The invention relates to 4, 4apos; synthesis method of-dihydroxybiphenyl

Abstract

The invention discloses a synthetic method of 4, 4 '-dihydroxybiphenyl. The method comprises the following steps: mixing 4, 4 '-dinitrobiphenyl, a metal catalyst and an organic solvent, introducing hydrogen, and carrying out hydrogenation reduction reaction to obtain 4, 4'-diaminobiphenyl; the preparation method comprises the following steps: mixing 4, 4 '-diaminobiphenyl and a silicon dioxide grafted modified multi-branched carboxylic acid polymer, carrying out a heating reaction, and removing a solvent from a reaction solution to obtain 4, 4'-dihydroxybiphenyl. 4, 4 '-dinitrobiphenyl is used as a substrate of the reaction, and an intermediate 4, 4'-diaminobiphenyl is obtained after hydrogenation reduction; the target product 4, 4 '-dihydroxybiphenyl is synthesized by taking the silicon dioxide grafted and modified multi-branched carboxylic acid polymer as a hydrolysis reagent, so that the efficiency and selectivity of the reaction for preparing the 4, 4'-dihydroxybiphenyl are effectively improved, the reaction condition is mild, the operation process is simple and convenient, and the method has wide industrial application potential.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and specifically to a method for synthesizing 4,4'-dihydroxybiphenyl. Background Technology

[0002] 4,4'-Dihydroxybiphenyl, also known as 4,4'-biphenyldiphenol, is a widely used and important organic intermediate, commonly used as a rubber antioxidant and plastic antioxidant in medical latex products, food packaging rubber products, and colorless vulcanized rubber products. 4,4'-Dihydroxybiphenyl is also a dye intermediate and a petroleum product stabilizer. Due to its excellent heat resistance, 4,4'-dihydroxybiphenyl is often used as a modifying monomer for polymers such as polyesters, polyurethanes, polycarbonates, polysulfones, and epoxy resins to produce engineering plastics and composite materials. Currently, its high-purity products are mainly used in the synthesis of liquid crystal polymers.

[0003] Currently, the main methods for synthesizing 4,4'-dihydroxybiphenyl are as follows: Route 1: Biphenyl sulfonation alkaline melting method ; Patent US6410238A describes a method for preparing 4,4'-dihydroxybiphenyl using a sulfonation followed by hydrolysis approach. This process offers advantages such as a simple synthetic route and high yield. However, this route requires the consumption of large amounts of concentrated acid and strong base during the reaction, leading to severe environmental pollution. Furthermore, frequent side reactions occur under high-temperature conditions, resulting in low purity of the prepared 4,4'-dihydroxybiphenyl, making large-scale production difficult. Route 2: Oxidative coupling-reductive dealkylation of 2,6-di-tert-butylphenol ; Patent CN117776875A discloses a method for producing 4,4'-dihydroxybiphenyl from 2,6-di-tert-butylphenol via oxidative coupling and subsequent dealkylation. While this method achieves continuous reaction and catalyst reuse, effectively reducing waste emissions and production costs, the overall process is complex with numerous reaction steps, which directly impacts the final yield of the target product. Route 3: Hydrolysis of Halogenated Biphenyls ; Patent US5196605A uses 4,4'-dibromobiphenyl as a raw material, which is hydrolyzed in an alkaline system with a copper catalyst to produce 4,4'-dihydroxybiphenyl. This method uses highly toxic and polluting raw materials, which are expensive, have limited sourcing channels, and require strict purity control. Therefore, exploring and developing an economically feasible, safe, and efficient production route for 4,4'-dihydroxybiphenyl is of great significance. Summary of the Invention

[0004] In view of the above-mentioned prior art, the purpose of this invention is to provide a method for synthesizing 4,4'-dihydroxybiphenyl. This invention uses 4,4'-dinitrobiphenyl as the reaction substrate, which is hydrogenated and reduced to obtain the intermediate 4,4'-diaminobiphenyl. A silica-grafted modified multibranched carboxylic acid polymer is used as a hydrolysis reagent to synthesize the target product 4,4'-dihydroxybiphenyl. This method effectively improves the efficiency and selectivity of the 4,4'-dihydroxybiphenyl preparation reaction, with mild reaction conditions, simple operation, and broad industrial application potential.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for synthesizing 4,4'-dihydroxybiphenyl, the method comprising the following steps: (1) 4,4'-dinitrobiphenyl, a metal catalyst and an organic solvent are mixed and hydrogen is introduced to carry out a hydrogenation reduction reaction to obtain 4,4'-diaminobiphenyl; (2) Mix 4,4'-diaminobiphenyl and silica-grafted modified multibranched carboxylic acid polymer, heat to react, and remove solvent from the reaction solution to obtain 4,4'-dihydroxybiphenyl.

[0006] Its synthetic route is as follows: .

[0007] Preferably, in step (1), 4,4'-dinitrobiphenyl and an organic solvent are added to a storage tank to obtain a mixture, and the mixture is passed into a hydrogenation reduction reactor filled with a metal catalyst to carry out a hydrogenation reduction reaction to obtain 4,4'-diaminobiphenyl.

[0008] Preferably, the organic solvent is selected from at least one of methanol, ethanol, isopropanol, and tetrahydrofuran; the mass ratio of 4,4'-dinitrobiphenyl to the organic solvent is 0.25~0.5:1.

[0009] Preferably, the feed rate of the mixture is 0.04~0.065 kg / min; the hydrogen feed rate is 0.75~1.1 g / min; the heating temperature of the hydrogenation reduction reactor is 25~100℃; and the metal catalyst is selected from palladium, platinum or ruthenium.

[0010] Preferably, in step (2), 4,4'-diaminobiphenyl is pumped into a two-stage tandem tower reactor filled with silica-grafted modified multibranched carboxylic acid polymer for reaction. The resulting 4,4'-dihydroxybiphenyl reaction solution is desolventized by a desolventizing tank to obtain purified 4,4'-dihydroxybiphenyl. The desolventized solvent is recycled.

[0011] Preferably, the silica-grafted modified multibranched carboxylic acid polymer is a silica-grafted compound having at least two of the following structural formulas A, B, and C; Where the structure of A is or The structure of B is or The C structure is .

[0012] Preferably, the silica-grafted modified multibranched carboxylic acid polymer is prepared by the following method: Silica and a silane coupling agent were dispersed in toluene, and benzoic acid containing sulfonic acid group and dicarboxylic acid were added. The mixture was heated under nitrogen protection and refluxed. The resulting product was evaporated to dryness, and then washed and dried successively with organic solvent and deionized water to obtain silica-grafted modified multibranched carboxylic acid polymer.

[0013] Preferably, the silane coupling agent is KH-550; the sulfonic acid is 2-sulfonobenzoic acid or 2-hydroxy-5-sulfonobenzoic acid; the dicarboxylic acid is succinic acid or terephthalic acid; the molar ratio of silicon dioxide, sulfonic acid, and dicarboxylic acid is 1:2~3:3~4; and the amount of silane coupling agent added is 0.5~1% of the mass of silicon dioxide.

[0014] Preferably, the pumped pressure is 1.0~1.2 MPa; the temperature of the two-stage series tower reactor is 60~85℃.

[0015] A second aspect of the present invention provides the application of the above method in at least one of the following 1) to 3): 1) Shorten the synthesis time of 4,4'-dihydroxybiphenyl; 2) Improve the selectivity of 4,4'-dihydroxybiphenyl; 3) Reduce impurities in the 4,4'-dihydroxybiphenyl reaction solution and increase the yield of 4,4'-dihydroxybiphenyl.

[0016] A third aspect of the present invention provides a reaction apparatus for synthesizing 4,4'-dihydroxybiphenyl, comprising a hydrogenation reduction reactor connected to a first-stage tower reactor via a first high-pressure plunger pump; the first-stage tower reactor connected to a second-stage tower reactor via a second high-pressure plunger pump; the second-stage tower reactor connected to a desolvation tank via a third high-pressure plunger pump; the desolvation tank connected to a storage tank, and the storage tank connected to the hydrogenation reduction reactor.

[0017] The hydrogenation reduction reactor is equipped with a catalyst filter.

[0018] The beneficial effects of this invention are: (1) The method of the present invention can significantly shorten the reaction time, significantly improve the reaction selectivity, significantly reduce impurities in the reaction solution, significantly improve the yield of 4,4'-dihydroxybiphenyl, up to 89%, and the subsequent purification steps are simple, greatly improving the production efficiency.

[0019] (2) Compared with the traditional halogenated biphenyl hydrolysis process, the present invention can effectively prevent the environmental pollution risks that may be caused by highly toxic raw materials. It adopts a continuous production process, the process route is refined, the process is simple, and it is more suitable for industrial production.

[0020] (3) The purification stage of this invention requires less equipment, is simple to operate, significantly improves production efficiency, and allows for solvent recycling, resulting in better economic benefits and making it suitable for large-scale application. Attached Figure Description

[0021] Figure 1 This is the liquid chromatogram of the product obtained in Example 1; Figure 2 This is a system equipment connection diagram for synthesizing 4,4'-dihydroxybiphenyl according to the present invention; in the diagram, 1-hydrogenation reduction reactor; 2-first-stage tower reactor; 3-second-stage tower reactor; 4-solvent removal tank; 5-first high-pressure plunger pump; 6-second high-pressure plunger pump; 7-third high-pressure plunger pump; 8-storage tank; 9-ball valve; Figure 3 The infrared spectrum of the silica-grafted modified multibranched carboxylic acid polymer hydrolysis reagent prepared in Example 1 is shown below. Figure 4 This is the infrared spectrum of the silica-grafted modified multibranched carboxylic acid polymer hydrolysis reagent prepared in Example 2; Figure 5 The image shows the infrared spectrum of the silica-grafted modified multibranched carboxylic acid polymer hydrolysis reagent prepared in Example 3. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0023] As described in the background section, existing technologies for preparing 4,4'-dihydroxybiphenyl suffer from problems such as high raw material costs or high toxicity and pollution of raw materials, complex process routes, harsh process conditions, low selectivity and yield, and difficulty in product recovery and purification.

[0024] Therefore, the objective of this invention is to provide a method for synthesizing 4,4'-dihydroxybiphenyl. The synthetic route of this invention is as follows: , A comparison of the synthetic routes of this invention with those of existing technologies reveals that this invention, which involves the hydrogenation reduction of 4,4'-dinitrobiphenyl followed by hydrolysis to phenol in a tower reactor, avoids contact between personnel and highly toxic 4,4'-dibromobiphenyl or other hazardous materials such as strong acids and bases. Furthermore, the reaction conditions are milder and easier to control compared to other processes, resulting in fewer safety hazards.

[0025] This invention utilizes a silane coupling agent to treat silica, enabling the hydroxyl groups on its surface to form esters with carboxyl groups, thus achieving grafting modification. 2-Sulfobenzoic acid has only one carboxyl group, allowing it to be grafted onto the silica surface, while terephthalic acid contains two carboxyl groups, enabling it to crosslink with the hydroxyl groups on the silica surface, achieving "crosslinking + branching" and forming a denser and more stable functional layer. Furthermore, the mixed acid hydrolysis reagent contains sulfonic acid, specifically 2-sulfobenzoic acid or 2-hydroxy-5-sulfobenzoic acid, which are strong acids. Terephthalic acid, being a moderately strong acid, acts as a buffer, making the hydrolysis reaction more gentle. When only sulfobenzoic acid is used, the acidity of the system is mainly dominated by the "sulfonic acid strong acid sites," easily forming localized strong acid microregions at the feeding point or solid-liquid interface, leading to instantaneous exothermic reactions and abrupt acidity changes, thereby inducing side reactions (such as azo compounds, biphenyl compounds, etc.).

[0026] In the preparation process of this invention, 4,4'-dinitrobiphenyl and an organic solvent are added to storage tank 8 and mixed. The feed rate of the mixed solution is controlled by ball valve 9. 4,4'-diaminobiphenyl is generated in hydrogenation reduction reactor 1. 4,4'-diaminobiphenyl is pumped into primary tower reactor 2 by first high-pressure plunger pump 5. Under the action of hydrolysis reagent, 4,4'-dihydroxybiphenyl is generated. The reaction solution continuously passes through secondary tower reactor 3 at the same flow rate. Primary tower reactor 2 and secondary tower reactor 3 are connected by second high-pressure plunger pump 6. The obtained 4,4'-dihydroxybiphenyl reaction solution flows out of secondary tower reactor 3 and is pumped into desolvation tank 4 by third high-pressure plunger pump 7 to remove the solvent. The purified 4,4'-dihydroxybiphenyl is recovered at the bottom of the tank, and the solvent collected from the top of the tank is fed into storage tank 8 for reuse.

[0027] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0028] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0029] Example 1: Preparation of silica-grafted modified multibranched carboxylic acid polymer 1 kg of silica with a particle size of 50 nm and 0.01 kg of KH-550 were added to 5 kg of toluene. The system was uniformly dispersed by mechanical stirring. Then, 8.90 kg of 2-sulfobenzoic acid and 10.63 kg of terephthalic acid (molar ratio of silica:2-sulfobenzoic acid:terephthalic acid = 1:2.2:3.2) were added. The mixture was heated to 125 °C and refluxed for 3 h under nitrogen protection. The resulting product was dried by rotary evaporation and washed successively with acetone and deionized water. After drying at 140 °C, silica-grafted modified multibranched carboxylic acid polymer was obtained with a yield of 95%.

[0030] The silica-grafted modified multibranched carboxylic acid polymer prepared in Example 1 was subjected to infrared spectroscopy. Figure 3 The curve shows: 2834.68cm -1 927.55cm -1 The characteristic absorption peak for hydroxyl groups is 1682.43 cm⁻¹. -1 The characteristic absorption peak for the carboxyl group is 1176.26 cm⁻¹. -1 1015.75cm -1 This is a characteristic absorption peak for sulfonic acid groups.

[0031] Example 2: Preparation of silica-grafted modified multibranched carboxylic acid polymer 1 kg of silica with a particle size of 30 nm and 0.005 kg of KH-550 were added to 4 kg of toluene. The system was uniformly dispersed by mechanical stirring. 10.11 kg of 2-sulfobenzoic acid and 8.27 kg of succinic acid (molar ratio of silica:2-sulfobenzoic acid:succinic acid = 1:2.5:3.5) were added. The mixture was heated to 125 °C and refluxed for 4 h under nitrogen protection. The resulting product was dried by rotary evaporation and washed successively with ethanol and deionized water. After drying at 140 °C, silica-grafted modified multibranched carboxylic acid polymer was obtained with a yield of 95%.

[0032] The silica-grafted modified multibranched carboxylic acid polymer prepared in Example 2 was subjected to infrared spectroscopy. According to... Figure 4 The curve shows that: 2836.93cm -1 928.02cm -1 The characteristic absorption peak for hydroxyl groups is 1682.56 cm⁻¹. -1 The characteristic absorption peak for the carboxyl group is 1176.36 cm⁻¹. -1 1015.78cm -1 This is a characteristic absorption peak for sulfonic acid groups.

[0033] Example 3: Preparation of silica-grafted modified multibranched carboxylic acid polymer 1 kg of silica with a particle size of 100 nm and 0.009 kg of KH-550 were added to 4.7 kg of toluene. The system was uniformly dispersed by mechanical stirring. Then, 13.09 kg of 2-hydroxy-5-sulfobenzoic acid and 7.09 kg of succinic acid (molar ratio of silica:2-hydroxy-5-sulfobenzoic acid:succinic acid = 1:3:3) were added. The mixture was heated to 125 °C and refluxed for 3.5 h under nitrogen protection. The resulting product was dried by rotary evaporation and washed successively with acetone and deionized water. After drying at 140 °C, the silica-grafted modified polymer was obtained with a yield of 96%.

[0034] The silica-grafted modified multibranched carboxylic acid polymer prepared in Example 3 was subjected to infrared spectroscopy. According to... Figure 5 The curve shows that: 2838.33cm -1 929.14cm -1 The characteristic absorption peak for hydroxyl groups is 1682.99 cm⁻¹. -1 The characteristic absorption peak for the carboxyl group is 1176.31 cm⁻¹. -1 1015.65cm -1 This is a characteristic absorption peak for sulfonic acid groups.

[0035] Example 4: Preparation of 4,4'-dihydroxybiphenyl (1) 0.36 kg of 4,4'-dinitrobiphenyl and 1.2 kg of ethanol were added to a carbon steel-lined plastic storage tank to obtain a mixture. The mixture was continuously passed through a hydrogenation reduction reactor at a rate of 0.04 kg / min, while hydrogen was introduced into the hydrogenation reduction reactor at a rate of 0.764 g / min. The mixture underwent a reduction reaction in the hydrogenation reduction reactor. The hydrogenation reduction reactor was filled with palladium metal and heated to 50°C to obtain the intermediate 4,4'-diaminobiphenyl. The reaction solution was pumped out by the first high-pressure plunger pump and then fed into a first-stage tower reactor. The content of 4,4'-dinitrobiphenyl was found to be less than 0.1% by gas phase normalization analysis.

[0036] (2) The pressure of the first high-pressure plunger pump and the second high-pressure plunger pump is controlled at 1.0 MPa. 4,4'-diaminobiphenyl is continuously passed through the first-stage tower reactor and the second-stage tower reactor at a rate of 0.04 kg / min to undergo hydrolysis. The first-stage tower reactor and the second-stage tower reactor are filled with the hydrolysis reagent (silica-grafted modified multibranched carboxylic acid polymer) prepared in Example 1. The first-stage tower reactor and the second-stage tower reactor are heated to 65°C to obtain 4,4'-dihydroxybiphenyl reaction solution. After the reaction solution is pumped out of the second-stage tower reactor, it is stored in the desolvation tank. The content of 4,4'-diaminobiphenyl is less than 0.1% by gas phase normalization detection.

[0037] (3) 4,4'-dihydroxybiphenyl was desolventized in a desolventizing tank. The feed rate was controlled at 0.036 kg / min and the temperature of the desolventizing tank was 100℃. 4,4'-dihydroxybiphenyl with a purity of 99.95% was obtained. The yield of 4,4'-dihydroxybiphenyl in the whole process was 89%.

[0038] Example 5: Preparation of 4,4'-dihydroxybiphenyl (1) 0.54 kg of 4,4'-dinitrobiphenyl and 1.8 kg of ethanol were added to a carbon steel-lined plastic storage tank to obtain a mixture. The mixture was continuously passed through a hydrogenation reduction reactor at a rate of 0.052 kg / min, while hydrogen was introduced into the hydrogenation reduction reactor at a rate of 0.992 g / min. The mixture underwent a reduction reaction in the hydrogenation reduction reactor, which was filled with a palladium catalyst. The hydrogenation reduction reactor was heated to 63°C to obtain the intermediate 4,4'-diaminobiphenyl. The reaction solution was pumped out by the first high-pressure plunger pump and then fed into a first-stage tower reactor. The content of 4,4'-dinitrobiphenyl was found to be less than 0.1% by gas phase normalization analysis.

[0039] (2) The pressure of the first high-pressure plunger pump and the second high-pressure plunger pump is controlled at 1.2 MPa. 4,4'-diaminobiphenyl is continuously passed through the first-stage tower reactor and the second-stage tower reactor at a rate of 0.052 kg / min and undergoes hydrolysis. The first-stage tower reactor and the second-stage tower reactor are filled with the hydrolysis reagent (silica grafted modified multibranched carboxylic acid polymer) prepared in Example 1. The first-stage tower reactor and the second-stage tower reactor are heated to 85°C to obtain 4,4'-dihydroxybiphenyl reaction solution. After the reaction solution is pumped out of the second-stage tower reactor, it is stored in the desolvation tank. The content of 4,4'-diaminobiphenyl is less than 0.1% by gas phase normalization detection.

[0040] (3) 4,4'-dihydroxybiphenyl was desolventized in a desolventizing tank. The feed rate was controlled at 0.05 kg / min and the temperature of the desolventizing tank was 100℃. 4,4'-dihydroxybiphenyl with a purity of 99.93% was obtained. The yield of 4,4'-dihydroxybiphenyl in the whole process was 86%.

[0041] Example 6: Preparation of 4,4'-dihydroxybiphenyl (1) 0.59 kg of 4,4'-dinitrobiphenyl and 2.2 kg of tetrahydrofuran were added to a carbon steel-lined plastic storage tank to obtain a mixture. The mixture was continuously passed through a hydrogenation reduction reactor at a rate of 0.062 kg / min, while hydrogen was introduced into the hydrogenation reduction reactor at a rate of 1.085 g / min. The mixture underwent a reduction reaction in the hydrogenation reduction reactor. The hydrogenation reduction reactor was filled with a platinum catalyst and heated to 58°C to obtain the intermediate 4,4'-diaminobiphenyl. The reaction solution was pumped out by the first high-pressure plunger pump and then fed into a first-stage tower reactor. The content of 4,4'-dinitrobiphenyl was found to be less than 0.1% by gas phase normalization analysis.

[0042] (2) The pressure of the first high-pressure plunger pump and the second high-pressure plunger pump is controlled at 1.5 MPa. 4,4'-diaminobiphenyl is continuously passed through the first-stage tower reactor and the second-stage tower reactor at a rate of 0.062 kg / min and undergoes hydrolysis. The first-stage tower reactor and the second-stage tower reactor are filled with the hydrolysis reagent (silica grafted modified multibranched carboxylic acid polymer) prepared in Example 1. The first-stage tower reactor and the second-stage tower reactor are heated to 70°C to obtain 4,4'-dihydroxybiphenyl reaction solution. After the reaction solution is pumped out of the second-stage tower reactor, it is stored in the desolvation tank. The content of 4,4'-diaminobiphenyl is less than 0.1% by gas phase normalization detection.

[0043] (3) 4,4'-dihydroxybiphenyl was desolventized in a desolventizing tank. The feed rate was controlled at 0.06 kg / min and the temperature of the desolventizing tank was 100℃. 4,4'-dihydroxybiphenyl with a purity of 99.95% was obtained. The yield of 4,4'-dihydroxybiphenyl in the whole process was 87%.

[0044] Comparative Example 1 (1) The difference from Example 1 is that terephthalic acid is not added, and silica-grafted modified branched carboxylic acid is finally prepared.

[0045] (2) The difference from Example 2 is that the hydrolysis reagent was replaced with an equal amount of silica-grafted modified branched carboxylic acid prepared in step (1). The final yield of 4,4'-dihydroxybiphenyl was 80.4%.

[0046] Comparative Example 2 (1) The difference from Example 1 is that 2-sulfobenzoic acid is not added, and the silica-grafted modified carboxylic acid polymer is finally prepared.

[0047] (2) The difference from Example 2 is that the hydrolysis reagent was replaced with an equal amount of silica-grafted modified carboxylic acid polymer prepared in step (1). The final yield of 4,4'-dihydroxybiphenyl was 42.2%.

[0048] Comparative Example 3 The difference from Example 2 is that the hydrolysis reagent was replaced with 2-sulfobenzoic acid and terephthalic acid (in the same amounts as those in the silica-grafted modified multibranched carboxylic acid polymer). The final yield of 4,4'-dihydroxybiphenyl was 74.1%.

[0049] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for synthesizing 4,4'-dihydroxybiphenyl, characterized in that, The synthesis method includes the following steps: (1) 4,4'-dinitrobiphenyl, a metal catalyst and an organic solvent are mixed and hydrogen is introduced to carry out a hydrogenation reduction reaction to obtain 4,4'-diaminobiphenyl; (2) Mix 4,4'-diaminobiphenyl and silica-grafted modified multibranched carboxylic acid polymer, heat to react, and remove solvent from the reaction solution to obtain 4,4'-dihydroxybiphenyl.

2. The synthesis method according to claim 1, characterized in that, In step (1), 4,4'-dinitrobiphenyl and organic solvent are stored in a storage tank to obtain a mixture. The mixture is then passed into a hydrogenation reduction reactor filled with a metal catalyst to carry out a hydrogenation reduction reaction to obtain 4,4'-diaminobiphenyl.

3. The synthesis method according to claim 2, characterized in that, The organic solvent is selected from at least one of methanol, ethanol, isopropanol, and tetrahydrofuran; the mass ratio of 4,4'-dinitrobiphenyl to the organic solvent is 0.25~0.5:

1.

4. The synthesis method according to claim 2, characterized in that, The feed rate of the mixture is 0.04~0.065 kg / min; the hydrogen feed rate is 0.75~1.1 g / min; the heating temperature of the hydrogenation reduction reactor is 25~100℃; and the metal catalyst is selected from palladium, platinum or ruthenium.

5. The synthesis method according to claim 1, characterized in that, In step (2), 4,4'-diaminobiphenyl is pumped into a two-stage tandem tower reactor filled with silica-grafted modified multibranched carboxylic acid polymer for reaction. The resulting 4,4'-dihydroxybiphenyl reaction solution is desolventized in a desolventizing tank to obtain purified 4,4'-dihydroxybiphenyl. The desolventized solvent is recycled.

6. The synthesis method according to claim 5, characterized in that, The silica-grafted modified multibranched carboxylic acid polymer is a silica-grafted compound having at least two of the following structural formulas A, B, and C. Where the structure of A is or The structure of B is or The C structure is .

7. The synthesis method according to claim 6, characterized in that, The silica-grafted modified multibranched carboxylic acid polymer is prepared by the following method: Silica and a silane coupling agent were dispersed in toluene, and benzoic acid containing sulfonic acid group and dicarboxylic acid were added. The mixture was heated under nitrogen protection and refluxed. The resulting product was evaporated to dryness, and then washed and dried successively with organic solvent and deionized water to obtain silica-grafted modified multibranched carboxylic acid polymer.

8. The synthesis method according to claim 7, characterized in that, The silane coupling agent is KH-550; the sulfonic acid-containing benzoic acid is 2-sulfobenzoic acid or 2-hydroxy-5-sulfobenzoic acid; the dicarboxylic acid is succinic acid or terephthalic acid; the molar ratio of silicon dioxide, sulfonic acid-containing benzoic acid and dicarboxylic acid is 1:2~3:3~4; the amount of silane coupling agent added is 0.5~1% of the mass of silicon dioxide.

9. The synthesis method according to claim 5, characterized in that, The pump pressure is 1.0~1.2 MPa; the temperature of the two-stage series tower reactor is 60~85℃.

10. The application of the method according to any one of claims 1 to 9 in at least one of the following 1) to 3): 1) Shorten the synthesis time of 4,4'-dihydroxybiphenyl; 2) Improve the selectivity of 4,4'-dihydroxybiphenyl; 3) Reduce impurities in the 4,4'-dihydroxybiphenyl reaction solution and increase the yield of 4,4'-dihydroxybiphenyl.

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