Method for preparing 4, 4 '-biphenol compound by electrochemical method

Abstract

The invention provides a method for preparing a 4, 4 '-biphenol compound by an electrochemical method, which is characterized in that in a diaphragm-free electrolytic bath, a phenol compound and a salt solution thereof are used as raw materials, a boron-phosphorus doped graphene electrode is used as an anode electrode, and an electrolytic reaction is carried out to generate the 4, 4'-biphenol compound. According to the method provided by the invention, the para-coupled product 4, 4 '-biphenol compound can be obtained with high selectivity through electrochemical phenol oxidative coupling, the selectivity is high, only trace electrolyte salt is used in the whole process, and basically no three wastes are generated. Compared with the traditional catalytic reaction, the method has the advantages of open reaction, mild reaction conditions, no generation of isomerized products, great shortening of the separation and purification process, and very good industrial application scenario.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical technology, and in particular relates to a method for preparing 4,4'-biphenyl diphenol compounds by electrochemical method. Background Art

[0002] 4,4'-Biphenol can be used to manufacture excellent engineering plastics and composite materials. It has an important anti-aging effect on aging caused by oxygen and heat, and is often added to rubber and latex. Due to its good heat resistance, it can be used as a modified monomer for polyesters, polycarbonates, and epoxy resins, and has important applications in the field of materials. In addition, 4,4'-Biphenol is an important intermediate for manufacturing liquid crystal materials and is the main monomer for synthesizing type I high heat-resistant LCP. It has the characteristics of high molding temperature and high heat deformation temperature, and is widely used.

[0003] At present, the main methods for synthesizing 4,4'-biphenyl diphenol include benzidine diazotization method, biphenyl sulfonation alkali fusion method, and chlorination hydrolysis method. The main reaction routes are as follows:

[0004] Benzidine diazotization method:

[0005]

[0006] Biphenyl sulfonation alkali fusion method:

[0007]

[0008] Biphenyl chlorination hydrolysis method:

[0009]

[0010] However, the above methods all require the use of biphenyl as a raw material, which is expensive and has limited sources. In addition, they require the use of explosive diazonium salts, high-temperature alkali fusion, chlorine chlorination and other harsh conditions, which are very unfriendly to the environment and seriously restrict their further development.

[0011] In recent years, the synthesis of 4,4'-biphenol by metal-catalyzed oxidative coupling has also developed rapidly. For example, biphenol compounds can be directly obtained by oxidative coupling reaction of 2,6-di-tert-butylphenol and p-chlorophenol.

[0012] This method needs to be carried out under a noble metal catalyst such as a palladium catalyst, and there are problems such as low yield, poor product quality, high requirements for reaction conditions, high toxicity, and high cost. For example, patent CN101817713B uses peroxide as an oxidant in a low-boiling organic solvent or in an aqueous solution to obtain 4,4'-biphenyldiphenol, but in this method, peroxide is easily exploded when undergoing oxidation reaction in a low-boiling organic solvent at high temperature, which poses a great safety risk. Patent CN103936560B performs oxidative coupling through phenolic compounds to form diphenylquinone compounds, but this method still requires hydrogenation to obtain 4,4'-biphenyldiphenol.

[0013] Therefore, there is an urgent need to invent a green and safe synthesis process to ensure safe and stable production while ensuring product benefits. Summary of the invention

[0014] The present invention aims to provide a method for preparing 4,4'-biphenol by electrochemical method.

[0015] The present invention uses boron-phosphorus-doped graphene as an anode to catalyze the oxidation of phenol compounds and phenolate compounds in water and alcohol solutions to undergo oxidative coupling, and by controlling conditions such as reaction temperature and pH value, 4,4'-biphenyldiphenol compounds are generated in one step. In the method provided by the present invention, electrochemical phenol oxidative coupling can highly selectively obtain a para-coupled product to replace 4,4'-biphenyldiphenol compounds, with high selectivity. Only a trace amount of electrolyte salt is used in the whole process, and basically no three wastes are generated. Compared with traditional catalytic reactions, the reaction can be carried out in the open, and the reaction conditions are mild, and no isomerized products are generated, which greatly shortens the separation and purification process and has a good industrial application scenario.

[0016] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0017] The invention discloses an electrochemical method for preparing 4,4'-biphenyldiphenol compounds. In a membraneless electrolytic cell, phenol compounds and their salt solutions are used as raw materials, and a boron-phosphorus doped graphene electrode is used as an anode electrode to carry out an electrolytic reaction to generate 4,4'-biphenyldiphenol compounds.

[0018] Preferably, the structure of the 4,4'-biphenyl diphenol compound is as follows:

[0019]

[0020] The number of substituents R and R' is 0-4, R and R' are the same or different, and are independently selected from C1-C8 long-chain or branched alkyl, alkoxy, and aryl compounds, preferably methyl, ethyl, propyl, butyl, methoxy, ethoxy, and tert-butoxy.

[0021] The boron-phosphorus doped graphene electrode refers to an electrode with boron-phosphorus doped graphene sprayed or deposited on the surface, which is prepared by spraying or depositing boron-phosphorus doped graphene on the surface of an electrode substrate, and the substrate can be a valve-type metal such as titanium, tantalum, niobium, etc.

[0022] Preferably, in the boron-phosphorus doped graphene, the doping mass ratio of phosphorus to boron is greater than or equal to 3:1, and the mass ratio of P, B and C in the boron-phosphorus doped graphene is preferably 3:1:50-6:1:100.

[0023] Preferably, the graphene includes but is not limited to one or more of two-dimensional graphene, three-dimensional fullerene, etc., and the electrode thickness is 0.5-1um.

[0024] Boron and phosphorus can be doped into graphene using known methods. The boron source can be selected from phenylboric acid, boric acid, etc., and the phosphorus source can be selected from phosphoric acid, trimethyl phosphate, triethyl phosphate, tributyl phosphate, etc.

[0025] In some specific embodiments of the present invention, the boron-phosphorus doped graphene can be prepared by method one or method two:

[0026] Method 1: In a reaction inert atmosphere, graphene is mixed with boric acid and phosphoric acid, heated to 700°C to 800°C and maintained for 2-3.5 hours, and then heated to 1200°C to 1500°C to obtain boron-phosphorus doped graphene.

[0027] Preferably, in the boric acid, phosphoric acid and graphene, the mass ratio of P, B and C is preferably 3:1:50-6:1:100.

[0028] Method 2: In an inert atmosphere, a boric acid compound, a phosphate ester and a carbon source are mixed to obtain a modified boron-phosphorus organic solution, which is then heated under vacuum conditions to obtain boron-phosphorus-doped graphene powder.

[0029] Preferably, the mass ratio of P, B and C in the boric acid compound, phosphate and carbon source is 3:1:50-6:1:100.

[0030] Preferably, the boric acid compound is selected from one or more of phenylboric acid, tolueneboric acid and alkylboric acid.

[0031] Preferably, the phosphate ester is selected from one or more of trimethyl phosphate, triethyl phosphate, dimethyl phosphate, and diethyl phosphate.

[0032] Preferably, the carbon source is selected from benzene, toluene, ethylbenzene, cumene and other carbon sources containing benzene rings;

[0033] Preferably, the boric acid compound, phosphate ester and carbon source are ultrasonically treated at 50-70° C. for 2-5 hours to obtain a suspension;

[0034] Preferably, the obtained modified boron-phosphorus organic solution mixture is heated in a vacuum tube furnace;

[0035] Preferably, the mixture is heated to 600-750° C. under vacuum conditions for 12 h-16 h, the obtained black powder is cooled to room temperature, ground and sieved to obtain boron-phosphorus doped graphene powder;

[0036] Preferably, the particle size of the boron-phosphorus doped graphene is 100-1000 nm, and the boron-phosphorus doped graphene can be loaded on the electrode surface by common methods such as spraying and deposition.

[0037] The structure of the phenol compound is as follows:

[0038] The number of substituents R may be 0-4, and the substitution position is not para to the hydroxyl group. The substituents R may be C1-C8 long-chain or branched alkyl, alkoxy, or aryl compounds. The substituents R are preferably selected from methyl, ethyl, propyl, butyl, methoxy, ethoxy, and tert-butoxy.

[0039] Preferably, the salt of the phenol compound includes an alkali metal salt such as a lithium salt, a sodium salt and a potassium salt of the phenol compound. Preferably, during the reaction, the salt of the phenol compound is added to the phenol compound or an alkali metal hydroxide is added to the phenol compound to generate the salt of the phenol compound.

[0040] Preferably, the electrolytic cell is a monopolar type diaphragmless electrolytic cell, comprising an anode, a cathode and an electrolytic chamber, and can be in the form of a plate-and-frame type, a three-dimensional filler type, a capillary gap type, or the like.

[0041] The mass ratio of the phenol compound to the salt of the phenol compound is 1:2-2:1, and the molar fraction of the phenol compound and the salt of the phenol compound in the solution is 0.1 mol / L-2 mol / L.

[0042] The cathode electrode includes but is not limited to one or more of platinum, nickel, copper, lead, carbon, etc.; such as alloy materials or porous materials thereof.

[0043] The electrolysis reaction is carried out in a mixed solution of water and an organic solvent, wherein the organic solvent includes but is not limited to alcohols, amides, sulfoxides, phosphoramides, etc. Preferably, the mass ratio of water to the organic solvent is 1:1-1:3.

[0044] The electrolysis temperature is 20-80°C, preferably 25-45°C.

[0045] The electrolysis current density is 500-5000A / m 2 , preferably 1000-2000A / m 2 , under this condition, the cell voltage range is 4.3-8.1V.

[0046] Compared with the prior art, this application has the following beneficial effects:

[0047] 1. Prepare 4,4'-biphenyldiphenol compounds by electrochemical method, use phenol compounds to react on boron-phosphorus doped graphene electrodes, and obtain electrochemically coupled reaction products 4,4'-biphenyldiphenol compounds in one step. This method does not require the use of metal reagents and additional equivalent oxidants, and the reaction conditions are mild. By partially salting the phenol compounds in the system, 4,4'-biphenyldiphenol compounds can be obtained with high selectivity. Compared with traditional alkali fusion sulfonation, metal coupling reaction, etc., it has unique advantages and has good industrialization prospects.

[0048] 2. The present invention avoids the self-oxidation reaction of phenol on the one hand, and activates the para-coupling site on the other hand, greatly improving the para-coupling selectivity, and can obtain the para-coupling product 4,4'-biphenyl diphenol compound with high selectivity, avoiding the generation of multiple isomers, thereby reducing the difficulty of subsequent separation and purification and improving production efficiency.

[0049] 3. During the entire reaction process, only a trace amount of electrolyte salt is used, and basically no three wastes are generated, which not only reduces costs but also reduces environmental pollution.

[0050] 4. The method of the present invention has mild reaction conditions and does not require the use of a large amount of precious metals, thereby reducing production costs. Compared with the prior art, the method of the present invention is more economical.

[0051] 5. The entire reaction can be carried out under open reaction conditions without the need for special equipment and environment. The reaction conditions are mild and no isomerized products are generated, which greatly simplifies the reaction process and improves production efficiency. Compared with the prior art, the operation is simple. The method of the present invention is suitable for large-scale production and is more suitable for industrial application. DETAILED DESCRIPTION

[0052] The preparation method provided by the present invention is further described in detail below through examples, but the present invention is not limited thereto.

[0053] Purchase of chemical reagents:

[0054] Phenol compounds: Aladdin reagent, reagent grade, >99.0% (GC)

[0055] Organic solvent: Aladdin reagent, reagent grade, >99% (GC), industrial product, >98.0%

[0056] Cosolvent (water and organic solvent): Aladdin reagent, purity AR, 98wt%

[0057] Boron-phosphorus doped graphene electrode is self-made. Boron-phosphorus doped graphene 1: In an argon atmosphere, 63.7g of graphene was mixed with 5.73g of boric acid and 14.89g of phosphoric acid (mass fraction 85%), heated to 700℃ for 2h, and then heated to 1200℃ to obtain graphene powder with a particle size of 200nm, and boron-phosphorus doped graphene. The mass ratio of P, B, and C is about 4:1:64.

[0058] Boron-phosphorus doped graphene 2: Under an argon atmosphere, 101.5 g of phenylboric acid, 120.9 g of trimethyl phosphate, and 513.3 g of toluene were mixed to obtain a modified boron-phosphorus organic solution. The mixture was ultrasonicated at 70°C for 5 h to obtain a suspension. The modified boron-phosphorus organic solution mixture was heated to 750°C in a vacuum tube furnace for 16 h. The obtained black powder was cooled to room temperature, ground and sieved to obtain boron-phosphorus doped graphene micropowder with a particle size of 1000 nm. The mass ratio of P, B, and C was approximately 3:1:60.

[0059] Boron-phosphorus doped graphene 3: The same preparation method as that of boron-phosphorus doped graphene 1 is adopted, the main difference being that 50 g of graphene, 5.73 g of boric acid, and 13.45 g of phosphoric acid (mass fraction 85%) are added.

[0060] Boron-phosphorus doped graphene four: The same preparation method as that of boron-phosphorus doped graphene one is adopted, the main difference being that 91g of graphene, 5.73g of boric acid and 18.5g of phosphoric acid (mass fraction 85%) are added.

[0061] The boron-phosphorus modified graphene powder can be deposited on the surface of the electrode substrate by a high-pressure spray gun or ultrasonic spraying. The substrate can be a valve-type metal such as titanium, tantalum, niobium, etc.

[0062] Embodiment 1:

[0063] Preparation of sodium phenol salt drop solution: Mix 2 mol of phenol required for the reaction with 2 mol of sodium hydroxide to prepare sodium phenol solution, and then add the sodium phenol solution to a mixed solvent with a mass ratio of 1:3 of deionized water and ethanol to prepare a solution with a concentration of 0.1 mol / L. Add 1 mol of phenol to a 75wt% ethanol aqueous solution to prepare a 0.1 mol / L solution, and add the sodium phenol solution to the phenol solution for electrolysis. Boron-phosphorus doped graphene was used as the anode coating with a coating thickness of 0.5um, titanium material was used as the substrate for the anode, and platinum sheet was used as the cathode in a plate-frame electrolytic cell at 30°C and 1200A / m 2 The electrolysis was carried out at a current density of 4.6 V and a cell voltage of 4.6 V. The final yield of 4,4'-biphenol was 95%.

[0064] Embodiment 2:

[0065] Preparation of phenol salt drop solution: Mix 3-methylphenol with an equimolar amount of potassium hydroxide, and then add it to a mixed solvent of deionized water and N, N-dimethylformamide (mass ratio 1:1) to prepare a solution with a concentration of 0.2 mol / L. Add phenol to a mixed solvent of deionized water and N, N-dimethylformamide (mass ratio 1:1) to prepare a 0.2 mol / L solution, and add the phenol salt solution to the phenol solution for electrolysis. The mass ratio of 3-methylphenol to 3-methylphenol potassium is 1:1. Boron-phosphorus doped graphene II is used as the anode coating with a coating thickness of 0.8um. ​​Titanium is used as the substrate to form the anode, and nickel sheet is used as the cathode. At 20°C and 500A / m 2 The electrolysis was carried out at a current density of 4.3 V and a cell voltage of 4.3 V. The final yield of 4,4'-biphenol was 92%.

[0066] Embodiment 3:

[0067] Preparation of phenol salt drop solution: Mix 2-ethylphenol with an equimolar amount of lithium hydroxide, and then add it to a mixed solvent of deionized water and dimethyl sulfoxide (mass ratio of 1:2) to prepare a solution with a concentration of 0.2 mol / L. Add phenol to a mixed solvent of deionized water and dimethyl sulfoxide (mass ratio of 1:2) to prepare a 0.2 mol / L solution, and add the phenol salt solution to the phenol solution for electrolysis. The ratio of 2-ethylphenol to 2-ethylphenol lithium is 2:1. Electrolysis reaction conditions: Boron-phosphorus doped graphene trioxide is used as the anode coating with a coating thickness of 1um, titanium material is used as the anode substrate, and copper sheet is used as the cathode at 60°C and 2000A / m 2 The electrolysis was carried out at a current density of 5.7 V and a cell voltage of 5.7 V. The final yield of 4,4'-biphenol was 87%.

[0068] Embodiment 4:

[0069] Preparation of phenol salt drop solution: Mix 3-methyl-5-methoxyphenol with an equimolar amount of lithium hydroxide, and then add it to a mixed solvent of deionized water and hexamethylphosphoric acid triamide in a mass ratio of 1:1 to prepare a solution with a concentration of 0.1 mol / L. Add phenol to a mixed solvent of deionized water and hexamethylphosphoric acid triamide (mass ratio 1:1) to prepare a 0.1 mol / L solution, and add the phenol salt solution to the phenol solution for electrolysis. The ratio of 3-methyl-5-methoxyphenol to 3-methyl-5-methoxyphenol sodium is 2:1. Electrolysis reaction conditions: Boron-phosphorus doped graphene tetrachloride is used as the anode coating with a coating thickness of 0.5um, titanium material is used as the anode substrate, and carbon sheet is used as the cathode at 25°C and 1500A / m 2 The electrolysis was carried out at a current density of 5.3 V and a cell voltage of 5.3 V. The final yield of 4,4'-biphenol was 89%.

[0070] Embodiment 5:

[0071] Preparation of phenol salt drop solution: Mix 2,6-dipropylbenzene with an equimolar amount of sodium hydroxide, and then add it to a mixed solvent of deionized water and hexamethylphosphoric acid triamide in a mass ratio of 1:1 to prepare a solution with a concentration of 0.1 mol / L. Add phenol to a mixed solvent of deionized water and hexamethylphosphoric acid triamide (mass ratio 1:1) to prepare a 0.1 mol / L solution, and add the phenol salt solution to the phenol solution for electrolysis. The ratio of 2,6-dipropylphenol to 2,6-dipropylphenol sodium is 2:1. Electrolysis reaction conditions: Boron-phosphorus doped graphene is used as the anode coating with a coating thickness of 0.5um, titanium material is used as the anode substrate, and lead sheet is used as the cathode at 80°C and 5000A / m 2 The electrolysis was carried out at a current density of 8.1 V and a cell voltage of 8.1 V. The final yield of 4,4'-biphenol was 76%.

[0072] Embodiment 6:

[0073] Preparation of phenol salt drop solution: Mix 2,3-dibutyl-4-ethyl-5-tert-butoxyphenol with an equimolar amount of potassium hydroxide, and then add it to a mixed solvent of deionized water and hexamethylphosphoric acid triamide (mass ratio 1:1) to prepare a solution with a concentration of 0.1 mol / L. Add phenol to a mixed solvent of deionized water and hexamethylphosphoric acid triamide (mass ratio 1:1) to prepare a 0.1 mol / L solution, and add the phenol salt solution to the phenol solution for electrolysis. The ratio of 2,3-dibutyl-4-ethyl-5-tert-butoxyphenol to 2,3-dibutyl-4-ethyl-5-tert-butoxyphenol sodium is 1:1. Electrolysis reaction conditions: Boron-phosphorus doped graphene tris is used as the anode coating, the coating thickness is 0.8um, titanium material is used as the anode substrate, and platinum sheet is used as the cathode at 40°C and 800A / m 2 The electrolysis was carried out at a current density of 500 nm and a cell voltage of 6.9 V. The final yield of 4,4'-biphenol was 87%.

Claims

1. A method for preparing 4,4'-biphenyl diphenol compounds by electrochemical method, characterized in that: In a diaphragmless electrolytic cell, phenol compounds and their salt solutions are used as raw materials, and a boron-phosphorus-doped graphene electrode is used as an anode electrode to carry out an electrolytic reaction to generate 4,4'-biphenyldiphenol compounds.

2. The method according to claim 1, characterized in that The structure of the 4,4'-biphenyl diphenol compound is as follows: The number of substituents R and R' is 0-4, R and R' are the same or different, and are independently selected from C1-C8 long-chain or branched alkyl, alkoxy, and aryl compounds, preferably methyl, ethyl, propyl, butyl, methoxy, ethoxy, and tert-butoxy.

3. The method according to claim 1, characterized in that The boron-phosphorus doped graphene electrode refers to an electrode with boron-phosphorus doped graphene sprayed or deposited on the surface, and is prepared by spraying or depositing boron-phosphorus doped graphene on the surface of an electrode substrate; Preferably, the substrate is a valve metal, preferably titanium, tantalum or niobium.

4. The method according to any one of claims 1 to 3, characterized in that: In the boron-phosphorus doped graphene, the doping mass ratio of phosphorus to boron is greater than or equal to 3:1, and the mass ratio of P, B, and C in the boron-phosphorus doped graphene is preferably 3:1:50-6:1:

100.

5. The method according to any one of claims 1 to 4, characterized in that: The graphene includes but is not limited to one or more of two-dimensional graphene and three-dimensional fullerene, and the thickness of the boron-phosphorus doped graphene coating is 0.5-1 um.

6. The method according to any one of claims 1 to 5, characterized in that: The boron-phosphorus doped graphene can be prepared by method one or method two: Method 1: In a reaction inert atmosphere, graphene is mixed with boric acid and phosphoric acid, heated to 700°C to 800°C and maintained for 2-3.5 hours, and then heated to 1200°C to 1500°C to obtain boron-phosphorus doped graphene; Preferably, in the boric acid, phosphoric acid and graphene, the mass ratio of P, B and C is preferably 3:1:50-6:1:100; The boron-phosphorus organic solution is then heated under vacuum conditions to obtain boron-phosphorus doped graphene micropowder.

7. The method according to claim 6, characterized in that The mass ratio of P, B and C in the boric acid compound, phosphate and carbon source is 3:1:50-6:1:100; Preferably, the boric acid compound is selected from one or more of phenylboric acid, tolueneboric acid, and alkylboric acid; Preferably, the phosphate ester is selected from one or more of trimethyl phosphate, triethyl phosphate, tributyl phosphate, dimethyl phosphate, and diethyl phosphate; Preferably, the carbon source is selected from benzene, toluene, ethylbenzene, cumene and other carbon sources containing benzene rings; Preferably, the boric acid compound, phosphate ester and carbon source are ultrasonically treated at 50-70° C. for 2-5 hours to obtain a suspension; Preferably, the obtained modified boron-phosphorus organic solution mixture is heated in a vacuum tube furnace; Preferably, the mixture is heated to 600-750° C. under vacuum conditions for 12 h-16 h, the obtained black powder is cooled to room temperature, ground and sieved to obtain boron-phosphorus doped graphene powder; Preferably, the particle size of the boron-phosphorus doped graphene is 100-1000 nm.

8. The method according to any one of claims 1 to 7, characterized in that: The structure of the phenol compound is as follows: The number of substituents R may be 0-4, and the substitution position is not para to the hydroxyl group. The substituents R may be C1-C8 long-chain or branched alkyl, alkoxy, or aryl compounds. The substituents R are preferably selected from methyl, ethyl, propyl, butyl, methoxy, ethoxy, and tert-butoxy.

9. The method according to any one of claims 1 to 8, characterized in that: The salts of phenol compounds include alkali metal salts of the phenol compounds; Preferably, during the reaction, a salt of a phenolic compound is added to the phenolic compound or an alkali metal hydroxide is added to the phenolic compound to generate a salt of the phenolic compound.

10. The method according to any one of claims 1 to 9, characterized in that: The electrolytic cell is a monopolar diaphragmless electrolytic cell, comprising an anode, a cathode and an electrolytic chamber; Preferably, the mass ratio of the phenol compound to the salt of the phenol compound is 1:2-2:1, and the molar fraction of the phenol compound and the salt of the phenol compound in the solution is 0.1 mol / L-2 mol / L; Preferably, the cathode electrode includes but is not limited to one or more of platinum, nickel, copper, lead, and carbon; Preferably, the electrolysis reaction is carried out in a mixed solution of water and an organic solvent, wherein the organic solvent includes but is not limited to alcohols, amides, sulfoxides, and phosphoramides; preferably, the mass ratio of water to the organic solvent is 1:1-1:3; Preferably, the electrolysis temperature is 20-80°C, preferably 25-45°C; Preferably, the electrolysis current density is 500-5000A / m 2 , preferably 1000-2000A / m 2 .

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