A method for purifying cyclobutane tetracarboxylic acid ester

Abstract

The present invention belongs to the field of fine chemicals, and specifically relates to a method for purifying cyclobutane tetracarboxylic acid ester. The purification method of the present invention comprises the following steps: placing a crude cyclobutane tetracarboxylic acid ester in a heating device for heat treatment, placing a plate in the heating device, and sublimating and condensing impurities in the crude cyclobutane tetracarboxylic acid ester on the surface of the plate under heating conditions, and the impurities that are not sublimated are high-purity cyclobutane tetracarboxylic acid ester; wherein the temperature of the heat treatment is 30 to 80°C, and the heat transfer coefficient of the plate is lower than the heat transfer coefficient of the inner wall material of the heating device. The present invention utilizes the difference in sublimation points between the cyclobutane tetracarboxylic acid ester and the impurities in the crude cyclobutane tetracarboxylic acid ester, and the difference in thermal conductivity between the plate and the inner wall material of the heating device, and can achieve solid-solid separation of the cyclobutane tetracarboxylic acid ester and the impurities through heating treatment, and the obtained cyclobutane tetracarboxylic acid ester has high purity, and no additional solvent is required, thereby avoiding environmental pollution.

Description

Technical Field

[0001] The invention belongs to the field of fine chemicals, and in particular relates to a method for purifying cyclobutane tetracarboxylic acid ester. Background Art

[0002] Cyclobutane tetracarboxylic acid esters are key intermediate raw materials for synthesizing cyclobutane tetracarboxylic dianhydride. CN1765870A discloses a path for preparing cyclobutane tetracarboxylic acid esters by photocyclization of fumaric acid esters. The method for preparing cyclobutane tetracarboxylic dianhydride has the characteristics of high yield and is conducive to industrial production. However, the application does not disclose the purity and purification method of cyclobutane tetracarboxylic acid esters prepared by photocyclization.

[0003] Studies have found that cyclobutane tetracarboxylic acid ester and its raw material fumaric acid ester have similar polarity and are difficult to separate by chromatographic column method, and the chromatographic column method uses expensive instruments and is costly. How to achieve convenient and efficient purification to obtain high-purity cyclobutane tetracarboxylic acid ester is still one of the problems that need to be solved in the art. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a method for purifying cyclobutane tetracarboxylic acid ester, which is simple and efficient, and the obtained finished cyclobutane tetracarboxylic acid ester has high purity.

[0005] The present invention provides a method for purifying cyclobutane tetracarboxylic acid ester, comprising the following steps: placing a crude cyclobutane tetracarboxylic acid ester in a heating device for heat treatment, placing a plate in the heating device, and sublimating and condensing impurities in the crude cyclobutane tetracarboxylic acid ester on the surface of the plate under heating conditions, and the impurities that are not sublimated are high-purity cyclobutane tetracarboxylic acid ester;

[0006] Wherein, the temperature of the heat treatment is 30-80° C., and the heat transfer coefficient of the plate is lower than the heat transfer coefficient of the inner wall material of the heating device.

[0007] The present invention utilizes the difference in sublimation temperature between cyclobutane tetracarboxylic acid ester and impurities (such as unreacted raw materials) in the crude cyclobutane tetracarboxylic acid ester, as well as the difference in thermal conductivity between the plate and the inner wall material of the heating device, and can effectively achieve solid-solid separation of cyclobutane tetracarboxylic acid ester and impurities through heat treatment. The obtained cyclobutane tetracarboxylic acid ester has high purity, and no additional solvent needs to be added during the purification process, thereby avoiding environmental pollution.

[0008] Preferably, the heat treatment temperature is 40-60°C.

[0009] Preferably, the heat treatment time is 1 to 5 hours, more preferably 3 to 5 hours.

[0010] Preferably, the heat transfer coefficient of the plate at 20°C is lower than 5.0 W / (m·K), and more preferably, the heat transfer coefficient of the plate at 20°C is lower than 1.0 W / (m·K).

[0011] Preferably, the plate material includes at least one of a glass plate and a plastic plate.

[0012] Preferably, the plastic plate is made of a high temperature resistant material, including but not limited to polypropylene (PP), nylon (PA), polycarbonate (PC), polytetrafluoroethylene (PTFE), etc.

[0013] Preferably, the heat transfer coefficient of the inner wall material of the heating device at 20°C is ≥10 W / (m·K), and more preferably, the heat transfer coefficient of the inner wall material of the heating device at 20°C is ≥16 W / (m·K).

[0014] Preferably, the inner wall material of the heating device includes at least one of stainless steel and iron.

[0015] Preferably, the heating device is a vacuum drying oven.

[0016] Preferably, the purification process is carried out under vacuum, and the vacuum degree of the heating equipment is lower than 2000Pa, more preferably lower than 1000Pa, including but not limited to 200Pa, 300Pa, 500Pa, 700Pa, 1000Pa, etc.

[0017] Preferably, the crude cyclobutane tetracarboxylic acid ester can be placed directly in the heating device, or the crude cyclobutane tetracarboxylic acid ester can be placed in a container and then placed in the heating device; the material of the container can be the same as or different from the material of the inner wall of the heating device, and the material of the container is a metal material, including but not limited to stainless steel, iron, copper, aluminum, etc.

[0018] Preferably, the main components of the crude cyclobutane tetracarboxylic ester include cyclobutane tetracarboxylic ester and trans-butene dicarboxylic ester.

[0019] Preferably, the mass percentage of cyclobutane tetracarboxylic acid ester in the crude cyclobutane tetracarboxylic acid ester is above 80%, more preferably above 84%.

[0020] Preferably, the purity of the cyclobutane tetracarboxylic acid ester after the purification treatment is ≥99%, more preferably ≥99.6%.

[0021] Preferably, the yield of cyclobutane tetracarboxylic acid ester in the crude cyclobutane tetracarboxylic acid ester is ≥97.2%.

[0022] Preferably, the source of the crude cyclobutane tetracarboxylic acid ester is not limited, and it can be commercially available cyclobutane tetracarboxylic acid ester of lower purity, or it can be an intermediate product or crude product in the production process. The present invention is illustrated by taking the crude cyclobutane tetracarboxylic acid ester prepared by photocyclization reaction of trans-butylene dicarboxylic acid ester as an example.

[0023] Preferably, the cyclobutane tetracarboxylate has the following general formula:

[0024]

[0025] Among them, R 1 , R 2 , R 3 , R 4 Can be independently selected from C 1 ~C 4 Alkyl; more preferably R 1 , R 2 , R 3 , R 4 It can be independently selected from one of methyl and ethyl.

[0026] Preferably, the cyclobutane tetracarboxylate is prepared by photocyclization of trans-butene dicarboxylate, and the general formula of the trans-butene dicarboxylate is as follows:

[0027]

[0028] Among them, R 5 , R 6 Independently selected from C 1 ~C 4 Alkyl; more preferably R 5 , R 6 Independently selected from C 1 ~C 3 Alkyl; more preferably R 5 , R 6 It is methyl or ethyl.

[0029] Preferably, the temperature of the light irradiation ring is 10 to 30° C., more preferably 10 to 20° C.; the time of the light irradiation ring is 18 to 30 hours, more preferably about 24 hours.

[0030] Preferably, water is also included in the preparation process of the cyclobutane tetracarboxylic acid ester, and the mass ratio of the trans-butene dicarboxylic acid ester to water is 1:8-15, more preferably 1:10-13.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] (1) The present invention uses a simple heat treatment method to sublime the unreacted fumarate raw material in the crude cyclobutane tetracarboxylic acid ester and condense it on a plate with a low heat transfer coefficient, thereby separating the fumarate from the cyclobutane tetracarboxylic acid ester. The operation is simple and the effect is remarkable.

[0033] (2) The present invention realizes the solid-solid separation of cyclobutane tetracarboxylic acid ester and unreacted fumarate raw material without adding additional solvent, thus avoiding environmental pollution;

[0034] (3) The present invention provides a low heat transfer coefficient plate in the vacuum drying oven, which is beneficial to the collection of fumarate raw materials and avoids material waste.

[0035] (4) The present invention adopts a low-temperature sublimation process and can use ordinary vacuum drying equipment. It does not require high-vacuum multi-temperature zone sublimation furnace equipment, has low investment cost and energy consumption, and can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0037] Figure 1 is a gas chromatogram of a crude product of tetramethyl cyclobutanetetracarboxylate used in a specific embodiment of the present invention;

[0038] Figure 2 This is a gas chromatogram of the finished product tetramethyl cyclobutanetetracarboxylate obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0040] The raw materials used in the following examples, unless otherwise specified, can be obtained from conventional commercial sources; the processes used, unless otherwise specified, are conventional processes in the art; the operating temperatures used, unless otherwise specified, are room temperature (20±5° C.).

[0041] The preparation process of tetramethyl cyclobutanetetracarboxylate used in the embodiment of the present invention is as follows:

[0042] 60 g of dimethyl fumarate and 650 g of water were added into a 1 L photocatalytic reaction device, the reaction temperature was controlled at 10-20° C., and a high-pressure mercury lamp was used for 24 h under stirring conditions. The crude product of tetramethyl cyclobutanetetracarboxylate was obtained after filtration and drying.

[0043] The gas phase analysis spectrum of crude cyclobutane tetracarboxylic acid tetramethyl ester is as follows Figure 1 , wherein the purity of tetramethyl cyclobutanetetracarboxylate is 84.12%, wherein most (15.2%) of the impurities are unreacted dimethyl fumarate raw materials.

[0044] Table 1 GC analysis results of crude cyclobutane tetracarboxylic acid tetramethyl ester

[0045]

[0046] Example 1

[0047] 10 g of the above-mentioned crude tetramethyl cyclobutanetetracarboxylate was placed in a vacuum drying oven with a glass plate, and heated at 40° C. for 5 h under a vacuum degree of less than 200 Pa to obtain 8.3 g of high-purity cyclobutanetetracarboxylate (GC purity 99.7%). Figure 2 ); 0.9 g of dimethyl fumarate (GC purity 97%) was collected on a glass plate in a vacuum drying oven.

[0048] Table 2 GC analysis results of the purified finished product tetramethyl cyclobutanetetracarboxylate

[0049]

[0050] Example 2

[0051] 10 g of the above-mentioned crude tetramethyl cyclobutanetetracarboxylate was placed in a vacuum drying oven with a glass plate inside, and heated at 60°C for 3 h under a vacuum degree below 1000 Pa to obtain 8.2 g of high-purity cyclobutanetetracarboxylic acid ester (GC purity 99.7%); 1.2 g of dimethyl fumarate (GC purity 96%) was collected on the glass plate in the vacuum drying oven.

[0052] Example 3

[0053] 10 g of the above-mentioned crude tetramethyl cyclobutanetetracarboxylate was placed in a vacuum drying oven with a PP plate inside, and heated at 50°C for 5 h under a vacuum degree below 300 Pa to obtain 8.5 g of high-purity cyclobutanetetracarboxylic acid ester (GC purity 99.7%); 1.0 g of dimethyl fumarate (GC purity 98%) was collected on the PP plate in the vacuum drying oven.

[0054] Comparative Example 1

[0055] The main difference from Example 1 is that the heating temperature is adjusted to 90° C., and the other conditions are the same as those in Example 1; 8.1 g of high-purity cyclobutane tetracarboxylic acid ester (GC purity 99.5%) is obtained; and 0.9 g of dimethyl fumarate (GC purity 90%) is collected on a glass plate in a vacuum drying oven.

[0056] Comparative Example 2

[0057] The main difference from Example 1 is that the low thermal conductivity plate of the vacuum drying oven is removed, and other conditions are the same as Example 1; 8.9 g of high-purity cyclobutane tetracarboxylic acid ester (GC purity 89%) is obtained; 0.5 g of dimethyl fumarate (GC purity 96%) is collected on the inner wall of the vacuum drying oven.

[0058] Test example

[0059] GC analysis:

[0060] The above-mentioned crude tetramethyl cyclobutanetetracarboxylate and the purified tetramethyl cyclobutanetetracarboxylate were dissolved in acetonitrile solution at a concentration of 25 mg / mL, and the solution was detected according to the following chromatographic conditions:

[0061] Instrument: Fuli 9720Plus, FID hydrogen flame ionization detector;

[0062] Chromatographic column: DB-5 weak polar capillary (30m*0.32mm*0.50μm) containing 5% diphenyl-95% dimethylpolysiloxane as stationary phase;

[0063] Carrier gas: nitrogen, flow rate 1 mL / min;

[0064] Flow rate: 1 mL / min;

[0065] Split ratio: 30:1;

[0066] Injection volume: 1 μL;

[0067] Sample port temperature: 300℃;

[0068] Detector temperature: 300°C;

[0069] Temperature program: the initial column temperature is 100°C, maintained for 1 min; then increased to 150°C at 10°C / min; then increased to 280°C at 30°C / min, maintained for 10 min.

[0070] Yield = actual mass × 100% / theoretical mass = finished product output × finished product purity × 100% / (raw material amount × raw material purity)

[0071] Table 3 Finished product properties of Examples 1 to 3 and Comparative Examples 1 to 2

[0072]

[0073] Depend on Figure 1As shown in Table 1, the peaks at 5.798min and 10.849min correspond to the raw material dimethyl fumarate and the product tetramethyl cyclobutanetetracarboxylate, respectively. It can be seen that the main components of the crude tetramethyl cyclobutanetetracarboxylate obtained by the photocyclization reaction of dimethyl fumarate are the raw material dimethyl fumarate and the product tetramethyl cyclobutanetetracarboxylate. Figure 2 As shown in Tables 2 to 3, the present invention utilizes the characteristics of the lower sublimation temperature of the fumarate raw material and adopts a low heat transfer coefficient plate to achieve solid-solid separation of the raw material dimethyl fumarate and the product cyclobutane tetracarboxylic acid tetramethyl ester, without the need to add additional solvent, and the purity of the obtained cyclobutane tetracarboxylic acid tetramethyl ester is above 99.6%, and the yield is high; the purity of dimethyl fumarate is above 96%. However, the heating temperature of Comparative Example 1 is too high, and part of the product sublimates with the raw material dimethyl fumarate, resulting in a low recovery amount of the finished product cyclobutane tetracarboxylic acid tetramethyl ester and a decrease in the purity of dimethyl fumarate; after the low thermal conductivity plate is removed from Comparative Example 2, it is not conducive to the condensation of dimethyl fumarate, resulting in a low purity of dimethyl fumarate, and the separation efficiency and purity of cyclobutane tetracarboxylic acid tetramethyl ester are significantly reduced.

[0074] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for purifying cyclobutane tetracarboxylic acid ester, characterized in that: The method comprises the following steps: placing a crude cyclobutane tetracarboxylic acid ester product in a heating device for heat treatment, placing a plate in the heating device, and sublimating and condensing impurities in the crude cyclobutane tetracarboxylic acid ester product on the surface of the plate under heating conditions, and the impurities that are not sublimated are high-purity cyclobutane tetracarboxylic acid ester; Wherein, the temperature of the heat treatment is 40-60°C, the heat transfer coefficient of the plate is lower than the heat transfer coefficient of the inner wall material of the heating device, the purification process is carried out under vacuum, and the vacuum degree in the purification process is lower than 2000Pa; The plate material includes at least one of a glass plate and a plastic plate; the inner wall material of the heating device includes at least one of stainless steel and iron.

2. The purification method according to claim 1, characterized in that The heat treatment time is 1 to 5 h.

3. The purification method according to claim 1, characterized in that The heating device is a vacuum drying oven.

4. The purification method according to claim 1, characterized in that The main components of the crude cyclobutane tetracarboxylic acid ester include cyclobutane tetracarboxylic acid ester and trans-butene dicarboxylic acid ester.

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