Synthesis method of polymerization inhibitor DNBP

Abstract

This invention discloses a highly efficient synthesis method for the low-byproduct polymerization inhibitor DNBP, belonging to the field of polymerization inhibitor synthesis technology. The method first prepares PVP-PS / [BMIM]NO3 composite microspheres, then disperses o-sec-butylphenol and the composite microspheres in ethyl acetate, adds 40%~45% nitric acid (molar ratio 1:2.0~2.2), and reacts at 40℃ and 500~700 r / min for 5 h. After post-treatment and crystallization, the product is obtained. The composite microspheres achieve a synergistic effect through PS core thermal conduction temperature control, PVP shell directional enrichment, and [BMIM]NO3 regulating nitric acid release. This solves the problems of high byproducts and low nitric acid utilization in traditional processes, meeting the requirements of clean production.

Description

Technical Field

[0001] This invention belongs to the field of polymerization inhibitor synthesis technology, specifically relating to an efficient synthesis method for the polymerization inhibitor DNBP with low by-product yield. Background Technology

[0002] DNBP (2,4-dinitro-6-sec-butylphenol) is an important phenolic polymerization inhibitor. Due to its excellent polymerization inhibitory activity and thermal stability, it is widely used in the storage and polymerization processes of olefin monomers such as acrylates and methacrylates. It can effectively inhibit monomer self-polymerization and deterioration, ensuring production continuity and product quality. Currently, the industrial synthesis of DNBP mainly adopts the direct nitration method with o-sec-butylphenol and nitric acid, that is, the nitration reaction is carried out in an autoclave using 35%~45% nitric acid as the nitrating agent, and the temperature is controlled.

[0003] However, existing synthetic methods have two major drawbacks:

[0004] (1) Many byproducts and low purity: Nitric acid has both nitration and oxidation effects. During the reaction, it is easy to trigger side reactions such as hydroxyl oxidation of o-sec-butylphenol and nitro dislocation substitution (such as 2,6-dinitro-4-sec-butylphenol), which often result in the purity of DNBP products being less than 80%. Multiple purifications are required, which is not only time-consuming but also causes yield loss.

[0005] (2) Low utilization rate of nitric acid and high pollution: In the existing process, the molar ratio of o-sec-butylphenol to nitric acid is as high as 1:2.7~2.8. Excess nitric acid cannot react fully. Although the waste nitric acid formed can be adjusted and recycled, the accumulation of impurities after multiple cycles will further aggravate the side reaction. At the same time, the unrecovered nitric acid remains in the wastewater system, which has high treatment costs and is also prone to equipment corrosion and environmental risks.

[0006] Therefore, developing a new method for synthesizing DNBP that can suppress side reactions and improve the utilization rate of nitric acid is of great significance for reducing production costs and enhancing product competitiveness. Summary of the Invention

[0007] To address the shortcomings of existing methods for synthesizing DNBP using the "direct nitration of o-sec-butylphenol" method, which results in numerous byproducts and low nitric acid utilization, this invention provides a highly efficient synthesis method for the low-byproduct polymerization inhibitor DNBP. Through the synergistic effect of "confined nitration-nitric acid regulation" of PVP-PS / [BMIM]NO3 composite microspheres, a highly efficient synthesis of DNBP with low byproducts and high purity is achieved.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A highly efficient synthesis method for the polymerization inhibitor DNBP with low by-product yield, the preparation method is as follows:

[0010] Preparation of S1 PVP-PS / [BMIM]NO3 composite microspheres: 0.5-1.5 g PS microspheres were dispersed in 50-80 mL N,N-dimethylformamide and ultrasonically dispersed for 15 min until homogeneous; 1-3 g PVP (polyvinylpyrrolidone K-30) and 0.8-2 g azobisisobutyronitrile were added, and the reaction was carried out under nitrogen protection. PVP was grafted onto the surface of PS microspheres through free radical polymerization to form PVP-PS core-shell microspheres; the core-shell microspheres were dispersed in 30-50 mL ethanol, and 0.5-1.2 g [BMIM]NO3 (1-butyl-3-methylimidazolium nitrate) was added dropwise. The mixture was stirred at 50 °C for 3 h to load the ionic liquid onto the PVP shell. After centrifugation and vacuum drying, PVP-PS / [BMIM]NO3 composite microspheres were obtained.

[0011] S2. Preparation of reaction system: Add 5-10g of o-sec-butylphenol to the autoclave, add 30-40mL of ethyl acetate, and stir until completely dissolved; add 0.3-0.8g of PVP-PS / [BMIM]NO3 composite microspheres, and stir for 10min to disperse the system evenly.

[0012] S3. Nitration reaction implementation: Add 40%~45% nitric acid dropwise into the autoclave, control the molar ratio of o-sec-butylphenol to nitric acid to be 1:2.0~2.2, heat to 40℃, maintain the temperature for reaction, and stir magnetically.

[0013] S4. Post-reaction treatment;

[0014] S5. Product purification.

[0015] The composite microspheres have a core-shell structure, with polystyrene (PS) as the core and polyvinylpyrrolidone (PVP) as the shell. The shell is grafted with 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]NO3) ionic liquid. Its structural design is the basis for realizing the synergistic function of "catalysis-temperature control-confinement-recovery".

[0016] Core layer (PS microspheres): As a supporting framework, it maintains the stable morphology of the composite microspheres and avoids 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 exothermic reaction generated by the nitration reaction and prevents oxidation side reactions caused by a sudden increase in temperature.

[0017] Shell (PVP segment): Through hydrogen bonding with the hydroxyl groups of o-sec-butylphenol, o-sec-butylphenol is enriched in the shell of the microsphere, forming a "local high-concentration reaction zone"; at the same time, the steric hindrance of the PVP segment can directionally expose the active sites of o-sec-butylphenol, guiding nitrate ions to preferentially attack the target sites and inhibiting the nitro dislocation substitution side reaction.

[0018] The active component ([BMIM]NO3 ionic liquid) is loaded onto the PVP shell and regulates the release rate of nitrate ions through the coordination of imidazole ring cations, avoiding excessive local nitric acid concentration that could lead to oxidation side reactions. At the same time, the presence of the ionic liquid can enhance the solubility of nitric acid in the organic phase, improve the efficiency of the nitration reaction, and reduce the amount of nitric acid used.

[0019] Directed nitration inhibits side reactions: The dual effect of "enrichment-steric hindrance" of the PVP shell enables the 2- and 4-positions of o-sec-butylphenol to preferentially react with the controllably released nitrate ions, significantly reducing the content of misaligned nitration and oxidation byproducts, and increasing the product purity from 79.5% in the traditional process to over 89.2%.

[0020] Reduce nitric acid usage and recycle it: The catalytic synergistic effect of [BMIM]NO3 reduces nitric acid usage by 20%~25% (molar ratio from 1:2.7 to below 1:2.2); the nitric acid recovered from the aqueous phase can be reused after simple preparation.

[0021] To avoid over-alkylation: the steric hindrance of the PVP shell restricts the generated DNBP from approaching the active site, while the weak acidity of the ionic liquid cannot activate the aromatic ring of DNBP, thus blocking the third alkylation pathway.

[0022] Temperature control synergy: PS cores can quickly disperse local heat; at the same time, microspheres are evenly dispersed under stirring, enhancing heat exchange, resulting in smaller temperature fluctuations in the system and suppressing temperature-sensitive side reactions.

[0023] Further optimization of an efficient synthesis method for DNBP, a low-by-product polymerization inhibitor.

[0024] Preferably, in step S1, the particle size of the PS microspheres is 100~160nm.

[0025] Preferably, in step S1, the temperature and time for vacuum drying are 50°C and 10 hours, respectively.

[0026] Preferably, in step S1, the reaction temperature under nitrogen protection is 60~70℃, and the reaction time is 4~6h.

[0027] Preferably, in step S3, the heat preservation reaction time is 5 hours and the magnetic stirring speed is 500~700 r / min.

[0028] Preferably, in step S4, the post-reaction processing is performed as follows: after the reaction is completed, the condenser is turned on to lower the temperature inside the reactor to room temperature, and the composite microspheres are filtered and recovered; the filtrate is transferred to a separatory funnel, allowed to stand and separate into layers, the aqueous layer is a recovery liquid containing trace amounts of nitric acid, which can be recycled after being adjusted to a concentration of 40% by adding concentrated nitric acid, and the organic phase is a crude DNBP solution.

[0029] Preferably, in step S5, the product purification operation is as follows: the organic phase is removed by vacuum distillation to remove ethyl acetate at a vacuum distillation temperature of 50°C to obtain a crude product; the crude product is dissolved in 15-20 mL of ethanol, and the product is slowly cooled to crystallize at a cooling temperature of 0-5°C for 2 hours; the product is then filtered and vacuum dried to obtain a high-purity DNBP product.

[0030] The advantages of this invention compared to the prior art are as follows:

[0031] (1) High product purity and improved yield: Through the “enrichment-steric hindrance” orientation effect of PVP-PS / [BMIM]NO3 composite microspheres, nitrate ions are precisely guided to attack the active sites of o-sec-butylphenol, effectively inhibiting hydroxyl oxidation and nitro dislocation substitution side reactions, and improving product purity. The product purity has increased from 79.5% in the traditional process to over 89.2%.

[0032] (2) High utilization rate of nitric acid and reduced cost: Relying on the controllable release and solubilization effect of [BMIM]NO3 on nitrate ions, the molar ratio of o-sec-butylphenol to nitric acid is reduced from 1:2.7~2.8 to 1:2.0~2.2 compared with the traditional method, and the amount of nitric acid used is reduced by 20%~25%; and the nitric acid recovered from the aqueous phase can be recycled after simple adjustment, which significantly reduces the cost of raw materials.

[0033] (3) Strong controllability and batch stability of reaction: The high thermal conductivity of PS micronuclei and the uniform dispersion of composite microspheres work together to reduce the temperature fluctuation of the reaction and avoid side reactions caused by local overheating; at the same time, the immobilized active components ensure stable catalytic performance. Attached Figure Description

[0034] Figure 1 This is a scanning electron microscope (SEM) image of the PVP-PS / [BMIM]NO3 composite microspheres prepared in Example 1;

[0035] Figure 2 It is the polymerization inhibitor DNBP prepared in Example 1. 1 H NMR;

[0036] Figure 3 The conversion rates of the polymerization inhibitor DNBP prepared in Examples 1-3 and Comparative Example 1 at different times are shown.

[0037] Figure 4 The yield of the polymerization inhibitor DNBP prepared in Examples 1-3 and Comparative Example 1 is shown. Detailed Implementation

[0038] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the concept of the invention, they should all fall within the protection scope of the present invention.

[0039] The preparation method of the present invention will be described below through specific embodiments and comparative examples.

[0040] Example 1

[0041] A highly efficient synthesis method for the polymerization inhibitor DNBP with low by-product yield, the preparation method is as follows:

[0042] Preparation of S1 PVP-PS / [BMIM]NO3 composite microspheres: 0.5 g PS microspheres were dispersed in 50 mL N,N-dimethylformamide and ultrasonically dispersed for 15 min until homogeneous; 1 g PVP and 0.8 g azobisisobutyronitrile were added, and the mixture was stirred at 60 °C for 4 h under nitrogen protection to graft PVP onto the surface of PS microspheres through free radical polymerization, forming PVP-PS core-shell microspheres; the core-shell microspheres were dispersed in 30 mL ethanol, and 0.5 g [BMIM]NO3 was added dropwise, and the mixture was stirred at 50 °C for 3 h to load the PVP shell with ionic liquid. After centrifugation and vacuum drying, PVP-PS / [BMIM]NO3 composite microspheres were obtained.

[0043] S2. Preparation of reaction system: Add 5g of o-sec-butylphenol to the autoclave, add 30mL of ethyl acetate, and stir until completely dissolved; add 0.3g of PVP-PS / [BMIM]NO3 composite microspheres, and stir for 10min to disperse the system evenly;

[0044] S3. Nitration reaction implementation: 40% nitric acid was added dropwise to the autoclave, the molar ratio of o-sec-butylphenol to nitric acid was controlled at 1:2.0, the temperature was raised to 40℃, the reaction was kept at this temperature for 5 hours, and the stirring rate was 500 r / min.

[0045] S4. Post-reaction treatment: After the reaction is completed, turn on the cooling water to lower the temperature inside the reactor to room temperature, filter and recover the composite microspheres; transfer the filtrate to a separatory funnel, let it stand to separate into layers, the aqueous layer is the recovery liquid containing trace amounts of nitric acid, which can be recycled after adding concentrated nitric acid to adjust to a concentration of 40%; the organic phase is the crude DNBP solution.

[0046] S5. Product purification: The organic phase was distilled under reduced pressure at 50°C to remove ethyl acetate, and the crude product was obtained. The crude product was dissolved in 15 mL of ethanol, stirred at 50°C to dissolve, and then slowly cooled to 0°C to crystallize for 2 hours. After filtration and vacuum drying, high-purity DNBP product was obtained.

[0047] Example 2

[0048] A highly efficient synthesis method for the polymerization inhibitor DNBP with low by-product yield, the preparation method is as follows:

[0049] Preparation of S1 PVP-PS / [BMIM]NO3 composite microspheres: 1g of PS microspheres were dispersed in 60mL of N,N-dimethylformamide and ultrasonically dispersed for 15min until homogeneous; 2g of PVP and 1.3g of azobisisobutyronitrile were added, and the mixture was stirred at 65℃ for 5h under nitrogen protection. PVP was grafted onto the surface of PS microspheres through free radical polymerization to form PVP-PS core-shell microspheres; the core-shell microspheres were dispersed in 40mL of ethanol, and 0.8g of [BMIM]NO3 was added dropwise. The mixture was stirred at 50℃ for 3h to load the ionic liquid onto the PVP shell. After centrifugation and vacuum drying, PVP-PS / [BMIM]NO3 composite microspheres were obtained.

[0050] S2. Preparation of reaction system: Add 7g of o-sec-butylphenol to the autoclave, add 35mL of ethyl acetate, and stir until completely dissolved; add 0.5g of PVP-PS / [BMIM]NO3 composite microspheres, and stir for 10min to disperse the system evenly;

[0051] S3. Nitration reaction implementation: 43% nitric acid was added dropwise to the autoclave, the molar ratio of o-sec-butylphenol to nitric acid was controlled at 1:2.1, the temperature was raised to 40℃, the reaction was kept at this temperature for 5 hours, and the stirring rate was 600 r / min.

[0052] S4. Post-reaction treatment: After the reaction is completed, turn on the cooling water to lower the temperature inside the reactor to room temperature, filter and recover the composite microspheres; transfer the filtrate to a separatory funnel, let it stand to separate into layers, the aqueous layer is the recovery liquid containing trace amounts of nitric acid, which can be recycled after adding concentrated nitric acid to adjust to a concentration of 40%; the organic phase is the crude DNBP solution.

[0053] S5. Product purification: The organic phase was distilled under reduced pressure at 50°C to remove ethyl acetate, yielding a crude product. The crude product was dissolved in 17 mL of ethanol, stirred at 50°C until dissolved, and then slowly cooled to 3°C for 2 hours to crystallize. The product was then filtered and dried under vacuum to obtain a high-purity DNBP product.

[0054] Example 3

[0055] A highly efficient synthesis method for the polymerization inhibitor DNBP with low by-product yield, the preparation method is as follows:

[0056] Preparation of S1 PVP-PS / [BMIM]NO3 composite microspheres: 1.5g of PS microspheres were dispersed in 80mL of N,N-dimethylformamide and ultrasonically dispersed for 15min until homogeneous; 3g of PVP and 2g of azobisisobutyronitrile (initiator) were added, and the mixture was stirred at 70℃ for 6h under nitrogen protection. PVP was grafted onto the surface of PS microspheres through free radical polymerization to form PVP-PS core-shell microspheres; the core-shell microspheres were dispersed in 50mL of ethanol, and 1.2g of [BMIM]NO3 was added dropwise. The mixture was stirred at 50℃ for 3h to load the ionic liquid onto the PVP shell. After centrifugation and vacuum drying, PVP-PS / [BMIM]NO3 composite microspheres were obtained.

[0057] S2. Preparation of reaction system: Add 10g of o-sec-butylphenol to the autoclave, add 40mL of ethyl acetate, and stir until completely dissolved; add 0.8g of PVP-PS / [BMIM]NO3 composite microspheres, and stir for 10min to disperse the system evenly;

[0058] S3. Nitration reaction implementation: 45% nitric acid was added dropwise to the autoclave, the molar ratio of o-sec-butylphenol to nitric acid was controlled at 1:2.2, the temperature was raised to 40℃, the reaction was kept at this temperature for 5 hours, and the stirring rate was 700 r / min.

[0059] S4. Post-reaction treatment: After the reaction is completed, turn on the cooling water to lower the temperature inside the reactor to room temperature, filter and recover the composite microspheres; transfer the filtrate to a separatory funnel, let it stand to separate into layers, the aqueous layer is the recovery liquid containing trace amounts of nitric acid, which can be recycled after adding concentrated nitric acid to adjust to a concentration of 40%; the organic phase is the crude DNBP solution.

[0060] S5. Product purification: The organic phase was distilled under reduced pressure at 50°C to remove ethyl acetate, and the crude product was obtained. The crude product was dissolved in 20 mL of ethanol, stirred at 50°C to dissolve, and then slowly cooled to 5°C to crystallize for 2 h. After filtration and vacuum drying, high-purity DNBP product was obtained.

[0061] Comparative Example 1

[0062] S1. Raw material preparation: Take 8g of o-sec-butylphenol, 40% nitric acid (prepared according to the molar ratio of o-sec-butylphenol to nitric acid 1:2.7), and 40mL of ethyl acetate;

[0063] S2. Reaction process: Nitric acid and ethyl acetate were added to a high-pressure reactor and stirred evenly. Then, o-sec-butylphenol was slowly added along the reactor wall. The temperature was raised to 40°C, the stirring rate was 500 r / min, and the reaction was maintained at this temperature for 5 h.

[0064] S3. Post-processing and purification: After the reaction is completed, the temperature is lowered to room temperature, and the reaction solution is transferred to a separatory funnel to separate the layers. The organic phase is distilled under reduced pressure at 50°C to remove ethyl acetate, and the crude product is obtained. The crude product is dissolved in 20 mL of ethanol, cooled to 0°C and crystallized for 2 h. After filtration and drying, the DNBP product is obtained.

[0065] Figure 1 This is a scanning electron microscope (SEM) image of the PVP-PS / [BMIM]NO3 composite microspheres prepared in Example 1. The image shows the microstructure of the composite microspheres, revealing uniform particle size, a core-shell structure, smooth surface, and no obvious agglomeration. This morphology directly proves the successful construction of the "core-shell structure"—the PS core provides a stable supporting framework. The size of the PS microspheres can be measured to be 100-160 nm. The PVP shell is uniformly coated on the surface (the absence of agglomeration indicates uniform shell grafting), laying the structural foundation for subsequent loading of [BMIM]NO3 ionic liquid and achieving the "enrichment-steric hindrance" directional effect. If the microspheres agglomerate or the shell is incomplete, it will lead to uneven ionic liquid loading and inability to precisely control nitrate release, confirming the rationality of the microsphere preparation process of this invention.

[0066] Figure 2 It is the polymerization inhibitor DNBP prepared in Example 1. 1 The NMR spectrum shows that the positions and shapes of characteristic peaks (such as hydrogen signals from the methyl and methylene groups on the sec-butyl group, hydrogen signals from the phenolic hydroxyl group, and signals from unsubstituted hydrogens on the benzene ring) perfectly match those of the DNBP standard, and there are no obvious impurity peaks (such as the characteristic peak of the misaligned nitration byproduct 2,6-dinitro-4-sec-butylphenol). This molecular-level evidence confirms that the product is high-purity DNBP with no impurity peaks, indicating that the steric hindrance of the PVP shell successfully guides the nitrate ion to preferentially attack the 2 and 4 positions (target sites) of the o-sec-butylphenol, inhibiting the nitro misalignment substitution and hydroxyl oxidation side reactions, directly verifying the effectiveness of the "directional nitration" mechanism.

[0067] Figure 3 The graph shows the conversion rates of the polymerization inhibitor DNBP prepared in Examples 1-3 and Comparative Example 1 at different times. The conversion rate curves of Examples 1-3 (the method of this invention) are consistently higher than those of Comparative Example 1 (conventional process). The difference in conversion rate stems from the "solubilizing-controlled release" effect of the [BMIM]NO3 ionic liquid—the ionic liquid enhances the solubility of nitric acid in the organic phase (ethyl acetate) while slowly releasing nitrate ions, avoiding local nitric acid concentrations that could lead to reaction stagnation. In contrast, the conventional process has low solubility of nitric acid in the organic phase, and excess nitric acid (molar ratio 1:2.7) is prone to local aggregation but has low utilization, resulting in a slow reaction rate and a delayed increase in conversion rate. This graph visually demonstrates the advantage of this invention in "improving the efficiency of the nitration reaction."

[0068] Figure 4The figure shows the yields of the polymerization inhibitor DNBP prepared in Examples 1-3 and Comparative Example 1; the yields of Examples 1-3 (89.2%~92.3%) are significantly higher than those of Comparative Example 1 (79.5%). The PVP shell's "enrichment-steric hindrance" reduces byproduct formation and decreases yield loss during purification; temperature control synergy: the PS core efficiently disperses localized exothermic reactions, avoiding oxidation side reactions caused by temperature fluctuations and ensuring batch stability. Comparative Example 1, lacking temperature control and orientation, has more byproducts, greater purification losses, and a naturally lower yield. This figure directly confirms the innovative effect of this invention in "improving yield and ensuring batch stability".

Claims

1. A method for synthesizing the polymerization inhibitor DNBP, characterized in that, Includes the following steps: Preparation of S1 PVP-PS / [BMIM]NO3 composite microspheres: 0.5-1.5 g PS microspheres were dispersed in 50-80 mL N,N-dimethylformamide and ultrasonically dispersed for 15 min until homogeneous; 1-3 g PVP and 0.8-2 g azobisisobutyronitrile were added, and the reaction was carried out under nitrogen protection. PVP was grafted onto the surface of PS microspheres through free radical polymerization to form PVP-PS core-shell microspheres; the core-shell microspheres were dispersed in 30-50 mL ethanol, and 0.5-1.2 g [BMIM]NO3 was added dropwise. The mixture was stirred at 50 °C for 3 h to load the ionic liquid onto the PVP shell. After centrifugation and vacuum drying, PVP-PS / [BMIM]NO3 composite microspheres were obtained. S2. Preparation of reaction system: Add 5-10g of o-sec-butylphenol to the autoclave, add 30-40mL of ethyl acetate, and stir until completely dissolved; add 0.3-0.8g of PVP-PS / [BMIM]NO3 composite microspheres, and stir for 10min to disperse the system evenly. S3. Nitration reaction implementation: Add 40%~45% nitric acid dropwise into the autoclave, control the molar ratio of o-sec-butylphenol to nitric acid to be 1:2.0~2.2, heat to 40℃, maintain the temperature for reaction, and stir magnetically. S4. Post-reaction treatment; S5. Product purification.

2. The method for synthesizing the polymerization inhibitor DNBP according to claim 1, characterized in that, In step S1, the particle size of the PS microspheres is 100~160nm.

3. The method for synthesizing the polymerization inhibitor DNBP according to claim 1, characterized in that, In step S1, the temperature and time for vacuum drying are 50℃ and 10h, respectively.

4. The method for synthesizing the polymerization inhibitor DNBP according to claim 1, characterized in that, In step S1, the reaction temperature under nitrogen protection is 60~70℃, and the reaction time is 4~6h.

5. The method for synthesizing the 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 speed is 500~700 r / min.

6. The method for synthesizing the polymerization inhibitor DNBP according to claim 1, characterized in that, In step S4, the post-reaction processing is as follows: after the reaction is completed, turn on the cooling water to lower the temperature inside the reactor to room temperature, filter and recover the composite microspheres; transfer the filtrate to a separatory funnel, let it stand to separate into layers, the aqueous layer is the recovery liquid containing trace amounts of nitric acid, which can be recycled after adding concentrated nitric acid to adjust to a concentration of 40%, and the organic phase is a crude DNBP solution.

7. The method for synthesizing the polymerization inhibitor DNBP according to claim 1, characterized in that, In step S5, the product purification operation is as follows: the organic phase is distilled under reduced pressure to remove ethyl acetate at a temperature of 50°C to obtain a crude product; the crude product is dissolved in 15-20 mL of ethanol, and the product is slowly cooled to crystallize at a temperature of 0-5°C for 2 hours; the product is then filtered and vacuum dried to obtain a high-purity DNBP product.

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