Synthesis and separation process of high-purity 3-methyl-5-phenylpentanol

Abstract

The application discloses a synthesis and separation process of high-purity 3-methyl-5-phenylpentanol. The process comprises the following steps: condensation dehydration reaction, washing, neutralization and phase state enrichment, intermediate separation and modifier loading, selective hydrogenation ring opening, product refining and selective physical separation, and the whole process adopts a double-effect steric hindrance type polymerization modifier. The hindered amine derivative captures carbon center active free radicals to inhibit thermal polymerization of carbon-carbon double bonds in the condensation dehydration reaction; in the washing, neutralization and vacuum rectification, the hindered amine derivative is enriched in the intermediate material and enters the selective hydrogenation ring opening through desalination and free state and high-boiling characteristics; on the surface of the hydrogenation catalyst, the hindered amine derivative divides and continuously occupies a large number of active sites, limits the flat adsorption of the benzene ring multi-site, and makes the reaction only occur carbon-carbon double bond reduction and oxygen-containing heterocyclic ring opening. The application realizes the synergistic control across the reaction stages by using a single material, and improves the product purity and molar yield.

Description

Technical Field

[0001] This invention relates to the field of fine chemical synthesis technology, specifically to the synthesis and separation process of high-purity 3-methyl-5-phenylpentanol. Background Technology

[0002] 3-Methyl-5-phenylpentanol is an important fine chemical intermediate and synthetic fragrance. Because its molecular structure contains both a benzene ring and a fatty alcohol side chain, 3-methyl-5-phenylpentanol exhibits distinct rose and lily-of-the-valley aroma characteristics, making it widely applicable in the formulation of daily chemical fragrances and high-grade flavorings.

[0003] In existing industrial synthesis routes, the preparation of 3-methyl-5-phenylpentanol typically uses benzaldehyde and 3-methyl-3-buten-1-ol as starting materials, achieved through a two-step continuous chemical transformation reaction. The conventional preparation process involves: under acidic catalyst and high-temperature reflux conditions, the starting materials undergo a condensation dehydration reaction to generate a phenyl dihydropyran intermediate containing a carbon-carbon double bond and an oxygen-containing heterocycle; subsequently, the intermediate is transferred to a hydrogenation reactor, where a catalytic hydrogenation ring-opening reaction is carried out under a metal catalyst and high-pressure hydrogen atmosphere, reducing the carbon-carbon double bond and cleaving the oxygen-containing heterocycle to finally generate the target product.

[0004] In existing synthetic routes, the condensation dehydration reaction requires high temperatures, and the carbon-carbon double bonds in the raw materials and intermediates are prone to thermally initiated polymerization, generating high-molecular-weight tar-like polymers. In the subsequent catalytic hydrogenation stage, the benzene ring is susceptible to excessive hydrogenation reduction by a metal catalyst, leading to structural damage and loss of aroma characteristics in the product. To suppress these two distinct side reactions, existing technologies require the addition of conventional free radical polymerization inhibitors in the condensation dehydration stage, and the reintroduction of specific catalyst poisoning agents or modifiers in the hydrogenation ring-opening stage. This approach of introducing single-functional materials for different reaction stages results in a diverse range of materials in the production system. Conventional polymerization inhibitors added at the front end are often unsuitable for subsequent hydrogenation conditions, necessitating cumbersome physical separation or chemical washing steps in intermediate processes to completely remove them. The complexity of the material system increases the difficulty of process control in continuous production, making it difficult to achieve synergistic control of polymerization and excessive hydrogenation side reactions in successive chemical transformations, resulting in a lengthy process flow. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a synthesis and separation process for high-purity 3-methyl-5-phenylpentanol, which solves the problems of easy thermal polymerization of carbon-carbon double bonds in the condensation and dehydration reaction stage and excessive reduction of the benzene ring in the hydrogenation ring-opening reaction stage in existing synthetic routes.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a process for the synthesis and separation of high-purity 3-methyl-5-phenylpentanol, comprising the following steps:

[0007] Condensation and dehydration reaction: An azeotropic solvent, an acidic catalyst, and a double-effect steric hindrance polymerization inhibitor are mixed and heated. Under reflux, a mixture of benzaldehyde and 3-methyl-3-buten-1-ol is continuously added dropwise to carry out the reaction, while the generated water is separated and removed. Washing, neutralization, and phase enrichment: An alkaline aqueous solution is added to the cooled reaction system for washing and neutralization to remove the lower aqueous phase and obtain an organic oil phase enriched with the double-effect steric hindrance polymerization inhibitor and the phenyl dihydropyran intermediate.

[0008] Intermediate separation and modifier loading: The organic oil phase is separated by vacuum distillation, vaporized and the azeotropic solvent is removed. The dual-effect steric hindrance type polymerization inhibitor and the phenyl dihydropyran intermediate are retained together in the bottom liquid of the distillation unit to obtain a mixed intermediate material.

[0009] Selective hydrogenation ring-opening: The mixed intermediate materials are placed in a hydrogenation solvent and a hydrogenation catalyst, and hydrogen gas is introduced. The hydrogenation ring-opening reaction is carried out at a set operating temperature and pressure. A dual-effect steric hindrance type polymerization inhibitor is adsorbed on the surface of the hydrogenation catalyst and provides physical steric hindrance, limiting the catalytic activity of the hydrogenation catalyst. This ensures that the hydrogenation reaction only occurs at the reduction of carbon-carbon double bonds and the breaking and opening of oxygen-containing heterocycles, thus protecting the benzene ring skeleton. After the reaction, the solid hydrogenation catalyst is separated and removed to obtain a mixed clear liquid.

[0010] Product purification and selective physical separation: The mixed clear liquid is purified by vacuum distillation, and the hydrogenated solvent is preferentially removed by vaporization. Then, 3-methyl-5-phenylpentanol is vaporized under vacuum to obtain the finished product. The dual-effect steric hindrance polymerization inhibitor is retained in the residue of the distillation equipment and discharged.

[0011] Furthermore, the dual-effect sterically hindered polymerization modifier is a hindered amine derivative; the molecular structure of the hindered amine derivative contains one or more six-membered piperidine rings, and two alkyl substituents are attached to each of the two adjacent carbon atoms of the nitrogen atom on the piperidine ring; the alkyl substituents include methyl, ethyl or propyl; specific compounds of the hindered amine derivative include 2,2,6,6-tetramethylpiperidinol, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate or N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine.

[0012] Further, in the condensation dehydration reaction, the acidic catalyst is p-toluenesulfonic acid, benzenesulfonic acid, or methanesulfonic acid; the azeotropic solvent is xylene, toluene, or cyclohexane; the system is heated to the reflux temperature of the corresponding azeotropic solvent, and the operating temperature is controlled between 80℃ and 145℃. The nitrogen atom on the piperidine ring of the hindered amine derivative serves as the reactive site, transforming into a stable nitroxide radical or amino radical intermediate under trace oxygen or thermal excitation. This intermediate couples with the carbon-center active radical generated in the reaction system, blocking the chain growth process of the polymerization reaction. Based on the numerical difference between the chain growth rate constant and the radical capture rate constant of the polymerization reaction, the radical capture rate in the system is greater than the chain growth rate of the polymerization reaction, causing the dual-effect steric hindrance type polymerization inhibitor to preferentially consume the active radicals, maintaining the chemical stability of the condensation dehydration reaction system.

[0013] Furthermore, during the washing neutralization and phase enrichment, the alkaline aqueous solution is an aqueous solution of sodium carbonate, potassium carbonate, or sodium bicarbonate. In the condensation dehydration reaction, the hindered amine derivative combines with the acidic catalyst to form a water-soluble salt compound. During the washing neutralization stage, the alkaline aqueous solution neutralizes the acidic catalyst, causing the hindered amine derivative to desalinate and revert to its nonpolar free state. The nonpolar hydrocarbon skeleton in the molecular structure of the hindered amine derivative provides lipophilicity. The nonpolar free state, combined with the lipophilic structural characteristics of the hindered amine derivative, alters the octanol-water partition coefficient in the multiphase system, causing a decrease in the equilibrium concentration of the hindered amine derivative in the aqueous phase. It then distributes and enriches in the organic oil phase, preventing it from being discharged with the washing aqueous phase.

[0014] Furthermore, in the intermediate separation and modifier loading process, the reboiler operating temperature of the distillation unit is controlled below the thermal decomposition temperature of phenyl dihydropyran and the double-effect steric hindrance type polymerization inhibitor, and the azeotropic solvent is preferentially removed based on the difference in relative volatility. Due to its high boiling point, the double-effect steric hindrance type polymerization inhibitor remains in a liquid phase and coexists with the unvaporized phenyl dihydropyran in the bottom liquid of the distillation unit, which then enters the hydrogenation reaction process as a liquid-phase feedstock.

[0015] Further, in the selective hydrogenation ring-opening, the hydrogenation solvent is ethanol, methanol, or isopropanol; the hydrogenation catalyst is a palladium-on-carbon catalyst; and the operating temperature of the hydrogenation ring-opening reaction is controlled between 110°C and 120°C. The dual-effect steric hindrance polymerization inhibitor is converted into a selective poisoning agent for the palladium-on-carbon catalyst; the dual-effect steric hindrance polymerization inhibitor undergoes coordination with empty orbitals on the palladium metal surface to produce chemisorption, and multiple alkyl substituents above the adsorption sites form a physical space capping layer; the physical space capping layer divides the continuous large-area active sites on the palladium metal surface into isolated micro-active regions. These isolated micro-active regions cannot physically accommodate the flat adsorption of benzene rings, but they can accommodate smaller carbon-carbon double bonds and oxygen-containing heterocycles for lateral or end-group adsorption.

[0016] Furthermore, the coordination adsorption of the dual-effect sterically hindered polymerization inhibitor on the palladium metal surface is an exothermic process. The chemisorption equilibrium constant and surface coverage are controlled by the operating temperature; an increase in operating temperature leads to a decrease in the chemisorption equilibrium constant. By controlling the operating temperature of the hydrogenation ring-opening reaction within the range of 110°C to 120°C, the surface coverage of the dual-effect sterically hindered polymerization inhibitor is kept within a stable range. Surface coverage within the stable range can segment continuous active sites to protect the benzene ring, while retaining isolated active sites to maintain the ring-opening reduction reaction.

[0017] Furthermore, in the selective hydrogenation ring-opening process, after the hydrogenation reaction equipment is gas-purified, hydrogen is introduced to set the initial pressure to 0.6 MPa; the heating program is started to raise the system temperature to 110°C to 120°C. As the hydrogenation solvent is heated and vaporized to generate saturated vapor pressure, and the introduced hydrogen expands due to heating, the hydrogen partial pressure increases, thereby increasing the actual working pressure inside the hydrogenation reaction equipment and maintaining it at 0.8 MPa to 1.0 MPa.

[0018] Furthermore, in the product purification and selective physical separation, the mixed clear liquid containing the hydrogenated solvent, 3-methyl-5-phenylpentanol, and the dual-effect steric hindrance polymerization inhibitor is transferred to a distillation unit. Under normal or slightly negative pressure, the hydrogenated solvent is preferentially vaporized to remove it. Subsequently, the operating pressure of the distillation system is reduced to 0.1 kPa to 1.0 kPa using a vacuum generator. The actual boiling point decreases as the system pressure decreases, and the top outlet temperature is controlled at 110°C to 130°C, converting 3-methyl-5-phenylpentanol into a gaseous phase that rises to the top of the column and is condensed and collected. Under these operating pressure and temperature conditions, the dual-effect steric hindrance polymerization inhibitor does not meet the thermodynamic conditions required for vaporization and remains stably in the residual liquid of the distillation unit as a heavy component.

[0019] This invention provides a process for the synthesis and separation of high-purity 3-methyl-5-phenylpentanol. It offers the following advantages:

[0020] 1. This invention utilizes a single hindered amine derivative to exert dual functions at different reaction stages. In the high-temperature condensation and dehydration stage, it acts as a free radical scavenger to inhibit the thermal polymerization side reaction of unsaturated double bonds, and in the hydrogenation ring-opening stage, it acts as a selective poisoning agent to regulate the metal catalytic activity. The combination of these dual functions reduces the types of materials introduced into the production system.

[0021] 2. This invention utilizes the desalting and free transformation characteristics of hindered amine derivatives in acidic and alkaline environments, as well as their lipophilic structure, to achieve oil phase enrichment in the alkaline washing process; and utilizes the high boiling point and low saturated vapor pressure characteristics of hindered amine derivatives to achieve retention with the bottom liquid in the solvent removal distillation step, avoiding the intermediate steps of separating the polymerization inhibitor and refeeding the poisoning agent, and realizing the directional transfer of modified materials between different chemical reaction units.

[0022] 3. By matching the microscopic adsorption mechanism with thermodynamic temperature parameters, this invention divides the continuous active sites on the catalyst surface into isolated active regions. The spatial size sieving effect restricts the multi-site adsorption of benzene rings, solving the problems of excessive reduction of benzene rings and double bond polymerization, and improving the purity and molar yield of the final product. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Please see the appendix Figure 1 This invention provides a method for synthesizing 3-methyl-5-phenylpentanol. The synthesis process provided by this invention uses benzaldehyde and 3-methyl-3-buten-1-ol as starting materials, and obtains the target product through a two-step chemical transformation.

[0026] The first step is a condensation dehydration reaction, and the corresponding chemical equation for the first step is as follows:

[0027]

[0028] The second step is a hydrogenation ring-opening reaction, and the corresponding chemical equation for the second step is as follows:

[0029]

[0030] In the formula, This refers to benzaldehyde; It represents 3-methyl-3-buten-1-ol; Indicates an acidic catalyst; This indicates a dual-effect steric hindrance type polymerization inhibitor; Indicates an azeotropic solvent; This indicates the operating temperature of the first step; This indicates the intermediate phenyl dihydropyran produced in the reaction; This represents the water produced by condensation; It represents hydrogen gas; Indicates a hydrogenation catalyst; Indicates the solvent used in the hydrogenation system; This indicates the operating temperature for the second step; Indicates system workload; This indicates the final target product, 3-methyl-5-phenylpentanol.

[0031] The synthesis process provided by this invention specifically includes the following steps:

[0032] S100, azeotropic solvent Acidic catalysts With dual-effect steric hindrance type polymerization inhibitor The mixture is heated and, under reflux, a mixture of benzaldehyde and 3-methyl-3-buten-1-ol is continuously added dropwise to carry out the reaction, while the resulting water is separated and removed. In the aforementioned steps, an acidic catalyst... Specific implementation methods include p-toluenesulfonic acid, benzenesulfonic acid, or methanesulfonic acid. Azeotropic solvents. Specific implementation methods include xylene, toluene, or cyclohexane. Dual-effect steric hindrance polymerization inhibitors. The specific implementation method is hindered amine derivatives. Hindered amine derivatives need to possess specific structural features: their molecular structure contains a piperidine ring, and the carbon atom adjacent to the nitrogen atom on the piperidine ring has multiple alkyl substituents. The nitrogen atom on the piperidine ring provides free radical capture and metal coordination capabilities, while the multiple alkyl substituents on the adjacent carbon atom provide physical steric hindrance. Based on these structural features, specific compounds of hindered amine derivatives include 2,2,6,6-tetramethylpiperidinol, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, or N,N'-di(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine. Water is carried away through azeotropic reaction, and the water and oil phases are separated by a water separator. The separated upper oil phase is continuously refluxed back into the reactor. Hindered amine derivatives exert a polymerization inhibition effect at high temperatures, reducing the probability of thermal polymerization of the double bond in the 3-methyl-3-buten-1-ol molecule.

[0033] S200: The material after the reaction is cooled is washed and neutralized to remove the lower aqueous phase, yielding a product containing a dual-effect steric hindrance polymerization inhibitor. The organic oil phase with the intermediate phenyl dihydropyran. The residual acidic catalyst is neutralized by an alkaline aqueous solution. Due to the dual-effect steric hindrance type polymerization inhibitor modifier Lipophilic, dual-effect steric hindrance polymerization inhibitor It does not enter the aqueous phase, but remains in the organic oil phase along with the intermediate phenyl dihydropyran.

[0034] S300: Physically separates organic oil phase materials and removes azeotropic solvents. Retention generates a double-effect steric hindrance type polymerization inhibitor. Intermediate materials. The azeotropic solvent is preferentially removed through distillation. Evaporation removal. Due to the dual-effect steric hindrance type polymerization inhibitor modifier. Its boiling point is higher than that of azeotropic solvents. Dual-effect steric hindrance polymerization inhibitor During the physical separation process, it coexists with phenyl dihydropyran in the bottom liquid, forming a mixed intermediate material for use in the next step.

[0035] S400, the mixed intermediate materials are placed in a hydrogenation solvent. With hydrogenation catalyst In this process, hydrogen gas is introduced to carry out a ring-opening reduction reaction. In the aforementioned steps, a hydrogen solvent is added. Specific implementation methods include ethanol, methanol, or isopropanol. Hydrogenation catalyst The specific implementation involves a palladium-on-carbon catalyst. Hindered amine derivatives entrained in the mixed intermediate material adsorb onto the surface of the palladium-on-carbon particles at this stage. The steric hindrance of the hindered amine derivatives prevents the coordination of the benzene ring with the palladium active sites, limiting the hydrogenation reaction to the breaking of unsaturated double bonds and oxygen-containing heterocycles. After the ring-opening reduction reaction reaches its set endpoint, the solid hydrogenation catalyst is separated. .

[0036] S500: The clarified liquid after hydrogenation is purified by distillation to separate the target product, 3-methyl-5-phenylpentanol. During the distillation purification process, the hydrogenation solvent is preferentially removed by vaporization. Subsequently, 3-methyl-5-phenylpentanol monomer was extracted. A dual-effect steric hindrance polymerization inhibitor. It remains at the bottom of the distillation column and is discharged into the system as a high-boiling-point residue.

[0037] Specifically:

[0038] S100, azeotropic solvent Acidic catalysts With dual-effect steric hindrance type polymerization inhibitor The mixture is heated and, under reflux, a mixture of benzaldehyde and 3-methyl-3-buten-1-ol is continuously added dropwise to carry out the reaction, while the generated water is separated and removed. The condensation dehydration stage specifically includes the following sub-steps:

[0039] S101. Mix the azeotropic solvent in the reaction vessel. Acidic catalysts and dual-effect steric hindrance polymerization inhibitors The temperature is then increased until reflux occurs. Acidic catalyst. It is p-toluenesulfonic acid, benzenesulfonic acid, or methanesulfonic acid. Azeotropic solvent. It is xylene, toluene, or cyclohexane. A dual-effect steric hindrance polymerization inhibitor. These are hindered amine derivatives. The molecular structure of hindered amine derivatives includes a piperidine ring, with multiple alkyl substituents on the carbon atoms adjacent to the nitrogen atom of the piperidine ring. The nitrogen atom on the piperidine ring provides an active site for capturing the active free radical at the carbon center, while the multiple alkyl substituents on the adjacent carbon atoms provide physical steric hindrance. Specific substances of hindered amine derivatives include 2,2,6,6-tetramethylpiperidinol, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, or N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine. In one specific embodiment, a 500 ml three-necked flask is used as the reaction vessel. 100 g of xylene is added to the 500 ml three-necked flask as an azeotropic solvent. 0.2g of p-toluenesulfonic acid as an acidic catalyst Simultaneously with the addition of xylene and p-toluenesulfonic acid, 0.1 g of a dual-effect steric hindrance polymerization inhibitor was added to the three-necked flask. Turn on the stirring device and heat the system to the operating temperature. Operating temperature The temperature range is controlled between 80-145℃.

[0040] S102. Under reflux, a mixture of benzaldehyde and 3-methyl-3-buten-1-ol is slowly added dropwise to the system to carry out a condensation and dehydration reaction. In one specific embodiment, after the system shows obvious reflux, 100g of a mixture of benzaldehyde and 90g of 3-methyl-3-buten-1-ol is slowly added dropwise to the flask. The dropping rate is controlled so that the mixture is added completely over approximately 4 hours. Under the conditions of dropping and high-temperature heating, the carbon-carbon double bonds in the 3-methyl-3-buten-1-ol molecule tend to undergo thermal polymerization. A double-effect steric hindrance polymerization inhibitor is pre-added to the system. It binds to free radicals, blocking the chain growth process and inhibiting the polymerization of 3-methyl-3-buten-1-ol and the generated intermediate double bonds.

[0041] S103. Separate the water produced by the condensation reaction, monitor the dehydration rate, and stop water separation and cool down when the set target is reached. As benzaldehyde and 3-methyl-3-buten-1-ol are added dropwise, the condensation reaction continuously generates water. Water and azeotropic solvent... An azeotrope is formed and distilled off. The water and oil phases are separated using a water separator, and the upper oil phase is returned to the reactor. After the mixture is added dropwise, the reaction continues for 2-3 hours. The reaction progress is determined using the dehydration rate formula:

[0042]

[0043] In the formula, Indicates the dehydration rate; This indicates the total mass of the water phase collected by the distributor; This indicates the input quality of benzaldehyde. When the dehydration rate is monitored... When the water content reaches 13-16%, stop the water separation operation. Lower the system temperature to 50°C to complete the condensation and dehydration reaction stage.

[0044] S200: The cooled reaction system is washed and neutralized to remove the aqueous phase, yielding a mixture enriched with a dual-effect steric hindrance polymerization inhibitor. The oil phase of the phenyl dihydropyran intermediate. The washing, neutralization, and phase enrichment retention stage specifically includes the following sub-steps:

[0045] S201. Add an alkaline aqueous solution to the cooled reaction system and stir to mix. The alkaline aqueous solution can be sodium carbonate, potassium carbonate, or sodium bicarbonate solution. This is to neutralize any residual acidic catalyst from the preceding condensation reaction. The added alkaline aqueous solution needs to provide sufficient alkalinity. In one specific embodiment, 100 ml of water and 0.8 g of sodium carbonate are added to the reactants cooled to 50°C. The stirring device is turned on and maintained for 30 minutes to allow the sodium carbonate to fully contact and neutralize the residual p-toluenesulfonic acid, producing water-soluble sodium p-toluenesulfonate.

[0046] S202. Monitor the pH value of the aqueous phase in the mixed system. After reaching the set standard, allow it to stand and separate into layers. Separate and discharge the lower aqueous phase. The endpoint of the neutralization reaction is determined by the pH value of the aqueous phase. In one specific embodiment, after stirring, allow the reaction system to stand and extract the lower aqueous phase to test its pH value. The pH value of the aqueous phase is required to be greater than 6. After confirming that the pH value meets the standard, separate and discharge the aqueous phase containing the neutralization product from the system through a liquid-liquid separation operation, retaining the upper oil phase.

[0047] S203, a dual-effect steric hindrance polymerization inhibitor Phase enrichment occurs in the oil phase. Dual-effect steric hindrance polymerization inhibitor. Specific solubility properties are required. Considering the aforementioned molecular structure of hindered amine derivatives, the piperidine ring and multiple alkyl substituents on adjacent carbon atoms constitute a nonpolar hydrocarbon skeleton, endowing hindered amine derivatives with lipophilicity. In a multiphase system composed of the azeotropic solvent S1, the phenyl dihydropyran intermediate, and water, the phase distribution of the substances is controlled by the partition coefficient. The formula for calculating the partition coefficient is as follows:

[0048]

[0049] In the formula, Indicates the allocation coefficient; This indicates the equilibrium concentration of the dual-effect steric hindrance polymerization inhibitor M in the organic phase; Indicates a dual-effect steric hindrance type polymerization inhibitor modifier The equilibrium concentration in the washing and aqueous phase. Due to the lipophilic structure of hindered amine derivatives, their Kp values ​​are much greater than 1. During the physical processes of alkaline washing neutralization and settling separation, the dual-effect steric hindrance polymerization inhibitor... It is poorly soluble in the lower aqueous phase, but rather stably distributed and enriched in the upper organic oil phase composed of xylene and phenyl dihydropyran. This phase enrichment and retention mechanism ensures the effectiveness of this dual-effect sterically hindered polymerization inhibitor. It is not discharged with the washing wastewater, ensuring the effectiveness of the dual-effect steric hindrance type polymerization inhibitor. It then proceeds to the subsequent hydrogenation reaction stage.

[0050] S300: The oil phase material is separated by vacuum distillation to remove the azeotropic solvent. Retention generates a double-effect steric hindrance type polymerization inhibitor. The intermediate materials. The intermediate separation and modifier loading and retention stage specifically includes the following sub-steps:

[0051] S301. The obtained oil phase is transferred to the system for vacuum distillation to obtain the intermediate phenyl dihydropyran. Vacuum distillation can be implemented using a packed distillation column or a plate distillation column. Vacuum equipment is used to reduce the operating pressure of the system, lowering the boiling point of the material and preventing the intermediate phenyl dihydropyran from undergoing ring-opening or polymerization at high temperatures. In one specific embodiment, the oil phase after alkali washing and separation is input into a vacuum distillation vessel, and the vacuum pump is turned on to bring the system to a set negative pressure operating state.

[0052] S302. Control the bottom and top temperatures of the distillation system to preferentially vaporize and separate the azeotropic solvent. Gas-liquid separation in multi-component mixtures is based on differences in relative volatility. The formula for calculating relative volatility is as follows:

[0053]

[0054] In the formula, Indicates the relative volatility between the light and heavy components; This indicates the mole fraction of the light component in the gas phase; This indicates the mole fraction of the light component in the liquid phase; Indicates the mole fraction of the heavy component in the gas phase; This indicates the mole fraction of the heavier component in the liquid phase. In this stage of the multi-component mixture, the lighter component A represents the azeotropic solvent. The heavy component B represents a phenyl dihydropyran intermediate. Azeotropic solvents such as xylene are used. The boiling point of xylene is significantly lower than that of phenyl dihydropyran, and the relative volatility between xylene and phenyl dihydropyran is... Much greater than 1. The reboiler operating temperature is strictly controlled below the thermal decomposition temperature of phenyl dihydropyran and hindered amine derivatives. This is achieved by setting a matching azeotropic solvent. The azeotropic solvent corresponds to the column top operating temperature at the vacuum boiling point. The vapor rises to the top of the tower, is condensed in a condenser, and then removed.

[0055] S303, a dual-effect steric hindrance type polymerization inhibitor modifier The intermediate, phenyl dihydropyran, is retained together with the intermediate in the bottom liquid of the column, yielding a mixed intermediate product. Hindered amine derivatives have large molecular weights and contain both polar groups and a nonpolar macrostructure. They also exhibit extremely low saturated vapor pressures and significantly higher boiling points than azeotropic solvents. And phenyl dihydropyran. In the removal of the azeotropic solvent... In vacuum distillation, dual-effect steric hindrance polymerization inhibitors Gasification conditions were not met. Dual-effect steric hindrance polymerization inhibitor modifier. The mixture is kept in the liquid phase and coexists with unvaporized phenyl dihydropyran in the bottom liquid of the distillation unit. After the operation is completed, the remaining bottom liquid in the reboiler is collected. The bottom liquid of the distillation unit carries the dual-effect steric hindrance polymerization inhibitor. The intermediate material is directly used as a liquid-phase feedstock in the hydrogenation reaction process to complete the process of becoming a dual-effect steric hindrance polymerization inhibitor. Loading for the next reaction stage.

[0056] S400, the mixed intermediate materials are placed in a hydrogenation solvent. With hydrogenation catalyst In this process, hydrogen gas is introduced to carry out a ring-opening reduction reaction. The selective hydrogenation ring-opening stage specifically includes the following sub-steps:

[0057] S401, Mixing intermediate materials and hydrogenation solvent in a hydrogenation reaction unit. and hydrogenation catalysts The hydrogenation reaction equipment was then purged with gas. Hydrogenation solvent. Specific implementation methods include ethanol, methanol, or isopropanol. Hydrogenation catalyst Specific implementation methods include using 5% or 10% palladium-on-carbon catalyst by mass fraction. In one specific embodiment, 100 ml of the dual-effect steric hindrance polymerization inhibitor obtained in the aforementioned steps is added to the hydrogenation reactor. The intermediate material of phenyl dihydropyran. Add 300 ml of ethanol to the hydrogenation reactor as the hydrogenation solvent. 1g of palladium on carbon with a mass fraction of 5% was added as a hydrogenation catalyst. The hydrogenation reactor is sealed, and high-purity nitrogen is introduced to perform three gas replacement operations inside the reactor to purge the oxygen from the system. After the nitrogen replacement is completed, high-purity hydrogen is introduced to perform three more gas replacement operations to ensure that the hydrogenation reactor is filled with the hydrogen required for the reaction.

[0058] S402. Adjust the initial pressure inside the hydrogenation reactor and start the heating program to bring the system to the set operating temperature and operating pressure. In one specific embodiment, after gas replacement is completed, hydrogen is introduced into the hydrogenation reactor to reduce the initial hydrogen pressure. Set the pressure to 0.6 MPa. Turn on the stirring device and heating system of the hydrogenation reactor to raise the system temperature to the operating temperature. Operating temperature The temperature should be controlled at 110-120℃. As the system temperature increases, the hydrogenated solvent... The hydrogen gas vaporizes upon heating, generating vapor pressure. The introduced hydrogen gas expands upon heating, causing its partial pressure to rise. The actual working pressure inside the hydrogenation reactor is determined by the following physical relationship:

[0059]

[0060] In the formula, This indicates the actual working pressure inside the hydrogenation reactor; Indicates the initial pressure at which hydrogen gas is introduced; This indicates the operating temperature during the hydrogenation stage, expressed in Kelvin, the thermodynamic temperature unit. This indicates the initial temperature at which hydrogen is introduced, expressed in Kelvin, the thermodynamic unit of temperature. Indicates hydrogenated solvent Operating temperature The saturated vapor pressure of ethanol increases as the operating temperature rises to 110-120℃. Combined with the expansion of the initially introduced hydrogen, this increases the actual working pressure inside the hydrogenation reactor. It rises and remains at 0.8-1.0 MPa.

[0061] S403, a dual-effect steric hindrance polymerization inhibitor With hydrogenation catalyst Coordination adsorption occurs, leading to a selective hydrogenation ring-opening reaction under set temperature and pressure. Hindered amine derivatives, which enter the hydrogenation system along with intermediates, transform into selective poisoning agents for the catalyst during the hydrogenation stage. The nitrogen atom on the piperidine ring in the hindered amine derivative's molecular structure contains a lone pair of electrons. These lone pairs coordinate with empty orbitals on the palladium metal surface, causing the hindered amine derivative to adsorb onto the hydrogenation catalyst. The surface of the particles. Multiple alkyl substituents on the carbon atoms adjacent to the nitrogen atom on the piperidine ring form a physically sterically hindered covering region on the palladium metal surface. Under high temperature and high pressure conditions of 110-120℃ and 0.8-1.0 MPa, the benzene ring structure in the phenyl dihydropyran molecule tends to be hydrogenated and reduced to cyclohexyl derivatives. The sterically hindered covering layer formed by the hindered amine derivative physically prevents the adsorption of the large benzene ring facet to the active site of palladium metal, while allowing the smaller and more active carbon-carbon double bonds and oxygen-containing heterocycles to contact the incompletely covered palladium active sites. Physical barriers limit the hydrogenation catalyst. Its catalytic activity ensures that the hydrogenation reaction occurs only at the reduction of double bonds and the breaking and opening of oxygen-containing heterocycles, thus protecting the benzene ring skeleton. The reaction was continued for 8 hours while maintaining the specified temperature and pressure conditions.

[0062] S404. After the hydrogenation reaction is completed, the hydrogenation reactor is cooled and depressurized to separate and remove the solid hydrogenation catalyst. In one specific embodiment, the hydrogen inlet valve is closed after 8 hours of reaction. The cooling circulating water system of the hydrogenation reactor is turned on to cool the hydrogenated material. After the system temperature drops to room temperature, the residual pressure inside the hydrogenation reactor is released, and nitrogen is introduced for displacement to purge free hydrogen. The bottom valve of the hydrogenation reactor is opened to discharge the material, which is then filtered through a microporous filtration device to retain and recover the solid palladium-on-carbon catalyst. The clear liquid obtained after filtration is the product containing the target product and the dual-effect steric hindrance polymerization inhibitor. A mixed solution.

[0063] S500: The clarified liquid after the hydrogenation reaction is completed and filtered is purified by vacuum distillation to remove the hydrogenation solvent. The target product, 3-methyl-5-phenylpentanol, was isolated, and a dual-effect steric hindrance polymerization inhibitor was retained. The product purification and targeted separation stage specifically includes the following sub-steps:

[0064] S501. Transfer the filtered mixed solution to a distillation unit, control the bottom heating temperature and system operating pressure, and vaporize and remove the hydrogenated solvent. The mixed solution contains hydrogenated solvents. 3-Methyl-5-phenylpentanol and dual-effect steric hindrance polymerization inhibitors Hydrogenated solvents Specifically, ethanol or isopropanol are low-boiling-point light components in the mixed solution. In one specific embodiment, the operating pressure of the distillation equipment is set to atmospheric pressure or slightly negative pressure, and the bottom temperature of the distillation equipment is controlled at a temperature slightly higher than that of the hydrogenated solvent. Within the boiling point range. Hydrogenated solvents. It is heated, vaporized, rises, and is collected and removed after being condensed in the condenser at the top of the tower.

[0065] S502. Reduce the operating pressure of the distillation system to a high vacuum state to collect the 3-methyl-5-phenylpentanol monomer. The boiling point of 3-methyl-5-phenylpentanol at atmospheric pressure is approximately 260℃. Direct heating to 260℃ at atmospheric pressure will cause thermal oxidation or decomposition of 3-methyl-5-phenylpentanol, destroying its inherent rose and lily-of-the-valley aroma characteristics. By significantly reducing the system operating pressure using a vacuum generator, the actual boiling point of the liquid decreases as the system pressure decreases. The physical relationship between the actual boiling point and the system pressure follows the Clausius-Clapeyron equation, expressed as follows:

[0066]

[0067] In the formula, This indicates the system's environmental pressure under normal atmospheric pressure conditions. This indicates the decompression operation pressure of the system after the vacuum generator is turned on. The boiling point of 3-methyl-5-phenylpentanol under normal pressure is expressed in Kelvin, the thermodynamic temperature unit. Indicates operating pressure The actual boiling point of 3-methyl-5-phenylpentanol is given in Kelvin, the thermodynamic temperature unit. Represents the molar enthalpy of vaporization of 3-methyl-5-phenylpentanol; This represents the ideal gas constant. It is achieved by setting an extremely low system decompression operating pressure. This makes the actual boiling point of 3-methyl-5-phenylpentanol... Reduce the temperature to a mild range permissible by thermal stability. Adjust the bottom temperature of the distillation unit to the corresponding actual boiling point. 3-Methyl-5-phenylpentanol is converted into a gas phase and rises to the top of the column. After condensation, it is collected to obtain a pure 3-methyl-5-phenylpentanol monomer product.

[0068] S503, a dual-effect steric hindrance type polymerization inhibitor modifier As a high-boiling-point residue, it is retained at the bottom of the distillation unit and discharged. A dual-effect steric hindrance polymerization inhibitor composed of hindered amine derivatives. It has a relatively large molecular weight and an extremely low saturated vapor pressure. The reduced pressure operation during the extraction of 3-methyl-5-phenylpentanol... Compared with actual boiling point Under these conditions, dual-effect steric hindrance polymerization inhibitors The thermodynamic conditions required for vaporization cannot be met. Dual-effect steric hindrance polymerization inhibitor modifier. It remains in the liquid phase throughout, stably residing as a heavy component in the bottom residue of the distillation unit. This retention operation achieves a dual-effect steric hindrance type polymerization inhibitor modifier. Targeted physical separation from the target product ensures that no nitrogen-containing impurities are mixed into the extracted monomer fragrance products.

[0069] In the preparation process, a dual-effect steric hindrance type polymerization inhibitor modifier The ability to synergistically control the condensation dehydration reaction and the hydrogenation ring-opening reaction is mainly due to the dual-effect steric hindrance type polymerization inhibitor modifier. The molecular structure characteristics. The following section focuses on dual-effect sterically hindered polymerization inhibitors. The structural selection criteria are explained.

[0070] Dual-effect steric hindrance polymerization inhibitor The molecular structure contains hindered amine functional groups. Specifically, the structure features one or more six-membered piperidine rings, with two alkyl substituents attached to each of the two adjacent carbon atoms of the nitrogen atom on the piperidine ring. This steric hindrance occurs because the nitrogen atom is surrounded by four alkyl groups on the adjacent carbon atoms of the piperidine ring. The alkyl substituents specifically include methyl, ethyl, or propyl.

[0071] In the structural layout of the piperidine ring and alkyl substituents, the nitrogen atom on the piperidine ring has the ability to capture active free radicals, inhibiting polymerization during the high-temperature condensation stage. Simultaneously, the lone pair electrons on the nitrogen atom can coordinate with the metal catalyst, utilizing the steric hindrance screening effect of the four alkyl groups surrounding the lone pair electrons to achieve selective catalysis during the hydrogenation stage. Based on these principles, a dual-effect steric hindrance polymerization inhibitor modifier... The selection should follow these criteria:

[0072] Selection is based on molecular weight and boiling point distribution characteristics. This is to ensure the effectiveness of dual-effect steric hindrance polymerization inhibitors. A dual-effect steric hindrance polymerization inhibitor that can achieve simultaneous retention with intermediates during physical separation. The molecular weight must be greater than 150. Specific compounds involved in the selection include 2,2,6,6-tetramethylpiperidinol, with the molecular formula [missing information]. ; Bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, molecular formula is ; and N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine, with the molecular formula [missing information]. 2,2,6,6-Tetramethylpiperidinol, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, and N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine were removed from the azeotropic solvent by vacuum distillation. At that time, due to its high boiling point, it can remain in the distillation column bottom of the distillation equipment, thus entering the subsequent hydrogenation reaction section.

[0073] Screening was conducted based on lipophilicity parameters. This was to ensure the effectiveness of dual-effect steric hindrance polymerization inhibitors. It does not flow away with the aqueous phase during the alkaline washing stage, and is a dual-effect steric hindrance polymerization inhibitor. Its lipophilicity is provided by the nonpolar hydrocarbon skeleton in its molecular structure. The piperidine ring and the multiple alkyl substituents attached to the ring together constitute the hydrophobic region. The octanol-water partition coefficient should be considered when selecting a model. value. The formula for calculating the value is as follows:

[0074]

[0075] In the formula, Indicates the octanol-water partition coefficient; Indicates a dual-effect steric hindrance type polymerization inhibitor modifier Equilibrium concentration in the octanol phase; Indicates a dual-effect steric hindrance type polymerization inhibitor modifier The equilibrium concentration in the aqueous phase of a standard octanol-water system. The hindered amine derivatives selected in this invention... All values ​​are greater than 1.5. In the first step of the condensation and dehydration reaction, the hindered amine derivative combines with the acidic catalyst in the system to form a water-soluble salt compound. In the alkaline washing and neutralization stage, the added alkaline aqueous solution neutralizes the acidic catalyst, allowing the hindered amine derivative to desalinate and return to its nonpolar free state. This free state, combined with the lipophilic structure of the hindered amine derivative, ensures its effectiveness as a dual-effect sterically hindered polymerization inhibitor. During the alkaline washing and neutralization process, it is distributed in the organic oil phase to avoid being discharged with the neutralization wastewater and to ensure the effective concentration in the subsequent hydrogenation stage.

[0076] Screening was conducted based on steric hindrance strength and coordination ability. The selected double-effect steric hindrance polymerization inhibitor was... In a hydrogenation environment, selective inhibition of benzene ring reduction reactions is required. After hindered amine derivatives adsorb onto the palladium metal surface, the arrangement of the four ortho-alkyl groups forms a physical shielding region with an open size above the catalyst active site. The size of this physical shielding region is smaller than the physical space required for the flat adsorption of the benzene ring, but larger than the physical space required for lateral contact of the unsaturated bonds in 3-methyl-3-buten-1-ol and phenyl dihydropyran. Through physical size matching, a dual-effect steric hindrance polymerization inhibitor is achieved. It guides hydrogen molecules to act on the target chemical bond, inhibiting the reduction of the benzene ring.

[0077] During the condensation and dehydration reaction stage, the reaction system is in a high-temperature environment of 130-140℃, and an acidic catalyst is present within the system. Under these high-temperature and acidic conditions, the unsaturated carbon-carbon double bonds in the 3-methyl-3-buten-1-ol molecule and the phenyl dihydropyran intermediate molecule formed by condensation are easily thermally initiated, generating carbon-centered active free radicals that initiate chain polymerization side reactions. These polymerization side reactions consume the reactants, leading to increased viscosity of the reaction system and a darker color of the product.

[0078] Dual-effect steric hindrance polymerization inhibitor During the condensation and dehydration stage, polymerization side reactions are suppressed through the synergistic effect of physical steric hindrance and chemical free radical capture. The nitrogen atom on the piperidine ring in the hindered amine derivative molecular structure serves as a reactive site, transforming into stable nitroxide or amino radical intermediates under trace oxygen or thermal excitation. These nitroxide or amino radical intermediates can couple with the carbon-center reactive free radicals generated in the system. The coupling reaction consumes the reactive free radicals, thus blocking the chain growth process of the polymerization reaction.

[0079] Based on the molecular structure of hindered amine derivatives, multiple alkyl substituents attached to the carbon atoms adjacent to the nitrogen atom on the piperidine ring construct a physical barrier around the nitrogen atom. When the nitrogen atom captures active free radicals to form an intermediate complex, the physical barrier prevents the intermediate complex from colliding and bonding with other 3-methyl-3-buten-1-ol molecules or phenyl dihydropyran molecules. This physical barrier effect terminates the free radical chain reaction, preventing the formation of high molecular weight polymers.

[0080] The kinetics of the aforementioned polymerization inhibition mechanism are described using a free radical reaction rate formula. The chain growth rate of the polymerization reaction without the addition of a modifier is calculated as follows:

[0081]

[0082] The formula for calculating the free radical capture rate in the system after adding the modifier is as follows:

[0083]

[0084] In the formula, Indicates the chain growth rate of a polymerization reaction; This represents the constant of the polymer chain growth rate; Indicates the concentration of reactive free radicals in the reaction system; This indicates the concentration of monomers containing double bonds (including 3-methyl-3-buten-1-ol and phenyl dihydropyran) in the reaction system; Indicates a dual-effect steric hindrance type polymerization inhibitor modifier The reaction rate for capturing active free radicals; This represents the free radical capture rate constant; This indicates a dual-effect steric hindrance polymerization inhibitor in the reaction system. The molar concentration.

[0085] Because hindered amine derivatives exhibit high reaction rate constants for carbon-centered radicals, the radical capture rate constant... The value is greater than the chain growth rate constant. The value. Combined with the 0.1g addition parameter specified in step S101 above, the dual-effect steric hindrance polymerization inhibitor... molar concentration in the reaction system It remains within the effective inhibition range. Under the combined influence of the rate constant and concentration, the free radical capture rate... Greater than the chain growth rate of the polymerization reaction The kinetic relationship enables dual-effect steric hindrance polymerization inhibitors. It preferentially consumes active free radicals, maintains the chemical stability of the condensation dehydration reaction system, and ensures the azeotropic water separation operation.

[0086] During the hydrogenation reaction, the reaction system is subjected to a high-temperature and high-pressure environment of 110-120℃ and 0.8-1.0 MPa. Hydrogenation catalyst. The surface is covered with highly active palladium metal sites. The phenyl dihydropyran molecule entering the hydrogenation reaction apparatus simultaneously contains easily reducible carbon-carbon double bonds, oxygen-containing heterocycles, and a benzene ring. Under the catalysis of the active palladium metal, the benzene ring readily undergoes an over-hydrogenation side reaction to transform into a cyclohexyl structure, resulting in the loss of the aroma characteristics of the target product, 3-methyl-5-phenylpentanol.

[0087] Dual-effect steric hindrance polymerization inhibitor It is converted into a hydrogenation catalyst during the hydrogenation reaction stage. Selective poisoning agents. The nitrogen atom on the piperidine ring in the hindered amine derivative molecular structure contains a lone pair of electrons. These lone pairs of electrons coordinate with empty orbitals on the palladium metal surface, causing the hindered amine derivative to undergo chemisorption and immobilize on the hydrogenation catalyst. The surface.

[0088] In the context of hindered amine derivatives, multiple alkyl substituents attached to adjacent carbon atoms on the piperidine ring form a physical space covering layer above the adsorption sites. The hydrogenation reduction of the benzene ring requires multi-site planar adsorption on the palladium metal surface, necessitating a large, continuous surface area of ​​active sites. The physical space covering layer fragments this continuous, large-area active site on the palladium metal surface into isolated, small active regions. These isolated, small active regions are physically small enough to accommodate the planar adsorption of the benzene ring, but they can accommodate the lateral or end-group adsorption of smaller carbon-carbon double bonds and oxygen-containing heterocycles. This physical barrier and size sieving mechanism restricts the occurrence of multi-site concerted reactions, causing the hydrogenation reaction to occur only at the reduction of carbon-carbon double bonds and the ring-opening process of oxygen-containing heterocycles.

[0089] The surface coverage state of the selective poisoning mechanism is quantitatively described using the Langmuir isotherm adsorption equation. The formula for calculating the surface coverage is as follows:

[0090]

[0091] In the formula, Indicates a dual-effect steric hindrance type polymerization inhibitor modifier hydrogenation catalyst Surface coverage; Represents the equilibrium constant for chemisorption; Indicates a dual-effect steric hindrance polymerization inhibitor in the hydrogenation reaction system. The molar concentration.

[0092] The chemisorption equilibrium constant is affected by the system temperature and follows the van der Hoff equation:

[0093]

[0094] In the formula, Indicates the pre-exponential factor; The molar adsorption enthalpy of hindered amine derivatives on palladium metal surface; As mentioned above, this represents the ideal gas constant; This indicates the hydrogenation operation temperature, expressed in Kelvin, the thermodynamic temperature unit.

[0095] Molar adsorption enthalpy formed by coordination A negative value indicates that the chemisorption process is exothermic. Hydrogenation operating temperature. An increase in will lead to an increase in the chemisorption equilibrium constant. Decrease, thereby reducing surface coverage. If the hydrogenation operation temperature Above 120°C, hindered amine derivatives undergo significant desorption, leading to reduced surface coverage. Below the effective range of selective protection, a large area of ​​continuous active sites on the palladium metal surface is re-exposed, triggering an excessive hydrogenation side reaction of the benzene ring; if the hydrogenation operating temperature... Below 110°C, the hydrogenation ring-opening reaction cannot overcome the reaction energy barrier, leading to the stagnation of the formation of the target product.

[0096] Therefore, the hydrogenation operation temperature is strictly controlled within the range of 110-120℃, in conjunction with the molar concentration cut-off introduced by the distillation in the aforementioned S300 step. This results in a higher surface coverage. Maintain within a stable effective range. Surface coverage within the effective range. It is sufficient to divide the continuous active sites to protect the benzene ring, while at the same time retaining enough isolated active sites to maintain the ring-opening reduction reaction.

[0097] Example:

[0098] The preparation process of Example 1 specifically includes the following steps: 100g of xylene is added as an azeotropic solvent to a reaction vessel equipped with a water separator. 0.2g of p-toluenesulfonic acid as an acidic catalyst And 0.1 g of 2,2,6,6-tetramethylpiperidinol as a dual-effect steric hindrance polymerization inhibitor. Turn on the heating device and raise the temperature to 135℃ to induce reflux in the reaction system. Control the dropping rate and slowly add a mixture of 100g benzaldehyde and 90g 3-methyl-3-buten-1-ol to the reaction vessel, ensuring the dropping process is completed within 4 hours. After the dropping is complete, continue the reaction at this temperature for 2 hours, while simultaneously separating the generated water. After the water separation is complete, lower the temperature of the reaction system to 50℃. Add an alkaline aqueous solution prepared by mixing 100ml of water and 0.8g of sodium carbonate to the cooled material. Turn on the stirring device and maintain stirring for 30 minutes to neutralize the residual p-toluenesulfonic acid. After settling and separating the layers, separate and discharge the lower aqueous phase, retaining the upper oil phase.

[0099] Transfer the upper oil phase to a distillation unit and turn on the vacuum pump. Control the operating pressure of the distillation unit to 5 kPa and the top product temperature to 45°C, vaporizing and collecting xylene. Collect the bottom liquid from the distillation unit. The bottom liquid contains phenyl dihydropyran intermediate and unvaporized 2,2,6,6-tetramethylpiperidinol. Transfer the collected bottom liquid from the distillation unit to a hydrogenation reactor. Add 300 ml of ethanol to the hydrogenation reactor as the hydrogenation solvent. And 1g of palladium on carbon with a mass fraction of 5% as a hydrogenation catalyst. The hydrogenation reactor was sealed and purged with nitrogen and hydrogen. Hydrogen was introduced into the reactor to an initial pressure of 0.6 MPa. The reactor was heated to 115°C, raising the actual working pressure inside to and maintaining it at 0.9 MPa. The ring-opening hydrogenation reaction was maintained at 115°C and 0.9 MPa for 8 hours.

[0100] After the reaction, the hydrogenation reactor was cooled and vented. The solid palladium-on-carbon catalyst was recovered by filtration through a microporous membrane, yielding a mixed clear liquid. This mixed clear liquid was transferred to a distillation column. The operating pressure of the distillation column was controlled at 10 kPa, and the bottom heating temperature was 85 °C. Under these conditions, ethanol was vaporized and removed. Subsequently, the operating pressure of the distillation column was reduced to 0.5 kPa using a vacuum generator, and the top outlet temperature was controlled at 120 °C. The 3-methyl-5-phenylpentanol product after vaporization and condensation was collected. 2,2,6,6-Tetramethylpiperidinol was retained in the bottom residue of the distillation column and discharged.

[0101] The yield of the target product in the reaction process is calculated and determined using the following formula:

[0102]

[0103] In the formula, Indicates the molar yield of the 3-methyl-5-phenylpentanol product; This indicates the actual mass of the 3-methyl-5-phenylpentanol product collected by distillation; This represents the theoretical maximum yield mass of 3-methyl-5-phenylpentanol calculated based on the mass of benzaldehyde added.

[0104] The molar yield of the 3-methyl-5-phenylpentanol product in Example 1 was calculated by weighing and gas chromatography. The purity was 82.5%, and the purity detected by gas chromatography was 99.2%.

[0105] The preparation process of Example 2 specifically includes the following steps: 100g of toluene is added to the reaction vessel as an azeotropic solvent. 0.3g benzenesulfonic acid as an acidic catalyst And 0.15 g of bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate as a dual-effect steric hindrance polymerization inhibitor. Heat the system to 110-115℃ to induce reflux. Add 100g of a mixture of benzaldehyde and 90g of 3-methyl-3-buten-1-ol dropwise, controlling the dropping rate, completing the process within 4 hours. After the dehydration reaction is complete, cool the system to 50℃. Neutralize the cooled material by adding an alkaline aqueous solution containing potassium carbonate. Stir and allow the mixture to stand for separation, discarding the lower aqueous phase and retaining the upper oil phase.

[0106] The upper oil phase was subjected to vacuum distillation at an operating pressure of 8 kPa and a top product temperature of 40 °C to remove toluene. The bottom liquid containing the phenyl dihydropyran intermediate and bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate was collected. The bottom liquid and 300 ml of methanol were used as the hydrogenation solvent. And 1.5g of palladium on carbon with a mass fraction of 10% as a hydrogenation catalyst. The mixture was placed in a hydrogenation reactor. After purging the internal gas, hydrogen was introduced to an initial pressure of 0.6 MPa. The hydrogenation reactor was heated to 110°C, raising the working pressure to and maintaining it at 0.8 MPa. After reacting at 110°C and 0.8 MPa for 8 hours, the mixture was cooled and the gas was vented. The mixture was then filtered to obtain a clear liquid.

[0107] The clarified liquid was subjected to distillation to remove methanol under operating conditions of 15 kPa and a reboiler temperature of 70°C. The distillation pressure was then reduced to 0.8 kPa, and the top product temperature was controlled at 125°C to collect 3-methyl-5-phenylpentanol. Bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate was discharged as a residue. The molar yield of 3-methyl-5-phenylpentanol in Example 2 was calculated and measured. It has a purity of 98.8% and a content of 80.1%.

[0108] The preparation process of Example 3 specifically includes the following steps: 100g of cyclohexane is added to the reaction vessel as an azeotropic solvent. 0.25g of methanesulfonic acid as an acidic catalyst And 0.12 g of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine as a dual-effect steric hindrance polymerization inhibitor. Heat to 80-85℃ until reflux occurs. Slowly add a mixture of 100g benzaldehyde and 90g 3-methyl-3-buten-1-ol. After the reaction is complete and the water is separated, cool to 50℃. Add an aqueous solution of sodium bicarbonate to neutralize the methanesulfonic acid. Separate the aqueous phase, retaining the upper oil phase.

[0109] The upper oil phase was subjected to vacuum distillation at an operating pressure of 12 kPa and a top product temperature of 35°C to remove cyclohexane, and the mixed bottom liquid was collected. The mixed bottom liquid and 300 ml of isopropanol were used as the hydrogenation solvent. And 1.2g of palladium on carbon with a mass fraction of 5% was used as a hydrogenation catalyst. Place the mixture in a hydrogenation reactor. Purge with hydrogen to an initial pressure of 0.6 MPa and heat to 120°C, raising the working pressure to and maintaining it at 1.0 MPa. After reacting at 120°C and 1.0 MPa for 8 hours, filter and collect the clear liquid.

[0110] The clarified liquid was transferred to a distillation column, where isopropanol was removed under operating conditions of 8 kPa and a bottom heating temperature of 90°C. After isopropanol removal, 3-methyl-5-phenylpentanol was collected as the final product under operating conditions of 0.3 kPa and a top temperature of 115°C. N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine was retained at the bottom of the distillation column. The molar yield of 3-methyl-5-phenylpentanol in Example 3 was calculated and measured. It has a content of 81.4% and a purity of 99.0%.

[0111] Comparative example:

[0112] The preparation process of Comparative Example 1 is basically the same as that of Example 1, except that 2,2,6,6-tetramethylpiperidinol was not added to the reaction vessel during the condensation and dehydration reaction stage, meaning that a dual-effect steric hindrance polymerization inhibitor was not present in the system. .

[0113] Under reflux conditions at 135°C, due to the lack of hindered amine derivatives to capture the active free radicals at the carbon center, the carbon-carbon double bond in the 3-methyl-3-buten-1-ol molecule undergoes a chain polymerization reaction upon heating. A high molecular weight tar-like polymer is formed at the bottom of the reaction system, consuming the reactants. In the subsequent hydrogenation stage, due to the hydrogenation catalyst... The surface lacks dual-effect steric hindrance polymerization inhibitors. The physical spatial covering layer exposes the palladium metal active sites continuously. Under the catalysis of these continuously exposed active sites, the benzene ring in the phenyl dihydropyran intermediate undergoes planar adsorption and excessive hydrogenation side reactions, generating byproducts containing cyclohexyl groups.

[0114] The molar yield of 3-methyl-5-phenylpentanol in Comparative Example 1 was determined by distillation, weighing, and gas chromatography. The purity was 31.2%, and the product's aroma contained a burnt polymer smell, failing to meet the purity requirements for fragrance grade.

[0115] The preparation process of Comparative Example 2 is basically the same as that of Example 1, except that 0.1 g of 2,2,6,6-tetramethylpiperidinol is replaced with an equal mass of the traditional phenolic polymerization inhibitor 2,6-di-tert-butyl-4-methylphenol.

[0116] In the first step of condensation and dehydration, 2,6-di-tert-butyl-4-methylphenol provides active hydrogen via its phenolic hydroxyl groups, terminating the free radical chain reaction and inhibiting the formation of polymers. During the alkaline washing and neutralization process after cooling, the acidic phenolic hydroxyl groups in the 2,6-di-tert-butyl-4-methylphenol molecule neutralize with the alkaline aqueous solution, forming water-soluble phenolate compounds. These phenolate compounds enter the aqueous phase and are discharged from the system during the liquid-liquid separation process. Because 2,6-di-tert-butyl-4-methylphenol is lost during the alkaline washing stage, no polymerization inhibitor or modifier enters the hydrogenation reactor with the upper oil phase.

[0117] In the hydrogenation reaction stage, the hydrogenation catalyst The surface failed to form a physical shielding region, making it impossible to separate the continuous palladium metal active sites. Under hydrogenation conditions of 115 °C and 0.9 MPa, some benzene rings were reduced and destroyed. The molar yield of 3-methyl-5-phenylpentanol in Comparative Example 2 was calculated and measured. The figure is 45.8%. Technical data proves that traditional single-effect phenolic polymerization inhibitors cannot adapt to the alkaline washing process and cannot enter the hydrogenation stage to achieve selective protection of chemical bonds.

[0118] The preparation process of Comparative Example 3 is basically the same as that of Example 1, except that: in the hydrogenation reaction stage, the heating temperature of the hydrogenation reactor is increased to 145°C, so that the working pressure is increased to and maintained at 1.2 MPa.

[0119] The hydrogenation operation temperature exceeded the 110-120°C range specified in this invention. According to the thermodynamic principle of chemisorption as described by the aforementioned van der Hoff equation, coordination adsorption is an exothermic process. When the hydrogenation operation temperature rises to 145°C, the high temperature causes a change in the chemisorption equilibrium constant. The concentration decreases, and 2,2,6,6-tetramethylpiperidinol desorbs from the palladium metal surface. The desorption of hindered amine derivatives leads to the desorption of hydrogenation catalysts. Surface coverage Below the effective range for selective poisoning. Reduced physical spatial coverage exposes continuous palladium metal active sites to the reaction system, leading to excessive hydrogenation of the benzene ring.

[0120] The molar yield of 3-methyl-5-phenylpentanol in Comparative Example 3 was determined through calculation and testing. The figure decreased to 52.4%. Technical data validates the technical necessity of controlling the temperature boundary of hydrogenation operations for maintaining the selective poisoning mechanism of the catalyst.

[0121] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for the synthesis and separation of high-purity 3-methyl-5-phenylpentanol, characterized in that, Includes the following steps: Condensation dehydration reaction: An azeotropic solvent, an acidic catalyst, and a double-effect steric hindrance polymerization inhibitor are mixed and heated. Under reflux, a mixture of benzaldehyde and 3-methyl-3-buten-1-ol is continuously added dropwise to carry out the reaction, while the generated water is separated and removed. Washing, neutralization and phase enrichment: The cooled reaction system was washed and neutralized with an alkaline aqueous solution to remove the lower aqueous phase and obtain an organic oil phase enriched with a dual-effect steric hindrance polymerization inhibitor and a phenyl dihydropyran intermediate. Intermediate separation and modifier loading: The organic oil phase is separated by vacuum distillation, vaporized and the azeotropic solvent is removed. The dual-effect steric hindrance type polymerization inhibitor and the phenyl dihydropyran intermediate are retained together in the bottom liquid of the distillation unit to obtain a mixed intermediate material. Selective hydrogenation ring-opening: The mixed intermediate materials are placed in a hydrogenation solvent and a hydrogenation catalyst, and hydrogen gas is introduced. The hydrogenation ring-opening reaction is carried out at a set operating temperature and pressure. A dual-effect steric hindrance type polymerization inhibitor is adsorbed on the surface of the hydrogenation catalyst and provides physical steric hindrance, limiting the catalytic activity of the hydrogenation catalyst. This ensures that the hydrogenation reaction only occurs at the reduction of carbon-carbon double bonds and the breaking and opening of oxygen-containing heterocycles, thus protecting the benzene ring skeleton. After the reaction, the solid hydrogenation catalyst is separated and removed to obtain a mixed clear liquid. Product purification and selective physical separation: The mixed clear liquid is purified by vacuum distillation, and the hydrogenated solvent is preferentially removed by vaporization. Then, 3-methyl-5-phenylpentanol is vaporized under vacuum to obtain the finished product. The dual-effect steric hindrance polymerization inhibitor is retained in the residue of the distillation equipment and discharged.

2. The synthesis and separation process of high-purity 3-methyl-5-phenylpentanol according to claim 1, characterized in that, The dual-effect sterically hindered polymerization modifier is a hindered amine derivative; the molecular structure of the hindered amine derivative contains one or more six-membered piperidine rings, and two alkyl substituents are attached to each of the two adjacent carbon atoms of the nitrogen atom on the piperidine ring; the alkyl substituents include methyl, ethyl or propyl; specific compounds of the hindered amine derivative include 2,2,6,6-tetramethylpiperidinol, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate or N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine.

3. The synthesis and separation process of high-purity 3-methyl-5-phenylpentanol according to claim 2, characterized in that, In the condensation and dehydration reaction, the acidic catalyst is p-toluenesulfonic acid, benzenesulfonic acid, or methanesulfonic acid; the azeotropic solvent is xylene, toluene, or cyclohexane; the system is heated to the reflux temperature of the corresponding azeotropic solvent, and the operating temperature is controlled between 80℃ and 145℃; the nitrogen atom on the piperidine ring in the hindered amine derivative serves as a reactive site, which is converted into a stable nitric oxide radical or amino radical intermediate under trace oxygen or thermal excitation, and couples with the carbon-center active radical generated in the reaction system, thereby blocking the chain growth process of the polymerization reaction.

4. The synthesis and separation process of high-purity 3-methyl-5-phenylpentanol according to claim 2, characterized in that, During the washing and neutralization phase enrichment, the alkaline aqueous solution is an aqueous solution of sodium carbonate, potassium carbonate, or sodium bicarbonate. In the condensation dehydration reaction, the hindered amine derivative combines with the acidic catalyst to form a water-soluble salt compound. During the washing and neutralization stage, the alkaline aqueous solution neutralizes the acidic catalyst, causing the hindered amine derivative to desalinate and return to its nonpolar free state. The nonpolar free state, combined with the lipophilicity provided by the nonpolar hydrocarbon skeleton in the molecular structure of the hindered amine derivative, makes the hindered amine derivative difficult to dissolve in the lower aqueous phase, and it is distributed and enriched in the organic oil phase.

5. The synthesis and separation process of high-purity 3-methyl-5-phenylpentanol according to claim 1, characterized in that, In the intermediate separation and modifier loading process, the reboiler operating temperature of the distillation unit is controlled below the thermal decomposition temperature of phenyl dihydropyran and the double-effect steric hindrance type polymerization inhibitor, and the azeotropic solvent is preferentially removed based on the difference in relative volatility. Due to its high boiling point, the double-effect steric hindrance type polymerization inhibitor remains in a liquid phase and coexists with the unvaporized phenyl dihydropyran in the bottom liquid of the distillation unit, which then enters the hydrogenation reaction process as a liquid-phase feedstock.

6. The synthesis and separation process of high-purity 3-methyl-5-phenylpentanol according to claim 2, characterized in that, In the selective hydrogenation ring-opening process, the hydrogenation solvent is ethanol, methanol, or isopropanol; the hydrogenation catalyst is a palladium-on-carbon catalyst; and the operating temperature of the hydrogenation ring-opening reaction is controlled at 110°C-120°C.

7. The synthesis and separation process of high-purity 3-methyl-5-phenylpentanol according to claim 6, characterized in that, The dual-effect steric hindrance polymerization inhibitor is transformed into a selective poisoner for the palladium on carbon catalyst; the dual-effect steric hindrance polymerization inhibitor interacts with the empty orbitals on the surface of palladium metal to produce chemical adsorption, and multiple alkyl substituents above the adsorption sites form a physical spatial capping layer. The physical space covering layer divides the continuous large-area active sites on the palladium metal surface into isolated small active regions. These isolated small active regions cannot accommodate the flat adsorption of benzene rings in terms of physical size, but they can accommodate the lateral or end-group adsorption of small carbon-carbon double bonds and oxygen-containing heterocycles.

8. The synthesis and separation process of high-purity 3-methyl-5-phenylpentanol according to claim 6, characterized in that, In the selective hydrogenation ring-opening process, after the hydrogenation reaction equipment is purged with gas, hydrogen is introduced to set the initial pressure to 0.6 MPa. Subsequently, the heating program is started to raise the system temperature to 110°C-120°C. As the hydrogenation solvent is heated and vaporized to generate vapor pressure, and the introduced hydrogen expands due to heat, the partial pressure increases, causing the actual working pressure inside the hydrogenation reaction equipment to rise and be maintained at 0.8 MPa-1.0 MPa.

9. The synthesis and separation process of high-purity 3-methyl-5-phenylpentanol according to claim 1, characterized in that, In the product purification and selective physical separation process, a mixed clear liquid containing hydrogenated solvent, 3-methyl-5-phenylpentanol, and a dual-effect steric hindrance polymerization inhibitor is transferred to a distillation unit. Under normal or slightly negative pressure, the hydrogenated solvent is preferentially vaporized and removed. Subsequently, the system operating pressure is reduced to a high vacuum state by a vacuum generator, and the bottom temperature of the distillation unit is adjusted to the corresponding actual boiling point to convert 3-methyl-5-phenylpentanol into a gas phase that rises to the top of the column and is condensed and collected.

10. The synthesis and separation process of high-purity 3-methyl-5-phenylpentanol according to claim 9, characterized in that, When 3-methyl-5-phenylpentanol is collected as the finished product, the operating pressure of the distillation system is reduced to 0.1 kPa-1.0 kPa, and the top collection temperature is controlled at 110℃-130℃. Under these operating pressure and temperature conditions, the dual-effect steric hindrance polymerization inhibitor does not reach the thermodynamic conditions required for vaporization and remains stably in the residual liquid of the distillation equipment as a heavy component.

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