A method for purifying crude 2-methyl-1,4-naphthoquinone

Abstract

The application provides a purification method of crude 2-methyl-1,4-naphthoquinone, and belongs to the field of fine chemical product purification. The application provides a purification method of crude 2-methyl-1,4-naphthoquinone, which comprises the following steps: mixing crude 2-methyl-1,4-naphthoquinone with a butanol-water mixed solvent, then performing extraction and phase separation to obtain an organic phase; and cooling and crystallizing the organic phase to obtain pure 2-methyl-1,4-naphthoquinone. The application utilizes the significant difference in solubility of 2-methyl-1,4-naphthoquinone and impurities contained in 2-methyl-1,4-naphthoquinone in a n-butanol-water binary partially miscible two-phase system, removes inorganic impurities such as chromium through extraction, and achieves the purification effect by coupling cooling and crystallization, so that the purity of 2-methyl-1,4-naphthoquinone after purification reaches more than 98%, the removal rate of chromium can be more than 99%, and the requirements of high-quality vitamin K3 production are fully met.

Description

Technical Field

[0001] This invention relates to the field of fine chemical product purification, specifically to a method for purifying crude 2-methyl-1,4-naphthoquinone. Background Technology

[0002] 2-Methyl-1,4-naphthoquinone is a core intermediate in the synthesis of vitamin K3. As an important fat-soluble vitamin, vitamin K3 is widely used in pharmaceutical preparations, livestock and aquatic feed additives, and other fields. Its purity directly determines the safety and efficacy of downstream preparations. Therefore, the preparation process of high-purity 2-methyl-1,4-naphthoquinone has extremely high industrial application value.

[0003] Currently, the mainstream industrial process for mass production of 2-methyl-1,4-naphthoquinone is the oxidation reaction of 2-methylnaphthalene with sodium dichromate. This process uses readily available raw materials, has mild reaction conditions, and low production costs, making it suitable for large-scale industrial production. However, it also has significant technical drawbacks: the oxidation reaction is accompanied by a large number of side reactions, generating various organic impurities that are poorly soluble in water. The chromium content is usually greater than 3000 ppm, resulting in the purity of crude 2-methyl-1,4-naphthoquinone generally being less than 95%, making it unsuitable for direct use in the synthesis of high-quality vitamin K3.

[0004] The existing purification processes for 2-methyl-1,4-naphthoquinone mostly employ the following methods: 1. Water washing process: Because impurities are encapsulated, only a small portion of the impurities can be removed, and a large amount of washing wastewater will be generated; 2. Recrystallization process using a single pure organic solvent (such as acetic acid, ethanol, or butanol): This method is not effective in removing water-soluble inorganic impurities, and chromium residues are prone to exceed the standard. Secondly, crude naphthoquinone contains about 40% water, requiring an additional drying step to remove the water. Otherwise, the mother liquor for crystallization needs to be distilled and then purified to recover the pure solvent, which will greatly increase energy consumption costs. At the same time, compared with the organic solvent-water system, 2-methyl-1,4-naphthoquinone retains a larger amount in the mother liquor for crystallization at the same temperature, resulting in a lower single-pass recrystallization yield. 3. Column chromatography: It has a good purification effect, but the process is complex, the equipment investment is large, the processing efficiency is low, and the solvent loss is high, making it unsuitable for industrial mass production.

[0005] Therefore, there is an urgent need to develop a 2-methyl-1,4-naphthoquinone purification process that is simple, requires little investment, has high purification efficiency, and thoroughly removes impurities, in order to solve the technical problems of low purity, high chromium impurity content, and poor economic efficiency of existing industrial crude 2-methyl-1,4-naphthoquinone. Summary of the Invention

[0006] This invention provides a method for purifying crude 2-methyl-1,4-naphthoquinone. The 2-methyl-1,4-naphthoquinone obtained by this invention has high purity and low chromium impurity content, and the purification method has good process economy.

[0007] This invention provides a method for purifying crude 2-methyl-1,4-naphthoquinone, comprising the following steps: The crude 2-methyl-1,4-naphthoquinone was mixed with a butanol-water mixed solvent and then extracted and phase-separated to obtain an organic phase. The organic phase was cooled and crystallized to obtain pure 2-methyl-1,4-naphthoquinone.

[0008] Preferably, the volume ratio of butanol to water in the mixed solvent is 2.5 to 5:1.

[0009] Preferably, the crude 2-methyl-1,4-naphthoquinone has a purity of over 60 wt%, a water content of 0-50 wt%, and a chromium content of less than 2 wt%.

[0010] Preferably, the ratio of 2-methyl-1,4-naphthoquinone in the crude 2-methyl-1,4-naphthoquinone to the butanol-water mixed solvent is 1g:3~6mL.

[0011] Preferably, the extraction is carried out under stirring conditions, and the extraction temperature is 50~75℃, and the extraction time is 30~60min.

[0012] Preferably, after extraction and before phase separation, the process further includes: allowing the obtained extraction system to stand. The settling time is 15-40 minutes.

[0013] Preferably, before the cooling crystallization, the process further includes: washing the organic phase with water, and then performing phase separation on the resulting mixture.

[0014] Preferably, the cooling crystallization temperature is 5~20℃, and the cooling rate to the cooling crystallization temperature is 0.1~3℃ / min.

[0015] Preferably, after cooling and crystallization, the process further includes: performing solid-liquid separation on the obtained system to obtain a wet 2-methyl-1,4-naphthoquinone and a mother liquor for crystallization; distilling the mother liquor to obtain recovered butanol; and drying the wet 2-methyl-1,4-naphthoquinone to obtain the purified 2-methyl-1,4-naphthoquinone. The recovered butanol is reused in the extraction process.

[0016] Preferably, before drying, the wet 2-methyl-1,4-naphthoquinone is mixed with a butanol-water mixed solvent, then extracted and separated again, and the resulting organic phase is cooled and crystallized.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Excellent purification effect and high product purity: This invention utilizes 2-methyl-1,4-naphthoquinone and its impurities in an organic-aqueous two-phase system in which n-butanol and water are partially miscible (2-methyl-1,4-naphthoquinone has good solubility in the butanol phase; the aqueous phase, as a strongly polar solvent, has high solubility for inorganic and organic acid impurities, which can efficiently extract water-soluble impurities). Coupled with cooling crystallization, inorganic chromium impurities in crude 2-methyl-1,4-naphthoquinone are efficiently removed. After purification, the purity of 2-methyl-1,4-naphthoquinone reaches over 98%, and the chromium removal rate can reach over 99%, solving the technical problems of low product purity and high chromium impurity content in traditional processes.

[0018] 2. Simple process and strong adaptability: The entire purification process involves only four core steps: extraction, phase separation, recrystallization, and distillation recovery. Recrystallization and extraction are completed in one purification tank, requiring low equipment investment, simple operation, and mild process conditions, making it easy for industrial-scale mass production. In addition, this invention cleverly utilizes the water contained in crude 2-methyl-1,4-naphthoquinone to form an aqueous phase, reducing the raw material drying process. At the same time, depending on the impurity content of the raw material, multiple water washings can be performed to remove impurities. This invention is highly advantageous when used for purifying crude products with high inorganic impurity content.

[0019] 3. Green and environmentally friendly, with high resource utilization and strong economic efficiency: Crude naphthoquinone does not require drying treatment, and solvent recovery does not require distillation. It can be efficiently recovered through low-energy distillation, and the overall production cost is far lower than the existing purification process. The aqueous phase and butanol phase mother liquor can be reused after being recovered by distillation, and the process can achieve water self-balance. The chromium contained in the crude 2-methyl-1,4-naphthoquinone can be effectively recovered and utilized, reducing environmental pressure and meeting the standards of green chemical production. Attached Figure Description

[0020] Figure 1 This is a partial miscible solution-liquid phase diagram of n-butanol-water. Detailed Implementation

[0021] This invention provides a method for purifying 2-methyl-1,4-naphthoquinone, comprising the following steps: The crude 2-methyl-1,4-naphthoquinone was extracted with a mixed solvent of butanol and water to obtain an organic phase. The organic phase was cooled and crystallized to obtain pure 2-methyl-1,4-naphthoquinone.

[0022] In this invention, crude 2-methyl-1,4-naphthoquinone is mixed with a butanol-water mixed solvent and then extracted to obtain an organic phase.

[0023] In this invention, the preferred ratio of 2-methyl-1,4-naphthoquinone to the butanol-water mixed solvent in the crude 2-methyl-1,4-naphthoquinone is 1 g: 2.5-6 mL. In specific embodiments of this invention, it can be 1 g: 3 mL, 1 g: 3.5 mL, 1 g: 4.5 mL, 1 g: 5 mL, or 1 g: 5.5 mL. This ensures that the crude 2-methyl-1,4-naphthoquinone is fully dispersed and dissolved, improving the extraction and crystallization effects.

[0024] In this invention, the volume ratio of butanol to water in the mixed solvent is preferably 2.5 to 5:1, and in specific embodiments of this invention, it can be 3:1, 3.5:1, 4:1, or 4.5:1. The purity of the crude 2-methyl-1,4-naphthoquinone is preferably greater than 60%, the water content is 0 to 50%, the chromium content is preferably less than 2%, and the purity of the crude 2-methyl-1,4-naphthoquinone (dry basis) is preferably 90 to 96%. The crude 2-methyl-1,4-naphthoquinone is preferably prepared by sodium dichromate oxidation. For crude 2-methyl-1,4-naphthoquinone with a water content of about 40%, the volume ratio of butanol to water in the added mixed solvent is preferably 3:1. Under this ratio, the two-phase separation effect is optimal, 2-methyl-1,4-naphthoquinone has high solubility in butanol, and the extraction efficiency of chromium and other inorganic impurities in water is relatively high.

[0025] In this invention, the extraction is preferably carried out under stirring conditions, with the stirring speed preferably being 200-400 r / min; the extraction temperature is preferably 50-75℃, and the extraction time is preferably 30-60 min. In specific embodiments of this invention, the extraction temperature can be 55℃, 60℃, 65℃, or 70℃, and the extraction time can be 35 min, 40 min, 45 min, 50 min, or 55 min. Under these temperature conditions, the solubility of 2-methyl-1,4-naphthoquinone in butanol is significantly increased, while ensuring the extraction efficiency of impurities and avoiding the deterioration of 2-methyl-1,4-naphthoquinone due to excessively high temperatures, while the dissolution and extraction efficiency decreases due to excessively low temperatures.

[0026] The target product 2-methyl-1,4-naphthoquinone in the crude 2-methyl-1,4-naphthoquinone was fully extracted into the butanol layer, while the inorganic chromium impurities and some acidic organic impurities in the crude product were extracted into the aqueous phase, thus completing the preliminary removal of impurities.

[0027] After extraction and before phase separation, the present invention preferably further includes: allowing the obtained extract to stand.

[0028] In this invention, after phase separation, it is preferable to further include: recovering the aqueous phase obtained from phase separation and reusing it in extraction or washing.

[0029] In this invention, the settling time is preferably 15-40 minutes, and in specific embodiments of this invention, it can be 20 minutes, 25 minutes, 30 minutes, or 35 minutes. Settling ensures complete separation of the two phases and avoids the organic phase carrying aqueous phase impurities.

[0030] After obtaining the organic phase, the present invention cools and crystallizes the organic phase to obtain pure 2-methyl-1,4-naphthoquinone.

[0031] Prior to the cooling and crystallization, the present invention preferably further includes: repeatedly washing the organic phase with water, and then performing phase separation on the resulting mixture. The water obtained from the phase separation is preferably distilled and reused in the extraction or washing process. Washing can further remove inorganic impurities.

[0032] In this invention, the preferred temperature for cooling crystallization is 5~25℃, and in specific embodiments of this invention, it can be 10℃ or 15℃. This invention does not have a specific limitation on the cooling crystallization time; it is sufficient to allow 2-methyl-1,4-naphthoquinone to crystallize completely.

[0033] In this invention, the cooling rate to the cooling crystallization temperature is preferably 0.1~3℃ / min. Slow cooling yields well-formed, high-purity 2-methyl-1,4-naphthoquinone crystals, avoiding the formation of impurities within the crystals due to rapid cooling.

[0034] At high temperatures, 2-methyl-1,4-naphthoquinone dissolves in large quantities in the butanol phase, but its solubility drops sharply at low temperatures. High-purity products can be precipitated by recrystallization after cooling.

[0035] After cooling and crystallization, the present invention preferably further includes: performing solid-liquid separation on the obtained system to obtain a wet 2-methyl-1,4-naphthoquinone and a mother liquor for crystallization; distilling the mother liquor for crystallization to obtain recovered butanol; and washing and drying the wet 2-methyl-1,4-naphthoquinone to obtain the purified 2-methyl-1,4-naphthoquinone.

[0036] The recovered butanol phase can be reused in the extraction process.

[0037] Before drying, the wet 2-methyl-1,4-naphthoquinone product is mixed with a butanol-water mixed solvent, and then extracted and separated again. The resulting organic phase is then cooled and crystallized.

[0038] In this invention, the extraction, phase separation and cooling crystallization are the same as described above, and will not be repeated here.

[0039] The purification method for crude 2-methyl-1,4-naphthoquinone provided by the present invention will be described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0040] The crude 2-methyl-1,4-naphthoquinone described in this invention is an industrial crude product prepared by the oxidation reaction of 2-methylnaphthalene with sodium dichromate.

[0041] Figure 1 The chromatogram of the n-butanol-water partially miscible solution used in the examples shows that there are no obvious impurity peaks on the chromatogram, indicating that the product has high purity.

[0042] Example 1 S1: Weigh 300g of industrial 2-methyl-1,4-naphthoquinone (dry basis purity 93.2%, chromium content 0.42%, water content 38%), add 900mL of butanol-water mixed solvent, butanol to water volume ratio 4:1, control the temperature at 65℃, stir at 300r / min, stir for 45min to ensure the system is fully mixed, the target product dissolves in the butanol phase, and impurities are extracted to the aqueous phase; S2: Let the mixture stand for 20 min to separate the layers, remove the lower aqueous phase, add 100 mL of water while keeping it warm, stir and wash, let it stand for 20 min to separate the layers, separate the aqueous phase again, retain the upper clear butanol phase, slowly cool the butanol phase to 15 °C at a rate of 0.3 °C / min, let it stand for 2 h to crystallize, filter, wash with the recovered aqueous phase to obtain 2-methyl-1,4-naphthoquinone wet product; S3: The crystallization mother liquor is transferred to a distillation kettle and butanol is recovered by vacuum distillation; the aqueous phase is collected and chromium resources are recovered by chemical precipitation, with a chromium recovery rate of 98%. The aqueous phase after chromium recovery is recovered and reused by distillation.

[0043] After drying the wet 2-methyl-1,4-naphthoquinone, the product purity was found to be 98.2%, the chromium impurity removal rate was 95.4%, and the product yield was 72.2%.

[0044] Example 2 S1: Weigh 300g of industrial crude 2-methyl-1,4-naphthoquinone (dry basis purity 90.8%, chromium content 0.45%, water content 41%), add 1000mL of butanol-water mixed solvent, butanol to water volume ratio 3:1, control temperature 75℃, stirring speed 200r / min, stir for 60min; S2: Let stand for 30 min to separate the aqueous phase, add 100 mL of water under heat preservation, stir and wash, let stand for 30 min to separate the aqueous phase again, and slowly cool the butanol phase to 5 °C at 1.5 °C / min to crystallize for 2.5 h. Filter and wash with the recovered aqueous phase to obtain 2-methyl-1,4-naphthoquinone wet product. S3: The mother liquor was distilled to recover butanol, and 105g of the obtained 2-methyl-1,4-naphthoquinone wet product (wet weight) was added to 300mL of butanol-water solvent with a butanol to water volume ratio of 3:1. The product was then processed according to steps S1 and S2. The aqueous phase was distilled back for reuse, and chromium was recovered.

[0045] After drying in S2, the product purity is 98.4%, the chromium impurity removal rate is 94.1%, and the product yield is 80.5%.

[0046] Recrystallization from S3 yielded 2-methyl-1,4-naphthoquinone (dry basis) with a purity of 98.1%, a yield of 11%, and a chromium content of 0.015%.

[0047] The total yield of 2-methyl-1,4-naphthoquinone obtained from S2 and S3 was 91.5%.

[0048] Example 3 S1: Weigh 300g of industrial crude 2-methyl-1,4-naphthoquinone (dry basis purity 93.5%, chromium content 0.35%), add 800mL of butanol-water mixed solvent, butanol to water volume ratio 4:1, control the temperature at 70℃, stir at 400r / min, and stir for 30min. S2: Let stand for 20 min to separate the aqueous phase. Then, under heat preservation, add 100 mL of water, stir and wash, let stand for 20 min to separate the aqueous phase again, cool the butanol phase to 10 °C at 2 °C / min, crystallize for 1.5 h, filter, wash with the recovered aqueous phase to obtain 2-methyl-1,4-naphthoquinone wet product. S3: The mother liquor is distilled to recover butanol and 2-methyl-1,4-naphthoquinone; the aqueous phase is distilled and reused, and chromium is recovered.

[0049] After drying, the product purity was 98.9%, the chromium impurity removal rate was 98.1%, and the product yield was 77.3%.

[0050] Example 4 S1: Weigh 300g of industrial crude 2-methyl-1,4-naphthoquinone (dry basis purity 93.5%, chromium content 0.35%, water content 17%), add 1200mL of butanol-water mixed solvent, butanol to water volume ratio 2.5:1, control temperature 65℃, stirring speed 400r / min, stir for 30min; S2: Let stand for 20 min to separate the aqueous phase. Then, under heat preservation, add 200 mL of the recovered aqueous phase (butanol content 3.8%), stir and wash, let stand for stratification, separate the aqueous phase again, add 200 mL of the recovered aqueous phase (butanol content 3.8%) a second time, stir and wash, let stand for stratification, separate the aqueous phase a third time, slowly cool the butanol phase to 25℃ at a rate of 0.5℃ / min, crystallize for 1.5 h, filter, wash with the recovered aqueous phase to obtain 2-methyl-1,4-naphthoquinone wet product; S3: The mother liquor is distilled to recover butanol and 2-methyl-1,4-naphthoquinone; the aqueous phase is distilled to recover the aqueous phase and chromium.

[0051] After drying, the product purity is 99.1%, the chromium impurity removal rate is 99.8%, the product yield is 75.3%, and the chromium content in the product is 0.0041%.

[0052] Example 5 S1: Weigh 300g of industrial crude 2-methyl-1,4-naphthoquinone (dry basis purity 80%, chromium content 1.2%, water content 43%), add 800mL of butanol-water mixed solvent, butanol to water volume ratio 4:1, control the temperature at 70℃, stir at 400r / min, and stir for 40min; S2: Let stand for 30 min to separate the aqueous phase. Then, under heat preservation, add 100 mL of water, stir and wash for 10 min, let stand for separation, separate the aqueous phase again, cool the butanol phase to 15 °C at a rate of 1 °C / min, crystallize for 1.5 h, filter, wash with the recovered aqueous phase to obtain 2-methyl-1,4-naphthoquinone wet product. S3: The mother liquor is distilled to recover butanol, and the aqueous phase is distilled and reused, and chromium is recovered.

[0053] After drying, the product purity was 94.5%, the chromium impurity removal rate was 91%, and the product yield was 65.3%.

[0054] Comparative Example 1 Weigh 300g of industrial crude 2-methyl-1,4-naphthoquinone (dry basis purity 93.5%, chromium content 0.35%, water content 38%), add 1000mL of butanol solvent, dissolve at 65℃, and allow to stand without stratification. Then recrystallize at 20℃ at a rate of 1℃ / min, filter, wash with water, and dry. The product purity is 96.8%, the chromium impurity removal rate is 64.5%, the product yield is 68.3%, and the chromium content in the product is 0.124%. Comparative Example 2 Weigh 300g of industrial crude 2-methyl-1,4-naphthoquinone (dry basis purity 93.5%, chromium content 0.35%, water content 38%), add 1500mL of anhydrous ethanol solvent, dissolve at 60℃, and allow to stand without stratification. Then recrystallize at 20℃ at a rate of 1℃ / min, filter and dry. The product has a dry basis purity of 98.2%, a chromium impurity removal rate of 72.3%, a product yield of 61.3%, and a chromium content of 0.0965%.

[0055] Comparative Example 3 Weigh 300g of industrial crude 2-methyl-1,4-naphthoquinone (dry basis purity 93.5%, chromium content 0.35%, water content 38%), add 1500mL of anhydrous ethanol + 400mL of water as solvent, dissolve at 60℃, and after standing, no layering occurs. Then, cool to 20℃ at a rate of 0.5℃ / min for recrystallization, filter and dry. The product has a dry basis purity of 97.4%, a chromium impurity removal rate of 86.3%, a product yield of 67.9%, and a chromium content of 0.0480%.

[0056] The results above show that using butanol and water as solvents results in better recrystallization than using a single solvent, especially in the removal of chromium impurities. In addition, the water separation process can be omitted during solvent recovery.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for purifying crude 2-methyl-1,4-naphthoquinone, characterized in that, Includes the following steps: The crude 2-methyl-1,4-naphthoquinone was mixed with a butanol-water mixed solvent and then extracted and phase-separated to obtain an organic phase. The organic phase was cooled and crystallized to obtain pure 2-methyl-1,4-naphthoquinone.

2. The purification method according to claim 1, characterized in that, The volume ratio of butanol to water in the mixed solvent is 2.5~5:

1.

3. The purification method according to claim 1, characterized in that, The crude 2-methyl-1,4-naphthoquinone has a purity of over 60 wt%, a water content of 0-50 wt%, and a chromium content of less than 2 wt%.

4. The purification method according to any one of claims 1 to 3, characterized in that, The ratio of 2-methyl-1,4-naphthoquinone to butanol-water mixed solvent in the crude 2-methyl-1,4-naphthoquinone is 1 g : 3~6 mL.

5. The purification method according to claim 1, characterized in that, The extraction is carried out under stirring conditions, at a temperature of 50-75°C, for a time of 30-60 minutes.

6. The purification method according to claim 1, characterized in that, The process after extraction and before phase separation also includes: allowing the obtained extraction system to stand. The settling time is 15-40 minutes.

7. The purification method according to claim 1, characterized in that, Before cooling and crystallization, the process further includes: washing the organic phase with water, and then performing phase separation on the resulting mixture.

8. The purification method according to claim 1, characterized in that, The cooling crystallization temperature is 5~20℃, and the cooling rate to the cooling crystallization temperature is 0.1~3℃ / min.

9. The purification method according to claim 1, characterized in that, After cooling and crystallization, the process further includes: performing solid-liquid separation on the obtained system to obtain a wet 2-methyl-1,4-naphthoquinone and a mother liquor for crystallization; distilling the mother liquor to obtain recovered butanol; and drying the wet 2-methyl-1,4-naphthoquinone to obtain the purified 2-methyl-1,4-naphthoquinone. The recovered butanol is reused in the extraction process.

10. The purification method according to claim 9, characterized in that, Before drying, the wet 2-methyl-1,4-naphthoquinone product is mixed with a butanol-water mixed solvent, and then extracted and separated again. The resulting organic phase is then cooled and crystallized.

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