JP2509097B2 - Purification method of dimethyl biphenyl dicarboxylic acid dialkyl ester - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating and purifying an isomer mixture of dimers obtained by an oxidative coupling reaction of alkyl orthotoluate.

2. Description of the Related Art The present inventors have already proposed P
A method for synthesizing a dimer dimethylbiphenyldicarboxylic acid dialkyl ester by an oxidative coupling reaction of an alkyl orthotoluylate using a d catalyst has been proposed. In this method, 3,3′-dimethyl is mainly used as an isomer. High yields of biphenyl-4,4'-dicarboxylic acid dialkyl ester (hereinafter abbreviated as P acid ester) and 3,4'-dimethylbiphenyl-4,3'-dicarboxylic acid dialkyl ester (hereinafter abbreviated as Q acid ester) In addition, 4,4'-dimethylbiphenyl-3,3'-dicarboxylic acid dialkyl ester (hereinafter, abbreviated as R acid ester) and the like can be obtained in the ratio (JP-A-2-115143).
These dimers are useful compounds as raw materials for polyesters, polyamides, etc., which are attracting attention as liquid crystal polymers.

The dimer isomer obtained by the above reaction is treated at high temperature after removing unreacted raw materials from the reaction mixture.
It can be separated by vacuum distillation under high vacuum, but since it is a mixture of the above isomers, it is necessary to isolate each isomer. So far, the solubility of P acid ester in methanol is extremely low. Therefore, after separating the methanol insoluble portion as P acid ester, recrystallization was performed using ethanol. However, this method requires a two-step operation for purification, and the solubility of the P acid ester in ethanol is low. Therefore, a large amount of ethanol must be used in recrystallization, which is problematic in terms of separation and purification costs. there were.

[0003]

The present invention provides a method for easily separating and purifying an isomer mixture of a dimer obtained by an oxidative coupling reaction of alkyl orthotoluate using a specific crystallization solvent. provide. The present invention, from the isomer mixture of dimers obtained by the oxidative coupling reaction of alkyl orthotoluylate, when separating and purifying dimethylbiphenyldicarboxylic acid dialkyl ester, toluene, ethyl acetate, chlorobenzene, acetone as a crystallization solvent, First, 3,3'-dimethylbiphenyl-4,4'-is prepared using at least one solvent selected from the group consisting of acetonitrile and xylene.
The present invention relates to a method for separating and purifying dimethylbiphenyldicarboxylic acid dialkyl ester, which is characterized by selectively separating dicarboxylic acid dialkyl ester as crystals. The alkyl group in the above-mentioned esters is an aliphatic hydrocarbon group having 1 to 5 carbon atoms.

In the present invention, after the completion of the oxidative coupling reaction, the unreacted raw materials are distilled off from the reaction mixture, and further, mainly P acid ester and Q acid ester, other R acid ester and the like are separated by vacuum distillation. The isomer mixture consisting of is crystallized, separated and purified using a specific solvent. The isomer mixture is heated and dissolved in toluene, ethyl acetate, chlorobenzene, acetone, acetonitrile, xylene, or a mixture of these solvents, and cooled to first crystallize and precipitate the P acid ester. The amount of solvent used is
Although it depends on the type of solvent, it is usually 80 to 1000 per 100 parts by weight of the isomer mixture from the viewpoint of purification cost.
Parts by weight. The heating temperature is not particularly limited, but is preferably not higher than the reflux temperature of the solvent used. Although the P acid ester crystallized and precipitated has a high purity in itself, if an even higher purity is required, recrystallization can be performed with the above crystallization solvent.

Next, the crystallization solvent is distilled off from the solution after separating the crystallized P acid ester, the residual solid is redissolved in a lower alcohol such as methanol, and the Q acid ester is selectively cooled by cooling. It can be crystallized and precipitated. Higher purity Q acid ester can be obtained by recrystallization with alcohol. At the time of recrystallization, it is possible to separate and purify a higher purity ester compound by using activated carbon or activated clay together with a solvent.

[0006]

Embodiments of the present invention will be described below. Example 1 (Preparation of a mixture of isomers) A glass four-necked flask (5
000 ml) was equipped with a thermometer, a stirrer, an air introduction tube, and a reflux condenser. In this container, 2500 ml (2675 g) of methyl orthotoluate and palladium acetate 2.
807 g (12.5 mM), 1,10-phenanthroline monohydrate 3.469 g (17.5 mM), copper acetate
2.50 g (12.5 mM) of monohydrate was charged, and the reaction was carried out at 200 ° C. for 15 hours while rotating at 300 rpm while aerating air at 1500 ml / min. After completion of the reaction, the reaction mixture was subjected to vacuum distillation to obtain a fraction 2 composed of unreacted methyl orthotoluate at 120 ° C./2 torr or less.
398 g, 10-g fraction of 80-180 ° C / 1 torr,
180-220 ° C / 1 to consist of desired isomer mixture
208 g of a fraction of rr was separated to obtain 34 g of residue.

(Separation and purification of isomers) To 208 g of a distillate consisting of the isomer mixture was added 200 ml of toluene and heated under reflux to obtain a homogeneous solution. The solution was allowed to cool to room temperature to precipitate white crystals, which were filtered to obtain 99% pure 3,
It was possible to separate 79 g of dimethyl 3'-dimethylbiphenyl-4,4'-dicarboxylate (P acid ester). When recrystallized with toluene, the purity is 100.
71 g of an ester compound having a yield of close to 71% was obtained. Then, the toluene solution (mother liquor) without the first crystallized ester compound
Was evaporated to dryness, and 129 g of the residue was added with methanol 350
ml was added and dissolved by heating. The solution was allowed to cool to room temperature to precipitate white crystals, and 75 g of dimethyl 3,4′-dimethylbiphenyl-4,3′-dicarboxylate (Q acid ester) could be separated by filtration. By recrystallizing the ester compound twice more with methanol, 64 g of an ester compound having a purity close to 100% was obtained.

Example 2 From 200 g of a isomer mixture prepared in the same manner as in Example 1 and 600 ml of ethyl acetate, 72 g of white crystalline P acid ester could be separated by heating dissolution and cooling. Subsequently, the ethyl acetate mother liquor was evaporated to dryness, dissolved by heating in 400 ml of methanol, and allowed to cool to isolate 76 g of a white crystalline Q acid ester.

Example 3 From 200 g of a fraction consisting of an isomer mixture prepared in the same manner as in Example 1 and 200 ml of chlorobenzene, 76 g of white crystalline P acid ester could be separated. continue,
The chlorobenzene mother liquor was evaporated to dryness, and 63 g of white crystalline Q acid ester could be separated from methanol.

Example 4 From 200 g of a fraction consisting of an isomer mixture prepared in the same manner as in Example 1 and 900 ml of acetone, 72 g of white crystalline P acid ester could be separated. Subsequently, the acetone mother liquor was evaporated to dryness, and 65 g of white crystalline Q acid ester could be separated from methanol.

Example 5 From 200 g of a fraction consisting of an isomer mixture prepared in the same manner as in Example 1 and 500 ml of acetonitrile, 78 g of white crystalline P acid ester could be separated. continue,
The acetonitrile mother liquor was evaporated to dryness, and 60 g of white crystalline Q acid ester could be separated from methanol.

Example 6 From 200 g of a fraction consisting of an isomer mixture prepared in the same manner as in Example 1 and 200 ml of mixed xylene, white crystals of P were obtained.
51 g of acid ester could be separated. Subsequently, the mixed xylene mother liquor was evaporated to dryness, and 87 g of white crystalline Q acid ester could be separated from methanol.

Claims (1)

(57) [Claims] 1. Toluene, ethyl acetate, chlorobenzene, and acetone as crystallization solvents when dimethylbiphenyldicarboxylic acid dialkyl ester is separated and purified from an isomer mixture of dimers obtained by an oxidative coupling reaction of alkyl orthotoluyl acid. First, 3,3′-dimethylbiphenyl-4,4′-dicarboxylic acid dialkyl ester is selectively separated as a crystalline substance by using at least one solvent selected from the group consisting of benzene, acetonitrile, and xylene. A method for separating and purifying dimethylbiphenyldicarboxylic acid dialkyl ester, which is characterized.