JPH0967314A - Method for purifying 4,4'-biphenyldicarboxylic acid dimethyl ester - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a purification method for obtaining 4,4'-biphenyldicarboxylic acid dimethyl ester having a low carboxylic acid content, which is useful as a new highly functional resin raw material. When purifying crude 4,4′-biphenyldicarboxylic acid dimethyl ester, impurities having a carboxyl group are extracted with an alkaline aqueous solution, and an organic solvent is added to obtain 4,4′-biphenyldicarboxylic acid dimethyl ester. After dissolution, oil-water separation is performed, and 4,4′-biphenyldicarboxylic acid dimethyl ester is precipitated and recovered from the organic solvent phase.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying 4,4′-biphenyldicarboxylic acid dimethyl ester, which is useful as a raw material for a novel highly functional resin.

[0002]

2. Description of the Related Art As a method for synthesizing 4,4'-biphenyldicarboxylic acid dimethyl ester, a method of coupling benzoic acid methyl ester or a derivative thereof with nickel, palladium, etc. as a catalyst or a biphenyl di-substituted product in a liquid phase is used. There is known a method of esterifying 4,4′-biphenyldicarboxylic acid obtained by oxidation with an acid catalyst. Crude 4,4'-biphenyldicarboxylic acid dimethyl ester produced by the former contains impurities such as benzoic acid methyl ester and catalytic metal, and crude 4,4'-biphenyldicarboxylic acid dimethyl ester produced by the latter is Contains impurities such as esterification products, catalytic metals, and unreacted carboxylic acids, which come from oxidation reaction intermediates. All of them are unsuitable as polymer raw materials that require high purity, and establishment of a crude 4,4′-biphenyldicarboxylic acid dimethyl ester purification method was an important issue. .

Since 4,4'-biphenyldicarboxylic acid dimethyl ester is more easily dissolved in an organic solvent than 4,4'-biphenyldicarboxylic acid, an organic solvent is used as a purification method for crude 4,4'-biphenyldicarboxylic acid. Conventional recrystallization is known. For example, JP-A-49-1315
No. 7, chlorobenzene is disclosed in JP-A-53-4075.
Purification by recrystallization of crude 4,4′-biphenyldicarboxylic acid dimethyl ester using acetic acid in JP-A No. 0 and JP-A No. 7-2739 is described in JP-A-7-2739. However, a trace amount of carboxylic acid remains only by recrystallization with the above organic solvent, and when 4,4′-biphenyldicarboxylic acid dimethyl ester is used as a polymer raw material, the trace amount of carboxylic acid has a large effect on polymer performance. It was a problem because it affected.

[0004]

SUMMARY OF THE INVENTION In view of such circumstances, an object of the present invention is to provide a method for purifying 4,4'-biphenyldicarboxylic acid dimethyl ester capable of completely removing carboxylic acid. .

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to establish the above method. As a result, carboxylic acid as an impurity in crude 4,4′-biphenyldicarboxylic acid dimethyl ester was treated with an alkaline aqueous solution. It was found that 4,4′-biphenyldicarboxylic acid dimethyl ester having an extremely low carboxylic acid content can be obtained by contacting with and extracting this into an aqueous solution, and completed the present invention. That is, the present invention is characterized in that in purifying crude 4,4′-biphenyldicarboxylic acid dimethyl ester containing carboxylic acid as an impurity, crude 4,4′-biphenyldicarboxylic acid dimethyl ester is contacted with an alkaline aqueous solution. Is a method for purifying 4,4′-biphenyldicarboxylic acid dimethyl ester.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention will be described in detail below. The types of alkaline aqueous solutions used in the present invention include lithium, sodium, potassium, rubidium,
Although any ordinary alkaline aqueous solution such as ammonium may be used, an alkaline aqueous solution having sodium or potassium as an alkali metal ion is preferable in view of easy availability. Further, it is more preferable to use an aqueous solution of sodium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, potassium carbonate or the like in view of the relationship with the pH described later.

The pH of the alkaline aqueous solution is pH 7.
5-13 are preferable. If the pH is more than 7.5, the carboxylic acid is not sufficiently dissolved in the aqueous solution and the pH is 1 or less.
If it is more alkaline than 3, it is not preferable because hydrolysis of the ester occurs during the extraction operation into the aqueous solution.

The amount of the alkaline aqueous solution used is such that the amount of the alkali is 1.2 to 10 times the amount of the carboxyl group of the carboxylic acid contained in the crude 4,4'-biphenyldicarboxylic acid dimethyl ester to be purified. Is. Coarse 4,
The amount of carboxyl groups in 4'-biphenyldicarboxylic acid dimethyl ester can be calculated by the acid value.
The acid value can be usually determined by titration of an aqueous KOH solution. The alkali concentration of the alkaline aqueous solution is 0.
It may be in the range of 1% by weight to 30% by weight.

The operating method of the present invention is as follows:
A method may be used in which an aqueous alkali solution is directly added to dimethyl biphenyldicarboxylic acid and brought into contact with each other in a slurry state to extract an impurity carboxylic acid. After extracting the carboxylic acid, 4,4′-biphenyldicarboxylic acid dimethyl ester purified by a known means such as solid-liquid separation, washing or recrystallization can be recovered. However, after extracting the carboxylic acid, an organic solvent is added thereto to form a phase of an organic solvent in which 4,4′-biphenyldicarboxylic acid dimethyl ester is dissolved and a phase of an alkaline aqueous solution, and then phase separation, 4,4'- from organic solvent phase
It is advantageous to carry out precipitation and recovery of dimethyl biphenyldicarboxylic acid ester.

As another operation method, coarse 4, 4 '
An aqueous alkali solution and an organic solvent are added to the dimethyl ester of biphenyldicarboxylic acid, the carboxylic acid is extracted and dissolved in the aqueous solution phase, and the dimethyl ester of 4,4′-biphenyldicarboxylic acid is extracted and dissolved in the organic solvent phase.
A method in which phase separation is performed, 4,4′-biphenyldicarboxylic acid dimethyl ester is precipitated from the organic solvent phase, and solid-liquid separation is also possible. When the carboxylic acid content in the crude 4,4′-biphenyldicarboxylic acid dimethyl ester is high, the latter operation method is effective.

The operating temperature in the present invention is room temperature to 250 ° C, preferably room temperature to 200 ° C. When the temperature is higher than the boiling point of water or the organic solvent, it is performed under pressure. When purifying in the presence of an organic solvent, it is preferable to select a temperature at which 4,4′-biphenyldicarboxylic acid dimethyl ester is completely dissolved in the organic solvent used. If the temperature is raised more than necessary, the amount of 4,4'-biphenyldicarboxylic acid dimethyl ester hydrolyzed increases, which is not preferable.

When an organic solvent is used, any solvent may be used as long as it dissolves 4,4'-biphenyldicarboxylic acid dimethyl ester and separates it from water into two layers. Paraffin such as hexane and heptane, and toluene. , Alkylbenzenes such as xylene, and substituted benzenes such as nitrobenzene and chlorobenzene can be mentioned. Toluene and xylene are preferable from the viewpoints of appropriate solubility and easy industrial handling. The amount of the organic solvent used is preferably a sufficient amount to dissolve 4,4′-biphenyldicarboxylic acid dimethyl ester.

As a method of recovering 4,4'-biphenyldicarboxylic acid dimethyl ester from a phase of an organic solvent in which 4,4'-biphenyldicarboxylic acid dimethyl ester is dissolved, washing and concentration are carried out if necessary, followed by cooling. There is a method of depositing and separating this by filtration or the like.

[0014]

EXAMPLES The present invention will be specifically described below based on examples. In addition, part and% in an Example show a weight part and weight%, respectively.

Example 1 Crude 4,4'-biphenyldicarboxylic acid dimethyl ester having a purity of 96% obtained by liquid phase oxidation and esterification of 4,4'-dialkylbiphenyl in an autoclave equipped with a magnetic stirrer. To 10 parts, add 5 parts of 5% sodium hydrogen carbonate aqueous solution and 100 parts of xylene isomer mixture, and add 130 parts.
Crude 4,4'-biphenyldicarboxylic acid dimethyl ester was completely dissolved at 0 ° C. After the dissolution, the temperature was maintained at 130 ° C. with stirring for 30 minutes, and then the aqueous phase was removed by oil-water separation. After 20 parts of water was added to the oil phase and the mixture was kept at 130 ° C. for 1 hour, the water phase was removed again by oil-water separation. The oil phase was cooled to 30 ° C., and the precipitated crystals were subjected to solid-liquid separation, washed with xylene and dried to obtain 9 parts of 4,4′-biphenyldicarboxylic acid dimethyl ester having a purity of 99.9% or more. The acid value of the obtained 4,4′-biphenyldicarboxylic acid dimethyl ester was 0.005 mg · KOH / g
The amount of the remaining carboxyl groups was extremely small.

Comparative Example 1 To a glass flask equipped with a stirrer, 10 parts of 96% crude 4,4'-biphenyldicarboxylic acid dimethyl ester having the same purity as in Example 1 and 200 parts of xylene were added, and the mixture was stirred at 100 ° C. for 1 hour. , 4'-biphenyldicarboxylic acid dimethyl ester was dissolved. Filter at 100 ° C. to remove small amounts of insolubles, mainly carboxylic acids, then 30
After cooling to ° C, the precipitated crystals were subjected to solid-liquid separation, washed with xylene, and dried to obtain 8 parts of 4,4'-biphenyldicarboxylic acid dimethyl ester having a purity of 99.9%. The acid value of the obtained dimethyl ester of 4,4′-biphenyldicarboxylic acid is 0.1 mg · KOH / g, and the residual amount of this carboxyl group has a great adverse effect on the polymer performance when used as a polymer raw material.

EXAMPLE 2 Crude 4,4'-biphenyldicarboxylic acid dimethyl ester 2 having a purity of 99.7% was placed in an autoclave equipped with a magnetic stirrer.
To 0 part, 200 parts of a 5% sodium hydrogen carbonate aqueous solution was added, and the mixture was stirred at 50 ° C. for 4 hours. The solid after the solid-liquid separation was washed with water and dried to obtain 9 parts of 4,4′-biphenyldicarboxylic acid dimethyl ester having a purity of 99.9% or more. The acid value of the obtained 4,4′-biphenyldicarboxylic acid dimethyl ester was 0.01 mg · KOH / g, and the amount of remaining carboxyl groups was small.

[0018]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, 4,4'-biphenyldicarboxylic acid dimethyl ester having a low carboxylic acid content, which is useful as a raw material for a new high-performance resin, can be produced and is industrially used. Is meaningful to.

Claims (5)

[Claims] 1. When purifying crude 4,4′-biphenyldicarboxylic acid dimethyl ester containing carboxylic acid as an impurity, the crude 4,4′-biphenyldicarboxylic acid dimethyl ester is brought into contact with an alkaline aqueous solution. A method for purifying 4,4'-biphenyldicarboxylic acid dimethyl ester. 2. A crude 4,4′-biphenyldicarboxylic acid dimethyl ester containing a carboxylic acid as an impurity is brought into contact with an alkaline aqueous solution to extract the carboxylic acid, and then an organic solvent is added to add 4,4′-biphenyldicarboxylic acid. A characteristic is that an organic solvent phase in which acid dimethyl ester is dissolved and an alkaline aqueous solution phase are formed, and then phase separation is performed, and 4,4′-biphenyldicarboxylic acid dimethyl ester is precipitated and recovered from the organic solvent phase. And 4,
A method for purifying 4'-biphenyldicarboxylic acid dimethyl ester. 3. An aqueous alkaline solution and an organic solvent are added to and contacted with crude 4,4′-biphenyldicarboxylic acid dimethyl ester containing carboxylic acid as an impurity,
A phase of an organic solvent in which 4,4′-biphenyldicarboxylic acid dimethyl ester is dissolved and a phase of an aqueous alkaline solution containing the extracted carboxylic acid content are formed, and subsequently, phase separation,
A method for purifying 4,4'-biphenyldicarboxylic acid dimethyl ester, which comprises depositing and recovering 4,4'-biphenyldicarboxylic acid dimethyl ester from an organic solvent phase. 4. The method for purifying 4,4′-biphenyldicarboxylic acid dimethyl ester according to claim 1, 2 or 3, wherein the alkaline aqueous solution is one or two selected from an aqueous sodium hydrogen carbonate solution and an aqueous potassium hydrogen carbonate solution. 5. The method for purifying 4,4′-biphenyldicarboxylic acid dimethyl ester according to claim 2, 3 or 4, wherein the organic solvent is xylene or toluene.