Process for recycling propiconazole 4-h isomer

Abstract

The application discloses a recycling process of propiconazole 4-H isomer, and aims at solving the problems of low yield and serious pollution caused by the waste of 4-H isomer in traditional processes. The closed loop cycle process is constructed. After condensation reaction, the process is subjected to sectional pressure change and four-stage gradient temperature rectification, so that toluene, unreacted raw materials, propiconazole products, and mixtures of propiconazole and 4-H isomer and rectification kettle residues are separated in sequence and enriched. The kettle residue polymers are selectively hydrolyzed by using acetic acid-sodium acetate buffer solution, the effective components physically wrapped are released and recovered. After the above isomer mixtures and the recovered organic phase are combined and purified, the isomer mixtures are efficiently converted into starting raw material propyl bromo-ketone under the catalysis of Lewis acid and by using trimethyl bromosilane. Finally, high-purity propyl bromo-ketone is recovered by rectification and is reused in the condensation section. The yield loss of chiral by-products is completely eliminated, the atom economy maximization and solid waste near zero emission are realized, and the economic and environmental benefits are remarkable.

Description

Technical Field

[0001] This invention relates to the field of pesticide production chemicals, and in particular to a process for recycling propiconazole 4-H isomer. Background Technology

[0002] Propiconazole is a widely used triazole fungicide. Its chemical structure contains a dioxolane ring, giving it a chiral center. In mainstream industrial production, propiconazole is typically prepared by condensation of propyl bromide ketal and triazole under alkaline conditions via a nucleophilic substitution reaction. However, due to the stereochemical factors involved in this nucleophilic substitution reaction, the triazole anion may attack the substrate from different directions, inevitably resulting in the formation of a considerable proportion of diastereomers, commonly referred to as the 4-H isomer, in addition to the target propiconazole configuration. The biological activity of this isomer is far lower than that of propiconazole, and the two are extremely similar in physical properties, with very close boiling points, making it a recognized separation challenge in the industrial production of propiconazole.

[0003] Currently, there are two main strategies in the industry for handling the 4-H isomer generated in the reaction. First, during the distillation purification of propiconazole, the fraction rich in the 4-H isomer and the distillation vessel residue are directly discharged as waste liquid or residue. While this method is simple to operate, it results in the loss of a significant portion of the active ingredient along with the isomer, leading to a low overall yield of propiconazole. This not only results in a huge waste of the expensive raw material propyl bromide ketal but also generates a large amount of hazardous waste requiring specialized treatment, significantly increasing production costs and environmental burden. Second, attempts are made to use high-precision distillation with high reflux ratios to separate propiconazole and its 4-H isomer. However, due to the extremely small difference in their boiling points, effective separation requires a very high number of theoretical plates and a long operating time, resulting in huge energy consumption and low separation efficiency. Often, only a small amount of propiconazole with low purity can be recovered, leading to poor economic benefits and making it difficult to promote on an industrial scale. In addition, during high-temperature distillation, the components in the reaction solution are prone to side reactions such as thermal polymerization and thermal decomposition, forming viscous polymers. These polymers physically encapsulate some propiconazole and 4-H isomers, causing them to precipitate at the bottom of the vessel, further exacerbating the loss of active ingredients. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention employs a closed-loop recycling process involving distillation to enrich isomers, buffer hydrolysis to release inclusions, catalytic ring-opening chemical conversion, and recovery of high-purity raw materials. This process solves the technical issues of low yield, significant raw material waste, and high hazardous waste emissions caused by the discarding of the 4-H isomer in propiconazole production due to difficulties in physical separation. Specifically, this is achieved through the following technical solutions.

[0005] The process for recycling the propiconazole 4-H isomer includes the following steps: Step 1 Potassium hydroxide and triazole were added to a condensation vessel, along with N,N-dimethylformamide and propyl bromide ketal. The mixture was heated under stirring and vacuum conditions. During the reaction, water and N,N-dimethylformamide were distilled off and condensed for recovery. After the reaction, N,N-dimethylformamide was removed by vacuum distillation. Toluene and deionized water were added to the vessel, and the mixture was stirred and allowed to stand for separation. The upper organic phase was removed under vacuum to remove toluene, yielding crude propiconazole. Step 2 The crude propiconazole obtained in step 1 was added to a distillation vessel, and toluene, unreacted propyl bromide ketal, propiconazole, and a mixture of propiconazole and its 4-H isomer were distilled off sequentially using a segmented pressure swing and gradient temperature method. The residue at the bottom of the distillation vessel was collected for later use. Step 3 Add the residue from step 2 into the dissolving vessel, add toluene, heat and stir to fully disperse and swell the residue to form a toluene solution, then cool the solution, add an acetate-sodium acetate buffer solution dropwise into the vessel while stirring continuously, slowly heat and keep the temperature while stirring the reaction, after the reaction is completed, let it stand and separate into layers, and take the upper organic phase for later use. Step 4 The mixture of propiconazole distilled in step 2 and the 4-H isomer was mixed with the organic phase obtained in step 3. Toluene was added and stirred until homogeneous to form a toluene mixture. The mixture was washed successively with sodium bicarbonate solution and deionized water, and then dried and dehydrated by adding anhydrous sodium sulfate. The desiccant was then filtered out through a filter to obtain a purified mixture. Step 5 The purified mixture obtained in step 4 is put into a reaction vessel, Lewis acid catalyst is added, stirring is started, the temperature is lowered under nitrogen protection, and bromine reagent is added dropwise. During the dropwise addition, the temperature inside the vessel is controlled not to exceed 15°C. After the dropwise addition is completed, the temperature is raised to 25-50°C and kept at this temperature for 4-8 hours. After the reaction is completed, the temperature is lowered, and sodium bicarbonate aqueous solution is slowly added dropwise while stirring. The temperature inside the vessel is controlled not to exceed 25°C. After the dropwise addition is completed, stirring is stopped, the mixture is transferred to a separatory vessel, allowed to stand and separate into layers, the lower aqueous phase is discharged, and the upper organic phase is retained. Step 6 The organic phase retained in step 5 was washed with deionized water and then transferred to a distillation vessel. It was then subjected to desolvation under reduced pressure and distillation under reduced pressure to obtain propyl bromide ketal.

[0006] Preferably, the segmented voltage transformation and gradient heating method described in step 2 specifically adopts a four-stage gradient heating. First-stage gradient: Under normal pressure, with a vessel temperature of 100–130°C and a column top temperature of 90–110°C, the distillation time is 1.0–1.5 hours, to distill off toluene from the crude propiconazole product; Second-stage gradient: absolute pressure 0.025-0.04 MPa, pot temperature 150-170℃, top temperature 130-150℃, distillation time 1.5-2.0 hours, to distill off the propyl bromide acetal from the crude propiconazole. Third-stage gradient: absolute pressure ≤ 0.01 MPa, pot temperature 220~240℃, top temperature 190~210℃, distillation time 4~6 hours, distillate is propiconazole; Fourth-stage gradient: absolute pressure ≤ 0.01 MPa, pot temperature 240~255℃, top temperature 220~235℃, distillation time 2~3 hours, distillate is a mixture of propiconazole and 4-H isomer.

[0007] Preferably, the mass ratio of the residue to toluene added in step 3 is 1:1.8 to 2.2; The acetate-sodium acetate buffer solution has a pH of 4.2–4.8, an acetate concentration of 1.8–2.3 mol / L, and a mass ratio of acetate-sodium acetate buffer solution to the added residue of 0.2–0.3:1. During the dropwise addition process, keep the temperature inside the vessel below 35°C. After the dropwise addition is complete, slowly raise the temperature to 30-40°C and keep it at this temperature while stirring for 2-4 hours.

[0008] Preferably, in step 3, the liquid is cooled to 25-35°C, and the addition time of the acetate-sodium acetate buffer solution to the reactor is controlled at 0.5-1 hour. After adding toluene in step 3, the temperature is raised to 45-55°C and stirred for 1.0-1.5 hours.

[0009] Preferably, the mass of toluene added in step 4 is 40% to 65% of the mass of the mixture of propiconazole and 4-H isomer distilled in step 2; The alkaline washing process uses a 5wt% sodium bicarbonate solution, with a mass ratio of sodium bicarbonate solution to toluene mixture of 0.1–0.3:1. During the water washing process, the mass ratio of deionized water to toluene mixture used in each wash is 0.2–0.5:1; The amount of anhydrous sodium sulfate used is 5% to 8% of the mass of the toluene mixture, and the moisture content during the drying and dehydration process is ≤500ppm.

[0010] Preferably, the Lewis acid catalyst in step 5 is bismuth trifluoromethanesulfonate, and its dosage is 1% to 3% of the mass of the purified mixture; The brominating agent is trimethylbromosilane, and its addition amount is 45% to 55% of the mass of the purified mixture; The sodium bicarbonate solution has a mass concentration of 8%, and the mass ratio of the added sodium bicarbonate solution to the purified mixture is 0.3–0.5:1.

[0011] Preferably, in step 5, the system is cooled to 0–10°C, and the bromine reagent is added dropwise over a period of 1.5–2.5 hours. After the reaction is complete, the reaction vessel is cooled to 0-10°C, and the sodium bicarbonate aqueous solution is added dropwise over 0.8-1.2 hours.

[0012] Preferably, the mass ratio of potassium hydroxide, triazole, propyl bromide ketal and N,N-dimethylformamide added in step 1 is 22-31:32-38:100:110-130; When removing N,N-dimethylformamide by vacuum distillation, the distillation temperature is 70–85℃ and the absolute pressure is ≤0.01MPa; when removing toluene by vacuum distillation, the distillation temperature is 45–60℃ and the absolute pressure is ≤0.02MPa.

[0013] Preferably, in step 6, the mass ratio of deionized water to organic phase during the organic phase washing process is 0.3 to 0.5:1, and the mixture is stirred at 40 to 50°C for 20 to 30 minutes. After standing and separating into layers, the lower aqueous phase is discharged. During the depressurization desolvation process, the absolute pressure value is ≤0.015MPa, the temperature inside the vessel is 70~80℃, the temperature at the top of the column is 50~60℃, and the desolvation time is 1.5~2.5 hours. The absolute pressure during the vacuum distillation process is ≤0.005MPa, the kettle temperature is 155~165℃, the column top temperature is 140~155℃, and the distillation time is 3~5 hours.

[0014] After adopting the above technical solution, the beneficial effects of the present invention are: 1. By employing a closed-loop process encompassing synthesis, separation, isomer enrichment, hydrolysis release, chemical transformation, and recovery, the yield loss problem caused by the formation of the chiral byproduct 4-H isomer in propiconazole production is fundamentally solved. This process no longer treats the isomer as waste; instead, it precisely deconstructs the isomer and the encapsulated polymers formed during distillation using a gentle chemical method, directionally converting them all into the starting material propyl bromide ketal and re-introducing them into the reaction. This maximizes atom economy from raw material to product, significantly improving the overall yield of propiconazole.

[0015] 2. This method abandons the traditional direct waste disposal approach and employs a mild, weakly acidic buffer solution system to selectively catalyze the hydrolysis of ketal and ether bonds in the polymer residue, causing the cross-linked network to disintegrate. This allows for the full release and recovery of propiconazole and the 4-H isomer, which are physically encapsulated and cannot be recovered using conventional physical methods. This process not only transforms solid waste into reusable resources and improves the recovery rate of active ingredients, but also effectively protects the integrity of the triazole ring and ketal structure due to the mild nature of the buffer system, avoiding irreversible damage and side reactions caused by strong acids, thus combining high efficiency and high selectivity.

[0016] 3. By employing Lewis acid-catalyzed selective ring-opening and bromination reactions, the chemically stable ineffective isomers are reverse-deconstructed and efficiently converted into propyl bromide ketal, the original chemical raw material for the production of propiconazole. This chemical conversion pathway bypasses the inherent difficulties of physical separation, ensuring thorough conversion. The recovered propyl bromide ketal has a purity of over 99% and can be directly used in the upstream condensation reaction, achieving a high-quality closed-loop recycling of materials.

[0017] 4. By organically integrating the three streams of 4-H isomer enrichment, residual water release, and chemical conversion, a clean production process with no 4-H isomer emissions was constructed. The entire process not only minimizes the loss of active ingredients and greatly reduces raw material consumption, but also achieves the reduction or even zero emission of hazardous solid waste at the source, saving high hazardous waste treatment costs. This process transforms the traditional environmental burden into a considerable economic benefit growth point, making propiconazole production greener, lower carbon, and more sustainable. While enhancing the product's market competitiveness, it meets increasingly stringent environmental regulations, demonstrating outstanding economic and environmental benefits. Detailed Implementation

[0018] To make the objectives, technical solutions, and technical effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0019] The process for recycling the propiconazole 4-H isomer includes the following steps: Step 1 Potassium hydroxide and triazole were fed into the condensation reactor via a solid feeder. N,N-dimethylformamide (DMF) and propyl bromide ketal were pumped into the condensation reactor via a metering pump. The stirring and vacuum systems were turned on to maintain an absolute pressure of 0.02–0.05 MPa inside the reactor. The temperature was raised to 130–140 °C and the reaction was carried out for 7–9 hours. The water and DMF distilled off during the reaction were condensed and recovered. After the reaction was completed, DMF was removed by vacuum distillation. Toluene and deionized water were added to the reactor. After stirring, the mixture was allowed to stand and separate into layers. The upper organic phase was taken and toluene was removed under vacuum to obtain crude propiconazole.

[0020] In the above steps, the mass ratio of potassium hydroxide, triazole, propyl bromide ketal and DMF is 22-31:32-38:100:110-130.

[0021] In the above steps, the mass ratio of propyl bromide ketal, toluene, and deionized water is 1:1:0.8.

[0022] In the above steps, when removing DMF by vacuum distillation, the distillation temperature is 70-85℃ and the absolute pressure is ≤0.01MPa.

[0023] In the above steps, when removing toluene by vacuum distillation, the distillation temperature is 45-60℃ and the absolute pressure is ≤0.02MPa.

[0024] In the above steps, a condensation reaction is completed. The condensation reaction is a nucleophilic substitution reaction. Triazole forms a triazole anion under the action of potassium hydroxide. This anion acts as a nucleophile to attack the brominated carbon in the propyl bromide ketal molecule, resulting in SN2 substitution and the formation of a CN bond to generate propiconazole. At the same time, due to the presence of a chiral center in the propyl bromide ketal molecule and the stereochemical factors in the reaction process, the triazole anion may attack from different directions, generating the target propiconazole and its diastereomer 4-H isomer.

[0025] Step 2 The crude propiconazole obtained in step 1 was added to a distillation vessel, and toluene, unreacted propyl bromide ketal, propiconazole, and a mixture of propiconazole and its 4-H isomer were distilled off sequentially using segmented pressure swing and four-stage gradient heating. The residue at the bottom of the distillation vessel was collected for later use.

[0026] The segmented voltage transformation and four-stage gradient temperature rise in the above steps are as follows: First-stage gradient: At atmospheric pressure, kettle temperature 100-130℃, column top temperature 90-110℃, distillation time 1.0-1.5 hours. This temperature gradient mainly distills off toluene from the crude propiconazole and condenses it for recovery. The second-stage gradient has an absolute pressure of 0.025–0.04 MPa, a vessel temperature of 150–170 °C, a column top temperature of 130–150 °C, and a distillation time of 1.5–2.0 hours. This temperature gradient is mainly used to distill off the propyl bromide ketal from the crude propiconazole product and then condense and recover it for reuse as a reactant. The third gradient: absolute pressure ≤ 0.01 MPa, pot temperature 220~240℃, top temperature 190~210℃, distillation time 4~6 hours. The product distilled in this process is propiconazole. In order to ensure the purity of the product, a relatively slow distillation rate must be maintained. Fourth-stage gradient: absolute pressure ≤ 0.01 MPa, kettle temperature 240~255℃, column top temperature 220~235℃, distillation time 2~3 hours. The substance distilled in this process is a mixture of propiconazole and the 4-H isomer, which is condensed and stored for later use.

[0027] In the above steps, based on the differences in boiling points of the components in the crude propiconazole, a segmented pressure swing distillation and four-stage gradient temperature strategy are adopted to achieve highly selective separation. By gradually increasing the system vacuum and the still temperature, the low-boiling-point solvent toluene, the unreacted raw material propyl bromide ketal, the main product propiconazole, and the propiconazole / 4-H isomer mixture with similar boiling points are distilled off sequentially. The high vacuum conditions significantly reduce the boiling point of the high-boiling-point components, preventing thermal decomposition or polymerization during the separation process. This not only yields a high-purity propiconazole product, but also concentrates and enriches the 4-H isomer and a portion of the propiconazole together in a specific fraction, providing a dedicated feedstock stream for subsequent isomer conversion and reuse. At the same time, the residue at the bottom of the still is collected and processed separately, achieving full utilization of the materials.

[0028] This process achieves precise separation of solvents, excess raw materials, products, and isomers. The recovered toluene and propyl bromide ketal can be directly reused, reducing material consumption and costs. The high-purity propiconazole product fraction ensures commercial value. The 4-H isomer is enriched, distilled off, and collected separately to prevent its accumulation in the distillation system from interfering with the purity of subsequent batches of products and to prevent resource waste caused by direct discharge as waste residue, providing a key link for closed-loop reuse.

[0029] Step 3 Add the residue from step 2 to the dissolving vessel, add toluene to the dissolving vessel, heat to 45-55°C, and stir for 1.0-1.5 hours to fully disperse and swell the residue to form a toluene solution. Then cool the solution to 25-35°C, and then add an acetate-sodium acetate buffer solution dropwise to the vessel while continuously stirring. The dropwise addition time is controlled at 0.5-1 hour. After the dropwise addition is completed, keep the vessel at the temperature and stir for 2-4 hours. After the reaction is completed, let it stand and separate into layers, and take the upper organic phase for later use.

[0030] In the above steps, the mass ratio of the residue to toluene is 1:1.8 to 2.2.

[0031] In the above steps, the pH value of the acetate-sodium acetate buffer solution added is 4.2 to 4.8, and the acetate concentration is 1.8 to 2.3 mol / L. The mass ratio of the acetate-sodium acetate buffer solution to the added residue is 0.2 to 0.3:1, and the temperature inside the reactor is kept below 35°C during the dropwise addition process.

[0032] The polymers in the distillation vessel residue mainly originate from the intermolecular or intramolecular thermal polymerization of propiconazole and the polymerization of propyl bromide ketal. These polymers physically encapsulate some of the 4-H isomers and propiconazole. The buffer solution provides a stable weakly acidic environment, in which hydrated hydrogen ions generated by the ionization equilibrium of acetic acid act as a catalyst, selectively catalyzing the hydrolysis of sterically hindered linear ketal bonds and ether bonds in the polymers, causing the cross-linked network to disintegrate, thereby releasing the physically encapsulated propiconazole and 4-H isomers. These dissolve in toluene to form the upper organic phase, while the lower aqueous phase mainly consists of buffer waste containing sodium acetate, oligomer fragments, and a small amount of salt.

[0033] This process transforms the waste residue from traditional processes into recyclable resources, releasing physically encapsulated target components, significantly improving the overall yield of propiconazole and its isomers, and reducing the loss of active ingredients. The buffer solution environment is mild, avoiding the damage of strong acids to the triazole ring or ketal structure. The process is safe, reliable, and highly selective. This step also reduces solid waste and lowers hazardous waste treatment costs, resulting in significant environmental and economic benefits.

[0034] Step 4 The mixture of propiconazole distilled from the fourth stage in step 2 and the 4-H isomer was mixed with the organic phase obtained in step 3, and toluene was added and stirred until homogeneous to form a toluene mixture. The mixture was washed once with sodium bicarbonate solution and then twice with deionized water. The mixture was then placed in a drying vessel, anhydrous sodium sulfate was added, and the mixture was dried and dehydrated by stirring at 20-35°C. The desiccant was then removed by filtering through a filter to obtain a purified mixture.

[0035] The mass of toluene added during this process is 40% to 65% of the mass of the mixture of propiconazole and 4-H isomer distilled from the fourth stage.

[0036] In the alkaline washing process, a 5wt% sodium bicarbonate solution is used, and the mass ratio of sodium bicarbonate solution to toluene mixture is 0.1 to 0.3:1. In the water washing process, the mass ratio of deionized water to toluene mixture used in each water washing is 0.2 to 0.5:1.

[0037] The amount of anhydrous sodium sulfate used is 5% to 8% of the mass of the toluene mixture. During the drying and dehydration process, after the moisture content is detected to be ≤500ppm, the desiccant is removed by filtering.

[0038] The above steps combine the processing of two streams containing the target components, simplifying the process and reducing equipment usage. The process involves sequential washing with sodium bicarbonate and deionized water to neutralize any trace acidic substances and thoroughly remove salts and water-soluble impurities from the organic phase. Subsequently, anhydrous sodium sulfate is used for drying and dehydration, which provides absolute assurance for the anhydrous reaction system in the subsequent step 5, ensuring the high efficiency and reproducibility of the isomer conversion reaction. The washing and drying conditions in this process are mild, do not damage the product structure, and the resulting purified mixture has stable quality.

[0039] Step 5 The purified mixture obtained in step 4 is added to a reaction vessel, a Lewis acid catalyst is added, and stirring is started. Under nitrogen protection, the system is cooled to 0–10°C, stirring continues, and a brominating reagent is added dropwise to the reaction vessel. During the dropwise addition process, the temperature inside the vessel is controlled to not exceed 15°C, and the dropwise addition time is 1.5–2.5 hours. After the dropwise addition is completed, the reaction mixture is heated to 25–50°C and kept at this temperature for 4–8 hours. After the reaction is completed, the reaction vessel is cooled to 0–10°C, and sodium bicarbonate aqueous solution is slowly added dropwise to the vessel while stirring. The dropwise addition rate is controlled to keep the temperature inside the vessel below 25°C, and the dropwise addition time is 0.8–1.2 hours. After the dropwise addition is completed, stirring is stopped, the mixture is transferred to a separatory vessel, and allowed to stand for separation. The lower aqueous phase is discharged and treated, while the upper organic phase is retained in the vessel for later use.

[0040] In the above steps, the Lewis acid catalyst bismuth trifluoromethanesulfonate is used in an amount of 1% to 3% of the mass of the purified mixture.

[0041] The brominating agent is trimethylbromosilane, and its addition amount is 45% to 55% of the mass of the purified mixture.

[0042] The sodium bicarbonate solution has a mass concentration of 8%, and the mass ratio of the added sodium bicarbonate solution to the purified mixture is 0.3–0.5:1.

[0043] In the above steps, propiconazole and its 4-H isomer both contain a dioxolane ring structure composed of a ketal. Under the action of the Lewis acid catalyst bismuth trifluoromethanesulfonate, the brominating reagent trimethylbromosilane provides a bromide anion source, which can selectively break the less sterically hindered CO bond in the ring to generate a dibromo intermediate, and finally regenerate propyl bromide ketal.

[0044] This reaction reverses the destructive structure of the ineffective isomer skeleton, returning it to the starting material for the condensation reaction. Through a one-step chemical transformation, the 4-H isomer, which would otherwise be discarded, is efficiently converted into the starting point for synthesis, propyl bromide ketal. This essentially eliminates yield losses caused by chiral byproducts and maximizes atom economy.

[0045] Step 6 The remaining organic phase in the separatory vessel was washed twice with deionized water and then transferred to a distillation vessel. After desolvation under reduced pressure and distillation under reduced pressure, propyl bromide ketal was obtained.

[0046] During the organic phase washing process, the mass ratio of deionized water to organic phase is 0.3 to 0.5:1. The washing is carried out at 40 to 50°C for 20 to 30 minutes. After standing and separating into layers, the lower aqueous phase is discharged.

[0047] In the above-mentioned depressurization desolventizing process, the absolute pressure value is ≤0.015MPa, the temperature inside the vessel is 70~80℃, the temperature at the top of the tower is 50~60℃, the desolventizing time is 1.5~2.5 hours, and the solvent toluene is distilled off and condensed for recovery.

[0048] In the above-mentioned vacuum distillation process, the absolute pressure value is ≤0.005MPa, the pot temperature is 155~165℃, the column top temperature is 140~155℃, and the distillation time is 3~5 hours.

[0049] In the above steps, the organic phase mainly consists of toluene, the product propyl bromide ketal, and trace impurities. Residual salts are further removed by heated water washing, followed by desolventizing under reduced pressure. Taking advantage of the significant decrease in boiling point of toluene under vacuum, the toluene is distilled off at a lower temperature and condensed for recovery. The crude propyl bromide ketal after desolventizing is then purified by high-vacuum distillation. Based on its boiling point, it is distilled off steadily under a certain vacuum, separating it from high-boiling-point residual impurities. The final propyl bromide ketal has a purity ≥99%, which is then recycled as solvent and recovered as product, providing qualified raw materials for step 1.

[0050] The entire process chain thus forms a circular process of synthesis, separation, isomer enrichment, hydrolysis and release, chemical conversion, raw material recovery, and resynthesis. The entire process has no 4-H isomer emissions, while improving economic and environmental benefits.

[0051] To facilitate a further understanding of the above process, several embodiments and comparative examples are given below: Example 1: Step 1: 26.5 kg of potassium hydroxide and 35 kg of triazole are fed into the condensation kettle via a solid feeder. 120 kg of N,N-dimethylformamide (DMF) and 100 kg of propyl bromide are pumped into the condensation kettle via a metering pump.

[0052] Turn on the stirring and vacuum system, maintain the absolute pressure inside the vessel at 0.035 MPa, raise the temperature to 135℃ and react for 8 hours. During the reaction, the distilled water and DMF are condensed and recovered. After the reaction is completed, DMF is removed by vacuum distillation at a distillation temperature of 77℃ and an absolute pressure of 0.01 MPa.

[0053] Subsequently, 100 kg of toluene and 80 kg of deionized water were added to the reactor. After stirring, the mixture was allowed to stand and separate into layers. The upper organic phase was then subjected to depressurization at a distillation temperature of 53°C and an absolute pressure of 0.01 MPa to remove toluene, yielding approximately 97.6 kg of crude propiconazole.

[0054] Step 2: Add all 97.6 kg of the crude propiconazole obtained in Step 1 to a distillation vessel and separate the product using the following four-stage gradient temperature and pressure swing strategy: First stage: Atmospheric pressure, kettle temperature 115℃, column top temperature 100℃, distillation for 1.5 hours, 1.3 kg of toluene was distilled off, and the product was condensed and recycled.

[0055] Second stage: Absolute pressure 0.03 MPa, kettle temperature 160℃, column top temperature 140℃, distillation for 1.8 hours, 4.9 kg of unreacted propyl bromide acetal was distilled off, condensed and recovered, and reused as reactants.

[0056] Third stage: Absolute pressure 0.01MPa, kettle temperature 230℃, column top temperature 200℃, distillation for 5 hours, to obtain 78.4kg of propiconazole product at a slower distillation rate.

[0057] Fourth stage: Absolute pressure 0.005MPa, kettle temperature 248℃, column top temperature 230℃, distillation for 2.5 hours, distilling off 11.0kg of a mixture of propiconazole and 4-H isomer, which is then condensed and stored for later use.

[0058] Collect 2.0 kg of residue from the bottom of the distillation vessel for later use.

[0059] Step 3: Add 2.0 kg of the residue from Step 2 to the dissolving vessel, add 4.0 kg of toluene, heat to 50°C, and stir for 1.25 hours to fully disperse and swell the residue. Cool the solution to 30°C, and while stirring continuously, add 0.5 kg of an acetate-sodium acetate buffer solution with pH=4.5 and an acetate concentration of 2.0 mol / L dropwise to the vessel over 0.75 hours, controlling the temperature to not exceed 35°C.

[0060] After the addition is complete, the material in the reactor is slowly heated to 35°C and stirred for 3 hours. After the reaction is complete, the mixture is allowed to stand and separate into layers. 4.3 kg of the upper organic phase is then taken for later use.

[0061] Step 4: Combine 11.0 kg of the mixture distilled from the fourth stage in Step 2 with 4.3 kg of the organic phase obtained in Step 3, add 5.6 kg of toluene, and stir until homogeneous to form 20.9 kg of toluene mixture.

[0062] Then wash once with 4.3 kg of 5 wt% sodium bicarbonate solution, and then wash twice with deionized water, using 7.5 kg of water each time. Put the washed organic phase into a drying kettle, add 1.4 kg of anhydrous sodium sulfate, stir and dry at 27°C to remove water. After the moisture content is tested to be ≤500 ppm, filter out the desiccant through a filter to obtain 20.8 kg of purified mixture.

[0063] Step 5: Add 20.8 kg of the purified mixture from Step 4 into the reactor, add 0.43 kg of Lewis acid catalyst bismuth trifluoromethanesulfonate, start stirring, cool down to 5°C under nitrogen protection, continue stirring and add 10.0 kg of bromine reagent trimethylbromosilane dropwise over 2 hours, keeping the temperature below 15°C.

[0064] After the addition is complete, the reaction mixture is heated to 35°C and kept at this temperature for 6 hours. After the reaction is complete, the system is cooled to 5°C and 8.5 kg of 8 wt% sodium bicarbonate aqueous solution is slowly added dropwise with stirring over 1 hour. The temperature inside the vessel is controlled to not exceed 25°C. After the addition is complete, stirring is stopped, and the mixture is transferred to a separatory vessel to stand and separate into layers. The lower aqueous phase is discharged, and 21.3 kg of the upper organic phase is retained.

[0065] Step 6: Wash the 21.3 kg organic phase retained in Step 5 twice with deionized water, using 8.8 kg of water each time. Stir at 45°C for 25 minutes, let stand to separate the layers, and then drain the aqueous phase.

[0066] The washed organic phase was transferred to a distillation vessel and desolventized for 2 hours under conditions of 0.008 MPa absolute pressure, 75°C vessel temperature, and 55°C top temperature. Toluene was distilled off and condensed for recovery. Then, it was distilled for 4 hours under conditions of 0.003 MPa absolute pressure, 160°C vessel temperature, and 147.5°C top temperature, yielding 11.3 kg of propyl bromide acetal with a purity of 97.8%.

[0067] Example 2 This embodiment is based on Example 1, with adjustments made to the pH value and amount of the acetate-sodium acetate buffer solution in step 3, specifically: Step 1: 26.5 kg of potassium hydroxide and 35 kg of triazole are fed into the condensation kettle via a solid feeder. 120 kg of N,N-dimethylformamide (DMF) and 100 kg of propyl bromide acetal are pumped into the condensation kettle via a metering pump.

[0068] Turn on the stirring and vacuum system, maintain the absolute pressure inside the vessel at 0.035 MPa, raise the temperature to 135°C and react for 8 hours. During the reaction, the distilled water and DMF are condensed and recovered. After the reaction is completed, DMF is removed by vacuum distillation at a distillation temperature of 77°C and an absolute pressure of 0.01 MPa.

[0069] Subsequently, 100 kg of toluene and 80 kg of deionized water were added to the reactor. After stirring, the mixture was allowed to stand and separate into layers. The upper organic phase was then subjected to depressurization at a distillation temperature of 53°C and an absolute pressure of 0.01 MPa to remove toluene, yielding approximately 97.9 kg of crude propiconazole.

[0070] Step 2: Add all 97.9 kg of the crude propiconazole obtained in Step 1 to a distillation vessel and separate the product using the following four-stage gradient temperature and pressure swing strategy: First stage: Atmospheric pressure, kettle temperature 115℃, column top temperature 100℃, distillation for 1.5 hours, 1.1 kg of toluene was distilled off, and the product was condensed and recycled.

[0071] Second stage: Absolute pressure 0.03 MPa, kettle temperature 160℃, column top temperature 140℃, distillation time 1.8 hours. 5.1 kg of unreacted propyl bromide acetal was distilled off, condensed and recovered, and reused as reactants.

[0072] Third stage: Absolute pressure 0.01 MPa, kettle temperature 230℃, column top temperature 200℃, distillation for 5 hours. 78.5 kg of propiconazole product was obtained at a slower distillation rate.

[0073] Fourth stage: Absolute pressure 0.005MPa, kettle temperature 248℃, column top temperature 230℃, distillation for 2.5 hours, distilling off 11.1kg of a mixture of propiconazole and 4-H isomer, which is then condensed and stored for later use.

[0074] Collect 2.1 kg of residue from the bottom of the distillation vessel for later use.

[0075] Step 3: Add 2.0 kg of the residue from Step 2 to the dissolving vessel, add 4.0 kg of toluene, heat to 50°C, and stir for 1.25 hours to fully disperse and swell the residue. Cool the solution to 30°C, and while stirring continuously, add 0.4 kg of an acetate-sodium acetate buffer solution with pH=4.2 and an acetate concentration of 2.0 mol / L dropwise to the vessel over 0.75 hours, controlling the temperature to not exceed 35°C.

[0076] After the addition is complete, the material in the reactor is slowly heated to 35°C and stirred for 3 hours. After the reaction is complete, the mixture is allowed to stand and separate into layers. 4.2 kg of the upper organic phase is then taken for later use.

[0077] Step 4: Combine the 11.1 kg mixture from the fourth stage of distillation in Step 2 with the 4.2 kg organic phase obtained in Step 3, add 5.7 kg of toluene, and stir until homogeneous to form a toluene mixture of 21.0 kg.

[0078] Then wash once with 4.3 kg of 5 wt% sodium bicarbonate solution, and then wash twice with deionized water, using 7.5 kg of water each time. Put the washed organic phase into a drying kettle, add 1.4 kg of anhydrous sodium sulfate, stir and dry at 27°C to remove water. After the moisture content is tested to be ≤500 ppm, filter out the desiccant through a filter to obtain 20.9 kg of purified mixture.

[0079] Step 5: Add 20.9 kg of the purified mixture from Step 4 into the reactor, add 0.43 kg of Lewis acid catalyst bismuth trifluoromethanesulfonate, start stirring, cool down to 5°C under nitrogen protection, continue stirring and add 10.0 kg of bromine reagent trimethylbromosilane dropwise over 2 hours, controlling the temperature not to exceed 15°C.

[0080] After the addition is complete, the reaction mixture is heated to 35°C and kept at this temperature for 6 hours. After the reaction is complete, the system is cooled to 5°C and 8.5 kg of 8 wt% sodium bicarbonate aqueous solution is slowly added dropwise with stirring over 1 hour. The temperature inside the vessel is controlled to not exceed 25°C. After the addition is complete, stirring is stopped, and the mixture is transferred to a separatory vessel to stand and separate into layers. The lower aqueous phase is discharged, and 21.4 kg of the upper organic phase is retained.

[0081] Step 6: Wash the 21.4 kg organic phase retained in Step 5 twice with deionized water, using 8.8 kg of water each time. Stir at 45°C for 25 minutes, let stand to separate the layers, and then drain the aqueous phase.

[0082] The washed organic phase was transferred to a distillation vessel and desolventized for 2 hours under conditions of 0.008 MPa absolute pressure, 75°C vessel temperature, and 55°C column top temperature. Toluene was distilled off and condensed for recovery. Then, it was distilled for 4 hours under conditions of 0.003 MPa absolute pressure, 160°C vessel temperature, and 147.5°C column top temperature, yielding 11.4 kg of propyl bromide acetal with a purity ≥97.5%.

[0083] Example 3 This embodiment is based on Example 1, with adjustments made to the pH value and amount of the acetate-sodium acetate buffer solution in step 3, specifically: Step 1: 26.5 kg of potassium hydroxide and 35 kg of triazole are fed into the condensation kettle via a solid feeder. 120 kg of N,N-dimethylformamide (DMF) and 100 kg of propyl bromide acetal are pumped into the condensation kettle via a metering pump.

[0084] Turn on the stirring and vacuum system, maintain the absolute pressure inside the vessel at 0.035 MPa, raise the temperature to 135℃ and react for 8 hours. During the reaction, the distilled water and DMF are condensed and recovered. After the reaction is completed, DMF is removed by vacuum distillation at a distillation temperature of 77℃ and an absolute pressure of 0.01 MPa.

[0085] Subsequently, 100 kg of toluene and 80 kg of deionized water were added to the reactor, stirred, and allowed to stand to separate into layers. The upper organic phase was then removed from the reactor under reduced pressure at a distillation temperature of 53°C and an absolute pressure of 0.01 MPa to remove toluene, yielding approximately 97.7 kg of crude propiconazole.

[0086] Step 2: Add all 97.7 kg of the crude propiconazole obtained in Step 1 to the distillation vessel and separate the product using the following four-stage gradient temperature and pressure swing strategy: First stage: Atmospheric pressure, kettle temperature 115℃, column top temperature 100℃, distillation for 1.5 hours, 1.2 kg of toluene was distilled off, and the product was condensed and recycled.

[0087] Second stage: Absolute pressure 0.03 MPa, kettle temperature 160℃, column top temperature 140℃, distillation for 1.8 hours. 5.0 kg of unreacted propyl bromide ketal was distilled off, condensed and recovered, and reused as reactants.

[0088] Third stage: Absolute pressure 0.01 MPa, kettle temperature 230℃, column top temperature 200℃, distillation for 5 hours. 78.7 kg of propiconazole product was obtained at a slower distillation rate.

[0089] Fourth stage: Absolute pressure 0.005MPa, kettle temperature 248℃, column top temperature 230℃, distillation for 2.5 hours, distilling off 10.9kg of a mixture of propiconazole and 4-H isomer, which is then condensed and stored for later use.

[0090] Collect 1.9 kg of residue from the bottom of the distillation vessel for later use.

[0091] Step 3: Add 1.9 kg of the residue from Step 2 to the dissolving vessel, add 4.0 kg of toluene, heat to 50°C, and stir for 1.25 hours to fully disperse and swell the residue. Cool the solution to 30°C, and while stirring continuously, add 0.6 kg of an acetate-sodium acetate buffer solution with pH=4.8 and an acetate concentration of 2.0 mol / L dropwise to the vessel over 0.75 hours, controlling the temperature to not exceed 35°C.

[0092] After the addition is complete, the material in the reactor is slowly heated to 35°C and stirred for 3 hours. After the reaction is complete, the mixture is allowed to stand and separate into layers. 4.6 kg of the upper organic phase is then taken for later use.

[0093] Step 4: Combine 10.9 kg of the mixture distilled from the fourth stage in Step 2 with 4.6 kg of the organic phase obtained in Step 3, add 5.9 kg of toluene, and stir until homogeneous to form 21.4 kg of toluene mixture.

[0094] Then wash once with 4.3 kg of 5 wt% sodium bicarbonate solution, and then wash twice with deionized water, using 7.5 kg of water each time. Put the washed organic phase into a drying kettle, add 1.4 kg of anhydrous sodium sulfate, stir and dry at 27°C to remove water. After the moisture content is tested to be ≤500 ppm, filter out the desiccant through a filter to obtain 21.3 kg of purified mixture.

[0095] Step 5: Add 21.3 kg of the purified mixture from Step 4 into the reactor, add 0.43 kg of Lewis acid catalyst bismuth trifluoromethanesulfonate, start stirring, cool down to 5°C under nitrogen protection, continue stirring and add 10.1 kg of bromine reagent trimethylbromosilane dropwise over 2 hours, keeping the temperature below 15°C.

[0096] After the addition is complete, the reaction mixture is heated to 35°C and kept at this temperature for 6 hours. After the reaction is complete, the system is cooled to 5°C and 8.5 kg of 8 wt% sodium bicarbonate aqueous solution is slowly added dropwise with stirring over 1 hour. The temperature inside the vessel is controlled to not exceed 25°C. After the addition is complete, stirring is stopped, and the mixture is transferred to a separatory vessel to stand and separate into layers. The lower aqueous phase is discharged, and 21.8 kg of the upper organic phase is retained.

[0097] Step 6: Wash the 21.8 kg organic phase retained in Step 5 twice with deionized water, using 8.8 kg of water each time. Stir at 45°C for 25 minutes, let stand to separate the layers, and then drain the aqueous phase.

[0098] The washed organic phase was transferred to a distillation vessel and desolventized for 2 hours under conditions of 0.008 MPa absolute pressure, 75°C vessel temperature, and 55°C top temperature. Toluene was distilled off and condensed for recovery. Then, it was distilled for 4 hours under conditions of 0.003 MPa absolute pressure, 160°C vessel temperature, and 147.5°C top temperature, yielding 11.8 kg of propyl bromide acetal with a purity ≥98.0%.

[0099] Example 4 This embodiment is based on Example 1, but with adjustments made to the amount of brominating reagent in step 5, specifically: Step 1: 26.5 kg of potassium hydroxide and 35 kg of triazole are fed into the condensation kettle via a solid feeder. 120 kg of N,N-dimethylformamide (DMF) and 100 kg of propyl bromide are pumped into the condensation kettle via a metering pump.

[0100] Turn on the stirring and vacuum system, maintain the absolute pressure inside the vessel at 0.035 MPa, raise the temperature to 135℃ and react for 8 hours. During the reaction, the distilled water and DMF are condensed and recovered. After the reaction is completed, DMF is removed by vacuum distillation at a distillation temperature of 77℃ and an absolute pressure of 0.01 MPa.

[0101] Subsequently, 100 kg of toluene and 80 kg of deionized water were added to the reactor. After stirring, the mixture was allowed to stand and separate into layers. The upper organic phase was then subjected to depressurization at a distillation temperature of 53°C and an absolute pressure of 0.01 MPa to remove toluene, yielding approximately 97.8 kg of crude propiconazole.

[0102] Step 2: Add all 97.8 kg of the crude propiconazole obtained in Step 1 to the distillation vessel and separate the product using the following four-stage gradient temperature and pressure swing strategy: First stage: Atmospheric pressure, kettle temperature 115℃, column top temperature 100℃, distillation for 1.5 hours, 1.2 kg of toluene was distilled off, and the product was condensed and recycled.

[0103] Second stage: Absolute pressure 0.03MPa, kettle temperature 160℃, column top temperature 140℃, distillation for 1.8 hours, 5.0kg of unreacted propyl bromide acetal was distilled off, condensed and recovered, and reused as reactants.

[0104] Third stage: Absolute pressure 0.01 MPa, kettle temperature 230℃, column top temperature 200℃, distillation for 5 hours. 78.6 kg of propiconazole product was obtained at a slower distillation rate.

[0105] Fourth stage: Absolute pressure 0.005MPa, kettle temperature 248℃, column top temperature 230℃, distillation for 2.5 hours, distilling off 11.0kg of a mixture of propiconazole and 4-H isomer, which is then condensed and stored for later use.

[0106] Collect 2.0 kg of residue from the bottom of the distillation vessel for later use.

[0107] Step 3: Add 2.0 kg of the residue from Step 2 to the dissolving vessel, add 4.0 kg of toluene, heat to 50°C, and stir for 1.25 hours to fully disperse and swell the residue. Cool the solution to 30°C, and while stirring continuously, add 0.5 kg of an acetate-sodium acetate buffer solution with pH=4.5 and an acetate concentration of 2.0 mol / L dropwise to the vessel over 0.75 hours, controlling the temperature to not exceed 35°C.

[0108] After the addition is complete, the material in the reactor is slowly heated to 35°C and stirred for 3 hours. After the reaction is complete, the mixture is allowed to stand and separate into layers. 4.4 kg of the upper organic phase is then taken for later use.

[0109] Step 4: Combine 11.0 kg of the mixture distilled from the fourth stage in Step 2 with 4.4 kg of the organic phase obtained in Step 3, add 5.8 kg of toluene, and stir until homogeneous to form 21.2 kg of toluene mixture.

[0110] Then wash once with 4.3 kg of 5 wt% sodium bicarbonate solution, and then wash twice with deionized water, using 7.5 kg of water each time. Put the washed organic phase into a drying vessel, add 1.4 kg of anhydrous sodium sulfate, stir and dry at 27°C to remove water. After the moisture content is tested to be ≤500 ppm, filter out the desiccant through a filter to obtain 21.1 kg of purified mixture.

[0111] Step 5: Add 21.1 kg of the purified mixture from Step 4 into the reactor, add 0.43 kg of Lewis acid catalyst bismuth trifluoromethanesulfonate, start stirring, cool down to 5°C under nitrogen protection, continue stirring and add 9.5 kg of bromine reagent trimethylbromosilane dropwise over 2 hours, keeping the temperature below 15°C.

[0112] After the addition is complete, the reaction mixture is heated to 35°C and kept at this temperature for 6 hours. After the reaction is complete, the system is cooled to 5°C and 8.5 kg of 8 wt% sodium bicarbonate aqueous solution is slowly added dropwise with stirring over 1 hour. The temperature inside the vessel is controlled to not exceed 25°C. After the addition is complete, stirring is stopped, and the mixture is transferred to a separatory vessel to stand and separate into layers. The lower aqueous phase is discharged, and 21.3 kg of the upper organic phase is retained.

[0113] Step 6: Wash the 21.3 kg organic phase retained in Step 5 twice with deionized water, using 8.7 kg of water each time. Stir at 45°C for 25 minutes, let stand to separate the layers, and then drain the aqueous phase.

[0114] The washed organic phase was transferred to a distillation vessel and desolventized for 2 hours under conditions of 0.008 MPa absolute pressure, 75°C vessel temperature, and 55°C top temperature. Toluene was distilled off and condensed for recovery. Then, it was distilled for 4 hours under conditions of 0.003 MPa absolute pressure, 160°C vessel temperature, and 147.5°C top temperature, yielding 11.3 kg of propyl bromide acetal with a purity ≥97.6%.

[0115] Example 5 This embodiment is based on Example 1, but with adjustments made to the amount of brominating reagent in step 5, specifically: Step 1: 26.5 kg of potassium hydroxide and 35 kg of triazole are fed into the condensation kettle via a solid feeder. 120 kg of N,N-dimethylformamide (DMF) and 100 kg of propyl bromide are pumped into the condensation kettle via a metering pump.

[0116] Turn on the stirring and vacuum system, maintain the absolute pressure inside the vessel at 0.035 MPa, raise the temperature to 135℃ and react for 8 hours. During the reaction, the distilled water and DMF are condensed and recovered. After the reaction is completed, DMF is removed by vacuum distillation at a distillation temperature of 77℃ and an absolute pressure of 0.01 MPa.

[0117] Subsequently, 100 kg of toluene and 80 kg of deionized water were added to the reactor. After stirring, the mixture was allowed to stand and separate into layers. The upper organic phase was then subjected to depressurization at a distillation temperature of 53°C and an absolute pressure of 0.01 MPa to remove toluene, yielding approximately 97.9 kg of crude propiconazole.

[0118] Step 2: Add all 97.9 kg of the crude propiconazole obtained in Step 1 to a distillation vessel and separate the product using the following four-stage gradient temperature and pressure swing strategy: First stage: Atmospheric pressure, kettle temperature 115℃, column top temperature 100℃, distillation for 1.5 hours, 1.3 kg of toluene was distilled off, and the product was condensed and recycled.

[0119] Second stage: Absolute pressure 0.03MPa, kettle temperature 160℃, column top temperature 140℃, distillation for 1.8 hours, 5.0kg of unreacted propyl bromide acetal was distilled off, condensed and recovered, and reused as reactants.

[0120] Third stage: Absolute pressure 0.01 MPa, kettle temperature 230℃, column top temperature 200℃, distillation for 5 hours. 78.5 kg of propiconazole product was obtained at a slower distillation rate.

[0121] Fourth stage: Absolute pressure 0.005MPa, kettle temperature 248℃, column top temperature 230℃, distillation for 2.5 hours, distilling off 11.1kg of a mixture of propiconazole and 4-H isomer, which is then condensed and stored for later use.

[0122] Collect 2.0 kg of residue from the bottom of the distillation vessel for later use.

[0123] Step 3: Add 2.0 kg of the residue from Step 2 to the dissolving vessel, add 4.0 kg of toluene, heat to 50°C, and stir for 1.25 hours to fully disperse and swell the residue. Cool the solution to 30°C, and while stirring continuously, add 0.5 kg of an acetate-sodium acetate buffer solution with pH=4.5 and an acetate concentration of 2.0 mol / L dropwise to the vessel over 0.75 hours, controlling the temperature to not exceed 35°C.

[0124] After the addition is complete, the material in the reactor is slowly heated to 35°C and stirred for 3 hours. After the reaction is complete, the mixture is allowed to stand and separate into layers. 4.4 kg of the upper organic phase is then taken for later use.

[0125] Step 4: Combine the 11.1 kg mixture from the fourth stage of distillation in Step 2 with the 4.4 kg organic phase obtained in Step 3, add 5.8 kg of toluene, and stir until homogeneous to form a toluene mixture of 21.3 kg.

[0126] Then wash once with 4.3 kg of 5 wt% sodium bicarbonate solution, and then wash twice with deionized water, using 7.5 kg of water each time. Put the washed organic phase into a drying vessel, add 1.4 kg of anhydrous sodium sulfate, stir and dry at 27°C to remove water. After the moisture content is tested to be ≤500 ppm, filter out the desiccant through a filter to obtain 21.2 kg of purified mixture.

[0127] Step 5: Add 21.2 kg of the purified mixture from Step 4 into the reactor, add 0.43 kg of Lewis acid catalyst bismuth trifluoromethanesulfonate, start stirring, cool down to 5°C under nitrogen protection, continue stirring and add 11.6 kg of bromine reagent trimethylbromosilane dropwise over 2 hours, keeping the temperature below 15°C.

[0128] After the addition is complete, the reaction mixture is heated to 35°C and kept at this temperature for 6 hours. After the reaction is complete, the system is cooled to 5°C, and 8.5 kg of 8 wt% sodium bicarbonate aqueous solution is slowly added dropwise with stirring over 1 hour. The temperature inside the vessel is controlled to not exceed 25°C. After the addition is complete, stirring is stopped, and the mixture is transferred to a separatory vessel to stand and separate into layers. The lower aqueous phase is discharged, and 22.0 kg of the upper organic phase is retained.

[0129] Step 6: Wash the 22.0 kg organic phase retained in Step 5 twice with deionized water, using 8.9 kg of water each time. Stir at 45°C for 25 minutes, let stand to separate the layers, and then drain the aqueous phase.

[0130] The washed organic phase was transferred to a distillation vessel and desolventized for 2 hours under conditions of 0.008 MPa absolute pressure, 75°C vessel temperature, and 55°C column top temperature. Toluene was distilled off and condensed for recovery. Then, it was distilled for 4 hours under conditions of 0.003 MPa absolute pressure, 160°C vessel temperature, and 147.5°C column top temperature, yielding 11.9 kg of propyl bromide acetal with a purity ≥98.0%.

[0131] Comparative Example 1 This comparative example is based on Example 1, except that the acetate-sodium acetate buffer solution in step 3 is replaced with dilute hydrochloric acid, specifically: Step 1: 26.5 kg of potassium hydroxide and 35 kg of triazole are fed into the condensation kettle via a solid feeder. 120 kg of N,N-dimethylformamide (DMF) and 100 kg of propyl bromide acetal are pumped into the condensation kettle via a metering pump.

[0132] Turn on the stirring and vacuum system, maintain the absolute pressure inside the vessel at 0.035 MPa, raise the temperature to 135℃ and react for 8 hours. During the reaction, the distilled water and DMF are condensed and recovered. After the reaction is completed, DMF is removed by vacuum distillation at a distillation temperature of 77℃ and an absolute pressure of 0.01 MPa.

[0133] Subsequently, 100 kg of toluene and 80 kg of deionized water were added to the reactor, stirred, and allowed to stand to separate into layers. The upper organic phase was then removed from the reactor under reduced pressure at a distillation temperature of 53°C and an absolute pressure of 0.01 MPa to remove toluene, yielding approximately 97.7 kg of crude propiconazole.

[0134] Step 2: Add all 97.7 kg of the crude propiconazole obtained in Step 1 to the distillation vessel and separate the product using the following four-stage gradient temperature and pressure swing strategy: First stage: Atmospheric pressure, kettle temperature 115℃, column top temperature 100℃, distillation for 1.5 hours, 1.2 kg of toluene was distilled off, and the product was condensed and recycled.

[0135] Second stage: Absolute pressure 0.03 MPa, kettle temperature 160℃, column top temperature 140℃, distillation time 1.8 hours. 4.9 kg of unreacted propyl bromide ketal was distilled off, condensed and recovered, and reused as reactants.

[0136] Third stage: Absolute pressure 0.01 MPa, kettle temperature 230℃, column top temperature 200℃, distillation for 5 hours. 78.5 kg of propiconazole product was obtained at a slower distillation rate.

[0137] Fourth stage: Absolute pressure 0.005MPa, kettle temperature 248℃, column top temperature 230℃, distillation for 2.5 hours, distilling off 11.0kg of a mixture of propiconazole and 4-H isomer, which is then condensed and stored for later use.

[0138] Collect 2.1 kg of residue from the bottom of the distillation vessel for later use.

[0139] Step 3: Add 2.1 kg of the residue from Step 2 to the dissolving vessel, add 4.0 kg of toluene, heat to 50°C, and stir for 1.25 hours to fully disperse and swell the residue. Cool the liquid to 30°C, and while stirring continuously, add 0.5 kg of a 3.5% dilute hydrochloric acid solution dropwise to the vessel over 0.75 hours, controlling the temperature not to exceed 35°C. After the addition is complete, slowly heat the material in the vessel to 35°C, keep it warm and stir for 3 hours. After the reaction is complete, let it stand and separate into layers, and take 3.0 kg of the upper organic phase for later use.

[0140] Step 4: Combine 11.0 kg of the mixture distilled from the fourth stage in Step 2 with 3.0 kg of the organic phase obtained in Step 3, add 5.2 kg of toluene, and stir until homogeneous to form 19.2 kg of toluene mixture.

[0141] Then wash once with 3.9 kg of 5 wt% sodium bicarbonate solution, and then wash twice with deionized water, using 6.8 kg of water each time. Put the washed organic phase into a drying kettle, add 1.3 kg of anhydrous sodium sulfate, stir and dry at 27°C to remove water. After the moisture content is tested to be ≤500 ppm, filter out the desiccant through a filter to obtain 18.9 kg of purified mixture.

[0142] Step 5: Add 18.9 kg of the purified mixture from Step 4 into the reactor, add 0.38 kg of Lewis acid catalyst bismuth trifluoromethanesulfonate, start stirring, cool down to 5°C under nitrogen protection, continue stirring and add 9.0 kg of bromine reagent trimethylbromosilane dropwise over 2 hours, keeping the temperature below 15°C.

[0143] After the addition is complete, the reaction mixture is heated to 35°C and kept at this temperature for 6 hours. After the reaction is complete, the system is cooled to 5°C, and 7.7 kg of 8 wt% sodium bicarbonate aqueous solution is slowly added dropwise with stirring over 1 hour, controlling the temperature inside the vessel to not exceed 25°C. After the addition is complete, stirring is stopped, and the mixture is transferred to a separatory vessel to stand and separate into layers. The lower aqueous phase is discharged, and 19.1 kg of the upper organic phase is retained.

[0144] Step 6: Wash the 19.1 kg organic phase retained from Step 5 twice with deionized water, using 7.7 kg of water each time. Stir at 45°C for 25 minutes, allow to stand and separate into layers, then drain the aqueous phase. Transfer the washed organic phase to a distillation vessel and desolvate for 2 hours under conditions of 0.008 MPa absolute pressure, 75°C vessel temperature, and 55°C column top temperature. Distill off toluene and condense for recovery. Then, distill for 4 hours under conditions of 0.003 MPa absolute pressure, 160°C vessel temperature, and 147.5°C column top temperature to obtain 6.9 kg of propyl bromide acetal with a purity of 94.3%.

[0145] Comparative Example 2 This comparative example omits the residual hydrolysis and chemical transformation processes in steps 3 to 6 of Example 1, collecting only the propiconazole produced by the third-stage distillation. Specifically: Step 1: 26.5 kg of potassium hydroxide and 35 kg of triazole are fed into the condensation kettle via a solid feeder. 120 kg of N,N-dimethylformamide (DMF) and 100 kg of propyl bromide are pumped into the condensation kettle via a metering pump.

[0146] Turn on the stirring and vacuum system, maintain the absolute pressure inside the vessel at 0.035 MPa, raise the temperature to 135℃ and react for 8 hours. During the reaction, the distilled water and DMF are condensed and recovered. After the reaction is completed, DMF is removed by vacuum distillation at a distillation temperature of 77℃ and an absolute pressure of 0.01 MPa.

[0147] Subsequently, 100 kg of toluene and 80 kg of deionized water were added to the reactor. After stirring, the mixture was allowed to stand and separate into layers. The upper organic phase was then subjected to depressurization at a distillation temperature of 53°C and an absolute pressure of 0.01 MPa to remove toluene, yielding approximately 97.8 kg of crude propiconazole.

[0148] Step 2: Add all 97.8 kg of the crude propiconazole obtained in Step 1 to the distillation vessel and separate the product using the following three-stage gradient temperature and pressure swing strategy: First stage: Atmospheric pressure, kettle temperature 115℃, column top temperature 100℃, distillation for 1.5 hours, 1.2 kg of toluene was distilled off, and the product was condensed and recycled.

[0149] Second stage: Absolute pressure 0.03MPa, kettle temperature 160℃, column top temperature 140℃, distillation for 1.8 hours, 5.1kg of unreacted propyl bromide acetal was distilled off, condensed and recovered, and reused as reactants.

[0150] Third stage: Absolute pressure 0.01MPa, kettle temperature 230℃, column top temperature 200℃, distillation for 5 hours, to obtain 78.6kg of propiconazole product.

[0151] The remaining 12.9 kg of residue was disposed of as hazardous waste.

[0152] Comparative Example 3 This comparative example, based on Example 1, no longer converts the recovered propiconazole and 4-H isomer mixture into propyl bromide ketal. Instead, propiconazole is separated and recovered by distillation. Specifically: Step 1: 26.5 kg of potassium hydroxide and 35 kg of triazole were fed into the condensation reactor via a solid feeder. 120 kg of N,N-dimethylformamide (DMF) and 100 kg of propyl bromide acetal were pumped into the condensation reactor via a metering pump. The stirring and vacuum systems were turned on, maintaining an absolute pressure of 0.035 MPa inside the reactor. The temperature was raised to 135°C and the reaction was carried out for 8 hours. During the reaction, the distilled water and DMF were condensed and recovered. After the reaction was completed, DMF was removed by vacuum distillation at a distillation temperature of 77°C and an absolute pressure of 0.01 MPa. Subsequently, 100 kg of toluene and 80 kg of deionized water were added to the reactor. After stirring, the mixture was allowed to stand and separate into layers. The upper organic phase was taken and toluene was removed by vacuum distillation at a distillation temperature of 53°C and an absolute pressure of 0.01 MPa to obtain approximately 97.9 kg of crude propiconazole.

[0153] Step 2: Add all 97.9 kg of the crude propiconazole obtained in Step 1 to a distillation vessel and separate the product using the following four-stage gradient temperature and pressure swing strategy: First stage: Atmospheric pressure, kettle temperature 115℃, column top temperature 100℃, distillation for 1.5 hours, 1.2 kg of toluene was distilled off, and the product was condensed and recycled.

[0154] Second stage: Absolute pressure 0.03 MPa, kettle temperature 160℃, column top temperature 140℃, distillation for 1.8 hours. 5.0 kg of unreacted propyl bromide ketal was distilled off, condensed and recovered, and reused as reactants.

[0155] Third stage: Absolute pressure 0.01 MPa, kettle temperature 230℃, column top temperature 200℃, distillation for 5 hours. 78.7 kg of propiconazole product was obtained at a slower distillation rate.

[0156] Fourth stage: Absolute pressure 0.005MPa, kettle temperature 248℃, column top temperature 230℃, distillation for 2.5 hours, distilling off 11.0kg of a mixture of propiconazole and 4-H isomer, which is then condensed and stored for later use.

[0157] Collect 2.0 kg of residue from the bottom of the distillation vessel for later use.

[0158] Step 3: Add 2.0 kg of the residue from Step 2 to the dissolving vessel, add 4.0 kg of toluene, heat to 50°C, and stir for 1.25 hours to fully disperse and swell the residue. Cool the solution to 30°C, and while continuously stirring, add 0.5 kg of an acetate-sodium acetate buffer solution with pH=4.5 and an acetate concentration of 2.0 mol / L dropwise over 0.75 hours, controlling the temperature not to exceed 35°C. After the addition is complete, slowly heat the material in the vessel to 35°C and maintain the temperature while stirring for 3 hours. After the reaction is complete, allow it to stand and separate into layers, and take 4.3 kg of the upper organic phase for later use.

[0159] Step 4: Combine 11.0 kg of the mixture distilled from the fourth stage in Step 2 with 4.3 kg of the organic phase obtained in Step 3, add 5.8 kg of toluene, and stir until homogeneous to form 21.1 kg of toluene mixture.

[0160] Then wash once with 4.3 kg of 5 wt% sodium bicarbonate solution, and then wash twice with deionized water, using 7.5 kg of water each time. Put the washed organic phase into a drying kettle, add 1.4 kg of anhydrous sodium sulfate, stir and dry at 27°C to remove water. After the moisture content is tested to be ≤500 ppm, filter out the desiccant through a filter to obtain 21.0 kg of purified mixture.

[0161] Step 5: Transfer all 21.0 kg of the purified mixture obtained in Step 4 to a distillation vessel. Under the conditions of absolute pressure of 0.005 MPa, vessel temperature of 240-252℃ and column top temperature of 230℃, distillate at a reflux ratio of 20:1 for 12 hours to collect 2.7 kg of propiconazole fraction with a purity of 94.80%. The remaining residue is treated as hazardous waste.

[0162] Comparative Example 4 This comparative example, based on Example 1, abandons the residue recovery in step 3, directly discarding the residue at the bottom of the distillation vessel, and only performs chemical conversion on the fourth-stage mixture to recover propyl bromide ketal, specifically as follows: Step 1: 26.5 kg of potassium hydroxide and 35 kg of triazole are fed into the condensation kettle via a solid feeder. 120 kg of N,N-dimethylformamide (DMF) and 100 kg of propyl bromide acetal are pumped into the condensation kettle via a metering pump.

[0163] The stirring and vacuum systems were turned on, maintaining an absolute pressure of 0.035 MPa inside the reactor. The temperature was raised to 135°C and the reaction was carried out for 8 hours. During the reaction, the distilled water and DMF were condensed and recovered. After the reaction was completed, DMF was removed by vacuum distillation at a distillation temperature of 77°C and an absolute pressure of 0.01 MPa. Subsequently, 100 kg of toluene and 80 kg of deionized water were added to the reactor, stirred, and allowed to stand for separation. The upper organic phase was taken and toluene was removed by vacuum distillation at a distillation temperature of 53°C and an absolute pressure of 0.01 MPa to obtain approximately 97.8 kg of crude propiconazole.

[0164] Step 2: Add all 97.8 kg of the crude propiconazole obtained in Step 1 to the distillation vessel and separate the product using the following four-stage gradient temperature and pressure swing strategy: First stage: Atmospheric pressure, kettle temperature 115℃, column top temperature 100℃, distillation for 1.5 hours, 1.3 kg of toluene was distilled off, and the product was condensed and recycled.

[0165] Second stage: Absolute pressure 0.03 MPa, kettle temperature 160℃, column top temperature 140℃, distillation time 1.8 hours. 4.9 kg of unreacted propyl bromide ketal was distilled off, condensed and recovered, and reused as reactants.

[0166] Third stage: Absolute pressure 0.01 MPa, kettle temperature 230℃, column top temperature 200℃, distillation for 5 hours. 78.5 kg of propiconazole product was obtained at a slower distillation rate.

[0167] Fourth stage: Absolute pressure 0.005MPa, kettle temperature 248℃, column top temperature 230℃, distillation for 2.5 hours, distilling off 11.0kg of a mixture of propiconazole and 4-H isomer, which is then condensed and stored for later use.

[0168] 2.1 kg of residue was collected from the bottom of the distillation vessel and disposed of as hazardous solid waste.

[0169] Step 3: Add 11.0 kg of the mixture distilled from the fourth stage in Step 2 into the preparation vessel, add 5.8 kg of toluene, and stir evenly to form 16.7 kg of toluene mixture.

[0170] Then wash once with 3.4 kg of 5 wt% sodium bicarbonate solution, and then wash twice with deionized water, using 5.9 kg of water each time. Put the washed organic phase into a drying kettle, add 1.1 kg of anhydrous sodium sulfate, stir and dry at 27°C to remove water. After the moisture content is ≤500 ppm, filter out the desiccant through a filter to obtain 16.6 kg of purified mixture.

[0171] Step 4: Add 16.6 kg of the purified mixture from Step 3 into the reactor, add 0.33 kg of Lewis acid catalyst bismuth trifluoromethanesulfonate, start stirring, cool down to 5°C under nitrogen protection, continue stirring and add 7.9 kg of bromine reagent trimethylbromosilane dropwise over 2 hours, controlling the temperature not to exceed 15°C.

[0172] After the addition is complete, the reaction mixture is heated to 35°C and kept at this temperature for 6 hours. After the reaction is complete, the system is cooled to 5°C, and 6.7 kg of 8 wt% sodium bicarbonate aqueous solution is slowly added dropwise with stirring over 1 hour. The temperature inside the vessel is controlled to not exceed 25°C. After the addition is complete, stirring is stopped, and the mixture is transferred to a separatory vessel to stand and separate into layers. The lower aqueous phase is discharged, and 17.0 kg of the upper organic phase is retained.

[0173] Step 5: Wash the 17.0 kg organic phase retained in Step 4 twice with deionized water, using 6.8 kg of water each time. Stir at 45°C for 25 minutes, let stand to separate the layers, and then drain the aqueous phase.

[0174] The washed organic phase was transferred to a distillation vessel and desolventized for 2 hours under conditions of 0.008 MPa absolute pressure, 75°C vessel temperature, and 55°C column top temperature. Toluene was distilled off and condensed for recovery. Then, it was distilled for 4 hours under conditions of 0.003 MPa absolute pressure, 160°C vessel temperature, and 147.5°C column top temperature, yielding 9.2 kg of propyl bromide acetal with a purity ≥97.5%.

[0175] The feeding and conversion data of the above embodiments and comparative examples are summarized and calculated as follows:

[0176] In the above data, the input amount of propyl bromide ketal in each embodiment and comparative example is 100 kg. The propiconazole yield can be obtained by comparing the mass of the produced propiconazole with the amount of output. The mass of propyl bromide ketal consumed can be obtained by comparing the mass of the distilled propyl bromide ketal, the mass of the recovered propyl bromide ketal, and its purity. The theoretical mass of propiconazole can be obtained by comparing the actual mass of produced propiconazole with the theoretical mass of propiconazole. The actual conversion rate can be obtained by comparing the actual mass of produced propiconazole with the theoretical mass of propiconazole.

[0177] The yields of propiconazole in Examples 1-5 were all between 81.11% and 81.42%, with actual conversion rates as high as 96.62% to 97.73%. Furthermore, the purity of the recovered propyl bromide acetal remained stable at 97.5% to 98.0%. This indicates that the process achieved a closed-loop cycle of synthesis, separation, isomer enrichment, residue hydrolysis and release, chemical conversion, and raw material recovery. The chiral byproducts were efficiently converted into raw materials and reintroduced into the reaction, almost eliminating the yield loss caused by the formation of the 4-H isomer. The recovered material could be directly reused in step 1, ensuring full utilization of the materials.

[0178] Example 3 increased the pH of the buffer solution and the amount of brominated reagent, recovering 11.8 kg of propyl bromide ketal with an actual conversion rate of 97.73%. Example 5 increased the amount of brominated reagent, recovering 11.9 kg of propyl bromide ketal with an actual conversion rate of 97.63%. Both were better than Example 1, indicating that moderately enhancing hydrolysis in a weakly acidic buffer solution and appropriately increasing the amount of brominated reagent are more conducive to polymer depolymerization and ring-opening conversion of the 4-H isomer, thereby further improving the recovery of raw materials.

[0179] In Comparative Example 1, when the buffer solution was replaced with dilute hydrochloric acid, the recovery of propyl bromide ketal plummeted to 6.9 kg, with a purity of only 94.3% and an actual conversion rate of 91.68%. This was because the strong acid caused the destruction of structures such as the ketal and triazole ring, resulting in poor hydrolysis selectivity and the generation of irreversible byproducts, which directly reduced the recovery efficiency and conversion rate. This fully demonstrates that a mild buffer system is the key to ensuring hydrolysis selectivity and maintaining a high recovery rate.

[0180] Comparative Example 2 completely eliminated isomer conversion and residue treatment, and there was no propyl bromide ketal recovery. The net consumption was as high as 94.9 kg, and the actual conversion rate was only 85.69%. This shows that if the 4-H isomer is not reused, a large amount of raw materials are lost in the form of isomers, the atom economy of the reaction is greatly reduced, and a large amount of hazardous waste is generated. This verifies the core value of the closed-loop reuse process from the opposite perspective.

[0181] Comparative Example 3 relied solely on distillation to separate the isomer mixture, recovering only 2.7 kg of propiconazole with a purity of 94.8%, resulting in a very small recovery of propyl bromide acetal. The actual conversion rate was 88.13%. Because propiconazole and the 4-H isomer have very similar boiling points, physical separation is difficult to achieve efficiently, and a large amount of active ingredients remain in the residue and are wasted. This highlights the high selectivity and irreplaceability of the chemical conversion method.

[0182] Comparative Example 4 abandoned residue hydrolysis and only processed the fourth-stage mixture, recovering 9.2 kg of propyl bromide acetal with a conversion rate of 94.43%, which was significantly lower than that of the Example. This indicates that if the 4-H isomer and propiconazole encapsulated in the distillation vessel residue are directly discarded without being released by hydrolysis, it will result in a waste of resources. The residue hydrolysis step makes a significant contribution to improving the overall recovery rate.

[0183] It should be understood that the embodiments of the present invention described above do not exhaustively describe all details, nor does it mean that the present invention is limited to the specific embodiments disclosed. 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 process for recycling the 4-H isomer of propiconazole, characterized in that, Includes the following steps: Step 1 Potassium hydroxide and triazole were added to a condensation vessel, along with N,N-dimethylformamide and propyl bromide ketal. The mixture was heated under stirring and vacuum conditions. During the reaction, water and N,N-dimethylformamide were distilled off and condensed for recovery. After the reaction, N,N-dimethylformamide was removed by vacuum distillation. Toluene and deionized water were added to the vessel, and the mixture was stirred and allowed to stand for separation. The upper organic phase was removed under vacuum to remove toluene, yielding crude propiconazole. Step 2 The crude propiconazole obtained in step 1 was added to a distillation vessel, and toluene, unreacted propyl bromide ketal, propiconazole, and a mixture of propiconazole and its 4-H isomer were distilled off sequentially using a segmented pressure swing and gradient temperature method. The residue at the bottom of the distillation vessel was collected for later use. Step 3 Add the residue from step 2 into the dissolving vessel, add toluene, heat and stir to fully disperse and swell the residue to form a toluene solution, then cool the solution, add an acetate-sodium acetate buffer solution dropwise into the vessel while stirring continuously, slowly heat and keep the temperature while stirring the reaction, after the reaction is completed, let it stand and separate into layers, and take the upper organic phase for later use. Step 4 The mixture of propiconazole distilled in step 2 and the 4-H isomer was mixed with the organic phase obtained in step 3. Toluene was added and stirred until homogeneous to form a toluene mixture. The mixture was washed successively with sodium bicarbonate solution and deionized water, and then dried and dehydrated by adding anhydrous sodium sulfate. The desiccant was then filtered out through a filter to obtain a purified mixture. Step 5 The purified mixture obtained in step 4 is put into a reaction vessel, bismuth trifluoromethanesulfonate is added, stirring is started, the temperature is lowered under nitrogen protection, and trimethylbromosilane is added dropwise. During the dropwise addition, the temperature inside the vessel is controlled not to exceed 15°C. After the dropwise addition is completed, the temperature is raised to 25-50°C and kept at this temperature for 4-8 hours. After the reaction is completed, the temperature is lowered, and sodium bicarbonate aqueous solution is slowly added dropwise while stirring. The temperature inside the vessel is controlled not to exceed 25°C. After the dropwise addition is completed, stirring is stopped, the mixture is transferred to a separatory vessel, allowed to stand and separate into layers, the lower aqueous phase is discharged, and the upper organic phase is retained. Step 6 The organic phase retained in step 5 was washed with deionized water and then transferred to a distillation vessel. It was then subjected to desolvation under reduced pressure and distillation under reduced pressure to obtain propyl bromide ketal.

2. The process for recycling the 4-H isomer of propiconazole according to claim 1, characterized in that, The segmented voltage transformation and gradient heating method described in step 2 specifically adopts a four-stage gradient heating method; First-stage gradient: Under normal pressure, with a vessel temperature of 100–130°C and a column top temperature of 90–110°C, the distillation time is 1.0–1.5 hours, to distill off toluene from the crude propiconazole product; Second-stage gradient: absolute pressure 0.025-0.04 MPa, pot temperature 150-170℃, top temperature 130-150℃, distillation time 1.5-2.0 hours, to distill off the propyl bromide acetal from the crude propiconazole. Third-stage gradient: absolute pressure ≤ 0.01 MPa, pot temperature 220~240℃, top temperature 190~210℃, distillation time 4~6 hours, distillate is propiconazole; Fourth-stage gradient: absolute pressure ≤ 0.01 MPa, pot temperature 240~255℃, top temperature 220~235℃, distillation time 2~3 hours, distillate is a mixture of propiconazole and 4-H isomer.

3. The process for recycling the 4-H isomer of propiconazole according to claim 1, characterized in that, The mass ratio of the residue to toluene added in step 3 is 1:1.8 to 2.2; The acetate-sodium acetate buffer solution has a pH of 4.2–4.8, an acetate concentration of 1.8–2.3 mol / L, and a mass ratio of acetate-sodium acetate buffer solution to the added residue of 0.2–0.3:

1. During the dropwise addition process, keep the temperature inside the vessel below 35°C. After the dropwise addition is completed, keep the vessel warm and stir for 2 to 4 hours.

4. The process for recycling the 4-H isomer of propiconazole according to claim 1, characterized in that, In step 3, the liquid is cooled to 25-35°C, and the addition of the acetate-sodium acetate buffer solution to the reactor is controlled at a time of 0.5-1 hour. After adding toluene in step 3, the temperature is raised to 45-55°C and stirred for 1.0-1.5 hours.

5. The process for recycling the 4-H isomer of propiconazole according to claim 1, characterized in that, The mass of toluene added in step 4 is 40% to 65% of the mass of the mixture of propiconazole and 4-H isomer distilled off in step 2; The alkaline washing process uses a 5wt% sodium bicarbonate solution, with a mass ratio of sodium bicarbonate solution to toluene mixture of 0.1–0.3:

1. During the water washing process, the mass ratio of deionized water to toluene mixture used in each wash is 0.2–0.5:1; The amount of anhydrous sodium sulfate used is 5% to 8% of the mass of the toluene mixture, and the moisture content during the drying and dehydration process is ≤500ppm.

6. The process for recycling the 4-H isomer of propiconazole according to claim 1, characterized in that, The amount of bismuth trifluoromethanesulfonate used in step 5 is 1% to 3% of the mass of the purified mixture; The amount of trimethylbromosilane added is 45% to 55% of the mass of the purified mixture; The sodium bicarbonate solution has a mass concentration of 8%, and the mass ratio of the added sodium bicarbonate solution to the purified mixture is 0.3–0.5:

1.

7. The process for recycling the 4-H isomer of propiconazole according to claim 6, characterized in that, In step 5, the system is cooled to 0–10°C, and the bromine reagent is added dropwise over 1.5–2.5 hours. After the reaction is complete, the reaction vessel is cooled to 0-10°C, and the sodium bicarbonate aqueous solution is added dropwise over 0.8-1.2 hours.

8. The process for recycling the 4-H isomer of propiconazole according to claim 1, characterized in that, The mass ratio of potassium hydroxide, triazole, propyl bromide ketal and N,N-dimethylformamide added in step 1 is 22-31:32-38:100:110-130; When removing N,N-dimethylformamide by vacuum distillation, the distillation temperature is 70–85℃ and the absolute pressure is ≤0.01MPa; when removing toluene by vacuum distillation, the distillation temperature is 45–60℃ and the absolute pressure is ≤0.02MPa.

9. The process for recycling the 4-H isomer of propiconazole according to claim 1, characterized in that, In step 6, during the washing of the organic phase, the mass ratio of deionized water to organic phase is 0.3 to 0.5:

1. The mixture is stirred at 40 to 50°C for 20 to 30 minutes, and after standing and separating into layers, the lower aqueous phase is discharged. During the depressurization desolvation process, the absolute pressure value is ≤0.015MPa, the temperature inside the vessel is 70~80℃, the temperature at the top of the column is 50~60℃, and the desolvation time is 1.5~2.5 hours. The absolute pressure during the vacuum distillation process is ≤0.005MPa, the kettle temperature is 155~165℃, the column top temperature is 140~155℃, and the distillation time is 3~5 hours.

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