The catalyst is N, N-(2-ethyoxyl phenyl)-Napos; preparation method of-(2-ethylphenyl)-oxamide

Abstract

The invention relates to the field of chemical synthesis, and discloses a preparation method of N-(2-ethoxyphenyl)-N '-(2-ethylphenyl)-oxamide, which comprises the following steps: by taking oxalic acid and o-ethylaniline as raw materials, carrying out dehydration condensation reaction under the action of a catalyst to obtain an oxamic acid intermediate; reacting the obtained oxamic acid intermediate with o-aminophenetole, and carrying out amidation reaction, so as to generate N-(2-ethoxyphenyl)-N '-(2-ethylphenyl)-oxamide; the obtained crude product is recrystallized and purified, the target product N-(2-ethoxyphenyl)-N '-(2-ethylphenyl)-oxamide is obtained, and the catalyst comprises at least one of phosphotungstic acid, phosphomolybdic acid or sulfonated resin. According to the invention, high-purity, high-yield, low-energy-consumption and environment-friendly production of the target product is realized through a green catalyst, optimization of reaction conditions and a solvent system and introduction of a moisture removal device and a recrystallization technology.

Description

Technical Field

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

[0002] With the widespread use of materials such as plastics and coatings in modern industry and daily life, the UV resistance of materials has become a key factor affecting their service life and performance stability. Long-term exposure to ultraviolet rays can cause polymer materials to degrade, manifested as discoloration, cracking or reduced mechanical properties. Therefore, adding efficient UV absorbers has become an important means to improve the anti-aging properties of materials.

[0003] In the prior art, the method for preparing N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxamide mainly uses ethyl oxalyl chloride or diethyl oxalate as the starting material, and uses different amine compounds to complete the condensation reaction and amidation reaction. These methods have a certain effect in improving the yield of the target product, especially the process using ethyl oxalyl chloride as the raw material, which can significantly accelerate the reaction rate through high reaction activity. At the same time, some processes show strong by-product suppression ability by reacting at high temperature, which can improve the purity of the product to a certain extent.

[0004] Although the prior art has certain advantages in terms of efficiency improvement and process stability, it still has many shortcomings, which directly affect the application effect of industrialization. First, the high pollution problem is more prominent. Raw materials such as ethyl oxalyl chloride will release toxic gases during use, posing a threat to both the environment and equipment. Secondly, the energy consumption is high, and many processes rely on high temperature conditions above 150°C, which increases production costs and energy consumption. In addition, the moisture generated during the reaction process is easy to accumulate, and there is a lack of effective means for removing moisture, resulting in a decrease in reaction efficiency. Finally, impurity separation and purification are difficult, and traditional methods are difficult to meet the demand for high-purity products, especially in mass production, where the problem is more significant. The present invention solves these shortcomings in the prior art from the source by systematically optimizing the entire preparation process, and provides a more efficient, green, and low-cost preparation method. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide, which solves the problems of high pollution, high energy consumption, inhibition of reaction efficiency due to water accumulation, and difficulty in separating and purifying impurities in the prior art.

[0006] To achieve the above object, the present invention is implemented by the following technical scheme: a method for preparing N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide, comprising the following steps: Oxalic acid and o-ethylaniline are used as raw materials, and a dehydration condensation reaction is carried out under the action of a catalyst to obtain an oxalamide acid intermediate; the obtained oxalamide acid intermediate is reacted with o-aminophenyl ether to carry out an amidation reaction to generate N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide; The obtained crude product was purified by recrystallization to obtain the target product N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide.

[0007] Preferably, the catalyst comprises: The catalyst includes at least one of phosphotungstic acid, phosphomolybdic acid or sulfonated resin, preferably phosphotungstic acid, which can be dehydrated efficiently under low temperature conditions, and generates less by-products, which is convenient for subsequent separation and purification; The catalyst is added in an amount of 0.1% to 5% of the total mass of the reactants to ensure the reaction rate and reaction selectivity while reducing process costs and environmental pollution.

[0008] Preferably, the dehydration condensation reaction comprises: The reaction temperature ranges from 40°C to 60°C. When the temperature is lower than this, the reaction rate is too low and the reaction efficiency decreases. When the temperature is higher than this, it is easy to cause side reactions, reducing the yield and purity of the intermediate. The dehydration condensation reaction time is 4 to 8 hours. The specific time is adjusted according to the proportion of the reaction materials and the activity of the catalyst to ensure complete reaction. In order to further improve the reaction efficiency and environmental friendliness, a slight negative pressure condition (20 to 50 mmHg) is adopted during the reaction to accelerate the removal of water generated by the reaction and promote the reaction equilibrium to move towards the direction of generating oxalamide acid intermediates.

[0009] Preferably, the moles of oxalic acid and o-ethylaniline include: When the molar ratio is 1:1, the waste of raw materials can be effectively reduced and the purity of the intermediate can be improved. However, too low a molar ratio can easily lead to incomplete reaction. When the molar ratio is 1:1.5, an appropriate excess of o-ethylaniline can promote the complete reaction and improve the yield of the oxalamide acid intermediate. It has been verified experimentally that the range of the raw material ratio can enable the yield of the generated oxalamide acid intermediate to reach more than 92%, while avoiding the increase in economic costs caused by a large excess of raw materials.

[0010] Preferably, the efficient reaction of the oxalamide acid intermediate with o-aminophenyl ether comprises: The reaction temperature is controlled between 100°C and 130°C. When the reaction temperature is lower than 100°C, the reaction rate is too low, which affects the production efficiency. When the reaction temperature is higher than 130°C, it is easy to cause an increase in side reactions or decomposition of the target product, which affects the purity of the product. The reaction time is 4 to 6 hours. If the time is too short, the conversion of the oxalamide acid intermediate will be incomplete. If the time is too long, the energy consumption will increase without significant effect improvement. By installing a moisture removal device in the reaction system, the generated water is continuously removed to avoid the interference of moisture on the amidation reaction, thereby improving the yield and purity of the target product.

[0011] Preferably, the process of using oxalic acid and o-ethylaniline as raw materials to carry out a dehydration condensation reaction under the action of a catalyst to obtain an oxalamide acid intermediate specifically comprises: Dimethyl carbonate is preferably used as the reaction solvent, which has the characteristics of low toxicity, environmental protection, easy recycling, etc., can provide good solubility at higher temperatures, and is convenient for mixing the reactants and reacting; If a solvent-free system is used, it is necessary to increase the reaction temperature and optimize the stirring conditions to ensure sufficient contact of the reactants and complete reaction in order to maximize the yield and purity of the product.

[0012] Preferably, the molar ratio of the oxalamide intermediate to o-phenylamino ether is 1:1 to 1:1.2, comprising: When the molar ratio is 1:1, the reactant resources can be effectively utilized and the raw material cost can be reduced; when the molar ratio is 1:1.2, an appropriate excess of o-aminophenyl ether can accelerate the reaction and reduce the generation of by-products; By optimizing the molar ratio range, the reaction yield is ensured to be above 90%, and the purity of the generated target product can reach above 99%.

[0013] Preferably, the recrystallization purification comprises: The recrystallization solvent is selected from ethanol, a water-ethanol mixed solvent or isopropanol, so as to select the best solvent according to the solubility characteristics of the target product to achieve the purpose of removing impurities and improving purity; The recrystallization temperature is controlled at 0°C to 5°C. Low-temperature operation promotes the crystallization of the target product, while effectively avoiding product loss caused by excessive dissolution. Through optimized recrystallization operation, the purity of the target product can be increased to over 99%.

[0014] Preferably, the purification process of the target product is optimized and designed to ensure the purity and yield of the final target product, including: After the target product is generated by amidation reaction, the unconverted substances and impurities in the reaction can be effectively removed by a purification method combining cooling precipitation, vacuum filtration and recrystallization, and finally UV-312 with a purity of ≥99% is obtained; On the basis of optimizing the reaction conditions, the yield of the final product reaches over 90%, and the entire production process is highly environmentally friendly, with significantly reduced waste liquid discharge.

[0015] Preferably, the preparation method further comprises: The oxalic acid and o-ethylaniline are subjected to a dehydration condensation reaction in the presence of a green catalyst, the reaction temperature is 40° C. to 60° C., the reaction time is 4 hours to 8 hours, and negative pressure conditions are used to accelerate the removal of generated water to generate an oxalamide acid intermediate; the oxalamide acid intermediate is mixed with o-aminophenyl ether, and an amidation reaction is performed in a dimethyl carbonate solvent at 100° C. to 130° C. for a reaction time of 4 hours to 6 hours, and the water generated during the reaction is continuously removed by a water removal device to obtain a crude target product; After the crude target product is cooled to room temperature, a water-ethanol solution is added for separation and crystallization. The obtained crystalline product is purified by recrystallization. The recrystallization solvent is ethanol or isopropanol. The recrystallization temperature is controlled at 0° C. to 5° C. to obtain the target product N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide with a purity of ≥99%.

[0016] The present invention provides a method for preparing N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide. Beneficial effects: 1. The present invention adopts a technical solution of preparing an oxalamide acid intermediate by a low-temperature dehydration condensation reaction catalyzed by a catalyst using oxalic acid and o-ethylaniline as starting materials, thereby achieving the technical effect of reducing energy consumption and improving reaction selectivity. Compared with the acidic catalytic method under high temperature conditions in the prior art, the present invention solves the problems of more side reactions and excessive energy consumption under high temperature, while avoiding the corrosive effects of strong acid catalysis on equipment and the environment.

[0017] 2. The present invention optimizes the amidation reaction conditions of the oxalamic acid intermediate and o-aminophenyl ether, uses dimethyl carbonate as the reaction solvent, and uses a moisture removal device to continuously remove by-product water, thereby significantly improving the reaction yield and the purity of the target product. Compared with the traditional high-temperature uncontrolled water removal technical solution, the present invention effectively solves the problem of water accumulation inhibiting the reaction during the reaction, while reducing the amount of solvent used, achieving the goal of both environmental protection and economic efficiency.

[0018] 3. The present invention adopts an optimized recrystallization purification method, uses ethanol or a water-ethanol mixed solvent as the recrystallization system, and controls the crystal precipitation conditions by step-by-step cooling to achieve efficient purification of the target product. Compared with the prior art that only relies on a single solvent or rapid cooling, the present invention solves the problems of difficult separation of impurities and poor crystal morphology during the purification process, while increasing the purity of the target product to more than 99%, providing a guarantee for industrial application.

[0019] 4. In the overall process design, the present invention utilizes green catalysts, low-toxic solvents and mild reaction conditions, avoiding the use of harmful reagents in traditional methods, while reducing energy consumption and waste emissions. Compared with the existing technology that relies on highly polluting processes such as strong acids and halogenated solvents, the present invention solves the problem of insufficient environmental protection from the source, and achieves the goal of energy conservation and emission reduction, meets the requirements of green chemistry, and provides a more sustainable production solution for industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is one of the flow charts of the method of the present invention. DETAILED DESCRIPTION

[0021] 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.

[0022] Please refer to the attached Figure 1 The present invention provides a method for preparing N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide, comprising the following steps: S1, using oxalic acid and o-ethylaniline as raw materials, carrying out a dehydration condensation reaction under the action of a catalyst to obtain an oxalamide acid intermediate; Oxalic acid and o-ethylaniline are used as starting materials, and oxalamic acid intermediate is prepared by dehydration condensation reaction under the action of catalyst. This step is an important basis of the whole process flow, which directly affects the subsequent reaction and the yield and purity of the target product. In order to achieve green and efficient reaction design, this embodiment adopts a specific catalyst and optimized reaction conditions, including temperature, reaction time, pressure control of the reaction system and timely removal of water.

[0023] The reaction in this step can be expressed by the chemical formula as follows: catalyst C2H2(COOH)2+C6H4(C2H5)NH2→C6H4(C2H5)NHCOCOOH+H2O in: C2H2(COOH)2 is oxalic acid; C6H4(C2H5)NH2 is o-ethylaniline; C6H4(C2H5)NHCOCOOH is an oxalamide acid intermediate.

[0024] Generally, the reaction can be carried out under mild conditions. By using specific catalysts, such as phosphotungstic acid, the reaction temperature can be further reduced and the conversion efficiency can be significantly improved. Timely removal of the water generated by the reaction under negative pressure conditions helps to inhibit the occurrence of side reactions and promote the transfer of chemical equilibrium to the target direction.

[0025] In this embodiment, oxalic acid and o-ethylaniline are mixed in a molar ratio of 1:1.2, and then reacted with a phosphotungstic acid catalyst in a solvent-free system. First, 88.0 g (1 mol) of oxalic acid and 121.2 g (1.2 mol) of o-ethylaniline are added to a 500 mL three-necked flask, and 1 g of phosphotungstic acid is added as a catalyst. The reaction vessel is equipped with a mechanical stirring device, a condensing device and a temperature control device to maintain the reaction temperature and remove the generated moisture in time.

[0026] Specifically, the speed of the agitator is set to 300 rpm to ensure sufficient mixing of the reactants. Oxalic acid and o-ethylaniline react at 50°C for 6 hours. During this process, the reaction gradually changes from a liquid state to a viscous state until solids begin to precipitate in the system. The water generated by the reaction is removed in time through a condensation device under negative pressure (20 to 50 mmHg). This operation can effectively improve the yield of the intermediate.

[0027] In some embodiments, oxalic acid and o-ethylaniline may be mixed in a molar ratio of 1:1 to reduce the waste of raw materials. If it is necessary to further improve the thoroughness of the reaction, the molar ratio of o-ethylaniline may be adjusted to 1:1.5. In this case, the yield of the oxalamide acid intermediate can reach more than 92%, and at the same time, it has a positive effect on subsequent reactions.

[0028] In one possible implementation, other green catalysts can be used instead of phosphotungstic acid, such as phosphomolybdic acid or sulfonated resin. These catalysts can catalyze dehydration condensation reactions under low temperature conditions, avoiding the byproduct pollution problem of traditional acidic catalysts. Specifically, the amount of phosphomolybdic acid used is generally 0.5% to 2% of the total mass of the reactants. Sulfonated resin is suitable for processes that require solid catalyst recovery, and its addition amount is 0.2% to 1.5%.

[0029] In another embodiment, in order to increase the reaction rate, a small amount of solvent, such as anhydrous ethanol or a water-ethanol mixed solvent, can also be introduced. Taking a water-ethanol mixed solvent as an example (volume ratio 1: 1), the solubility of oxalic acid can be significantly improved, the viscosity of the initial reaction can be reduced, and the mixing of the reaction system can be facilitated. Under this condition, the reaction temperature can be appropriately reduced to 40 ° C, and the reaction time can be extended to 8 hours to ensure that the purity of the generated oxalamide acid intermediate is not affected.

[0030] Generally, the temperature range of the reaction needs to be strictly controlled between 40°C and 60°C. If the reaction temperature is lower than 40°C, the reaction rate will drop significantly; and if it is higher than 60°C, side reactions are more likely to occur, resulting in reduced purity of the intermediate. Experimental verification shows that 50°C is the optimal reaction temperature.

[0031] The time of the dehydration condensation reaction needs to be adjusted according to the ratio of the reactants and the activity of the catalyst. In the case of less catalyst, the time can be appropriately extended to 8 hours. In the case of high catalyst activity, the reaction can be completed within 4 hours.

[0032] In terms of separation and treatment of the reaction product, the method of cooling precipitation and vacuum filtration is adopted in this embodiment, which is simple and efficient to operate. Specifically, after the reaction is completed, the reaction vessel is cooled to room temperature, and 200mL of cold water is slowly added thereto to wash the system and remove catalyst residues. Subsequently, the generated oxalamide acid intermediate solid is separated by a vacuum filtration device and dried to constant weight at 60 ° C using a vacuum drying oven. The oxalamide acid intermediate finally obtained is a light brown powder, and after testing, its purity is 97%, and the yield is 92%.

[0033] In some expansion methods, the reaction vessel can be replaced with a more efficient continuous reactor, such as one with automatic water separation. In continuous operation, the reaction time can be further shortened and the recycling efficiency of the catalyst can be improved, thus achieving a more environmentally friendly production method.

[0034] The oxalamide acid intermediate prepared by the above method can be directly used in the subsequent amidation reaction and has high chemical activity and stability. The successful preparation of this intermediate provides a reliable guarantee for the efficient synthesis of the target product, while significantly optimizing the environmental protection and economic efficiency of the production process.

[0035] S2, reacting the obtained oxalamide acid intermediate with o-aminophenyl ether to perform an amidation reaction to generate N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide; The amidation reaction of the oxalamide acid intermediate and o-aminophenyl ether is a key step in achieving the synthesis of the target product N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide. The efficiency of the reaction and the optimization of the conditions directly determine the yield and purity of the final product. In order to ensure that the reaction proceeds smoothly, the present invention adopts a precisely controlled temperature range and reaction time, and promotes the reaction balance by continuously removing the generated moisture. At the same time, the present invention has carried out systematic optimization for the selection of solvents, striving to balance the reaction rate and the convenience of operation while ensuring green environmental protection.

[0036] The reaction formula is as follows: in: R represents o-ethylphenyl; R' represents 2-ethoxyphenyl; The reaction generates the target product N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide and water.

[0037] The oxalamic acid intermediate and o-aminophenyl ether were mixed in a molar ratio of 1:1 and reacted. 120.5 g (0.9 mol) of the oxalamic acid intermediate and 125.5 g (1 mol) of o-aminophenyl ether were added to a 500 mL three-necked flask, and 200 mL of dimethyl carbonate (DMC) was added as a solvent. The flask was equipped with a condensation reflux device and a Dean-Stark device to remove the water generated in the reaction.

[0038] Specifically, the reaction temperature was controlled at 120°C and the stirring speed was maintained at 300 rpm to ensure that the reactants in the system were fully mixed. The reaction time was 5 hours, during which the generated water was continuously removed by a Dean-Stark device, thereby effectively improving the conversion rate of the reaction.

[0039] Generally, the reaction temperature needs to be controlled within the range of 100°C to 130°C. If the temperature is lower than 100°C, the reaction rate will drop significantly, resulting in a lower conversion efficiency of the oxalamide acid intermediate; while when the temperature is higher than 130°C, side reactions are more likely to occur, resulting in product decomposition or reduced purity. Experiments have shown that the best balance between reaction rate and product purity is achieved at 120°C.

[0040] As an option, the molar ratio of the oxalamide intermediate to o-phenylamino ether can be adjusted to 1:1.2, with an appropriate excess of o-phenylamino ether to promote the reaction and reduce the residual unreacted oxalamide intermediate. At this ratio, the conversion rate of the reaction can be increased by about 5%, but a step of removing o-phenylamino ether needs to be added in the subsequent purification process.

[0041] In one possible implementation, other solvents can be used instead of dimethyl carbonate, such as toluene or dichloromethane. Specifically, toluene has a higher boiling point and is suitable for reactions under high temperature conditions, but a water separation device is required to remove the generated water; while the low boiling point of dichloromethane facilitates subsequent solvent recovery. However, experimental results show that dimethyl carbonate is the best choice due to its green and environmentally friendly properties and excellent solubility.

[0042] During the post-treatment of the reaction, the reaction product needs to be cooled to room temperature, and then 300 mL of cold water is slowly added to precipitate the target product. The product is separated as a crude solid and collected by a vacuum filtration device. To further improve the purity, the crude product needs to be dissolved in a small amount of hot ethanol (reflux heating until completely dissolved), and then recrystallized at 0°C to 5°C. The obtained product is white to light yellow needle-shaped crystals, and the purity is more than 99% after testing.

[0043] In some embodiments, the yield and purity of the product can be further improved by optimizing the reaction time and the use of a moisture removal device. For example, by extending the reaction time to 6 hours, the thoroughness of the reaction can be ensured; while using an efficient moisture removal device, the inhibitory effect of moisture accumulation on the reaction rate can be avoided. Under these optimized conditions, the yield of the target product can be increased from 90% to 95%.

[0044] In another embodiment, a small amount of acidic promoter can be introduced to accelerate the reaction. In this case, the reaction temperature needs to be lowered to 110°C to avoid side reactions. Although the addition of promoters will slightly increase the complexity of the operation, under certain industrial conditions, the reaction time can be significantly shortened and the production capacity can be increased.

[0045] S3, the obtained crude product is recrystallized and purified to obtain the target product N-(2-ethoxyphenyl)-N′-(2-ethylphenyl)-oxalamide; Recrystallization and purification of the crude product is an important step to improve the purity of the target product and remove impurities. This step directly determines the chemical purity of the final product and its performance in the application field. By selecting a suitable solvent system and optimizing the dissolution and crystallization conditions, the unreacted substances and by-products in the crude product can be efficiently removed to obtain a high-purity target product. The present invention combines the optimization design of temperature control and solvent selection in this step to achieve efficient purification of the target product.

[0046] Generally speaking, the choice of solvent is crucial in the recrystallization process. The solvent needs to have both good solubility for the target product and selective solubility for impurities. For example, the target product should have a high solubility at high temperatures, while the solubility decreases significantly at low temperatures, so that high-purity crystals can be easily precipitated.

[0047] In this embodiment, the crude product is dissolved in a small amount of 95% ethanol. Specifically, the crude product is added to a three-necked flask, and about 100 mL of 95% ethanol is added at the same time. Then, the flask is placed on a reflux heating device and heated until the target product is completely dissolved to form a uniform solution. The dissolution temperature is usually controlled near the boiling point of ethanol, and the adequacy of the dissolution is ensured by stirring.

[0048] After the solution is completely dissolved, the solution is slowly cooled to room temperature (about 25° C.), at which time the system begins to precipitate crystals. Subsequently, the solution is placed in an ice water bath and continues to cool for 4 hours to promote the precipitation of crystals of the target product.

[0049] Specifically, the temperature gradient during the cooling process has an important influence on the quality of the crystal. Rapid cooling may result in a smaller crystal size or a crystal with impurities, so in this embodiment, a gradual cooling method is used to avoid the generation of crystal structure defects.

[0050] Generally, the precipitated crystals are separated by a vacuum filtration device. In the specific operation, the cooled crystallization solution is filtered through a glass sand core funnel, and the filtrate is collected as a mother liquor for later use. In order to further remove the adsorbed impurities on the surface of the crystals, a small amount of cold ethanol can be used.

[0051] As an option, if the crude product contains more soluble impurities, a water-ethanol mixed solvent can also be used for recrystallization. Specifically, the crude product is dissolved in a water-ethanol mixed solvent with a volume ratio of 1:1 and heated to completely dissolve under reflux conditions. Subsequently, the target crystals are precipitated by cooling and filtering methods similar to those described above. Experiments have shown that the use of a water-ethanol mixed solvent can effectively improve the separation efficiency of impurities during the recrystallization process, but it may have a certain effect on the crystal morphology of the target product.

[0052] In one possible implementation, the recrystallization operation can be optimized on an industrial scale. For example, the dissolution and crystallization process can be automated by using an automatically controlled temperature gradient device, and the product purity can be further improved by combining a multi-stage washing device. This method is particularly suitable for the purification of target products under batch production conditions.

[0053] The target product after recrystallization is white to light yellow needle-shaped crystals. The purity can reach more than 99% by high performance liquid chromatography (HPLC). The recrystallization step removes most impurities, such as unreacted oxalamide intermediates and o-aminophenyl ether, while improving the stability and optical properties of the product.

[0054] In some embodiments, the yield of recrystallization can be further improved by adjusting the crystallization temperature range and the amount of solvent used. For example, when the cooling temperature is adjusted to -5°C, although the precipitation time is slightly longer, the amount of crystal precipitation can be significantly increased, and the purity and yield of the final target product can reach excellent levels.

[0055] 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 preparing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide, characterized in that: The following steps are involved: Oxalic acid and o-ethylaniline are used as raw materials, and dehydration condensation reaction is carried out under the action of a catalyst to obtain an oxalamide acid intermediate; The obtained oxalamide acid intermediate reacts with o-aminophenyl ether to perform an amidation reaction to generate N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide; The obtained crude product was purified by recrystallization to obtain the target product N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide.

2. The method for preparing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The catalyst comprises: The catalyst includes at least one of phosphotungstic acid, phosphomolybdic acid or sulfonated resin, preferably phosphotungstic acid, which can be dehydrated efficiently under low temperature conditions, and generates less by-products, which is convenient for subsequent separation and purification; The catalyst is added in an amount of 0.1% to 5% of the total mass of the reactants to ensure the reaction rate and reaction selectivity while reducing process costs and environmental pollution.

3. The method for preparing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The dehydration condensation reaction comprises: The reaction temperature ranges from 40°C to 60°C. When the temperature is lower than this, the reaction rate is too low and the reaction efficiency decreases. When the temperature is higher than this, it is easy to cause side reactions, reducing the yield and purity of the intermediate. The dehydration condensation reaction time is 4 to 8 hours. The specific time is adjusted according to the proportion of the reaction materials and the activity of the catalyst to ensure complete reaction. In order to further improve the reaction efficiency and environmental friendliness, a slight negative pressure condition (20 to 50 mmHg) is adopted during the reaction to accelerate the discharge of water generated by the reaction and push the reaction equilibrium toward the direction of generating oxalamide acid intermediates.

4. The method for preparing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The moles of oxalic acid and o-ethylaniline include: When the molar ratio is 1:1, the waste of raw materials can be effectively reduced and the purity of the intermediate can be improved. However, too low a molar ratio can easily lead to incomplete reaction. When the molar ratio is 1:1.5, an appropriate excess of o-ethylaniline can promote the complete reaction and improve the yield of the oxalamide acid intermediate. The range of the raw material ratio has been experimentally verified to enable the yield of the generated oxalamide acid intermediate to reach more than 92%, while avoiding the increase in economic costs caused by a large excess of raw materials.

5. The method for preparing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The efficient reaction of the oxalamide acid intermediate and o-phenylamino ether comprises: The reaction temperature is controlled between 100°C and 130°C. When the reaction temperature is lower than 100°C, the reaction rate is too low, which affects the production efficiency. When the reaction temperature is higher than 130°C, it is easy to cause an increase in side reactions or decomposition of the target product, which affects the purity of the product. The reaction time is 4 to 6 hours. If the time is too short, the conversion of the oxalamide acid intermediate will be incomplete. If the time is too long, the energy consumption will increase without significant effect improvement. By installing a moisture removal device in the reaction system, the generated water is continuously removed to avoid the interference of moisture on the amidation reaction, thereby improving the yield and purity of the target product.

6. The method for preparing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The method uses oxalic acid and o-ethylaniline as raw materials, performs a dehydration condensation reaction under the action of a catalyst to obtain an oxalamide acid intermediate, specifically comprising: Dimethyl carbonate is preferably used as the reaction solvent, which has the characteristics of low toxicity, environmental protection, easy recycling, etc., can provide good solubility at higher temperatures, and is convenient for mixing the reactants and reacting; If a solvent-free system is used, it is necessary to increase the reaction temperature and optimize the stirring conditions to ensure sufficient contact of the reactants and complete reaction in order to maximize the yield and purity of the product.

7. The method for preparing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The molar ratio of the oxalamide intermediate to o-phenylamino ether is 1:1 to 1:1.2 and includes: When the molar ratio is 1:1, the reactant resources can be effectively utilized and the raw material cost can be reduced; when the molar ratio is 1:1.2, an appropriate excess of o-aminophenyl ether can accelerate the reaction and reduce the generation of by-products; By optimizing the molar ratio range, the reaction yield is ensured to be above 90%, and the purity of the generated target product can reach above 99%.

8. The method for preparing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: Recrystallization purification includes: The recrystallization solvent is selected from ethanol, a water-ethanol mixed solvent or isopropanol, so as to select the best solvent according to the solubility characteristics of the target product to achieve the purpose of removing impurities and improving purity; The recrystallization temperature is controlled at 0°C to 5°C. Low-temperature operation promotes the crystallization of the target product, while effectively avoiding product loss caused by excessive dissolution. After optimized recrystallization operation, the purity of the target product can be increased to over 99%.

9. The method for preparing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The purification process of the target product is optimized and designed to ensure the purity and yield of the final target product, including: After the target product is generated by amidation reaction, the unconverted products and impurities in the reaction can be effectively removed by a purification method combining cooling precipitation, vacuum filtration and recrystallization, and UV-312 with a purity of ≥99% can be finally obtained; Based on the optimization of reaction conditions, the yield of the final product reaches more than 90%, and the entire production process is highly environmentally friendly, with waste liquid emissions significantly reduced.

10. The method for preparing N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide according to claim 1, characterized in that: The preparation method further comprises: The oxalic acid and o-ethylaniline are subjected to a dehydration condensation reaction in the presence of a green catalyst, the reaction temperature is 40° C. to 60° C., the reaction time is 4 hours to 8 hours, and negative pressure conditions are used to accelerate the removal of generated water to generate an oxalamide acid intermediate; After mixing the oxalamic acid intermediate with o-aminophenyl ether, an amidation reaction is carried out in a dimethyl carbonate solvent at 100° C. to 130° C. for 4 to 6 hours, and the water generated during the reaction is continuously removed by a water removal device to obtain a crude target product; After the crude target product is cooled to room temperature, a water-ethanol solution is added for separation and crystallization. The resulting crystalline product is purified by recrystallization. The recrystallization solvent is ethanol or isopropanol. The recrystallization temperature is controlled at 0°C to 5°C to obtain the target product N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)-oxalamide with a purity of ≥99%.

Images