Method for detecting cis-trans isomers of 1, 4-cyclohexanedimethanol

Abstract

The invention discloses a 1, 4-cyclohexanedimethanol cis-trans isomer detection method, which comprises: 1, respectively weighing a 1, 4-cyclohexanedimethanol cis-isomer and a 1, 4-cyclohexanedimethanol trans-isomer, and preparing a reference substance solution; the method comprises the following steps: weighing a mixed sample of 1, 4-cyclohexanedimethanol containing cis-trans isomers, and preparing a test solution; 2, liquid chromatography is adopted for sample introduction analysis, and chromatographic conditions are as follows: silica is used as a chromatographic column filler, a mobile phase solution A is n-hexane, a mobile phase solution B is isopropanol, the flow velocity of a mobile phase is 0.8-1.2 mL / min, and the sample introduction amount is 20 [mu] L. The method is simple and rapid to operate, good in reproducibility, high in sensitivity and easy for standardized operation, and can be used for detection and quality control of 1, 4-cyclohexanedimethanol in industrial production.

Description

Technical Field

[0001] The present invention relates to a method for detecting cis - trans isomers of 1,4 - cyclohexanedimethanol, and the content analysis of the two structures is carried out by liquid chromatography. Background Art

[0002] 1,4 - Cyclohexanedimethanol (CHDM) is an alicyclic diol with a symmetric structure formed by replacing the hydrogen atoms at positions 1 and 4 on the cyclohexane ring with hydroxyl groups. It is a white waxy solid at room temperature. As an important polyester monomer in industry, the polyester fiber produced from it has advantages such as good thermal stability and chemical stability, and is widely used in the manufacture of various high - performance polyesters, bottle - grade polyesters, unsaturated polyesters, coatings, etc. For example, polyethylene terephthalate - 1,4 - cyclohexanedimethanol ester (PETG) modified from polyethylene terephthalate (PET) with CHDM has excellent transparency, colorability, etc., and has broad application prospects in the fields of food packaging, medical treatment, etc.

[0003] 1,4 - Cyclohexanedimethanol has two structures, cis and trans. Different chemical structures also lead to certain differences in their physical properties. The melting point of the cis isomer is 43°C, the melting point of the trans isomer is 70°C, and the melting point of the mixture of the two is 41 - 61°C. At present, in industry, the DMT method is mostly used, that is, dimethyl terephthalate is prepared into 1,4 - cyclohexanedimethanol through two - step hydrogenation reactions, and the ratio of cis - trans isomers of the produced 1,4 - cyclohexanedimethanol depends on the type of catalyst used. In industry, when using cuprous chromite catalyst of copper chromite oxide, CHDM is prepared with a ratio of cis - CHDM and trans - CHDM of about 3:7. Since the melting point of the polyester prepared by modifying the trans isomer of CHDM is higher than that of the polyester prepared by the cis isomer, the change in the ratio of the two structures is of great significance for preparing polyester materials with higher melting points. If we want to study the influence of cis and trans isomers of CHDM on the properties of polyester, then the separation and purification of its cis and trans isomers are particularly important.

[0004] Currently, most existing patents are about the preparation of CHDM and the catalysts used for preparing CHDM. For the separation of cis - trans isomers of CHDM, it is mostly based on the different boiling points of the two through distillation and recrystallization. For example, Chinese Patent CN107200677A dissolves CHDM with acetone or ethyl acetate as the solvent, and then collects the trans isomer of 1,4 - cyclohexanedimethanol with high content through steps such as preheating, crystal cultivation, sweating, etc. Chinese Patent CN114436779B involves a purification device for the trans isomer of 1,4 - cyclohexanedimethanol including structures such as a crystallizer, a heat exchanger, a feed pipe, a filter, etc. By adjusting the temperature, the trans - cis ratio of the purified CHDM crystals is >92%, and the influence of solvent residues on polyester modification is effectively avoided. Summary of the Invention

[0005] The object of the present invention is to provide a method for detecting the cis - trans isomers of 1,4 - cyclohexanedimethanol, which can quickly determine the presence of the cis - trans isomers of 1,4 - cyclohexanedimethanol and effectively detect them, and further can control the ratio of cis - trans isomers in CHDM.

[0006] A method for detecting the cis - trans isomers of 1,4 - cyclohexanedimethanol comprises the following steps:

[0007] Step 1: Weigh the cis - isomer and trans - isomer of 1,4 - cyclohexanedimethanol respectively, prepare a reference solution, shake well, and filter; weigh a mixed sample containing the cis - trans isomers of 1,4 - cyclohexanedimethanol, and prepare a test solution, shake well, and filter.

[0008] Step 2: Take the reference solution and the test solution respectively, use high - performance liquid chromatography for injection analysis, and record the chromatogram.

[0009] The chromatographic conditions are as follows: a silica gel chromatographic column, mobile phase A is n - hexane, mobile phase B is isopropanol, the flow rate of the mobile phase is 0.8 - 1.2 mL / min, the injection volume is 20 μL, and the injection concentration is 1 - 5 mg / mL.

[0010] Further, the diluents of the reference solution and the test solution are both mobile phase solutions (n - hexane / isopropanol = 60:40 - 75:25).

[0011] Further, the chromatographic column uses normal - phase spherical silica gel as the packing material, and the size of the chromatographic column is 4.6×250 mm, 5 μm.

[0012] Further, the elution mode is isocratic elution.

[0013] Further, in the chromatographic conditions, the detector is an evaporative light - scattering detector, and the column temperature is 35°C.

[0014] Adopting the above - mentioned technical solutions, compared with the prior art, the present invention has the following technical effects:

[0015] The present invention uses a normal - phase spherical silica gel chromatographic column to effectively separate and analyze the cis - and trans - isomers of 1,4 - cyclohexanedimethanol. The whole detection process is fast and the operation is simple, which has important practical significance in the detection and analysis of synthesis and products. By using a high - performance liquid chromatography detection method to separate the cis - and trans - isomers of CHDM, a fast and accurate method for the separation and analysis of the cis - and trans - isomers of CHDM is provided. Brief Description of the Drawings

[0016] Figure 1It is the chromatogram of the test results of the cis isomer of 1,4 - cyclohexanedimethanol.

[0017] Figure 2 It is the chromatogram of the test results of the trans isomer of 1,4 - cyclohexanedimethanol.

[0018] Figure 3 It is the chromatogram of the test results of 1,4 - cyclohexanedimethanol with a mixture of cis and trans isomers. Detailed implementation mode

[0019] A method for separating and detecting cis - trans isomers of 1,4 - cyclohexanedimethanol includes the following steps:

[0020] Step 1: Weigh the cis isomer and trans isomer of 1,4 - cyclohexanedimethanol respectively, and place them in a diluent to prepare a reference solution; weigh a mixed sample of 1,4 - cyclohexanedimethanol containing cis - trans isomers, and place it in a diluent to prepare a test solution.

[0021] The diluents of the reference solution and the test solution are both mixed solutions of mobile phase n - hexane and isopropanol.

[0022] Step 2: Perform injection analysis using liquid chromatography. The chromatographic conditions are as follows: silica is used as the chromatographic column packing material, mobile phase solution A is n - hexane, mobile phase solution B is isopropanol, the mobile phase flow rate is 0.8 - 1.2 mL / min, and the injection volume is 20 μL.

[0023] In the mobile phase solution, the volume ratio of n - hexane to isopropanol is 60:40 - 75:25. The silica chromatographic column uses normal - phase spherical silica as the packing material, with dimensions of 4.6×250 mm and 5 μm. The injection concentration is 1 - 5 mg / mL. In the chromatographic conditions, an isocratic elution mode is adopted, the detector is an evaporative light - scattering detector, and the column temperature is 35°C.

[0024] A high - performance liquid chromatography detection method for cis - trans isomers of 1,4 - cyclohexanedimethanol provided by the present invention includes the selection of chromatographic conditions, the preparation of test solutions and reference solutions, and the injection detection process. Among them, the chromatographic conditions use a normal - phase spherical silica column as the chromatographic column, with the volume ratio of n - hexane to isopropanol being 60:40 - 75:25, and the detector is an evaporative light - scattering detector.

[0025] The following combines examples to elaborate in detail on the detection of cis - trans isomers of 1,4 - cyclohexanedimethanol under liquid chromatography conditions in the present invention:

[0026] Example 1

[0027] Chromatographic conditions:

[0028] Chromatographic column: normal-phase spherical silica gel chromatographic column (4.6 mm × 250 mm, 5 μm), mobile phase: n-hexane / isopropanol = 75 / 25, injection volume is 20 μL, sample concentration is 5 mg / mL, mobile phase flow rate is 1 mL / min, elution mode is isocratic elution, detector is evaporative light scattering detector, column temperature is 35 °C.

[0029] Detection steps:

[0030] (1) Preparation of test solution: Weigh 1,4-cyclohexanedimethanol with a concentration of 5 mg / ml and mixed with cis-isomer and trans-isomer, place it in a beaker, dissolve it with the mobile phase and dilute it to 5 mg / mL, shake well, filter, and use it as the test solution.

[0031] (2) Preparation of reference solution: Weigh a certain mass of trans-1,4-cyclohexanedimethanol and cis-1,4-cyclohexanedimethanol respectively, place them in a beaker, dissolve them with the mobile phase and dilute them to 5 mg / mL, shake well, filter, and use it as the reference solution.

[0032] (3) Take the reference solution and test solution, and perform external standard method high-performance liquid analysis according to this chromatographic condition, and record the chromatogram.

[0033] The test results are shown in the attached figure, where Figure 1 is the chromatogram of the test results of the cis-isomer of 1,4-cyclohexanedimethanol, Figure 2 is the chromatogram of the test results of the trans-isomer of 1,4-cyclohexanedimethanol, Figure 3 is the chromatogram of the test results of the mixed 1,4-cyclohexanedimethanol. The cis and trans isomers of the test sample are well separated, the resolution is 2.7, the relative content ratio of trans-1,4-cyclohexanedimethanol is about 94%, and the relative content ratio of cis-1,4-cyclohexanedimethanol is about 6%.

[0034] Example 2

[0035] Chromatographic conditions:

[0036] Chromatographic column: normal-phase spherical silica gel chromatographic column (4.6 mm × 250 mm, 5 μm), mobile phase: n-hexane / isopropanol = 60 / 40, elution mode is isocratic elution, detector is evaporative light scattering detector, mobile phase flow rate is 1 ml / min, sample concentration is 5 mg / mL, column temperature is 35 °C, injection volume is 20 μL;

[0037] Detection steps:

[0038] The preparation of the test solution and reference solution refers to Example 1.

[0039] Take the reference substance and the test solution, and perform external standard method high performance liquid analysis according to this chromatographic condition. Record the chromatogram. The resolution of the sample is 1.8.

[0040] Example 3

[0041] Refer to some chromatographic conditions and operation steps of Example 1. The chromatographic column is a reversed-phase chromatographic column. Take the reference substance and the test solution, and perform external standard method high performance liquid analysis according to this chromatographic condition. Record the chromatogram. The resolution is 0.5.

[0042] Example 4

[0043] Chromatographic conditions:

[0044] Chromatographic column: normal-phase spherical silica chromatographic column (4.6 mm × 250 mm, 5 μm), mobile phase: n-hexane / isopropanol = 60 / 40, elution mode is isocratic elution, detector is evaporative light scattering detector, mobile phase flow rate is 1 ml / min, sample concentration is 5 mg / mL, column temperature is 30 °C, injection volume is 20 μL;

[0045] The preparation of the test solution and the reference substance solution refers to Example 1. Take the reference substance and the test solution, and perform external standard method high performance liquid analysis according to this chromatographic condition. Record the chromatogram. The resolution is 1.3.

[0046] Example 5

[0047] Chromatographic conditions:

[0048] Chromatographic column: normal-phase spherical silica chromatographic column (4.6 mm × 250 mm, 5 μm), mobile phase: n-hexane / isopropanol = 75 / 25, injection volume is 20 μL, sample concentration is 5 mg / mL, mobile phase flow rate is 1.2 mL / min, elution mode is isocratic elution, detector is evaporative light scattering detector, column temperature is 35 °C.

[0049] The preparation of the test solution and the reference substance solution refers to Example 1. Take the reference substance and the test solution, and perform external standard method high performance liquid analysis according to this chromatographic condition. Record the chromatogram. The resolution is 2.2.

[0050] Example 6

[0051] Chromatographic conditions:

[0052] Chromatographic column: normal-phase spherical silica chromatographic column (4.6 mm × 250 mm, 5 μm), mobile phase: n-hexane / isopropanol = 75 / 25, injection volume is 20 μL, sample concentration is 2 mg / mL, mobile phase flow rate is 1.2 mL / min, elution mode is isocratic elution, detector is evaporative light scattering detector, column temperature is 35 °C.

[0053] The preparation of the test sample and reference substance solutions was carried out with reference to Example 1. The reference substance and test sample solutions were taken, and external standard method high performance liquid chromatography analysis was performed according to this chromatographic condition. The chromatogram was recorded, and the resolution was 0.7.

Claims

1. A method for detecting cis-trans isomers of 1,4-cyclohexanedimethanol, characterized in that, It includes the following steps: Step 1: Weigh the cis isomer and trans isomer of 1,4-cyclohexanedimethanol respectively to prepare a reference solution; weigh a mixed sample of 1,4-cyclohexanedimethanol containing cis and trans isomers to prepare a test solution. Step 2: Perform injection analysis using liquid chromatography. The chromatographic conditions are as follows: silica gel is used as the chromatographic column packing material, mobile phase solution A is n-hexane, mobile phase solution B is isopropanol, the flow rate of the mobile phase is 0.8 - 1.2 mL / min, and the injection volume is 20 μL.

2. The detection method of cis-trans isomers of 1,4-cyclohexanedimethanol according to claim 1, characterized in that, The diluents of the reference solution and the test solution are both mixed solutions of mobile phase n-hexane and isopropanol.

3. The detection method of the cis-trans isomers of 1,4-cyclohexanedimethanol according to claim 2, characterized in that, The volume ratio of n-hexane to isopropanol in the mobile phase solution is 60:40 - 75:

25.

4. The detection method of cis-trans isomers of 1,4-cyclohexanedimethanol according to claim 1, characterized in that, The silica gel chromatographic column uses normal-phase spherical silica gel as the filler, with dimensions of 4.6×250 mm and 5 μm.

5. The detection method of cis-trans isomers of 1,4-cyclohexanedimethanol according to claim 1, characterized in that, The injection concentration in Step 2 is 1 - 5 mg / mL.

6. The detection method of cis-trans isomers of 1,4-cyclohexanedimethanol according to claim 1, characterized in that, Under the chromatographic conditions, the detector is an evaporative light scattering detector, and the column temperature is 35°C.

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