Synthesis method of hydroquinone

Abstract

This invention relates to a method for synthesizing hydroquinone, a pharmaceutical and chemical intermediate. The invention comprises the following steps: (1) hydrolysis of p-chloronitrobenzene in an alkaline solution, adjusting the pH to 5-6 with acid to obtain p-nitrophenol; (2) reduction of p-nitrophenol and hydrogen under catalytic conditions to obtain p-aminophenol; (3) diazotization of a dilute acid solution of p-aminophenol with sodium nitrite; the reaction solution reacts with a dilute acid solution used for hydrolysis to obtain hydroquinone; after the reaction, solvent extraction is performed, followed by concentration, centrifugation, and drying. The reactions are carried out in a microreactor system. Compared with existing hydroquinone production processes, this invention uses continuous flow technology for continuous production, greatly improving production efficiency and saving production costs. It solves the problems of high levels of waste, low selectivity, and high purification costs associated with traditional batch processes. Furthermore, the continuous flow production process has a lower scale-up effect, easier process control, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to a method for synthesizing hydroquinone, a pharmaceutical and chemical intermediate, and belongs to the field of pharmaceutical and chemical intermediate synthesis. Background Technology

[0002] Hydroquinone is mainly used in photosensitive materials, fertilizer additives, polymerization inhibitors in synthetic materials, antioxidants, anthraquinone dyes, azo dyes, and pharmaceutical intermediates. Currently, there are three main production processes for hydroquinone: phenol oxidation, p-diisopropylbenzene, and aniline oxidation.

[0003] The phenol oxidation method uses 50-70% hydrogen peroxide for oxidation. This process has high equipment requirements, generates catechol, has a low conversion rate, requires a huge amount of separation work, and consumes a lot of energy.

[0004]

[0005] The p-diisopropylbenzene process is mainly used in foreign production processes (Mitsui Chemicals, Japan; Eastman Chemical, USA). It involves an alkylation reaction of benzene and propylene to produce two isopropylbenzene isomers. p-Cumene and m-Cumene are then separated. p-Cumene is then oxidized to diisopropylbenzene oxide, which is subsequently decomposed into hydroquinone and acetone using an acidic catalyst. The main disadvantages of this process are the complexity of the byproducts, the difficulty in separation and purification, and the high storage costs and hazard associated with the reaction due to the flammable and explosive nature of propylene.

[0006]

[0007] The aniline redox process uses manganese dioxide to oxidize and then reduce iron powder to obtain hydroquinone. This is a traditional synthesis process with a history of 80 years. Although it has been phased out abroad, many factories in China still use it. The main disadvantages of this process are that it produces large amounts of manganese and iron slurries, causing serious pollution, and high energy consumption.

[0008]

[0009] Existing technologies use p-nitrochlorobenzene as a starting material, followed by hydrolysis and catalytic hydrogenation to obtain hydroquinone. This process employs a traditional batch reactor method, solving the pollution problems of high-salt and nitro-containing wastewater during the production of p-nitrophenol, avoiding the high pollution issues associated with the oxidation and reduction of aniline to produce hydroquinone, and also avoiding the safety issues arising from phenol oxidation. Although this method overcomes some of the shortcomings of traditional hydroquinone production, it still has serious problems, such as: long production cycles, a large number of operators, high energy consumption, and low safety of catalytic hydrogenation. Summary of the Invention

[0010] To address the shortcomings of traditional hydroquinone production, this invention provides a continuous flow synthesis process for hydroquinone that is less polluting, lower in cost, and safer.

[0011] The present invention provides a continuous flow synthesis process for hydroquinone, which uses p-chloronitrobenzene as a starting material and obtains hydroquinone through hydrolysis, reduction, and diazotization hydrolysis. The reaction is carried out in a microreactor system.

[0012]

[0013] This invention includes the following steps:

[0014] Step 1: p-Chloronitrobenzene undergoes a hydrolysis reaction in an alkaline solution, and the pH is adjusted to 5-6 with acid to obtain p-nitrophenol;

[0015] Step 2: p-Nitrophenol and hydrogen undergo a reduction reaction under catalytic conditions to obtain p-aminophenol;

[0016] Step 3: The dilute acid solution of p-aminophenol undergoes a diazotization reaction with sodium nitrite; the reaction solution reacts with the dilute acid solution of hydrolysis to obtain hydroquinone; after the reaction is completed, solvent extraction is used, followed by concentration, centrifugation, and drying.

[0017] In the first step reaction, the alkaline solution is a solution of one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, barium hydroxide, sodium carbonate, potassium carbonate, sodium tert-butoxide, potassium tert-butoxide, sodium ethoxide, potassium ethoxide, sodium methoxide, and potassium methoxide, preferably a solution of sodium hydroxide, potassium hydroxide, sodium ethoxide, and sodium methoxide.

[0018] The solvent of the alkaline solution is: methanol, ethanol, isopropanol, water, acetonitrile, chloroform, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, or a mixture of the above solvents in a certain proportion;

[0019] The alkaline solution is preferably an aqueous solution of sodium hydroxide or potassium hydroxide, a methanol solution, or an ethanol solution;

[0020] The reaction temperature is 130-180℃, preferably 150-180℃;

[0021] The reaction time is 2.5-15 min, preferably 10-15 min;

[0022] The reaction pressure is 0.5-5 MPa; preferably 1.1 MPa.

[0023] The molar ratio of alkali to p-chloronitrobenzene is 1:1-4:1; preferably 2:1-4:1.

[0024] In the second step of the reaction, the reaction solvent is methanol, ethanol, isopropanol, water, acetonitrile, ethyl acetate, dichloromethane, chloroform, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, or a mixture of the above solvents in a certain proportion; preferably methanol, ethanol, ethyl acetate, and N,N-dimethylformamide.

[0025] The catalyst is one or more of the following: carbon, elemental palladium, platinum on carbon, palladium hydroxide, palladium acetylacetone, palladium acetate, Raney nickel, and reduced nickel.

[0026] The reaction temperature is 25-120℃, preferably 40-80℃; the reaction time is 2-10min, preferably 4-8min; and the reaction pressure is 1-10MPa, preferably 3-10MPa.

[0027] The molar ratio of p-nitrophenol to hydrogen is 1:2-1:10, preferably 1:4-1:10;

[0028] In the third step of the reaction, the dilute acid solution of p-aminophenol is an aqueous solution of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, or a mixture of the above in a certain proportion; the reaction solvent is methanol, ethanol, isopropanol, water, acetonitrile, acetone, N,N-dimethylformamide, or a mixture of the above solvents in a certain proportion.

[0029] The reaction temperature of p-aminophenol with sodium nitrite is -10 to 30°C, preferably 0 to 30°C;

[0030] The concentration of the para-aminophenol in dilute acid is 10%-15%;

[0031] The dilute acid used for hydrolysis is an aqueous solution of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, or a mixture of the above in a certain proportion; the reaction solvent is methanol, ethanol, isopropanol, water, acetonitrile, acetone, N,N-dimethylformamide, or a mixture of the above solvents in a certain proportion.

[0032] The concentration of the dilute acid used for hydrolysis is 10-15%.

[0033] The diazotization reaction occurs under normal pressure, and the reaction time is 0.5-20 min, preferably 1-10 min.

[0034] The reaction solution undergoes a hydrolysis reaction with the dilute hydrolyzable acid at a temperature of 100-180℃ and a reaction time of 5-60 min, preferably 10-60 min. The reaction pressure is 1-10 MPa, preferably 2-5 MPa.

[0035] The molar ratio of para-aminophenol to sodium nitrite is 1:1-1:5, preferably 1:2-1:5;

[0036] The molar ratio of p-aminophenol to hydrolyzed dilute acid is 1:10-1:20;

[0037] Furthermore, the specific steps of the present invention include:

[0038] Step 1: Heat p-chloronitrobenzene to a molten state as material A, and prepare an alkaline solution with a concentration of 5-30% as material B. Introduce materials A and B into micro-mixer 1 via a feed pump for mixing to obtain a mixed reaction mixture. Introduce the mixture into microreactor 1 for hydrolysis. After the reaction, adjust the pH of the reaction solution to 5-6 using hydrochloric acid, causing solid precipitation. Then, filter and dry to obtain p-nitrophenol.

[0039] The reaction takes place in microreaction system 1;

[0040] The microreactor system 1 consists of a feed pump, a check valve, a micromixer 1, a microreactor 1, and a back pressure valve.

[0041] The microreactor 1 is a tubular reactor with an inner diameter of 3-8 mm and a length of 7000-8000 mm.

[0042] Step 2: A solution of p-nitrophenol and hydrogen gas are introduced into micro-mixer 2 via a feed pump for mixing to obtain a mixed reactant. The mixed reactant is then introduced into microreactor 2 while maintaining a stable system pressure. The gas and liquid flow rates are controlled to ensure the material remains in the system for a certain period of time. After the reaction is complete, the mixture is concentrated under reduced pressure to obtain p-aminophenol.

[0043] The reaction takes place in microreaction system 2:

[0044] The microreactor system 2 consists of a feed pump, a check valve, a micromixer 2, a microreactor 2, and a back pressure valve;

[0045] The microreactor 2 is a fixed-bed plate reactor, with an inner diameter of 20-30 mm and a length of 2000-3000 mm.

[0046] Step 3: Dissolve p-aminophenol in dilute acid to prepare solution A, prepare sodium nitrite aqueous solution to prepare solution B, and prepare dilute acid to prepare solution C. Pump solutions B and A separately into the third micro-mixer, then into microreactor 3 for reaction. After the reaction, pass the resulting reaction solution and solution C into micro-mixer 4, then into microreactor 4 for further reaction. After the reaction, extract with solvent, concentrate, centrifuge, and dry to obtain hydroquinone.

[0047] The reaction takes place in microreaction system 3:

[0048] The microreactor system 3 consists of a feed pump, a check valve, a micro mixer 3, a microreactor 3, a micro mixer 4, a microreactor 4, and a back pressure valve.

[0049] Microreactor 3 and microreactor 4 are connected by micromixer 4;

[0050] The microreactors 3 and 4 are tubular reactors with an inner diameter of 3-8 mm and a length of 7000-8000 mm.

[0051] The extraction solvent is one or a mixture of several of the following: dichloromethane, chloroform, methyl formate, ethyl formate, ethyl acetate, methyl acetate, n-butyl acetate, isobutyl acetate, isoamyl acetate, butyl lactate, and methyl isobutyl ketone.

[0052] The micromixers 1, 2, 3, and 4 can be any one of the following: static mixer, T-type micromixer, Y-type micromixer, cross-shaped micromixer, coaxial flow micromixer, and flow focusing micromixer.

[0053] Beneficial effects of the present invention

[0054] 1. Compared with the existing traditional hydroquinone production process, the continuous flow technology enables continuous production, and all three reaction steps are completed within 20 minutes, which greatly improves production efficiency, significantly reduces labor costs, and substantially lowers the total cost of hydroquinone production.

[0055] 2. Traditional batch reactor processes involve three steps with high reaction temperatures. The continuous flow technology used in this invention results in lower reaction temperatures, reduced energy consumption, and is more equipment-friendly.

[0056] 3. Traditional batch reactor processes use large quantities of alkalis such as sodium hydroxide and acids such as sulfuric acid. The continuous flow technology used in this invention greatly reduces the amount of acid and alkali used, thereby reducing material costs and significantly reducing the generation of waste, making it environmentally friendly.

[0057] 4. Traditional batch reactor processes such as diazotization and catalytic hydrogenation are classified as 18 hazardous processes. Adopting continuous flow technology can significantly reduce the safety risks of traditional batch reactor processes.

[0058] 5. In addition, the continuous flow production process has a lower scale-up effect, easier process conditions to control, and is easier to industrialize. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the synthesis method of hydroquinone according to the present invention.

[0060] Figure 2 This is the 1H NMR spectrum of hydroquinone. Detailed Implementation

[0061] Process screening process

[0062] First step reaction

[0063] p-Chlorotibene undergoes hydrolysis in an alkaline solution to yield sodium p-nitrophenolate. Adjusting the pH to 5-6 with acid yields p-nitrophenol. 1. Selection of the type of alkali:

[0064]

[0065] The results showed that when the base was sodium hydroxide and potassium hydroxide, the product yield could reach more than 50% and the purity was high.

[0066] 2. Selection of the molar ratio of alkali to p-chloronitrobenzene: wherein the alkali is potassium hydroxide;

[0067]

[0068] The results showed that when the molar ratio of potassium hydroxide to p-chloronitrobenzene was 2:1-4:1, the purity could reach over 85% and the yield over 85%.

[0069] 3. Selection of reaction temperature and time: The alkali is potassium hydroxide, and the molar ratio of potassium hydroxide to p-chloronitrobenzene is 2.5:1;

[0070]

[0071] The results showed that when the reaction temperature was 130-180℃ and the reaction time was 2.5-15 min, the product yield could reach more than 50%. When the reaction temperature was 150-180℃ and the reaction time was 10-15 min, the yield could reach more than 80% and the purity could reach more than 85%. When the reaction temperature was 180℃ and the reaction time was 10-12 min, both the yield and the purity could reach more than 90%.

[0072] Second step reaction:

[0073] p-Nitrophenol and hydrogen undergo a reduction reaction under catalytic conditions to yield p-aminophenol;

[0074] 1. Screening of reaction solvents:

[0075] When the catalytic hydrogenation reaction was carried out directly using an alkaline aqueous solution of potassium p-nitrophenol as the starting material, the results showed that the reaction yield and purity were both good. However, the alkaline aqueous solution led to catalyst deactivation, and the yield and purity decreased significantly after the reaction time exceeded 12 hours, which was detrimental to the reaction. Therefore, in the first step of the reaction, the pH of the hydrolysis product was adjusted to 5-6 with acid to obtain p-nitrophenol, thus avoiding an alkaline solution.

[0076] The second step of the reaction uses p-nitrophenol as a raw material and organic solvents such as methanol, ethanol, ethyl acetate, and DMF as reaction solvents for catalytic hydrogenation. Reaction conditions: reaction temperature 40℃, reaction pressure 4MPa, p-nitrophenol:hydrogen molar ratio 1:4.

[0077] Serial Number reaction solvent purity yield Catalyst continuous working time 1 methanol 82.7％ 80％ >300h 2 ethanol 80.7％ 80％ >300h 3 Ethyl acetate 70.9％ 70％ >300h 4 N,N-Dimethylformamide 72.1％ 70％ >300h 5 water 80.0％ 79％ <12h

[0078] The results showed that when p-nitrophenol was used as the starting material and methanol and ethanol were used as the reaction solvents, the catalyst could work continuously for more than 300 hours and the yield and purity were both high.

[0079] 2. Selection of catalyst type:

[0080]

[0081] The results show that, using methanol as a solvent, the selected hydrogenation reduction catalysts all exhibit superior performance.

[0082] 3. Selection of the molar ratio of p-nitrophenol to hydrogen: using palladium on carbon as the catalyst;

[0083]

[0084] The results showed that when the molar ratio of p-nitrophenol to hydrogen was 1:4 to 1:10, the yield of the product could reach 82% and the purity could reach over 85%.

[0085] 4. Selection of reaction temperature: Palladium on carbon was used as the catalyst, and the molar ratio of p-nitrophenol to hydrogen was 1:4;

[0086]

[0087] The results showed that temperature had little effect on the reaction yield and purity.

[0088] 5. Selection of reaction time: Palladium on carbon was used as the catalyst, the molar ratio of p-nitrophenol to hydrogen was 1:4, and the reaction temperature was 40℃;

[0089]

[0090] The results showed that when the reaction time was 2-8 min, the yield was over 50%; when the reaction time was 4-8 min, the yield could reach over 80%; and when the reaction time was 4-6 min, the yield could reach over 95%.

[0091] 6. Selection of reaction pressure: Palladium on carbon was used as the catalyst, the molar ratio of p-nitrophenol to hydrogen was 1:4, the reaction temperature was 40℃, and the reaction time was 4 min;

[0092]

[0093] The results showed that the yield was over 50% when the reduction reaction pressure was 1-10 MPa, and the product yield and purity were optimal when the reduction pressure was 3-10 MPa.

[0094] Third step reaction

[0095] 1. Selection of the molar ratio of p-aminophenol to sodium nitrite:

[0096]

[0097] The results showed that the purity of the diazonium salt was better when the molar ratio of p-aminophenol to sodium nitrite was 1:2-1:5 during the diazotization reaction.

[0098] 2. Selection of reaction temperature (diazonium salt): The molar ratio of p-aminophenol to sodium nitrite is 1:3;

[0099]

[0100] The results showed that the diazonium salt had good purity when the diazotization reaction temperature was between 0 and 30℃.

[0101] 3. Selection of reaction time (diazonium salt): The molar ratio of p-aminophenol to sodium nitrite is 1:3, and the reaction temperature is 0℃;

[0102]

[0103] The results showed that the diazonium salt had good purity when the reaction time was 0.5-10 min, and the purity reached over 85% when the reaction time was 1-10 min.

[0104] 4. Selection of the molar ratio of p-aminophenol to hydrolyzed sulfuric acid: The molar ratio of p-aminophenol to sodium nitrite is 1:3, the reaction temperature is 0℃, and the reaction time is 1 min;

[0105]

[0106] The results showed that when the molar ratio of p-aminophenol to hydrolyzed sulfuric acid was 1:10-1:20, the yield and purity of hydroquinone were both good.

[0107] 5. Selection of reaction temperature: The molar ratio of p-aminophenol to sodium nitrite is 1:3, the reaction temperature 1 is 0℃, the reaction time 1 is 1min, and the molar ratio of p-aminophenol to hydrolyzed sulfuric acid is 1:10;

[0108]

[0109] The results showed that hydroquinone had better purity and yield when the hydrolysis temperature was 100-180℃, while the purity and yield were better when the temperature was 100-150℃.

[0110] 6. Selection of reaction time: The molar ratio of p-aminophenol to sodium nitrite is 1:3, the reaction temperature 1 is 0℃, the reaction time 1 is 1min, the molar ratio of p-aminophenol to hydrolyzed sulfuric acid is 1:10, and the reaction temperature 2 is 100℃;

[0111]

[0112] The results showed that when the hydrolysis reaction time was 5-60 min and the reaction pressure was 0.5-1 MPa, the product yield and purity reached over 50%; when the hydrolysis reaction time was 10-60 min and the reaction pressure was 0.5-1 MPa, the hydrolysis product yield and purity could both reach over 80%.

[0113] 7. Selection of reaction pressure: The molar ratio of p-aminophenol to sodium nitrite is 1:3, the reaction temperature 1 is 0℃, the reaction time 1 is 1min, the molar ratio of p-aminophenol to hydrolyzed sulfuric acid is 1:10, the reaction temperature 2 is 100℃, and the reaction time 2 is 10min;

[0114]

[0115] The results showed that when the reaction pressure was 2-5 MPa, the reaction purity and yield could both reach over 80%, and when the reaction pressure was 4-5 MPa, the reaction purity and yield were both over 90%.

[0116] Example 1

[0117] 20g of p-chloronitrobenzene was heated to 120℃ to melt it and set aside. A 10% aqueous solution of sodium hydroxide was prepared and set aside. The tubular reactor was preheated to 180℃. Using a plunger pump, the p-chloronitrobenzene and sodium hydroxide aqueous solution were separately introduced into the tubular reactor for reaction. The system pressure was maintained at 1.1MPa, the reaction temperature at 180℃, and the reaction time at 10min. The molar ratio of p-nitrobenzene to sodium hydroxide was 1:4. After the reaction, an aqueous solution of p-nitrophenol was obtained. The pH was adjusted to 5-6 with sulfuric acid, at which point a solid precipitated. The solid was then filtered and dried to obtain p-nitrophenol with a purity of 92.02% and a yield of 88%.

[0118] 50g of p-nitrophenol was added to 200mL of ethanol and stirred until dissolved. 3-5 drops of DMSO were then added dropwise. The ethanol solution of p-nitrophenol and hydrogen were separately pumped into a fixed-bed reactor pre-packed with platinum-carbon using a plunger pump. The reaction temperature was 40℃, the reaction pressure was 10MPa, the reaction time was 4min, and the molar ratio of p-nitrophenol to hydrogen was 1:4. After the reaction, an ethanol solution of p-aminophenol was obtained. This solution was distilled to dryness under reduced pressure to obtain p-aminophenol with a purity of 98.4% and a yield of 98%.

[0119] 45g of p-aminophenol was dissolved in 40% dilute sulfuric acid (p-aminophenol concentration: 15%) and stirred to obtain solution A. A 10% sodium nitrite aqueous solution was prepared as solution B, and a 15% dilute sulfuric acid solution was prepared as solution C. Solutions A and B were introduced into tubular reactor 1 using a plunger pump for reaction at 0℃ for 1 min. The resulting reaction solution was then introduced into tubular reactor 2 with solution C to obtain hydroquinone solution at 100℃ for 60 min. The molar ratio of p-aminophenol:sodium nitrite:sulfuric acid was 1:3:10, and the overall reaction pressure was 1.0 MPa. Finally, hydroquinone was obtained by extraction with ethyl acetate, concentration, centrifugation, and drying, with a purity of 85.04% and a yield of 82%.

[0120] Example 2

[0121] 20g of p-chloronitrobenzene was heated to a molten state and set aside. A 5% potassium hydroxide ethanol-water (50:50) solution was prepared and set aside. The tubular reactor was preheated to 180℃. The p-chloronitrobenzene and sodium hydroxide solution were fed into the tubular reactor using a plunger pump for reaction. The reaction pressure was 1.1MPa, the reaction time was 15min, and the molar ratio of p-nitrophenol to sodium hydroxide was 2.5:1. After the reaction was completed, a p-nitrophenol solution was obtained. When the pH was adjusted to 5-6 with hydrochloric acid, a solid precipitated out. The solid p-nitrophenol was obtained by filtration and drying, with a purity of 89.5% and a yield of 82%.

[0122] 1 g of p-nitrophenol was added to 20 mL of acetone and stirred until dissolved. 3–5 drops of DMSO were added dropwise and set aside. A fixed-bed reactor was pre-filled with Raney nickel catalyst. The acetone solution of p-nitrophenol and hydrogen were introduced into the fixed-bed reactor. The reaction temperature was 40 °C, the reaction time was 4 min, the reaction pressure was 4 MPa, and the molar ratio of p-nitrophenol to hydrogen was 1:10. After the reaction, a p-aminophenol solution was obtained, which was concentrated to dryness under reduced pressure to obtain p-aminophenol with a purity of 86.0% and a yield of 82%.

[0123] 10g of p-aminophenol was dissolved in 200g of 60% dilute sulfuric acid (p-aminophenol concentration: 15%) to form solution A. A 10% sodium nitrite aqueous solution was prepared as solution B, and 10% dilute sulfuric acid was prepared as solution C. Solutions A and B were added to tubular reactor 1 using a plunger pump for reaction at 0℃ for 1 min. The resulting reaction solution and solution C were then introduced into tubular reactor 2 for reaction at 100℃ for 10 min. The overall reaction pressure was 5 MPa, and the molar ratio of p-aminophenol:sodium nitrite:sulfuric acid was 1:3:10. After the reaction, a hydroquinone solution was obtained. Hydroquinone was obtained by extraction with ethyl acetate, concentration, and centrifugation, with a purity of 95.36% and a yield of 92%.

[0124] Example 3

[0125] Weigh 20g of p-chloronitrobenzene and heat it to 120℃ to melt it. Prepare a 30% potassium hydroxide methanol aqueous solution. Preheat the entire tubular reactor to 180℃. Use a plunger pump to deliver the p-chloronitrobenzene and potassium hydroxide solution into the tubular reactor for reaction. The reaction time is 10 min, the reaction pressure is 1.1 MPa, and the molar ratio of p-nitrochlorobenzene to potassium hydroxide is 2.5:1. After the reaction is complete, a p-nitrophenol solution is obtained. Adjust the pH to 5-6 with sulfuric acid. A solid precipitates out. Filter and dry to obtain p-nitrophenol solid with a purity of 94.26% and a yield of 93%.

[0126] 1 g of p-nitrophenol was added to 20 mL of acetonitrile and stirred until dissolved. 3–5 drops of DMSO were then added dropwise. The p-nitrophenol acetonitrile solution and hydrogen were fed into a fixed-bed reactor pre-filled with palladium-on-carbon catalyst. The reaction was carried out at 40 °C for 4 min at a pressure of 3 MPa, with a p-nitrophenol to hydrogen molar ratio of 1:4. After the reaction, an acetonitrile solution of p-aminophenol was obtained. This solution was concentrated to dryness under reduced pressure to obtain p-aminophenol with a purity of 98.7% and a yield of 98%.

[0127] 10g of p-aminophenol was dissolved in 200g of 80% sulfuric acid (p-aminophenol concentration was 15%) to prepare solution A. 380g of a 5% sodium nitrite ethanol aqueous solution was prepared as solution B, and 1500g of a 10% dilute sulfuric acid solution was prepared as solution C. Solutions A and B were added to tubular reactor 1 using a plunger pump for reaction at 0℃ for 1 min. The resulting reaction solution and solution C were then passed into tubular reactor 2 at 100℃ for 10 min under a pressure of 4 MPa and a p-aminophenol:sodium nitrite:sulfuric acid molar ratio of 1:3:10. After the reaction, a hydroquinone solution was obtained. Hydroquinone was obtained by extraction with ethyl acetate, concentration, and centrifugation, with a purity of 99.02% and a yield of 95%.

[0128] 1 H NMR (400MHz, DMSO-d6) δ8.60 (s, 2H), 6.56 (s, 4H).

[0129] First step reaction

[0130]

[0131]

[0132] Second step reaction

[0133]

[0134] Third step reaction

[0135]

Claims

1. A method for synthesizing hydroquinone, characterized in that, Hydroquinone is obtained from p-chloronitrobenzene via hydrolysis, reduction, and diazotization hydrolysis. The reaction is carried out in a microreactor system and includes the following steps: Step 1: p-Chloronitrobenzene undergoes a hydrolysis reaction in an alkaline solution, and the pH is adjusted to 5-6 with acid to obtain p-nitrophenol; Step 2: p-Nitrophenol and hydrogen undergo a reduction reaction under catalytic conditions to obtain p-aminophenol; Step 3: The dilute acid solution of p-aminophenol undergoes a diazotization reaction with sodium nitrite; the reaction solution reacts with the hydrolyzed dilute acid solution to obtain hydroquinone; after the reaction is completed, solvent extraction is used, followed by concentration, centrifugation, and drying. The first step reaction is carried out in micro-reaction system 1; the micro-reaction system 1 consists of a feed pump, a one-way valve, a micro-mixer 1, a tubular reactor 1, and a back pressure valve; the tubular reactor has an inner diameter of 3-8 mm and a length of 7000-8000 mm. The alkaline solution is an aqueous solution of potassium hydroxide, the molar ratio of alkali to p-chloronitrobenzene is 2.5:1, the reaction temperature is 180℃, the reaction time is 10-12 min, and the reaction pressure is 1.1 MPa. The second step reaction is carried out in micro-reaction system 2: the micro-reaction system 2 consists of a feed pump, a one-way valve, a micro-mixer 2, a fixed bed plate reactor 2, and a back pressure valve; the fixed bed plate reactor 2 has an inner diameter of 20-30 mm and a length of 2000-3000 mm. The reaction solvent is methanol or ethanol, the catalyst is platinum on carbon or palladium on carbon, the reaction temperature is 40℃, the reaction time is 4 min, the molar ratio of p-nitrophenol to hydrogen is 1:4, and the reaction pressure is 3 MPa or 10 MPa. The third reaction step is carried out in the micro-reaction system 3: the micro-reaction system 3 consists of a feed pump, a one-way valve, a micro mixer 3, a tubular reactor 3, a micro mixer 4, a tubular reactor 4, and a back pressure valve; wherein the tubular reactor 3 and the tubular reactor 4 are connected through the micro mixer 4; the tubular reactor has an inner diameter of 3-8 mm and a length of 7000-8000 mm. The reaction temperature of p-aminophenol with sodium nitrite is 0℃, and the diazotization reaction occurs under normal pressure for 1 min. The molar ratio of p-aminophenol to sodium nitrite is 1:

3. The dilute acid used for hydrolysis is dilute sulfuric acid; the reaction solvent is water. The hydrolysis reaction temperature was 100℃, the reaction time was 10 min, the reaction pressure was 4.0 MPa, and the molar ratio of p-aminophenol to sulfuric acid was 1:

10.

2. The application of the hydroquinone synthesis method according to claim 1 in the preparation of hydroquinone.

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