A process for the preparation of 4,4'-diamino-2,2'-dimethylbiphenyl

Abstract

The application provides a preparation method of 4,4'-diamino-2,2'-dimethylbiphenyl, which comprises the following steps: under the protection of a protective gas, m-methylaniline is reacted in a mixed solvent of water and an organic solvent under the catalysis of potassium ferricyanide and an alkali to obtain 4,4'-diamino-2,2'-dimethylbiphenyl shown in formula I. The m-methylaniline is used for oxidative coupling to obtain 4,4'-diamino-2,2'-dimethylbiphenyl, the reaction steps are short, the selectivity is higher, the reaction yield is high, and the cost is lower, so that the preparation method is novel, the selectivity is good, the overall preparation cost is low, and the yield is high.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of synthesis of polyimide monomers, and particularly relates to a preparation method of 4,4'-diamino-2,2'-dimethylbiphenyl. BACKGROUND

[0002] 4,4'-diamino-2,2'-dimethylbiphenyl (M-Tolidine), also known as m-tolidine, is an important monomer for synthesizing high-performance polyimides. Polyimides (PI for short) are one of the best heat-resistant varieties among thermoplastic engineering plastics, and are widely used in the fields of aviation, aerospace, electromechanical, electronics, etc., and are known as one of the most promising engineering plastics in the 21st century. M-Tolidine can be polymerized with multifunctional anhydrides to form polyimides with more excellent performance, and is mainly used in the fields of microelectronics and optoelectronics. M-Tolidine can be used to prepare polyimide materials with extremely low dielectric constant, extremely low surface free energy, extremely high wear resistance, extremely high mechanical strength, and colorless transparency. Therefore, it has high theoretical significance and practical application value to efficiently, simply and low-cost synthesize 4,4'-diamino-2,2'-dimethylbiphenyl through molecular design.

[0003] The structural formula of 4,4'-diamino-2,2'-dimethylbiphenyl is as follows:

[0004] At present, the methods for synthesizing 4,4'-diamino-2,2'-dimethylbiphenyl mainly include: 1. coupling rearrangement method: 3,3'-dimethylhydrazobenzene is obtained by coupling reduction with zinc powder from m-nitrotoluene, and then M-Tolidine is obtained by rearrangement in an acidic medium. This method uses zinc powder reduction, which causes serious environmental pollution and has low yield, and is not suitable for industrialization. In addition, besides zinc powder reduction, there are sodium borohydride reduction and catalytic hydrogenation, and generally, palladium-carbon hydrogenation reduction is adopted, but the effect is not ideal, and it is difficult to control the reduction to stay in the hydrazine stage; 2. coupling reduction method: 4,4'-dinitro-2,2'-dimethylbiphenyl is obtained by coupling 2-methyl-4-nitrohalobenzene under copper catalysis, and then M-Tolidine is obtained by reduction. The raw material 2-methyl-4-nitrohalobenzene of this method is relatively expensive, and the yield of copper catalytic coupling reaction is not high. (US4948904A, US2004265392A, US6706897A, US4808731, CN1324794A, CN111187240A, JP80136246, EP0119576A) SUMMARY

[0005] Therefore, the present application aims to provide a preparation method of 4,4'-diamino-2,2'-dimethylbiphenyl, which has a simple synthesis route and improves the reaction selectivity and product yield.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A preparation method of 4,4'-diamino-2,2'-dimethylbiphenyl comprises the following steps:

[0008] Under a protective gas, m-methylaniline is reacted in a mixed solution of water and an organic solvent under the catalysis of potassium ferricyanide and a base to obtain 4,4'-diamino-2,2'-dimethylbiphenyl;

[0009] The synthesis route is as follows:

[0010]

[0011] Further, potassium ferricyanide and a base are dissolved in water under a protective gas, and then m-methylaniline is dissolved in an organic solvent and added dropwise into the reaction system, the temperature is controlled at 20-30 DEG C, and the system is stirred at 25 DEG C for 2 h. After the reaction is completed by HPLC detection, the filtrate is concentrated to remove tetrahydrofuran, cooled, filtered, washed with water, eluted with ethanol, and dried to obtain 4,4'-diamino-2,2'-dimethylbiphenyl. By controlling the reaction temperature and the dropwise addition mode of m-methylaniline, the reaction of the raw material is maximally avoided.

[0012] Further, the molar ratio of m-methylaniline, potassium ferricyanide and the base is 1:(1.1-2):(1.1-2). Within this range, m-methylaniline is most completely reacted and has the highest yield.

[0013] Further, the organic solvent is one of tetrahydrofuran, acetone, acetonitrile, 1,4-dioxane and ethylene glycol dimethyl ether.

[0014] Further, the base is any one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and cesium carbonate.

[0015] Further, the protective gas is an inert gas, preferably nitrogen.

[0016] Compared with the prior art, the preparation method of 4,4'-diamino-2,2'-dimethylbiphenyl has the following advantages:

[0017] The present application takes m-toluidine as a main raw material, and 4,4'-diamino-2,2'-dimethylbiphenyl is obtained through potassium ferricyanide catalytic oxidation coupling, the reaction steps are simple, the oxidation coupling method used in the present application utilizes the intermolecular reaction of m-toluidine, the reaction selectivity is higher, and the reaction yield is high, therefore, the preparation method described in the present application is novel, the reaction steps are short, the selectivity is good, the overall preparation cost is low, and the yield is high. DETAILED DESCRIPTION

[0018] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0019] The present application will be described in detail below with reference to the embodiments.

[0020] The synthesis route of 4,4'-diamino-2,2'-dimethylbiphenyl is as follows:

[0021]

[0022] Embodiment 1:

[0023] A preparation method of 4,4'-diamino-2,2'-dimethylbiphenyl, comprising the following steps:

[0024] The molar ratio of m-toluidine and potassium ferricyanide is 1:1.1, under the protection of nitrogen, potassium ferricyanide (676.0g, 1.1eq), sodium hydroxide (82.1g, 1.1eq) and water (2000mL) are added into a 5L four-necked flask, stirred uniformly, a solution of m-toluidine (200g, 1eq) and tetrahydrofuran (400mL) is added dropwise, the temperature is controlled at 20-30℃, and the stirring is maintained at 25℃ for 2h. After the reaction is completed by HPLC detection, the filtrate is concentrated to remove tetrahydrofuran, cooled, filtered, washed with water, eluted with ethanol, and dried to obtain 187.8g of the compound 4,4'-diamino-2,2'-dimethylbiphenyl shown in formula I, with a yield of 94.8%.

[0025] In the above reaction, in order to make the substrate m-toluidine fully contact with the aqueous potassium ferricyanide solution and participate in the reaction, the solvent should be selected as a water-soluble organic solvent, therefore, tetrahydrofuran can also be replaced by acetone, acetonitrile, 1,4-dioxane, or glycol dimethyl ether.

[0026] The base serves as an acid-binding agent, and a commonly used inorganic base can be selected, therefore, sodium hydroxide can also be replaced by potassium hydroxide, sodium carbonate, potassium carbonate, or cesium carbonate.

[0027] Embodiment 2:

[0028] A preparation method of 4,4'-diamino-2,2'-dimethylbiphenyl, comprising the following steps:

[0029] The molar ratio of m-toluidine and potassium ferricyanide is 1:1.5. Under the protection of nitrogen, potassium ferricyanide (921.8 g, 1.5 eq), potassium hydroxide (157.1 g, 1.5 eq) and water (2000 mL) are added into a 5L four-necked flask, stirred uniformly, a solution of m-toluidine (200 g, 1 eq) and acetone (400 mL) is added dropwise, temperature is controlled at 20-30°C, and stirred at 25°C for 2 h. After HPLC detection shows that the reaction is completed, the acetone is removed by concentrating the filtrate, cooled, filtered, washed with water, eluted with ethanol, and dried to obtain 4,4'-diamino-2,2'-dimethylbiphenyl of formula I, 193.8 g, yield: 97.8%.

[0030] Example 3:

[0031] A method for preparing 4,4'-diamino-2,2'-dimethylbiphenyl, comprising the following steps:

[0032] The molar ratio of m-toluidine and potassium ferricyanide is 1:2.0. Under the protection of nitrogen, potassium ferricyanide (1229.1 g, 2.0 eq), potassium carbonate (515.9 g, 2.0 eq) and water (2000 mL) are added into a 5L four-necked flask, stirred uniformly, a solution of m-toluidine (200 g, 1 eq) and ethylene glycol dimethyl ether (400 mL) is added dropwise, temperature is controlled at 20-30°C, and stirred at 25°C for 2 h. After HPLC detection shows that the reaction is completed, the ethylene glycol dimethyl ether is removed by concentrating the filtrate, cooled, filtered, washed with water, eluted with ethanol, and dried to obtain 4,4'-diamino-2,2'-dimethylbiphenyl of formula I, 183.5 g, yield: 92.6%.

[0033] Comparative Example:

[0034] Under the protection of nitrogen, potassium hydroxide (157.1 g, 1.5 eq) and water (2000 mL) are added into a 5L four-necked flask, stirred uniformly, a solution of m-toluidine (200 g, 1 eq) and acetone (400 mL) is added dropwise, temperature is controlled at 20-30°C, and stirred at 25°C for 2 h. HPLC detection shows that no target product is generated.

[0035] The above only describes preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the preparation of 4,4'-diamino-2,2'-dimethylbiphenyl, characterized in that: The method comprises the following steps: reacting m-methylaniline with potassium ferricyanide and a base in a mixed solvent of water and an organic solvent under a protective gas to obtain 4,4'-diamino-2,2'-dimethylbiphenyl shown in formula I; （Ⅰ）； The molar ratio of m-methylaniline, potassium ferricyanide and the base is 1: (1.1-2): (1.1-2); The organic solution of m-methylaniline is added into the aqueous solution of potassium ferricyanide and the base by dropwise addition, and the system temperature is 20-30 ℃; The base comprises one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and cesium carbonate.

2. A process for the preparation of 4,4'-diamino-2,2'-dimethylbiphenyl according to claim 1, characterized in that: The organic solvent comprises one of tetrahydrofuran, acetone, acetonitrile, 1,4-dioxane and ethylene glycol dimethyl ether.

3. The process for the preparation of 4,4'-diamino-2,2'-dimethylbiphenyl according to claim 1, characterized in that: The protective gas is an inert gas.

4. A process for the preparation of 4,4'-diamino-2,2'-dimethylbiphenyl according to claim 3, characterized in that: The inert gas is preferably nitrogen.

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