Karl Fischer reagent for detecting moisture content in cyclic ether compound by coulomb coulometry
By employing coulometric electrophoresis and a specific ratio of mixed solvent and imidazole stabilizer, the side reaction problem in the moisture detection of cyclic ether compounds was solved, achieving high-precision and stable moisture detection results.
Patent Information
- Application Number
- CN202511491330.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-18
- Publication Date
- 2025-12-09
AI Technical Summary
The existing Karl Fischer method is prone to side reactions when detecting the water content in cyclic ether compounds, resulting in low detection accuracy and making it difficult to meet high precision requirements.
Karl Fischer reagents were prepared using the coulometric method and with a specific ratio of mixed solvents and the organic base imidazole as a stabilizer. The reagents included ethylene glycol methyl ether, trifluoroethanol, and diethylene glycol ethyl ether as solvents, imidazole as a buffer, and sulfur dioxide as an oxidant to avoid side reactions and improve detection accuracy.
It achieves high-precision detection of water content in cyclic ether compounds, with a standard deviation of less than 5% and a relative standard deviation of less than 0.1%, significantly improving the stability and anti-interference ability of the detection.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of water detection, in particular, to a Karl Fischer reagent for detecting water content in cyclic ether compounds by coulomb charge method. BACKGROUND
[0002] Cyclic ether compounds are important organic chemical raw materials containing three-membered ring oxygen structure. Due to their unique cyclic structure and active chemical properties, they play an irreplaceable role in the fields of food and medicine, such as polyester synthesis, preparation of pharmaceutical intermediates, and production of surfactants. The quality and purity of these compounds (such as propylene oxide, ethylene oxide, and epichlorohydrin) directly affect the performance of downstream products. Among the various quality indicators of cyclic ether compounds, water content is one of the key indicators of their quality. Due to the active chemical properties of cyclic ether compounds, they are prone to hydrolysis when exposed to water, which not only destroys their chemical stability but also generates impurity derivatives, interfering with subsequent polymerization, synthesis, and other processes, resulting in a decline in product performance or even scrap. Therefore, accurately measuring the water content in cyclic ether compounds is of great practical significance to ensure the stability of production processes and improve product quality.
[0003] Currently, common methods for detecting water content include drying weight loss, gas chromatography, infrared water determination, and Karl Fischer method. The drying weight loss method is simple to operate and widely used in the traditional Chinese medicine industry, but its accuracy is low and it is easily affected by other volatile components in the sample (cyclic ether compounds are highly volatile), making it difficult to accurately measure the trace water in cyclic ether compounds. Gas chromatography has high accuracy, but it requires strict equipment and operation, and has limited qualitative ability. The infrared water determination method is based on the absorption characteristics of specific wavelengths and can quickly and continuously measure, but it is affected by the surface state of the sample and has lower accuracy than the Karl Fischer method.
[0004] In contrast, the Karl Fischer method, as a classic method for measuring trace water in the chemical industry, has the advantages of high sensitivity, high accuracy, and wide applicability. This method is based on the quantitative reaction between iodine and water and can accurately detect water in various forms of samples such as liquids, solids, and gases, especially for fine chemical products with strict requirements for trace water (μg / g level). However, cyclic ether compounds are prone to hydrolysis, and they can easily undergo ring-opening side reactions with methanol, which poses a special challenge for their water determination.
[0005] Therefore, it is of great practical significance to develop a new type of Karl Fischer reagent that can eliminate matrix interference and accurately detect the water content in cyclic ether compounds. SUMMARY
[0006] The application provides a Karl Fischer reagent for detecting water content in a cyclic ether compound by using a coulomb charge method.
[0007] The technical scheme of the application is as follows: The application provides a Karl Fischer reagent for detecting water content in a cyclic ether compound by using a coulomb charge method, and raw materials include the following components in parts by weight: Iodine 7-8 parts, mixed solution 330-340 parts, imidazole 60-70 parts, 2-methyl imidazole 6-7 parts, sulfur dioxide 25-35 parts; The mixed solution includes ethylene glycol methyl ether, trifluoroethanol and diethylene glycol ethyl ether; The weight ratio of the trifluoroethanol and diethylene glycol ethyl ether to the ethylene glycol methyl ether is 1:1; The weight ratio of the trifluoroethanol and diethylene glycol ethyl ether is 0.5-1.5:1.
[0008] As a further technical scheme, the weight ratio of the trifluoroethanol and diethylene glycol ethyl ether is 1:1.
[0009] As a further technical scheme, the raw materials include the following components in parts by weight: Iodine 7.4 parts, mixed solution 335 parts, imidazole 64 parts, 2-methyl imidazole 6.7 parts, sulfur dioxide 30 parts.
[0010] In the application, imidazole is used as an organic alkali stabilizer, the chemical stability of imidazole is better than that of pyridine, the alkalinity is lower, and the imidazole cannot cause ring-opening reaction with a sample, meanwhile, the imidazole has small peculiar smell and far smaller toxicity than pyridine, so that the experimental environment can be improved and the health risk can be reduced by using the imidazole; as a stabilizing reagent, the potential jump of a titration system is clearer, and the end point is more obvious, so that the end point can be judged and the titration error can be reduced by using the imidazole; in addition, the addition of 2-methyl imidazole enhances the stability of the reagent and avoids the appearance of crystals.
[0011] As a further technical scheme, the preparation method of the mixed solution includes the following steps: The ethylene glycol methyl ether, trifluoroethanol and diethylene glycol ethyl ether are uniformly mixed to obtain the mixed solution.
[0012] As a further technical scheme, the cyclic ether compound includes one of propylene oxide, ethylene oxide and epichlorohydrin, and the propylene oxide is preferred.
[0013] In this invention, the preferred cyclic ether compound is propylene oxide. Propylene oxide has a relatively low boiling point (34°C), which is relatively controllable at room temperature. In Karl Fischer reagent, propylene oxide has strong chemical stability and low moisture content, which meets the objective of this invention to detect trace moisture in cyclic ether compounds.
[0014] This invention proposes a method for preparing a Karl Fischer reagent for detecting the water content in cyclic ether compounds using coulometric spectroscopy. The method comprises the following steps: S1. After mixing the iodine and the mixed solution evenly, add imidazole and 2-methylimidazolium, mix evenly again, and cool in the dark to obtain a blended solution; S2. Sulfur dioxide is introduced into the blended liquid, mixed evenly, sealed, and allowed to stand in the dark to obtain the Karl Fischer reagent for detecting the water content in cyclic ether compounds.
[0015] As a further technical solution, the sulfur dioxide is liquid sulfur dioxide.
[0016] In this invention, the sulfur dioxide is liquid sulfur dioxide, and when adding liquid sulfur dioxide, the reaction temperature is controlled at 25~35℃.
[0017] As a further technical solution, in step S2, the time for the light-protected standing is 12~24h, for example, it can be 12h, 15h, 18h, 20h, or 24h, preferably 24h.
[0018] The present invention also proposes the application of the Karl Fischer reagent described herein or the Karl Fischer reagent prepared by the described preparation method in the detection of moisture content in cyclic ether compounds using coulometric spectroscopy.
[0019] As a further technical solution, when using the coulometric method to detect the water content in cyclic ether compounds, the relative humidity of the detection environment is <50%.
[0020] In this invention, the coulometric method is used to detect the moisture content in cyclic ether compounds. The coulometric method is more suitable for detecting trace amounts of moisture (moisture content <1% in the sample). It involves electrolysis to generate iodine, which reacts with water molecules in the sample. Using Faraday's law, the moisture content of the sample is indirectly obtained based on the amount of electricity consumed during electrolysis. The core principle is that iodine, sulfur dioxide, and organic bases in Karl Fischer reagent undergo a redox reaction with water in an aqueous sample. During the reaction, iodine and water are reacted in a 1:1 ratio. According to Faraday's law, the amount of iodine involved in the reaction is proportional to the amount of electricity consumed. Therefore, the moisture content in the sample can be calculated based on the generation and consumption of iodine during electrolysis.
[0021] The working principle and beneficial effects of this invention are as follows: In this invention, a Karl Fischer reagent suitable for determining the moisture content of epoxy ether compounds was prepared using ethylene glycol methyl ether, diethylene glycol ethyl ether, and trifluoroethanol as a mixed solvent and imidazole as a buffer. The hydroxyl groups of ethylene glycol methyl ether, diethylene glycol ethyl ether, and trifluoroethanol in the mixed solvent have lower reactivity than methanol, resulting in greater chemical stability, lower nucleophilicity, and no side reactions with cyclic ethers. Furthermore, they exhibit higher solubility for cyclic ethers, leading to better sample dissolution. Additionally, the long molecular chains and steric hindrance of ethylene glycol methyl ether and diethylene glycol ethyl ether, along with the fluorine atoms in trifluoroethanol, enhance chemical stability. By using these three solvents in combination, the possibility of side reactions with cyclic ether compounds can be effectively reduced when detecting the moisture content of epoxy ether compounds. The Karl Fischer reagent prepared by this invention can test propylene oxide with a standard deviation of <5 and a relative standard deviation of <0.1 even after more than 5 consecutive measurements. This indicates that the Karl Fischer reagent prepared by this invention has the advantages of reliability, stability and strong anti-interference ability when detecting the water content in cyclic ether compounds, demonstrating good precision and repeatability. Detailed Implementation
[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0023] In the following examples and comparative examples, the iodine, with a purity of 99.99%, was sourced from Safran Chemical Handan Co., Ltd. Sulfur dioxide, with a purity of 99%, comes from Henan Hongguan Chemical Co., Ltd. Imidazole, with a purity of 98%, is sourced from Shandong Daike Biotechnology Co., Ltd. Ethylene glycol methyl ether, with a purity of 99%, is sourced from Safran Chemical Handan Co., Ltd. Diethylene glycol ethyl ether, with a purity of 99%, is sourced from Safrui Chemical Handan Co., Ltd. Propylene oxide, with a purity of 99%, is sourced from Wanhua Chemical Group Co., Ltd. Trifluoroethanol, with a purity of 99%, is sourced from Tianjin Saifure Technology Co., Ltd.
[0024] Example 1 The method for preparing the mixed solution includes the following steps: mixing 167.5g of ethylene glycol methyl ether, 83.75g of trifluoroethanol and 83.75g of diethylene glycol ethyl ether evenly to obtain a mixed solution; A method for preparing Karl Fischer reagent for detecting water content in cyclic ether compounds using coulometric spectroscopy includes the following steps: S1. After mixing 7.4g of iodine and 335g of mixed solution evenly, add 64g of imidazole and 6.7g of 2-methylimidazole, mix evenly again, cool in the dark, and obtain a blend solution. S2. Pass 30g of sulfur dioxide gas into the blended liquid, mix thoroughly, seal, and let stand in the dark for 24h to obtain the Karl Fischer reagent for detecting the water content in cyclic ether compounds.
[0025] Example 2 The method for preparing the mixed solution includes the following steps: mixing 165g of ethylene glycol methyl ether, 110g of diethylene glycol ethyl ether and 55g of trifluoroethanol evenly to obtain the mixed solution; A method for preparing Karl Fischer reagent for detecting water content in cyclic ether compounds using coulometric spectroscopy includes the following steps: S1. After mixing 7g of iodine and 330g of mixed solution evenly, add 60g of imidazole and 6g of 2-methylimidazole, mix evenly again, cool in the dark, and obtain a blend solution. S2. Pass 25g of sulfur dioxide gas into the blended liquid, mix thoroughly, seal, and let stand in the dark for 24h to obtain the Karl Fischer reagent for detecting the water content in cyclic ether compounds.
[0026] Example 3 The method for preparing the mixed solution includes the following steps: mixing 170g of ethylene glycol methyl ether, 68g of diethylene glycol ethyl ether and 102g of trifluoroethanol evenly to obtain a mixed solution; A method for preparing Karl Fischer reagent for detecting water content in cyclic ether compounds using coulometric spectroscopy includes the following steps: S1. After mixing 8g of iodine and 340g of mixed solution evenly, add 70g of imidazole and 7g of 2-methylimidazole, mix evenly again, cool in the dark, and obtain a blend solution. S2. Pass 35g of sulfur dioxide gas into the blended liquid, mix thoroughly, seal, and let stand in the dark for 24h to obtain the Karl Fischer reagent for detecting the water content in cyclic ether compounds.
[0027] Comparative Example 1 The only difference between this comparative example and Example 1 is that diethylene glycol ethyl ether was not added in this comparative example, while 167.5g of ethylene glycol methyl ether and 167.5g of trifluoroethanol were added.
[0028] Comparative Example 2 The only difference between this comparative example and Example 1 is that ethylene glycol methyl ether was not added in this comparative example, and 167.5g of trifluoroethanol and 167.5g of diethylene glycol ethyl ether were added.
[0029] Comparative Example 3 The only difference between this comparative example and Example 1 is that trifluoroethanol was not added in this comparative example, and 167.5g of ethylene glycol methyl ether and 167.5g of diethylene glycol ethyl ether were added.
[0030] Comparative Example 4 The only difference between this comparative example and Example 1 is that the mixed solution is replaced with an equal amount of anhydrous methanol in this comparative example.
[0031] Experimental Example After cleaning and drying the 831-type moisture analyzer with anhydrous ethanol, the Karl Fischer reagents prepared in Examples 1-3 and Comparative Examples 1-4 were added to the cathode and anode chambers of the 831-type moisture analyzer. The Karl Fischer reagent in the anode chamber was ensured to cover the electrode, and the reagent level in the cathode chamber was slightly lower than or equal to the level in the anode chamber. The power supply was turned on, and the electromagnetic stirring was activated to ensure the instrument's drift value remained stable below 20 μg / min. The moisture analyzer was then calibrated with pure water to test the accuracy of the reagents. After passing the calibration, the propylene oxide sample was tested. Before using the sample, the syringe needed to be rinsed three times. After preparation, the test solution was weighed using the weight reduction method and injected into the container for testing. The test results are as follows; Before using Karl Fischer reagent to determine the propylene oxide sample, Karl Fischer reagent with different drift values was calibrated multiple times using 1 μL of pure water. The test results are as follows. Table 1. Results of Karl Fischer reagent calibration for different drift values in Example 1 using 1 μL of pure water in 6 trials.
[0032] Table 2. Results of Karl Fischer reagent calibration for different drift values in Example 2 using 1 μL of pure water in 6 trials.
[0033] Table 3. Results of Karl Fischer reagent calibration for different drift values in Example 3 using 1 μL of pure water in 6 trials.
[0034] Table 4. Results of Karl Fischer reagent calibration for different drift values of Comparative Example 1 using 1 μL of pure water in 6 trials.
[0035] Table 5. Results of Karl Fischer reagent calibration for different drift values in Comparative Example 2 using 1 μL of pure water in 6 trials.
[0036] Table 6. Results of Karl Fischer reagent calibration for different drift values in Comparative Example 3 using 1 μL of pure water in 6 trials.
[0037] Table 7. Results of Karl Fischer reagent calibration for different drift values in Comparative Example 4 using 1 μL of pure water in 6 trials.
[0038] As shown in Tables 1-7, compared with Comparative Examples 1-4, the experiments in Examples 1-3 controlled the introduction of moisture. When the initial drift value was <10, the reaction time was concentrated between 68 and 88 seconds. The average of multiple detection values was used to represent the typical detection result of the reagent on 1 μL of pure water. Compared with the standard (1000), the difference was less than 2%, indicating that the overall detection result of the reagent was close to the true value with no systematic bias. The relative standard deviation was 0.0011-0.0014, far less than 1, indicating that the fluctuation of the detection value was negligible compared to the average value. The Karl Fischer reagent showed very high precision, indicating that the Karl Fischer reagent prepared in Examples 1-3 had a stable chemical reaction rate with the standard water sample, and the system's response rhythm to moisture was consistent. Meanwhile, the detection value was around 1012 μg / g, initially demonstrating that the detection system had good repeatability, high accuracy and precision for the standard water sample, and could fully support the subsequent detection of propylene oxide samples.
[0039] Table 8 Results of Karl Fischer reagent detection of propylene oxide in Example 1
[0040] Table 9 Results of Karl Fischer reagent detection of propylene oxide in Example 2
[0041] Table 10 Results of Karl Fischer reagent detection of propylene oxide in Example 3
[0042] Table 11 Results of Karl Fischer reagent detection of propylene oxide in Comparative Example 1
[0043] Table 12 Results of Karl Fischer reagent detection of propylene oxide in Comparative Example 2
[0044] Table 13 Results of Karl Fischer reagent detection of propylene oxide in Comparative Example 3
[0045] Table 14 Results of Karl Fischer reagent detection of propylene oxide in Comparative Example 4
[0046] As can be seen from Tables 8-14, compared with Comparative Examples 1-4, when using the Karl Fischer reagents prepared in Examples 1-3 to detect propylene oxide, the initial drift value was relatively stable and did not show a continuously rising trend, indicating that there were no side reactions that made the results difficult to detect. The injection amount was between 0.2 and 0.3 g, and the response time was stable between 52 and 75 s, indicating that after the reaction reached equilibrium, the detection could quickly reach a stable state. Observing the relationship between the detection value and the injection amount, the detection value was relatively stable regardless of the change in the injection amount, fluctuating around 120 μg / g, reflecting the central trend of the detection by the Karl Fischer reagents prepared in Examples 1-3. The standard deviation is a constant representing the degree of dispersion of a reaction value. The standard deviation of 2.57 in Example 1 indicates that the detection value fluctuated to some extent, but was relatively stable overall. The relative standard deviation is used to represent the precision of the test results. The lower the value, the higher the repeatability and reliability of the Karl Fischer reagent test. The relative standard deviation of 0.021 in Example 1 corresponds to the standard deviation of 2.57, which confirms that the Karl Fischer reagent has the advantages of reliability, stability and strong anti-interference ability when detecting the water content in cyclic ether compounds.
[0047] Furthermore, as shown in Tables 8-14, the Karl Fischer reagents prepared in Examples 1-3 showed lower detection values than those in Comparative Examples 1-3 when detecting the water content in propylene oxide. This indicates that when ethylene glycol methyl ether, diethylene glycol ethyl ether, and trifluoroethanol are used together in the mixed solvent of the Karl Fischer reagent, the precision and repeatability for detecting the water content in propylene oxide are higher. The detection value of Example 1 was much lower than that of Comparative Example 4, indicating that a side reaction between methanol and propylene oxide led to a higher result. In terms of standard deviation and relative standard deviation, Comparative Example 4 was also much higher than that of Example 1. This demonstrates that the Karl Fischer reagent prepared in this invention has stronger precision and repeatability than the traditional Karl Fischer reagent using methanol.
[0048] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A Karl Fischer reagent for detecting the water content in cyclic ether compounds using coulometric spectroscopy, characterized in that, The raw materials consist of the following components in parts by weight: Iodine 7-8 parts, mixed solution 330-340 parts, imidazole 60-70 parts, 2-methylimidazolium 6-7 parts, sulfur dioxide 25-35 parts; The mixed solution includes ethylene glycol methyl ether, trifluoroethanol and diethylene glycol ethyl ether; The weight ratio of the trifluoroethanol and diethylene glycol ethyl ether to the weight of the ethylene glycol methyl ether is 1:
1. The weight ratio of trifluoroethanol to diethylene glycol ether is 0.5~1.5:
1.
2. The Karl Fischer reagent for detecting water content in cyclic ether compounds using coulometric spectroscopy according to claim 1, characterized in that, The weight ratio of trifluoroethanol to diethylene glycol ether is 1:
1.
3. The Karl Fischer reagent for detecting water content in cyclic ether compounds using coulometric spectroscopy according to claim 1, characterized in that, The raw materials consist of the following components in parts by weight: Iodine 7.4 parts, mixed solution 335 parts, imidazole 64 parts, 2-methylimidazolium 6.7 parts, sulfur dioxide 30 parts.
4. The Karl Fischer reagent for detecting water content in cyclic ether compounds using coulometric spectroscopy according to claim 1, characterized in that, The method for preparing the mixed solution includes the following steps: The ethylene glycol methyl ether, trifluoroethanol and diethylene glycol ethyl ether are mixed evenly to obtain the mixed solution.
5. The Karl Fischer reagent for detecting water content in cyclic ether compounds using coulometric spectroscopy according to claim 1, characterized in that, The cyclic ether compounds include one of propylene oxide, ethylene oxide, and epichlorohydrin.
6. A method for preparing a Karl Fischer reagent for detecting the water content in cyclic ether compounds using coulometric spectroscopy, used to prepare the Karl Fischer reagent for detecting the water content in cyclic ether compounds using coulometric spectroscopy as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. After mixing the iodine and the mixed solution evenly, add imidazole and 2-methylimidazolium, mix evenly again, and cool in the dark to obtain a blended solution; S2. Sulfur dioxide is introduced into the blended liquid, mixed evenly, sealed, and allowed to stand in the dark to obtain the Karl Fischer reagent for detecting the water content in cyclic ether compounds.
7. The method for preparing Karl Fischer reagent for detecting water content in cyclic ether compounds by coulometric spectroscopy according to claim 6, characterized in that, The sulfur dioxide is liquid sulfur dioxide.
8. The method for preparing Karl Fischer reagent for detecting water content in cyclic ether compounds by coulometric spectroscopy according to claim 6, characterized in that, In step S2, the time for the light-protected standing period is 12-24 hours.
9. The application of the Karl Fischer reagent according to any one of claims 1 to 5 or the Karl Fischer reagent prepared by the preparation method according to any one of claims 6 to 8 in the determination of moisture content in cyclic ether compounds by coulometric spectroscopy.
10. The application according to claim 9, characterized in that, When using the coulometric method to detect the water content in cyclic ether compounds, the relative humidity of the detection environment should be <50%.