Preparation method of p-acetoxystyrene

Abstract

The invention relates to the field of organic synthesis, and discloses a preparation method of p-acetoxystyrene, which comprises the following steps: S1, carrying out acetylation reaction on p-hydroxyacetophenone to prepare p-acetoxyacetophenone M1; s2, carrying out hydrogenation reduction on the p-acetoxyacetophenone, so as to prepare 1-(4-acetoxyphenyl)-1-ethanol M2; s3, 1-(4-acetoxyphenyl)-1-ethanol is subjected to an elimination reaction, and p-acetoxystyrene is prepared. According to the preparation method, multiple times of water washing and an extraction aftertreatment technology are adopted, the purity of a product obtained in each step is well improved, and therefore the high-purity and high-yield p-acetoxystyrene preparation technology is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a method for preparing p-acetoxystyrene. Background Art

[0003] There are two main methods for synthesizing 4-acetoxystyrene. The first method is to prepare 4-acetoxystyrene from hydroxyacetophenone through three steps of acetylation, hydrogenation reduction and dehydration elimination. The second method is to prepare 4-acetoxystyrene from hydroxybenzaldehyde through decarboxylation of hydroxycinnamic acid. Jiang Xiaoping (Synthesis of 4-acetoxystyrene by catalytic hydrogenation, Fine Chemicals, 2011, 28 (9): 920-923) uses 4-hydroxyacetophenone as a raw material, and obtains 4-acetoxystyrene through acetylation, catalytic hydrogenation and dehydration reactions. However, the yield is low, only 68.5%. Invention patent CN1106554624 uses 4-hydroxyacetophenone as a raw material, and prepares 4-acetoxystyrene through acetylation, hydrogenation reduction and alkaline dehydration reactions. The dehydration is carried out using strong bases such as sodium hydroxide and potassium hydroxide. The reaction yield is improved, but it is still less than 80%. In addition, the use of strong bases for dehydration reactions will produce a large amount of three wastes pollution. Invention patent CN111087303 uses p-acetoxyphenylethanol as raw material and solid acid as catalyst for dehydration reaction to prepare p-acetoxystyrene by one-pot method. The method has simple steps, but the raw material p-acetoxyphenylethanol is not easy to obtain and the yield is not high, less than 78%. Invention patent CN 116102422 uses p-acetoxyacetophenone as raw material, first catalytic hydrogenation of carbonyl to obtain 4-acetoxyphenyl-1-ethanol, then p-toluenesulfonyl chloride or methanesulfonyl chloride is used to protect the hydroxyl group to obtain 4-{1-[(methylsulfonyl / p-toluenesulfonyl)oxy]ethyl}phenyl acetate, and finally potassium hydrogen sulfate is used as catalyst to perform reflux elimination reaction in trifluorotoluene to obtain p-acetoxystyrene, but the yield is also not high, less than 80%. Invention patent CN 112694402 acetylates p-hydroxyacetophenone to generate p-acetoxyacetophenone, then catalytically reduces it to 4-acetoxyphenyl-1-ethanol in a hydrogen environment, and finally dehydrates it in an alkaline ionic liquid to obtain p-acetoxystyrene, and the product yield is improved, with a yield of up to 90%. Invention patent CN 112409176 acetylates p-bromophenol to generate p-acetoxybromobenzene, then couples p-acetoxybromobenzene with a vinyl boric acid compound to obtain p-acetoxystyrene, with a yield of more than 90%. Invention patent CN 113336645 uses p-hydroxybenzaldehyde as a raw material and adopts a one-pot method to synthesize p-acetoxystyrene. First, p-hydroxybenzaldehyde and acetic anhydride are subjected to an acylation reaction to obtain p-acetoxybenzaldehyde, and then the p-acetoxycinnamic acid is generated by a Purkin reaction with acetic anhydride, and finally p-acetoxystyrene is prepared by a decarboxylation reaction, with a yield of less than 83%.

[0004] In summary, the existing technology for synthesizing acetoxystyrene has low yield and purity. As the core resin of photoresist, the purity needs to reach more than 98% to meet the requirements. In addition, the yield is low and a large amount of by-products will be produced, making post-processing difficult and difficult to meet large-scale production. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing p-acetoxystyrene. The preparation method of the present invention adopts multiple water washing and extraction post-treatment technology, which greatly improves the purity of the product obtained in each step and reduces the content of by-products, thereby realizing a high-purity and high-yield p-acetoxystyrene preparation technology, which is more suitable for industrial production.

[0006] The above technical purpose of the present invention is achieved through the following technical scheme: The present invention provides a method for preparing acetoxystyrene, comprising the following steps and equation:

[0007]

[0008] S1: acetylation of p-hydroxyacetophenone to prepare p-acetoxyacetophenone M1;

[0009] S2: hydrogenating and reducing p-acetoxyacetophenone to prepare 1-(4-acetoxyphenyl)-1-ethanol M2;

[0010] S3: subjecting 1-(4-acetoxyphenyl)-1-ethanol to an elimination reaction to prepare p-acetoxystyrene.

[0011] The bulk preparation method of acetoxystyrene, the synthesis steps are as follows:

[0012] In the first step (S1), under nitrogen protection, 1120-1360 parts by weight of p-hydroxyacetophenone, 950-1300 parts by weight of the first solvent, 450-600 parts by weight of deionized water, and 785-808 parts by weight of a base are added to a three-necked flask, stirring is started, and 920-1105 parts by weight of an acetylating agent are slowly added dropwise at a temperature of 0-60°C. After the addition is completed, the reaction temperature is controlled at 45-120°C, and the reaction is continued for 6-10 hours. After the reaction is completed, 2650-2865 parts by weight of 8-10% alkali solution is added, the temperature is controlled at 35-60°C, and stirring is performed for 15-30 minutes. The reaction liquid is layered, the water layer is cut off, and the organic layer is retained. Add 540-800 parts by weight of deionized water to the organic layer, stir at room temperature for 20-40 minutes, cut off the water phase, retain the organic phase, repeat the water washing process twice, concentrate the collected organic phase solution under negative pressure to 10-15% solid content, then add 400-750 parts by weight of the second solvent, place it in an environment of 0-5°C for 1-2 hours, precipitate crystals, filter, wash the filtrate with deionized water for 3-10 times, place it in a vacuum drying oven at 40°C and dry it for 72 hours to obtain 4-acetoxyacetophenone M1. Yield: 87-89%, purity: 99.2-99.5%.

[0013] The first step (S1) reaction is the acetylation reaction of the hydroxyl group of p-hydroxyacetophenone with the acetylating agent to generate p-acetoxyacetophenone M1. The mechanism is that under the catalysis of the base, the hydroxyl group in the p-hydroxyacetophenone structure reacts with the acetyl group in the acetylating agent, and an acidic substance is generated at the same time. The generated acidic substance immediately forms a salt with the base in the reaction system to ensure the smooth progress of the reaction. The system of the first step reaction includes the product, the salt generated by the acidic substance and the base, the p-hydroxyacetophenone that has not reacted completely, and the acetylating agent. The reaction product M1 is dissolved in the organic phase and is finally purified by recrystallization; the hydrophilicity of the reaction raw material p-hydroxyacetophenone is better than that of the reaction product M1, and the residual amount is very small, which enters the water phase and is removed by water washing. Another reaction raw material acetylating agent and the generated salt are both water-soluble and can be removed by water washing.

[0014] Step 2 (S2), under nitrogen protection, add 760-860 parts by weight of M1 and 1100-1500 parts by weight of the third solvent to the reactor, control the reaction temperature at 20-40°C, add 46-53 parts by weight of the reducing agent in three batches, and react for 2-4 hours. After the reaction is completed, adjust the pH to 6.5-6.8 with 20-30% inorganic acid, add 360-480 parts by weight of the fourth solvent, separate the layers, separate the water phase, retain the organic phase, add 650-700 parts by weight of 20-25% alkali solution to the organic phase, stir at room temperature for 10-20 minutes, separate the layers, separate the water phase, and retain the organic phase; add 420-600 parts by weight of desalted water to the organic phase, stir at room temperature for 20-35 minutes, separate the layers, separate the water phase, and retain the organic phase; the operation of washing the organic phase with desalted water is repeated twice. The organic phase is dried over 4A molecular sieves for 48-72 hours, and the solvent is removed under reduced pressure to obtain the intermediate M2; yield: 91-93%, purity: 99.5-99.7%.

[0015] The second step (S2) reaction is to reduce the acetoxyacetophenone M1 obtained in the first step by a reducing agent to prepare 1-(4-acetoxyphenyl)-1-ethanol M2. The reaction mechanism is that the ethyl ketone group in the structure of the acetoxyacetophenone M1 obtained in the first step is reduced to an ethanol group to obtain 1-(4-acetoxyphenyl)-1-ethanol M2. After the reaction is completed, the reaction system contains the reaction product M2, the reaction raw material acetoxyacetophenone M1, the reducing agent, the inorganic acid, and the inorganic salt obtained by the neutralization reaction of the inorganic acid with the alkali solution. Among them, the reducing agent, the inorganic acid, and the inorganic salt obtained by the neutralization reaction of the inorganic acid with the alkali solution in the reaction raw materials are all water-soluble substances and can be completely removed by washing with water. The reducing agent is excessive in the reaction, so the reaction of the reaction raw material acetoxyacetophenone M1 is relatively complete, and the unreacted M1 residue is less than 0.5%, and does not need to be treated separately.

[0016] Step 3 (S3), in a three-necked flask, under nitrogen protection, add 450-570 parts by weight of M2, 1.35-8.95 parts by weight of inhibitor and 0.85-2.65 parts by weight of catalyst, stir and react at 150-210°C for 2-4 hours, after the reaction, add 350-500 parts by weight of the fifth solvent, separate the layers, separate the water phase, retain the organic phase, add 300-450 parts by weight of 15-20% alkali solution (sodium hydroxide solution) to the organic phase, stir at room temperature for 20-50 minutes, separate the layers, separate the water phase, retain the organic phase; add 200-300 parts by weight of deionized water to the organic phase, stir at room temperature for 10-20 minutes, separate the layers, separate the water phase, retain the organic phase; the operation of washing the organic phase with deionized water is repeated twice. The organic phase is dried with anhydrous magnesium sulfate for 48-96 hours, the solvent is removed under reduced pressure, and the organic phase is adsorbed with activated carbon to obtain acetoxystyrene. Yield: 86-88%, purity: 98.5-98.8%.

[0017] The third step (S3) reaction is that 1-(4-acetoxyphenyl)-1-ethanol M2 is prepared into a p-acetoxystyrene product under the action of a catalyst. The reaction mechanism is that the ethanol group in 1-(4-acetoxyphenyl)-1-ethanol M2 removes a water molecule to form a vinyl group under the action of a catalyst to obtain the product p-acetoxystyrene. After the reaction is completed, there is a p-acetoxystyrene product in the reaction system, and the reaction raw materials 1-(4-acetoxyphenyl)-1-ethanol M2, an inhibitor, a catalyst and an alkali solution. The reaction raw materials inhibitor, catalyst and alkali solution are also all water-soluble, and are removed by cutting off the water phase, and then completely removed by multiple water washings. The reaction product enters the organic phase, and after removing the solvent, the trace amount of residual incompletely reacted raw material (4-acetoxyphenyl)-1-ethanol M2 can be adsorbed with activated carbon to obtain a high-purity p-acetoxystyrene product.

[0018] The first solvent described in the first step is preferably one or more combinations of ethyl acetate, acetone, butanone, tetrahydrofuran, dichloromethane, dichloroethane, propylene carbonate, etc.

[0019] The base described in the first step can be an organic base or an inorganic base, preferably one or more of sodium carbonate, potassium carbonate, triethylamine, di-n-butylamine, dipropylamine, pyridine, and diisopropylamine.

[0020] The acetylating agent described in the first step is preferably one or more of acetyl chloride, acetic anhydride and glacial acetic acid.

[0021] The alkali solution in the first step, the second step and the third step is an inorganic alkali solution, preferably 8-10% concentration of sodium carbonate, potassium carbonate, sodium hydroxide, sodium bicarbonate and potassium hydroxide solution.

[0022] The second solvent in the first step is preferably one or more of petroleum ether, n-hexane and cyclohexane.

[0023] The third solvent and the fourth solvent described in the second step are preferably one or more of ethyl acetate, dimethyl carbonate, methanol, ethanol, n-butanol, toluene and xylene.

[0024] The reducing agent in the second step is preferably one or more of sodium borohydride, lithium borohydride, lithium aluminum hydride, and aluminum isopropoxide.

[0025] The inorganic acid in the second step is preferably one or more of phosphoric acid, hydrochloric acid, sulfuric acid, nitric acid and carbonic acid.

[0026] The inhibitor described in the third step is preferably one or more of p-tert-butylcatechol, p-hydroxyanisole, phenothiazine, hydroquinone, N-oxyl (nitroxide) and 1,6-hexylene-bis(N-formyl-N-(1-oxyl-2,2,6,6,-tetramethylpiperidinyl)-4-yl)amine.

[0027] The catalyst in the third step is preferably one or more of phthalic anhydride, acetic anhydride, phosphoric acid, and glacial acetic acid.

[0028] The fifth solvent in the third step is preferably one or more of chloroform, dichloromethane, dichloroethane and carbon tetrachloride.

[0029] The beneficial effects of the present invention are:

[0030] The target product, acetoxystyrene, is completed in three steps. The purity and yield of each step will affect the final yield. In the present invention, the intermediates of the first and second steps are post-treated by water washing, acid washing or alkali washing, and the unreacted raw materials, the generated by-products, salts and acids are completely removed, which greatly improves the purity of the product of each step, and finally obtains a product with a yield of 86-88% and a purity of 98.5-98.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 is the H NMR spectrum of 4-acetoxystyrene in Example 1 of the present invention;

[0033] Figure 2 It is the liquid chromatogram of acetoxystyrene in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than 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. DETAILED DESCRIPTION

[0036] Example 1: Preparation of p-acetoxystyrene

[0037] Step 1: Under nitrogen protection, add 1360g of p-hydroxyacetophenone, 1300g of dichloromethane, 600g of deionized water, and 808g of sodium carbonate into a three-necked flask, start stirring, and slowly add 1105g of acetyl chloride at 0°C. After the addition is complete, the reaction temperature is controlled at 45°C and the reaction is continued for 10 hours. After the reaction is completed, add 2650g of 10% sodium bicarbonate aqueous solution, control the temperature at 35°C, stir for 30min, and separate the reaction liquid into layers. Cut off the upper water layer and retain the lower solution. 800 g of deionized water was added to the lower solution, stirred at room temperature for 20 min, the upper aqueous phase was cut off, the lower solution was retained, the water washing process was repeated twice, the collected lower solution was concentrated to 10% solid content under negative pressure, and then 750 g of petroleum ether was added, placed in an environment of 5°C for 2 hours, crystals were precipitated, filtered, the filtrate was washed with deionized water 3 times, placed in a vacuum drying oven at 45°C for 48 hours, and 4-acetoxyacetophenone M1 was obtained. Yield: 89%, purity: 99.0%.

[0038] Step 2: Under nitrogen protection, add 860g of M1 and 1500g of methanol to the reactor, control the reaction temperature at 20°C, add 53g of sodium borohydride in three batches, and react for 4 hours. After the reaction, adjust the pH to 6.5 with 30% sulfuric acid, add 380g of xylene, separate the layers, separate the water phase, retain the organic phase, add 650g of 20% sodium carbonate solution to the organic phase, stir at room temperature for 20min, separate the layers, separate the water phase, and retain the organic phase; add 600g of desalted water to the organic phase, stir at room temperature for 20min, separate the layers, separate the water phase, and retain the organic phase; repeat the operation of washing the organic phase with desalted water twice. The organic phase is dried with anhydrous magnesium sulfate for 48 hours, and the solvent is removed under reduced pressure to obtain the intermediate M2; yield: 91%, purity: 98.1%.

[0039] Step 3: In a three-necked flask, under nitrogen protection, add 450g of M2, 1.35g of p-tert-butylcatechol and 0.85g of phosphoric acid, stir and react at 150°C for 4 hours. After the reaction, add 500g of dichloromethane, separate the layers, separate the water phase, retain the organic phase, add 300g of 20% sodium carbonate solution to the organic phase, stir at room temperature for 20min, separate the layers, separate the water phase, retain the organic phase; add 200g of deionized water to the organic phase, stir at room temperature for 20min, separate the layers, separate the water phase, retain the organic phase; repeat the operation of washing the organic phase with deionized water twice. Dry the organic phase with anhydrous magnesium sulfate for 48 hours, remove the solvent under reduced pressure, and adsorb the organic phase with activated carbon to obtain p-acetoxystyrene. Yield: 89%, purity: 98.5%.

[0040] Figure 1 is the H-NMR spectrum; Figure 2 It is a liquid chromatogram.

[0041] Example 2: Preparation of p-acetoxystyrene

[0042] Step 1: Under nitrogen protection, add 1120g of p-hydroxyacetophenone, 950g of ethyl acetate, 450g of deionized water, and 785g of potassium carbonate into a three-necked flask, start stirring, and slowly add 920g of acetic anhydride at a temperature of 60°C. After the addition is complete, the reaction temperature is controlled at 120°C and the reaction is continued for 6 hours. After the reaction is completed, add 2865g of 8% sodium carbonate aqueous solution, control the temperature at 60°C, stir for 15min, and the reaction liquid is layered, the upper water layer is cut off, and the lower solution is retained. 540 g of deionized water was added to the lower solution, stirred at room temperature for 40 min, the upper aqueous phase was cut off, the lower solution was retained, the water washing process was repeated twice, the collected lower solution was concentrated to 15% solid content under negative pressure, and then 400 g of n-hexane was added, placed in a 0°C environment for 1 hour, crystals were precipitated, filtered, the filtrate was washed with deionized water 10 times, placed in a vacuum drying oven at 40°C and dried for 72 hours to obtain 4-acetoxyacetophenone M1. Yield: 87%, purity: 99.5%.

[0043] Step 2: Under nitrogen protection, add 760g of M1 and 1100g of ethanol to the reactor, control the reaction temperature at 40°C, add 46g of lithium borohydride in three batches, and react for 2 hours. After the reaction, adjust the pH to 6.8 with 20% phosphoric acid, add 480g of toluene, separate the layers, separate the water phase, retain the organic phase, add 700g of 25% sodium hydroxide solution to the organic phase, stir at room temperature for 10min, separate the layers, separate the water phase, and retain the organic phase; add 420g of desalted water to the organic phase, stir at room temperature for 35min, separate the layers, separate the water phase, and retain the organic phase; repeat the operation of washing the organic phase with desalted water twice. The organic phase is dried with 4A molecular sieve for 72 hours, and the solvent is removed under reduced pressure to obtain the intermediate M2; yield: 93%, purity: 99.7%.

[0044] Step 3: In a three-necked flask, under nitrogen protection, add 450g of M2, 1.35g of p-tert-butylcatechol and 0.85g of phosphoric acid, stir and react at 150°C for 4 hours. After the reaction, add 500g of dichloromethane, separate the layers, separate the water phase, retain the organic phase, add 300g of 20% sodium carbonate solution to the organic phase, stir at room temperature for 20min, separate the layers, separate the water phase, retain the organic phase; add 200g of deionized water to the organic phase, stir at room temperature for 20min, separate the layers, separate the water phase, retain the organic phase; repeat the operation of washing the organic phase with deionized water twice. Dry the organic phase with anhydrous magnesium sulfate for 48 hours, remove the solvent under reduced pressure, and adsorb the organic phase with activated carbon to obtain p-acetoxystyrene. Yield: 86%, purity: 98.3%.

[0045] Example 3: Preparation of p-acetoxystyrene

[0046] Step 1: Under nitrogen protection, add 1250g of p-hydroxyacetophenone, 1100g of butyl acetate, 530g of deionized water, and 790g of triethylamine to a three-necked flask, start stirring, and slowly add 950g of acetic acid at a temperature of 30°C. After the addition is complete, the reaction temperature is controlled at 60°C and the reaction is continued for 8 hours. After the reaction is completed, add 2710g of 9% sodium hydroxide aqueous solution, control the temperature at 40°C, stir for 20min, separate the reaction liquid into layers, cut off the upper water layer, and retain the lower solution. 600 g of deionized water was added to the lower solution, stirred at room temperature for 30 min, the upper aqueous phase was cut off, the lower solution was retained, the water washing process was repeated twice, the collected lower solution was concentrated to 12% solid content under negative pressure, and then 600 g of cyclohexane was added, placed in an environment of 2°C for 1.5 hours, crystals were precipitated, filtered, the filtrate was washed with deionized water 5 times, placed in a vacuum drying oven at 40°C for 48 hours, and acetoxyacetophenone M1 was obtained. Yield: 88%, purity: 99.4%.

[0047] Step 2: Under nitrogen protection, add 820g of M1 and 1300g of isopropanol to the reactor, control the reaction temperature at 30°C, add 50g of lithium aluminum hydride in three batches, and react for 3 hours. After the reaction, adjust the pH to 6.7 with 25% nitric acid, add 420g of propylene carbonate, separate the layers, separate the water phase, retain the organic phase, add 680g of 22% sodium bicarbonate solution to the organic phase, stir at room temperature for 15min, separate the layers, separate the water phase, and retain the organic phase; add 450g of deionized water to the organic phase, stir at room temperature for 25min, separate the layers, separate the water phase, and retain the organic phase; repeat the operation of washing the organic phase with deionized water twice. The organic phase is dried with 4A molecular sieve for 56 hours, and the solvent is removed under reduced pressure to obtain the intermediate M2; yield: 92%, purity: 99.6%.

[0048] Step 3: In a three-necked flask, under nitrogen protection, add 550g of M2, 4.52g of p-phenothiazine and 1.35g of glacial acetic acid, stir and react at 180°C for 3 hours. After the reaction, add 400g of dichloroethane, separate the layers, separate the water phase, retain the organic phase, add 400g of 18% potassium hydroxide solution to the organic phase, stir at room temperature for 30min, separate the layers, separate the water phase, retain the organic phase; add 280g of deionized water to the organic phase, stir at room temperature for 15min, separate the layers, separate the water phase, retain the organic phase; repeat the operation of washing the organic phase with deionized water twice. Dry the organic phase with anhydrous magnesium sulfate for 56 hours, remove the solvent under reduced pressure, and adsorb the organic phase with activated carbon to obtain p-acetoxystyrene. Yield: 87%, purity: 98.6%.

[0049] Example 4: Preparation of p-acetoxystyrene

[0050] Step 1: Under nitrogen protection, add 1180g of p-hydroxyacetophenone, 1080g of ether, 540g of deionized water, and 800g of pyridine to a three-necked flask, start stirring, and slowly add 980g of glacial acetic acid at 20°C. After the addition is complete, the reaction temperature is controlled at 65°C and the reaction is continued for 7 hours. After the reaction is completed, add 2700g of 10% potassium carbonate aqueous solution, control the temperature at 45°C, stir for 20min, separate the reaction liquid into layers, cut off the upper water layer, and retain the lower solution. 650 g of deionized water was added to the lower solution, stirred at room temperature for 35 min, the upper aqueous phase was cut off, the lower solution was retained, the water washing process was repeated twice, the collected lower solution was concentrated to 15% solid content under negative pressure, and then 620 g of petroleum ether was added, placed in an environment of 2°C for 1 hour, crystals were precipitated, filtered, the filtrate was washed with deionized water 6 times, and placed in a vacuum drying oven at 40°C for 72 hours to obtain 4-acetoxyacetophenone M1. Yield: 87.5%, purity: 99.4%.

[0051] Step 2: Under nitrogen protection, add 810g of M1 and 1300g of n-butanol to the reactor, control the reaction temperature at 25°C, add 52g of aluminum isopropoxide in three batches, and react for 2.5 hours. After the reaction, adjust the pH to 6.7 with 30% hydrochloric acid, add 420g of xylene, separate the layers, separate the water phase, retain the organic phase, add 680g of 22% sodium hydroxide solution to the organic phase, stir at room temperature for 10min, separate the layers, separate the water phase, and retain the organic phase; add 450g of deionized water to the organic phase, stir at room temperature for 30min, separate the layers, separate the water phase, and retain the organic phase; repeat the operation of washing the organic phase with deionized water twice. The organic phase is dried with 4A molecular sieve for 48 hours, and the solvent is removed under reduced pressure to obtain the intermediate M2; yield: 92.5%, purity: 99.7%.

[0052] Step 3: In a three-necked flask, under nitrogen protection, add 520g of M2, 6.25g of N-oxyl (nitroxide) and 1.45g of acetic anhydride, stir and react at 200°C for 3.5 hours. After the reaction, add 450g of dichloromethane, separate the layers, separate the water phase, retain the organic phase, add 380g of 19% potassium hydroxide solution to the organic phase, stir at room temperature for 40min, separate the layers, separate the water phase, retain the organic phase; add 280g of deionized water to the organic phase, stir at room temperature for 15min, separate the layers, separate the water phase, retain the organic phase; repeat the operation of washing the organic phase with deionized water twice. Dry the organic phase with anhydrous magnesium sulfate for 72 hours, remove the solvent under reduced pressure, and adsorb the organic phase with activated carbon to obtain p-acetoxystyrene. Yield: 86.5%, purity: 98.1%.

[0053] Example 5: Preparation of p-acetoxystyrene

[0054] Step 1: Under nitrogen protection, add 1228g of p-hydroxyacetophenone, 1150g of xylene, 500g of deionized water, and 795g of diisopropylamine to a three-necked flask, start stirring, and slowly add 985g of acetyl chloride at a temperature of 35°C. After the addition is complete, the reaction temperature is controlled at 105°C and the reaction is continued for 7 hours. After the reaction is completed, add 2730g of 10% sodium bicarbonate aqueous solution, control the temperature at 45°C, stir for 25min, and separate the reaction liquid into layers. Cut off the upper water layer and retain the lower solution. 740 g of deionized water was added to the lower solution, stirred at room temperature for 35 min, the upper aqueous phase was cut off, the lower solution was retained, the water washing process was repeated twice, the collected lower solution was concentrated under negative pressure to 12% solid content, and then 650 g of petroleum ether was added, placed in a 0°C environment for 1.5 hours, crystals were precipitated, filtered, the filtrate was washed with deionized water 6 times, placed in a vacuum drying oven at 40°C for 72 hours, and acetoxyacetophenone M1 was obtained. Yield: 88.5%, purity: 99.4%.

[0055] Step 2: Under nitrogen protection, add 820g of M1 and 1350g of isopropanol to the reactor, control the reaction temperature at 30°C, add 48g of sodium borohydride in three batches, and react for 3.5 hours. After the reaction, adjust the pH to 6.7 with 25% sulfuric acid, add 450g of xylene, separate the layers, separate the water phase, retain the organic phase, add 690g of 20% sodium carbonate solution to the organic phase, stir at room temperature for 15min, separate the layers, separate the water phase, and retain the organic phase; add 550g of deionized water to the organic phase, stir at room temperature for 35min, separate the layers, separate the water phase, and retain the organic phase; repeat the operation of washing the organic phase with deionized water twice. The organic phase is dried with 4A molecular sieve for 56 hours, and the solvent is removed under reduced pressure to obtain the intermediate M2; yield: 92.6%, purity: 99.7%.

[0056] Step 3: In a three-necked flask, under nitrogen protection, add 510g of M2, 6.25g of 1,6-hexylene-bis(N-formyl-N-(1-oxy-2,2,6,6,-tetramethylpiperidinyl)-4-yl)amine and 1.35g of acetic anhydride, stir and react at 170°C for 3.5 hours. After the reaction, add 550g of dichloromethane, separate the layers, separate the water phase, retain the organic phase, add 380g of 20% potassium hydroxide solution to the organic phase, stir at room temperature for 35min, separate the layers, separate the water phase, retain the organic phase; add 260g of deionized water to the organic phase, stir at room temperature for 15min, separate the layers, separate the water phase, retain the organic phase; repeat the operation of washing the organic phase with deionized water twice. Dry the organic phase with anhydrous magnesium sulfate for 48 hours, remove the solvent under reduced pressure, and adsorb the organic phase with activated carbon to obtain p-acetoxystyrene. Yield: 87.6%, purity: 98.8%.

[0057] Example 6: Preparation of p-acetoxystyrene

[0058] Step 1: Under nitrogen protection, add 1180g of p-hydroxyacetophenone, 1060g of ethyl acetate, 580g of deionized water, and 800g of pyridine to a three-necked flask, start stirring, and slowly add 995g of glacial acetic acid at a temperature of 35°C. After the addition is complete, the reaction temperature is controlled at 115°C and the reaction is continued for 8 hours. After the reaction is completed, add 2800g of 8% sodium bicarbonate aqueous solution, control the temperature at 40°C, stir for 15min, and the reaction liquid is layered, the upper water layer is cut off, and the lower solution is retained. 710 g of deionized water was added to the lower solution, stirred at room temperature for 30 min, the upper aqueous phase was cut off, the lower solution was retained, the water washing process was repeated twice, the collected lower solution was concentrated to 10% solid content under negative pressure, and then 470 g of petroleum ether was added, placed in an environment of 3°C for 1 hour, crystals were precipitated, filtered, the filtrate was washed with deionized water 5 times, and placed in a vacuum drying oven at 40°C for 72 hours to obtain 4-acetoxyacetophenone M1. Yield: 89%, purity: 99.4%.

[0059] Step 2: Under nitrogen protection, add 810g of M1 and 1340g of methanol to the reactor, control the reaction temperature at 30°C, add 49g of sodium borohydride in three batches, and react for 2.5 hours. After the reaction, adjust the pH to 6.5 with 25% hydrochloric acid, add 410g of xylene, separate the layers, separate the water phase, retain the organic phase, add 680g of 20% potassium carbonate solution to the organic phase, stir at room temperature for 15min, separate the layers, separate the water phase, and retain the organic phase; add 510g of desalted water to the organic phase, stir at room temperature for 28min, separate the layers, separate the water phase, and retain the organic phase; repeat the operation of washing the organic phase with desalted water twice. Dry the organic phase with 4A molecular sieve for 48 hours, remove the solvent under reduced pressure, and obtain the intermediate M2; yield: 92%, purity: 99.5%.

[0060] Step 3: In a three-necked flask, under nitrogen protection, add 470g of M2, 3.55g of p-hydroxyanisole and 1.03g of phosphoric acid, stir and react at 170°C for 3 hours. After the reaction, add 420g of carbon tetrachloride, separate the layers, separate the water phase, retain the organic phase, add 420g of 20% sodium bicarbonate solution to the organic phase, stir at room temperature for 25min, separate the layers, separate the water phase, retain the organic phase; add 240g of deionized water to the organic phase, stir at room temperature for 15min, separate the layers, separate the water phase, retain the organic phase; repeat the operation of washing the organic phase with deionized water twice. Dry the organic phase with anhydrous magnesium sulfate for 56 hours, remove the solvent under reduced pressure, and adsorb the organic phase with activated carbon to obtain p-acetoxystyrene. Yield: 87.5%, purity: 98.8%.

[0061] Comparative Example 1:

[0062] Step 1: 185 g of p-hydroxyacetophenone was dissolved in 850 ml of chloroform, 210 g of triethylamine was added, and the mixture was cooled to 0°C. 175 g of acetic anhydride was slowly added dropwise under stirring. After the addition was completed, the mixture was heated to 25°C and the reaction was continued for 2.5 hours. After the reaction was completed, 350 mL of water was added to quench the reaction, and the organic phase and the aqueous phase were separated. The aqueous phase was extracted three times with 200 mL of chloroform, and the organic phases were combined and concentrated to obtain p-acetoxyacetophenone with a yield of 78.5% and a yield of 90.5%.

[0063] Step 2: 95 g of p-acetoxyacetophenone was dissolved in 400 mL of ethanol, 8 g of Pd / C was added under nitrogen protection, hydrogen was introduced to replace the protected nitrogen, and the reaction was carried out under a hydrogen atmosphere at 2 MPa and 25 ° C for 5 hours. After the reaction was completed, Pd / C was removed by diatomaceous earth filtration, and the filtrate was directly concentrated to obtain 4-acetoxyphenylmethylmethanol with a yield of 71.5% and a yield of 89.5%.

[0064] Step 3: Add 45 g of 4-acetoxyphenylmethylmethanol, 0.1 g of phenothiazine and 180 g of 1-hexyl-3-methylimidazolium bromide to a reaction bottle, heat to 160°C and react for 4 hours. After the reaction, extract three times with 100 ml of toluene, add 150 ml of water to the organic phase, wash, and vacuum concentrate to obtain a crude product. Purify by reduced pressure distillation to obtain 4-acetoxystyrene with a yield of 65.8% and a purity of 88.6%.

[0065] Comparative Example 2:

[0066] Step 1: First, 450 g of hydroxyacetophenone was dissolved in 720 g of sodium hydroxide solution to form a pre-liquid, and then 28 g of 2-mercapto-R-butyrolactone was added into a reaction kettle, and then 610 g of acetic anhydride was added, and the temperature was raised to 60° C. to react for 4.5 hours;

[0067] Step 2: Under nitrogen protection, add the mixed solution generated by S1 and 36g of tetrabutylphenol hydroxybenzoate to the reactor, add 10.5g of lithium borohydride at 25°C, react for 1 hour, add 4.5g of concentrated hydrochloric acid dropwise, and filter under reduced pressure to obtain an intermediate oily substance;

[0068] Step 3: Under nitrogen protection, add the S2 oil to a reactor, add 110 g of acetic anhydride and 0.22 g of phosphoric acid, control the temperature at 195°C, react for 30 minutes, and distill under reduced pressure to obtain a crude product; the crude product is fractionated under reduced pressure at 105°C to obtain the product. The yield is 60% and the purity is 91.4%.

[0069] Compared with Comparative Examples 1 and 2, the present invention adopts multiple washing, recrystallization and other processes to remove a large number of by-products, so that a high-purity product can be obtained only by activated carbon adsorption in the later stage. However, in the comparative example, due to the presence of a large number of by-products in the synthesis process, especially the unsaturated double bonds in the product, polymerization will occur during high-temperature and reduced-pressure treatment, which greatly reduces the yield, and the polarity between the by-product and the product is equivalent, and they will also come out together during the vacuum distillation process, so the product purity is also low.

Claims

1. A method for preparing acetoxystyrene, characterized in that: The method comprises the following preparation steps: S1: acetylation of p-hydroxyacetophenone to prepare p-acetoxyacetophenone; S2: hydrogenating and reducing p-acetoxyacetophenone to prepare 1-(4-acetoxyphenyl)-1-ethanol; S3: subjecting 1-(4-acetoxyphenyl)-1-ethanol to an elimination reaction to prepare p-acetoxystyrene.

2. The method for preparing acetoxystyrene according to claim 1, wherein: The specific preparation method of step S1 is as follows: under nitrogen protection, 1120-1360 parts by weight of p-hydroxyacetophenone, 950-1300 parts by weight of the first solvent, 450-600 parts by weight of deionized water, and 785-808 parts by weight of a base are added to a three-necked flask, stirred, and 920-1105 parts by weight of an acetylating agent are slowly added dropwise at a temperature of 0-60° C.; after the addition is completed, the reaction temperature is controlled at 45-120° C., and the reaction is continued for 6-10 hours; after the reaction is completed, 2650-2865 parts by weight of 8-10% alkali solution is added, the temperature is controlled at 35-60° C., stirred for 15-30 minutes, the reaction liquid is separated into layers, the water layer is cut off, and the organic layer is retained; then the organic layer is washed with water, concentrated, crystallized, filtered, washed, and dried to obtain p-acetoxyacetophenone.

3. The method for preparing acetoxystyrene according to claim 1, characterized in that: The specific preparation method of step S2 is as follows: under nitrogen protection, adding 760-860 parts by weight of M1 and 1100-1500 parts by weight of the third solvent to a reactor, controlling the reaction temperature at 20-40° C., adding 46-53 parts by weight of a reducing agent in three batches, and reacting for 2-4 hours; after the reaction, adjusting the pH to 6.5-6.8 with 20-30% inorganic acid, adding 360-480 parts by weight of a fourth solvent, separating the layers, removing the water phase, retaining the organic phase, adding 650-700 parts by weight of 20-25% alkali solution to the organic phase, stirring at room temperature for 10-20 minutes, separating the layers, removing the water phase, and retaining the organic phase; adding 420-600 parts by weight of desalted water to the organic phase, stirring at room temperature for 20-35 minutes, separating the layers, removing the water phase, and retaining the organic phase; washing the organic phase with desalted water, drying it, and removing the solvent under reduced pressure to obtain the intermediate 1-(4-acetoxyphenyl)-1-ethanol.

4. The method for preparing acetoxystyrene according to claim 1, wherein: The specific preparation method of step S3 is as follows: in a three-necked flask, under nitrogen protection, 450-570 parts by weight of 1-(4-acetoxyphenyl)-1-ethanol, 1.35-8.95 parts by weight of a polymerization inhibitor and 0.85-2.65 parts by weight of a catalyst are added, and the mixture is stirred at 150-210° C. for 2-4 hours. After the reaction is completed, 350-500 parts by weight of a fifth solvent are added to separate the layers, the water phase is separated, and the organic phase is retained. 300-450 parts by weight of a 15-20% sodium hydroxide solution is added to the organic phase, and the mixture is stirred at room temperature for 20-50 minutes, separated, and the organic phase is retained; 200-300 parts by weight of deionized water are added to the organic phase, and the mixture is stirred at room temperature for 10-20 minutes, separated, and the water phase is separated, and the organic phase is retained; and the solvent is removed by drying and reduced pressure to obtain 4-acetoxystyrene.

5. The method for preparing p-acetoxystyrene according to claim 2, characterized in that: The first solvent is one or more of ethyl acetate, acetone, butanone, tetrahydrofuran, dichloromethane, dichloroethane, and propylene carbonate.

6. The method for preparing p-acetoxystyrene according to claim 3, characterized in that: The third solvent and the fourth solvent are one or more of ethyl acetate, dimethyl carbonate, methanol, ethanol, n-butanol, toluene and xylene.

7. The method for preparing p-acetoxystyrene according to claim 3, characterized in that: The reducing agent is preferably one or more of sodium borohydride, lithium borohydride, lithium aluminum hydride, and aluminum isopropoxide.

8. The method for preparing p-acetoxystyrene according to claim 3, characterized in that: The inorganic acid is preferably one or more of phosphoric acid, hydrochloric acid, sulfuric acid, nitric acid and carbonic acid.

9. The method for preparing p-acetoxystyrene according to claim 4, characterized in that: The inhibitor is preferably one or more of p-tert-butylcatechol, p-hydroxyanisole, phenothiazine, hydroquinone, N-oxyl (nitroxide) and 1,6-hexylene-bis(N-formyl-N-(1-oxyl-2,2,6,6,-tetramethylpiperidinyl)-4-yl)amine.

10. The method for preparing p-acetoxystyrene according to claim 4, characterized in that: The catalyst is preferably one or more of phthalic anhydride, acetic anhydride, phosphoric acid, and glacial acetic acid.

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