-cyanobutanedioic acid diethyl ester is a new type of internal electron donor. Compared with the phthalate internal electron donors used in traditional fourth-generation Z-N catalysts, it not only avoids the use of phthalates (plasticizers), but also endows the catalysts with different properties. The catalysts using this compound as an internal electron donor have excellent comprehensive performance, and the polymers prepared therefrom have characteristics such as a wide molecular weight distribution (MWD>12).

[0003] As an excellent new type of internal electron donor, the preparation method of 2,3-diisopropyl-2-cyanobutanedioic acid diethyl ester has always been a research hotspot. Chinese patents CN101811983B, CN101811982B, CN106608935B, and WO2010094211 disclose the synthesis methods of this type of compound and its derivatives and their applications in the preparation of Z-N catalysts. There are two chiral carbon atoms in the 2,3-diisopropyl-2-cyanobutanedioic acid diethyl ester compound, so there are four optically active isomers, and its structure is as Figure 1as shown by A, B, C, and D therein. Among them, compound A and B are enantiomers; compound C and D are enantiomers. Except for the difference in optical rotation performance, the physical and chemical properties of enantiomers are the same. Therefore, their retention times in the achiral capillary column of gas chromatography are the same, and the peak emergence times are the same. Therefore, diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate shows two chromatographic peaks in the achiral capillary column of gas chromatography. In patent CN106608935B, the component with a shorter retention time is defined as component a, and the component with a longer retention time is defined as component b. Both component a and component b are racemates. Component a may be either the racemate of compound A and B or the racemate of C and D, and it is also uncertain which racemate component b is. A and C or D are diastereomers of each other, and B and C or D are diastereomers of each other. From stereochemical knowledge, it can be known that diastereomers not only have different optical rotation abilities, but also many physical and chemical properties are different. This difference in chemical properties has been confirmed in the application of patent CN106608935B. Due to technical limitations, patent CN106608935B cannot obtain pure racemic components a and b. The patent prepared a polypropylene catalyst using a mixture of two racemates of component a and component b in different proportions. Experiments have shown that when the proportion of component a (whose relative configuration cannot be determined) in the two racemic mixtures is higher, it will affect the hydrogen regulation sensitivity of the polypropylene catalyst and the molecular weight distribution of the prepared polyolefin is narrower. When the proportion of component b (whose relative configuration cannot be determined) is higher, the prepared catalyst has higher activity, better orientation ability (higher isotactic index of the prepared polyolefin), is less sensitive to hydrogen (lower melt index of the prepared polyolefin), and the molecular weight distribution of the prepared polymer is wider, which is beneficial to the preparation of a better catalyst for pipes.

[0004] Due to technical limitations, the preparation methods reported in current patents and literature can only obtain a mixture composed of two racemates of component a and component b, and cannot obtain pure racemates. There is also no literature report that can identify the relative configuration of component a or component b. Summary of the Invention

[0005] In view of the limitations of the prior art, the present invention creatively obtains one of the pure racemates of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate, namely the compound rel-(2S,3S)-diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate, and its preparation method. The identification of the relative structure of this racemate is completed, and it is determined that rel-(2S,3S)-diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate is component b in the mixture of two racemates of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate reported in CN106608935B. This method has low requirements for equipment, mild reaction conditions, simple operation and is easy to scale up. It is environmentally friendly and can efficiently resolve the two racemates, obtaining high - purity racemates simultaneously.

[0006] The first aspect of the present invention provides a rel-(2S,3S)-diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate compound, which has the structure shown in formula (Ⅰ):

[0007]

[0008] The compound is a pure racemate with an impurity content of less than 0.1%, and has a nuclear magnetic resonance hydrogen spectrum Figure 5 substantially consistent with...

[0009] The second aspect of the present invention provides a preparation method of the above - mentioned compound, including the following steps:

[0010] React metal alkoxide, aprotic solvent, and ethyl 3 - methyl - 2 - cyanobutyrate to form a salt; add ethyl 2 - bromoisovalerate and continue the reaction to form diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate, then filter, remove the solvent, extract, wash, and dry to obtain the crude reaction product; purify the crude reaction product by distillation in a distillation column, collect the bottom heavy fraction, and then take the purified crude product and further purify and separate it by using column chromatography or recrystallization or a combination of column chromatography and recrystallization methods to finally obtain the pure rel-(2S,3S)-diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate compound; the operating temperature of the distillation column is 60 - 260 °C, the operating pressure is 0.1 - 2800 Pa, and the reflux ratio of distillation is controlled such that the draw - off ratio to reflux is 1:50 - 10:1.

[0011] The third aspect of the present invention provides the application of the above - mentioned compound in the preparation of a solid catalyst component for olefin polymerization, wherein the compound is used as at least part of the internal electron donor.

[0012] The present invention provides a pure rel-(2S,3S)-diisopropyl 2-cyanobutanedioate compound and a preparation method thereof, and the relative configuration thereof has been identified. This preparation method is not only applicable to the industrial-scale production of pure (2S,3S)-diisopropyl 2-cyanobutanedioate, enabling it to be used independently as an internal electron donor in the preparation of Ziegler-Natta polypropylene catalysts. It is also possible to prepare different proportions of two racemic mixtures by mixing the pure rel-(2S,3S)-diisopropyl 2-cyanobutanedioate with a mixture of two racemates of rel-(2S,3S)-diisopropyl 2-cyanobutanedioate or 2,3-diisopropyl 2-cyanobutanedioate prepared by the prior art, and use these mixtures as electron donors with different functions in the preparation of Ziegler-Natta polypropylene catalysts.

[0013] Other features and advantages of the present invention will be described in detail in the following specific implementation section. Brief Description of the Drawings

[0014] The exemplary embodiments of the present invention will be described in more detail by combining the accompanying drawings.

[0015] Figure 1 The structures of four optically active isomers of diisopropyl 2-cyanobutanedioate are shown.

[0016] Figure 2 The gas chromatography results of the product after the first rectification in Example 1 are shown.

[0017] Figure 3 The gas chromatography results of the product after the second rectification in Example 1 are shown.

[0018] Figure 4 The gas chromatography results of the purified product in Example 1 are shown.

[0019] Figure 5 The 1H NMR results of the purified product in Example 1 are shown.

[0020] Figure 6 The 13C NMR results of the purified product in Example 1 are shown.

[0021] Figure 7 The HMBC results of the purified product in Example 1 are shown.

[0022] Figure 8 The NOESY structure of the purified product in Example 1 is shown.

[0023] Figure 9Shows the gas chromatography results of the product after the first rectification in Example 5.

[0024] Figure 10 Shows the gas chromatography results of the product after the second rectification in Example 5.

[0025] Figure 11 Shows the gas chromatography results of the product after the first rectification in Comparative Example 1. Detailed Description of the Invention

[0026] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0027] The present invention provides a rel-(2S,3S)-diisopropyl 2-cyanobutanedioate compound having the structure shown in Formula (I):

[0028]

[0029] The compound is a pure racemate, that is, a mixture of (2S,3S)-diisopropyl 2-cyanobutanedioate and (2R,3R)-diisopropyl 2-cyanobutanedioate in equal proportions, with an impurity content of less than 0.1%, and has a nuclear magnetic resonance hydrogen spectrum Figure 5 substantially consistent with.

[0030] Specifically, the characteristic nuclear magnetic resonance hydrogen spectrum of the compound is: 1 1H-NMR (CDCl3 / TMS, 500 MHz) (δ ppm): 0.975–0.989 (d, 3H, CH(CH3)2), 1.055 - 1.068 (d, 3H, CH(CH3)2), 1.190–1.204 (d, 3H, CH(CH3)2), 1.212–1.226 (d, 3H, CH(CH3)2), 1.249–1.277 (t, 3H, CH2CH3), 1.284–1.313 (t, 3H, CH2CH3), 2.052–2.133 (m, 1H, CH(CH3)2), 2.282–2.364 (m, 1H, CH(CH3)2), 2.992 (s, 1H, O=CCHCH(CH3)2), 4.122 - 4.252 (m, 4H, 2OCH2CH3). It can be confirmed that the compound is a rel-(2S,3S)-diisopropyl 2-cyanobutanedioate compound having the structure shown in Formula (I).

[0031] The preparation method of the compound includes the following steps:

[0032] React a metal alkoxide, an aprotic solvent, and ethyl 3-methyl-2-cyanobutyrate to form a salt; add ethyl 2-bromo-3-methylbutyrate and continue the reaction to form diethyl 2,3-diisopropyl-2-cyanosuccinate, then filter, remove the solvent, extract, wash, and dry to obtain the crude reaction product; subject the crude reaction product to rectification purification in a rectification column, collect the bottom heavy fraction, and then take the rectified and purified crude product (i.e., the said heavy fraction), and further purify and separate it by using column chromatography or recrystallization or a combination of column chromatography and recrystallization to finally obtain the pure product rel-(2S,3S)-diethyl 2,3-diisopropyl-2-cyanosuccinate; the operating temperature of the rectification column is 60-260°C, the operating pressure is 0.1-2800 Pa, and the reflux ratio of rectification is controlled such that the draw ratio to reflux is 1:50-10:1.

[0033] According to the method of the present invention, the aprotic solvent may be selected from one or more of tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and acetonitrile.

[0034] According to the method of the present invention, the metal alkoxide may be an alkali metal alkoxide, preferably selected from one or more of potassium methoxide, potassium ethoxide, potassium n-propoxide, potassium isopropoxide, potassium n-butoxide, potassium isobutoxide, potassium tert-butoxide, sodium methoxide, sodium ethoxide, sodium n-propoxide, sodium isopropoxide, sodium n-butoxide, sodium isobutoxide, and sodium tert-butoxide.

[0035] In the present invention, the dosage of each component is preferably as follows: the molar ratio of the metal alkoxide to ethyl 3-methyl-2-cyanobutyrate is 1:0.5-2; the dosage of the aprotic solvent is 1-50 mL per gram of ethyl 3-methyl-2-cyanobutyrate; the molar ratio of the raw material ethyl 3-methyl-2-cyanobutyrate to ethyl 2-bromo-3-methylbutyrate is 1:0.5-2.

[0036] In the present invention, the temperature of the mixing reaction and the continuous reaction may each independently be 10-150°C, preferably 20-120°C; the pressure of the mixing reaction and the continuous reaction may each independently be 0.8-2 atmospheres.

[0037] In the present invention, the number of trays of the rectification column may be 1-150, preferably 1-60.

[0038] The operating temperature of the rectification column is preferably 100-240°C, for example, it may be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, and the values between any two of the above numerical points, and more preferably 150-210°C.

[0039] The present invention uses a higher vacuum degree than conventional distillation, and better separation effects can be obtained. Specifically, the operating pressure of the distillation column is preferably 10 - 2000 Pa, more preferably 50 - 1500 Pa. For example, it can be 50 Pa, 60 Pa, 70 Pa, 80 Pa, 90 Pa, 100 Pa, 200 Pa, 300 Pa, 400 Pa, 500 Pa, 600 Pa, 700 Pa, 800 Pa, 900 Pa, 1000 Pa, 1100 Pa, 1200 Pa, 1300 Pa, 1400 Pa, 1500 Pa, and the values between any two of the above numerical points.

[0040] The reflux ratio of the distillation column is also a control condition. Different from the higher extraction amount in conventional distillation, the reflux ratio in the present invention is preferably controlled such that the extraction - to - reflux ratio is 5:1 - 1:45. Specifically, the extraction - to - reflux ratio can be 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, 1:25, 1:26, 1:27, 1:28, 1:29, 1:30, 1:31, 1:32, 1:33, 1:34, 1:35, 1:36, 1:37, 1:38, 1:39, 1:40, 1:41, 1:42, 1:43, 1:44, 1:45, and the values between any two of the above ratios. Preferably, the extraction - to - reflux ratio is controlled to be 1:2 - 1:40, and more preferably, the extraction - to - reflux ratio is controlled to be 1:10 - 1:30.

[0041] According to a specific embodiment of the present invention, after the product is distilled, it is further purified using column chromatography. In the column chromatography method after distillation, the filler used in the chromatography column is one or more of silica gel, alumina, silica - magnesium adsorbent, C18 filler, and ion - exchange column, and the eluent used is one or more combinations of petroleum ether, n - hexane, benzene, ethyl ether, tetrahydrofuran, ethyl acetate, chloroform, dichloromethane, toluene, xylene, isopropanol, n - butanol, acetonitrile, acetone, ethanol, methanol, and water.

[0042] According to another specific embodiment of the present invention, after the product is distilled, it is further purified using recrystallization. In the recrystallization method after distillation, the solvent for recrystallization is selected from one or more combinations of petroleum ether, n - hexane, benzene, ethyl ether, tetrahydrofuran, ethyl acetate, chloroform, dichloromethane, toluene, xylene, isopropanol, n - butanol, acetonitrile, acetone, ethanol, methanol, and water; the recrystallization temperature is - 30°C to 45°C, and the ratio of solute to solvent is 1:0.1 - 10.

[0043] The further purification of the product can also be achieved by column chromatography combined with recrystallization, and the specific conditions of the column chromatography and recrystallization are as described above.

[0044] The above-mentioned compound of the present invention can be used as an internal electron donor in the preparation of solid catalyst components for olefin polymerization, and the solid catalyst components can further be used to prepare Ziegler-Natta polypropylene catalysts.

[0045] There are two chiral carbons in the structure of diethyl 2,3-diisopropyl-2-cyanobutanedioate, so there are four optical isomers. The structures of the optical isomers are as Figure 1 shown by compounds A, B, C, and D in the figure. In component i in the figure, compound A and compound B are enantiomers; in component ii, compound C and compound D are enantiomers. The compound with the rel-(2S,3S)-2,3-diisopropyl-2-cyanobutanedioate structure prepared by the inventor was identified as component i through structure identification. The specific rotation was measured and the specific rotation was zero, indicating that component i is a racemate.

[0046] The rel-(2S,3S)-2,3-diisopropyl-2-cyanobutanedioate compound prepared using the synthesis technology of the present invention was subjected to analysis and testing such as gas chromatography, 1H NMR, 13C NMR, HMBC NMR, and NOESY NMR, and it was determined that the prepared target compound is a pure rel-(2S,3S)-2,3-diisopropyl-2-cyanobutanedioate compound.

[0047] The diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate prepared by the current process is a mixture of two racemates, which shows two chromatographic peaks in a gas chromatographic achiral capillary column, and each peak corresponds to one racemate respectively. Under the same gas chromatographic conditions as in CN106608935A, the gas chromatographic detection of pure rel-(2S,3S)-2,3 - diisopropyl - 2 - cyanobutanedioate racemate was carried out separately. Compared with the gas chromatogram of the mixture of two racemates of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate, it was found that the retention time of the peak of rel-(2S,3S)-2,3 - diisopropyl - 2 - cyanobutanedioate was relatively long, and it was the b component in the mixture of two racemates of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate reported in patent CN106608935A. CN106608935A reported that when the proportion of component b (whose relative configuration cannot be determined) was higher, the activity of the prepared catalyst was higher, the orientation ability was better (the isotactic index of the prepared polyolefin was higher), it was less sensitive to hydrogen (the melt index of the prepared polyolefin was lower), and the molecular weight distribution of the prepared polymer was wider, which was beneficial to the preparation of a better catalyst for pipes. The inventor creatively prepared pure rel-(2S,3S)-2,3 - diisopropyl - 2 - cyanobutanedioate, which is not only suitable for industrial scale - up production of pure (2S,3S)-2,3 - diisopropyl - 2 - cyanobutanedioate as an internal electron donor for the preparation of Ziegler - Natta polypropylene catalysts. It can also be mixed with another racemate rel-(2S,3S)-2,3 - diisopropyl - 2 - cyanobutanedioate or a mixture of two racemates of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate prepared by the prior art in proportion to prepare different proportions of two racemic mixtures, which are used as electron donors with different functions for the preparation of Ziegler - Natta polypropylene catalysts.

[0048] The present invention will be further described below in conjunction with examples, but the scope of the present invention is not limited to these examples.

[0049] Example 1

[0050] Prepare rel-(2S,3S)-2,3 - diisopropyl - 2 - cyanobutanedioate.

[0051] Take 500 g of N-methylpyrrolidone and add it to a 2 L three-necked flask. Under stirring conditions, add 143.2 g of potassium ethoxide, and then add 264 g of ethyl 3-methyl-2-cyanobutyrate to the reaction flask. Stir at room temperature and atmospheric pressure for 30 min, then add 355.6 g of ethyl 2-bromo-3-methylvalerate. Control the reaction temperature at 30 °C and the reaction pressure at atmospheric pressure. React for 8 h. After the reaction is completed, filter, remove the solvent, wash with 100 ml of water, then extract three times with 300 mL of ether, and collect the organic phase. Wash twice with 100 mL of saturated aqueous sodium bicarbonate solution until the organic phase is neutral. Dry the organic phase and concentrate to obtain 610.7 g of the crude product after removing ether.

[0052] Add 300 g of the crude product to a 500 mL high-efficiency rectification column with 35 theoretical plates. Rectify the product under the conditions that the bottom temperature of the column is 185 °C, the vacuum degree is 400 Pa, and the reflux ratio is controlled such that the take-off ratio to reflux is 1:20. Distill out and collect the fraction with a distillation range of 80 - 160 °C. After the collected amount reaches 176 g, collect 113 g of the heavy fraction at the bottom of the column as the crude product and conduct gas chromatography analysis. The results are shown in Figure 2 , after deducting the dilution solvent, the purity of diethyl 2,3-diisopropyl-2-cyanobutanedioate is 96.280%, which is a mixture of two racemates. Among them, the content of the racemate with a longer retention time for peak emergence is 79.240%, and the content of the racemate with a shorter retention time for peak emergence is 17.040%. Subject the heavy fraction crude product obtained from the first rectification to secondary rectification under the same conditions as the first rectification. Take the heavy fraction at the bottom of the column and conduct gas chromatography analysis. The results are shown in Figure 3 , the purity of diethyl 2,3-diisopropyl-2-cyanobutanedioate is 98.104%, among which the content of the racemate with a longer retention time for peak emergence is 85.038%, and the content of the racemate with a shorter retention time for peak emergence is 13.066%. Then, use column chromatography with a mobile phase of ethyl acetate and petroleum ether in a ratio of 1:9 for separation and purification to obtain a pure racemate. Through gas chromatography detection, it is the compound with a longer retention time for peak emergence. Gas chromatography analysis is shown in Figure 4 , and its purity is greater than 99.9%. Identify its structure by proton nuclear magnetic resonance spectroscopy. The proton nuclear magnetic resonance spectrum is as follows: 11H-NMR (CDCl3 / TMS, 500 MHz) (δ ppm): 0.975–0.989 (d, 3H, CH(CH3)2), 1.055 - 1.068 (d, 3H, CH(CH3)2), 1.190–1.204 (d, 3H, CH(CH3)2), 1.212–1.226 (d, 3H, CH(CH3)2), 1.249–1.277 (t, 3H, CH2CH3), 1.284–1.313 (t, 3H, CH2CH3), 2.052–2.133 (m, 1H, CH(CH3)2), 2.282–2.364 (m, 1H, CH(CH3)2), 2.992 (s, 1H, O=CCHCH(CH3)2), 4.122 - 4.252 (m, 4H, 2OCH2CH3). The 1H NMR spectrum is shown in Figure 5 。

[0053] The relative configuration was identified and analyzed by 13C NMR, HMBC, and NOESY NMR analysis methods, and its relative structure was determined to be rel-(2S,3S)-diisopropyl 2-cyanobutanedioate. The test results are shown in Figures 6 - 8 。

[0054] Example 2

[0055] Preparation of rel-(2S,3S)-diisopropyl 2-cyanobutanedioate.

[0056] 20 g of the crude product obtained in Example 1 was taken, and 15 g of petroleum ether was used as the recrystallization solvent. Recrystallization was carried out at 25 °C - 8 °C to obtain 3 g of pure racemic rel-(2S,3S)-diisopropyl 2-cyanobutanedioate. Its relative configuration was identified by gas chromatography, 1H NMR, 13C NMR, HMBC, and NOESY analysis methods, and the structure was consistent with that of Example 1.

[0057] Example 3

[0058] Preparation of rel-(2S,3S)-diisopropyl 2-cyanobutanedioate.

[0059] Take 500 g of dimethylformamide and add it to a 2 L three-necked flask. Under stirring conditions, add 190.93 g of potassium tert-butoxide to the reaction flask, and then add 264 g of ethyl 3-methyl-2-cyanobutyrate to the reaction flask. Stir and react at room temperature and atmospheric pressure for 30 min. Then add 355.6 g of ethyl 2-bromo-3-methylvalerate, heat to 40 °C, and react at atmospheric pressure for 6 h. After the reaction is completed, filter, remove the solvent, wash with 100 mL of water, then extract three times with 300 mL of ether, collect the organic phase, wash twice with 100 mL of saturated aqueous sodium bicarbonate solution until the organic phase is neutral. Dry the organic phase and concentrate the crude product after removing ether.

[0060] Add the crude product to a 500 mL high-efficiency rectification column with 35 theoretical plates. Under the conditions of a column still temperature of 185 °C and a vacuum degree of 400 Pa, control the reflux ratio to be 1:20 (take-off ratio to reflux ratio) and rectify the product. Collect the fraction with a distillation range of 80 - 160 °C and collect the bottom heavy fraction to obtain 113 g of crude product. Further rectify the crude product obtained after the first rectification by vacuum rectification. Obtain a compound of diethyl 2,3-diisopropyl-2-cyanobutanedioate composed of two racemates, with a purity of 96.477%. Among them, the content of the racemate with a longer retention time for peak emergence is 78.324%, and the content of the racemate with a shorter retention time for peak emergence is 18.153%. Then use column chromatography with a mobile phase of ethyl acetate and petroleum ether in a ratio of 1:9 for separation and purification to obtain the compound with a longer retention time for peak emergence, whose purity is greater than 99.9%. Analyze it by gas chromatography, 1H NMR, 13C NMR, HMBC NMR, and NOESY. The product structure is consistent with the target compound structure, and its relative structure is rel-(2S,3S)-diethyl 2,3-diisopropyl-2-cyanobutanedioate.

[0061] Example 4

[0062] Prepare rel-(2S,3S)-diethyl 2,3-diisopropyl-2-cyanobutanedioate.

[0063] Take 20 g of the crude product prepared in Example 3, use 15 g of petroleum ether as the recrystallization solvent, and recrystallize under the conditions of 25 °C - 8 °C to obtain 2.3 g of rel-(2S,3S)-diethyl 2,3-diisopropyl-2-cyanobutanedioate with a purity greater than 99.4%. Identify its relative configuration by gas chromatography, 1H NMR, 13C NMR, HMBC NMR, and NOESY analysis methods. The product structure is consistent with that of Example 1.

[0064] Example 5

[0065] Adopt the synthesis method and rectification steps of Example 1, with the difference that the reflux ratio in the rectification step is controlled to be 6:1 (take-off ratio to reflux ratio).

[0066] The crude product was prepared using the synthesis method of Example 1. 300 g of the crude product was added to a 500 mL high-efficiency rectification column with 35 plates. The product was rectified under the conditions that the bottom temperature of the column was 195 °C, the vacuum degree was 400 Pa, and the reflux ratio was controlled such that the draw ratio to reflux was 6:1. After collecting the fraction with a distillation range of 80 - 160 °C, the bottom heavy fraction was collected and analyzed by gas chromatography. The results are shown in Figure 9 . Among them, the purity of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate was 96.545%. The content of the racemate with a shorter peak retention time was 37.500%, and the content of the racemate with a longer peak retention time was 59.045%. It was subjected to secondary rectification. Similarly, the reflux ratio was controlled such that the draw ratio to reflux was 6:1. After collecting the fraction with a distillation range of 80 - 160 °C, the bottom heavy fraction was collected and subjected to chromatographic analysis. The results are shown in Figure 10 . After deducting the dilution solvent used for chromatography, the purity of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate was 97.463%. It was a mixture of two racemates. The content of the racemate with a shorter peak retention time was 25.361%, and the content of the racemate with a longer peak retention time was 72.102%.

[0067] By comparing Example 5 and Example 1, it was found that when the reflux ratio was controlled such that the draw ratio to reflux was 1:20, the purity of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate after rectification was 98.104%, which was higher than 97.463% when the reflux ratio was controlled such that the draw ratio to reflux was 6:1. Moreover, when the reflux ratio was controlled such that the draw ratio to reflux was 1:20, the ratio of the racemate with a shorter peak retention time to the racemate with a longer peak retention time in the rectified diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate was 6.51:1, which was higher than 2.84:1 when the reflux ratio was controlled such that the draw ratio to reflux was 6:1. This shows that using a reflux ratio controlled such that the draw ratio to reflux is 1:20 can not only improve the purity of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate, but also increase the ratio of the two racemates, facilitating the further separation of the two racemates.

[0068] Comparative Example 1

[0069] The synthesis method and rectification steps of Example 1 were adopted, with the difference that the vacuum degree used in the rectification step was 3000 Pa, and the corresponding temperature inside the rectification kettle was 270 °C.

[0070] The crude product was prepared using the synthesis method of Example 1. 300 g of the crude product was added to a 500 mL high-efficiency rectification column with 35 theoretical plates. The product was rectified under the conditions that the bottom temperature of the column was 270 °C, the vacuum degree was 3000 Pa, and the reflux ratio was controlled such that the draw ratio to reflux was 1:20. After removing the light fractions, the heavy fractions at the bottom of the column were collected and analyzed by gas chromatography. The results are shown in Figure 11 . The purity of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate was 89.899%. The content of the racemate with a short retention time for the peak was 17.653%, and the content of the racemate with a long retention time for the peak was 72.246%.

[0071] It can be seen that the vacuum degree used in the rectification step was 3000 Pa, and the temperature inside the rectification kettle was 270 °C. After one - stage rectification, obvious thermal decomposition of the product occurred, generating more by - products, which seriously affected the further separation and yield of the product.

[0072] The embodiments of the present invention have been described above. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

[0073] The endpoints and any values disclosed in this document are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this document.

Claims

1. A rel-(2S,3S)-diisopropyl 2-cyanobutanedioate compound, having the structure shown in formula (Ⅰ): The compound is a pure racemate with an impurity content of less than 0.1%, and has a proton nuclear magnetic resonance spectrum substantially consistent with that of Figure 5.

2. The compound according to claim 1, wherein, The characteristic 1H-NMR spectrum of the compound is as follows: 1 1H-NMR(CDCl3 / TMS, 500 MHz)(δ ppm): 0.975–0.989 (d, 3H, CH(CH3)2), 1.055 - 1.068 (d, 3H, CH(CH3)2), 1.190–1.204 (d, 3H, CH(CH3)2), 1.212–1.226 (d, 3H, CH(CH3)2), 1.249–1.277 (t, 3H, CH2CH3), 1.284–1.313 (t, 3H, CH2CH3), 2.052–2.133 (m, 1H, CH(CH3)2), 2.282–2.364 (m, 1H, CH(CH3)2), 2.992 (s, 1H, O=CCHCH(CH3)2), 4.122 - 4.252 (m, 4H, 2OCH2CH3).

3. A method for preparing the compound according to claim 1 or 2, comprising the following steps: Reacting metal alkoxide, an aprotic solvent, and ethyl 3-methyl-2-cyanobutyrate to form a salt; adding ethyl 2-bromo-3-methylbutyrate and continuing the reaction to form diisopropyl 2-cyanobutanedioate, then filtering, desolventizing, extracting, washing, and drying to obtain a crude reaction product; subjecting the crude reaction product to rectification purification in a rectification column, collecting the bottom heavy fraction, and then taking the purified crude product and further purifying and separating it by column chromatography or recrystallization or a combination of column chromatography and recrystallization to finally obtain a pure rel-(2S,3S)-diisopropyl 2-cyanobutanedioate compound; the operating temperature of the rectification column is 60-260 °C, the operating pressure is 0.1-2800 Pa, and the reflux ratio of rectification is controlled such that the draw ratio to reflux is 1:50-10:

1.

4. The preparation method according to claim 3, wherein The aprotic solvent is one or more of tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and acetonitrile.

5. The preparation method according to claim 3, wherein, The metal alkoxide is an alkali metal alkoxide, preferably selected from one or more of potassium methoxide, potassium ethoxide, potassium n-propoxide, potassium isopropoxide, potassium n-butoxide, potassium isobutoxide, potassium tert-butoxide, sodium methoxide, sodium ethoxide, sodium n-propoxide, sodium isopropoxide, sodium n-butoxide, sodium isobutoxide, and sodium tert-butoxide.

6. The preparation method according to claim 3, wherein, The molar ratio of the metal alkoxide to ethyl 3-methyl-2-cyanobutyrate is 1:0.5-2; for every gram of ethyl 3-methyl-2-cyanobutyrate, the amount of the aprotic solvent used is 1-50 mL; the molar ratio of the raw material ethyl 3-methyl-2-cyanobutyrate to ethyl 2-bromo-3-methylbutyrate is 1:0.5-2.

7. The preparation method according to claim 3, wherein, The temperature of the mixing reaction and the continuing reaction are each independently 10-150 °C, preferably 20-120 °C; the pressure of the mixing reaction and the continuing reaction are each independently 0.8-2 atmospheres.

8. The preparation method according to claim 3, wherein, The number of trays in the rectification column is 1-150, preferably 1-60; the operating temperature is 100-240 °C, preferably 150-210 °C; the operating pressure is 10-2000 Pa, preferably 50-1500 Pa; the reflux ratio is controlled such that the draw ratio to reflux is 5:1-1:45, preferably 1:2-1:40, more preferably 1:10-1:

30.

9. The preparation method according to claim 3, wherein In the column chromatography method after rectification, the packing used in the chromatography column is one or more of silica gel, alumina, silica-magnesia adsorbent, C18 packing, and ion exchange column, and the developing agent used is one or more combinations of petroleum ether, n-hexane, benzene, diethyl ether, tetrahydrofuran, ethyl acetate, chloroform, dichloromethane, toluene, xylene, isopropanol, n-butanol, acetonitrile, acetone, ethanol, methanol, and water.

10. The preparation method according to claim 3, wherein In the recrystallization method after rectification, the solvent for recrystallization is selected from one or a combination of petroleum ether, n-hexane, benzene, ether, tetrahydrofuran, ethyl acetate, chloroform, dichloromethane, toluene, xylene, isopropanol, n-butanol, acetonitrile, acetone, ethanol, methanol, and water; the temperature for recrystallization is from -30°C to 45°C, and the ratio of solute to solvent is 1:0.1 - 10.

11. Use of the compound according to claim 1 or 2 in the preparation of a solid catalyst component for olefin polymerization, wherein, The compound serves as at least a partial internal electron donor.

12. The application according to claim 11, wherein The internal electron donor further includes a mixture of two racemates of diethyl 2,3 - diisopropyl - 2 - cyanobutanedioate.

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