A process for the preparation of cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol

Abstract

This invention discloses a method for preparing cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol. The method comprises the following steps: S1: Under a hydrogen atmosphere, using 2,2,4,4-tetramethyl-1,3-cyclobutanedione as a raw material, a reaction is carried out in the presence of a modified transition metal catalyst and an auxiliary agent to obtain a cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol reaction solution; S2: The auxiliary agent is separated to obtain crude cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol; S3: After washing and drying, cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol product with a purity of over 99.9% is obtained. This method features mild reaction conditions, a simple process, recyclable catalyst, and the ability to obtain pure cis-structured CBDO product, providing high-quality monomers for downstream polyester production.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis, specifically to a method for preparing cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol. Background Technology

[0002] 2,2,4,4-Tetramethyl-1,3-cyclobutanediol (CBDO) is an important aliphatic glycol polyester monomer, primarily used in the production of high-performance copolyester products to replace traditional polycarbonate (PC). The molecular formula of CBDO is C8H2O. 16 O2 has two isomers, cis and trans, as shown in the following formula. The cis-trans ratio of CBDO (the mass ratio of cis CBDO to trans CBDO) has a significant impact on subsequent copolyesterification processes and even product performance. A higher proportion of the cis isomer results in superior glass transition temperature, impact strength, and crystallization rate; therefore, increasing the cis-trans isomer ratio is desirable.

[0003]

[0004] Currently, the preparation of 2,2,4,4-tetramethyl-1,3-cyclobutanedione from 2,2,4,4-tetraalkyl-1,3-cyclobutanediol mainly utilizes noble metal catalysts. For example, patent US20080132742A1 discloses the preparation of CBDO with a cis-trans ratio of 0.34–1.68 using a Cu-based catalyst; patent US20080132738A1 discloses the preparation of CBDO with a cis-trans ratio of 0.4–1.2 using a Ni-based catalyst; patent US8420868B2 discloses the preparation of CBDO with a cis-trans ratio of 1.26–1.38 using a Ru-based catalyst; and patent CN112023919B discloses the preparation of CBDO with a cis-trans ratio of 0.54–32.18 using a combined catalyst consisting of a main catalyst composed of multiple noble metals such as Ru / Ni / Pd / Pt and a co-catalyst composed of Cu / Fe / Co / Zn. Patent 112371192B discloses a composite ruthenium catalyst obtained by loading a chiral ruthenium chloride precursor onto a heterogeneous ruthenium-carbon support. This catalyst can produce CBDO with a high cis-trans isomer ratio. However, due to the inherent characteristics of heterogeneous catalysts, their performance deteriorates significantly after repeated use over a period of time, leading to a marked increase in the proportion of trans isomers in the product, making it impossible to continuously and stably produce CBDO with a high cis-trans isomer ratio. Therefore, obtaining a high cis-trans isomer ratio and improving catalyst stability are urgent problems that the industry needs to solve. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for synthesizing cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol. This method can directly produce pure cis-structured CBDO, providing optimal monomers for downstream polyester polymerization.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] A method for synthesizing cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol, comprising the following steps:

[0008] S1: Under a hydrogen atmosphere, cis-2,2,4,4-tetramethyl-1,3-cyclobutanedione was used as a raw material and reacted with a modified transition metal catalyst and an auxiliary agent to obtain cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol reaction solution.

[0009] S2: The auxiliary agent was separated to obtain crude cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol;

[0010] S3: After washing and drying, a product of cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol with a purity of over 99.9% is obtained.

[0011] In this invention, the modified transition metal catalyst in S1 is a transition metal catalyst coordinated with N-heterocyclic carbene, with the following structural formula: The transition metal M is one of Pd, Cu, Ag, Au, Ru, etc.; R1 to R4 are mutually independent and are alkyl or phenyl, and R5 to R6 are mutually independent and are alkyl or Cl.

[0012] In this invention, the transition metal catalyst in S1, coordinated with an N-heterocyclic carbene, forms a very stable CM bond with the transition metal in the reaction system. The enhanced metal active site first combines with a ketone functional group of 2,2,4,4-tetramethyl-1,3-cyclobutanedione to form an intermediate transition state of an M-alkoxy metal complex. Due to the sterically hindered benzene ring environment around the M atom (R1 to R5 are mostly alkyl substituents with benzene rings), the alkoxy intermediate formed by the combination of the ketone functional group of 2,2,4,4-tetramethyl-1,3-cyclobutanedione and M is compressed and extended in the same plane (cis structure), and finally hydrogenated to cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol.

[0013] In this invention, the amount of transition metal catalyst added in S1 is 0.01 to 0.1% of the mass of 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

[0014] In this invention, the auxiliary agent in S1 is one or more of methanol, ethanol, ethyl acetate, isobutyl acetate, butyl butyrate, octyl acetate, isobutyl isobutyrate, methyl isobutyl ketone, methyl isobutyl alcohol, diisobutyl ketone, butyl ether, and octane.

[0015] In this invention, the mass ratio of the adjuvant to 2,2,4,4-tetramethyl-1,3-cyclobutanedione is 1 to 50.

[0016] As a preferred embodiment, in this invention, the hydrogenation reaction conditions in S1 are: a batch reactor, a reaction temperature of 60-120℃, a reaction pressure of 1.0-5.0MPa, a stirring speed of 500-1200rpm, and a reaction time of 0.5-5h.

[0017] In this invention, the separation method in S2 uses distillation, rectification, flash evaporation or rotary evaporation to separate the auxiliary agent, and cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol solid crude product is precipitated.

[0018] In this invention, the detergent in S3 is one or more of hexane, heptane, and cyclohexane.

[0019] In this invention, the crude cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol is washed with detergent to remove any auxiliaries and catalyst impurities that may be present in it. The detergent is then removed by drying to obtain a high-purity cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol product.

[0020] In this invention, after the washing mother liquor in step S3 is separated to remove the detergent, the collected catalyst can be reused.

[0021] The beneficial effects of the technical solution of the present invention are as follows: (1) Using the above method, the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione is ≥99.99%, the yield of 2,2,4,4-tetramethyl-1,3-cyclobutanediol is ≥99.5%, and all of them are cis structure, which can provide the best polymerization monomers for downstream polyester.

[0022] (2) The modified transition metal catalyst used in this invention can be reused, which reduces costs and improves the overall economic efficiency of the device. Detailed Implementation

[0023] The method provided by the present invention will be described in detail below with reference to the embodiments. It should be noted that the scope of the present invention includes, but is not limited to, such embodiments.

[0024] Sources of reagents in the examples and comparative examples:

[0025] 2,2,4,4-Tetramethyl-1,3-cyclobutanedione: Qingdao World Chemical Co., Ltd.;

[0026] Metal nitrogen heterocyclic carbene catalysts: NHC-Cu (Aladdin), NHC-Pd (Beijing Greenchem Technology Co., Ltd.); NHC-Ru (Shanghai Dongfan Chemical Technology Co., Ltd., Grubbs second-generation catalyst);

[0027] Additives and detergents: Industrial grade, Aladdin;

[0028] The analytical instruments and methods used in the examples and comparisons of the patented products are as follows:

[0029] Gas chromatograph: Agilent-7820

[0030] Gas chromatography column: 0.25 mm × 30 m HP-5 capillary column, FID detector, vaporization chamber temperature 280 °C, column oven temperature 280 °C, FID detector temperature 280 °C, hydrogen flow rate 40 mL / min, air flow rate 400 mL / min, make-up flow rate 25 mL / min, injection volume 0.2 μL, split ratio 30:1. The conversion and selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanedione were calculated using the area normalization method. Temperature program: Preheat to column temperature 60 °C, hold for 1 min, increase from 60 °C to 80 °C at a rate of 10 °C / min, hold for 1 min, increase from 80 °C to 250 °C at a rate of 15 °C / min, hold for 8 min.

[0031] Example 1:

[0032] Accurately weigh 50g of 2,2,4,4-tetramethyl-1,3-cyclobutanedione, 500g of isobutyl isobutyrate, and 0.025g of NHC-Cu catalyst. The product was added to a reaction vessel and stirred until dissolved into a homogeneous liquid phase. After sealing the reaction vessel, nitrogen was purged three times. The temperature was then increased, and when the temperature inside the vessel reached 80°C, hydrogen gas was introduced, and the pressure was increased to 2.5 MPa. The stirring speed was adjusted to 800 rpm, and the reaction was stopped after 2.0 h. After cooling, the pressure was released, nitrogen was purged, and the reaction solution was transferred to a rotary evaporator. The solution was heated to 76-86°C at 10 kPa to rotary evaporate isobutyl isobutyrate, yielding crude solid 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The crude solid 2,2,4,4-tetramethyl-1,3-cyclobutanediol was washed with 100 mL of cyclohexane at room temperature, filtered, and washed four times. The filter cake was dried at 80°C for 2 h to obtain 51.3 g of 2,2,4,4-tetramethyl-1,3-cyclobutanediol product.

[0033] Gas chromatography analysis of the hydrogenated reaction solution showed that the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 99.99%, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 99.8%. Gas chromatography analysis of the dried product dissolved in ethanol showed that all 2,2,4,4-tetramethyl-1,3-cyclobutanediols were in the cis configuration.

[0034] Example 2:

[0035] Accurately weigh 50g of 2,2,4,4-tetramethyl-1,3-cyclobutanedione, 800g of ethyl acetate, and 0.005g of NHC-Pd catalyst. The solution was added to a reaction vessel and stirred until a homogeneous liquid phase was formed. After sealing the reaction vessel, nitrogen was purged three times. The temperature was then increased, and when the temperature inside the vessel reached 60°C, hydrogen gas was introduced, and the pressure was increased to 1.0 MPa. The stirring speed was adjusted to 500 rpm, and the reaction was stopped after 5.0 h. After cooling, the pressure was released, nitrogen was purged, and the reaction solution was transferred to a rotary evaporator. The solution was heated to 77°C under normal pressure, and ethyl acetate was rotary evaporated to obtain crude solid 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The crude solid 2,2,4,4-tetramethyl-1,3-cyclobutanediol was washed with 50 mL of hexane at room temperature, filtered, washed three times, and the filter cake was dried at 80°C for 2 h to obtain 50.4 g of 2,2,4,4-tetramethyl-1,3-cyclobutanediol product.

[0036] Gas chromatography analysis of the hydrogenated reaction solution showed that the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was >99.99%, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 98%. Gas chromatography analysis of the dried product dissolved in ethanol showed that all 2,2,4,4-tetramethyl-1,3-cyclobutanediols were in the cis configuration.

[0037] Example 3:

[0038] Accurately weigh 80g of 2,2,4,4-tetramethyl-1,3-cyclobutanedione, 300g of methyl isobutyl alcohol, and 0.08g of NHC-Ru catalyst. The mixture was added to a reaction vessel and stirred until a homogeneous liquid phase was formed. After sealing the reaction vessel, nitrogen was purged three times. The temperature was then increased, and when the temperature inside the vessel reached 120°C, hydrogen gas was introduced, and the pressure was increased to 5.0 MPa. The stirring speed was adjusted to 1200 rpm, and the reaction was stopped after 0.5 h. After cooling, the pressure was released, nitrogen was purged, and the reaction solution was transferred to a rotary evaporator. The mixture was heated to 70-76°C at 8 kPa to rotary evaporate methyl isobutyl alcohol, yielding crude solid 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The crude solid 2,2,4,4-tetramethyl-1,3-cyclobutanediol was washed with 100 mL of heptane at room temperature, filtered, washed three times, and the filter cake was dried at 80°C for 4 h to obtain 82 g of 2,2,4,4-tetramethyl-1,3-cyclobutanediol product.

[0039] Gas chromatography analysis of the hydrogenated reaction solution showed that the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was >99.99%, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 99.7%. Gas chromatography analysis of the dried product dissolved in ethanol showed that all 2,2,4,4-tetramethyl-1,3-cyclobutanediols were in the cis configuration.

[0040] Examples 4-5:

[0041] This embodiment illustrates the catalyst addition amount applicable to the process of the present invention.

[0042] Using the same preparation method as in Example 1, the reaction of the NHC-Cu catalyst with 0.01% and 0.1% 2,2,4,4-tetramethyl-1,3-cyclobutanedione was investigated, and the results are as follows:

[0043]

[0044] Examples 6-9:

[0045] This embodiment illustrates the reaction temperature applicable to the process of the present invention.

[0046] Using the same preparation method as in Example 1, the reaction conditions at reaction temperatures of 25 / 60 / 120 / 150°C were investigated, and the results are as follows:

[0047] Example Reaction temperature / °C TMCB conversion rate / % CBDO yield / % Cis-inverse ratio Example 6 25 2.55 ＜1 100% cis Example 7 60 99.9 99.5 100% cis Example 8 120 99.9 99.6 100% cis Example 9 150 99.9 95.4 100% cis

[0048] Examples 10-11:

[0049] This embodiment illustrates the reaction pressure applicable to the process of the present invention.

[0050] Using the same preparation method as in Example 2, the reaction was investigated at reaction pressures of 3 and 5 MPa, and the results are as follows:

[0051]

[0052] Examples 12-13:

[0053] This embodiment illustrates the reaction time applicable to the process of the present invention.

[0054] Using the same preparation method as in Example 3, the reaction was investigated at reaction times of 2.5 h and 5 h, respectively, and the results are as follows:

[0055] Example Reaction time / h TMCB conversion rate / % CBDO yield / % Cis-inverse ratio Example 12 2.5 99.9 99.66 100% cis Example 13 5.0 99.9 99.51 100% cis

[0056] Example 14:

[0057] Catalyst reuse: The experimental procedure was the same as in Example 3, but the catalyst was reused. The results of the reuse are shown in Table 1 below:

[0058] Table 1

[0059] Number of times to apply TMCB conversion rate / % CBDO yield / % Cis-inverse ratio 10 99.9 99.7 100% cis 20 99.9 99.6 100% cis 30 99.9 99.5 100% cis 50 99.9 99.5 100% cis

[0060] Comparative Example 1:

[0061] Accurately weigh 50g of 2,2,4,4-tetramethyl-1,3-cyclobutanedione, 500g of isobutyl isobutyrate, and 1.0g of chiral Ru / C catalyst (the catalyst described in Example 1 of patent CN 112371192B) and add them to a reaction vessel. After sealing the reaction vessel, purge with nitrogen three times, begin heating, and when the temperature inside the vessel reaches 115℃, begin introducing hydrogen gas, pressurize to 3.0MPa, adjust the stirring speed to 800rpm, and stop the experiment after reacting for 4.0h. After cooling, release the pressure, purge with nitrogen, and transfer the reaction solution to a rotary evaporator flask. Heat to 76-86℃ at 10KPa to rotary evaporate isobutyl isobutyrate, obtaining crude solid 2,2,4,4-tetramethyl-1,3-cyclobutanediol. At room temperature, 50 mL of cyclohexane was added to wash the crude 2,2,4,4-tetramethyl-1,3-cyclobutanediol product. The mixture was filtered and washed three times. The filter cake was dried at 80 °C for 2 h to obtain 48 g of 2,2,4,4-tetramethyl-1,3-cyclobutanediol product.

[0062] Gas chromatography analysis of the hydrogenated reaction solution showed that the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was >99.9%, and the yield of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 93.3%. Gas chromatography analysis of the dried product dissolved in ethanol showed that the ratio of cis isomer to trans isomer of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 70:30, indicating that it was not a pure cis structure product.

[0063] Comparative Example 2:

[0064] Accurately weigh 50g of 2,2,4,4-tetramethyl-1,3-cyclobutanedione, 500g of isobutyl isobutyrate, and 2.5g of Ru / C heterogeneous catalyst (the powdered Ru / C catalyst described in Example 1 of patent CN112047813 A) and add them to a reaction vessel. After sealing the reaction vessel, purge with nitrogen three times, begin heating, and when the temperature inside the vessel reaches 115°C, begin introducing hydrogen gas, pressurize to 3.5MPa, adjust the stirring speed to 800rpm, and stop the experiment after reacting for 4.0h. After cooling, release the pressure, purge with nitrogen, and transfer the reaction solution to a rotary evaporator flask. Heat to 76-86°C at 10KPa to rotary evaporate isobutyl isobutyrate, obtaining crude solid 2,2,4,4-tetramethyl-1,3-cyclobutanediol. At room temperature, 50 mL of cyclohexane was added to wash the crude 2,2,4,4-tetramethyl-1,3-cyclobutanediol product. The product was filtered, washed three times, and the filter cake was dried at 80 °C for 2 h to obtain 49.5 g of 2,2,4,4-tetramethyl-1,3-cyclobutanediol product.

[0065] Gas chromatography analysis of the hydrogenated reaction solution showed that the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was >99.9%, and the yield of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 96.3%. Gas chromatography analysis of the dried product dissolved in ethanol showed that the ratio of cis to trans isomers of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was only about 50:50 to 60:40, indicating it was not a pure cis product. The heterogeneous Ru / C ratio did not regulate the chiral diol.

Claims

1. A method for preparing cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol, comprising the following steps: S1: Under a hydrogen atmosphere, using 2,2,4,4-tetramethyl-1,3-cyclobutanedione as a raw material, and with the action of a modified transition metal catalyst and an auxiliary agent, the reaction temperature is 60-120℃ to obtain cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol reaction solution. S2: The auxiliary agent was separated to obtain crude cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol; S3: After washing and drying, a product of cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol with a purity of over 99.9% is obtained. The modified transition metal catalyst in S1 is a transition metal catalyst coordinated with N-heterocyclic carbene, with the following structural formula: The transition metal M is one of Pd, Cu, Ag, Au, and Ru; R1 to R4 are mutually independent and are phenyl, while R5 to R6 are mutually independent and are Cl.

2. A method for preparing cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol, comprising the following steps: S1: Under a hydrogen atmosphere, using 2,2,4,4-tetramethyl-1,3-cyclobutanedione as a raw material, and with the action of a modified transition metal catalyst and an auxiliary agent, the reaction temperature is 60-120℃ to obtain cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol reaction solution. S2: The auxiliary agent was separated to obtain crude cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol; S3: After washing and drying, a product of cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol with a purity of over 99.9% is obtained. The modified transition metal catalyst in S1 is selected from... One or more of them.

3. The method according to claim 1 or 2, characterized in that, The amount of transition metal catalyst added in S1 is 0.01 to 0.1% of the mass of 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

4. The method according to claim 1 or 2, characterized in that, The auxiliary agent in S1 is one or more of methanol, ethanol, ethyl acetate, isobutyl acetate, butyl butyrate, octyl acetate, isobutyl isobutyrate, methyl isobutyl ketone, methyl isobutyl alcohol, diisobutyl ketone, butyl ether, and octane.

5. The method according to claim 1 or 2, characterized in that, The mass ratio of the adjuvant to 2,2,4,4-tetramethyl-1,3-cyclobutanedione is 1 to 50.

6. The method according to claim 1 or 2, characterized in that, The hydrogenation reaction conditions in S1 are as follows: a batch reactor is used, the reaction pressure is 1.0-5.0 MPa, and the reaction time is 0.5-5 h.

7. The method according to claim 1 or 2, characterized in that, The separation method in S2 involves separating the auxiliary agent by distillation, rectification, flash evaporation, or rotary evaporation, resulting in the precipitation of crude cis-2,2,4,4-tetramethyl-1,3-cyclobutanediol solid.

8. The method according to claim 1 or 2, characterized in that, The detergent in S3 is one or more of hexane, heptane, and cyclohexane.

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