Process for the synthesis of N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide

Abstract

The application relates to the fine chemical technology field and discloses a synthesis method of N-(2-ethoxyphenyl)-N'-(2-ethylphenyl) oxamide, which comprises the following steps: carrying out a dehydration condensation reaction on oxalic acid and o-ethylaniline in a green catalyst and a green solvent system to prepare an oxamide acid intermediate; separating and recovering a solvent from the obtained oxamide acid intermediate to improve reaction efficiency and reduce solvent waste; and reacting the prepared oxamide acid intermediate with o-amino phenetole in a synergistic catalyst and a 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, the application realizes efficient, low-energy-consumption preparation of oxamide ultraviolet absorbers and green production of high-purity products.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fine chemical technology, in particular to a synthesis method of N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide. BACKGROUND

[0002] With the development of social economy and the progress of industrial technology, the use of polymer materials, plastic products and coatings is increasing year by year. However, these materials are prone to photodegradation when exposed to sunlight for a long time, which is caused by ultraviolet radiation. The photodegradation is manifested as color change, mechanical property reduction or surface cracking, which not only affects the appearance and service life of the materials, but also can cause serious degradation of the material performance. Therefore, in order to improve the ultraviolet aging resistance of the materials, ultraviolet absorbers are widely used in polymer materials and coatings.

[0003] At present, there is a certain research basis for the synthesis of oxamide compounds. Traditional methods usually use high-temperature condensation reaction, homogeneous catalyst and organic solvent system to successfully realize the industrial production of oxamide compounds. These methods have certain advantages in terms of fast reaction rate and high initial yield of products. Some processes also reduce the generation of by-products by improving the catalyst system, further improving the selectivity of the target product.

[0004] However, the existing technology still has many deficiencies, which restricts the wide application of oxamide ultraviolet absorbers. First of all, most of the traditional processes rely on high temperature and high pressure conditions, which consumes a lot of energy. The post-treatment of homogeneous catalysts is complex and difficult to reuse, which increases the production cost and environmental pollution. Secondly, although some processes improve the selectivity of the target product, the separation and purification efficiency of the crude product is still low, and there are many residual by-products, which cannot meet the demand of high-purity ultraviolet absorbers. In addition, the existing recrystallization process is not fully optimized, and the crystal morphology of the product is irregular during the purification process, which further affects the subsequent processing performance. Finally, the traditional process is not designed well in terms of resource recycling and utilization, and the solvent loss rate is high. The unreacted substances are often directly discarded, which leads to resource waste and environmental pollution. SUMMARY

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

[0006] To achieve the above purpose, the present application realizes the following technical scheme: a synthesis method of N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide, comprising the following steps:

[0007] Dehydrating and condensing oxalic acid and o-ethylaniline in a green catalyst and green solvent system to prepare oxamic acid intermediate;

[0008] Separating and recovering the obtained oxamic acid intermediate to improve reaction efficiency and reduce solvent waste;

[0009] Reacting the prepared oxamic acid intermediate with o-aminophenyl ether in a synergistic catalyst and green solvent system to prepare crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide;

[0010] Solvent extraction of the generated crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide to separate by-products and purify the target product;

[0011] Purifying the obtained target product by recrystallization to improve the purity of N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide;

[0012] Recycling unreacted raw materials and generated water by-products to resource recycling and reduce environmental pollution.

[0013] Preferably, the dehydrating and condensing oxalic acid and o-ethylaniline in a green catalyst and green solvent system comprises:

[0014] Mixing oxalic acid and o-ethylaniline in a molar ratio of 1:2;

[0015] Adding a mixed solvent of ethanol and water in a volume ratio of 3:1 to 5:1 in the presence of sulfonated zirconium oxide or H-ZSM-5 catalyst;

[0016] Stirring the reaction at a temperature range of 85°C to 95°C for 1.5 hours to 2.5 hours, and removing the generated water in real time by a vacuum auxiliary system maintaining a pressure of 0.7 atm to 0.9 atm.

[0017] Preferably, the separating and recovering the obtained oxamic acid intermediate comprises:

[0018] Cooling the reaction liquid to room temperature, removing the catalyst by filtration, and recovering the catalyst by washing with ethanol;

[0019] Transferring the filtrate to a rotary evaporation device, recovering the ethanol and water solvent by reduced pressure distillation for the next batch reaction;

[0020] Obtaining the oxamic acid intermediate from the residue after rotary evaporation as a crude product for subsequent reactions.

[0021] Preferably, the reaction of the obtained oxamic acid intermediate with o-aminophenethyl ether in a synergistic catalyst and green solvent system comprises:

[0022] The oxamic acid intermediate was mixed with o-aminophen ether at a molar ratio of 1:1 and dissolved in a mixed solvent of ethanol and water, with a volume ratio of ethanol to water of 3:1 to 5:1.

[0023] In the presence of a supported palladium catalyst (Pd / C, palladium content 5%), the temperature was raised to 100°C to 120°C, and the reaction was stirred for 2.5 to 3.5 hours.

[0024] The generated water byproducts are removed online using a vacuum distillation apparatus, with the vacuum conditions controlled at 0.7 atm to 0.9 atm, to improve reaction selectivity and the yield of the target product.

[0025] Preferably, the solvent extraction of the generated crude N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide includes:

[0026] The reaction product was extracted three times with ethyl acetate, with each extraction adding ethyl acetate at a volume twice that of the crude product.

[0027] Combine the organic phases, dry them with anhydrous sodium sulfate, and then filter.

[0028] The organic solvent was removed by evaporation under reduced pressure to obtain the crude target product.

[0029] Preferably, the recrystallization purification includes:

[0030] The crude target product was dissolved in 40 mL to 60 mL of acetonitrile, and the dissolution temperature was controlled at 55 °C to 65 °C.

[0031] Cool the solution to room temperature and let it stand for 12 to 24 hours to precipitate crystals.

[0032] The crystals were washed with a small amount of cold acetonitrile (10 mL to 20 mL), filtered, and dried to constant weight to obtain high-purity N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide.

[0033] Preferably, the recovery of unreacted raw materials and generated aqueous byproducts includes:

[0034] The water produced after dehydration condensation reaction and solvent extraction is separated online using a vacuum distillation device, and the purified water is used for equipment cooling or process cleaning.

[0035] Unreacted o-ethylaniline in the reaction solution was recovered by vacuum distillation, with a recovery rate of 90% to 95%.

[0036] The unreacted o-aminophenetole is separated from the aqueous phase and purified for use in subsequent reactions.

[0037] Preferably, the dehydration condensation reaction and solvent extraction are completed by a continuous flow reactor, comprising:

[0038] The dehydration condensation module of oxalic acid and o-ethylaniline has a reaction temperature of 85-95°C and a flow rate controlled at 0.8-1.2 mL / min;

[0039] The reaction module of oxamidic acid intermediate and o-aminophenetole has a reaction temperature of 100-120°C and a flow rate controlled at 0.4-0.6 mL / min;

[0040] The by-product online separation module is used for removing water by-products in real time and recycling solvents.

[0041] Preferably, the continuous flow reactor further comprises:

[0042] The online mixing module is used for uniformly mixing reaction raw materials and solvents;

[0043] The precise temperature control module is used for controlling the reaction temperature of each module within a range of 0.5-1.5°C;

[0044] The online monitoring module is used for real-time detection of the conversion rate of reactants and the separation of by-products.

[0045] Preferably, the N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide obtained by the method is an ultraviolet absorber, which is used for anti-ultraviolet aging of polymer materials, and specific uses include:

[0046] It is added to polyurethane materials to improve the ultraviolet aging resistance of the materials;

[0047] It is added to nylon materials to improve the yellowing resistance of the materials;

[0048] When used in combination with optical brighteners, it does not interfere with the whitening effect of the optical brighteners and is used for light stabilization protection of plastic products;

[0049] It has good compatibility with base resins in coating systems and is used for improving the light stability and weather resistance of coatings;

[0050] It is stable in performance and has low discoloration when used in environments containing residual metal catalysts or basic conditions.

[0051] The present application provides a synthesis method of N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide. It has the following advantages:

[0052] Advantages:

[0053] 1、The present application successfully realizes the efficient preparation of oxamide acid intermediates by adopting green catalysts and green solvent systems, combining vacuum assisted technology in 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 catalyst and serious system pollution are solved.

[0054] 2、The present application optimizes the recrystallization purification process, uses acetonitrile as the solvent, and combines slow cooling crystallization to make the purity of the target product reach more than 99%. Compared with the existing technology of extensive purification, this method ensures that the crystal form is more regular and the impurities are removed more thoroughly. At the same time, the solvent can be recycled by distillation and used again, further reducing production costs.

[0055] 3、The present application constructs a systematic resource recycling strategy, fully recycles solvents, by-products water and unreacted substances, and greatly improves resource utilization. Compared with the high-loss process of traditional technology, this design effectively reduces waste emissions, reduces waste in production, and significantly improves the environmental friendliness and economy of the process, providing a practical solution for the development of green chemistry. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 The flowchart of the method of the present application. DETAILED DESCRIPTION

[0057] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the specification of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0058] Please refer to the accompanying Figure 1 The present application provides a synthesis method of N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide, which comprises the following steps:

[0059] S1, dehydration condensation reaction: oxalic acid and o-ethylaniline are subjected to dehydration condensation reaction in a green catalyst and green solvent system to prepare oxamide acid intermediates;

[0060] The generation of oxamic acid intermediate directly influences the yield and purity of the subsequent target product, thus this step needs to be realized by precise catalyst selection, solvent optimization and reaction condition control to achieve efficient conversion. Generally, this step is realized by the dehydration condensation reaction of oxalic acid and o-ethylaniline to generate oxamic acid intermediate, which provides the basis for the subsequent reaction. In order to ensure the implementation of the concept of green chemical engineering, this step uses green catalyst and green solvent system to reduce the generation of by-products while achieving efficient reaction.

[0061] Specifically, in this step, oxalic acid provides the acyl source required for the reaction, and o-ethylaniline serves as an amino provider, which undergoes dehydration condensation reaction with oxalic acid under the synergistic action of a specific catalyst and solvent system to generate oxamic acid intermediate. As an option, 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 easy to separate, recover and reuse. The green solvent system uses a mixed solvent of ethanol and water, and the volume ratio of ethanol to water is usually 3:1 to 5:1. In some embodiments, this ratio can be appropriately adjusted according to the specific reaction requirements to optimize the solvent's solubility and reaction rate.

[0062] 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 11 N, which form a uniform reaction system in the mixed solvent. In one possible implementation, oxalic acid and o-ethylaniline are added to the reaction vessel according to the above molar ratio, and the selected catalyst is added. Specifically, the amount of catalyst added is usually 0.8% to 1.2% of the total mass of the reactants, which can ensure the reaction activity while avoiding waste of the catalyst.

[0063] In this reaction system, the reaction temperature is controlled at 85°C to 95°C, which can effectively promote the dehydration condensation reaction. 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 keeping it constant. 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 time.

[0064] In practice, a vacuum-assisted system is used to remove the generated aqueous byproducts in real time, thereby shifting the chemical equilibrium towards the formation of the oxalamidic acid intermediate. Alternatively, vacuum conditions are typically maintained between 0.7 atm and 0.9 atm, which efficiently removes moisture while preventing excessive solvent evaporation. In this reaction system, the generated aqueous byproducts can be collected and recycled using a condenser. In some embodiments, the byproducts can be further processed and used as process cooling water, achieving resource recycling.

[0065] To ensure efficient intermediate formation, a stirring system can be used in this step to ensure sufficient contact of the reactants. For example, a stirring speed of 300 to 350 rpm can be used to maintain the homogeneity of the reaction system. In some embodiments, a magnetic stirrer can be used to improve operational stability.

[0066] The chemical equations for the above reactions are shown below:

[0067]

[0068] Among them, C2H2O4 is oxalic acid, and C8H 11 N is o-ethylaniline, C 18 H 20 N2O3 is an intermediate of oxalamidic acid, and H2O is a dehydration byproduct;

[0069] Generally, after the reaction is complete, the reaction solution is cooled to room temperature, and the catalyst is separated by filtration. The catalyst can be washed with ethanol and reused, typically more than five times without significantly reducing its catalytic activity. The resulting filtrate can be directly used in subsequent separation steps.

[0070] In one possible implementation, reaction conditions can be optimized by monitoring the conversion rate of oxalic acid and the amount of oxalamidic acid intermediate generated in the reaction system online. For example, the concentration changes of the target product in the reaction solution can be analyzed in real time using high-performance liquid chromatography (HPLC). Specifically, a C18 column can be used with acetonitrile and water as the mobile phase, and detection can be performed at a wavelength of 254 nm.

[0071] S2. Intermediate separation and solvent recovery: The obtained oxalamidic acid intermediate is separated and the solvent is recovered to improve reaction efficiency and reduce solvent waste;

[0072] By properly separating the reaction solution and recovering the solvent, resource waste can be effectively reduced, and the purity of the oxamic acid intermediate and the efficiency of subsequent reactions can be further improved. Generally, this step needs to consider both catalyst recovery and solvent recycling in the reaction system, thereby reducing process costs and conforming to the principles of green chemistry.

[0073] Specifically, the separation of oxamic acid intermediate is mainly achieved by physical separation means, such as filtration and reduced pressure distillation. The solid catalyst can be quickly recovered by filtration, avoiding the influence of its residues on subsequent reactions. The recovery of the solvent is mainly achieved by a reduced pressure distillation device, which can simultaneously achieve the separation and purification of ethanol and water. As an option, the unconverted raw materials can be further separated and recovered, so that they can be used in the next batch of reactions. Through the above measures, the resources can be efficiently utilized, and the sustainability of the process can be further improved.

[0074] In this embodiment, the reaction liquid generated in step S1 is first cooled to room temperature after being taken out of the reaction kettle. This operation can avoid solvent loss and side reactions caused by high temperature in subsequent operations. Specifically, the cooling can be achieved by natural cooling or circulating water cooling. In some embodiments, in order to accelerate the cooling rate, a jacketed cooling device can be used to ensure that the reaction liquid quickly reaches the operating temperature.

[0075] After the reaction liquid is cooled, the solid catalyst is separated by a filtering device. Generally, a vacuum filtering device is used for the filtering operation, which can effectively improve the separation efficiency. As an option, the filtering medium used can be filter cloth with a pore size of 10-20 microns to ensure complete recovery of the catalyst. The separated solid catalyst is usually washed with ethanol for 3-5 times to remove the attached oxamic acid intermediate and other impurities. Specifically, the amount of ethanol used for washing is generally 2-3 times the mass of the catalyst. In some embodiments, a vacuum drying device can be further used to dry the catalyst, making it convenient for storage and reuse.

[0076] The obtained filtrate mainly consists of oxamic acid intermediate, unreacted o- ethylaniline and mixed solvents. In order to extract the oxamic acid intermediate, the solvent and unreacted substances need to be separated by reduced pressure distillation. In one possible implementation, the filtrate is transferred to a rotary evaporation device, and the ethanol and water solvents are evaporated under reduced pressure. Specifically, the reduced pressure condition is controlled at 0.06-0.08 MPa, and the evaporation temperature is 60-70°C. By controlling the evaporation rate, the complete recovery of the solvent and the purity of the oxamic acid intermediate can be ensured at the same time.

[0077] 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 for subsequent reactions. In some specific implementations, the recovery rate of ethanol can reach more than 95%, and the recovery rate of water can be stabilized at more than 90%.

[0078] For the residual substance after evaporation, mainly oxamic acid intermediate and a small amount of unreacted o-ethyl aniline. By further processing, the purified oxamic acid intermediate can be extracted. As a possible option, the oxamic acid intermediate can be separated from o-ethyl aniline by freeze crystallization. Specifically, the residual liquid can be cooled to below 5°C, so that the oxamic acid intermediate is precipitated in solid form. After vacuum filtration, a high-purity intermediate can be obtained.

[0079] The chemical structure of the oxamic acid intermediate is as follows:

[0080] C 18 H 20 N2O3

[0081] It is mainly a linear molecular structure, and the amide groups at both ends can further react with o-aminophenetole to produce the target product. In this step, the recovery rate of the oxamic acid intermediate can generally reach 85% to 90%, and the purity detected by high performance liquid chromatography (HPLC) can reach more than 95%.

[0082] Generally, unreacted o-ethyl aniline is separated from the solvent by vacuum distillation and readded to the reaction system; as an improved measure, the recovery rate can be further improved by adjusting the amount of o-ethyl aniline added, and in some embodiments, the recovery rate of the solvent and unreacted substance is detected in real time by online monitoring technology to optimize the process conditions;

[0083] S3, synthesis of crude product: the prepared oxamic acid intermediate is reacted with o-aminophenetole in a synergistic catalyst and green solvent system to prepare crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide;

[0084] This step generates crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide by using the amide group of the intermediate and the amino group of o-aminophenetole through synergistic catalysis. Generally, in order to improve the reaction efficiency and selectivity, a suitable synergistic catalyst needs to be added to the reaction system, and the reaction conditions also need to be precisely controlled. By optimizing the type of catalyst, the ratio of solvent and reaction parameters, the generation of by-products can be minimized and the yield of crude product can be improved.

[0085] Specifically, the oxamic acid intermediate used in this step is directly obtained from step S2;

[0086] In this embodiment, the oxalamic acid intermediate and the o-aminophenyl ethyl ether are mixed in a 1:1 molar ratio to form the reaction system. In general, to ensure sufficient contact between the reactants, the two reactants are first dissolved in a mixed solvent of ethanol and water. As an option, the volume ratio of ethanol to water is generally controlled between 3:1 and 5:1 to balance solubility and reaction rate.

[0087] Specifically, the synergistic catalyst used in this step is a supported palladium catalyst (Pd / C), and the loading 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, a small amount of cuprous iodide (CuI) can be added as a cocatalyst in some embodiments to further improve the catalytic efficiency of the reaction. The choice and amount of catalyst directly affect the selectivity and yield of the target product, so it needs to be adjusted appropriately according to the specific process conditions.

[0088] In terms of control of reaction conditions, the reaction temperature is generally set to 100°C to 120°C, and the reaction time is generally 2.5 hours to 3.5 hours. In one possible implementation, the reaction can be carried out in a stepwise heating manner, for example, from room temperature to 100°C, and the final temperature is maintained constant to complete the reaction process. In some embodiments, to avoid over-reaction, the amount of water by-product generated can be monitored online to adjust the reaction time in real time.

[0089] In the reaction system, the water by-product generated is removed in real time by a vacuum-assisted system to promote the chemical equilibrium to move in the direction of generating the target product. The vacuum condition is generally controlled within the range of 0.7 atm to 0.9 atm. 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 by-products in real time and reduce the accumulation of impurities in the reaction system.

[0090] In some embodiments, to ensure the uniformity of the reaction, a magnetic stirring device can 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 temperature from being too high to trigger side reactions.

[0091] After the reaction is completed, the reaction liquid is cooled to room temperature, and the catalyst is separated by vacuum filtration. The separated catalyst can be reused after being washed with ethanol, and it can generally 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 material. After removing most of the solvent by vacuum distillation, the crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide is obtained.

[0092] Generally, the purity of the obtained crude product can reach 85% to 90%. In some embodiments, to further improve the purity of the crude product, a small amount of ethanol can be added for secondary washing after the distillation is completed to remove the unreacted o-aminophenyl ether. The final obtained crude product can be directly used in the subsequent solvent extraction step;

[0093] S4, solvent extraction: the generated crude N-(2-ethoxyphenyl)-N'-(2- ethylphenyl)-oxamide is subjected to solvent extraction for separating byproducts and purifying the target product;

[0094] The key of this step lies in the selection of the solvent and the optimization of the extraction operation conditions. Through a reasonable solvent system and extraction process, the target crude product can be maximally extracted while reducing the residual impurities in the target product.

[0095] Generally, the solvent extraction operation adopts the principle of layered extraction of the aqueous phase and the organic phase. The target product tends to be distributed in the organic phase, while the impurities and unreacted substances are mainly left in the aqueous phase. As an option, the separation efficiency can be further improved by repeating the extraction multiple times. In order to meet the needs of industrial production, the solvent used in the extraction process should have low toxicity, good distribution coefficient and easy recovery characteristics, such as ethyl acetate. Specifically, ethyl acetate has high solubility and is easy to evaporate, which is the preferred extractant in this step.

[0096] In this embodiment, the crude product solution obtained in step S3 is placed in a separatory funnel, and ethyl acetate with a volume ratio of 2 times the crude product is added. Generally, the crude product solution mainly consists of a small amount of solvent, unreacted substances and byproducts, while ethyl acetate can efficiently dissolve the target crude product to form clear organic and aqueous phase layers.

[0097] As a possible implementation, the separation operation can be repeated three times to improve the extraction efficiency of the target product. In each extraction, ethyl acetate is added to the separatory funnel and mixed thoroughly, and then left to separate into two phases. Specifically, the mixing can be achieved by gently shaking the funnel and timely venting to avoid excessive internal pressure causing damage to the separatory funnel. In some embodiments, 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.

[0098] The separated organic phase is dried by 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 water. As an option, other drying agents 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 the organic solution containing the target product.

[0099] The key to isolating 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 evaporation device, and the ethyl acetate is evaporated under reduced pressure. The reduced pressure is typically controlled at 0.06 MPa to 0.08 MPa, and the evaporation temperature is 45°C to 55°C. This condition ensures the rapid evaporation of the solvent while avoiding the decomposition of the target product caused by high temperature. In some embodiments, the evaporated ethyl acetate can be further collected by a continuous flow solvent recovery system for reuse.

[0100] Through the above operation, the crude target product is obtained, which is usually in the form of a light yellow solid. Generally, 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 trace amount of unreacted substances that may exist, the obtained crude product can be washed twice. As an option, the second washing solvent can be a small amount of cold ethanol, which is 1 to 2 times the mass of the crude product. After stirring and washing, the purity is further improved by filtration.

[0101] In some embodiments, in order to optimize the use efficiency of the solvent, the aqueous phase after extraction can be distilled to separate and recover the unreacted o-aminophenyl ether. The purity of the recovered o-aminophenyl ether is usually more than 95%, which can be used for the next batch of reaction after simple purification. By using ethyl acetate as the extractant, this step realizes the efficient separation and purification of the target product;

[0102] S5, recrystallization purification: the obtained target product is purified by recrystallization to improve the purity of N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide;

[0103] By appropriately selecting the solvent system and optimizing the crystallization conditions, this step effectively removes impurities and unreacted substances in the crude product, and finally obtains the target product N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide with high purity. Generally, the recrystallization process not only improves the purity of the target product, but also improves its physical properties, such as crystal morphology and thermal stability, providing better performance for subsequent applications.

[0104] Specifically, a solvent with moderate solubility is required in this step, and the best crystallization effect is achieved by controlling the temperature, cooling rate and crystal precipitation conditions. As an option, acetonitrile is the 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 temperature gradient, the target product is precipitated in the form of regular crystals, while impurities and by-products are left in the mother liquor.

[0105] In this embodiment, the crude product obtained by solvent extraction in step S4 is dissolved in acetonitrile. Generally, 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 a uniform solution is formed. In order to accelerate dissolution, the solution can be heated to a range of 55°C to 65°C, and the temperature is kept constant until the solid is completely dissolved. In some embodiments, in order to further improve the dissolution efficiency, the solution can be subjected to moderate stirring, for example using a magnetic stirrer, and the stirring rate is controlled at 200 to 300 rpm.

[0106] The solubility of the product increases with increasing temperature, while the solubility of the impurities changes less, so that 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 / min to avoid too fast cooling causing the crystals to be too small. In some embodiments, the solution can be further cooled to below 5°C in an ice bath to promote the target product to be fully precipitated.

[0107] The precipitated crystals are separated by vacuum filtration, and the filter cake is the target product after preliminary purification. Generally, the filtration operation should avoid excessive breaking of the crystals to maintain the integrity of the crystals. As an option, a small amount of cold acetonitrile (10 mL to 20 mL) 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 dried to constant weight by vacuum drying, and the drying temperature is controlled at 35°C to 45°C to avoid decomposition of the target product caused by too high temperature.

[0108] In some embodiments, in order to further optimize the purification effect, two times of recrystallization can be used. Specifically, the first recrystallization is mainly used to remove most of the impurities in the crude product, and the second recrystallization further improves the purity and crystal morphology of the product by fine control of the conditions.

[0109] 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 used, the mobile phase is a mixture of acetonitrile and water, and the detection wavelength is set to 254 nm. Generally, the purity of the target product after this step of purification can reach ≥99%, meeting the requirements of subsequent applications.

[0110] In addition, the acetonitrile solvent used in this step can be recycled by distillation. As one possible implementation, the recrystallization mother liquor is evaporated under reduced pressure by a rotary evaporation device, and the acetonitrile is further purified by a separation device. The recovery rate can generally reach more than 95%, thereby further reducing the process cost;

[0111] S6. Resource Recycling: Recovering unreacted raw materials and generated water byproducts for resource recycling and reducing environmental pollution; resource recycling, through reasonable recovery 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 materials.

[0112] Specifically, the main byproducts generated in the dehydration condensation reaction, crude product synthesis, and solvent extraction are water and minor impurities, while the solvents mainly include ethyl acetate, acetonitrile, and ethanol. By implementing recovery measures in this step, the consumption of raw materials can be significantly reduced, production efficiency improved, and the design principles of green chemistry can be aligned.

[0113] In this embodiment, solvent recovery is mainly achieved through vacuum distillation. Generally, the solvent recovery system includes a rotary evaporator, a condenser, and a separation device. Taking ethyl acetate as an example, the aqueous and organic phases remaining after solvent extraction are collected separately, and a small amount of ethyl acetate in the aqueous phase is recovered into the organic phase using a separatory funnel. The separated organic phase is directly placed in the rotary evaporator, where ethyl acetate is evaporated under reduced pressure of 0.06 to 0.08 MPa, with the evaporation temperature controlled between 45°C and 55°C to ensure complete solvent recovery and prevent the target product from remaining in the mother liquor. As another possible implementation, the evaporated ethyl acetate is cooled to a liquid state through a condenser, purified, and returned to the solvent storage tank for later use.

[0114] Acetonitrile recovery primarily focuses on the recrystallization mother liquor. Typically, this mother liquor contains small amounts of impurities and incompletely dissolved target product. Acetonitrile can be efficiently distilled off using vacuum distillation and collected via a condenser. The distillate residue can be further processed to separate impurities and extract as much of the remaining target product as possible. In some embodiments, acetonitrile recovery rates have reached over 95%, while the loss rate of the target product is less than 1%.

[0115] The recovery of unreacted products is a crucial part of resource recycling. In dehydration condensation reactions and crude product synthesis reactions, unreacted o-ethylaniline and o-aminophenethyl ether can be separated and recovered using distillation techniques. Specifically, after removing most of the solvent from the reaction liquid by rotary evaporation, the unreacted products are separated from the products. Unreacted o-ethylaniline has a low boiling point (approximately 183°C), so it can be recovered at atmospheric pressure using a fractionating column, typically achieving a purity of over 95%. Similarly, o-aminophenethyl ether, with its moderate boiling point (approximately 218°C), can be recovered at a slightly lower temperature via vacuum distillation to avoid thermal decomposition. In some embodiments, the purity of the recovered products is monitored online, and distillation conditions are adjusted to ensure that the quality of the recovered products meets the requirements of the next batch of reactions.

[0116] In one possible implementation, the byproduct water is recovered using a continuous separation device, which collects the generated water during the reaction process by condensation and purifies it. Generally, the water can contain a small amount of solvent or impurities, which can be purified by activated carbon adsorption or distillation and then used for equipment cooling or production cleaning. For example, in this embodiment, the water generated from the dehydration condensation reaction is returned to the cooling circulation system after purification by the separation device, and the recovery rate can reach more than 90%.

[0117] To further optimize resource utilization, this step can be combined with online separation technology in a continuous flow process. For example, in a continuous flow reaction module, the simultaneous separation and recovery of water byproducts and organic solvents can be achieved by integrating online separation devices. This design not only simplifies the operation process, but also enables real-time monitoring of resource recovery efficiency. In some embodiments, by installing flow meters and concentration analyzers, the yield and purity of the recovered materials can be accurately measured, and the operation parameters can be adjusted in a timely manner.

[0118] Example 1: Synthesis of oxamic acid intermediate using a green catalytic system

[0119] Oxalic acid and o-ethylaniline were used as raw materials. Oxalic acid and o-ethylaniline were added to the reaction kettle at a molar ratio of 1:2, using a mixture of ethanol and water as the reaction medium, with a volume ratio of ethanol to water set at 4:1. The sulfonated zirconium oxide catalyst was added at 1% of the total mass of the reactants. The reaction temperature was raised to 90°C, and the reaction was stirred under vacuum conditions (pressure 0.8 atm) for 2 hours. During the reaction, the generated water byproduct was separated and collected in real time by a condenser. After the reaction was completed, the reaction liquid was cooled to room temperature, the catalyst was separated by vacuum filtration, and the filtrate was directly transferred to the subsequent separation step. The yield of the oxamic acid intermediate obtained by the reaction was 93%, and the purity of the intermediate reached 92%.

[0120] Example 2: Synthesis of crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamide In the condensation reaction of the oxamic acid intermediate and o-aminophenyl ether, the oxamic acid intermediate and o-aminophenyl ether were mixed at a molar ratio of 1:1 and dissolved in a mixture of ethanol and water as the solvent, with a solvent ratio of 3:1. A supported palladium catalyst (palladium loading 5%) was used, and the catalyst was added at 1.2% of the total mass of the reactants. The reaction temperature was controlled at 110°C, the vacuum pressure was maintained at 0.7 atm, and the reaction was stirred for 3 hours. After the reaction liquid was cooled, the catalyst was recovered by vacuum filtration, and the filtrate was transferred to a rotary evaporation device for vacuum distillation to recover the solvent, obtaining a light yellow solid as the crude product. The yield of the target crude product reached 89%, and its purity was 88%.

[0121] Example 3: Purification by recrystallization and resource recovery

[0122] The crude product obtained from Example 2 was dissolved in acetonitrile solvent, the solvent amount was 5 times of the crude product mass, the dissolution temperature was set to 60°C, and the stirring was maintained until complete dissolution. The dissolved solution was slowly cooled at a rate of 2°C / min at room temperature and further placed in an ice bath to cool to below 5°C to precipitate crystals. The precipitated crystals were separated by vacuum filtration and washed with 10 mL of cold acetonitrile. The washed crystals were dried at 45°C under vacuum to constant weight, and the final target product was obtained as white crystals with a purity of 99%. The mother liquor after recrystallization was recovered by rotary evaporation, and the recovery rate reached 96%. The unreacted o-aminophenetole was separated and purified from the aqueous phase, and the purity reached 95%, which could be directly used for the next batch reaction.

[0123] Comparative Example 1 (corresponding to Example 1: optimization of green catalytic system)

[0124] In the synthesis of oxamidic acid intermediates, oxalic acid was mixed with o- ethylaniline at a molar ratio of 1:2, using ethanol 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 catalyst was added in an amount of 1% of the total mass of the reactants. The reaction temperature was set to 110°C, and the stirring reaction was carried out at normal pressure for 3 hours without vacuum-assisted operation 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 the subsequent separation step.

[0125] Comparative Example 2 (corresponding to Example 2: optimization of catalytic system and reaction conditions)

[0126] In the condensation reaction of oxamidic acid intermediates and o-aminophenetole, the oxamidic acid intermediates were mixed with o-aminophenetole at a molar ratio of 1:1 and dissolved in ethanol (without using a water mixed solvent). The catalyst was a conventional non-supported palladium catalyst (Pd black), and the catalyst was added in an amount of 2% of the total mass of the reactants. The reaction temperature was set to 130°C, and the stirring reaction was carried out at normal pressure for 3 hours without using a vacuum-assisted system to remove the water byproduct. After the reaction was completed, the catalyst was directly separated by filtration, and the filtrate was obtained for the subsequent step.

[0127] Comparative Example 3 (corresponding to Example 3: optimization of solvent and recrystallization process)

[0128] In the recrystallization purification of the crude target product, the crude product was dissolved in methanol, the solvent amount was 3 times of the crude product mass, the dissolution temperature was 50°C, and the stirring dissolution was directly cooled to room temperature. The cooling rate was not controlled, the solution was quickly cooled to below 5°C, the precipitated crystals were separated by filtration, and ethanol washing was not performed. The obtained crystals were not subjected to secondary recrystallization, and were directly dried by air at room temperature.

[0129] Comparative Example 4 (corresponding to Example 3: resource recovery optimization)

[0130] For solvent recovery, instead of vacuum distillation, the solvent was directly evaporated, with the evaporation temperature controlled at 70-80°C, and the evaporation system was not equipped with a condenser, so the solvent vapor was directly discharged. For the unreacted o-aminophenetole after extraction, instead of vacuum distillation, it was simply washed with water and discarded, without purification and recovery.

[0131] Comparative Example 5 (corresponding to the combination of Example 1 and Example 2: optimization of green chemistry and energy consumption)

[0132] In the preparation of oxamidic acid intermediates and target products, instead of using green catalyst systems, homogeneous acid catalysts (such as sulfuric acid) and traditional palladium catalysts (such as PdCl2) were used respectively. The reactions were carried out at 120°C and 140°C respectively, without using vacuum auxiliary system to remove water byproducts, and the reaction time was not optimized (each was extended to 4 hours). The separation of the crude product directly used single filtration, without multi-step separation or extraction.

[0133] Experiment 1: experimental explanation of the preparation efficiency and purity of oxamidic acid intermediates

[0134] Experimental procedure

[0135] Example 1 experimental process

[0136] Oxalic acid (0.1 mol) and o-ethylaniline (0.2 mol) were mixed in a molar ratio of 1:2 and 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 temperature was kept constant for 2 hours. The water generated during the reaction was collected by the condenser 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 evaporation device. After the solvent was removed by vacuum evaporation, the crude oxamidic acid intermediate was obtained.

[0137] Comparative Example 1 experimental process

[0138] Oxalic acid (0.1 mol) and o-ethylaniline (0.2 mol) were mixed in a molar ratio of 1:2 and added to a 250 mL three-necked reaction flask, 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, with the temperature set to 110°C and the stirring rate set to 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 evaporation device to remove the solvent by vacuum evaporation, obtaining the crude oxamidic acid intermediate.

[0139] Detection and data recording

[0140] The purity of oxamic acid intermediates obtained from two sets of experiments was analyzed using high performance liquid chromatography (HPLC) with a C18 column, mobile phase of acetonitrile / water (50:50), and detection wavelength of 254 nm. The yield of intermediates (ratio of actual yield to theoretical yield) was recorded and calculated. The presence of byproducts was quantified by HPLC peak area ratio.

[0141] Experimental results of oxamic acid intermediate preparation efficiency and purity

[0142]

[0143] In this experiment, Example 1 achieved efficient preparation of oxamic acid intermediates at lower reaction temperatures and shorter reaction times through the introduction of a green catalyst, sulfated zirconium oxide, and the application of a vacuum-assisted system. Mechanistically, as a solid acid catalyst, sulfated zirconium oxide significantly reduces the activation energy of the amidation reaction through its surface active sites, thereby improving the selectivity of the reaction. In addition, the vacuum-assisted removal of generated water byproducts effectively drives the chemical equilibrium to move in the direction of product generation, resulting in a yield of over 92%.

[0144] In contrast, Comparative Example 1 used a traditional homogeneous acid catalyst (p-toluenesulfonic acid), which significantly reduced the catalytic efficiency of the reaction. 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 byproducts generated. At the same time, since the reaction is carried out at atmospheric pressure, the generated water cannot be removed in time, further inhibiting the generation of the target product, which can be verified from the results of significantly higher byproduct content.

[0145] Experiment 2: Purity of target crude product and byproduct control experiment

[0146] Experimental procedure

[0147] Example 2 experimental process

[0148] Oxamic acid intermediates (0.1 mol) were mixed with o-aminophenetole (0.1 mol) at a molar ratio of 1:1, and a mixed solvent of ethanol and water (volume ratio of 3:1, total volume of 80 mL) was added. A supported palladium catalyst (Pd / C, 5% palladium, catalyst dosage of 1.2 g) was added, and the reaction was stirred under vacuum conditions (pressure of 0.7 atm) at 100°C for 3 hours. The generated water byproducts were removed online through a condensation device during the reaction. After the reaction, the system was cooled to room temperature, the catalyst was separated by vacuum filtration, and the filtrate was transferred to a rotary evaporation device. The solvent was removed under reduced pressure to obtain the crude target product.

[0149] Comparative Example 2 experimental process

[0150] The oxamic acid intermediate (0.1 mol) was mixed with o-aminophenyl ether (0.1 mol) in a 1:1 molar ratio, and 80 mL of pure ethanol was added as a solvent. A non-supported palladium catalyst (Pd black, catalyst amount 2.0 g) was added. The reaction was heated to 130°C under normal pressure and stirred for 3 hours. The generated water by-product was not removed with vacuum assistance. After the reaction was completed, it was cooled to room temperature, and the catalyst was directly separated by filtration. After the solvent was removed by rotary evaporation, the crude target product was obtained.

[0151] Detection and data recording

[0152] The purity of the crude target product was detected using high-performance liquid chromatography (HPLC).

[0153] The types and contents of by-products were analyzed using mass spectrometry.

[0154] Chromatographic conditions: C18 column, mobile phase: methanol / water (60:40), detection wavelength: 280 nm.

[0155] Mass spectrometry conditions: electrospray ionization (ESI), mass range m / z 50-500.

[0156] Purity of the crude target product and results of the by-product control experiment

[0157] Sample number Purity of the target product (%) Types (species) of by-products Byproduct content (mg / L) Example 2 89.4 3 21.7 Comparative Example 2 78.6 6 65.3

[0158] The optimized catalytic system and vacuum-assisted technology of Example 2 effectively improved the purity of the target product and significantly reduced the amount of by-products. The supported palladium catalyst (Pd / C) provided uniform catalytic active sites due to its higher surface activity and good stability, avoiding the problem of easy side reactions caused by non-supported catalysts (such as Pd black). Combined with the online water removal strategy assisted by vacuum, the reaction equilibrium was further shifted towards the target product, so that the purity of the crude target product reached more than 89%, and the types and contents of by-products were significantly reduced.

[0159] In contrast, the non-supported palladium catalyst used in Comparative Example 2 had lower catalytic efficiency due to uneven distribution of surface active sites and easy agglomeration. In addition, the generated water by-product was not removed during the reaction, leading to competitive side reactions between water and reactants, generating various by-products. This phenomenon can be verified from the results of mass spectrometry analysis, where the number of by-product types significantly increased and the content was high. Especially in Comparative Example 2, some by-products with cyclic or crosslinked structures were detected, further indicating a higher probability of side reactions.

[0160] Experiment 3: Recrystallization purification effect experiment

[0161] Experimental steps

[0162] Example 3 Experimental procedure The crude target product (20 g) was dissolved in acetonitrile, the solvent amount was 5 times the mass of the crude product (100 mL). The dissolution process was carried out at 60 °C, 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, the crystals were completely precipitated. The crystals were separated using a vacuum filtration device, and the crystals were washed with cold acetonitrile (15 mL, 5 °C) to remove residual impurities and mother liquor. The washed crystals were placed in a vacuum drying oven at 45 °C to dry to constant weight, and the purity and morphology of the final product were recorded.

[0163] Comparative Example 3 Experimental procedure The crude target product (20 g) was dissolved in methanol, the solvent amount was 3 times the mass of the crude product (60 mL). The dissolution process was carried out at 50 °C, the stirring speed was 300 rpm until the solid was completely dissolved. After the dissolution was completed, the solution was quickly cooled to below 5 °C, the crystals were quickly precipitated. The crystals were separated by vacuum filtration, and no solvent was used for washing. The obtained crystals were naturally dried at room temperature, and the purity and morphology of the final product were recorded.

[0164] Detection and data recording

[0165] The purity of the target product after purification was detected by high performance liquid chromatography (HPLC).

[0166] The crystal morphology, including size, uniformity and surface state, was observed by scanning electron microscopy (SEM).

[0167] The thermal stability and melting point of the crystals were tested by differential scanning calorimetry (DSC).

[0168] HPLC conditions: C18 column, mobile phase acetonitrile / water (70:30), detection wavelength 254 nm.

[0169] SEM conditions: accelerating voltage 15 kV, magnification 1000x.

[0170] DSC conditions: heating rate 10 °C / min, nitrogen protection.

[0171] Experimental results of recrystallization purification effect

[0172]

[0173] Example 3 By optimizing the solvent system and cooling strategy, the purity and crystal morphology of the target product were significantly improved in the recrystallization purification process. Acetonitrile as a recrystallization solvent not only has good solubility for the target product, but also can effectively control the solubility gradient during cooling. This solvent property makes the crystals gradually precipitate, forming regular crystals with uniform size and smooth surface. In addition, the slow cooling strategy provides sufficient crystallization time, further reducing the impurities in the crystal, so that the purity of the final crystal reaches more than 99%.

[0174] In contrast, Comparative Example 3 uses methanol as a solvent, although the dissolution speed is faster, but the solubility gradient is difficult to effectively control when cooling quickly. This leads to the rapid precipitation of crystals, forming uneven particles, while containing more impurities, thereby significantly reducing 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, also has a negative impact on the thermal stability and morphology of the target product. The SEM observation results show that the crystal surface in Comparative Example 3 is rough, and the particle size distribution range is large, further verifying the importance of the cooling strategy in the crystallization process.

[0175] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application 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 includes the following steps: Oxalic acid and o-ethylaniline were dehydrated and condensed in a supported palladium catalyst and a mixed solvent of ethanol and water to prepare oxamic acid intermediates. The obtained oxamic acid intermediate was separated and the solvent was recovered to improve reaction efficiency and reduce solvent waste. The obtained oxamic acid intermediate was reacted with o-aminophenethyl ether in a supported palladium catalyst and a mixed solvent of ethanol and water to prepare crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxamyl; The crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide was subjected to solvent extraction to separate byproducts and purify the target product. The obtained target product was purified by recrystallization to improve the purity of N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide; Unreacted raw materials and generated water byproducts 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 supported palladium catalyst and a mixed solvent of ethanol and water includes: Oxalic acid and o-ethylaniline were mixed in a molar ratio of 1:

2. A mixed solvent of ethanol and water is added in the presence of zirconium oxide sulfonate or H-ZSM-5 catalyst, wherein the volume ratio of ethanol to water is 3:1 to 5:

1. The reaction is stirred for 1.5 to 2.5 hours within a temperature range of 85°C to 95°C, and the generated water is removed in real time by maintaining a pressure of 0.7 atm to 0.9 atm using a vacuum-assisted 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 oxalamidic acid intermediate includes: The reaction solution was cooled to room temperature, the catalyst was removed by filtration, and the catalyst was recovered by washing with ethanol. The filtrate was transferred to a rotary evaporator, where ethanol and water solvent were recovered by vacuum distillation for use in the next batch of reaction. Oxalic acid intermediates were obtained from the residue after rotary evaporation as crude products for subsequent reactions.

4. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that, The reaction of the prepared oxamic acid intermediate with o-aminophenethyl ether in a supported palladium catalyst and a mixed solvent of ethanol and water includes: The oxamic acid intermediate was mixed with o-aminophen ether at a molar ratio of 1:1 and dissolved in a mixed solvent of ethanol and water, with a volume ratio of ethanol to water of 3:1 to 5:

1. In the presence of a supported palladium catalyst, the temperature was raised to 100°C to 120°C, and the reaction was stirred for 2.5 to 3.5 hours. The generated water byproducts are removed online using a vacuum distillation apparatus, with the vacuum conditions controlled at 0.7 atm to 0.9 atm, to improve reaction selectivity and target product yield.

5. The method for synthesizing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that, The solvent extraction of the generated crude N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide includes: The reaction product was extracted three times with ethyl acetate, with each extraction adding ethyl acetate at a volume twice that of the crude product. Combine the organic phases, dry them with anhydrous sodium sulfate, and then filter. The organic solvent was removed by evaporation 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 includes: The crude target product was dissolved in 40 mL to 60 mL of acetonitrile, and the dissolution temperature was controlled at 55 °C to 65 °C. Cool the solution to room temperature and let it stand for 12 to 24 hours to precipitate crystals. The crystals were washed with a small amount of cold acetonitrile and then filtered. The filtered crystals were 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 recovered unreacted raw materials and generated aqueous byproducts include: The water produced after dehydration condensation reaction and solvent extraction is separated online using a vacuum distillation device, and the purified water is used for equipment cooling or process cleaning. Unreacted o-ethylaniline in the reaction solution was recovered by vacuum distillation, with a recovery rate of 90% to 95%. Unreacted o-aminophenethyl ether was separated from the aqueous phase and purified for use in subsequent reactions.

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 carried out in a continuous flow reactor, including: The dehydration condensation module of oxalic acid and o-ethylaniline was used at a reaction temperature of 85℃ to 95℃ and a flow rate of 0.8 mL / min to 1.2 mL / min. The reaction module for oxalamic acid intermediate with o-aminophenethyl ether was used, with a reaction temperature of 100℃ to 120℃ and a flow rate controlled at 0.4 mL / min to 0.6 mL / min. The online byproduct separation module is used to remove water byproducts 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 includes: An online mixing module is used to uniformly mix reaction raw materials and solvents; A precision temperature control module is used to control the reaction temperature of each module within the range of 0.5 to 1.5℃; The online monitoring module is used to detect the reactant conversion rate and by-product separation in real time.

10. The application of 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)-oxalamide obtained by the method is a UV absorber used for UV aging protection of polymer materials. Its application is as follows: It is added to polyurethane materials to improve their resistance to ultraviolet aging. It is added to nylon materials to improve their resistance to yellowing. When used in combination with optical brighteners, it does not interfere with their whitening effect and is used for light stability protection of plastic products. It exhibits good compatibility with the base resin in coating systems and is used to improve the light stability and weather resistance of coatings; It can be used in environments containing residual metal catalysts or under alkaline conditions, and its performance is stable with low discoloration.

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