A styrene polymerization inhibitor and a method for preparing the same

Abstract

The application discloses a green and efficient styrene polymerization inhibitor and a preparation method thereof. The general structure of the polymerization inhibitor is as follows: wherein the substituent group R1 is independently selected from a hydrogen atom and a methyl group, and R2 is independently selected from a hydrogen atom and a tert-butyl group. The polymerization inhibitor is high in efficiency, low in toxicity, and small in environmental pollution, effectively alleviates the problems of large use amount, high cost and environmental pollution caused by the common polymerization inhibitor in the existing process production, and can be used in the storage, transportation and production process of styrene to effectively prevent the occurrence of the styrene polymerization problem, thereby providing a new selection for the use of the styrene polymerization inhibitor.

Description

Technical Field

[0001] This invention relates to a green and efficient styrene polymerization inhibitor and its preparation method, belonging to the field of organic synthesis technology. Background Technology

[0002] Styrene is an important chemical raw material, widely used in the synthesis of resins and rubber. However, due to the highly reactive exocyclic double bonds, styrene is prone to thermal initiation of free radicals and polymerization during production, especially in the distillation stage. This not only reduces yield but also causes pipeline blockage. Therefore, polymerization inhibitors must be added during styrene production to ensure safe operation of the plant and increase styrene production.

[0003] Styrene polymerization inhibitors can be classified into true inhibitors and retarders based on their inhibitory effect. True inhibitors have an induction period during which the inhibitor is consumed, but virtually no polymer is produced. Once the induction period ends, the polymer content rises rapidly. Retarders have no induction period and are chemically stable, allowing for repeated use, but they cannot completely prevent polymerization. The polymer content increases slowly over time. Common styrene polymerization inhibitors used in chemical production include 2,4-dinitrophenol, benzoquinone, hydroquinone, 2,6-dinitro-p-cresol, 4,6-dinitro-2-sec-butylphenol, o-sec-butyl-4,6-dinitrophenol, and p-tert-butylcatechol. These inhibitors are highly toxic, have a short polymerization inhibition lifespan, and cause serious environmental pollution.

[0004] Compound polymerization inhibitors effectively utilize the advantages of both retarders and true polymerization inhibitors. Due to the synergistic effect of each component, the polymerization inhibition efficiency is increased several times, the amount of polymerization inhibitor used is significantly reduced, and the toxicity is significantly reduced. However, there are still some defects in the actual operation of the production process. First, it is inconvenient to use, as the two or three components need to be compounded in advance before being added. Second, compound polymerization inhibitors are expensive and require a large amount of usage, which increases the production cost of styrene.

[0005] Therefore, there is an urgent need to provide a single type of polymerization inhibitor that is low in cost, has minimal harm to human health and the environment, and can be effectively used in the styrene production process to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a styrene polymerization inhibitor, its preparation method, and its uses. This polymerization inhibitor has the advantages of low toxicity, low environmental pollution, and good polymerization inhibition effect. It can be used in the storage, transportation, and production of styrene to effectively prevent the occurrence of styrene polymerization problems.

[0007] To achieve the above objectives, in one respect, the present invention provides a styrene polymerization inhibitor with the following general structural formula: The substituent R1 is independently selected from hydrogen atom and methyl, and R2 is independently selected from hydrogen atom and tert-butyl.

[0008] In some preferred embodiments of the present invention, the structure of the polymerization inhibitor is as follows:

[0009]

[0010] On the other hand, the present invention also provides a method for preparing this type of polymerization inhibitor, comprising the following steps:

[0011] Step 1): N-ethylbenzylamine, oxidant, and catalyst are added to solvent one, heated and stirred to react. After the reaction is completed, the solvent is removed and recrystallized to obtain N-ethyl-N-hydroxybenzylamine.

[0012] Step 2): Phthalic anhydride compounds and N-ethyl-N-hydroxybenzamine obtained in step (1) are mixed and then acid and catalyst are added. The mixture is heated to react. After the reaction is completed, the reaction is quenched with ice water. After extraction, concentration, solvent removal and recrystallization, intermediate product c is obtained.

[0013] Step 3): N-(1,3-dimethylbutyl)-N-phenyl-p-quinone diimine compound, catalyst, and chloromethylating agent are stirred at low temperature. After the reaction is completed, the mixture is extracted and washed, and then purified by separation to obtain intermediate product e.

[0014] Step 4): Add the intermediate product e obtained in step (3) to solvent 2, and under nitrogen protection, add magnesium shavings to react and prepare intermediate product f; dissolve intermediate product c in solvent 2 and add it to the reaction system. After the reaction is completed, quench the reaction, concentrate and remove the solvent, and obtain the polymerization inhibitor by separation and purification.

[0015] Preferably, in step 1), the oxidant is selected from hydrogen peroxide or sodium periodate;

[0016] Preferably, in step 1), the catalyst is selected from Na2WO4, RuO4, and RuO2;

[0017] Preferably, in step 1), the molar ratio of N-ethylbenzylamine to the oxidant is 1:1-2;

[0018] Preferably, in step 1), the molar ratio of N-ethylbenzylamine to the catalyst is 1:0.1-0.5;

[0019] Preferably, in step 1), the reaction temperature is 20-40°C;

[0020] Preferably, in step 1), the reaction time is 3-6 hours;

[0021] Preferably, in step 1), the solvent is methanol or ethanol;

[0022] Preferably, in step 1), the recrystallization solvent is diethyl ether or tetrahydrofuran;

[0023] Preferably, in step 2), the structural formula of the phthalic anhydride compound is: R1 is independently selected from hydrogen atom and methyl group, and the molar ratio of the phthalic anhydride compound to N-ethyl-N-hydroxybenzylamine is 1:1-2;

[0024] Preferably, in step 2), the reaction temperature is 100-120℃ and the reaction time is 3-4 hours.

[0025] Preferably, in step 2), the acid is concentrated sulfuric acid or concentrated phosphoric acid, and the molar ratio of the acid to the phthalic anhydride compound is 20-30:1.

[0026] Preferably, in step 2), the catalyst is selected from anhydrous AlCl3, CaCl2, ZnCl2, FeCl3, SnCl4, TiCl4, and the molar ratio of the catalyst to the phthalic anhydride compound is 1-3:1;

[0027] Preferably, in step 2), the extraction solvent is dichloromethane or ethyl acetate;

[0028] Preferably, in step 2), the recrystallization solvent is methanol or ethanol;

[0029] Preferably, in step 3), the catalyst is selected from anhydrous AlCl3, CaCl2, ZnCl2, FeCl3, SnCl4, and TiCl4.

[0030] Preferably, in step 3), the chloromethylating agent is selected from methyl acetal-chlorosulfonic acid, formaldehyde-chlorosulfonic acid, formaldehyde-hydrochloric acid, methyl acetal-hydrochloric acid, paraformaldehyde-hydrochloric acid, and paraformaldehyde-trifluoroacetic acid;

[0031] Preferably, in step 3), the molar ratio of N-(1,3-dimethylbutyl)-N-phenyl-p-quinone diimine compound to catalyst is 1:0.1-0.5;

[0032] Preferably, in step 3), the molar ratio of N-(1,3-dimethylbutyl)-N-phenyl-p-quinone diimine compound to chloromethylating agent is 1:0.8-1.5;

[0033] Preferably, in step 3), the reaction temperature is 0-10℃;

[0034] Preferably, in step 3), the reaction time is 4-8 hours;

[0035] Preferably, in step 3), the extractant in the extraction step is selected from chloroform, dichloromethane, and ethyl acetate;

[0036] Preferably, in step 3), the detergent is selected from aqueous solution, saturated sodium chloride aqueous solution, and sodium carbonate solution;

[0037] In step 4), the molar ratio of magnesium shavings to intermediate product e is 1:1-5;

[0038] Preferably, in step 4), solvent two is tetrahydrofuran or anhydrous diethyl ether;

[0039] Preferably, in step 4), the reaction time of the intermediate product e with magnesium shavings is 0.5-1 h, and the reaction temperature is 0-20 °C.

[0040] Preferably, in step 4), the molar ratio of intermediate product f to intermediate product c is 1:1-5;

[0041] Preferably, in step 4), the reaction time between intermediate product f and intermediate product c is 0.5-4 h, and the reaction temperature is 0-20 °C.

[0042] Preferably, in step 4), the target product is post-processed as follows: after the reaction is completed, the reaction is quenched with saturated ammonium chloride, the organic phase is extracted with tetrahydrofuran, the water is removed by drying with anhydrous sodium sulfate, the solvent is removed by rotary evaporation, and the target product is obtained by column chromatography using petroleum ether and ethyl acetate as eluents.

[0043] The present invention also provides a polymerization inhibitor prepared by the above method and the application of the polymerization inhibitor in inhibiting styrene polymerization.

[0044] Compared with the prior art, the present invention has the following advantages:

[0045] This invention features a simple reaction process, convenient post-processing, and low cost while achieving high yields of the target product. It utilizes a synthesized single-type polymerization inhibitor to replace a compound-type inhibitor, reducing inconvenience during material feeding and improving production efficiency. The quinone and imine groups in this type of inhibitor form non-radical substances or low-activity free radicals that cannot be initiated through coupling or disproportionation reactions, thus rapidly terminating the polymerization reaction. The ethyl hydroxylamine group can capture free radicals on the active chain, generating stable molecular compounds, thereby inhibiting polymerization. This type of inhibitor combines the advantages of both true inhibitors and retarders, significantly increasing inhibition efficiency, reducing inhibitor dosage, and substantially lowering toxicity, providing a new option for styrene polymerization inhibitors. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to specific embodiments.

[0047] Raw materials and sources:

[0048] Phthalic anhydride: Beijing Inokai Technology Co., Ltd.

[0049] 4-Methylphthalic anhydride: Beijing Innocare Technology Co., Ltd.

[0050] N-Ethylbenzylamine: Beijing Inokay Technology Co., Ltd.

[0051] N-(1,3-Dimethylbutyl)-N-phenyl-p-quinone diimide: CAS No.: 52870-46-9, Beijing Innocare Technology Co., Ltd. Example 1: Synthesis of polymerization inhibitor NBQ-1

[0052] The synthesis route is as follows:

[0053]

[0054] Synthesis of compound 1a:

[0055] 0.54 g (4 mmol) of N-ethylbenzylamine, 1 mL (30%, 9.8 mmol) of hydrogen peroxide, and 0.12 g (0.4 mmol) of sodium tungstate were weighed and added to 10 mL of methanol. The mixture was heated and stirred at 30 °C for 5 h. After the reaction was completed, the organic solvent was removed by rotary evaporation under vacuum. The product was then recrystallized from diethyl ether to obtain N-ethyl-N-hydroxybenzylamine with a yield of 51%.

[0056] 1 H NMR (500MHz, DMSO-d6): δ1.01(t,3H),2.52(q,2H),3.81(s,2H),7.29-7.31(m,5H),10.4(s,1H).

[0057] Synthesis of compound 1c:

[0058] Weigh 1.02 g (7 mmol) of compound 1b and 1.15 g (7 mmol) of compound 1a into a 50 mL single-necked flask. Add 2.31 g (0.015 mol) of dry anhydrous aluminum trichloride. Add 10 mL of concentrated sulfuric acid dropwise to the round-bottom flask in batches (add slowly in batches, waiting for the flask to cool down after each addition before adding the next). After the addition is complete, heat the mixture in an oil bath to 120 °C and continue the reaction for 4 h. After the reaction is complete, quench the reaction in 20 mL of ice water. Extract the mixture three times with 30 mL of ethyl acetate. Wash the extracted organic phase three times with 5% sodium bicarbonate solution, then wash three times with saturated NaCl solution. Collect the ethyl acetate phase, dry it with anhydrous sodium sulfate, filter off the sodium sulfate, and evaporate the solvent. Recrystallize from 95% ethanol to obtain the final product with a yield of 52%.

[0059] 1H NMR (500MHz, DMSO-d6): δ1.03(t,3H),2.62(q,2H),3.84(s,2H),7.48(m,1H),7.81(d,1H),7.89(d,1H),8.27-8.34(m,4H),10.7(s,1H).

[0060] Synthesis of compound 1e:

[0061] 5.33 g (20 mmol) of compound 1d, 5.33 g (2.5 mmol) of zinc chloride, 3.51 g (30 mmol) of chlorosulfonic acid, and 0.92 g (30 mmol) of formaldehyde were weighed and stirred at 0 °C for 7 h. After the reaction was completed, 10 mL of water was added to quench the reaction. After extraction with 30 mL of dichloromethane, the organic phase was washed with 5% sodium carbonate aqueous solution, the solvent was removed by rotary evaporation, and the intermediate product 1e was obtained by column chromatography with silica gel, with a yield of 73%.

[0062] 1 H NMR (500MHz, DMSO-d6): δ0.92(d,6H),1.03(d,3H),1.21(t,2H),1.59-1.63(m,1 H),2.30-2.37(m,1H),4.64(s,2H),6.25(s,2H),7.23-7.29(m,4H),8.04(s,2H).

[0063] Synthesis of polymerization inhibitor NBQ-1:

[0064] Weigh 1.08 g (3 mmol) of compound 1e into a dry 100 mL two-necked flask, add 30 mL of dried anhydrous tetrahydrofuran and 0.03 g (1 mmol) of magnesium shavings. After purging the air with nitrogen, initiate the reaction at room temperature under nitrogen protection. After 1 hour of reaction, once the Grignard reagent is prepared, slowly inject 5 mL of 0.3 g (1 mmol) of compound 1c dissolved in tetrahydrofuran into the system using a dried syringe. Continue the reaction at room temperature for 4 hours, monitoring the reaction process with thin-layer chromatography. After stopping the reaction, quench the remaining Grignard reagent in the system with 10 mL of saturated ammonium chloride, extract with tetrahydrofuran, separate the organic phase, and after multiple extractions, combine the organic phases. Dry with anhydrous sodium sulfate, place the organic phase in a rotary evaporator, set the pressure to 20-30 kPa, and the temperature to 40-50 °C to remove the solvent, and perform silica gel column chromatography with petroleum ether and ethyl acetate as eluents to obtain the target product.

[0065] 1H NMR (500MHz, DMSO-d6): δ0.91(d,6H),1.01(t,3H),1.05(d,3H),1.24(t,2H),1.69(m,1H),2.39(m,1H),2.61(q,2H),3.84(s,2H),6.25(s,2 H),6.91(s,1H),7.22(d,2H),7.35(d,1H),7.54-7.64(m,3H),7.68(m, 1H),7.75(d,1H),7.89(d,2H),7.95(m,1H),8.04(s,2H),10.5(s,1H).

[0066] Example 2: Synthesis of polymerization inhibitor NBQ-2

[0067] The synthesis route is as follows:

[0068]

[0069] Synthesis of compound 2a:

[0070] Same as compound 1a.

[0071] Synthesis of compound 2c:

[0072] Weigh 1.14 g (0.007 mol) of compound 2b and 1.15 g (0.007 mol) of compound 2a into a 50 mL single-necked flask. Add 2.31 g (0.015 mol) of dry anhydrous aluminum trichloride. Add 10 mL of concentrated sulfuric acid dropwise to the round-bottom flask in batches (add slowly in batches, waiting for the flask to cool down after each addition before adding the next). After the addition is complete, heat the mixture in an oil bath and slowly raise the temperature to 120 °C, and continue to maintain the temperature for 4 h. After the reaction is complete, quench the reaction in 20 mL of ice water. Extract the mixture three times with 30 mL of ethyl acetate. Wash the extracted organic phase three times with 5% sodium bicarbonate solution, and then wash it three times with saturated NaCl solution. Collect the ethyl acetate phase, dry it with anhydrous sodium sulfate, filter off the sodium sulfate, and evaporate the solvent. Recrystallize the mixture with 95% ethanol to obtain the final product, with a yield of 49%.

[0073] 1 H NMR (500MHz, DMSO-d6): δ1.01(t,3H),2.42(s,3H),2.59(q,2H),3.81(s,2H),7.45(m,1H),7.71-7.92(m,3H),10.51(s,1H).

[0074] Synthesis of compound 2e:

[0075] Same as compound 1e.

[0076] Synthesis of polymerization inhibitor NBQ-2:

[0077] Weigh 1.08 g (0.003 mol) of compound 2e into a dry 100 mL two-necked flask, add 30 mL of dried anhydrous tetrahydrofuran and 0.03 g (0.001 mol) of magnesium shavings. After purging the air with nitrogen, initiate the reaction at room temperature under nitrogen protection. After 1 hour of reaction, once the Grignard reagent is prepared, slowly inject 5 mL of 0.3 g (1 mmol) of compound 2c dissolved in tetrahydrofuran into the system using a dried syringe. Continue the reaction at room temperature for 4 hours, monitoring the reaction process with thin-layer chromatography. After stopping the reaction, quench the remaining Grignard reagent in the system with 10 mL of saturated ammonium chloride, extract with tetrahydrofuran, separate the organic phase, and after multiple extractions, combine the organic phases. After drying with anhydrous sodium sulfate, place the organic phase in a rotary evaporator at a pressure of 20-30 kPa and a temperature of 40-50 °C to remove the solvent. Perform silica gel column chromatography with petroleum ether and ethyl acetate as eluents to obtain the target product.

[0078] 1 H NMR (500MHz, DMSO-d6): δ0.90(d,6H),0.99(t,3H),1.03(d,3H),1.20(t,2H),1.62(m,1H),2.34(m,1H),2.42(s,3H),2.59(q,2H),3.81(s ,2H),6.25(s,2H),6.92(s,1H),7.23(d,2H),7.31-7.39(m,2H),7.51-7.62(m,3H),7.68(s,1H),7.89(d,2H),8.07(s,2H),10.53(s,1H).

[0079] Example 3: Synthesis of polymerization inhibitor NBQ-3

[0080] The synthesis route is as follows:

[0081]

[0082] Synthesis of compound 3a:

[0083] Same as compound 1a.

[0084] Synthesis of compound 3c:

[0085] Same as compound 1c.

[0086] Synthesis of compound 3e:

[0087] 6.45 g (20 mmol) of compound 3d, 5.33 g (2.5 mmol) of zinc chloride, 3.51 g (30 mmol) of chlorosulfonic acid, and 0.92 g (30 mmol) of formaldehyde were weighed and stirred at 0 °C for 7 h. After the reaction was completed, 10 mL of water was added to quench the reaction. After extraction with 30 mL of dichloromethane, the organic phase was washed with 5% sodium carbonate aqueous solution, the solvent was removed by rotary evaporation, and the intermediate product 3e was obtained by column chromatography with silica gel, with a yield of 69%.

[0088] 1 H NMR (500MHz, DMSO-d6): δ0.91(d,6H),1.03(d,3H),1.20(t,2H),1.38(s,9H),1.58-1.64(m,1 H),2.30-2.38(m,1H),4.66(s,2H),6.23(s,2H),6.98-7.08(m,2H),7.34(s,1H),8.04(s,2H).

[0089] Synthesis of polymerization inhibitor NBQ-3:

[0090] Weigh 1.11 g (0.003 mol) of compound 3e into a dry 100 mL two-necked flask, add 30 mL of dried anhydrous tetrahydrofuran and 0.03 g (0.001 mol) of magnesium shavings. After purging the air with nitrogen, initiate the reaction at room temperature under nitrogen protection. After 1 hour of reaction, once the Grignard reagent is prepared, slowly inject 5 mL of 0.3 g (1 mmol) of compound 3c dissolved in tetrahydrofuran into the system using a dried syringe. Continue the reaction at room temperature for 4 hours, monitoring the reaction process with thin-layer chromatography. After stopping the reaction, quench the remaining Grignard reagent in the system with 10 mL of saturated ammonium chloride, extract with tetrahydrofuran, separate the organic phase, and after multiple extractions, combine the organic phases. After drying with anhydrous sodium sulfate, place the organic phase in a rotary evaporator at a pressure of 20-30 kPa and a temperature of 40-50 °C to remove the solvent. Perform silica gel column chromatography with petroleum ether and ethyl acetate as eluents to obtain the target product.

[0091] 1H NMR (500MHz, DMSO-d6): δ0.89(d,6H),0.98(t,3H),1.01(d,3H),1.19(t,2H),1.35(s,9H),1.58(m,1H),2.31(m,1H),2.56(q,2H),3.78(s ,2H),6.21(s,2H),6.88(s,1H),7.02(d,1H),7.32(d,1H),7.41(s,1H),7.56-7.81(m,6H),7.92-8.01(m,1H),8.01(s,2H),10.32(s,1H).

[0092] Example 4: Synthesis of polymerization inhibitor NBQ-4

[0093] The synthesis route is as follows:

[0094]

[0095] Synthesis of compound 4a:

[0096] Same as compound 1a.

[0097] Synthesis of compound 4c:

[0098] Same as compound 2c.

[0099] Synthesis of compound 4e:

[0100] Same as compound 3e.

[0101] Synthesis of polymerization inhibitor NBQ-4:

[0102] Weigh 1.11 g (0.003 mol) of compound 4e into a dry 100 mL two-necked flask, add 30 mL of dried anhydrous tetrahydrofuran and 0.03 g (0.001 mol) of magnesium shavings. After purging the air with nitrogen, initiate the reaction at room temperature under nitrogen protection. After 1 hour of reaction, once the Grignard reagent is prepared, slowly inject 5 mL of 0.3 g (1 mmol) of compound 4c dissolved in tetrahydrofuran into the system using a dried syringe. Continue the reaction at room temperature for 4 hours, monitoring the reaction process with thin-layer chromatography. After stopping the reaction, quench the remaining Grignard reagent in the system with 10 mL of saturated ammonium chloride, extract with tetrahydrofuran, separate the organic phase, and after multiple extractions, combine the organic phases. Dry with anhydrous sodium sulfate, place the organic phase in a rotary evaporator, set the pressure to 20-30 kPa, and the temperature to 40-50 °C to remove the solvent, and perform silica gel column chromatography with petroleum ether and ethyl acetate as eluents to obtain the target product.

[0103] 1H NMR (500MHz, DMSO-d6): δ0.90(d,6H),0.99(t,3H),1.03(d,3H),1.23(t,2H),1.38(s,9H),1.62(m,1H),2.36(m,1H),2.40(s,3H),2.62(q ,2H),3.83(s,2H),6.27(s,2H),6.93(s,1H),7.06(d,1H),7.32-7.41(m,2H),7.43(s,1H),7.49-7.72(m,5H),8.05(s,2H),10.53(s,1H).

[0104] Example 5:

[0105] The polymerization inhibition properties of compounds NBQ-1, NBQ-2, NBQ-3, and NBQ-4 in Examples 1, 2, 3, and 4 on styrene:

[0106] Add a certain amount of the styrene polymerization inhibitor solution and TBC solution (phenolic polymerization inhibitor for styrene) from Examples 1-4 to the stoppered colorimetric tube.

[0107] Subsequently, 50±0.001g of pure styrene monomer was weighed and added to the corresponding colorimetric tubes mentioned above. After thorough mixing, the tubes were plugged and placed in a preheated 100℃ oil bath for 2 hours. The tubes were then removed and the polymer was washed out with methanol. The tubes were dried in an oven to constant weight, and the mass of the polymer was measured. The specific results are recorded below.

[0108] Table 1. Results of Polymer Quality Evaluation Based on Inhibitor Dosage.

[0109]

[0110] As can be seen from the data in the table, in Examples 1-4, the polymer mass continuously decreased with the increase of the amount of inhibitor solution added, thus indicating a decrease in the degree of polymerization of styrene. Compared with commonly used inhibitors, the inhibitors provided in this invention can achieve good polymerization inhibition effects even with very small amounts used, and the polymerization inhibition effects of methyl and tert-butyl substituted compounds are superior to those of other compounds.

Claims

1. A styrene polymerization inhibitor, having the following general structural formula: The substituent R1 is independently selected from hydrogen atom and methyl, and R2 is independently selected from hydrogen atom and tert-butyl.

2. The styrene polymerization inhibitor as described in claim 1, characterized in that, The structure of the polymerization inhibitor is as follows:

3. The method for preparing the polymerization inhibitor as described in claim 1 or 2, characterized in that, Includes the following steps: Step 1): N-ethylbenzylamine, oxidant, and catalyst are added to solvent one, heated and stirred to react. After the reaction is completed, the solvent is removed and recrystallized to obtain N-ethyl-N-hydroxybenzylamine. Step 2): Phthalic anhydride compounds and N-ethyl-N-hydroxybenzamine obtained in step (1) are mixed and then acid and catalyst are added. The mixture is heated to react. After the reaction is completed, the reaction is quenched with ice water. After extraction, concentration, solvent removal and recrystallization, intermediate product c is obtained. Step 3): N-(1,3-dimethylbutyl)-N-phenyl-p-quinone diimine compound, catalyst, and chloromethylating agent are stirred at low temperature. After the reaction is completed, the mixture is extracted and washed, and then purified by separation to obtain intermediate product e. Step 4): Add the intermediate product e obtained in step (3) to solvent 2, and under nitrogen protection, add magnesium shavings to react and prepare intermediate product f; dissolve intermediate product c in solvent 2 and add it to the reaction system. After the reaction is completed, quench the reaction, concentrate and remove the solvent, and obtain the polymerization inhibitor by separation and purification.

4. The preparation method according to claim 3, characterized in that, In step 1), the oxidant is selected from hydrogen peroxide or sodium periodate; and / or, the catalyst is selected from Na2WO4, RuO4, or RuO2; and / or, the molar ratio of N-ethylbenzylamine to the oxidant is 1:1-2; and / or, the molar ratio of N-ethylbenzylamine to the catalyst is 1:0.1-0.5; and / or, the reaction temperature is 20-40℃, and the reaction time is 3-6 h; and / or, the solvent is methanol or ethanol; and / or, the recrystallization solvent is diethyl ether or tetrahydrofuran.

5. The preparation method according to claim 3 or 4, characterized in that, In step 2), the structural formula of the phthalic anhydride compound is: Wherein R1 is independently selected from hydrogen atom and methyl group, the molar ratio of the phthalic anhydride compound to N-ethyl-N-hydroxybenzylamine is 1:1-2; and / or, the reaction temperature is 100-120℃, the reaction time is 3-4h; and / or, the acid is concentrated sulfuric acid or concentrated phosphoric acid, the molar ratio of the acid to the phthalic anhydride compound is 20-30:

1.

6. The preparation method according to any one of claims 3-5, characterized in that, In step 2), the catalyst is selected from anhydrous AlCl3, CaCl2, ZnCl2, FeCl3, SnCl4, TiCl4, and the molar ratio of the catalyst to phthalic anhydride is 1-3:1; and / or, the extraction solvent is dichloromethane or ethyl acetate; and / or, the recrystallization solvent is methanol or ethanol.

7. The preparation method according to any one of claims 3-6, characterized in that, In step 3), the catalyst is selected from anhydrous AlCl3, CaCl2, ZnCl2, FeCl3, SnCl4, TiCl4; and / or, the chloromethylating agent is selected from methylal-chlorosulfonic acid, formaldehyde-chlorosulfonic acid, formaldehyde-hydrochloric acid, methylal-hydrochloric acid, paraformaldehyde-hydrochloric acid, paraformaldehyde-trifluoroacetic acid; and / or, the molar ratio of N-(1,3-dimethylbutyl)-N-phenyl-p-quinone diimide compound to catalyst is 1:0.1-0.5; and / or, the molar ratio of N-(1,3-dimethylbutyl)-N-phenyl-p-quinone diimide compound to chloromethylating agent is 1:0.8-1.

5.

8. The preparation method according to any one of claims 3-7, characterized in that, In step 3), the reaction temperature is 0-10℃, the reaction time is 4-8h; and / or, the extractant in the extraction step is selected from chloroform, dichloromethane, ethyl acetate; and / or, the detergent is selected from aqueous solution, saturated sodium chloride aqueous solution, sodium carbonate solution.

9. The preparation method according to any one of claims 3-8, characterized in that, In step 4), the molar ratio of magnesium shavings to intermediate product e is 1:1-5; and / or, solvent two is tetrahydrofuran or anhydrous diethyl ether; and / or, the reaction time of intermediate product e with magnesium shavings is 0.5-1 h, and the reaction temperature is 0-20 °C; and / or, the molar ratio of intermediate product f to intermediate product c is 1:1-5; and / or, the reaction time of intermediate product f with intermediate product c is 0.5-4 h, and the reaction temperature is 0-20 °C.

10. The use of the polymerization inhibitor as described in claim 1 or 2, or the polymerization inhibitor prepared by any one of claims 3-9, in inhibiting styrene polymerization.

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