Method for preparing N, N '-di (4-ethyoxyl carbonyl phenyl)-N'-benzyl formamidine by using waste residues in production of UV-1

Abstract

The invention relates to the technical field of fine chemical engineering, and discloses a method for preparing N, N '-di (4-ethyoxyl carbonyl phenyl)-N'-benzyl formamidine by using waste residues in production of UV-1, which comprises the following steps: pretreating the UV-1 waste residues, and separating NE and NET by solvent dissolution, precipitation separation and liquid-liquid extraction; preparation of an intermediate NE: performing condensation reaction on ethyl p-aminobenzoate and trialkyl orthoformate to obtain NE; performing N-alkylation reaction, namely reacting NE with benzyl chloride under the alkaline catalysis condition to generate N, N '-di (4-ethyoxyl carbonyl phenyl)-N'-benzyl formamidine; and recycling the by-product NET. According to the method, through UV-1 waste residue resource utilization and optimization of the green technological process, efficient preparation of NEPA is achieved, the resource utilization rate is increased, the production cost is reduced, and environmental pollution is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemical industry, in particular to a method for preparing N,N'-bis(4-ethoxycarbonylphenyl)-N'-benzylformamidine by using waste residues from producing UV-1. Background Art

[0002] In modern industrial production, UV absorbers are widely used to improve the photostability of organic materials. UV absorbers can efficiently absorb ultraviolet light, thereby preventing the photodegradation of organic materials caused by ultraviolet light. UV absorbers represented by N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine (NEPA for short) have been widely used in the preparation of polymer materials such as plastic products, resins, cosmetics and textiles due to their excellent UV resistance and chemical stability.

[0003] In the prior art, the preparation method of NEPA generally adopts a process path combining condensation reaction and alkylation reaction. The typical process uses ethyl p-aminobenzoate as the starting material, condenses with trialkyl orthoformate to generate the intermediate NE, and then reacts with benzyl chloride to generate the target product NEPA through N-alkylation reaction. These methods have simple operation steps, mild reaction conditions, and high reaction selectivity, and have been initially applied in industrialization.

[0004] However, the existing technology still has significant deficiencies in resource utilization, economy and environmental protection. On the one hand, the existing technology usually uses new raw materials to prepare NEPA, and does not utilize the waste residue (mainly containing NE and NET) generated in the production process of UV-1 ultraviolet absorbers, resulting in a large amount of resource waste and increased production costs; on the other hand, the existing technology has few treatment measures for reaction by-products (such as NET), and the direct disposal of by-products not only wastes resources, but also increases the difficulty of industrial waste treatment. In addition, the existing process mostly uses highly toxic solvents such as benzene solvents, which not only pollutes the environment, but also does not conform to the development trend of green chemistry. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing N,N′-di(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1, which solves the problems of low resource utilization, high production cost and serious environmental pollution 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,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1, comprising the following steps: Pretreatment of UV-1 waste residue to separate NE and NET by solvent dissolution, precipitation separation and liquid-liquid extraction; Preparation of intermediate NE, by condensing ethyl p-aminobenzoate with trialkyl orthoformate to obtain NE; N-alkylation reaction, by reacting NE with benzyl chloride under alkaline catalysis to produce N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine; The byproduct NET is recycled to generate the target product N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine by reacting with benzyl chloride; The final product is separated and purified by crystallization and washing to obtain the target product with satisfactory purity.

[0007] Preferably, the pretreatment of the UV-1 waste residue comprises: Mix the waste residue with anhydrous ethanol in a weight ratio of 1:3 to 1:6, and stir and dissolve at 50° C. to 60° C. for 1 to 2 hours; After cooling to 20° C. to 25° C., add n-hexane, the volume ratio of n-hexane to ethanol solution is 2:1 to 4:1, and stand for stratification for 30 to 60 minutes; The n-hexane phase was separated and concentrated to 1 / 5 to 1 / 10 of the volume, and then cooled to 0°C to 5°C to precipitate NE crystals.

[0008] Preferably, the extraction of NE comprises: NE was separated using a mixed solvent of n-hexane and ethanol, with a volume ratio of n-hexane to ethanol ranging from 2:1 to 4:1; Wash the NE crystal with anhydrous ethanol, the washing amount being 2 to 3 times the mass of the NE crystal; After vacuum drying, NE with a purity of 95% to 98% was obtained.

[0009] Preferably, the preparation of the intermediate NE comprises: The molar ratio of ethyl p-aminobenzoate to trialkyl orthoformate is 1:1 to 1:1.2; The solvent is anhydrous ethanol, and the amount of the solvent is 5 to 10 times the total mass of the reactants; The amount of Lewis acid catalyst used is 1% to 5% of the total mass of the reactants, the reaction temperature is 50° C. to 60° C., and the reaction time is 1.5 hours to 2 hours.

[0010] Preferably, the N-alkylation reaction comprises: The molar ratio of NE to benzyl chloride is 1:1 to 1:1.2; The reaction solvent is anhydrous ethanol or ethyl acetate, and the amount of the solvent is 3 to 8 times the total mass of the reactants; The amount of the base catalyst used is 1% to 5% of the total mass of the reactants, the reaction temperature is 60° C. to 80° C., and the reaction time is 2 hours to 4 hours.

[0011] Preferably, the recycling of the NET comprises: The molar ratio of extracted NET to benzyl chloride was 1:1 to 1:1.2; The reaction solvent is anhydrous ethanol, and the catalyst is trifluoroacetic acid or other acidic catalysts, and the amount used is 1% to 3% of the total mass of the reactants; The reaction temperature is 70°C to 80°C, and the reaction time is 2 hours to 3 hours.

[0012] Preferably, the separation and purification of the final product comprises: The crude product was dissolved in ethanol, and n-hexane was added to form a mixed solution with a volume ratio of 1:2 to 1:3; Allow to stand at 20°C to 30°C to precipitate crystals; The crystals are filtered and washed with ethanol, and finally purified to obtain the target product with a purity of 98% to 99%.

[0013] Preferably, the UV-1 waste residue comprises: NE accounts for 40% to 60%; NET accounts for 15% to 30%; Other insoluble impurities account for 5% to 15%.

[0014] Preferably, the liquid-liquid extraction step comprises: Using ethyl acetate as the extraction solvent, the volume ratio of ethyl acetate to ethanol solution is 1:2 to 1:4; The extraction times range from 3 to 5 times, and the organic phase containing NET is separated.

[0015] Preferably, the neutralization treatment after the condensation reaction comprises: Add saturated sodium carbonate solution, the amount of sodium carbonate is 1% to 5% of the mass of the reaction solution; The pH of the system was adjusted to 7 to 8 by neutralization reaction, and the generated NE was separated after extraction with ethyl acetate.

[0016] The present invention provides a method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1. The method has the following beneficial effects: 1. The present invention adopts a technical solution for separation and recycling of NE and NET in UV-1 waste residue, and efficiently extracts the target components through multiple steps such as solvent dissolution, precipitation separation and liquid-liquid extraction, thereby realizing the maximum utilization of waste residue resources. At the same time, a green solvent system such as anhydrous ethanol, n-hexane and ethyl acetate is adopted and combined with a closed-loop recovery design, which greatly reduces the consumption of organic solvents and environmental pollution. Compared with the technical solution of directly discarding waste residue or using highly toxic solvents in the prior art, it solves the problems of serious waste of resources and serious environmental pollution.

[0017] 2. The present invention optimizes the separation and purification technical scheme of N-alkylation reaction and subsequent crystal precipitation and washing, combines efficient reaction conditions and separation step design, and prepares NEPA with a purity of more than 98%. At the same time, the reaction by-products are effectively recycled, realizing the industrial operability of the entire process. Compared with the technical scheme in the prior art that has low product purity and complex process that is difficult to scale up due to insufficient by-product treatment, this solves the problems of low product purity and process not being suitable for industrialization.

[0018] 3. The present invention adopts an optimized reaction path design combining Lewis acid catalysis and alkaline catalysis, which significantly improves the selectivity of condensation reaction and N-alkylation reaction and the yield of target product. At the same time, by gradually regulating the by-product conversion path and optimizing the solvent system, the side reaction is effectively suppressed. Compared with the technical solutions in the prior art that cause large amount of by-product generation due to mismatched catalyst selection or unreasonable reaction conditions, the shortcomings of low reaction efficiency and serious waste of raw materials are solved. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0021] Please refer to the attached Figure 1 The present invention provides a method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1, comprising the following steps: S1. Pretreatment of UV-1 waste residue: Pretreatment of UV-1 waste residue to separate NE and NET by solvent dissolution, precipitation separation and liquid-liquid extraction; Pretreatment of UV-1 waste residue is one of the key steps in the preparation of N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine (NEPA). This step efficiently separates the main components NE (ethyl imide formate) and NET (N,N′-bis(4-ethoxycarbonylphenyl)formamidine) in UV-1 waste residue through a combined process of solvent dissolution, precipitation separation and liquid-liquid extraction, providing high-purity intermediate raw materials for subsequent reaction steps; Generally, UV-1 waste residue contains 40-60% NE, 15-30% NET and 5-15% insoluble impurities. The mixed state of these components increases the difficulty of separation, but through the pretreatment process proposed in the present invention, NE and NET can be fully utilized while effectively removing impurities. This step not only realizes resource utilization, but also provides high-purity raw materials for subsequent reactions; As an option, the pretreatment of UV-1 waste residue can be based on the selective solubility and liquid-liquid partitioning properties of the solvent. Specifically, by precisely controlling the type of solvent, the amount of solvent, the separation conditions, etc., efficient separation and extraction of NE and NET in UV-1 waste residue was achieved; In some embodiments, to further optimize the operating efficiency, the solvent ratio, stirring time, and separation temperature may be appropriately adjusted to improve the purity of NE and NET and reduce the residual impurities; In this embodiment, UV-1 waste residue is mixed with anhydrous ethanol at a weight ratio of 1:3 to 1:6. Ethanol as a solvent has good solubility and selectivity. On the one hand, it can dissolve NE and NET, and on the other hand, it has a weak solubility for impurities, which facilitates subsequent separation.

[0022] In a specific implementation method, after UV-1 waste residue is mixed with ethanol, it is stirred and dissolved at 50-60° C. for 1-2 hours to ensure that NE and NET can be fully dissolved in the ethanol solution; In some embodiments, anhydrous ethanol with a higher purity may be used to further reduce the interference of impurity content. In addition, the amount of solvent may be appropriately adjusted according to the specific composition of the waste residue to ensure complete dissolution; In this embodiment, the mixed solution after dissolution is cooled to 20-25°C, and n-hexane is added for precipitation separation. The volume ratio of n-hexane to ethanol solution is 2:1-4:1, and the specific ratio can be adjusted according to actual needs. Under the action of n-hexane, the impurities are gradually precipitated and separated, while NE and NET are dissolved in the upper phase of n-hexane and ethanol; In some embodiments, in order to improve the precipitation effect, the standing time of n-hexane can be extended, usually 30 minutes to 1 hour. The precipitation effect is better under cooling conditions, and it is recommended to perform layering at 15-20°C.

[0023] The separated n-hexane phase mainly contains NE, while the ethanol phase mainly contains NET and a small amount of residual impurities. The n-hexane phase is concentrated to 1 / 5 to 1 / 10 of its volume by rotary evaporation and cooled to 0 to 5°C to precipitate NE crystals under low temperature conditions. The obtained crystals are washed with anhydrous ethanol, the washing amount being 2 to 3 times the mass of the crystals, and after vacuum drying, NE with a purity of 95 to 98% is obtained; Specifically, ethyl acetate is added to the ethanol phase, and the volume ratio of ethyl acetate to ethanol phase is 1:2 to 1:4, and the mixture is stirred evenly before extraction. Usually, the extraction times are 3 to 5 times to ensure that NET can be fully extracted into the organic phase; After the extraction is completed, the ethyl acetate phase is collected and the solvent is removed by rotary evaporation to obtain NET with a purity of 93-95%. In order to further improve the purification effect, a round of auxiliary extraction with n-hexane can be added after the extraction to further reduce the impurity content; in a possible implementation method, for UV-1 waste residue with high impurities, the extracted NE and NET can be added to activated carbon for adsorption treatment respectively, and then the purity can be further improved by simple filtration operation; The mass percentage of NE in UV-1 waste residue is 40-60%, the mass percentage of NET is 15-30%, and the mass percentage of impurities is 5-15%; The amount of ethanol used is 3 to 6 times the mass of the waste residue (weight ratio), and the amount of n-hexane used is 2 to 4 times the mass of the ethanol solution (volume ratio); the dissolution temperature is 50 to 60° C., the dissolution time is 1 to 2 hours, the separation temperature is 20 to 25° C., and the precipitation separation time is 30 minutes to 1 hour; The amount of ethyl acetate used as the extractant is 1 to 4 times the volume of the ethanol phase, the number of extractions is 3 to 5 times, and the extraction temperature is room temperature (20 to 25°C); In this embodiment, the separation of NE and NET is achieved by the polarity difference of the solvent and the optimization design of the liquid-liquid partition coefficient, and the separation effect is remarkable; Some extended technical contents include: During the dissolution process, an appropriate amount of phase transfer catalyst (such as tetrabutylammonium bromide) can be added to further improve the dissolution rate and purity of NE and NET; For UV-1 waste residue with high impurity content, NE and NET can be gradually extracted by pre-screening or step-by-step solvent dissolution to avoid impurities interfering with subsequent separation; In the low-temperature crystallization process of NE and NET, the seed introduction technology can be combined to further improve the uniformity and yield of the crystals; S2. Preparation of intermediate NE: Preparation of intermediate NE, by condensing ethyl p-aminobenzoate with trialkyl orthoformate to obtain NE; Through the above specific implementation methods, technicians can flexibly adjust the solvent dosage, temperature and operating conditions according to actual needs to obtain the best separation effect; In the technical scheme of the present invention, the preparation of the intermediate NE is an important intermediate step for realizing the preparation of N,N′-di(4-ethoxycarbonylphenyl)-N′-benzylformamidine (NEPA). By subjecting the pretreated ethyl p-aminobenzoate (PABA ethyl ester) to a condensation reaction with a trialkyl orthoformate, NE (ethyl imide formate) can be efficiently generated, providing a key intermediate raw material for the subsequent N-alkylation reaction.

[0024] Generally speaking, the condensation reaction is a highly selective reaction. By adjusting the reaction conditions (including catalyst type, dosage, temperature and reaction time, etc.), the formation of by-products (such as N,N′-bis(4-ethoxycarbonylphenyl)formamidine, NET) can be effectively avoided, and the yield and purity of NE can be improved. As an option, the reaction uses anhydrous ethanol as a solvent, taking advantage of its excellent solubility and low boiling point characteristics to facilitate the subsequent separation and purification of NE. Specifically, ethyl p-aminobenzoate and trialkyl orthoformate are condensed under the action of a Lewis acid catalyst (such as aluminum chloride, zinc chloride) at 50°C to 60°C to generate NE; In some embodiments, the reaction efficiency and the yield of the target product can be further optimized by adjusting the catalyst type and reaction time. For example, controlling the reaction time between 1.5 and 2 hours can effectively reduce the generation of by-products; In this embodiment, 20 g (about 0.1 mol) of ethyl p-aminobenzoate and 21.5 g (about 0.11 mol) of trialkyl orthoformate were first mixed, and 100 mL of anhydrous ethanol was added as a reaction solvent, and the amount of solvent used was 5 times the total mass of the reactants.

[0025] In a possible implementation, the amount of ethanol can be appropriately increased according to the dissolution rate, for example, the amount of solvent can be increased to 8 times the total mass of the reactants, thereby further improving the uniformity of the reaction mixture.

[0026] Specifically, a Lewis acid catalyst, such as aluminum chloride (0.5 g, the catalyst amount is 2.5% of the total mass of the reactants) is added, and the mixture is placed in a stirred reactor with a temperature control device, and stirred at 50° C. to 60° C. for 1.5 to 2 hours.

[0027] As an option, zinc chloride can also be used as a catalyst, and its amount can be in the range of 1% to 5% of the total mass of the reactants. The selection and amount of the catalyst have an important influence on the reaction rate and selectivity, and can be adjusted according to the specific reaction requirements.

[0028] In some embodiments, by optimizing the type of trialkyl orthoformate, such as selecting a methoxy or ethoxy substituent, the yield of the condensation reaction can be further improved and the residual unreacted raw materials can be reduced.

[0029] After the reaction is completed, the reaction mixture is neutralized by adding a saturated sodium carbonate solution, the amount of sodium carbonate used is 3% to 5% of the total mass of the reactants. The pH value of the neutralized solution is controlled between 7 and 8 to ensure the stability of the product and avoid the decomposition of the target product NE under acidic conditions; In this embodiment, the extraction and purification of NE is completed by liquid-liquid extraction, and the specific steps are as follows: the neutralized reaction mixture is subjected to liquid-liquid extraction with 100 mL of ethyl acetate, and the number of extractions is 3 to 4. After the extraction is completed, the organic phase is concentrated by rotary evaporation to a viscous state, and cooled at low temperature to precipitate NE crystals; In one possible implementation, a small amount of NE seed crystals (the amount of seed crystals is 1% to 3% of the mass of the target product) can be added to promote uniform precipitation of NE crystals and improve the purity and recovery rate of the product; The obtained crystals are washed with anhydrous ethanol, the amount of washing solvent used is 2 to 3 times the mass of the NE crystals, filtered and then vacuum dried to obtain NE solids with a purity of more than 90%; Some extended technical contents include: a small amount of water can be appropriately introduced into the reaction (controlled within 1% to 3% of the total solvent amount) to promote the activation of the Lewis acid catalyst and improve the reaction efficiency; In order to further reduce the generation of by-product NET, dynamic vacuum operation can be introduced in the later stage of the reaction to appropriately reduce the pressure of the reaction system and accelerate the conversion of the reaction products; In the extraction process of high-purity NE, the purity of NE can be further improved by increasing the number of liquid-liquid extractions (e.g., from 3 to 5 times) and combining it with activated carbon adsorption purification; Through the above specific implementation methods, the present invention can achieve efficient preparation of NE, provide high-purity key intermediates for subsequent N-alkylation reactions, and can further optimize the production process by adjusting reaction conditions and operating steps by technicians; S3, N-alkylation reaction: N-alkylation reaction, by reacting NE with benzyl chloride under alkaline catalysis to produce N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine; In the technical scheme of the present invention, the N-alkylation reaction is a key step of reacting NE (ethyl imide formate) prepared in the previous step with benzyl chloride to generate the target product N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine (hereinafter referred to as NEPA). This step realizes the efficient and selective reaction of benzyl chloride with NE by introducing an alkaline catalyst, while avoiding the occurrence of side reactions. Generally speaking, the imine group (–C=N–) in the NE molecule has a certain nucleophilicity, while the benzyl chloride (–CH2Cl) in benzyl chloride has a strong electrophilicity. The two are easy to undergo nucleophilic substitution reaction to generate NEPA in an alkaline environment. The yield and purity of the target product can be further improved by adjusting the type of alkaline catalyst, the molar ratio of the reactants, the reaction temperature and the amount of solvent. As an option, anhydrous ethanol or ethyl acetate can be used as a reaction solvent, taking advantage of its solubility to ensure good dispersion of NE and benzyl chloride in the reaction system. Specifically, NE and benzyl chloride react under the action of an alkaline catalyst (such as K2CO3 or NaOH) at 60°C to 80°C for 2 to 4 hours to generate NEPA; In some embodiments, to further optimize the reaction conditions, the amount of catalyst may be appropriately adjusted to control it within the range of 1% to 5% of the total mass of the reactants, thereby balancing the reaction rate and the occurrence of side reactions; In this example, 18 g (0.09 mol) of NE and 14.4 g (0.10 mol) of benzyl chloride were first mixed, and 90 mL of anhydrous ethanol was added as a reaction solvent, and the amount of solvent used was 4 times the total mass of the reactants. The choice of solvent is not only convenient for dissolving the reactants, but also conducive to the subsequent separation of the products.

[0030] As an option, ethyl acetate can also be used as the reaction solvent, and its amount can be adjusted in the range of 3 to 8 times the total mass of the reactants to meet different operating requirements; Specifically, 1.8 g (the amount of catalyst is 2% of the total mass of the reactants) of K2CO3 was added as a base catalyst and stirred to mix evenly. The reaction system was heated to 70°C and stirred for 3 hours to promote the complete N-alkylation reaction; In a possible implementation, NaOH can be selected as a catalyst, and its amount is 1% to 3% of the total mass of the reactants. Compared with K2CO3, NaOH as a strong base can more effectively activate the nucleophilic center of the NE molecule, thereby accelerating the reaction rate; In some embodiments, in order to further control the generation of reaction by-products, benzyl chloride can be added dropwise, and the addition time can be controlled between 30 and 60 minutes. Gradually adding benzyl chloride can not only avoid excessive local concentration, but also improve the yield of the target product; In this embodiment, the neutralization and separation steps after the reaction is completed are as follows: After the reaction is completed, the reaction mixture is first cooled to room temperature, and 270 mL of cold water (the amount of cold water is 3 times the volume of the reaction system) is added for neutralization and washing. The addition of the aqueous phase can not only neutralize the residual alkaline catalyst, but also effectively separate the by-products and impurities; As an option, saturated sodium chloride solution can be used instead of cold water, and the amount used is also 3 times the volume of the reaction system. By increasing the ionic strength of the aqueous phase, the solubility of NEPA in the aqueous phase is further reduced, thereby improving the recovery rate of the target product in the organic phase; Specifically, the neutralized mixture is subjected to liquid-liquid extraction using ethyl acetate (the amount used is 1.5 to 2 times of the reaction mixture), and the number of extractions is 3 to 4 times. The organic phase after extraction is concentrated by rotary evaporation to obtain a crude NEPA product; In this embodiment, the purification method of NEPA includes the following contents: The crude NEPA was dissolved in 90 mL of anhydrous ethanol, and 180 mL of n-hexane (the volume ratio of ethanol to n-hexane was 1:2) was added, and the mixture was allowed to stand at 20°C to 30°C for crystallization. The precipitated crystals were collected by filtration, washed with a small amount of ethanol (1 to 2 times the mass of the crystals), and finally vacuum dried to obtain NEPA with a purity of more than 98%; In a possible implementation, in order to further improve the purity, a dissolution-recrystallization method can be used to perform a secondary crystallization operation using ethanol and n-hexane as a solvent system; Some extended technical contents include: during the reaction process, a small amount of phase transfer catalyst (such as tetrabutylammonium bromide) can be introduced, with the amount being 0.5% to 1% of the total mass of the reactants, to further improve the mutual dispersibility of the reactants and the reaction rate; For NE with high impurity content, pre-filtration treatment can be performed before the reaction, or a small amount of activated carbon can be added to remove impurities by adsorption; during the cooling crystallization process, the precipitation rate of NEPA can be further increased by lowering the temperature to below 15°C; Through the above specific implementation methods, technicians can optimize the reaction conditions according to specific needs to obtain high-purity and high-yield NEPA products, while reducing the generation of by-products and improving the overall reaction efficiency; S4. Recycling of byproduct NET: Recycling of byproduct NET to generate target product N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine by reacting with benzyl chloride; In the technical scheme of the present invention, the recycling of the by-product NET (N, N'-bis (4-ethoxycarbonylphenyl) formamidine) is an important link to improve the efficiency of resource utilization. By reacting the by-product NET obtained by separation and purification in the previous step with benzyl chloride, it can be effectively converted into the target product N, N'-bis (4-ethoxycarbonylphenyl) -N'-benzyl formamidine (abbreviated as NEPA), thereby realizing efficient recycling of resources and reducing production costs; Generally, NET is a by-product that is difficult to avoid in condensation reactions. Its structure contains two condensation groups of ethyl p-aminobenzoate, which has strong nucleophilicity. Under alkaline or acidic catalytic conditions, NET can react with benzyl chloride to form NEPA by N-alkylation. By controlling the reaction conditions (such as temperature, catalyst dosage, reactant ratio, etc.), the utilization rate of by-products and the yield of target products can be further improved. As an option, anhydrous ethanol can be used as a reaction solvent in combination with an acidic catalyst (such as trifluoroacetic acid), which helps to enhance the selectivity of the reaction and reduce the formation of by-products. Specifically, NET and benzyl chloride can be completely converted into NEPA after 2 to 3 hours of reaction at 70 to 80°C. In some embodiments, in order to avoid waste of resources and reduce the interference of impurities on subsequent reactions, the NET may be pretreated before the reaction, for example, by removing impurities through liquid-liquid extraction or activated carbon adsorption, thereby ensuring the purity of the reaction system; In this example, 10 g (0.04 mol) of NET and 4.8 g (0.04 mol) of benzyl chloride were first mixed, and 50 mL of anhydrous ethanol was added as a solvent, and the amount of the solvent was 5 times the total mass of the reactants. As an option, ethyl acetate can also be used as a solvent, and its amount ranges from 4 to 8 times the total mass of the reactants; Specifically, 0.5 g of trifluoroacetic acid was added as a catalyst, and the amount of the catalyst was 1.5% of the total mass of the reactants. The mixture was placed in a stirred reactor with a temperature control device, heated to 70° C. and stirred for 2.5 hours to ensure that the N-alkylation reaction was completely carried out; In a possible implementation, other acidic catalysts (such as p-toluenesulfonic acid or concentrated hydrochloric acid) can also be used for the reaction, and the amount thereof is controlled at 1% to 3% of the total mass of the reactants. Compared with trifluoroacetic acid, these catalysts are less expensive but require a longer reaction time (usually 3 to 4 hours); As an improved solution, the reaction can be carried out by adding benzyl chloride dropwise. Adding dropwise can avoid the occurrence of side reactions caused by excessive local reaction and improve the yield of the target product NEPA; In this embodiment, the separation and purification steps after the reaction are as follows: After the reaction is completed, the reaction mixture is first cooled to room temperature, and 150 mL of cold water (the amount of cold water is 3 times the volume of the reaction system) is added for neutralization treatment. The addition of the aqueous phase can not only neutralize the residual acidic catalyst, but also effectively remove the unreacted benzyl chloride; As an option, a saturated sodium carbonate solution may be used instead of cold water for neutralization, with the amount being 2% to 5% of the total mass of the reaction mixture. The addition of sodium carbonate may further improve the stability of the reaction system and reduce the risk of product decomposition; Specifically, the neutralized reaction mixture is subjected to liquid-liquid extraction with ethyl acetate, the amount of ethyl acetate used is 2 to 3 times the total mass of the reaction system, the number of extractions is 3 to 4 times, and the organic phase after extraction is concentrated by rotary evaporation to obtain a crude NEPA product; in some embodiments, in order to improve the purity of the product, a small amount of n-hexane (with a volume ratio of 1:2 to ethyl acetate) can be added after concentration, and crystals are precipitated under cooling conditions to further reduce the residual impurities; In this embodiment, the purification step of NEPA includes the following: dissolving the crude NEPA in 90 mL of anhydrous ethanol, adding 180 mL of n-hexane (the volume ratio of ethanol to n-hexane is 1:2), and standing at 20° C. to 30° C. for crystallization. The precipitated crystals are collected by filtration, washed with a small amount of ethanol (1 to 2 times the mass of the crystals), and finally vacuum dried to obtain NEPA with a purity of more than 98%; As an optimization scheme, if the purity of the target product does not meet the requirements, NEPA can be further purified by dissolution-recrystallization method. The recrystallization solvent can be a mixed solution of ethyl acetate and n-hexane (volume ratio is 1:1); Some extended technical contents include: In the reaction system, an appropriate amount of phase transfer catalyst (such as tetrabutylammonium bromide) can be introduced, with the amount being 0.5% to 1% of the total mass of the reactants, to increase the reaction rate; For NETs with more impurities, they can be pre-treated by pre-filtration or solvent recrystallization to further improve the purity of the reaction system; In the separation process, a multi-stage extraction process can be introduced to improve the recovery rate of NEPA and reduce the loss of solvent. Through the above specific implementation method, technicians can optimize the reaction conditions according to actual production needs, improve the utilization rate of by-products and the yield of target product NEPA, thereby improving the resource level of the overall process. S5. Separation and purification of the final product: separation and purification of the final product, obtaining the target product with purity reaching the standard through crystal precipitation and washing; In the technical scheme of the present invention, the separation and purification of the final product N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine (NEPA) is an important step to ensure product quality. Through the selective evaporation of the solvent of the reaction mixture, crystal precipitation and washing, the residual solvent, by-products and impurities in the reaction can be effectively removed, thereby obtaining the target product NEPA with high purity.

[0031] In general, the separation and purification of NEPA depends on the coordination of the solvent system. The mixed solvent system of anhydrous ethanol and n-hexane can achieve efficient purification on the basis of controlling the crystal precipitation temperature and solubility gradient, while avoiding the introduction of impurities into the product during the purification process due to improper solvent selection; As an option, using anhydrous ethanol as the initial dissolving solvent and then adding n-hexane to reduce the solubility to precipitate NEPA crystals is a simple and efficient purification scheme. Specifically, after the reaction mixture is rotary evaporated to remove most of the solvent, the crude NEPA is dissolved in anhydrous ethanol, and then n-hexane is gradually added to precipitate crystals. This operation can significantly reduce the residual organic impurities; In some embodiments, in order to further improve the purity, the precipitated crystals may be subjected to a secondary recrystallization operation, for example, a mixed solvent system of ethyl acetate and n-hexane is selected to increase the uniformity and purity of the crystals while lowering the dissolution temperature; In this example, the crude NEPA (about 25 g) obtained from the reaction system was first added to 100 mL of anhydrous ethanol, stirred and heated until completely dissolved, and the dissolution temperature was controlled between 40° C. and 50° C. The amount of solvent used was usually 4 times the quality of the crude NEPA, and the specific amount could be adjusted according to the degree of solubility; As an option, ethyl acetate can also be used as a dissolving solvent, and its dosage can be controlled in the range of 3 to 5 times the crude quality. Compared with ethanol, ethyl acetate has stronger dissolving performance, but its boiling point is higher, which may lead to a lower removal efficiency of the solvent residue, so it is suitable for secondary crystallization under specific circumstances; Specifically, the completely dissolved NEPA crude solution is cooled to room temperature (20°C to 25°C), 200 mL of n-hexane (the volume ratio of ethanol to n-hexane is 1:2) is gradually added, and stirred evenly to promote crystal precipitation. The amount of n-hexane added is generally 1.5 to 3 times the volume of the dissolving solvent (ethanol), and the specific amount can be adjusted according to the saturation of the solution; In a possible implementation, the solution may be placed at a low temperature of 10° C. to 15° C. during the cooling process to further increase the crystal precipitation rate and reduce the possibility of the solvent carrying impurities.

[0032] In this embodiment, the precipitated crystals are further purified by washing and drying: the precipitated crystals are collected by filtration through a filter membrane, and the impurities on the surface of the crystals are washed with 30 mL of anhydrous ethanol. The amount of washing liquid used is usually 1 to 2 times the mass of the crystals. In some embodiments, a small amount of a mixture of n-hexane and ethanol (volume ratio 1:1) can be added as a washing solvent to further remove adsorbed impurities.

[0033] The washed crystals are vacuum dried at a temperature of 40°C to 50°C for 2 to 3 hours, and finally NEPA with a purity of 98% to 99% is obtained; Some extended technical contents include: during the precipitation process, the rapid formation of crystals can be induced by adding seed crystals (such as purified NEPA crystals, the addition amount is 1% to 2% of the crude quality), while controlling the uniformity of the crystal particle size; for crude NEPA with high impurity content, a secondary crystallization process can be used, that is, the crystals precipitated for the first time are dissolved again in a mixed solvent of ethyl acetate and n-hexane (volume ratio is 2:1), and allowed to stand for recrystallization at 15°C to 20°C; during the vacuum drying process, the solvent that may remain inside the crystals can be further reduced by gradually increasing the temperature (such as gradually increasing from 40°C to 50°C); through the above-mentioned specific implementation methods, technicians can adjust parameters and process steps according to actual needs to meet the requirements of industrial production for product purity and operating efficiency.

[0034] Example 1: NEPA preparation process based on UV-1 waste residue Step 1: Pretreatment of UV-1 waste residue 100 g of UV-1 waste residue was added to 500 mL of anhydrous ethanol (weight ratio 1:5), and stirred and dissolved at 50 ° C for 1 hour to ensure that NE and NET in the waste residue were completely dissolved. After cooling to room temperature, 1500 mL of n-hexane (volume ratio 3:1) was added, and the mixture was allowed to stand for 30 minutes before stratification. The upper n-hexane phase (mainly containing NE) and the lower ethanol phase (mainly containing NET) were collected.

[0035] The n-hexane phase was concentrated by rotary evaporation to 1 / 5 of its volume, and NE crystals were precipitated by cooling at 0-5°C. After washing with 100 mL of anhydrous ethanol, vacuum drying was performed to obtain NE (60 g) with a purity of 95%. 300 mL of ethyl acetate was added to the ethanol phase, and liquid-liquid extraction was performed 3 times, and NET (20 g) with a purity of 93% was obtained by rotary evaporation.

[0036] Step 2: Preparation of intermediate NE 20 g (0.1 mol) of ethyl p-aminobenzoate and 21.5 g (0.11 mol) of trialkyl orthoformate were added to 100 mL of anhydrous ethanol, stirred evenly, and then 0.5 g of aluminum chloride was added as a catalyst. After reacting at 50°C for 1.5 hours, the mixture was cooled to room temperature, and a saturated sodium carbonate solution (mass ratio 5%) was added to neutralize the mixture to pH 7. The mixture was extracted with 100 mL of ethyl acetate for 3 times, and concentrated by rotary evaporation to obtain NE (90% purity, 18 g).

[0037] Step 3: N-alkylation reaction 18 g (0.09 mol) NE and 14.4 g (0.10 mol) benzyl chloride were added to 90 mL anhydrous ethanol, and 1.8 g K2CO3 was added as an alkaline catalyst, and the mixture was stirred at 70°C for 3 hours. After the reaction was completed, the mixture was cooled to room temperature, washed with 270 mL cold water for 3 times, extracted with 100 mL ethyl acetate for 3 times, and concentrated by rotary evaporation to obtain crude NEPA (25 g).

[0038] Step 4: Recycling of by-product NET 10g (0.04mol) NET and 4.8g (0.04mol) benzyl chloride were added to 50mL anhydrous ethanol, and 0.5g trifluoroacetic acid was added as a catalyst, and the mixture was reacted at 70°C for 2.5 hours. After neutralization with 150mL cold water, 100mL ethyl acetate was added for extraction 3 times, and crude NEPA (10g) was obtained by rotary evaporation.

[0039] Step 5: Isolation and purification of the final product The crude NEPA (35 g) was dissolved in 100 mL of anhydrous ethanol, and 200 mL of n-hexane was gradually added, and the mixture was stirred at 20° C. to crystallize. The crystals were filtered, washed with 30 mL of anhydrous ethanol, and dried in vacuo at 40° C. to obtain NEPA (30 g) with a purity of 98%.

[0040] Example 2: Preparation of NEPA using ethyl acetate as solvent Step 1: Pretreatment of UV-1 waste residue 120g of UV-1 waste residue was added to 600mL of ethyl acetate, stirred and dissolved at 60°C for 2 hours, cooled to room temperature, and 2000mL of n-hexane (volume ratio 1:3) was added. After standing for 60 minutes, the mixture was separated into layers. The upper n-hexane phase was collected and concentrated by rotary evaporation to obtain NE crystals (purity 97%, 70g). The lower ethyl acetate phase was extracted 3 times and then rotary evaporated to obtain NET (purity 92%, 25g).

[0041] Step 2: Preparation of intermediate NE 25 g (0.125 mol) of ethyl p-aminobenzoate and 26.8 g (0.14 mol) of trialkyl orthoformate were added to 150 mL of ethyl acetate, and 1.0 g of zinc chloride was added as a catalyst, and the mixture was reacted at 60° C. for 2 hours. After cooling, the mixture was neutralized with sodium carbonate solution to pH 8, extracted with ethyl acetate for 4 times, and concentrated by rotary evaporation to obtain NE (purity 94%, 22 g).

[0042] Step 3: N-alkylation reaction 22 g NE and 18 g benzyl chloride were added to 120 mL ethyl acetate, 2.0 g NaOH was added as a catalyst, and the mixture was reacted at 80°C for 4 hours. After cooling, the mixture was washed with cold water 4 times, extracted with 150 mL ethyl acetate, and rotary evaporated to obtain crude NEPA (35 g).

[0043] Step 4: Recycling of by-product NET 15 g of NET and 8 g of benzyl chloride were added to 80 mL of ethyl acetate, and 1.2 g of p-toluenesulfonic acid was added. The mixture was reacted at 75° C. for 3 hours, and then extracted after neutralization with saturated sodium chloride solution. The crude NEPA (15 g) was obtained by rotary evaporation.

[0044] Step 5: Isolation and purification of the final product The crude NEPA (50 g) was dissolved in 200 mL of ethyl acetate, and 400 mL of n-hexane was added. The mixture was stirred at room temperature for 30 minutes to crystallize. After filtering, the crystals were washed with a mixed solvent (ethyl acetate and n-hexane, volume ratio 1:1). After drying, NEPA (45 g) with a purity of 98% was obtained.

[0045] Example 3: Cooling crystallization method to improve NEPA purity Step 1: Pretreatment of UV-1 waste residue 80g of UV-1 waste residue was added to 400mL of anhydrous ethanol, stirred and dissolved at 50°C for 1 hour, cooled and added with 1200mL of n-hexane, allowed to stand for 30 minutes and then separated, the upper n-hexane phase was collected and rotary evaporated to obtain NE crystals (purity 95%, 50g). NET (20g) was obtained by extraction of the ethanol phase.

[0046] Step 2: Preparation of intermediate NE 18 g of ethyl p-aminobenzoate and 19 g of trialkyl orthoformate were added to 100 mL of anhydrous ethanol, and 0.6 g of aluminum chloride was added. The mixture was reacted at 55° C. for 1.5 hours, and NE (purity 93%, 16 g) was obtained by extraction with ethyl acetate.

[0047] Step 3: N-alkylation reaction 16 g NE and 12 g benzyl chloride were added to 90 mL ethyl acetate, and 1.5 g K2CO3 was added. The mixture was stirred at 75°C for 3 hours. After cooling, the mixture was washed with cold water and ethyl acetate respectively to obtain a crude NEPA product (20 g).

[0048] Step 4: Recycling of by-product NET 12 g NET and 5 g benzyl chloride were added to 60 mL anhydrous ethanol, and 0.8 g trifluoroacetic acid was added as a catalyst. The mixture was reacted at 70° C. for 2 hours, and a crude NEPA product (10 g) was obtained by rotary evaporation.

[0049] Step 5: Isolation and purification of the final product The crude NEPA (30 g) was dissolved in 150 mL of ethyl acetate, gradually cooled to 10°C, and 300 mL of n-hexane was added to precipitate crystals at low temperature. The crystals were filtered and washed with anhydrous ethanol, and dried to obtain NEPA (28 g) with a purity of 99%.

[0050] Comparative Example 1: Direct treatment of UV-1 waste residue This comparative example does not use the solvent dissolution and separation technology of the present invention, but uses a direct dissolution method for processing: 100 g of UV-1 waste residue was directly added to 400 mL of anhydrous ethanol and stirred at room temperature (25°C) for 1 hour without further cooling or precipitation with n-hexane; The solution was directly subjected to liquid-liquid extraction three times with 300 mL of ethyl acetate, and a crude product (mainly a mixture of NE and impurities) was obtained after rotary evaporation; The ethanol phase was further concentrated by rotary evaporation to obtain a residue (mainly NET) without further purification.

[0051] Comparative Example 2: Preparation of Intermediate NE This comparative example uses catalysts and reaction conditions that are not optimized in the prior art: 20 g of ethyl p-aminobenzoate and 22 g of trialkyl orthoformate were added to 100 mL of anhydrous ethanol. Instead of using Lewis acid catalyst, NaOH was used as a catalyst, and the amount of catalyst was 1% of the total mass of the reactants. After reacting at 45°C for 2 hours, the mixture was cooled to room temperature, and the system was neutralized with water and then directly extracted; After extraction with 100 mL of ethyl acetate three times, the crude intermediate NE was obtained by rotary evaporation without subsequent purification.

[0052] Comparative Example 3: Conventional process of N-alkylation reaction (corresponding to Example 3) This comparative example uses conventional solvents and unoptimized reaction conditions in the prior art: 18 g NE and 15 g benzyl chloride were added to 100 mL toluene without using a basic catalyst; The reaction time was relatively long after stirring at 80°C for 4 hours and then cooling directly; Directly extract the mixture in layers with 300 mL of cold water without adding ethyl acetate to purify the organic phase; The organic phase was rotary evaporated to obtain crude NEPA without further purification.

[0053] Comparative Example 4: Treatment of byproduct NET (corresponding to Example 4) This comparative example does not use NET as a resource, but chooses a simple by-product disposal solution: The extracted NET (10 g) was not reacted with benzyl chloride but was directly discarded; In the experiment, only the main product NEPA was obtained through separation means, and there was no related process operation for recycling of any by-products.

[0054] Comparative Example 5: Separation and purification of the final product This comparative example uses an unoptimized separation and purification process; The crude NEPA product is directly distilled under reduced pressure to remove the solvent without a crystal precipitation step; Instead of using a mixed solvent system of n-hexane and ethanol, crystallization was attempted using only a single solvent of ethanol; After standing for 1 hour at room temperature (25°C) for crystallization, the product was directly filtered without low temperature treatment and subsequent recrystallization operation.

[0055] Experiment 1: Test on the efficiency of resource utilization of UV-1 waste residue Experimental steps: Sample processing: Take 100 g of UV-1 waste residue, add 500 mL of anhydrous ethanol according to the method of Example 1, and stir at 50° C. for 1 hour to dissolve NE and NET.

[0056] After the solution was cooled to room temperature, 1500 mL of n-hexane (volume ratio of 3:1) was added, and the mixture was allowed to stand for 30 minutes before stratification. The n-hexane phase was collected and concentrated by rotary evaporation, and crystallized by cooling at 0-5°C to obtain NE crystals, which were washed with anhydrous ethanol, dried in vacuo, and weighed for determination.

[0057] The ethanol phase was added with 300 mL of ethyl acetate for liquid-liquid extraction three times, and then concentrated by rotary evaporation to obtain NET crystals.

[0058] Comparative treatment: Take the same 100g UV-1 waste residue, and directly add 400mL anhydrous ethanol according to the method of Comparative Example 1, and stir at 25°C for 1 hour without further cooling operation.

[0059] Direct liquid-liquid extraction was performed three times with 300 mL of ethyl acetate, and the mixed product was collected after rotary evaporation and concentration, and the quality and purity of NE and NET were determined.

[0060] Determination indicators: The isolated yields of NE and NET (actual extracted mass / theoretical mass × 100%).

[0061] The purity of NE and NET was determined by high performance liquid chromatography (HPLC).

[0062] Comparison of resource utilization efficiency of NE and NET in UV-1 waste residue This experiment verified that the optimization of solvent selection and separation process in Example 1 significantly improved the resource utilization efficiency of UV-1 waste residue. Through the combined process of low-temperature crystallization and n-hexane precipitation, the separation yields of NE and NET were increased to more than 93%. At the same time, HPLC results showed that the purity of NE extracted in Example 1 reached 96.8%, and the purity of NET was 94.5%, which were significantly higher than the extraction results of Comparative Example 1; At high temperatures, the solubility of NE in ethanol is too high, and direct concentration may cause impurities to precipitate together. Low-temperature cooling effectively reduces the solubility of NE, allowing it to selectively crystallize. Compared with the simple room-temperature extraction in Comparative Example 1, the introduction of n-hexane also further enhances the stratification effect and reduces the interaction of impurities between solvents. Mechanistically, this stratified precipitation effectively utilizes the significant difference in polarity between n-hexane and ethanol, thereby maximizing the purity of the target product; However, this improvement is not only the result of solvent selection, but also the control of stirring and standing time is equally important. For the separation of NET, the extraction of ethyl acetate is better than the direct concentration in the ethanol system. The extraction efficiency of the solvent plays a decisive role in this process. These minor process changes are not reflected in Comparative Example 1, resulting in waste of resources and substandard product quality.

[0063] The above experimental results show that through the optimized solvent system and precise process control, Example 1 not only improves the resource utilization efficiency, but also significantly improves the quality of the target product.

[0064] Experiment 2: Preparation selectivity test of intermediate NE Experimental steps: Operation of Example 2: Take 20 g (0.1 mol) of ethyl p-aminobenzoate and 21.5 g (0.11 mol) of trialkyl orthoformate, and add 100 mL of anhydrous ethanol as the reaction solvent.

[0065] 0.5 g of aluminum chloride (Lewis acid catalyst) was added under stirring and stirred evenly.

[0066] The reaction was carried out at 50°C for 1.5 hours, and the reaction progress was monitored. After the reaction was completed, the mixture was cooled to room temperature and neutralized to pH 7 with saturated sodium carbonate solution.

[0067] The product was extracted with 100 mL of ethyl acetate three times, and NE was collected after rotary evaporation. The yield of NE and the content of byproduct (NET) were determined.

[0068] Operation of Comparative Example 2: The same raw materials and solvents as in Example 2 (20 g of ethyl p-aminobenzoate, 21.5 g of trialkyl orthoformate, and 100 mL of anhydrous ethanol) were used.

[0069] NaOH (0.5 g, 1% of the total mass of the reactants) was used as a catalyst and the reaction was carried out at 45° C. for 2 hours.

[0070] After the reaction, NE was directly neutralized and extracted with water without further optimization of the reaction conditions. After collecting NE, its yield and the content of the byproduct (NET) were determined.

[0071] Test items: NE yield: the ratio of actual NE production to theoretical production (%).

[0072] The amount of by-product NET generated: The mass fraction (%) of NET in the product was detected by HPLC.

[0073] Comparison of preparation efficiency and selectivity of intermediate NE It can be clearly seen from the experiment that the NE yield in Example 2 is significantly higher than that in Comparative Example 2, while the amount of byproduct NET generated is less. This result is mainly due to the specific catalytic selectivity of the Lewis acid catalyst for the condensation reaction. Compared with the NaOH catalyst, aluminum chloride can more efficiently activate the carbonyl group of trialkyl orthoformate, enhance the nucleophilic attack ability of ethyl p-aminobenzoate, and thus improve the reaction efficiency; Example 2 uses 50°C as the reaction temperature. Under this condition, the catalytic activity of Lewis acid can be fully exerted, while avoiding the occurrence of side reactions at too high a temperature. Although the use of NaOH catalyst in Comparative Example 2 has a certain promoting effect, its selectivity for the condensation reaction is low, resulting in a significant increase in NETs generated by side reactions; Example 2 reduces the generation of NET by selecting a suitable catalyst and optimizing the reaction conditions, thereby simplifying the subsequent treatment process. In contrast, Comparative Example 2 does not fully consider the inhibitory effect of catalyst selection on side reactions, resulting in waste of resources and reduced process efficiency. The experimental results fully verify the superiority of the technical solution of the present invention in terms of reaction selectivity and product purity.

[0074] Experiment 3: N-alkylation reaction yield and selectivity test Experimental steps: Operation of Example 3: Take 18 g (0.09 mol) of NE and 14.4 g (0.10 mol) of benzyl chloride, add 90 mL of anhydrous ethanol as solvent, and add 1.8 g of K2CO3 as a basic catalyst under stirring conditions.

[0075] The reaction mixture was heated to 70° C. and stirred for 3 hours. During this period, samples were taken every 30 minutes and HPLC was used to detect the conversion rate of NE and the formation of by-products.

[0076] After the reaction is completed, the mixture is cooled to room temperature, 270 mL of cold water is added for washing, and the organic phase is obtained by liquid-liquid separation. The organic phase is further extracted three times with 100 mL of ethyl acetate. The crude NEPA is obtained after rotary evaporation and concentration, and the actual mass of NEPA is recorded and purity is tested.

[0077] Operation of Comparative Example 3: Take 18 g (0.09 mol) of NE and 15 g (0.10 mol) of benzyl chloride, add 100 mL of toluene as solvent, and do not add any catalyst.

[0078] The reaction was carried out at 80°C for 4 hours, and samples were taken every hour to detect the NE conversion rate and the formation of side reactions.

[0079] After the reaction was completed, the mixture was directly washed with 300 mL of cold water, and the organic phase was obtained by liquid-liquid separation. The crude NEPA was obtained after rotary evaporation and concentration, and the actual mass and by-product content were determined.

[0080] Test items: The yield of NEPA is: the mass of NEPA actually produced / theoretical mass × 100%.

[0081] Types and contents of by-products: The mass fraction (%) of by-products was analyzed by GC-MS.

[0082] Comparison of N-alkylation reaction yield and by-product content The experimental results show that under the conditions of optimizing the solvent and the catalyst in Example 3, the yield of NEPA is significantly improved, and the types and contents of by-products are significantly reduced. The core of this is that the use of the alkaline catalyst K2CO3 has a selective promoting effect on the N-alkylation reaction. The catalyst can accelerate the nucleophilic attack of NE by stabilizing the electrophilic center in benzyl chloride, thereby increasing the generation rate of the target product. In addition, the choice of solvent is also crucial. In Example 3, anhydrous ethanol is used as the reaction solvent, which not only provides a good reaction medium, but also reduces the accumulation of by-products during the reaction. Although toluene in Comparative Example 3 can dissolve the reactants, it fails to effectively inhibit the side reactions at high temperatures, resulting in the generation of a variety of impurities. This shows that the polarity of the solvent has a direct impact on the reaction path. Non-polar solvents lack selectivity control and are difficult to achieve the same effect. In Example 3, the moderate reaction temperature (70° C.) and the short reaction time (3 hours) ensured the completion of the efficient reaction while avoiding the excessive alkylation of NE due to the long reaction time. However, the high temperature (80° C.) and the long reaction time (4 hours) of Comparative Example 3 resulted in the generation of more impurities. The above results fully verify the significant advantages of the technical solution of Example 3 in terms of reaction yield and selectivity control.

[0083] Experiment 4: Testing the recycling efficiency of byproduct NET Experimental steps: Operation of Example 4: Take 10 g (0.04 mol) of the by-product NET and 4.8 g (0.04 mol) of benzyl chloride, and add 50 mL of anhydrous ethanol as a solvent.

[0084] Under stirring conditions, 0.5 g of trifluoroacetic acid (1.5% of the total mass of the reactants) was added as a catalyst.

[0085] The mixture was heated to 70°C and reacted for 2.5 hours. Samples were taken every 30 minutes during the reaction and the conversion rate of NET was detected by HPLC.

[0086] After the reaction was completed, the mixture was cooled to room temperature, 150 mL of cold water was added for neutralization, the organic phase was separated, and the organic phase was extracted three times with 100 mL of ethyl acetate, and concentrated by rotary evaporation to obtain crude NEPA.

[0087] Operation of Comparative Example 4: 10 g (0.04 mol) of the by-product NET was extracted and directly discarded without any conversion or resource utilization of the NET.

[0088] Only the NEPA produced by the original N-alkylation reaction was purified and analyzed to determine the total NEPA production when NET was not utilized.

[0089] Test items: Additional NEPA generation: The mass of NEPA generated through recycling of by-product NET.

[0090] NET conversion rate: the conversion efficiency of by-product NET in the reaction system (%).

[0091] Effect of recycling of byproduct NET on NEPA production The experimental data clearly demonstrates the efficient resource utilization effect of Example 4 on the by-product NET. The by-product NET reacts with benzyl chloride to generate additional NEPA, which significantly increases the total yield of NEPA. The core mechanism lies in the catalytic effect of trifluoroacetic acid, which not only enhances the electrophilicity of benzyl chloride, but also activates the imine group in the NET molecule, improving the reaction selectivity. This dual catalytic effect effectively avoids the occurrence of side reactions and ensures high conversion rate and high yield of additional NEPA; at the same time, the experiment also shows that the use of anhydrous ethanol ensures the stability of solubility and has a significant impact on the reaction path. By optimizing the solvent system, NET can participate in the reaction more efficiently in the solution. In contrast, the direct disposal of NET in Example 4 not only wastes resources, but also causes the NEPA yield to be lower than the theoretical level; the waste of resources and the increase in environmental burden reflect the defects of the existing process in recycling; The high conversion rate of NET in Example 4 (94.8%) is due to the precise control of reaction conditions, including the amount of catalyst and the reaction time, which together construct an efficient byproduct resource recovery path. In contrast, in Comparative Example 4, NET was not used as a secondary raw material, which not only failed to increase the yield of the target product, but also lost the opportunity for resource recycling. This comparison further proves the industrial application value of the present invention in terms of resource utilization and economy.

[0092] Experiment 5: Separation and purification efficiency test of NEPA Experimental steps: Operation of Example 5: The crude NEPA (30 g) was dissolved in 150 mL of anhydrous ethanol, and the mixture was heated to 50°C with stirring to completely dissolve the crude product.

[0093] After complete dissolution, the temperature was gradually lowered to 20°C, and 300 mL of n-hexane (the volume ratio of ethanol to n-hexane was 1:2) was added in batches under stirring, and slow stirring was maintained to promote crystal precipitation.

[0094] The reaction system was further cooled to 10°C, allowed to stand for 1 hour, and then filtered to collect the precipitated crystals.

[0095] The crystals were washed twice with 50 mL of anhydrous ethanol and then dried under vacuum at 40°C. The purity, crystal morphology and total yield of NEPA were determined.

[0096] Operation of Comparative Example 5: The same amount of crude NEPA (30 g) was directly dissolved in 100 mL of anhydrous ethanol without heating and allowed to stand at room temperature (25° C.) to precipitate crystals without adding n-hexane or low-temperature treatment.

[0097] After standing for 1 hour, the crystals were filtered without washing and directly dried to determine the purity, crystal morphology and total yield of NEPA.

[0098] Test items: Purity of NEPA: The NEPA content (%) in the crystals was determined by high performance liquid chromatography (HPLC).

[0099] Residual solvent content: The mass (%) of the residual solvent in the crystals was determined by gas chromatography (GC).

[0100] Crystal morphology: X-ray diffraction (XRD) was used to examine the integrity and crystallinity of the crystals.

[0101] Comparison of NEPA purification effects The experimental results show that the optimized use of solvents and precise control of temperature in the separation and purification process of Example 5 improve the purity and crystal quality of NEPA. The mixed solvent system of n-hexane and anhydrous ethanol plays an important role in the crystal precipitation stage. The low polarity of n-hexane effectively reduces the solubility of NEPA in the solution, thereby accelerating the crystal precipitation process and reducing the impurity entrainment in the solution. The low-temperature static operation further improves the crystallinity and uniformity of the crystals, which is not reflected in Comparative Example 5; In addition, in Example 5, the ethanol washing step significantly reduced the residual solvent, reducing the residual amount from 1.5% in Comparative Example 5 to 0.2%. The unwashed crystals of Comparative Example 5 not only had a high residual solvent, but also made it difficult for the product purity to meet the standard. Mechanistically, the residual solvent and impurities on the surface of the crystals can form weak bond interactions with the target product, thereby affecting the chemical stability and optical properties of the final product. In Example 5, by low temperature control and step-by-step addition of n-hexane, the crystallinity of NEPA crystals reached 95.8%, indicating that the internal structure of the crystals was more orderly. However, due to the lack of solvent coordination and temperature optimization, the precipitated crystals in Comparative Example 5 showed an obvious non-uniform state, and the crystallinity was only 84.3%. These differences clearly reveal the profound impact of the solvent system and operating conditions on the quality of the target product, thereby verifying the purification effect of the present invention on NEPA, and at the same time providing a more feasible optimization path for industrial production.

[0102] 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,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1, characterized in that: The following steps are involved: Pretreatment of UV-1 waste residue to separate NE and NET by solvent dissolution, precipitation separation and liquid-liquid extraction; Preparation of intermediate NE, by condensing ethyl p-aminobenzoate with trialkyl orthoformate to obtain NE; N-alkylation reaction, by reacting NE with benzyl chloride under basic catalytic conditions to produce N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine; The byproduct NET is recycled to generate the target product N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine by reacting with benzyl chloride; The final product is separated and purified by crystallization and washing to obtain the target product with satisfactory purity.

2. The method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1 according to claim 1, characterized in that: The pretreatment of the UV-1 waste residue comprises: Mix the waste residue with anhydrous ethanol in a weight ratio of 1:3 to 1:6, and stir and dissolve at 50° C. to 60° C. for 1 to 2 hours; After cooling to 20° C. to 25° C., add n-hexane, the volume ratio of n-hexane to ethanol solution is 2:1 to 4:1, and stand for stratification for 30 to 60 minutes; The n-hexane phase was separated and concentrated to 1 / 5 to 1 / 10 of the volume, and then cooled to 0°C to 5°C to precipitate NE crystals.

3. The method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1 according to claim 1, characterized in that: The extraction of NE includes: NE was separated using a mixed solvent of n-hexane and ethanol, with a volume ratio of n-hexane to ethanol ranging from 2:1 to 4:1; Wash the NE crystal with anhydrous ethanol, the washing amount being 2 to 3 times the mass of the NE crystal; After vacuum drying, NE with a purity of 95% to 98% was obtained.

4. The method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1 according to claim 1, characterized in that: The preparation of the intermediate NE comprises: The molar ratio of ethyl p-aminobenzoate to trialkyl orthoformate is 1:1 to 1:1.2; The solvent is anhydrous ethanol, and the amount of the solvent is 5 to 10 times the total mass of the reactants; The amount of Lewis acid catalyst used is 1% to 5% of the total mass of the reactants, the reaction temperature is 50° C. to 60° C., and the reaction time is 1.5 hours to 2 hours.

5. The method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1 according to claim 1, characterized in that: The N-alkylation reaction comprises: The molar ratio of NE to benzyl chloride is 1:1 to 1:1.2; The reaction solvent is anhydrous ethanol or ethyl acetate, and the amount of the solvent is 3 to 8 times the total mass of the reactants; The amount of the base catalyst used is 1% to 5% of the total mass of the reactants, the reaction temperature is 60° C. to 80° C., and the reaction time is 2 hours to 4 hours.

6. The method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1 according to claim 1, characterized in that: The recycling of NET includes: The molar ratio of extracted NET to benzyl chloride was 1:1 to 1:1.2; The reaction solvent is anhydrous ethanol, and the catalyst is trifluoroacetic acid or other acidic catalysts, and the amount used is 1% to 3% of the total mass of the reactants; The reaction temperature is 70°C to 80°C, and the reaction time is 2 hours to 3 hours.

7. The method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1 according to claim 1, characterized in that: The separation and purification of the final product comprises: The crude product was dissolved in ethanol, and n-hexane was added to form a mixed solution with a volume ratio of 1:2 to 1:3; Allow to stand at 20°C to 30°C to precipitate crystals; The crystals are filtered and washed with ethanol, and finally purified to obtain the target product with a purity of 98% to 99%.

8. The method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1 according to claim 1, characterized in that: The composition of the UV-1 waste residue includes: NE accounts for 40% to 60%; NET accounts for 15% to 30%; Other insoluble impurities account for 5% to 15%.

9. The method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1 according to claim 1, characterized in that: The liquid-liquid extraction step comprises: Using ethyl acetate as the extraction solvent, the volume ratio of ethyl acetate to ethanol solution is 1:2 to 1:4; The extraction times range from 3 to 5 times, and the organic phase containing NET is separated.

10. The method for preparing N,N′-bis(4-ethoxycarbonylphenyl)-N′-benzylformamidine using waste residue from the production of UV-1 according to claim 1, characterized in that: The neutralization treatment after the condensation reaction comprises: Add saturated sodium carbonate solution, the amount of sodium carbonate is 1% to 5% of the mass of the reaction solution; The pH of the system was adjusted to 7 to 8 by neutralization reaction, and the generated NE was separated after extraction with ethyl acetate.

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