Efficient synthesis method of low-byproduct polymerization inhibitor DNBP

Abstract

The invention discloses an efficient synthesis method of a low-byproduct polymerization inhibitor DNBP, and relates to the technical field of polymerization inhibitor synthesis. The method comprises the following steps: firstly preparing PVP-PS / [BMIM] NO3 composite microspheres, then dispersing o-sec-butyl phenol and the composite microspheres in ethyl acetate, adding 40%-45% nitric acid (molar ratio of 1: (2.0-2.2)), reacting at 40 DEG C and 500-700r / min for 5 hours, and carrying out post-treatment and crystallization to obtain the product. The composite microspheres achieve a synergistic effect through heat conduction and temperature control of PS cores, oriented enrichment of PVP shell layers and regulation and control of nitric acid release by [BMIM] NO3. The method solves the problems of many byproducts and low nitric acid utilization rate in the traditional process, and meets the requirements of clean production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polymerization inhibitor synthesis, and particularly relates to a high-efficiency synthesis method of low-byproduct polymerization inhibitor DNBP. BACKGROUND

[0002] DNBP (2,4-dinitro-6-sec-butyl phenol) is an important phenolic polymerization inhibitor, which is widely used in the storage and polymerization process of olefin monomers such as acrylate and methacrylate due to its good polymerization inhibition activity and thermal stability, and can effectively inhibit the self-polymerization of monomers to ensure the continuity of production and product quality. At present, the synthesis of DNBP in industry mainly adopts the direct nitration method of o-sec-butyl phenol and nitric acid, that is, 35%-45% nitric acid is used as a nitration agent in an autoclave, and the nitration reaction is carried out by controlling the temperature.

[0003] However, the existing synthesis method has two core defects: (1) Many byproducts and low purity: nitric acid has both nitration and oxidation effects, and the hydroxyl oxidation of o-sec-butyl phenol and the nitro dislocation substitution (such as 2,6-dinitro-4-sec-butyl phenol) are easily caused in the reaction, which leads to the purity of DNBP product being usually lower than 80%, and the product needs to be purified for many times, which not only consumes time but also causes yield loss.

[0004] (2) Low utilization rate of nitric acid and large pollution: the molar ratio of o-sec-butyl phenol to nitric acid in the existing process is as high as 1:2.7-2.8, and the excess nitric acid cannot be fully reacted, the waste nitric acid formed can be recovered by adjustment, but the impurities accumulated after multiple cycles will further aggravate the side reactions; at the same time, the unrecycled nitric acid remains in the wastewater system, which has high treatment cost and is easy to cause equipment corrosion and environmental risk.

[0005] Therefore, it is of great significance to develop a new method for synthesizing DNBP that can inhibit side reactions and improve the utilization rate of nitric acid, so as to reduce production cost and improve product competitiveness. SUMMARY

[0006] In view of the defects of the existing "o-sec-butyl phenol direct nitration method" for synthesizing DNBP, such as many byproducts and low utilization rate of nitric acid, the application provides a high-efficiency synthesis method of low-byproduct polymerization inhibitor DNBP, which realizes the high-efficiency synthesis of low-byproduct and high-purity DNBP through the synergistic effect of "limited nitration-nitric acid regulation" of PVP-PS / [BMIM]NO3 composite microspheres.

[0007] To achieve the above purpose, the application provides the following technical scheme: A high-efficiency synthesis method of low-byproduct polymerization inhibitor DNBP, the operation steps of the preparation method are as follows: S1, Preparation of PVP-PS / [BMIM]NO3 composite microspheres: 0.5-1.5 g of PS microspheres were dispersed in 50-80 mL of N,N-dimethylformamide and ultrasonically dispersed for 15 min until uniform; 1-3 g of PVP (polyvinylpyrrolidone K-30) and 0.8-2 g of azobisisobutyronitrile were added, and the reaction was carried out under nitrogen protection; PVP was grafted onto the surface of the PS microspheres by free radical polymerization to form PVP-PS core-shell microspheres; the core-shell microspheres were dispersed in 30-50 mL of ethanol, 0.5-1.2 g of [BMIM]NO3 (1-butyl-3-methylimidazolium nitrate) was added dropwise, and stirring was carried out at 50°C for 3 h to load the ionic liquid on the PVP shell; after centrifugation and vacuum drying, PVP-PS / [BMIM]NO3 composite microspheres were obtained; S2, Preparation of the reaction system: 5-10 g of o-sec-butyl phenol was added to an autoclave, 30-40 mL of ethyl acetate was added, and stirring was carried out until complete dissolution; 0.3-0.8 g of PVP-PS / [BMIM]NO3 composite microspheres was added, and stirring was carried out for 10 min to disperse the system uniformly; S3, Nitration reaction: 40%-45% by mass of nitric acid was added dropwise to the autoclave, the molar ratio of o-sec-butyl phenol to nitric acid was controlled to be 1:2.0-2.2, the temperature was raised to 40°C, and the reaction was carried out under magnetic stirring; S4, Post-reaction treatment; S5, Product purification.

[0008] The composite microspheres have a core-shell structure, with polystyrene (PS) as the core and polyvinylpyrrolidone (PVP) as the shell, and the shell layer is grafted with 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]NO3) ionic liquid. The structural design is the basis for realizing the synergistic functions of "catalysis-temperature control-limitation-recovery".

[0009] The core layer (PS microspheres) serves as a support framework to maintain the stable morphology of the composite microspheres and prevent the loss of structural integrity due to swelling or high-temperature degradation during the reaction; at the same time, it utilizes its excellent thermal conductivity to quickly disperse the local heat generated by the nitration reaction, preventing a sudden temperature rise that can trigger oxidative side reactions.

[0010] The shell layer (PVP segment) binds to the hydroxyl groups of o-sec-butyl phenol through hydrogen bonds, enriching o-sec-butyl phenol in the shell layer of the microspheres and forming a "local high-concentration reaction zone"; at the same time, the steric hindrance of the PVP segment can direct the exposure of active sites of o-sec-butyl phenol, guiding the preferential attack of nitrate ions on the target sites and inhibiting the nitro misplacement substitution side reaction.

[0011] Active component ([BMIM]NO3 ionic liquid): loaded in PVP shell, the release rate of nitrate ions is controlled by the coordination of imidazole ring cations to avoid excessive local nitric acid concentration leading to oxidative side reactions; at the same time, the presence of ionic liquid can enhance the solubility of nitric acid in organic phase, improve the efficiency of nitration reaction, and reduce the amount of nitric acid.

[0012] Oriented nitration inhibits side reactions: the dual action of "enrichment-steric hindrance" of PVP shell makes the 2 and 4 positions of o-sec-butyl phenol preferentially react with controllably released nitrate ions, significantly reducing the content of mispositioned nitration and oxidative byproducts, and the product purity is increased from 79.5% in traditional process to more than 89.2%.

[0013] Reducing the amount of nitric acid and recycling: the catalytic synergy of [BMIM]NO3 reduces the amount of nitric acid by 20%-25% (molar ratio from 1:2.7 to 1:2.2 or less); the recovered nitric acid in aqueous phase can be reused after simple adjustment.

[0014] Avoiding excessive alkylation: the steric hindrance of PVP shell limits the generation of DNBP near the active site, and the weak acidity of ionic liquid cannot activate the aromatic ring of DNBP, blocking the third alkylation path.

[0015] Temperature control synergy: PS core can quickly disperse local heat; at the same time, the microspheres are uniformly dispersed under stirring, strengthening heat exchange, making the system temperature fluctuate less, and inhibiting temperature-sensitive side reactions.

[0016] Further optimization of the efficient synthesis method of a low byproduct polymerization inhibitor DNBP.

[0017] Preferably, in step S1, the particle size of the PS microspheres is 100-160 nm.

[0018] Preferably, in step S1, the temperature and time of vacuum drying are 50°C and 10 h, respectively.

[0019] Preferably, in step S1, the reaction temperature under nitrogen protection is 60-70°C, and the reaction time is 4-6 h.

[0020] Preferably, in step S3, the incubation reaction time is 5 h, and the magnetic stirring rate is 500-700 r / min.

[0021] Preferably, in step S4, the operation of the reaction post-treatment is as follows: after the reaction is completed, the temperature in the kettle is lowered to room temperature by opening the condensate water, and the composite microspheres are recovered by filtration; the filtrate is transferred to a separatory funnel, and is allowed to stand and separate into layers, the water layer is the recovered liquid containing trace nitric acid, which can be recycled after being adjusted to 40% concentration by adding concentrated nitric acid, and the organic phase is the DNBP crude product solution.

[0022] Preferably, in step S5, the product purification operation is: removing ethyl acetate from the organic phase by reduced pressure distillation, the reduced pressure distillation temperature is 50 DEG C, to obtain a crude product; dissolving the crude product in 15-20 mL of ethanol, slowly cooling to crystallize, the cooling crystallization temperature is 0-5 DEG C, the crystallization time is 2 h, filtering, vacuum drying, to obtain a high-purity DNBP product.

[0023] The beneficial effects of the present application compared with the prior art are: (1) High product purity and yield improvement: through the "enrichment-hindrance" directional effect of PVP-PS / [BMIM]NO3 composite microspheres, the nitrate ions are precisely guided to attack the active site of o-sec-butyl phenol, effectively inhibiting the hydroxyl oxidation and nitro dislocation substitution side reactions, improving the product purity, and the product purity is improved from 79.5% of the traditional process to more than 89.2%.

[0024] (2) High nitric acid utilization rate and cost reduction: relying on the controllable release and solubilization effect of [BMIM]NO3 on nitrate ions, compared with the traditional method, the molar ratio of o-sec-butyl phenol to nitric acid is reduced from 1:2.7-2.8 to 1:2.0-2.2, and the amount of nitric acid is reduced by 20%-25%; and the recovered nitric acid in the aqueous phase can be recycled after simple adjustment, significantly reducing the raw material cost.

[0025] (3) Strong controllability and batch stability: the synergistic effect of the high efficient heat conduction of PS micro-nuclei and the uniform dispersibility of composite microspheres makes the reaction temperature fluctuate less, avoiding the side reactions caused by local overheating; at the same time, the immobilized active components ensure the stability of the catalytic performance. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a scanning electron microscope (SEM) photograph of the PVP-PS / [BMIM]NO3 composite microspheres prepared in Example 1; Figure 2 is a H-nuclear magnetic resonance chart of the polymerization inhibitor DNBP prepared in Example 1; 1 H nuclear magnetic chart; Figure 3 is the conversion rate of the polymerization inhibitor DNBP prepared in Examples 1-3 and Comparative Example 1 at different times; Figure 4 is the yield of the polymerization inhibitor DNBP prepared in Examples 1-3 and Comparative Example 1. DETAILED DESCRIPTION

[0027] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below. The following content is only an example and description of the concept of the present application. Those skilled in the art can make various modifications or supplements to the described specific implementation cases or replace them with similar ways without deviating from the concept of the present application, which should belong to the protection scope of the present application.

[0028] The above preparation method of the present application will be described below through specific examples and comparative examples.

[0029] Example 1 A high-efficiency synthesis method of low-by-product inhibitor DNBP, the operation steps of the preparation method are as follows: S1, preparation of PVP-PS / [BMIM]NO3 composite microspheres: 0.5 g of PS microspheres was dispersed in 50 mL of N,N-dimethylformamide, and ultrasonic dispersion was carried out for 15 min until uniform; 1 g of PVP and 0.8 g of azobisisobutyronitrile were added, and the reaction was carried out at 60°C under nitrogen protection for 4 h, so that PVP was grafted on the surface of PS microspheres through free radical polymerization to form PVP-PS core-shell microspheres; the core-shell microspheres were dispersed in 30 mL of ethanol, 0.5 g of [BMIM]NO3 was added dropwise, and stirring was carried out at 50°C for 3 h to load the ionic liquid on the PVP shell layer; after centrifugation and vacuum drying, PVP-PS / [BMIM]NO3 composite microspheres were obtained; S2, preparation of reaction system: 5 g of o-sec-butyl phenol was added to an autoclave, 30 mL of ethyl acetate was added, and stirring was carried out until complete dissolution; 0.3 g of PVP-PS / [BMIM]NO3 composite microspheres was added, and stirring was carried out for 10 min to make the system uniformly dispersed; S3, nitration reaction: 40% nitric acid was added dropwise into the autoclave, the molar ratio of o-sec-butyl phenol to nitric acid was controlled to be 1:2.0, the temperature was increased to 40°C, and the reaction was carried out for 5 h at a stirring rate of 500 r / min; S4, post-reaction treatment: after the reaction was completed, the temperature in the autoclave was reduced to room temperature by opening the condensate water, and the composite microspheres were recovered by filtration; the filtrate was transferred to a separatory funnel, and was allowed to stand to separate into layers; the water layer was a recovered solution containing a small amount of nitric acid, which could be recycled after being adjusted to a concentration of 40% by adding concentrated nitric acid; the organic phase was a crude DNBP solution; S5, product purification: the organic phase was distilled under reduced pressure at 50°C to remove ethyl acetate, and a crude product was obtained; the crude product was dissolved in 15 mL of ethanol, and was stirred to dissolve at 50°C; then, the temperature was slowly reduced to 0°C, and crystallization was carried out for 2 h; after filtration and vacuum drying, a high-purity DNBP product was obtained.

[0030] Example 2 A high-efficiency synthesis method of low-by-product inhibitor DNBP, the operation steps of the preparation method are as follows: S1, Preparation of PVP-PS / [BMIM]NO3 composite microspheres: 1 g of PS microspheres was dispersed in 60 mL of N,N-dimethylformamide, and ultrasonic dispersion was performed for 15 min to be uniform; 2 g of PVP and 1.3 g of azobisisobutyronitrile were added, and the reaction was stirred at 65°C for 5 h under nitrogen protection, so that PVP was grafted onto the surface of the PS microspheres by free radical polymerization to form PVP-PS core-shell microspheres; the core-shell microspheres were dispersed in 40 mL of ethanol, 0.8 g of [BMIM]NO3 was added dropwise, and stirring was performed at 50°C for 3 h to load the ionic liquid on the PVP shell layer; after centrifugation and vacuum drying, PVP-PS / [BMIM]NO3 composite microspheres were obtained; S2, Preparation of the reaction system: 7 g of o-sec-butyl phenol was added to an autoclave, 35 mL of ethyl acetate was added, and stirring was performed until complete dissolution; 0.5 g of PVP-PS / [BMIM]NO3 composite microspheres was added, and stirring was performed for 10 min to make the system uniformly dispersed; S3, Nitration reaction: 43% nitric acid was added dropwise into the autoclave, the molar ratio of o-sec-butyl phenol to nitric acid was controlled to be 1:2.1, the temperature was increased to 40°C, and the reaction was performed for 5 h at a stirring rate of 600 r / min; S4, Post-reaction treatment: After the reaction was completed, the temperature in the autoclave was reduced to room temperature by opening the condensate water, and the composite microspheres were recovered by filtration; the filtrate was transferred to a separatory funnel, and was allowed to stand to separate into layers; the water layer was a recovered solution containing a small amount of nitric acid, which could be recycled after being adjusted to a concentration of 40% by adding concentrated nitric acid; and the organic phase was a crude DNBP solution; S5, Product purification: The organic phase was distilled under reduced pressure at 50°C to remove ethyl acetate, and a crude product was obtained; the crude product was dissolved in 17 mL of ethanol, and was stirred to dissolve at 50°C, and then was slowly cooled to 3°C to crystallize for 2 h, and then was filtered and vacuum dried to obtain a high-purity DNBP product.

[0031] Example 3 A high-efficiency synthesis method of a low-byproduct polymerization inhibitor DNBP is provided, and the operation steps of the preparation method are as follows: S1, Preparation of PVP-PS / [BMIM]NO3 composite microspheres: 1.5 g of PS microspheres was dispersed in 80 mL of N,N-dimethylformamide, and ultrasonic dispersion was performed for 15 min to be uniform; 3 g of PVP and 2 g of azobisisobutyronitrile (initiator) were added, and the reaction was stirred at 70°C for 6 h under nitrogen protection, so that PVP was grafted onto the surface of the PS microspheres by free radical polymerization to form PVP-PS core-shell microspheres; the core-shell microspheres were dispersed in 50 mL of ethanol, 1.2 g of [BMIM]NO3 was added dropwise, and stirring was performed at 50°C for 3 h to load the ionic liquid on the PVP shell layer; after centrifugation and vacuum drying, PVP-PS / [BMIM]NO3 composite microspheres were obtained; S2, reaction system preparation: 10 g of o-sec-butyl phenol was added to an autoclave, 40 mL of ethyl acetate was added, and stirring was performed until complete dissolution; 0.8 g of PVP-PS / [BMIM]NO3 composite microspheres was added, and stirring was performed for 10 min to uniformly disperse the system; S3, nitration reaction implementation: 45% by mass of nitric acid was added dropwise into the autoclave, the molar ratio of o-sec-butyl phenol to nitric acid was controlled to be 1:2.2, the temperature was increased to 40 DEG C, and the reaction was maintained for 5 h at a stirring rate of 700 r / min; S4, post-reaction treatment: after the reaction was completed, the temperature in the autoclave was reduced to room temperature by opening the condensate water, and the composite microspheres were recovered by filtration; the filtrate was transferred to a separatory funnel, and was allowed to stand to separate into layers; the water layer was a recovered solution containing a small amount of nitric acid, which could be recycled after being adjusted to a concentration of 40% by adding concentrated nitric acid; and the organic phase was a DNBP crude product solution; S5, product purification: the organic phase was subjected to vacuum distillation at 50 DEG C to remove ethyl acetate, and a crude product was obtained; the crude product was dissolved in 20 mL of ethanol, and was stirred to dissolve at 50 DEG C; then, the temperature was slowly reduced to 5 DEG C, and crystallization was performed for 2 h; the product was obtained by filtration and vacuum drying.

[0032] Comparative Example 1 S1, raw material preparation: 8 g of o-sec-butyl phenol, 40% nitric acid (configured according to a molar ratio of o-sec-butyl phenol to nitric acid of 1:2.7), and 40 mL of ethyl acetate were taken; S2, reaction process: the nitric acid and ethyl acetate were added to an autoclave, and o-sec-butyl phenol was slowly added along the wall of the autoclave after uniform stirring; the temperature was increased to 40 DEG C, the stirring rate was 500 r / min, and the reaction was maintained for 5 h; S3, post-treatment and purification: after the reaction was completed, the temperature was reduced to room temperature, and the reaction solution was transferred to a separatory funnel to separate into layers; the organic phase was subjected to vacuum distillation at 50 DEG C to remove ethyl acetate, and a crude product was obtained; the crude product was dissolved in 20 mL of ethanol, and was crystallized at 0 DEG C for 2 h; the DNBP product was obtained by filtration and drying.

[0033] Figure 1 FIG. 1 is a scanning electron microscope (SEM) photograph of the PVP-PS / [BMIM]NO3 composite microspheres prepared in Example 1; the microstructure of the composite microspheres is shown, and it can be observed that the microspheres have uniform particle sizes, are composed of a core-shell structure, have smooth surfaces, and have no obvious agglomeration; this morphology directly proves that the "core-shell structure" is successfully constructed, the PS core provides a stable support skeleton, and the size of the PS microspheres can be measured to be 100-160 nm; the PVP shell is uniformly coated on the surface (the uniform shell layer indicates uniform grafting of the shell layer), which lays a structural foundation for subsequent loading of the [BMIM]NO3 ionic liquid and realization of the "enrichment-hindering" directional effect; if the microspheres are agglomerated or the shell layer is incomplete, the ionic liquid will be unevenly loaded, the release of nitrate ions cannot be accurately controlled, and the rationality of the microsphere preparation process of the present application is verified.

[0034] Figure 2 is the polymerization inhibitor DNBP prepared in Example 1 1 H NMR chart, the positions of characteristic peaks (such as the hydrogen signals of the methyl groups on the sec-butyl groups, methylene groups, phenolic hydroxyl groups, and unsubstituted hydrogens on benzene rings) and the peak shapes of the NMR spectrum of the product completely match those of the DNBP standard sample, and there are no obvious impurity peaks (such as the characteristic peaks of the by-product 2,6-dinitro-4-sec-butyl phenol). From the molecular level, it is proved that the product is high-purity DNBP - the absence of impurity peaks indicates that the "steric hindrance" of the PVP shell successfully guided the nitrate to preferentially attack the 2-position and 4-position (target sites) of the ortho-sec-butyl phenol, inhibited the nitro para-substitution and hydroxyl oxidation side reactions, and directly verified the effectiveness of the "directed nitration" mechanism.

[0035] Figure 3 is the conversion rate of the polymerization inhibitor DNBP prepared in Examples 1-3 and Comparative Example 1 at different times; the conversion rate curve of Examples 1-3 (the method of the application) is always higher than that of Comparative Example 1 (the traditional process), and the difference in conversion rate is due to the "solubilization-control release" effect of the [BMIM]NO3 ionic liquid - the ionic liquid enhances the solubility of nitric acid in the organic phase (ethyl acetate) and slowly releases the nitrate, avoiding the reaction stagnation caused by the low local concentration of nitric acid; while in the traditional process, the solubility of nitric acid in the organic phase is low, and the excess nitric acid (molar ratio 1:2.7) is prone to local aggregation but has low utilization, resulting in slow reaction rate and lagging conversion rate. This graph directly proves the advantage of the application in "improving the efficiency of the nitration reaction".

[0036] Figure 4 is the yield of the polymerization inhibitor DNBP prepared in Examples 1-3 and Comparative Example 1; the yield of Examples 1-3 (89.2%-92.3%) is significantly higher than that of Comparative Example 1 (79.5%). The "enrichment-hindrance" of the PVP shell reduces the generation of by-products and reduces the yield loss during purification; temperature control: the PS core efficiently disperses local heat release, avoiding the oxidation side reactions caused by temperature fluctuations and ensuring batch stability. Comparative Example 1 has low yield due to the absence of temperature control and directional effect, more by-products, and large purification loss. This graph directly proves the innovative effect of the application in "improving yield and ensuring batch stability".

Claims

1. An efficient synthesis method of a low-byproduct polymerization inhibitor DNBP, characterized in that: The following steps are involved: S1. Preparation of PVP-PS / [BMIM]NO3 composite microspheres: Disperse 0.5-1.5 g of PS microspheres in 50-80 mL of N,N-dimethylformamide and ultrasonically disperse for 15 min until uniform. Add 1-3 g of PVP and 0.8-2 g of azobisisobutyronitrile and react under nitrogen protection to graft PVP onto the surface of the PS microspheres via free radical polymerization to form PVP-PS core-shell microspheres. Disperse the core-shell microspheres in 30-50 mL of ethanol and dropwise add 0.5-1.2 g of [BMIM]NO3. Stir at 50°C for 3 h to load the ionic liquid onto the PVP shell. Centrifuge and vacuum dry to obtain PVP-PS / [BMIM]NO3 composite microspheres. S2. Prepare the reaction system: add 5-10 g of o-sec-butylphenol to an autoclave, add 30-40 mL of ethyl acetate, and stir until completely dissolved; add 0.3-0.8 g of PVP-PS / [BMIM]NO3 composite microspheres and stir for 10 min to evenly disperse the system; S3. Nitration reaction: nitric acid with a mass fraction of 40% to 45% was dripped into the autoclave, and the molar ratio of o-sec-butylphenol to nitric acid was controlled to be 1:2.0 to 2.

2. The temperature was raised to 40° C., and the reaction was carried out at this temperature with magnetic stirring. S4, post-reaction treatment; S5. Product purification.

2. The efficient synthesis method of the low by-product polymerization inhibitor DNBP according to claim 1, characterized in that: In step S1, the particle size of the PS microspheres is 100-160 nm.

3. The efficient synthesis method of the low by-product polymerization inhibitor DNBP according to claim 1, characterized in that: In step S1, the vacuum drying temperature and time are 50° C. and 10 h, respectively.

4. The efficient synthesis method of the low by-product polymerization inhibitor DNBP according to claim 1, characterized in that: In step S1, the reaction temperature under nitrogen protection is 60-70° C., and the reaction time is 4-6 h.

5. The efficient synthesis method of the low by-product polymerization inhibitor DNBP according to claim 1, characterized in that: In step S3, the heat preservation reaction time is 5 hours, and the magnetic stirring rate is 500-700 r / min.

6. The efficient synthesis method of the low by-product polymerization inhibitor DNBP according to claim 1, characterized in that: In step S4, the post-reaction treatment operation is as follows: after the reaction is completed, the condensed water is opened to reduce the temperature in the kettle to room temperature, and the composite microspheres are filtered and recovered; the filtrate is transferred to a separatory funnel and allowed to stand for stratification. The aqueous layer is a recovered liquid containing a trace amount of nitric acid, which can be recycled after adding concentrated nitric acid to a concentration of 40%. The organic phase is a crude DNBP solution.

7. The efficient synthesis method of the low by-product polymerization inhibitor DNBP according to claim 1, characterized in that: In step S5, the product purification operation is as follows: removing ethyl acetate from the organic phase by vacuum distillation at a temperature of 50° C. to obtain a crude product; dissolving the crude product in 15-20 mL of ethanol, slowly cooling and crystallizing at a temperature of 0-5° C. for 2 h, filtering, and vacuum drying to obtain a high-purity DNBP product.

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