Preparation method of norbornene carboxylic acid

Abstract

The invention discloses a preparation method of norbornene carboxylic acid, which comprises the following steps: controlling the reaction temperature at-78-100 DEG C in an inert atmosphere, sequentially adding potassium tert-butoxide and n-butyllithium into an organic solution of norbornene, stirring for 0.5-24 hours to complete the reaction, then adding dry ice, continuously stirring for 0.5-24 hours, filtering, washing, and drying to obtain the norbornene carboxylic acid. After the system is heated to room temperature, extracting and purifying a product to obtain norbornene carboxylic acid; wherein the molar ratio of the norbornene to the potassium tert-butoxide to the n-butyllithium is 1: (0.5-10); the molar ratio of the dry ice to the norbornene is (10-1000): 1; according to the scheme, norbornene carboxylic acid can be directly prepared through a relatively simple preparation process on the basis of not adopting toxic and explosive chemicals, so that the safety and the production efficiency in the preparation process are fully improved, and industrial popularization and application are facilitated; and moreover, by controlling the molar ratio of norbornene to potassium tert-butoxide to n-butyllithium to dry ice, the yield of norbornene carboxylic acid is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of olefin polymerization catalysts, and particularly relates to a method for preparing norbornene carboxylic acid. Background Art

[0002] Norbornene is an organic compound with a cycloalkane structure and has a variety of applications. As a polymer material, norbornene can be polymerized into a polymer material with high thermal stability, low expansion coefficient, excellent optical properties and chemical stability, and is widely used in optoelectronic materials, high-temperature electronic materials, semiconductor materials and other fields. As a chemical reagent, norbornene can be used to participate in many important organic synthesis reactions, such as olefin cyclization, hydrogen transfer reaction, carbonylation reaction, etc. Norbornene can also be used as a ligand in certain catalysts to improve the selectivity of catalytic reactions in asymmetric catalytic reactions. In addition, norbornene can also be used to prepare high-efficiency fluorescent dyes, prepare high-performance coatings, prepare high-performance electrolytes, prepare new materials and other fields. Therefore, norbornene is an organic compound with broad application prospects and has important application value in materials science, organic synthesis, chemical catalysis and other fields.

[0003] Norbornene carboxylic acid derivatives include at least the following:

[0004]

[0005] It can be seen that various types of norbornene carboxylic acid derivatives are further prepared on the basis of norbornene carboxylic acid, that is, norbornene carboxylic acid is an important intermediate in the preparation process of norbornene carboxylic acid derivatives.

[0006] In 2016, Yu Jinquan's research group reported a method for synthesizing norbornene carboxylic acid (J.Am.Chem.Soc.2016,138,42,14092-14099). Using nadic anhydride as raw material, norbornene carboxylic acid was obtained through 5 steps of chemical reaction. The preparation method is as follows:

[0007]

[0008] It can be seen from the preparation process that the preparation method has a complicated preparation process, which will inevitably lead to a decrease in preparation efficiency. In addition, a variety of highly toxic and explosive compounds are used in the preparation process, such as red mercury (II) oxide, liquid bromine and hydrogen. The use of a large amount of highly toxic and explosive substances greatly reduces the production safety performance and is not conducive to industrial production.

[0009] In view of this, the present invention is proposed. Summary of the invention

[0010] The object of the present invention is to provide a method for preparing norbornene carboxylic acid in view of the above-mentioned problems in the prior art. Under inert atmosphere and certain temperature conditions, norbornene carboxylic acid is prepared using norbornene, potassium tert-butoxide, n-butyl lithium and carbon dioxide as raw materials, thereby avoiding the use of highly toxic and explosive substances, greatly simplifying the preparation process, and increasing the yield of norbornene by controlling the amount of carbon dioxide added.

[0011] In order to achieve the above object, the first aspect of the present invention provides a method for preparing norbornene carboxylic acid, comprising the following steps:

[0012] S1. Under an inert atmosphere and a preset reaction temperature, potassium tert-butoxide and n-butyl lithium are sequentially added to a norbornene solution, and the mixture is continuously stirred to obtain a product A;

[0013] S2. After completing step S1, an inert atmosphere is maintained, and carbon dioxide is introduced into product A at the reaction temperature while continuously stirring to obtain norbornene carboxylic acid.

[0014] In the above scheme, under certain atmosphere and temperature conditions, only potassium tert-butoxide, n-butyl lithium and carbon dioxide are sequentially added to the norbornene solution, and norbornene carboxylic acid can be obtained after stirring. Conventional chemicals are used as raw materials, and the preparation process is relatively safe. The preparation method is simple, the preparation efficiency is high, and it is conducive to large-scale production conversion.

[0015] Furthermore, step S1 is specifically as follows:

[0016] Dissolving norbornene in an organic solvent under an inert atmosphere, adjusting the temperature to a preset reaction temperature, adding a potassium tert-butoxide solution to the norbornene solution under stirring, and then adding an n-butyl lithium solution, and continuing to stir to obtain a product A;

[0017] The organic solvent for dissolving norbornene is an inactive organic solvent; the solvent in the potassium tert-butoxide solution is selected from an ether solvent or tetrahydrofuran; and the solvent in the n-butyl lithium solution is hexane.

[0018] Preferably, the organic solvent for dissolving norbornene is at least one of tetrahydrofuran and diethyl ether.

[0019] Further, in step S1, the molar ratio of norbornene to potassium tert-butoxide is 1:0.5-10;

[0020] The molar ratio of norbornene to n-butyllithium is 1:0.5-10.

[0021] In the above scheme, controlling the molar ratio of norbornene to n-butyl lithium and potassium tert-butoxide can ensure the stability of the yield. If the molar ratio of norbornene to n-butyl lithium and potassium tert-butoxide is too low, the yield of norbornene carboxylic acid will decrease; if it is too high, it will cause overflow of n-butyl lithium and potassium tert-butoxide in the reaction system, and carbon dioxide will preferentially react with n-butyl lithium and potassium tert-butoxide, increasing the amount of carbon dioxide used and thereby increasing the production cost.

[0022] Furthermore, in step S1, stirring is continued for 0.5 to 24 hours to complete step S1, and then proceed to step S2; in this process, the stirring time is controlled to achieve the intermittent addition of n-butyl lithium and carbon dioxide, so that norbornene and n-butyl lithium and potassium tert-butoxide are fully reacted, and then further reacted with carbon dioxide, thereby ensuring the yield of norbornene carboxylic acid.

[0023] Furthermore, in step S2, the molar ratio of dry ice to norbornene is 5 to 1000:1.

[0024] Preferably, the molar ratio of dry ice to norbornene is 10 to 100:1.

[0025] The above scheme limits the molar ratio of norbornene to dry ice, which can maximize the reaction speed while ensuring the yield and shorten the preparation cycle; if the molar ratio of norbornene to dry ice is reduced, too little will lead to incomplete reaction and reduced reaction yield, and too much will cause the reaction temperature to be too low and the reaction rate to be reduced.

[0026] Furthermore, in step S2, the stirring time is 0.5 to 24 hours.

[0027] Furthermore, after the stirring is completed and the reaction temperature reaches room temperature, norbornene carboxylic acid is obtained by extraction and purification.

[0028] Furthermore, the extract is a mixture of a weak acid / weak acid aqueous solution and an organic solution, and the ratio of the weak acid / weak acid aqueous solution to the organic solution is 1:(1-10).

[0029] Preferably, the weak acid is dilute hydrochloric acid; the weak acidic aqueous solution is preferably an aqueous ammonium chloride solution; and the organic solution is preferably ethyl acetate, dichloromethane or chloroform.

[0030] Further, carbon dioxide is added to product A in the form of dry ice.

[0031] Since carbon dioxide is usually in a gaseous state, the reaction rate is relatively low when carbon dioxide is directly introduced into product A in a gaseous state, and gaseous carbon dioxide cannot be added all at once and needs to be introduced continuously, which leads to a prolonged reaction time. Therefore, adding carbon dioxide to product A in the form of dry ice can shorten the reaction cycle to a certain extent.

[0032] Furthermore, the preset reaction temperature is -78 to 100°C.

[0033] Preferably, the preset reaction temperature is -30 to 20°C.

[0034] It should be noted that, since the reaction temperature range disclosed in the present invention includes a low temperature range of -78 to 0°C, when the reaction is carried out at low temperature, the volatility of dry ice can be utilized in step S2 to achieve low temperature maintenance to a certain extent, without the need for additional control of the reaction temperature, thereby simplifying the preparation process.

[0035] The advantages of the present invention are:

[0036] 1. The method of the present invention is used to synthesize norbornene carboxylic acid. During the synthesis process, no toxic and explosive substances such as mercuric oxide, liquid bromine and hydrogen are required, thereby improving the safety of the synthesis.

[0037] 2. Under an inert atmosphere and a certain reaction temperature, potassium tert-butoxide, n-butyl lithium and dry ice are sequentially added to the organic solution of norbornene. Norbornene carboxylic acid can be prepared by continuous stirring. The preparation process is simple and the preparation steps are few, which is conducive to the promotion of actual production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The hydrogen nuclear magnetic resonance spectrum of norbornene carboxylic acid prepared by the preparation method described in Example 1 is shown in FIG. DETAILED DESCRIPTION

[0039] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Those skilled in the art will appreciate that the following embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0040] Embodiment 1

[0041] As an embodiment of the present invention, this embodiment provides a method for preparing norbornene carboxylic acid, which is as follows:

[0042] S1, maintaining a nitrogen atmosphere, dissolving 30 mmol of norbornene in tetrahydrofuran to obtain a norbornene solution, adjusting the reaction temperature to -78°C, stirring the norbornene solution, and adding a tetrahydrofuran solution of potassium tert-butoxide to the norbornene solution while stirring, wherein the molar ratio of potassium tert-butoxide to norbornene is 2:1; after the addition of the tetrahydrofuran solution of potassium tert-butoxide is completed, stirring is continued, and then a hexane solution of n-butyl lithium is added, wherein the molar ratio of norbornene to n-butyl lithium is 0.5:1, and stirring is continued for 0.5h to obtain product A;

[0043] S2. Maintaining a nitrogen atmosphere, carbon dioxide was introduced into product A at 78° C., and the carbon dioxide was completely introduced into product A within a certain period of time, wherein the molar ratio of norbornene to carbon dioxide was 1:10, and the product B was obtained by stirring for 0.5 h after the carbon dioxide was completely introduced; in this process, only the reaction temperature was ensured not to exceed the range of -78 to 100° C., and the temperature change within the reaction temperature was not interfered;

[0044] S3. After the reaction temperature reaches room temperature, add saturated aqueous ammonium chloride solution and ethyl acetate to product B for separation and extraction, and then purify by column to obtain norbornene carboxylic acid; wherein the volume ratio between the saturated aqueous ammonium chloride solution and the ethyl acetate is 1:1.

[0045] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of norbornene carboxylic acid prepared by the preparation method described in Example 1. According to the characteristic peaks at 6.92, 3.20, 3.00, and 1.9-1.0 ppm in the figure, it can be clearly seen that 1 H-NMR (400 MHz, acetone-d6, δ): 6.92 (d, J = 3 Hz, 1H), 3.20 (m, 1H), 3.00 (m, 1H), 1.9-1.0 (m, 6H); It can be confirmed that the product obtained by the preparation method described in Example 1 is norbornene carboxylic acid.

[0046] The preparation method described in Example 1 was used to prepare norbornene carboxylic acid by only changing the ratio between the reactants. The ratio of the reactants is shown in the following table:

[0047]

[0048] Embodiment 5

[0049] As an embodiment of the present invention, this embodiment provides a method for preparing norbornene carboxylic acid, which is as follows:

[0050] S1. Under a nitrogen atmosphere, 30 mmol of norbornene was dissolved in ether to obtain a norbornene solution. The reaction temperature was adjusted to -30°C, and the norbornene solution was stirred. While stirring, a tetrahydrofuran solution of potassium tert-butoxide was added to the norbornene solution, wherein the molar ratio of potassium tert-butoxide to norbornene was 10:1. After the addition of the tetrahydrofuran solution of potassium tert-butoxide was completed, stirring was continued, and then a hexane solution of n-butyl lithium was added, wherein the molar ratio of norbornene to n-butyl lithium was 1:10, and stirring was continued for 24 hours to obtain product A.

[0051] S2, maintaining a nitrogen atmosphere, adding dry ice to product A at -20°C, wherein the molar ratio of norbornene to dry ice is 1:1000, and then stirring for 24 hours to obtain product B; in this process, only the reaction temperature is ensured not to exceed the range of -78 to 100°C, and the temperature change within the reaction temperature is not interfered;

[0052] S3. After the reaction temperature reaches room temperature, add saturated aqueous ammonium chloride solution and dichloromethane to product B for liquid separation and extraction; then purify by column to obtain norbornene carboxylic acid; wherein the volume ratio between the saturated aqueous ammonium chloride solution and the dichloromethane is 1:1.

[0053] Embodiment 6

[0054] As an embodiment of the present invention, this embodiment provides a method for preparing norbornene carboxylic acid, which is as follows:

[0055] S1. Under a nitrogen atmosphere, 30 mmol of norbornene is dissolved in tetrahydrofuran to obtain a norbornene solution, the reaction temperature is adjusted to 0° C., the norbornene solution is stirred, and a tetrahydrofuran solution of potassium tert-butoxide is added to the norbornene solution while stirring, wherein the molar ratio of potassium tert-butoxide to norbornene is 6:1; after the addition of the propylene oxide solution of potassium tert-butoxide is completed, stirring is continued, and then a hexane solution of n-butyl lithium is added, wherein the molar ratio of norbornene to n-butyl lithium is 6:1, and stirring is continued for 10 hours to obtain product A;

[0056] S2. Maintaining a nitrogen atmosphere, adding dry ice to product A at -30°C, wherein the molar ratio of norbornene to dry ice is 1:600, and then stirring for 18 hours to obtain product B; in this process, only ensuring that the reaction temperature does not exceed the range of -30 to 20°C, and not interfering with the temperature change within the reaction temperature;

[0057] S3. After the reaction temperature reaches room temperature, add saturated aqueous ammonium chloride solution and chloroform to product B for separation and extraction; then purify by column to obtain norbornene carboxylic acid; wherein the volume ratio of saturated aqueous ammonium chloride solution to chloroform is 1:10.

[0058] Embodiment 7

[0059] As an embodiment of the present invention, this embodiment provides a method for preparing norbornene carboxylic acid, which is as follows:

[0060] S1. Under a nitrogen atmosphere, 30 mmol of norbornene was dissolved in ether to obtain a norbornene solution. The reaction temperature was adjusted to 60° C., and the norbornene solution was stirred. While stirring, a potassium tert-butoxide ether solution was added to the norbornene solution, wherein the molar ratio of potassium tert-butoxide to norbornene was 1:1. After the addition of the potassium tert-butoxide ether solution was completed, stirring was continued, and then a hexane solution of n-butyl lithium was added, wherein the molar ratio of norbornene to n-butyl lithium was 1:1. Stirring was continued for 4 hours to obtain product A.

[0061] S2, maintaining a helium atmosphere, adding dry ice to product A at 80° C., wherein the molar ratio of norbornene to dry ice is 1:730, and then stirring for 12 hours to obtain product B; in this process, only the reaction temperature is ensured not to exceed the range of -78 to 100° C., and the temperature change within the reaction temperature is not interfered;

[0062] S3. After the reaction temperature reaches room temperature, add saturated aqueous ammonium chloride solution and chloroform to product B for separation and extraction; then purify by column to obtain norbornene carboxylic acid; wherein the volume ratio of saturated aqueous ammonium chloride solution to chloroform is 1:6.

[0063] Embodiment 8

[0064] As an embodiment of the present invention, this embodiment provides a method for preparing norbornene carboxylic acid, which is as follows:

[0065] S1. Under argon, 30 mol of norbornene is dissolved in tetrahydrofuran to obtain a norbornene solution, the reaction temperature is adjusted to -30°C, the norbornene solution is stirred, and a tetrahydrofuran solution of potassium tert-butoxide is added to the norbornene solution while stirring, wherein the molar ratio of potassium tert-butoxide to norbornene is 4:1; after the addition of the tetrahydrofuran solution of potassium tert-butoxide is completed, stirring is continued, and then a hexane solution of n-butyl lithium is added, wherein the molar ratio of norbornene to n-butyl lithium is 1:1.5; after the addition of the hexane solution of n-butyl lithium is completed, the reaction temperature is adjusted to 20°C, and stirring is continued for 5 hours to obtain product A;

[0066] S2, maintaining an argon atmosphere, adding dry ice to product A at 0°C, wherein the molar ratio of norbornene to dry ice is 1:20, and stirring for 2 hours to obtain product B; in this process, only ensuring that the reaction temperature does not exceed the range of -78 to 100°C, and not interfering with the temperature change within the reaction temperature;

[0067] S3. After the reaction temperature reaches room temperature, add saturated aqueous ammonium chloride solution and chloroform to product B for separation and extraction; then purify by column to obtain norbornene carboxylic acid; wherein the ratio between the saturated aqueous ammonium chloride solution and ethyl acetate is 1:4.

[0068] Embodiment 9

[0069] As an embodiment of the present invention, this embodiment provides a method for preparing norbornene carboxylic acid. The only difference from Example 1 is that carbon dioxide is added in the form of dry ice, which is intended to investigate the difference between gaseous carbon dioxide and solid carbon dioxide. The specific preparation method is as follows:

[0070] S1, maintaining a nitrogen atmosphere, dissolving 30 mmol of norbornene in tetrahydrofuran to obtain a norbornene solution, adjusting the reaction temperature to -78°C, stirring the norbornene solution, and adding a tetrahydrofuran solution of potassium tert-butoxide to the norbornene solution while stirring, wherein the molar ratio of potassium tert-butoxide to norbornene is 2:1; after the addition of the tetrahydrofuran solution of potassium tert-butoxide is completed, stirring is continued, and then a hexane solution of n-butyl lithium is added, wherein the molar ratio of norbornene to n-butyl lithium is 0.5:1, and stirring is continued for 0.5h to obtain product A;

[0071] S2, maintaining a nitrogen atmosphere, adding dry ice to product A at -78°C, wherein the molar ratio of norbornene to dry ice is 1:10, and then stirring for 0.5h to obtain product B; in this process, only the reaction temperature is ensured not to exceed the range of -78 to 100°C, and the temperature change within the reaction temperature is not interfered;

[0072] At 78° C., carbon dioxide is introduced into product A, and the carbon dioxide is completely introduced into product A within a certain period of time, wherein the molar ratio of norbornene to carbon dioxide is 1:10, and after the carbon dioxide is completely introduced, the mixture is stirred for 0.5 h to obtain product B; in this process, only the reaction temperature is ensured not to exceed the range of -78 to 100° C., and the temperature change within the reaction temperature is not interfered;

[0073] S3. After the reaction temperature reaches room temperature, add saturated aqueous ammonium chloride solution and ethyl acetate to product B for separation and extraction, and then purify by column to obtain norbornene carboxylic acid; wherein the volume ratio between the saturated aqueous ammonium chloride solution and the ethyl acetate is 1:1.

[0074] Embodiment 10

[0075] As another embodiment of the present invention, the difference between this embodiment and the sixth embodiment is that the ratio of norbornene to dry ice is different.

[0076] Specifically, S1. Under argon, 30 mol of norbornene is dissolved in tetrahydrofuran to obtain a norbornene solution, the reaction temperature is adjusted to -30°C, the norbornene solution is stirred, and a tetrahydrofuran solution of potassium tert-butoxide is added to the norbornene solution while stirring, wherein the molar ratio of potassium tert-butoxide to norbornene is 4:1; after the addition of the tetrahydrofuran solution of potassium tert-butoxide is completed, stirring is continued, and then a hexane solution of n-butyl lithium is added, wherein the molar ratio of norbornene to n-butyl lithium is 1:1.5, and after the addition of the hexane solution of n-butyl lithium is completed, the reaction temperature is adjusted to 20°C, and stirring is continued for 5 hours to obtain product A;

[0077] S2, maintaining an argon atmosphere, adding dry ice to product A at 0°C, wherein the molar ratio of norbornene to dry ice is 1:800, and stirring for 2 hours to obtain product B; in this process, only the reaction temperature is ensured not to exceed the range of -78 to 100°C, and the temperature change within the reaction temperature is not interfered;

[0078] S3. After the reaction temperature reaches room temperature, add saturated aqueous ammonium chloride solution and chloroform to product B for separation and extraction; then purify by column to obtain norbornene carboxylic acid; wherein the ratio between the saturated aqueous ammonium chloride solution and ethyl acetate is 1:4.

[0079] Embodiment 11

[0080] As another embodiment of the present invention, the difference between this embodiment and the fourth embodiment is that the ratio of norbornene to dry ice is different, which is as follows:

[0081] S1, maintaining a nitrogen atmosphere, dissolving 30 mmol of norbornene in tetrahydrofuran to obtain a norbornene solution, adjusting the reaction temperature to -78°C, stirring the norbornene solution, and adding a tetrahydrofuran solution of potassium tert-butoxide to the norbornene solution while stirring, wherein the molar ratio of potassium tert-butoxide to norbornene is 10:1; after the addition of the tetrahydrofuran solution of potassium tert-butoxide is completed, stirring is continued, and then a hexane solution of n-butyl lithium is added, wherein the molar ratio of norbornene to n-butyl lithium is 1:10, and stirring is continued for 0.5h to obtain product A;

[0082] S2. Maintaining a nitrogen atmosphere, carbon dioxide was introduced into product A at 78° C., and the carbon dioxide was completely introduced into product A within a certain period of time, wherein the molar ratio of norbornene to carbon dioxide was 1:60, and the product B was obtained by stirring for 0.5 h after the carbon dioxide was completely introduced; in this process, only the reaction temperature was ensured not to exceed the range of -78 to 100° C., and the temperature change within the reaction temperature was not interfered;

[0083] S3. After the reaction temperature reaches room temperature, add saturated aqueous ammonium chloride solution and ethyl acetate to product B for separation and extraction, and then purify by column to obtain norbornene carboxylic acid; wherein the volume ratio between the saturated aqueous ammonium chloride solution and the ethyl acetate is 1:1.

[0084] Comparative Example 1

[0085] This comparative example is a preparation method of norbornene carboxylic acid disclosed by Yu Jinquan's research group mentioned in the background technology, and the preparation process is as follows:

[0086]

[0087] The specific steps include:

[0088] S1. Dissolving nadic anhydride in methanol to obtain a nadic anhydride solution, adjusting the reaction temperature to 0°C, stirring the nadic anhydride solution, and adding triethylamine to the nadic anhydride solution while stirring, wherein the molar ratio of triethylamine to nadic anhydride is 1.3:1; after the addition of triethylamine, slowly raising the reaction temperature to room temperature and continuing stirring for 1 hour to obtain product A, then adding 6M hydrochloric acid solution and ethyl acetate for liquid separation and extraction, wherein the volume ratio of 6M hydrochloric acid solution to ethyl acetate is 1:1; then draining the organic phase to obtain a crude product of product A;

[0089] S2, dissolving product A in methanol to obtain a product A solution and slowly adding palladium carbon, wherein the molar ratio of palladium carbon to product A is 0.025:1; replacing the atmosphere of the system with hydrogen and inserting a balloon filled with hydrogen, the reaction mixture is stirred at room temperature overnight and then filtered through diatomaceous earth, and the solvent is evaporated to obtain product B;

[0090] S3, add dichloromethane to the mixture of product B, red HgO and anhydrous magnesium sulfate to obtain a dichloromethane suspension of product B, red HgO and anhydrous magnesium sulfate, wherein the molar ratio of product B, red HgO and anhydrous magnesium sulfate is 1:1.5:1.13, adjust the reaction temperature until dichloromethane begins to reflux, and then use a pressure equalization funnel to add a dichloromethane solution of liquid bromine within 40-50 minutes, wherein the molar ratio of product B to liquid bromine is 1:1.5. After the addition is completed, continue to reflux for 1.5 hours, then cool to room temperature, and quench with saturated sodium bicarbonate aqueous solution, stir vigorously for 15 minutes and filter through diatomaceous earth. The organic phase is washed with saturated sodium bicarbonate aqueous solution, water and sodium chloride aqueous solution and then concentrated to obtain product C; wherein the volume ratio of organic phase, saturated sodium bicarbonate aqueous solution, water and sodium chloride aqueous solution is 1:1:1:1;

[0091] S4. Dissolve product C in chloroform to obtain a chloroform solution of product C, and then add 1,8-diazobispiro[5.4.0]undec-7-ene, wherein the molar ratio of product C to 1,8-diazobispiro[5.4.0]undec-7-ene is 1:2. Heat the above solution to reflux chloroform and react for 2 hours. After the reaction temperature is cooled, pour it into a mixture of ice and 6M hydrochloric acid. The aqueous phase is extracted with dichloromethane, wherein the volume ratio of water to dichloromethane is 1:1; the organic layers are combined, dried over magnesium sulfate, and concentrated. The mixture is purified on silica gel and then distilled under vacuum to obtain product D.

[0092] S5, dissolving product D in tetrahydrofuran to obtain a tetrahydrofuran solution of product D, and then adding lithium hydroxide at room temperature, wherein the molar ratio of product C to lithium hydroxide is 1:5. The above solution is stirred for reaction for 12 hours. After the reaction is completed, the organic phase is separated and extracted with a saturated aqueous ammonium chloride solution, wherein the volume ratio of the organic phase to the saturated aqueous ammonium chloride solution is 1:1; separation and extraction are performed; and then column purification is performed to obtain norbornene carboxylic acid.

[0093] Experimental Example 1

[0094] In this experimental example, the yield of norbornene carboxylic acid prepared by some of the preparation methods in Examples 1 to 9 and Comparative Example 1 is calculated. It should be noted that the yield here refers to the yield of the entire process of preparing norbornene carboxylic acid using norbornene as a raw material. The calculation formula of the yield in this experimental example is:

[0095] (actual output / theoretical output)×100%;

[0096] At the same time, the actual reaction temperature during the preparation process of each embodiment was measured, and the calculation and measurement results are shown in the following table:

[0097]

[0098] As can be seen from the above table, the yield of norbornene carboxylic acid prepared by the preparation method of the present invention is greatly improved compared with the existing preparation method in the comparative example, and the preparation process is simple, avoiding the use of highly toxic, explosive and dangerous chemicals, and is easy to promote industrialization.

[0099] Secondly, it can be seen from the above table that Example 1, Example 2 and Example 3 are norbornene carboxylic acids prepared by the same preparation method with different proportions. As the molar ratio of potassium tert-butoxide, n-butyl lithium, carbon dioxide and norbornene decreases, the yield gradually decreases, but the decrease is relatively low, and the yield is still higher than that of the solution corresponding to the comparative example, indicating that the preparation method of the present invention can produce norbornene carboxylic acid with a relatively high yield.

[0100] Based on the provided examples and data, the following can be summarized about the effects of different operations or raw material ratios on the preparation method of norbornene carboxylic acid:

[0101] The molar ratio of potassium tert-butoxide, n-butyl lithium and norbornene:

[0102] In Examples 1, 2, 3 and 4, the molar ratios of potassium tert-butoxide to norbornene are 2:1, 1.2:1, 1.5:1 and 10:1, respectively; the molar ratios of n-butyl lithium to norbornene are 2:1, 1.2:1, 1.5:1 and 10:1, respectively; it can be seen that within the ratio range specified in the present application, as the molar ratios of n-butyl lithium, potassium tert-butoxide and norbornene increase, excess potassium tert-butoxide and n-butyl lithium can neutralize trace amounts of water in the system, thereby increasing the probability of norbornene reacting with the base, and ultimately the yield of norbornene carboxylic acid is also increased accordingly.

[0103] The molar ratio of carbon dioxide to norbornene:

[0104] In Examples 1, 2, 3 and 4, the molar ratio of carbon dioxide to norbornene is 10: 1, 10: 1, 4: 1 and 100: 1, respectively. It can be seen that the molar ratio of carbon dioxide also has an effect on the yield. The molar ratio of carbon dioxide in Example 4 is significantly higher, resulting in a higher yield.

[0105] Furthermore, the difference between Example 9 and Example 1 is only that the form of adding carbon dioxide is different. The corresponding yield of Example 1 is 77%, while the yield of Example 9 is 83%, which shows that adding carbon dioxide in the form of dry ice is more conducive to improving the yield; this is because, compared with gaseous carbon dioxide, dry ice can ensure that the reaction system is at a relatively lower temperature during the volatilization process, which is more conducive to the reaction, and thus can further improve the yield; at the same time, from the comparison between Example 5 and Example 6, it can be seen that although the addition of dry ice can ensure a low temperature in the reaction system, too much dry ice may cause the temperature of the reaction system to be too low, and a high yield cannot be achieved.

[0106] In general, the change of molar ratio can significantly affect the yield of norbornene carboxylic acid, and generally a higher molar ratio of potassium tert-butoxide, n-butyl lithium and carbon dioxide helps to improve the yield. In addition, controlling the reaction temperature is also an important factor to ensure that the reaction proceeds smoothly. These changes can be adjusted according to specific production requirements to obtain optimal preparation conditions. In addition, compared with Comparative Example 1, the preparation method in these embodiments can improve the yield and reduce the use of highly toxic, explosive and hazardous chemicals, which is conducive to industrial promotion.

[0107] The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modifications to equivalent embodiments of equivalent changes by using the technical content suggested above without departing from the scope of the technical solution of the present invention. The implementation scheme in the above embodiment can also be further combined or replaced. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the solution of the present invention.

Claims

1. A method for preparing norbornene carboxylic acid, characterized in that: The steps include: S1. Under an inert atmosphere and a preset reaction temperature, potassium tert-butoxide and n-butyl lithium are sequentially added to a norbornene solution, and the mixture is continuously stirred to obtain a product A; S2, after completing step S1, maintaining an inert atmosphere, introducing carbon dioxide into product A at a preset reaction temperature and continuously stirring to obtain norbornene carboxylic acid; In step S2, the molar ratio of carbon dioxide to norbornene is 5 to 1000:

1.

2. The method for preparing norbornene carboxylic acid according to claim 1, characterized in that: Step S1 is specifically as follows: Dissolving norbornene in an organic solvent under an inert atmosphere, adjusting the temperature to a preset reaction temperature, adding a potassium tert-butoxide solution to the norbornene solution under stirring, and then adding an n-butyl lithium solution, and continuing to stir to obtain a product A; The organic solvent for dissolving norbornene is an inactive organic solvent; the solvent in the potassium tert-butoxide solution is selected from an ether solvent or tetrahydrofuran; the solvent in the n-butyl lithium solution is hexane; Preferably, the organic solvent for dissolving norbornene is at least one of tetrahydrofuran and diethyl ether.

3. The method for preparing norbornene carboxylic acid according to claim 1, characterized in that: In step S1, the molar ratio of norbornene to potassium tert-butoxide is 1:0.5-10; The molar ratio of norbornene to n-butyllithium is 1:0.5-10.

4. The method for preparing norbornene carboxylic acid according to any one of claims 1 to 3, characterized in that: In step S1, stirring is continued for 0.5 to 24 hours to prepare substance A, and then proceeding to step S2.

5. The method for preparing norbornene carboxylic acid according to any one of claims 1 to 4, characterized in that: In step S2, the molar ratio of carbon dioxide to norbornene is 10 to 100:

1.

6. The method for preparing norbornene carboxylic acid according to any one of claims 1 to 4, characterized in that: In step S2, the stirring time is 0.5 to 24 hours.

7. The method for preparing norbornene carboxylic acid according to claim 6, characterized in that: After stirring is completed and the reaction temperature reaches room temperature, norbornene carboxylic acid is obtained through extraction and purification.

8. The method for preparing norbornene according to claim 7, characterized in that: The extract is a mixture of a weak acid / weak acid aqueous solution and an organic solution, and the ratio of the weak acid / weak acid aqueous solution to the organic solution is 1:(1-10); Preferably, the weak acid is dilute hydrochloric acid; the weak acidic aqueous solution is preferably an aqueous ammonium chloride solution; and the organic solution is preferably ethyl acetate, dichloromethane or chloroform.

9. The method for preparing norbornene carboxylic acid according to any one of claims 5 to 8, characterized in that: In step S2, carbon dioxide is added to product A in the form of dry ice.

10. The method for preparing norbornene carboxylic acid according to any one of claims 1 to 9, characterized in that: The preset reaction temperature is -78~100℃; Preferably, the preset reaction temperature is -30 to 20°C.

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