Synthesis method of N-(2-ethoxyphenyl)-N '-(2-ethylphenyl)-oxamide

Abstract

The invention relates to the technical field of fine chemical engineering, and discloses a synthesis method of N-(2-ethoxyphenyl)-N '-(2-ethylphenyl)-oxamide, which comprises the following steps: carrying out dehydration condensation reaction on oxalic acid and o-ethylaniline in a green catalyst and green solvent system to prepare an oxamic acid intermediate; the obtained oxamic acid intermediate is subjected to separation and solvent recovery, so that the reaction efficiency is improved, and the waste of the solvent is reduced; and reacting the prepared oxamic acid intermediate with o-aminophenetole in a synergistic catalyst and green solvent system to prepare crude N-(2-ethoxyphenyl)-N '-(2-ethylphenyl)-oxamide. Through a green catalytic system, an optimized purification process and a resource recovery strategy, efficient and low-energy-consumption preparation of the oxamide ultraviolet light absorber and green production of a high-purity product are realized.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemicals, in particular to a method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide. Background Art

[0002] With the development of social economy and the advancement of industrial technology, the use of polymer materials, plastic products and coatings has increased year by year. However, when these materials are exposed to sunlight for a long time, they are susceptible to photodegradation due to ultraviolet rays, which manifests as color change, reduced mechanical properties or surface cracks. This not only affects the appearance and service life of the material, but may also lead to serious degradation of the material performance. Therefore, in order to improve the material's resistance to ultraviolet aging, ultraviolet absorbers are widely used in polymer materials and coatings.

[0003] At present, the synthesis of oxalamide compounds has a certain research foundation. The traditional method usually adopts high-temperature condensation reaction, uses homogeneous catalysts and organic solvent systems, and successfully realizes the industrial preparation of oxalamide compounds. These methods have certain advantages in terms of faster reaction rate and higher initial product yield. Some processes also reduce the formation of by-products by improving the catalytic system, thereby further improving the selectivity of the target product.

[0004] However, the existing technology still has many shortcomings, which restricts the widespread application of oxalamide ultraviolet absorbers. First, most traditional processes rely on high temperature and high pressure conditions, which consume a lot of energy, and the post-processing of homogeneous catalysts is complicated and difficult to reuse, which increases production costs and environmental pollution. Secondly, although some processes have improved the selectivity of target products through improvements, the separation and purification efficiency of crude products is still low, and there are many residual by-products, which cannot meet the demand for high-purity ultraviolet absorbers. In addition, the existing recrystallization process has not been fully optimized, and the product crystal morphology is irregular during the purification process, which further affects the subsequent processing performance. Finally, the traditional process is insufficiently designed in terms of resource recovery and utilization, the solvent loss rate is high, and the unreacted products are often directly discarded, resulting in resource waste and aggravated environmental pollution. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method for synthesizing N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide, which solves the problems of high energy consumption under high temperature and high pressure conditions, difficulty in recovering homogeneous catalysts, low efficiency in separation and purification of crude products, and insufficient resource recovery and utilization in the prior art synthesis methods of oxalamide ultraviolet absorbers.

[0006] To achieve the above object, the present invention is implemented by the following technical scheme: a method for synthesizing N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide, the method comprising the following steps: The dehydration condensation reaction of oxalic acid and o-ethylaniline is carried out in a green catalyst and green solvent system to prepare an oxalamide acid intermediate; The obtained oxalamide acid intermediate is separated and the solvent is recovered to improve the reaction efficiency and reduce the solvent waste; The prepared oxalamide acid intermediate reacts with o-aminophenyl ethyl ether in a synergistic catalyst and a green solvent system to prepare crude N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide; The resulting crude N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide is subjected to solvent extraction to separate by-products and purify the target product; Purifying the obtained target product by recrystallization to improve the purity of N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide; Unreacted raw materials and generated water by-products are recovered for resource recycling and to reduce environmental pollution.

[0007] Preferably, the dehydration condensation reaction of oxalic acid and o-ethylaniline in a green catalyst and green solvent system comprises: Mix oxalic acid and o-ethylaniline in a molar ratio of 1:2; Adding a mixed solvent of ethanol and water in the presence of sulfonated zirconium oxide or H-ZSM-5 catalyst, wherein the volume ratio of ethanol to water is 3:1 to 5:1; The reaction was stirred at a temperature range of 85° C. to 95° C. for 1.5 to 2.5 hours, and the generated water was removed in real time by maintaining a pressure of 0.7 to 0.9 atm through a vacuum assist system.

[0008] Preferably, the separation of the obtained oxalamide acid intermediate and solvent recovery comprises: The reaction solution was cooled to room temperature, the catalyst was removed by filtration, and the catalyst was washed and recovered with ethanol; The filtrate is transferred to a rotary evaporator, and the ethanol and water solvents are recovered by vacuum distillation for use in the next batch of reactions; The oxalamide acid intermediate was obtained from the residue after rotary evaporation as a crude product for subsequent reactions.

[0009] Preferably, the step of reacting the prepared oxalamide acid intermediate with o-aminophenyl ether in a synergistic catalyst and green solvent system comprises: The oxalamic acid intermediate and o-phenylaminoethyl ether are mixed in a molar ratio of 1:1, and dissolved in a mixed solvent of ethanol and water, wherein the volume ratio of ethanol to water is 3:1 to 5:1; In the presence of a supported palladium catalyst (Pd / C, palladium content 5%), the temperature is raised to 100° C. to 120° C., and the reaction is stirred for 2.5 hours to 3.5 hours; The generated water by-product is removed online through a vacuum distillation apparatus, and the vacuum conditions are controlled to be 0.7 atm to 0.9 atm to improve the reaction selectivity and the yield of the target product.

[0010] Preferably, the solvent extraction of the generated crude N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide comprises: The reaction product was extracted three times with ethyl acetate, with ethyl acetate added each time at a volume twice that of the crude product; The organic phases were combined, dried over anhydrous sodium sulfate and filtered; The organic solvent was evaporated under reduced pressure to obtain the crude target product.

[0011] Preferably, the recrystallization purification comprises: Dissolve the crude target product in 40 mL to 60 mL of acetonitrile, and control the dissolution temperature at 55°C to 65°C; The dissolved solution is cooled to room temperature and allowed to stand for 12 to 24 hours to precipitate crystals; The crystals were washed with a small amount of cold acetonitrile (10 mL to 20 mL) and then filtered, and the filtered crystals were dried to constant weight to obtain high-purity N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide.

[0012] Preferably, the recovery of unreacted raw materials and generated water byproducts comprises: The generated water after dehydration condensation reaction and solvent extraction is separated online through a vacuum distillation device, and the water is purified and used for equipment cooling or process cleaning; Recovering the unreacted o-ethylaniline in the reaction solution by vacuum distillation, with a recovery rate of 90% to 95%; The unreacted o-phenylamino ether was separated and purified from the aqueous phase for subsequent reaction.

[0013] Preferably, the dehydration condensation reaction and solvent extraction are completed by a continuous flow reactor, comprising: The dehydration condensation module of oxalic acid and o-ethylaniline has a reaction temperature of 85°C to 95°C and a flow rate of 0.8 mL / min to 1.2 mL / min; The reaction module of the oxalamide acid intermediate and o-aminophenyl ether has a reaction temperature of 100°C to 120°C and a flow rate of 0.4 mL / min to 0.6 mL / min; The by-product online separation module is used to remove the water by-product in real time and recycle the solvent.

[0014] Preferably, the continuous flow reactor further comprises: Online mixing module, used to evenly mix the reaction raw materials and solvent; Precision temperature control module, used to control the reaction temperature of each module within the range of 0.5~1.5℃; Online monitoring module is used to detect the conversion rate of reactants and the separation of by-products in real time.

[0015] Preferably, the N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxamide obtained by the method is a UV absorber, which is used for anti-ultraviolet aging of polymer materials. The specific uses include: Added to polyurethane materials to improve the material's resistance to UV aging; Added to nylon materials to improve the material's anti-yellowing properties; When used in combination with optical brighteners, it does not interfere with the brightening effect and is used for light stabilization protection of plastic products. It has good compatibility with the base resin in the coating system and is used to improve the light stability and weather resistance of the coating; When used in environments containing residual metal catalysts or under alkaline conditions, its performance is stable and the degree of discoloration is low.

[0016] The present invention provides a method for synthesizing N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide. Beneficial effects: 1. The present invention successfully achieves efficient preparation of oxalamide acid intermediates by using green catalysts and green solvent systems and combining vacuum-assisted technology in the dehydration condensation reaction. This design not only reduces energy consumption, but also significantly reduces the occurrence of side reactions. Compared with the traditional high-temperature condensation method, the reaction efficiency is greatly improved, and the problems of difficult reuse of catalysts and large system pollution are solved.

[0017] 2. The present invention optimizes the recrystallization purification process, uses acetonitrile as a solvent, and combines the method of slow cooling and crystallization to make the purity of the target product reach more than 99%. Compared with the extensive purification of the prior art, this method ensures that the crystal morphology is more regular and the impurities are removed more thoroughly. At the same time, the solvent can be recycled by distillation, further reducing the production cost.

[0018] 3. The present invention constructs a systematic resource recovery strategy to fully recover solvents, byproduct water and unreacted products, greatly improving resource utilization. Compared with the high-loss process of traditional technology, this design effectively reduces waste emissions and waste in production, while significantly improving the environmental protection and economy of the process, providing a practical solution for the development of green chemistry. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a flow chart of the method. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Please refer to the attached Figure 1 The embodiment of the present invention provides a method for synthesizing N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide, the method comprising the following steps: S1. Dehydration condensation reaction: oxalic acid and o-ethylaniline are subjected to a dehydration condensation reaction in a green catalyst and green solvent system to prepare an oxalamide acid intermediate; The generation of oxalamide acid intermediate directly affects the yield and purity of the subsequent target product, so this step needs to achieve efficient conversion through accurate catalyst selection, solvent optimization and reaction condition control. Generally, this step generates oxalamide acid intermediate through dehydration condensation reaction of oxalic acid and o-ethylaniline, which provides a basis for subsequent reactions. In order to ensure the implementation of the green chemical industry concept, this step adopts a green catalyst and green solvent system to achieve efficient reaction while reducing the generation of by-products.

[0022] Specifically, in this step, oxalic acid provides the acyl source required for the reaction, and o-ethylaniline, as an amino provider, generates an oxalamide acid intermediate by undergoing a dehydration condensation reaction with oxalic acid under the synergistic effect of a specific catalyst and a solvent system. As a selection, a functionalized solid acid catalyst, such as sulfonated zirconium oxide (S-ZrO2) or H-ZSM-5 molecular sieve, can be used to catalyze the reaction. These catalysts have excellent catalytic activity and are convenient for separation, recovery and reuse. The green solvent system uses a mixed solvent of ethanol and water, and the volume ratio of ethanol to water is generally 3:1 to 5:1. In some embodiments, the ratio can be appropriately adjusted according to the specific reaction requirements to optimize the solubility and reaction rate of the solvent.

[0023] In this embodiment, the molar ratio of oxalic acid to o-ethylaniline is generally set to 1:2 to ensure the full reaction of o-ethylaniline and the complete conversion of oxalic acid. The chemical formula of oxalic acid is C2H2O4, and the chemical formula of o-ethylaniline is C8H 11N, the two form a uniform reaction system in a mixed solvent. In a possible implementation, oxalic acid and o-ethylaniline are added to a reaction vessel according to the above molar ratio, and a selected catalyst is added. Specifically, the amount of the catalyst added is usually 0.8% to 1.2% of the total mass of the reactants. The amount within this range can ensure the reaction activity while avoiding the waste of the catalyst.

[0024] In this reaction system, the reaction temperature is controlled at 85°C to 95°C, which can effectively promote the dehydration condensation. In some embodiments, in order to further optimize the reaction efficiency, the reaction temperature can be controlled by gradually increasing the temperature, for example, slowly increasing from 85°C to the target temperature and maintaining a constant temperature. In addition, the reaction time is generally controlled within 1.5 hours to 2.5 hours, which can ensure the full reaction of oxalic acid and o-ethylaniline, while avoiding side reactions caused by too long a time.

[0025] In a specific implementation, the generated water by-product is removed in real time by using a vacuum-assisted system, thereby pushing the chemical equilibrium to move in the direction of generating the oxalamide acid intermediate. As an option, the vacuum condition is usually maintained at 0.7atm to 0.9atm, which can not only efficiently remove moisture but also avoid excessive volatilization of the solvent. In this reaction system, the generated water by-product can be collected and recycled by a condenser. In some embodiments, the by-product can be further treated as process cooling water to achieve the recycling of resources.

[0026] In order to ensure efficient generation of the intermediate, a stirring system can be used in this step to ensure sufficient contact of the reactants. For example, the uniformity of the reaction system can be maintained by a stirring speed of 300 to 350 rpm. In some embodiments, a magnetic stirring device can be used to improve the stability of the operation.

[0027] The chemical equation for the above reaction is shown below: Among them, C2H2O4 is oxalic acid, C8H 11 N is o-ethylaniline, C 18 H 20 N2O3 is an intermediate of oxalamide acid, and H2O is a byproduct of dehydration; Generally, after the reaction is completed, the reaction solution is cooled to room temperature and the catalyst is separated by filtration. The catalyst can be reused after washing with ethanol, and can usually be reused more than 5 times without significantly reducing its catalytic activity. The obtained filtrate can be directly used in the subsequent separation step.

[0028] In a possible implementation, the reaction conditions can be optimized by online monitoring of the conversion rate of oxalic acid and the amount of oxalamic acid intermediates generated in the reaction system. For example, the concentration change of the target product in the reaction solution can be analyzed in real time by high performance liquid chromatography (HPLC). Specifically, a C18 column can be selected, acetonitrile and water can be used as the mobile phase, and detection can be performed at a wavelength of 254 nm; S2. Intermediate separation and solvent recovery: Separating the obtained oxalamide acid intermediate and recovering the solvent to improve the reaction efficiency and reduce solvent waste; By properly separating the reaction solution and recovering the solvent, resource waste can be effectively reduced, and the purity of the oxalamide acid intermediate and the efficiency of subsequent reactions can be further improved. Generally, this step needs to take into account the recycling of the catalyst and the recycling of the solvent in the reaction system, thereby reducing process costs and complying with the concept of green chemistry.

[0029] Specifically, the separation of oxalamide acid intermediates is mainly achieved by physical separation means, such as filtration and vacuum distillation. The solid catalyst can be quickly recovered by filtration to avoid the influence of its residue on subsequent reactions. The recovery of the solvent is mainly achieved by a vacuum distillation device, which can simultaneously separate and purify ethanol and water. As an option, the unconverted raw materials can be further separated and recovered so that they can be used for the next batch of reactions. Through the above measures, this step can efficiently utilize resources and further improve the sustainability of the process.

[0030] In this embodiment, the reaction solution generated in step S1 is taken out of the reactor and first cooled to room temperature. This operation can avoid solvent loss and side reactions caused by high temperature in subsequent operations. Specifically, cooling can be achieved by natural cooling or circulating water cooling. In some embodiments, in order to speed up the cooling rate, a jacket cooling device can be used to ensure that the reaction solution quickly reaches the operating temperature.

[0031] After the reaction liquid is cooled, the solid catalyst is separated by filtering equipment. Generally, the filtering operation uses a vacuum filtration device, which can effectively improve the separation efficiency. As an option, the filter medium used can be a filter cloth with a pore size of 10-20 microns to ensure the complete recovery of the catalyst. The separated solid catalyst is usually washed with ethanol 3-5 times to remove the attached oxalamide acid intermediates and other impurities. Specifically, the amount of ethanol used for washing is generally 2-3 times the mass of the catalyst. In some embodiments, the catalyst can be further dried using a vacuum drying device to facilitate storage and reuse.

[0032] The obtained filtrate is mainly composed of oxalamide acid intermediate, unreacted o-ethylaniline and mixed solvent. In order to extract the oxalamide acid intermediate, the solvent and the unreacted products need to be separated by reduced pressure distillation. In one possible implementation, the filtrate is transferred to a rotary evaporator, and the ethanol and water solvents are evaporated under reduced pressure. Specifically, the reduced pressure conditions are controlled at 0.06-0.08MPa, and the evaporation temperature is 60°C to 70°C. By controlling the evaporation rate, the complete recovery of the solvent and the purity of the oxalamide acid intermediate can be guaranteed at the same time.

[0033] In some embodiments, in order to further improve the efficiency of solvent recovery, a condenser can be installed in the evaporation device to cool the evaporated ethanol and water vapor. The condensed solvent can be separated by a liquid separator and stored separately for subsequent reactions. In some specific implementations, the recovery rate of ethanol can reach more than 95%, while the recovery rate of water can be stabilized at more than 90%.

[0034] The substances remaining after evaporation are mainly oxalamide acid intermediates and a small amount of unreacted o-ethylaniline. Purified oxalamide acid intermediates can be extracted through further treatment. As a possible option, the oxalamide acid intermediates can be separated from o-ethylaniline by freezing crystallization. Specifically, the residual liquid can be cooled to below 5°C to precipitate the oxalamide acid intermediate in solid form. After vacuum filtration, a high-purity intermediate can be obtained.

[0035] The chemical structure of the oxalamide acid intermediate is shown below: C 18 H 20 N2O3 It is mainly a linear molecular structure, and the amide groups at both ends can further react with o-aminophenyl ether to generate the target product. In this step, the recovery rate of the oxalamide acid intermediate can usually reach 85% to 90%, and its purity can reach more than 95% through high performance liquid chromatography (HPLC) detection.

[0036] Generally, the unreacted o-ethylaniline is separated from the solvent by vacuum distillation and then added back into the reaction system; as an improvement measure, the amount of o-ethylaniline added can be adjusted to further improve its recovery rate. In some embodiments, the recovery rates of the solvent and the unreacted products are detected in real time by online monitoring technology to optimize the process conditions; S3, synthesizing a crude product: reacting the obtained oxalamide acid intermediate with o-aminophenyl ethyl ether in a synergistic catalyst and a green solvent system to prepare crude N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide; In this step, the amide group of the intermediate and the amino group of o-aminophenyl ether are used for synergistic catalysis to generate crude N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxamide. Generally, in order to improve the reaction efficiency and selectivity, the reaction system needs to add a suitable synergistic catalyst, and the reaction conditions also need to be precisely controlled. By optimizing the catalyst type, solvent ratio and reaction parameters, the generation of by-products can be minimized and the yield of the crude product can be improved.

[0037] Specifically, the oxalamide acid intermediate used in this step is directly obtained from step S2; In the present embodiment, the oxalamide acid intermediate and o-phenylamino ether are mixed in a molar ratio of 1:1 to form a reaction system. Generally, in order to ensure sufficient contact of the reactants, it is necessary to first dissolve the two reactants in a mixed solvent of ethanol and water. As a choice, the volume ratio of ethanol to water is usually controlled between 3:1 and 5:1 to balance solubility and reaction rate.

[0038] Specifically, the synergistic catalyst used in this step is a supported palladium catalyst (Pd / C), and the loading amount of palladium is generally 5%. The amount of catalyst added is generally set to 0.5% to 1.5% of the total mass of the reactants. As an improvement measure, in some embodiments, a small amount of cuprous iodide (CuI) can be added as a co-catalyst to further improve the catalytic efficiency of the reaction. The selection and addition of the catalyst directly affect the selectivity and yield of the target product, and therefore need to be appropriately adjusted according to specific process conditions.

[0039] In terms of the control of reaction conditions, the reaction temperature is usually set to 100°C to 120°C, and the reaction time is generally 2.5 hours to 3.5 hours. In a possible implementation, the reaction can be carried out by gradually increasing the temperature, for example, from room temperature to 100°C, and maintaining a constant temperature at the final temperature to complete the reaction process. In some embodiments, in order to avoid overreaction, the reaction time can be adjusted in real time by online monitoring of the amount of water byproducts generated.

[0040] In the reaction system, the generated water byproduct is removed in real time by a vacuum-assisted system to push the chemical equilibrium toward the direction of generating the target product. The vacuum condition is generally controlled in the range of 0.7atm to 0.9atm. As an option, a condenser can be installed in the reactor to condense the generated water vapor into liquid and recycle it through a collection device. For larger-scale reaction systems, a continuous flow reactor module can be further designed to remove byproducts in real time and reduce the accumulation of impurities in the reaction system.

[0041] In some embodiments, in order to ensure the uniformity of the reaction, a magnetic stirring device may be used to stir the system, and the stirring rate is generally controlled between 300 and 400 rpm. Specifically, the purpose of stirring is to ensure sufficient contact between the reactants and the catalyst, while preventing local overheating from causing side reactions.

[0042] After the reaction is completed, the reaction solution is cooled to room temperature and the catalyst is separated by vacuum filtration. The separated catalyst can be reused after washing with ethanol, and can usually be reused 3 to 5 times without significantly reducing the catalytic activity. The obtained filtrate mainly consists of the target crude product, solvent and a small amount of unreacted matter. After removing most of the solvent by vacuum distillation, crude N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide can be obtained.

[0043] Generally, the purity of the crude product can usually reach 85% to 90%. In some embodiments, in order to further improve the purity of the crude product, a small amount of ethanol can be added after the distillation for secondary washing to remove unreacted o-phenylamino ether. The crude product finally obtained can be directly used in the subsequent solvent extraction step; S4, solvent extraction: subjecting the generated crude N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide to solvent extraction to separate by-products and purify the target product; The key to this step is the selection of solvent and the optimization of extraction operating conditions. Through a reasonable solvent system and extraction process, the target crude product can be extracted to the maximum extent while reducing the impurity residues in the target product.

[0044] Generally, solvent extraction operation adopts the principle of layered extraction of aqueous phase and organic phase, and the target product tends to be distributed in the organic phase, while impurities and unreacted parts are mainly left in the aqueous phase. As an option, separation efficiency can be further improved by repeated extraction. In order to meet the needs of industrial production, the solvent used in the extraction process should have lower toxicity, good distribution coefficient and easy recovery characteristics, such as ethyl acetate. Specifically, ethyl acetate has higher solubility and volatile characteristics, and is a preferred extraction agent in this step.

[0045] In this embodiment, the crude product solution obtained in step S3 is placed in a separatory funnel, and ethyl acetate is added thereto in a volume ratio of 2 times that of the crude product. Generally, the crude product solution is mainly composed of a small amount of solvent, unreacted substances and by-products, and ethyl acetate can efficiently dissolve the target crude product to form clear organic phase and aqueous phase stratification.

[0046] As a possible implementation method, the liquid separation operation can be repeated three times to improve the extraction efficiency of the target product. Each time the extraction is performed, ethyl acetate is added to the separatory funnel and mixed thoroughly, and then allowed to stand until the two phases are completely separated. Specifically, during mixing, the funnel can be gently shaken and vented in time to avoid damage to the separatory funnel due to excessive internal pressure. In some embodiments, in order to accelerate the phase separation, the temperature of the aqueous phase can be appropriately increased to 30°C to 40°C, thereby reducing the interfacial tension of the phases.

[0047] The separated organic phases are combined and dried over anhydrous sodium sulfate. The amount of anhydrous sodium sulfate added is usually 10% to 15% of the volume of the organic phase to fully absorb the residual moisture. As an option, other desiccants such as anhydrous magnesium sulfate can also be used, but anhydrous sodium sulfate is more commonly used due to its easy separation and wide applicability. The dried organic phase is filtered through filter paper or filter cloth, and the filtrate is an organic solution containing the target product.

[0048] The key to separating the target product from the organic phase is the evaporation of the solvent. In this embodiment, the dried organic solution is transferred to a rotary evaporator and ethyl acetate is evaporated under reduced pressure. The reduced pressure condition is usually controlled at 0.06MPa to 0.08MPa, and the evaporation temperature is 45°C to 55°C. This condition can ensure the rapid evaporation of the solvent while avoiding the decomposition of the target product due to high temperature. In some embodiments, the evaporated ethyl acetate can be further collected by a continuous flow solvent recovery system for reuse.

[0049] Through the above operation, a crude target product is obtained, which is usually a light yellow solid. In general, the purity of the crude product can be detected by high performance liquid chromatography (HPLC), and the purity is usually more than 90%. In order to remove the possible trace unreacted substances, the obtained crude product can be washed twice. As an option, a small amount of cold ethanol can be used as the secondary washing solvent, and the amount used is 1 to 2 times the mass of the crude product, and the purity can be further improved by stirring, washing and filtering.

[0050] In some embodiments, in order to optimize the efficiency of solvent use, the aqueous phase after extraction can be distilled to separate and recover the unreacted o-phenylamino ether. The purity of the recovered o-phenylamino ether can usually reach more than 95%, and can be used for the next batch of reactions after simple purification. In this step, by using ethyl acetate as an extractant, efficient separation and purification of the target product is achieved; S5, recrystallization purification: purifying the obtained target product by recrystallization to improve the purity of N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide; In this step, impurities and unreacted products in the crude product are effectively removed by appropriately selecting a solvent system and optimizing crystallization conditions, and finally a high-purity target product N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide is obtained. In general, the recrystallization process can not only improve the purity of the target product, but also improve its physical properties, such as crystal morphology and thermal stability, to provide better performance for subsequent applications.

[0051] Specifically, in this step, a solvent with moderate solubility is required, and the best crystallization effect is achieved by controlling temperature, cooling rate and crystal precipitation conditions. As a selection, acetonitrile is a preferred solvent for this step because of its moderate solubility, easy recovery and good compatibility with the target product. By dissolving and crystallizing under the control of the temperature gradient, the target product is separated out in the form of regular crystals, and impurities and by-products are then left in the mother liquor.

[0052] In this embodiment, the crude product obtained by solvent extraction in step S4 is dissolved in acetonitrile. In general, the amount of acetonitrile added is controlled to be 4 to 6 times the mass of the crude product to ensure that the crude product is completely dissolved and forms a uniform solution. In order to accelerate the dissolution, the solution can be heated to a range of 55°C to 65°C and the temperature can be kept constant until the solid is completely dissolved. In some embodiments, in order to further improve the dissolution efficiency, the solution can be properly stirred, for example, using a magnetic stirrer, and the stirring rate is controlled at 200 to 300rpm.

[0053] The solubility of the product increases with increasing temperature, while the solubility of impurities changes little, so the target product can be separated from the impurities by cooling and crystallization. In one possible implementation, the completely dissolved solution is slowly cooled to room temperature, and the cooling rate is controlled at 1°C to 3°C / minute to avoid too fast cooling resulting in too fine crystals. In some embodiments, the solution can be further placed in an ice bath and cooled to below 5°C to promote the full precipitation of the target product.

[0054] The precipitated crystals are separated by vacuum filtration, and the filter cake is the target product after preliminary purification. In general, the filtration operation should try to avoid excessive crushing of the crystals to maintain the integrity of the crystals. As an option, a small amount of cold acetonitrile (10mL to 20mL) can be used to wash the crystals after filtration to remove impurities and residual mother liquor adsorbed on the surface of the crystals. The washed crystals are further vacuum dried to constant weight, and the drying temperature is controlled between 35°C and 45°C to avoid decomposition of the target product caused by excessively high temperatures.

[0055] In some embodiments, in order to further optimize the purification effect, two recrystallizations can be used. Specifically, the first recrystallization is mainly used to remove most of the impurities in the crude product, while the second recrystallization further improves the purity and crystal morphology of the product by finely controlling the conditions.

[0056] During the recrystallization process, the purity of the target product can be monitored in real time by high performance liquid chromatography (HPLC). Specifically, a C18 column can be selected, the mobile phase is a mixed solvent of acetonitrile and water, and the detection wavelength is set to 254nm. Generally, the purity of the target product after purification in this step can reach ≥99%, which meets the requirements of subsequent applications.

[0057] In addition, the acetonitrile solvent used in this step can be recovered and reused by distillation. As a possible implementation method, the recrystallization mother liquor is decompressed and distilled to remove the solvent by a rotary evaporator, and the acetonitrile is further purified by a separation device. The recovery rate can usually reach more than 95%, thereby further reducing the process cost; S6, Resource Recovery: Recover unreacted raw materials and generated water byproducts for resource recycling and reducing environmental pollution; resource recycling, through reasonable recycling and reuse, not only effectively reduces production costs, but also significantly reduces waste emissions, playing a positive role in environmental protection. Generally, this step includes solvent recovery, separation and treatment of byproducts, and purification and recycling of unreacted products.

[0058] Specifically, the main by-products produced in the dehydration condensation reaction, crude product synthesis and solvent extraction are water and a small amount of impurities, and the solvents mainly include ethyl acetate, acetonitrile and ethanol, etc. These resources can be recycled through the measures in this step, which can greatly reduce the consumption of raw materials, improve production efficiency, and meet the design concept of green chemical industry.

[0059] In the present embodiment, the recovery of solvent is mainly achieved by vacuum distillation. Generally, the solvent recovery system includes a rotary evaporator, a condenser and a separator, etc. Taking ethyl acetate as an example, the aqueous phase and the organic phase remaining after solvent extraction are collected respectively, and a small amount of ethyl acetate in the aqueous phase is recovered into the organic phase by a separatory funnel. The organic phase after separation is directly placed in a rotary evaporator, and ethyl acetate is evaporated under a reduced pressure of 0.06 to 0.08MPa, and the evaporation temperature is controlled at 45°C to 55°C to ensure that the solvent is fully recovered while avoiding the target product remaining in the mother liquor. As a possible implementation method, the evaporated ethyl acetate is cooled into a liquid state by a condenser, and returned to the solvent storage tank for standby after purification.

[0060] For the recovery of acetonitrile, it is mainly concentrated in the recrystallization mother liquor. Generally, the mother liquor contains a small amount of impurities and incompletely dissolved target product. Through vacuum distillation, acetonitrile can be efficiently distilled out and collected by a condenser. The residual liquid after distillation can be further processed to separate impurities and extract the residual target product as much as possible. In some embodiments, the recovery rate of acetonitrile can reach more than 95%, and the loss rate of the target product is less than 1%.

[0061] The recovery of unreacted products is an important part of resource recycling. In the dehydration condensation reaction and the crude product synthesis reaction, the incompletely reacted o-ethylaniline and o-aminophenyl ether can be separated and recovered by distillation technology. Specifically, after the reaction solution is subjected to rotary evaporation to remove most of the solvent, the unreacted products are separated from the product. The unreacted o-ethylaniline has a relatively low boiling point (about 183°C), so it can be recovered at atmospheric pressure by a fractionating tower, and its purity can usually reach more than 95%. Similarly, o-aminophenyl ether can be recovered at a slightly lower temperature by vacuum distillation due to its moderate boiling point (about 218°C) to avoid thermal decomposition. In some embodiments, the purity of the recyclate is monitored online, and the distillation conditions are adjusted to ensure that the quality of the recyclate meets the requirements of the next batch of reactions.

[0062] In one possible implementation, the by-product water is recovered by a continuous separation device, and the generated water in the reaction process is collected by condensation and purified. Generally, the water may contain trace amounts of solvents or impurities, which can be used for equipment cooling or production cleaning after being purified by activated carbon adsorption or distillation. For example, in this embodiment, the water generated from the dehydration condensation reaction is purified by the separation device and returned to the cooling circulation system, and its recovery rate can reach more than 90%.

[0063] In order to further optimize resource utilization, this step can be combined with the online separation technology in the continuous flow process. For example, in the continuous flow reaction module, the synchronous separation and recovery of water byproducts and organic solvents can be achieved by integrating an online separation device. This design not only simplifies the operation process, but also monitors the efficiency of resource recovery in real time. In some embodiments, by installing a flow meter and a concentration analyzer, the yield and purity of the recyclate can be accurately measured, and the operating parameters can be adjusted in time.

[0064] Example 1: Synthesis of oxalamide acid intermediates using a green catalytic system Oxalic acid and o-ethylaniline are used as raw materials. Oxalic acid and o-ethylaniline are added to the reactor in a molar ratio of 1:2, and a mixed solvent of ethanol and water is used as the reaction medium, and the volume ratio of ethanol to water is set to 4:1. Sulfonated zirconium oxide catalyst is added at 1% of the total mass of the reactants. The reaction temperature is raised to 90°C, and the reaction is stirred for 2 hours under vacuum conditions (pressure 0.8atm). During the reaction, the generated water by-product is separated and collected in real time by a condenser. After the reaction is completed, the reaction solution is cooled to room temperature, the catalyst is separated by vacuum filtration, and the filtrate is directly transferred to the subsequent separation step. The yield of the oxalamide acid intermediate obtained by the reaction is 93%, and the purity of the intermediate reaches 92%.

[0065] Example 2: Synthesis of crude N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxamide In the condensation reaction of oxalamide acid intermediate and o-aminophenyl ether, the oxalamide acid intermediate and o-aminophenyl ether are mixed in a molar ratio of 1:1 and dissolved in a mixed solvent of ethanol and water, and the solvent ratio is 3:1. A supported palladium catalyst (palladium loading is 5%) is used, and the amount of catalyst added is 1.2% of the total mass of the reactants. The reaction temperature is controlled at 110°C, the vacuum pressure is maintained at 0.7atm, and the reaction is stirred for 3 hours. After the reaction solution is cooled, the catalyst is recovered by vacuum filtration, and the filtrate is transferred to a rotary evaporator for reduced pressure distillation to recover the solvent, and the crude product is a light yellow solid. The yield of the target crude product reaches 89%, and its purity is 88%.

[0066] Example 3: Recrystallization purification and resource recovery The crude product obtained in Example 2 is dissolved in an acetonitrile solvent, the amount of solvent is 5 times the mass of the crude product, the dissolution temperature is set to 60°C, and stirring is maintained until it is completely dissolved. The dissolved solution is slowly cooled at a rate of 2°C / min at room temperature, and is further placed in an ice bath, cooled to below 5°C, and crystals are precipitated. The precipitated crystals are separated by vacuum filtration and washed with 10mL of cold acetonitrile. The washed crystals are vacuum dried at 45°C to constant weight, and white crystals with a purity of 99% of the target product are finally obtained. The mother liquor after recrystallization is recovered from acetonitrile by rotary evaporation, and the recovery rate reaches 96%. Unreacted o-aminophenyl ether is separated and purified from the extracted aqueous phase, and the purity can reach 95%, which can be directly used for the next batch of reactions.

[0067] Comparative Example 1 (corresponding to Example 1: Optimization of green catalytic system) In the synthesis of the oxalamide acid intermediate, oxalic acid and o-ethylaniline were mixed in a molar ratio of 1:2, and ethanol was used as a single solvent, without adding water as a mixed solvent. The catalyst was changed to a traditional homogeneous acid catalyst (p-toluenesulfonic acid), and the amount of the catalyst added was 1% of the total mass of the reactants. The reaction temperature was set at 110°C, and the stirring reaction was carried out at normal pressure for 3 hours. No vacuum-assisted operation was performed to remove the generated water byproduct. After the reaction was completed, it was directly cooled to room temperature, the catalyst was separated by filtration, and the filtrate was used for subsequent separation steps.

[0068] Comparative Example 2 (corresponding to Example 2: Optimization of Catalytic System and Reaction Conditions) In the condensation reaction of the oxalamic acid intermediate and o-aminophenyl ether, the oxalamic acid intermediate and o-aminophenyl ether are mixed in a molar ratio of 1:1 and dissolved in ethanol (no water mixed solvent is used). The catalyst is a conventional non-supported palladium catalyst (Pd black), and the amount of the catalyst added is 2% of the total mass of the reactants. The reaction temperature is set to 130°C, and the reaction is stirred for 3 hours under normal pressure, and the water by-product is not removed by a vacuum-assisted system. After the reaction is completed, the catalyst is directly filtered and separated to obtain a filtrate for subsequent steps.

[0069] Comparative Example 3 (Corresponding to Example 3: Optimization of Solvent and Recrystallization Process) In the recrystallization purification of the crude target product, the crude product was dissolved in methanol, the amount of solvent used was 3 times the mass of the crude product, the dissolution temperature was 50°C, and the temperature was directly lowered to room temperature after stirring and dissolving. The cooling rate was not controlled, and the solution was quickly cooled to below 5°C. The precipitated crystals were separated by filtration without ethanol washing. The obtained crystals were not recrystallized for the second time, but were directly dried by air at room temperature.

[0070] Comparative Example 4 (corresponding to Example 3: resource recovery optimization) As for solvent recovery, the mother liquor after solvent extraction and recrystallization was not recovered by vacuum distillation, but directly evaporated the solvent, and the evaporation temperature was controlled at 70°C to 80°C. No condensation device was set for the evaporation system, and the solvent vapor was directly discharged. For the unreacted o-aminophenyl ether after extraction, it was not separated by vacuum distillation, but simply washed with water and discarded without purification and recovery.

[0071] Comparative Example 5 (corresponding to the combined comparison of Example 1 and Example 2: optimization of green chemistry and energy consumption) In the preparation of oxalamide acid intermediates and target products, a green catalyst system was not used, but a homogeneous acid catalyst (such as sulfuric acid) and a traditional palladium catalyst (such as PdCl2) were used respectively. The reactions were carried out at 120°C and 140°C, respectively, without using a vacuum-assisted system to remove water byproducts, and the reaction time was not optimized (extended to 4 hours each). The crude product was separated directly by single filtration without multi-step separation or extraction.

[0072] Experiment 1: Experimental description of the preparation efficiency and purity of oxalamide acid intermediates Experimental procedures Example 1 Experimental process Oxalic acid (0.1 mol) and o-ethylaniline (0.2 mol) were mixed in a molar ratio of 1:2, added to a 250 mL three-necked reaction flask, and a mixed solvent of ethanol and water (volume ratio of 4:1, total amount of 80 mL) was added. Sulfonated zirconium oxide catalyst (1.0 g, accounting for 1% of the total mass of the reactants) was added. The reaction flask was equipped with a condenser and a vacuum system, and the vacuum pressure was set to 0.8 atm. The stirring condition was set to 300 rpm, the reaction temperature was raised to 90 ° C, and the constant temperature was maintained for 2 hours. The water generated during the reaction was collected by a condensation device and quantitatively recorded. After the reaction was completed, it was cooled to room temperature, the catalyst was separated by vacuum filtration, and the filtrate was transferred to a rotary evaporator. The crude product of the oxalamide acid intermediate was obtained after the solvent was evaporated under reduced pressure.

[0073] Comparative Example 1 Experimental Process Oxalic acid (0.1 mol) and o-ethylaniline (0.2 mol) were mixed in a molar ratio of 1:2, added to a 250 mL three-necked reaction bottle, and 80 mL of pure ethanol was added as a single solvent. p-Toluenesulfonic acid catalyst (1.0 g) was added. The reaction was carried out under normal pressure, the temperature was set to 110 ° C, the stirring rate was 300 rpm, and the reaction time was 3 hours. After the reaction was completed, it was cooled to room temperature, the catalyst was separated by vacuum filtration, and the filtrate was transferred to a rotary evaporator to remove the solvent under reduced pressure to obtain a crude oxalamide acid intermediate product.

[0074] Testing and data recording The purity of the oxalamide intermediate obtained from the two sets of experiments was analyzed using high performance liquid chromatography (HPLC), using a C18 column, acetonitrile / water (50:50) as the mobile phase, and a detection wavelength of 254 nm. The yield of the intermediate (the ratio of actual yield to theoretical yield) was recorded and calculated. The presence of by-products was quantified by HPLC peak area ratio.

[0075] Experimental results on preparation efficiency and purity of oxalamide acid intermediates In this experiment, Example 1 achieved efficient preparation of oxalamide acid intermediates at a lower reaction temperature and a shorter reaction time by introducing the green catalyst sulfonated zirconium oxide and applying a vacuum-assisted system. Mechanistically, sulfonated zirconium oxide, as a solid acid catalyst, has surface active sites that can significantly reduce the activation energy of the amidation reaction, thereby improving the selectivity of the reaction. In addition, vacuum-assisted removal of the generated water byproduct effectively drives the chemical equilibrium toward the direction of generating the product, resulting in a yield of more than 92%.

[0076] In contrast, when the conventional homogeneous acid catalyst (p-toluenesulfonic acid) was used in Comparative Example 1, the catalytic efficiency of the reaction was significantly reduced. This difference may be due to the fact that the homogeneous acid catalyst cannot be completely separated after the reaction, which easily leads to the occurrence of side reactions and increases the amount of by-products generated. At the same time, since the reaction is carried out under normal pressure, the generated water cannot be removed in time, further inhibiting the generation of the target product, which can be verified from the result of significantly higher by-product content.

[0077] Experiment 2: Purity of target crude product and by-product control experiment description Experimental procedures Example 2 Experimental process The oxalamide intermediate (0.1 mol) and o-aminophenyl ether (0.1 mol) were mixed in a molar ratio of 1:1, and a mixed solvent of ethanol and water (volume ratio 3:1, total amount 80 mL) was added. A supported palladium catalyst (Pd / C, 5% palladium, catalyst dosage 1.2 g) was added, and the reaction was stirred at 100°C under vacuum conditions (pressure 0.7 atm) for 3 hours. The water byproduct generated during the reaction was removed online by a condensation device. After the reaction was completed, it was cooled to room temperature, the catalyst was separated by vacuum filtration, and the filtrate was transferred to a rotary evaporator, and the solvent was evaporated under reduced pressure to obtain a crude target product.

[0078] Comparative Example 2 Experimental Process The oxalamide intermediate (0.1 mol) and o-aminophenyl ether (0.1 mol) were mixed in a molar ratio of 1:1, and 80 mL of pure ethanol was added as a solvent. A non-supported palladium catalyst (Pd black, catalyst dosage was 2.0 g) was added. The mixture was heated to 130 ° C under normal pressure and stirred for 3 hours. The generated water byproduct was not removed by vacuum assistance. After the reaction was completed, the mixture was cooled to room temperature, the catalyst was directly filtered and separated, and the crude target product was obtained after the solvent was removed by rotary evaporation.

[0079] Testing and data recording The purity of the target crude product was checked by high performance liquid chromatography (HPLC).

[0080] Mass spectrometry was used to analyze the types and contents of by-products.

[0081] Chromatographic conditions: C18 column, mobile phase: methanol / water (60:40), detection wavelength: 280 nm.

[0082] Mass spectrometry conditions: electrospray ionization (ESI), mass range m / z 50–500.

[0083] Target crude product purity and by-product control experimental results Sample No. Purity of target product (%) Type of by-products By-product content (mg / L) Example 2 89.4 3 21.7 Comparative Example 2 78.6 6 65.3 The optimized catalytic system and vacuum-assisted technology of Example 2 effectively improve the purity of the target product while significantly reducing the amount of by-products generated. The supported palladium catalyst (Pd / C) provides uniform catalytic active sites through its high surface activity and good stability, avoiding the problem of non-supported catalysts (such as Pd black) easily inducing side reactions. Combined with the vacuum-assisted online water removal strategy, the reaction equilibrium is further promoted to move toward the target product, so that the purity of the target crude product reaches more than 89%, while the types and contents of by-products are significantly reduced.

[0084] In contrast, the non-supported palladium catalyst used in Comparative Example 2 has a low catalytic efficiency due to its uneven distribution of surface active sites and easy agglomeration. In addition, the water by-products generated during the reaction were not removed, resulting in competitive side reactions between water and reactants, generating a variety of by-products. This phenomenon can be verified by the results of a significant increase in the number of by-products and a high content in mass spectrometry. In particular, some by-products with cyclic or cross-linked structures were detected in Comparative Example 2, further indicating that the probability of side reactions is higher.

[0085] Experiment 3: Experimental description of the effect of recrystallization purification Experimental procedures Example 3 Experimental process The crude target product (20 g) was dissolved in acetonitrile, and the amount of solvent used was 5 times the mass of the crude product (100 mL). The dissolution process was carried out at 60 ° C, and the stirring speed was controlled at 250 rpm until the solid was completely dissolved. After the dissolution was completed, the solution was slowly cooled to room temperature (about 25 ° C) at a rate of 2 ° C / min, and continued to cool to below 5 ° C, and the crystals were completely precipitated. Use a vacuum filtration device to separate the crystals, wash the crystals with cold acetonitrile (15 mL, 5 ° C), and remove residual impurities and mother liquor. The washed crystals were placed in a vacuum drying oven at 45 ° C and dried to constant weight, and the purity and morphology of the final product were recorded.

[0086] Comparative Example 3 Experimental Process The crude target product (20 g) was dissolved in methanol, and the amount of solvent used was 3 times the mass of the crude product (60 mL). The dissolution process was carried out at 50 ° C, with a stirring speed of 300 rpm, until the solid was completely dissolved. After the dissolution was completed, the solution was quickly cooled to below 5 ° C, and crystals were quickly precipitated. The crystals were separated by vacuum filtration without solvent washing. The resulting crystals were naturally dried at room temperature, and the purity and morphology of the final product were recorded.

[0087] Testing and data recording High performance liquid chromatography (HPLC) was used to detect the purity of the purified target product.

[0088] Scanning electron microscopy (SEM) was used to observe the crystal morphology, including size, uniformity and surface state.

[0089] Differential scanning calorimetry (DSC) was used to test the thermal stability and melting point of the crystals.

[0090] HPLC conditions: C18 column, mobile phase acetonitrile / water (70:30), detection wavelength 254 nm.

[0091] SEM conditions: accelerating voltage 15 kV, magnification 1000×.

[0092] DSC conditions: heating rate 10 °C / min, nitrogen protection.

[0093] Recrystallization purification effect experimental results Example 3 significantly improves the purity and crystal morphology of the target product during the recrystallization purification process by optimizing the solvent system and cooling strategy. Acetonitrile, as a recrystallization solvent, not only has good solubility for the target product, but also can effectively control the solubility gradient during the cooling process. This solvent characteristic causes the crystals to gradually precipitate, forming regular crystals with uniform size and smooth surface. In addition, the slow cooling strategy provides sufficient crystallization time, further reducing the inclusion of impurities in the crystals, so that the purity of the final crystals reaches more than 99%.

[0094] In contrast, Comparative Example 3 uses methanol as a solvent. Although the dissolution rate is faster, the solubility gradient is difficult to effectively control during rapid cooling. This causes the crystals to precipitate rapidly, forming uneven particles with more impurities, which significantly reduces the purity and uniformity of the crystals. In addition, the natural drying method fails to completely remove the residual solvent and impurities in the crystals, and also has a negative impact on the thermal stability and morphology of the target product. SEM observations show that the crystal surface in Comparative Example 3 is rough and the particle size distribution range is large, which further verifies the importance of cooling strategy during the crystallization process.

[0095] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide, characterized in that: The method comprises the following steps: The dehydration condensation reaction of oxalic acid and o-ethylaniline is carried out in a green catalyst and green solvent system to prepare an oxalamide acid intermediate; The obtained oxalamide acid intermediate is separated and the solvent is recovered to improve the reaction efficiency and reduce the solvent waste; The prepared oxalamide acid intermediate is reacted with o-aminophenyl ethyl ether in a synergistic catalyst and a green solvent system to prepare crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide; The resulting crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide is subjected to solvent extraction to separate by-products and purify the target product; The obtained target product is purified by recrystallization to improve the purity of N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide; Unreacted raw materials and generated water by-products are recovered for resource recycling and to reduce environmental pollution.

2. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The dehydration condensation reaction of oxalic acid and o-ethylaniline in a green catalyst and green solvent system comprises: Mix oxalic acid and o-ethylaniline in a molar ratio of 1:2; Adding a mixed solvent of ethanol and water in the presence of sulfonated zirconium oxide or H-ZSM-5 catalyst, wherein the volume ratio of ethanol to water is 3:1 to 5:1; The reaction was stirred at a temperature range of 85° C. to 95° C. for 1.5 to 2.5 hours, and the generated water was removed in real time by maintaining a pressure of 0.7 to 0.9 atm through a vacuum assist system.

3. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The separation and solvent recovery of the obtained oxalamide acid intermediate comprises: The reaction solution was cooled to room temperature, the catalyst was removed by filtration, and the catalyst was washed and recovered with ethanol; The filtrate is transferred to a rotary evaporator, and the ethanol and water solvents are recovered by vacuum distillation for use in the next batch of reactions; The oxalamide acid intermediate was obtained from the residue after rotary evaporation as a crude product for subsequent reactions.

4. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The method of reacting the prepared oxalamide acid intermediate with o-aminophenyl ethyl ether in a synergistic catalyst and green solvent system comprises: The oxalamic acid intermediate and o-phenylaminoethyl ether are mixed in a molar ratio of 1:1, and dissolved in a mixed solvent of ethanol and water, wherein the volume ratio of ethanol to water is 3:1 to 5:1; In the presence of a supported palladium catalyst (Pd / C, palladium content 5%), the temperature is raised to 100° C. to 120° C., and the reaction is stirred for 2.5 hours to 3.5 hours; The generated water by-product is removed online through a vacuum distillation apparatus, and the vacuum conditions are controlled to be 0.7 atm to 0.9 atm to improve the reaction selectivity and the yield of the target product.

5. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The step of subjecting the generated crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide to solvent extraction comprises: The reaction product was extracted three times with ethyl acetate, with ethyl acetate added each time at a volume twice that of the crude product; The organic phases were combined, dried over anhydrous sodium sulfate and filtered; The organic solvent was evaporated under reduced pressure to obtain the crude target product.

6. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The recrystallization purification comprises: Dissolve the crude target product in 40 mL to 60 mL of acetonitrile, and control the dissolution temperature at 55°C to 65°C; The dissolved solution is cooled to room temperature and allowed to stand for 12 to 24 hours to precipitate crystals; The crystals are washed with a small amount of cold acetonitrile (10 mL to 20 mL) and then filtered, and the filtered crystals are dried to constant weight to obtain high-purity N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide.

7. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The recovery of unreacted raw materials and generated water byproducts comprises: The generated water after dehydration condensation reaction and solvent extraction is separated online through a vacuum distillation device, and the water is purified and used for equipment cooling or process cleaning; The unreacted o-ethylaniline in the reaction solution is recovered by vacuum distillation, with a recovery rate of 90% to 95%; The unreacted o-phenylamino ether was separated and purified from the aqueous phase for subsequent reaction.

8. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The dehydration condensation reaction and solvent extraction are completed by a continuous flow reactor, comprising: The dehydration condensation module of oxalic acid and o-ethylaniline has a reaction temperature of 85°C to 95°C and a flow rate of 0.8 mL / min to 1.2 mL / min; The reaction module of the oxalamide acid intermediate and o-aminophenyl ether has a reaction temperature of 100°C to 120°C and a flow rate of 0.4 mL / min to 0.6 mL / min; The by-product online separation module is used to remove the water by-product in real time and recycle the solvent.

9. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 8, characterized in that: The continuous flow reactor further comprises: Online mixing module, used to evenly mix the reaction raw materials and solvent; Precision temperature control module, used to control the reaction temperature of each module within the range of 0.5~1.5℃; Online monitoring module is used to detect the conversion rate of reactants and the separation of by-products in real time.

10. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide obtained by the method is a UV absorber, which is used for anti-UV aging of polymer materials. The specific uses include: Added to polyurethane materials to improve the material's resistance to UV aging; Added to nylon materials to improve the material's anti-yellowing properties; When used in combination with optical brighteners, it does not interfere with the brightening effect and is used for light stabilization protection of plastic products. It has good compatibility with the base resin in the coating system and is used to improve the light stability and weather resistance of the coating; When used in environments containing residual metal catalysts or under alkaline conditions, its performance is stable and the degree of discoloration is low.

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