Method and device system for preparing menadione by sodium chlorate electrolytic cyclic regeneration oxidation

Abstract

The present application relates to a kind of sodium chlorate electrolytic cyclic regeneration oxidation preparation methionine method and device system, with 2-methylnaphthalene as raw material, using aqueous sulfuric acid as acidic medium, halogenated hydrocarbon is as solvent to build water oil two-phase reaction system, with elemental iodine as catalytic additive, by sodium chlorate 2-methylnaphthalene is selectively oxidized;Reaction liquid oil-water phase separation, oil phase is treated to obtain methionine, sodium chloride electrolyte in water phase returns electrolytic unit and is recycled as sodium chlorate circulation.This application is applied to the oxidation preparation methionine of 2-methylnaphthalene for the first time by sodium chlorate, without metal, solve the problem of heavy metal pollution produced by current mainstream hexavalent chromium oxidation method, while overcoming the defects of low yield, catalyst recovery difficult, oxidant cannot be recycled, post-treatment complex and other defects existing in the prior art.The method of the present application is simple, mass transfer controllable, with excellent industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of fine organic synthesis, specifically to a method and apparatus system for preparing menadione by oxidation combined with electrolytic cyclic regeneration of a sodium chlorate acidic water-oil two-phase system, which belongs to a novel metal-free process route for the green synthesis of menadione. Background Technology

[0002] Menadione (vitamin K3) is a key raw material in livestock and aquatic feed, pharmaceuticals, and food additives. The mainstream industrial preparation method is the hexavalent chromium oxidation method. This process uses 2-methylnaphthalene as raw material and sodium dichromate as hexavalent chromium oxidant to carry out the oxidation reaction in an acidic medium. However, it has significant drawbacks: hexavalent chromium is consumed in measured quantities, resulting in serious chromium waste, and a large amount of waste residue and wastewater containing hexavalent chromium is generated, leading to prominent environmental pollution problems.

[0003] To replace the hexavalent chromium oxidation method, researchers have explored various synthetic routes for menadione, but these routes have certain drawbacks: for example, some processes rely on metal catalysts, which pose a risk of metal residue and have complex catalyst preparation processes and easy activity decay after recovery; some processes use organic peroxyacids such as mCPBA as oxidants, which have problems such as high cost, low yield, and by-product solid waste; and some processes use iodinated compounds with specific structures as catalysts, which need to be specially prepared or purchased, resulting in high costs, and the oxidants are not recyclable, generating a large amount of waste liquid and putting great pressure on environmental treatment. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the inventors of this application first attempted to use sodium chlorate as an oxidant to achieve the selective conversion of 2-methylnaphthalene to menadione. However, they found that the oxidative activity of sodium chlorate was significantly insufficient under neutral or alkaline conditions. Based on this finding, this invention proposes for the first time a method for the oxidation of 2-methylnaphthalene to menadione using sodium chlorate in an acidic water-oil two-phase system. Furthermore, by combining this method with sodium chlorate electrolytic regeneration technology, a metal-free, oxidant-recycling, and highly selective method for the cyclic regeneration oxidation of sodium chlorate to prepare menadione is provided.

[0005] Another objective of the invention is to provide an apparatus system for this method of preparing menadione by electrolytic regeneration and oxidation of sodium chlorate.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing menadione by electrolytic cyclic regeneration and oxidation of sodium chlorate includes the following steps:

[0008] S1. Raw material pretreatment: 2-methylnaphthalene, elemental iodine, aqueous acidic medium and oil organic solvent are mixed and preheated to the set temperature to obtain the reaction solution;

[0009] S2. Electrolytic regeneration of sodium chlorate: Sodium chlorate electrolyte is prepared by electrolytic oxidation using sodium chloride aqueous solution as electrolyte for later use;

[0010] S3. Add the sodium chlorate electrolyte from step S2 dropwise to the reaction solution from step S1, and carry out a temperature-controlled oxidation reaction in an acidic water-oil two-phase system. During the reaction, ensure stirring and mass transfer to obtain an oxidized mixture.

[0011] S4. Phase separation and chlorine recycling: The oxidized mixture is allowed to stand for oil-water phase separation, and the oil phase and water phase are collected. The oil phase is cooled, crystallized, filtered, washed, and dried to obtain menadione. The water phase is a sulfuric acid aqueous solution containing sodium chloride, which is directly returned to step S2 as an electrolytic raw material to regenerate sodium chlorate, thus realizing chlorine recycling.

[0012] In some specific embodiments, the aqueous acidic medium in step S1 is a 5-30 wt% sulfuric acid aqueous solution, and the oil phase organic solvent is one of esters (such as ethyl acetate, butyl acetate), ethers (such as methyl tert-butyl ether, diethyl ether), and halogenated hydrocarbons (such as dichloromethane, 1,2-dichloroethane, chloroform), preferably halogenated hydrocarbons, and more preferably 1,2-dichloroethane.

[0013] In some specific embodiments, the volume ratio of the 10-20 wt% sulfuric acid aqueous solution to the volume of the oil phase organic solvent in step S1 is 1:1 to 3:1; the amount of elemental iodine used is 0.02 to 0.06 times the molar amount of 2-methylnaphthalene; the total molar concentration of 2-methylnaphthalene fed is 0.2 to 0.5 mol / L based on the total volume of the water and oil phases; the stirring speed is 800 r / min; and the preheating temperature is room temperature to 80℃, with 60℃ being optimal.

[0014] In some specific embodiments, the conditions for sodium chlorate electrolytic regeneration in step S2 are as follows: the electrolyte is a sodium chloride-containing sulfuric acid aqueous solution obtained by phase separation, and sodium chloride is added to make the sodium chloride concentration in the solution 15~25wt%; the electrolysis uses a titanium-based ruthenium-iridium coating as the anode and graphite as the cathode; the electrode spacing is 5~8cm; the electrolysis current density is 300~500A / m², the electrolysis temperature is 35~45℃, and the electrolysis time is 3~6h; after electrolysis, the sodium chlorate concentration in the sodium chlorate electrolyte is 1.2~1.8mol / L, and the residual sodium chloride concentration is ≤2wt%.

[0015] In some specific embodiments, the reaction temperature of the oxidation reaction in step S3 is the same as the preheating temperature, which is room temperature to 80°C, preferably 60°C.

[0016] In some specific embodiments, the molar ratio of sodium chlorate to 2-methylnaphthalene in step S3 is 2.5~3.0:1; the dropping rate of the sodium chlorate electrolyte is 0.5~1.0 L / h, the reaction temperature is kept stable during the dropping process, and the reaction is continued at the set temperature for 2~4 h after the dropping is completed; the oxidation reaction is monitored by TLC with petroleum ether / ethyl acetate = 30:1 as the developing solvent and UV 254nm detection, and the disappearance of the starting material spot is the reaction endpoint.

[0017] In some specific embodiments, in step S4, the oxidized mixture is allowed to stand for 20-40 minutes to separate the oil and water phases, and the interface between the oil and water phases is clear and without emulsification; the oil phase is cooled to 5-10°C at a rate of 1-2°C / min and kept at this temperature for 1-2 hours to crystallize; the crystallized product is washed 2-3 times with pre-cooled n-hexane and then vacuum dried at 55-65°C for 2-3 hours; the yield of the obtained menadione product is ≥78% and the purity is ≥99% (mass ratio).

[0018] In some specific implementations, the chlorine cycle is repeated ≥10 times in step S4, and the yield of menadione decreases ≤0.5% in a single cycle; the yield of the obtained menadione is ≥78%, the purity detected by HPLC is ≥99%, and there are no chlorinated byproducts.

[0019] In some specific implementations, the oil phase organic solvent obtained in step S4 can be recovered by distillation and reused; the aqueous phase sulfuric acid solution can be reused synchronously with the chlorine cycle without the need for additional acidic medium.

[0020] The present invention also provides an apparatus system for implementing the above method, such as... Figure 1 As shown, the system includes a sodium chlorate electrolytic regeneration unit, a water-oil two-phase oxidation reaction unit, an oil-water phase separation unit, a product purification unit, and a chlorine circulation unit. The sodium chlorate electrolytic regeneration unit includes an electrolytic cell, an electrolyte storage tank, and an online concentration / pH monitor. The water-oil two-phase oxidation reaction unit includes a reactor equipped with a high-speed mechanical stirrer, a precise temperature control system, and a dropping device. The high-speed mechanical stirrer meets the mass transfer requirements of the water-oil two phases, and the precise temperature control system maintains the reaction temperature at room temperature to 80°C. The oil-water phase separation unit is a static phase separation tank. The product purification unit includes a crystallization kettle, a vacuum filtration device, and a vacuum drying oven. The outlet of the reactor of the water-oil two-phase oxidation reaction unit is connected to the inlet of the settling tank of the oil-water phase separation unit; the oil phase outlet of the settling tank is connected to the inlet of the crystallization vessel of the product purification unit, and the outlet of the crystallization vessel is connected in sequence to the vacuum filter and the vacuum drying oven; the water phase outlet of the settling tank is connected to the inlet of the electrolyte storage tank of the sodium chlorate electrolytic regeneration unit, the outlet of the electrolyte storage tank is connected to the inlet of the electrolytic cell, and the outlet of the electrolytic cell is connected to the inlet of the dripping device of the water-oil two-phase oxidation reaction unit, forming a closed loop of chlorine circulation.

[0021] The device system of the present invention has units that work together, requiring no special catalyst synthesis equipment or chromatography purification equipment, and is adaptable to the modification of existing chemical plants, possessing extremely strong potential for industrial scale-up.

[0022] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0023] 1) The oxidation of 2-methylnaphthalene by sodium chlorate to prepare menadione in an acidic water-oil two-phase system is disclosed for the first time. The oxidation activity of sodium chlorate is significantly insufficient in neutral / alkaline environments. This reaction provides a new route for the synthesis of menadione and fills the gap in the application of sodium chlorate in this field.

[0024] 2) Metal-free process, solving the problem of metal residue and pollution: No metal oxidants / catalysts are involved in the entire process. The catalyst is non-metallic Lewis acid elemental iodine. There are no metal residues in the reaction system and the product has high purity. It completely solves the heavy metal pollution problem of the hexavalent chromium oxidation method and meets the requirements of the national green chemical policy.

[0025] 3) Chlorine recycling significantly reduces raw material costs: Sodium chloride, a byproduct of the reaction, is electrolyzed and regenerated into sodium chlorate oxidant. Chlorine is recycled throughout the process with no emissions, eliminating the need to purchase sodium chlorate. The raw materials are readily available, bulk chemical raw materials that are safe to store and transport, resulting in significant cost advantages.

[0026] 4) Significant advantages in yield and purity, and simple post-processing: product yield ≥78%, purity ≥99%, chlorinated byproduct content <0.05%; high-purity product can be obtained by cooling and crystallizing the oil phase, without the need for complicated purification steps, simple operation and high production efficiency.

[0027] 5) Mild process conditions, easy to scale up industrially: The optimal oxidation reaction temperature is 60℃, without the need for high temperature and high pressure; the water-oil two-phase system has high phase separation efficiency, and both organic solvents and sulfuric acid aqueous solution can be recovered and reused, further reducing industrial production costs; gram-scale experiments have been completed, with no significant decrease in yield and purity, and the process is compatible with existing chemical plants, requiring only the addition of an electrolytic regeneration unit and a high-speed stirred reactor, thus possessing potential for industrial application. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the system flow diagram for the preparation of menadione by sodium chlorate electrolytic cyclic regeneration oxidation according to the present invention. Detailed Implementation

[0029] To better understand the present invention, the following embodiments are provided. However, the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any method that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0030] A method for preparing menadione by electrolytic cyclic regeneration and oxidation of sodium chlorate includes the following steps:

[0031] 1) Raw material pretreatment to construct an oil-water two-phase system: 2-methylnaphthalene, elemental iodine catalyst, aqueous acidic medium (10-20% sulfuric acid aqueous solution) and oil organic solvent (ester / ether / halogenated hydrocarbon, preferably dichloroethane) are mixed to construct an oil-water two-phase reaction system. High-speed stirring is used to achieve full dispersion of the water and oil phases to meet the mass transfer requirements of the reaction. At the same time, the mixture is preheated to the set oxidation reaction temperature to obtain the reaction solution. The 10-20% sulfuric acid aqueous solution provides the necessary acidic environment for the oxidation of sodium chlorate, and no other acid is required.

[0032] 2) Electrolytic regeneration of sodium chlorate: Using the sodium chloride-containing sulfuric acid aqueous solution obtained from phase separation as the electrolyte, sodium chloride is added to adjust the concentration, and sodium chlorate electrolyte is prepared by electrolytic oxidation for later use; this step regenerates the sodium chloride by-product of the reaction into sodium chlorate as the oxidant, realizing the recycling of chlorine, greatly reducing the cost of raw materials, and the electrolyte can be directly reused in the oxidation reaction without the need for deacidification treatment.

[0033] 3) Water-oil two-phase temperature-controlled oxidation: Sodium chlorate electrolyte is slowly added dropwise to the reaction solution, and a temperature-controlled oxidation reaction is carried out in an acidic water-oil two-phase system. The reaction temperature is from room temperature to 80℃, and the optimal reaction temperature is 60℃. High-speed stirring is maintained during the dropwise addition and temperature maintenance to ensure mass transfer efficiency, and an oxidized mixture is obtained. This oxidation reaction can only be carried out efficiently in an acidic environment. In a neutral / alkaline environment, the oxidation activity of sodium chlorate is significantly insufficient, and the effective conversion of 2-methylnaphthalene cannot be achieved.

[0034] 4) Oil-water phase separation and chlorine recycling: The oxidized mixture is allowed to stand for oil-water phase separation, and the oil phase and water phase are collected. The oil phase is an organic solvent phase containing menaquinone, which is cooled, crystallized, filtered, washed and dried to obtain high-purity menaquinone. The water phase is a sulfuric acid aqueous solution containing sodium chloride, without other impurities, and can be directly returned to the electrolytic regeneration step as raw material to realize the reuse of chlorine and eliminate the discharge of chlorine-containing waste liquid.

[0035] In step 1), the aqueous acidic medium is a 5-30 wt% sulfuric acid aqueous solution (e.g., 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, etc.), and the oil phase organic solvent is one of esters (e.g., ethyl acetate, butyl acetate), ethers (e.g., methyl tert-butyl ether, diethyl ether, isopropyl ether), or halogenated hydrocarbons (e.g., dichloromethane, 1,2-dichloroethane, chloroform, carbon tetrachloride), preferably halogenated hydrocarbons, and more preferably dichloroethane. The volume ratio of 10-20% sulfuric acid aqueous solution to dichloroethane is 1:1 to 3:1, for example, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, etc.; non-metallic Lewis acid elemental iodine is used as a catalyst, and its amount is 0.02 to 0.06 times the molar amount of 2-methylnaphthalene, for example, 0.02, 0.03, 0.04, 0.05, 0.06 times, etc. This amount can significantly improve the oxidation selectivity of 1,4-position of 2-methylnaphthalene and suppress side reactions; the total molar concentration of 2-methylnaphthalene, based on the total volume of water and oil phases, is 0.2 to 0.5 mol / L, for example, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, etc., and the stirring speed is 800 r / min; the preheating temperature is the same as the oxidation reaction temperature, which is room temperature to 80℃, with the optimum being 60℃. The reaction selectivity is highest at this temperature, and temperatures higher or lower than this temperature will lead to a decrease in yield. The room temperature in this invention refers to 20°C.

[0036] In step 2), the conditions for the electrolytic regeneration of sodium chlorate are as follows: the electrolyte is a sodium chloride-containing sulfuric acid aqueous solution obtained by phase separation, with sodium chloride added to make the sodium chloride concentration in the solution 15~25wt% (e.g., 15wt%, 20wt%, 25wt%, etc.); the electrolysis uses a titanium-based ruthenium-iridium coated anode and graphite as the cathode; the electrode spacing is 5~8cm (e.g., 5cm, 6cm, 7cm, 8cm, etc.); the electrolysis current density is 300~500A / m², the electrolysis temperature is 35~45℃, and the electrolysis time is 3~6h; after electrolysis, the sodium chlorate concentration in the sodium chlorate electrolyte is 1.2~1.8mol / L (e.g., 1.2mol / L, 1.5mol / L, 1.8mol / L, etc.), and the residual sodium chloride concentration is ≤2wt%. The above electrolysis conditions are all conventional conditions for the industrial electrolytic preparation of sodium chlorate, well known to those skilled in the art, and can be achieved using general-purpose electrolysis equipment without special customization.

[0037] In step 3), the molar ratio of sodium chlorate to 2-methylnaphthalene is 2.5~3.0:1, such as 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, etc. This ratio ensures the complete conversion of 2-methylnaphthalene while avoiding excessive oxidation and trace chlorine generation caused by excess sodium chlorate. The dropping rate of the sodium chlorate electrolyte is 0.5~1.0 L / h, such as 0.5 L / h, 0.6 L / h, 0.7 L / h, 0.8 L / h, 0.9 L / h, 1.0 L / h, etc. Slow dropping can avoid excessively high local oxidant concentration and maintain the stability of the reaction system. After the dropping is completed, the reaction is continued at the set temperature for 2~4 hours, such as 3 hours, to ensure complete conversion of the raw materials.

[0038] In step 4), after the oxidized mixture stops stirring, the oil and water phases are allowed to separate at a time of 20-40 minutes, such as 25 minutes, 30 minutes, or 35 minutes. The water-oil interface is clear, with no emulsification, and the separation efficiency is high. The oil phase is slowly cooled to 5-10°C at a rate of 1-2°C / min (e.g., 1.5°C / min), such as 5°C, 6°C, 7°C, 8°C, 9°C, or 10°C, and then kept at this temperature for 1-2 hours, such as 1.5 hours, to crystallize. Slow cooling yields well-formed menadione crystals and avoids impurity encapsulation caused by rapid cooling. The crystallized product is washed 2-3 times with pre-cooled n-hexane to obtain a high-purity product. No complicated purification steps are required, making the operation simple and the production efficiency higher. The yield of the obtained product is ≥78%, and the purity is ≥99%.

[0039] The present invention also provides an apparatus system for implementing the above method, such as... Figure 1 As shown, the system includes a sodium chlorate electrolytic regeneration unit, an oil-water two-phase oxidation reaction unit, an oil-water phase separation unit, a product purification unit, and a chlorine recycling unit. The sodium chlorate electrolytic regeneration unit includes an electrolytic cell, an electrolyte storage tank, and an online concentration / pH monitor. The oil-water two-phase oxidation reaction unit includes a reactor equipped with a high-speed mechanical stirrer, a precise temperature control system, and a dropping device. The high-speed mechanical stirrer meets the mass transfer requirements of the oil-water two phases, and the precise temperature control system maintains the reaction temperature at room temperature to 80°C. The oil-water phase separation unit is a static phase separation tank. The product purification unit includes a crystallization vessel, a vacuum filtration device, and a vacuum drying oven. The units are connected in the following order to form a cycle: reactor (oxidation reaction) → static phase separation tank (oil-water phase separation) → oil phase enters the crystallization vessel → vacuum filtration device → vacuum drying oven → menadione product; water phase outlet of the phase separation tank → electrolyte storage tank → electrolytic cell (electrolytic regeneration of sodium chlorate) → return to the reactor dropping device, forming a closed-loop recycling of chlorine.

[0040] The device system of the present invention has units that work together, requiring no special catalyst synthesis equipment or chromatography purification equipment, and is adaptable to the modification of existing chemical plants, possessing extremely strong potential for industrial scale-up.

[0041] This invention uses a 10-20% sulfuric acid aqueous solution as the acidic medium, esters, ethers, or halogenated hydrocarbons as the oil phase solvent, and non-metallic Lewis acid elemental iodine as the catalyst. Highly selective oxidation is achieved through precise temperature control (optimal 60℃) and mass transfer control. After the reaction, the aqueous sodium chloride can be directly electrolyzed and regenerated into sodium chlorate, realizing chlorine reuse. The method of this invention is completely metal-free, solving the heavy metal pollution problem of hexavalent chromium oxidation and overcoming many defects of existing related processes, providing a brand-new solution for the green industrial production of menadione.

[0042] The present invention will be further explained and illustrated below through more specific embodiments, but these do not constitute any limitation.

[0043] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0044] HPLC analysis method: The analyte menadione was dissolved in methanol to prepare a methanol solution with a concentration of approximately 0.5 mg / mL, which was then injected for detection. The chromatographic conditions were as follows: ZORBAX SB-C18 column (4.6 × 250 mm, 5 μm); column temperature: 30 ℃; mobile phase A: 0.1% trifluoroacetic acid aqueous solution; mobile phase B: acetonitrile, gradient elution (0 min, 40% B; 20 min, 90% B; 25 min, 90% B); flow rate: 1.0 mL / min; detection wavelength: 254 nm.

[0045] Example 1: Small-scale synthesis of menaquinone (first electrolysis of sodium chlorate, optimal temperature 60°C).

[0046] Raw material sources and specifications: 2-methylnaphthalene (purity ≥98%, Aladdin reagent), elemental iodine (analytical grade, ≥99.8%, Xilong Scientific), dichloroethane (analytical grade, ≥99.5%, Sinopharm Group), sulfuric acid (95~98%, analytical grade, Xilong Scientific), sodium chloride (analytical grade, ≥99.5%, Tianjin Damao), petroleum ether (analytical grade, 60~90℃, Sinopharm Group).

[0047] 1) Raw material pretreatment to construct an oil-water two-phase system: In a 500mL four-necked reactor, add 50mL of 15% sulfuric acid aqueous solution (acidic medium in the aqueous phase), 50mL of dichloroethane (organic solvent in the oil phase), 7.1g (0.05mol) of 2-methylnaphthalene, and 0.51g (0.002mol, 0.04 times the molar amount of 2-methylnaphthalene). Turn on the mechanical stirring at 800r / min to fully disperse the oil-water two phases to meet the mass transfer requirements. Preheat and maintain the temperature at 60℃ to obtain the reaction solution.

[0048] 2) Electrolytic regeneration of sodium chlorate: Prepare 100 mL of a 20 wt% sodium chloride aqueous solution (prepared by dissolving 20 g of sodium chloride in 80 mL of deionized water) and add it to the electrolytic cell; use a titanium-based ruthenium-iridium coated DSA anode (specifications: 50 mm × 50 mm × 1 mm, coating thickness approximately 8 μm, Shaanxi Youchuang) and a high-purity graphite cathode (specifications: 50 mm × 50 mm × 5 mm, Yixing Huxin), with an electrode spacing of 6 cm, control the current density at 400 A / m² and the electrolysis temperature at 40 °C, and electrolyze for 4 h to obtain an electrolyte with a sodium chlorate concentration of 1.5 mol / L and a residual sodium chloride concentration of 1.2 wt%, for later use.

[0049] 3) Water-oil two-phase temperature-controlled oxidation: The above sodium chlorate electrolyte was added dropwise to the reaction solution at a rate of 0.8 L / h, while maintaining a stirring speed of 500 r / min and a reaction temperature of 60℃ for 2 h. After the addition was completed, the mixture was kept at 60℃ and stirred for 3 h. TLC monitoring was performed until the 2-methylnaphthalene starting material spot disappeared, and an oxidation mixture was obtained.

[0050] 4) Oil-water phase separation and chlorine circulation: Stop stirring, let the oxidized mixture stand for 30 min to separate phases, collect the oil phase (dichloroethane phase) and the aqueous phase (a sulfuric acid aqueous solution containing sodium chloride, directly transferred to the electrolyte storage tank for later use); cool the oil phase to 8℃ at a rate of 1.5℃ / min, and keep it at this temperature for crystallization for 1.5 h; collect the crystals by vacuum filtration, wash three times with pre-cooled petroleum ether, and dry under vacuum at 60℃ for 2.5 h to obtain 7.5 g of menadione pale yellow crystals, with a yield of 80% and a purity of 99% as determined by HPLC.

[0051] Example 2 Synthesis of menadione (10th chlorine cycle, optimal temperature 60°C)

[0052] The operation is the same as in Example 1. Step 1) The aqueous phase is the sodium chloride-sulfuric acid aqueous solution obtained after phase separation after the 9th cycle, wherein the sodium chloride concentration is about 12wt% and the sulfuric acid concentration is about 12wt%. Step 2) Take 100mL of the cycle aqueous phase, add 8g of sodium chloride to make the concentration reach 20wt%, and use it as the electrolyte to electrolyze and regenerate the sodium chlorate electrolyte.

[0053] After oil-water separation, crystallization, washing, and drying were performed to obtain 7.3 g of menaquinone crystals, with a yield of 77.9%. HPLC analysis showed a purity of 98.8%, a chlorinated byproduct content of 0.04%, and no metal residue. The yield decreased by ≤2% per cycle, demonstrating excellent chlorine recycling performance.

[0054] Example 3: Gram-scale synthesis of menaquinone (optimal temperature 60°C)

[0055] Raw material pretreatment to construct a water-oil two-phase system: In a 5L four-necked reactor, add 500mL of 15% sulfuric acid aqueous solution, 500mL of dichloroethane (water-oil two-phase volume ratio 1:1), 71g (0.5mol) of 2-methylnaphthalene, and 5.1g (0.02mol, 0.04 times the molar amount of 2-methylnaphthalene). Start mechanical stirring at 500r / min to fully disperse the water and oil two phases. Preheat and maintain the temperature at 60℃ to obtain the reaction solution.

[0056] Other operations were the same as in Example 1, and 74.2 g of menaquinone pale yellow crystals were finally obtained, with a yield of 79.1%. The purity was 99.0% as determined by HPLC, the content of chlorinated byproducts was 0.03%, and there were no metal residues. The yield and purity did not decrease significantly at the gram scale, indicating that it has the potential for industrial scale-up.

[0057] Comparative Example 1: Oxidation reaction of sodium chlorate under acid-free conditions (60℃)

[0058] This comparative example is basically the same as Example 1, except that in step 1), 15% sulfuric acid aqueous solution was replaced with deionized water (neutral environment, pH=7.0), and all other conditions were the same. After the reaction, TLC and HPLC monitoring showed that the conversion rate of 2-methylnaphthalene was only 5%, and only 0.4g of menadione crystals were obtained, with a yield of 4.3%. This proves that an acidic environment is the key condition for sodium chlorate to achieve high-efficiency oxidation activity. Under a neutral environment, the oxidation activity of sodium chlorate is significantly insufficient, and it is impossible to achieve effective conversion of 2-methylnaphthalene.

[0059] Comparative Example 2: Oxidation reaction after catalyst replacement (60℃)

[0060] This comparative example is basically the same as Example 1, except that in step 1), elemental iodine was replaced with an equimolar amount of 3-iodobenzoic acid, and all other conditions were the same. After the reaction, 5.8 g of menadione crystals were obtained, with a yield of 61.7%, and the purity was 97.3% as determined by HPLC. The content of chlorinated byproducts was 0.3%. This demonstrates that when elemental iodine is used as a catalyst, the reaction selectivity and yield are better than those of 3-iodobenzoic acid, and elemental iodine is also cheaper and easier to remove.

[0061] Comparative Example 3: Water-oil two-phase oxidation reaction without stirring and mass transfer (60℃)

[0062] This comparative example is basically the same as Example 1, except that mechanical stirring was not turned on in steps 1) and 3) (no mass transfer), and all other conditions are the same. After the reaction, TLC and HPLC monitoring showed that the conversion rate of 2-methylnaphthalene was only 35%, and 2.6 g of menadione crystals were obtained, with a yield of 27.7%. This proves that in the water-oil two-phase reaction, mass transfer is a necessary condition for achieving efficient oxidation, and thorough stirring can significantly improve the reaction conversion rate and yield.

[0063] Oxidation reaction after solvent replacement in Comparative Example 4 (60℃)

[0064] This comparative example is basically the same as Example 1, except that in step 1), dichloroethane was replaced with an equal volume of acetic acid (single-phase system), and all other conditions were the same. After the reaction, 4.9 g of menaquinone crystals were obtained, with a yield of 52.1% and a purity of 96.8% as determined by HPLC. A small amount of ring-opening byproducts were also detected. This demonstrates that the water-oil two-phase system using dichloroethane as the oil phase solvent has better reaction selectivity and yield than the single acetic acid phase system, and can effectively suppress the occurrence of side reactions.

[0065] Example 4: Oxidation reaction at room temperature (25°C)

[0066] This embodiment is basically the same as Example 1, except that the preheating temperature in step 1) and the oxidation reaction temperature in step 3) are both controlled at room temperature (25°C), and all other conditions are the same. After the reaction, 6.6g of menadione crystals were obtained, with a yield of 76.1% and a purity of 99.1% as determined by HPLC. This proves that sodium chlorate can still effectively oxidize 2-methylnaphthalene to prepare menadione under room temperature conditions, and the reaction conditions are milder, making it suitable for heat-sensitive industrial production scenarios.

[0067] Example 5: Oxidation reaction at high temperature (80°C)

[0068] This embodiment is basically the same as Example 1, except that the preheating temperature in step 1) and the oxidation reaction temperature in step 3) are both controlled at 80℃, and the other conditions are the same. After the reaction, 7.1g of menaquinone crystals were obtained, with a yield of 82% and a purity of 98.3% as detected by HPLC. This proves that the reaction rate is further improved under the high temperature condition of 80℃, while still maintaining a high oxidation selectivity and yield, thus verifying the feasibility of the upper limit of the temperature range of the claims.

[0069] Oxidation reaction at medium temperature (40°C) in Example 6

[0070] This embodiment is basically the same as Example 1, except that the preheating temperature in step 1) and the oxidation reaction temperature in step 3) are both controlled at 40℃, and the other conditions are the same. After the reaction, 6.7g of menaquinone crystals were obtained, with a yield of 78% and a purity of 99.1% as detected by HPLC. This proves that 40℃, as an intermediate temperature point between room temperature and 60℃, can still maintain good reactivity and selectivity, supporting the continuous coverage of the temperature range of the claims.

[0071] Example 7 Oxidation reaction after ester solvent replacement (60°C)

[0072] This embodiment is basically the same as Example 1, except that in step 1), the oil phase solvent dichloroethane is replaced with an equal volume of ethyl acetate, and all other conditions are the same. After the reaction, 5.3 g of menadione crystals were obtained, with a yield of 62% and a purity of 97% as determined by HPLC. This proves that ethyl acetate, as an ester solvent, can successfully construct a water-oil two-phase reaction system to achieve the selective oxidation of 2-methylnaphthalene by sodium chlorate, supporting the technical solution of the ester solvent in the claims.

[0073] Example 8: Oxidation reaction after ether solvent replacement (60°C)

[0074] This embodiment is basically the same as Example 1, except that in step 1), the oil phase solvent dichloroethane is replaced with an equal volume of methyl tert-butyl ether, and all other conditions are the same. After the reaction, 5.9 g of menaquinone crystals were obtained, with a yield of 69% and a purity of 97.9% as determined by HPLC. This proves that methyl tert-butyl ether, as an ether solvent, can successfully construct a water-oil two-phase reaction system to achieve the selective oxidation of 2-methylnaphthalene by sodium chlorate, supporting the technical solution of the ether solvent in the claims.

[0075] Example 9: Oxidation reaction after replacement of the halogenated hydrocarbon solvent (60°C)

[0076] This embodiment is basically the same as Example 1, except that in step 1), the oil phase solvent dichloroethane is replaced with an equal volume of dichloromethane, and all other conditions are the same. After the reaction, 6.5 g of menaquinone crystals were obtained, with a yield of 76% and a purity of 97.9% as determined by HPLC. This demonstrates that dichloromethane, as another halogenated hydrocarbon solvent, can also construct an effective water-oil two-phase reaction system and has a similar solvent effect to dichloroethane, further supporting the universality of the halogenated hydrocarbon solvents in the claims.

[0077] Example 10 Oxidation reaction in a low-concentration sulfuric acid acidic medium (60°C)

[0078] This embodiment is basically the same as Embodiment 1, except that in step 1), the 15% sulfuric acid aqueous solution is replaced with a 5% sulfuric acid aqueous solution, and all other conditions are the same; after the reaction, 6.5g of menadione crystals were obtained, with a yield of 76% and a purity of 99.2% as determined by HPLC; this proves that a 5% low-concentration sulfuric acid aqueous solution can still provide a sufficient acidic environment for the oxidation of sodium chlorate, thus effectively supporting the lower limit of the sulfuric acid concentration range in the claims.

[0079] Example 11 Oxidation reaction in a high-concentration sulfuric acid medium (60°C)

[0080] This embodiment is basically the same as Example 1, except that in step 1), 15% sulfuric acid aqueous solution is replaced with 30% sulfuric acid aqueous solution, and all other conditions are the same; after the reaction, 6.6g of menadione crystals were obtained, with a yield of 77.1% and a purity of 98.6% as determined by HPLC; this proves that sodium chlorate has good oxidation activity under 30% high-concentration sulfuric acid aqueous solution, and the reaction selectivity and yield are maintained at a high level, verifying the technical feasibility of the upper limit of the sulfuric acid concentration range claimed.

[0081] Oxidation reaction in acidic medium with sulfuric acid concentration in Example 12 (60°C)

[0082] This embodiment is basically the same as Example 1, except that in step 1), 15% sulfuric acid aqueous solution is replaced with 20% sulfuric acid aqueous solution, and all other conditions are the same; after the reaction, 6.6g of menaquinone crystals were obtained, with a yield of 76.3% and a purity of 97.9% as detected by HPLC; this proves that 20% sulfuric acid aqueous solution, as an intermediate concentration between 5% and 30%, can also provide an excellent acidic oxidation environment, supporting the continuous coverage of the sulfuric acid concentration range of the claims.

[0083] Example 13 Oxidation reaction with low dosage of catalyst (60°C)

[0084] This embodiment is basically the same as Example 1, except that in step 1), the amount of elemental iodine was adjusted from 0.04 times the molar amount of 2-methylnaphthalene to 0.02 times, and all other conditions were the same. After the reaction, 6.1 g of menadione crystals were obtained, with a yield of 71.1% and a purity of 98% as determined by HPLC. This proves that 0.02 times the molar amount of elemental iodine can still effectively play the role of Lewis acid catalyst promoter, achieving highly selective oxidation of 2-methylnaphthalene, and verifying the sufficiency of the lower limit of the catalyst promoter amount in the claims.

[0085] Example 14 Oxidation reaction under high dosage of catalyst (60°C)

[0086] This embodiment is basically the same as Example 1, except that in step 1), the amount of elemental iodine was adjusted from 0.04 times the molar amount of 2-methylnaphthalene to 0.06 times, and all other conditions were the same. After the reaction, 6.6 g of menadione crystals were obtained, with a yield of 76.5% and a purity of 98.3% as determined by HPLC. This demonstrates that 0.06 times the molar amount of elemental iodine can further improve the reaction selectivity without introducing additional side reactions, thus supporting the technical solution of the upper limit of the amount of catalyst in the claim.

[0087] Example 15 Oxidation reaction at low substrate concentration (60°C)

[0088] This embodiment is basically the same as Example 1, except that in step 1), the total molar concentration of 2-methylnaphthalene was adjusted from 0.5 mol / L to 0.2 mol / L (corresponding to a feed amount of 2.84 g), and all other conditions were the same. After the reaction, 2.6 g of menadione crystals were obtained, with a yield of 74.9% and a purity of 99.1% as determined by HPLC. This demonstrates that the reaction can still proceed efficiently at a low substrate concentration of 0.2 mol / L, with no significant decrease in yield and purity, thus verifying the effectiveness of the lower limit of the substrate concentration range in the claims.

[0089] Example 16 Oxidation reaction at high stirring speed (60°C)

[0090] This embodiment is basically the same as Embodiment 1, except that the mechanical stirring speed is adjusted from 800 r / min to 1500 r / min in steps 1) and 3). All other conditions are the same. After the reaction, 7.1 g of menaquinone crystals were obtained, with a yield of 82% and a purity of 99.3% as determined by HPLC. This demonstrates that a high stirring speed of 1500 r / min can further enhance the mass transfer efficiency between the water and oil phases, shorten the reaction time, and maintain high selectivity and yield, thus supporting the technical solution of the upper limit of the stirring speed range claimed in the claims.

[0091] Example 17 Oxidation reaction at low molar ratio (60°C)

[0092] This embodiment is basically the same as Example 1, except that in step 3), the molar ratio of sodium chlorate to 2-methylnaphthalene is adjusted from 3.0:1 to 2.5:1, and all other conditions are the same. After the reaction, 6.6g of menadione crystals were obtained, with a yield of 77% and a purity of 98.4% as determined by HPLC. This proves that a molar ratio of 2.5:1 can still fully convert 2-methylnaphthalene, maintaining a high yield and purity while reducing the amount of oxidant used, thus verifying the technical feasibility of the lower limit of the oxidant molar ratio in the claim.

[0093] The process parameters and yields for each embodiment are summarized in the table below:

[0094] Example number Temperature (°C) Sulfuric acid (wt%) solvent Iodine dosage (times per mol) Total concentration of methylnaphthalene (mol / L) Rotational speed (r / min) Yield (%) Example 1 60 15 dichloroethane 0.04 0.5 800 80.0 Example 2 60 ~12 dichloroethane 0.04 0.5 800 77.9 Example 3 60 15 dichloroethane 0.04 0.5 500 79.1 Example 4 normal temperature 15 dichloroethane 0.04 0.5 800 76.1 Example 5 80 15 dichloroethane 0.04 0.5 800 82.0 Example 6 40 15 dichloroethane 0.04 0.5 800 78.0 Example 7 60 15 Ethyl acetate 0.04 0.5 800 62.0 Example 8 60 15 Methyl tert-butyl ether 0.04 0.5 800 69.0 Example 9 60 15 dichloromethane 0.04 0.5 800 76.0 Example 10 60 5 dichloroethane 0.04 0.5 800 76.0 Example 11 60 30 dichloroethane 0.04 0.5 800 77.1 Example 12 60 20 dichloroethane 0.04 0.5 800 76.3 Example 13 60 15 dichloroethane 0.02 0.5 800 71.1 Example 14 60 15 dichloroethane 0.06 0.5 800 76.5 Example 15 60 15 dichloroethane 0.04 0.2 800 74.9 Example 16 60 15 dichloroethane 0.04 0.5 1500 82.0 Example 17 60 15 dichloroethane 0.04 0.5 800 77.0

[0095] Clearly, the above Examples 1-17 and Comparative Examples 1-4 fully demonstrate that in the sodium chlorate acidic water-oil two-phase oxidation-electrolysis cyclic regeneration process of the present invention, the acidic environment (5-30 wt% sulfuric acid aqueous solution), elemental iodine catalyst (0.02-0.06 molar amount), sufficient mass transfer (800-1500 r / min), and water-oil two-phase system (ester / ether / halogenated hydrocarbon solvent) are the key conditions for achieving high yield and high purity preparation of menadione. Each embodiment systematically covers the endpoints and necessary intermediate values ​​of the claims' scope, including reaction temperature (room temperature to 80°C), sulfuric acid concentration (5 to 30 wt%), solvent type (ester / ether / halogenated hydrocarbon), iodine dosage (0.02 to 0.06 mol), total methylnaphthalene feed concentration (0.2 to 0.5 mol / L), stirring speed (800 to 1500 r / min), and oxidant molar ratio (2.5 to 3.0:1). This provides ample experimental support for the validity of the claims. The synergistic effect of these conditions significantly improves the selectivity and efficiency of the reaction, demonstrating outstanding technical advantages.

[0096] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Based on the technical solutions of the present invention, various modifications or variations that can be made by those skilled in the art without creative effort are still within the scope of protection of the present invention.

Claims

1. A method for preparing menadione by electrolytic cyclic regeneration and oxidation of sodium chlorate, characterized in that, Includes the following steps: S1. Raw material pretreatment: 2-methylnaphthalene, elemental iodine, aqueous acidic medium and oil organic solvent are mixed and preheated to the set temperature to obtain the reaction solution; S2. Electrolytic regeneration of sodium chlorate: Sodium chlorate electrolyte is prepared by electrolytic oxidation using sodium chloride aqueous solution as electrolyte for later use; S3. Add the sodium chlorate electrolyte from step S2 dropwise to the reaction solution from step S1, and carry out a temperature-controlled oxidation reaction in an acidic water-oil two-phase system. During the reaction, ensure stirring and mass transfer to obtain an oxidized mixture. S4. Phase separation and chlorine recycling: The oxidized mixture is allowed to stand for oil-water phase separation, and the oil phase and water phase are collected. The oil phase is cooled, crystallized, filtered, washed, and dried to obtain menadione. The water phase is a sulfuric acid aqueous solution containing sodium chloride, which is directly returned to step S2 as an electrolytic raw material to regenerate sodium chlorate, thus realizing chlorine recycling.

2. The method according to claim 1, characterized in that, The aqueous acidic medium in step S1 is a 5-30 wt% sulfuric acid aqueous solution, and the oil phase organic solvent is any one of esters, ethers, and halogenated hydrocarbons, preferably halogenated hydrocarbons, and more preferably 1,2-dichloroethane.

3. The method according to claim 2, characterized in that, In step S1, the volume ratio of the 10-20 wt% sulfuric acid aqueous solution to the oil phase organic solvent is 1:1 to 3:1; and / or The amount of elemental iodine used is 0.02 to 0.06 times the molar amount of 2-methylnaphthalene; and / or The total molar concentration of 2-methylnaphthalene, based on the total volume of the water and oil phases, is 0.2~0.5 mol / L; and / or Preheating temperature is from room temperature to 80°C, with 60°C being optimal; and / or The stirring speed is 800~1500 r / min.

4. The method according to any one of claims 1 to 3, characterized in that, The conditions for sodium chlorate electrolytic regeneration in step S2 are as follows: the electrolyte is a sodium chloride-containing sulfuric acid aqueous solution obtained by phase separation, sodium chloride is added to make the sodium chloride concentration in the solution 15~25wt%, and the initial pH of the electrolyte is 6.0~7.5; and / or Electrolysis uses a titanium-based ruthenium-iridium coated anode and graphite as the cathode, with an electrode spacing of 5-8 cm; and / or Electrolysis current density of 300~500 A / m², electrolysis temperature of 35~45℃, and electrolysis time of 3~6 h; and / or After electrolysis, the sodium chlorate concentration in the sodium chlorate electrolyte is 1.2~1.8 mol / L, and the residual sodium chloride concentration is ≤2wt%.

5. The method according to any one of claims 1 to 3, characterized in that, The reaction temperature of the oxidation reaction in step S3 is room temperature to 80°C, preferably 60°C.

6. The method according to claim 5, characterized in that, In step S3, the molar ratio of sodium chlorate to 2-methylnaphthalene is 2.5~3.0:1; and / or The dropping rate of the sodium chlorate electrolyte is 0.5~1.0 L / h. During the dropping process, the reaction temperature is maintained stable. After the dropping is complete, the reaction is continued at the set temperature for 2~4 h; and / or The reaction endpoint was monitored by TLC with petroleum ether / ethyl acetate as the developing solvent (30:1) and UV detection at 254 nm. The endpoint was defined as the disappearance of the starting material spot.

7. The method according to any one of claims 1 to 3, characterized in that, In step S4, the oxidized mixture is allowed to stand for 20-40 minutes to separate the oil and water phases, resulting in a clear, emulsified interface between the oil and water phases; and / or The oil phase is cooled to 5-10℃ at a rate of 1-2℃ / h and held at that temperature for crystallization for 1-2h; and / or The crystalline product was washed 2-3 times with pre-cooled n-hexane and then vacuum dried at 55-65°C for 2-3 hours; and / or The purity of the menaquinone product is ≥99%.

8. The method according to claim 7, characterized in that, In step S4, the chlorine cycle is repeated ≥10 times, and the yield of menaquinone decreases ≤0.5% during a single cycle; and / or The yield of the obtained menadione was ≥78%, the purity was ≥99% as determined by HPLC, and there were no chlorinated byproducts.

9. The method according to claim 8, characterized in that, The oil phase organic solvent obtained in step S4 can be recovered by distillation and reused; and / or Aqueous sulfuric acid solutions can be reused synchronously with the chlorine cycle without the need for additional acidic media.

10. An apparatus system for implementing the method of any one of claims 1 to 9, characterized in that, It includes a sodium chlorate electrolytic regeneration unit, an oil-water two-phase oxidation reaction unit, an oil-water phase separation unit, a product purification unit, and a chlorine recycling unit; The sodium chlorate electrolytic regeneration unit includes an electrolytic cell, an electrolyte storage tank, and an online concentration / pH monitor; The water-oil two-phase oxidation reaction unit includes a reaction vessel with a high-speed mechanical stirrer, a precise temperature control system and a dropping device. The high-speed mechanical stirrer meets the mass transfer requirements of the water-oil two-phase system, and the precise temperature control system maintains the reaction temperature at room temperature to 80°C. The oil-water phase separation unit is a static phase separation tank; The product purification unit includes a crystallization vessel, a vacuum filtration device, and a vacuum drying oven. The outlet of the reactor of the water-oil two-phase oxidation reaction unit is connected to the inlet of the settling tank of the oil-water phase separation unit; the oil phase outlet of the settling tank is connected to the inlet of the crystallization vessel of the product purification unit, and the outlet of the crystallization vessel is connected in sequence to the vacuum filter and the vacuum drying oven; the water phase outlet of the settling tank is connected to the inlet of the electrolyte storage tank of the sodium chlorate electrolytic regeneration unit, the outlet of the electrolyte storage tank is connected to the inlet of the electrolytic cell, and the outlet of the electrolytic cell is connected to the inlet of the dripping device of the water-oil two-phase oxidation reaction unit, forming a closed loop of chlorine circulation.

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