A method for preparing 4,4'-diphenylol compounds by electrochemical method

Abstract

The application provides a method for preparing 4,4'-diphenylol compound by an electrochemical method, in which a solution of a phenol compound and a salt thereof is used as raw material, a boron-phosphorus doped graphene electrode is used as an anode electrode, and an electrolysis reaction is carried out to generate 4,4'-diphenylol compound. In the method, electrochemical phenol oxidation coupling can obtain the para-coupled product 4,4'-diphenylol compound with high selectivity, the selectivity is high, only a trace amount of electrolyte salt is used in the whole process, and no three wastes are generated. Compared with a traditional catalytic reaction, the reaction can be carried out in an open state, the reaction condition is mild, no isomerized product is generated, the separation and purification process is greatly shortened, and the method has a good industrial application scene.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrochemistry, and particularly relates to a method for preparing 4,4'-diphenylol by an electrochemical method. BACKGROUND

[0002] 4,4'-diphenylol can be used to manufacture excellent engineering plastics and composite materials, and has important anti-aging effect on oxygen and heat-induced aging, and is often added to rubber and latex. Due to its good heat resistance, it can be used as a modified monomer of polyester, polycarbonate and epoxy resin, and has important application in the field of materials. In addition, 4,4'-diphenylol is an important intermediate for manufacturing liquid crystal materials, and is a main monomer for synthesizing type I high-heat-resistance LCP, has the characteristics of high molding temperature, high heat distortion temperature, and is widely used.

[0003] At present, the main synthesis methods of 4,4'-diphenylol include aniline diazotization, biphenyl sulfonation and alkali fusion, and chlorination hydrolysis, and the main reaction routes are as follows:

[0004] Aniline diazotization method:

[0005]

[0006] Biphenyl sulfonation and alkali fusion method:

[0007]

[0008] Biphenyl chlorination and hydrolysis method:

[0009]

[0010] However, the above methods all need to use biphenyl as raw material, which is high in price, limited in source, and needs to use explosive diazonium salt, high-temperature alkali fusion, chlorine chlorination and other harsh conditions, which is very harmful to the environment, and seriously restricts its further development.

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

[0012] The method needs to be carried out using a noble metal catalyst such as a palladium catalyst, and has problems of low yield, poor product quality, high reaction condition requirement, great toxicity, and high cost. For example, patent CN101817713B obtains 4,4'-diphenylphenol by using a peroxide as an oxidizing agent in a low-boiling organic solvent or an aqueous solution, but the peroxide is prone to explosion in the oxidation reaction at high temperature in the low-boiling organic solvent, and the safety risk is great. Patent CN103936560B forms a biphenylquinone compound by oxidative coupling of a phenol compound, but the method still needs to be subjected to hydrogenation to obtain 4,4'-diphenylphenol.

[0013] Therefore, it is urgent to invent a green and safe synthesis process to ensure the safety and stability of production while ensuring the product benefit. SUMMARY

[0014] The application aims to provide a method for preparing 4,4'-diphenylphenol by an electrochemical method.

[0015] In the method provided by the application, the electrochemical phenol oxidative coupling can obtain the para-coupled product, i.e., a substituted 4,4'-diphenylphenol compound, with high selectivity, the whole process only uses a small amount of electrolyte salt, and basically no three wastes are generated. Compared with the traditional catalytic reaction, the reaction can be carried out in an open state, the reaction condition is mild, no isomerized product is generated, the separation and purification process is greatly shortened, and the method has a good industrial application scene.

[0016] In order to achieve the above application purposes, the application provides the following technical solutions.

[0017] A method for preparing a 4,4'-diphenylphenol compound by an electrochemical method, in which a diaphragm-free electrolytic cell is used, a phenol compound and a salt thereof are used as raw materials, and a boron-phosphorus-doped graphene electrode is used as an anode electrode to perform an electrolysis reaction, thereby generating a 4,4'-diphenylphenol compound.

[0018] Preferably, the 4,4'-diphenylphenol compound has the following structure:

[0019]

[0020] wherein the substituents R and R' have 0-4, R and R' are the same or different, and are independently selected from C1-C8 long-chain or branched alkyl, alkoxy, 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. The substrate can be valve-type metals such as titanium, tantalum, and niobium.

[0022] Preferably, the mass ratio of phosphorus to boron in the boron-phosphorus doped graphene 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 thickness of the electrode is 0.5-1um.

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

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

[0026] Method one: under a reaction inert atmosphere, mix graphene with boric acid and phosphoric acid, heat to 700-800℃ for 2-3.5h, and then heat to 1200-1500℃ to obtain boron-phosphorus doped graphene.

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

[0028] Method two: under a reaction inert atmosphere, mix a boronic acid compound, a phosphoric acid ester, and a carbon source to obtain a modified boron-phosphorus organic solution, and then heat under vacuum to obtain boron-phosphorus doped graphene powder.

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

[0030] Preferably, the boronic acid compound is selected from one or more of phenylboronic acid, toluene boronic acid, and alkyl boronic acid.

[0031] Preferably, the phosphoric acid 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, isopropylbenzene, and other carbon sources containing benzene rings.

[0033] Preferably, the boronic acid compound, the phosphoric acid ester, and the carbon source are ultrasonically treated at 50-70℃ for 2-5h to obtain a suspension.

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

[0035] Preferably, the heating is carried out under vacuum at 600-750℃ for 12-16h, and the obtained black powder is cooled to room temperature, ground and sieved to obtain boron-phosphorus doped graphene powder;

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

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

[0038] The substituent group R can have 0-4 substituents, and the substitution position is not para to the hydroxyl group, which can be a C1-C8 long chain or branched alkyl group, an alkoxy group, an aryl compound, and the substituent group R is preferably selected from methyl, ethyl, propyl, butyl, methoxy, ethoxy and tert-butoxy.

[0039] Preferably, the salt of the phenolic compound includes lithium salt, sodium salt and potassium salt of the phenolic compound, and preferably, the salt of the phenolic compound is generated by adding the salt of the phenolic compound to the phenolic compound or adding an alkali hydroxide to the phenolic compound during the reaction.

[0040] Preferably, the electrolytic cell is a single-pole diaphragmless electrolytic cell, which includes an anode, a cathode and an electrolytic chamber. The electrolytic cell can be in the form of a plate-frame type, a three-dimensional filler type, a capillary gap type, etc.

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

[0043] The electrolysis reaction is carried out in a mixed solution of water and an organic solvent, and the organic solvent includes but is not limited to alcohol, amide, sulfoxide, phosphoramide, etc. Preferably, the mass ratio of water to organic solvent is 1:1-1:3.

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

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

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

[0047] 1. The 4,4'-diphenyl diol compound is prepared by an electrochemical method, phenol compounds are reacted on a boron-phosphorus doped graphene electrode, and the reaction product of electrochemical coupling, the 4,4'-diphenyl diol compound, is obtained in one step. This method does not need to use metal reagents and additional equivalents of oxidants, the reaction conditions are mild, the 4,4'-diphenyl diol compound can be obtained with high selectivity by salifying part of the phenol compounds in the system, and the method has unique advantages compared with traditional alkali fusion sulfonation and metal coupling reactions, and has good industrialization prospects.

[0048] 2. The application avoids the autoxidation of phenol on one hand and activates the para-coupling site on the other hand, greatly improves the para-coupling selectivity, and can obtain the para-coupling product, the 4,4'-diphenyl diol compound, with high selectivity, avoids the generation of multiple isomers, and thus reduces the difficulty of subsequent separation and purification and improves the production efficiency.

[0049] 3. In the whole reaction process, only a small amount of electrolyte salt is used, and no three wastes are generated, so that the cost is reduced and the environmental pollution is reduced.

[0050] 4. The method of the application has mild reaction conditions and does not need to use a large amount of noble metal, thereby reducing the production cost. Compared with the prior art, the method of the application has more economic benefits.

[0051] 5. The whole reaction can be carried out under open reaction conditions, without the need for special equipment and environment, the reaction conditions are mild, no isomerization product is generated, the reaction process is greatly simplified, the production efficiency is improved, compared with the prior art, the operation is simple, the method of the application is suitable for large-scale production and is more suitable for industrial application. DETAILED DESCRIPTION

[0052] The preparation method provided by the application is further described in detail through the following examples, but the application is not limited in any way by the examples.

[0053] Purchase of chemical reagents:

[0054] Phenol compound: Aldrin reagent, reagent grade, > 99.0% (GC)

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

[0056] Co-solvent (water and organic solvent): Aldrin reagent, purity AR, 98 wt%

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

[0058] Boron phosphorus doped graphene two: under argon atmosphere, 101.5g phenylboronic acid, 120.9g trimethyl phosphate and 513.3g toluene are mixed to obtain modified boron phosphorus organic solution, the mixture is ultrasonically treated at 70℃ for 5h to obtain a suspension, the obtained modified boron phosphorus organic solution mixture is heated to 750℃ in a vacuum tube furnace for 16h, the obtained black powder is cooled to room temperature, ground and sieved to obtain boron phosphorus doped graphene powder with a particle size of 1000nm, the mass ratio of P, B and C is about 3:1:60.

[0059] Boron phosphorus doped graphene three: the same preparation method as boron phosphorus doped graphene one is adopted, the main difference is that 50g graphene is added with 5.73g boric acid and 13.45g phosphoric acid (mass fraction 85%).

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

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

[0062] Example 1:

[0063] Sodium phenolate dropping solution is prepared: 2mol of phenol required for the reaction is mixed with 2mol of sodium hydroxide to prepare a sodium phenolate solution, then the sodium phenolate solution is added to a mixed solvent of deionized water and ethanol with a mass ratio of 1:3 to prepare a solution with a concentration of 0.1mol / L. 1mol of phenol is added to 75wt% ethanol aqueous solution to prepare a solution with a concentration of 0.1mol / L, and the sodium phenolate solution is added to the phenol solution for electrolysis reaction. Boron phosphorus doped graphene one is used as anode coating with a coating thickness of 0.5um, titanium is used as substrate to form an anode, and platinum sheet is used as cathode. The electrolysis is carried out in a plate-frame electrolytic cell at 30℃, 1200A / m 2 current density, and the cell voltage is 4.6V. The yield of 4,4'-diphenyldiol is 95%.

[0064] Example 2:

[0065] Preparation of phenol salt solution: 3-methylphenol was mixed with an equal amount of potassium hydroxide, and then added to a mixed solvent of deionized water and N, N-dimethylformamide in a mass ratio of 1:1 to prepare a solution with a concentration of 0.2 mol / L. Phenol was added to a mixed solvent of deionized water and N, N-dimethylformamide (mass ratio 1:1) to prepare a 0.2 mol / L solution. The salt solution of phenol was added to the phenol solution for electrolysis, and the mass ratio of 3-methylphenol to 3-methylphenol potassium was 1:1. The anode was composed of boron-phosphorus-doped graphene two as anode coating with a coating thickness of 0.8 um and titanium as the base material. The cathode was a nickel sheet. The electrolysis was carried out at 20°C and a current density of 500 A / m 2 The final yield of 4, 4'-diphenyl-diol was 92% under electrolysis at a current density of 500 A / m

[0066] Example 3:

[0067] Preparation of phenol salt solution: 3-methylphenol was mixed with an equal amount of potassium hydroxide, and then added to a mixed solvent of deionized water and N, N-dimethylformamide in a mass ratio of 1:1 to prepare a solution with a concentration of 0.2 mol / L. Phenol was added to a mixed solvent of deionized water and N, N-dimethylformamide (mass ratio 1:1) to prepare a 0.2 mol / L solution. The salt solution of phenol was added to the phenol solution for electrolysis, and the mass ratio of 3-methylphenol to 3-methylphenol potassium was 1:1. The anode was composed of boron-phosphorus-doped graphene two as anode coating with a coating thickness of 0.8 um and titanium as the base material. The cathode was a nickel sheet. The electrolysis was carried out at 20°C and a current density of 500 A / m 2 The final yield of 4, 4'-diphenyl-diol was 92% under electrolysis at a current density of 500 A / m

[0068] Example 4:

[0069] Preparation of phenol salt solution: 3-methylphenol was mixed with an equal amount of potassium hydroxide, and then added to a mixed solvent of deionized water and N, N-dimethylformamide in a mass ratio of 1:1 to prepare a solution with a concentration of 0.2 mol / L. Phenol was added to a mixed solvent of deionized water and N, N-dimethylformamide (mass ratio 1:1) to prepare a 0.2 mol / L solution. The salt solution of phenol was added to the phenol solution for electrolysis, and the mass ratio of 3-methylphenol to 3-methylphenol potassium was 1:1. The anode was composed of boron-phosphorus-doped graphene two as anode coating with a coating thickness of 0.8 um and titanium as the base material. The cathode was a nickel sheet. The electrolysis was carried out at 20°C and a current density of 500 A / m 2 The final yield of 4, 4'-diphenyl-diol was 92% under electrolysis at a current density of 500 A / m

[0070] Example 5:

[0071] The phenol salt solution was prepared by mixing 2,6-dipropylphenol with an equimolar amount of sodium hydroxide, and then adding it to a mixed solvent of deionized water and hexamethylphosphoramide in a mass ratio of 1:1 to prepare a solution with a concentration of 0.1 mol / L. The phenol solution was prepared by adding phenol to a mixed solvent of deionized water and hexamethylphosphoramide in a mass ratio of 1:1 to prepare a solution with a concentration of 0.1 mol / L. The salt solution of phenol was added to the phenol solution for electrolysis, and the ratio of 2,6-dipropylphenol to sodium 2,6-dipropylphenolate was 2:1. The electrolysis conditions were as follows: boron-phosphorus-doped graphene was used as the anode coating, the coating thickness was 0.5 um, titanium was used as the base material to form the anode, and lead was used as the cathode. The electrolysis was carried out at 80°C and a current density of 5000 A / m 2 The final yield of 4,4'-diphenylol was 76% under the electrolysis conditions of a current density of 5000 A / m and a cell voltage of 8.1 V.

[0072] Example 6:

[0073] The phenol salt solution was prepared by mixing 2,3-dibutyl-4-ethyl-5-tert-butoxyphenol with an equimolar amount of potassium hydroxide, and then adding it to a mixed solvent of deionized water and hexamethylphosphoramide in a mass ratio of 1:1 to prepare a solution with a concentration of 0.1 mol / L. The phenol solution was prepared by adding phenol to a mixed solvent of deionized water and hexamethylphosphoramide in a mass ratio of 1:1 to prepare a solution with a concentration of 0.1 mol / L. The salt solution of phenol was added to the phenol solution for electrolysis, and the ratio of 2,3-dibutyl-4-ethyl-5-tert-butoxyphenol to sodium 2,3-dibutyl-4-ethyl-5-tert-butoxyphenolate was 1:1. The electrolysis conditions were as follows: boron-phosphorus-doped graphene was used as the anode coating, the coating thickness was 0.8 um, titanium was used as the base material to form the anode, and platinum was used as the cathode. The electrolysis was carried out at 40°C and a current density of 800 A / m 2 The final yield of 4,4'-diphenylol was 87% under the electrolysis conditions of a current density of 800 A / m and a cell voltage of 6.9 V.

Claims

1. A method for preparing 4,4'-biphenyl compounds by electrochemical means, characterized in that, In a diaphragm-free electrolytic cell, phenolic compounds and their salt solutions are used as raw materials, and a boron-phosphorus-doped graphene electrode is used as the anode electrode to carry out an electrolytic reaction to generate 4,4'-biphenyl compounds. The structure of the phenolic compound is as follows: There are 0-4 substituents R, and the substitution position is not at the para-position of the hydroxyl group. The substituents R are C1-C8 long chains or branched alkyl, alkoxy, or aryl groups. The mass ratio of P, B, and C in the boron-phosphorus doped graphene is 3:1:50 to 6:1:

100.

2. The method according to claim 1, characterized in that, The structures of the 4,4'-biphenyl compounds are as follows: The substituents R and R' are 0 to 4 in number, and R and R' may be the same or different, and are independently selected from C1-C8 long chains or branched alkyl, alkoxy, and aryl groups.

3. The method according to claim 2, characterized in that, The substituents R and R' are independently selected from methyl, ethyl, propyl, butyl, methoxy, ethoxy, and tert-butoxy, respectively.

4. 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 its surface, which is prepared by spraying or depositing boron-phosphorus-doped graphene onto the surface of an electrode substrate.

5. The method according to claim 4, characterized in that, The substrate is a valve-type metal.

6. The method according to claim 5, characterized in that, The substrate is titanium, tantalum, or niobium.

7. The method according to claim 1, characterized in that, The thickness of the boron-phosphorus doped graphene coating is 0.5-1 μm.

8. The method according to claim 1, characterized in that, The boron-phosphorus-doped graphene can be prepared by method one or method two: Method 1: Under an inert reaction atmosphere, graphene is mixed with boric acid and phosphoric acid, heated to 700℃~800℃ and maintained for 2-3.5h, and then heated to 1200℃~1500℃ to obtain boron-phosphorus doped graphene. Method 2: Under an inert reaction atmosphere, a modified boron-phosphorus organic solution is obtained by mixing boric acid compounds, phosphate esters, and a carbon source, and then heated under vacuum conditions to obtain boron-phosphorus-doped graphene micropowder.

9. The method according to claim 8, characterized in that, The boric acid compound is selected from one or more of phenylboronic acid, tolueneboronic acid, and alkylboronic acid.

10. The method according to claim 8, characterized in that, The phosphate esters are selected from one or more of trimethyl phosphate, triethyl phosphate, tributyl phosphate, dimethyl phosphate, and diethyl phosphate.

11. The method according to claim 8, characterized in that, The carbon source is selected from benzene, toluene, ethylbenzene, and cumene.

12. The method according to claim 8, characterized in that, Boric acid compounds, phosphate esters, and carbon sources are sonicated at 50-70℃ for 2-5 hours to obtain a suspension.

13. The method according to claim 8, characterized in that, The resulting modified boron-phosphorus organic solution mixture was heated in a vacuum tube furnace.

14. The method according to claim 13, characterized in that, Heating to 600-750℃ under vacuum for 12-16 hours, the resulting black powder is cooled to room temperature, ground, and sieved to obtain boron-phosphorus-doped graphene micropowder.

15. The method according to claim 8, characterized in that, The particle size of boron-phosphorus doped graphene is 100-1000 nm.

16. The method according to claim 1, characterized in that, The substituent R in the phenolic compound is selected from methyl, ethyl, propyl, butyl, methoxy, ethoxy, and tert-butoxy.

17. The method according to claim 1, characterized in that, Salts of phenolic compounds include alkali metal salts of the aforementioned phenolic compounds.

18. The method according to claim 1, characterized in that, 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.

19. The method according to claim 1, characterized in that, The electrolytic cell is a single-polar, diaphragm-free electrolytic cell, comprising an anode, a cathode, and an electrolysis chamber.

20. The method according to claim 1, characterized in that, The mass ratio of the phenolic compound and its salt is 1:2 to 2:1, and the molar fraction of the phenolic compound and its salt in the solution is 0.1 mol / L to 2 mol / L.

21. The method according to claim 1, characterized in that, The cathode electrode is selected from one or more of platinum, nickel, copper, lead, and carbon.

22. The method according to claim 1, characterized in that, The electrolysis reaction is carried out in a mixed solution of water and an organic solvent, wherein the organic solvent is selected from alcohols, amides, sulfoxides, and phosphoramides.

23. The method according to claim 22, characterized in that, The mass ratio of water to organic solvent is 1:1 to 1:

3.

24. The method according to claim 1, characterized in that, The electrolysis temperature is 20℃-80℃.

25. The method according to claim 24, characterized in that, The electrolysis temperature is 25℃-45℃.

26. The method according to claim 1, characterized in that, Electrolysis current density is 500-5000 A / m 2 .

27. The method according to claim 26, characterized in that, The electrolysis current density is 1000-2000 A / m 2 .

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