JPH0645559B2 - Purification method of crude 2,3-dimethylnaphthalene - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Object of the Invention The present invention relates to a method for purifying crude 2,3-dimethylnaphthalene.

(Field of Industrial Application) The present invention separates and purifies high-purity 2,3-dimethylnaphthalene useful as various intermediates for organic synthesis from crude 2,3-dimethylnaphthalene of relatively low purity. Is used to advantage.

(Prior Art) Dimethylnaphthalene is produced by various methods such as a method by distillation of tars, a method by separating from a specific fraction of petroleum, and a method by dehydrogenation reaction of dimethyltetralin in terms of organic synthesis. There is also a method for producing a specific dimethylnaphthalene by isomerizing other isomers, as described in JP-A-50-154230.

2,3-Dimethylnaphthalene is also produced using such various methods, and the obtained crude 2,3-dimethylnaphthalene is usually 1,2-dimethylnaphthalene,
Other isomers having similar physical properties such as 1,3-dimethylnaphthalene, 1,4-dimethylnaphthalene, and 1,6-dimethylnaphthalene are mixed, and the purity of 2,3-dimethylnaphthalene is low as it is. Unless it is purified by any method, it is not useful as an intermediate for various organic synthesis.

As a method for purifying crude 2,3-dimethylnaphthalene, there is a method in which crude 2,3-dimethylnaphthalene is dissolved in methanol and crystallized and separated from the solution by utilizing a difference in solubility depending on temperature, that is, a recrystallization method. (U.S. Pat. No. 3,42
8,698). However, although this method can obtain high-purity 2,3-dimethylnaphthalene, the present inventors have found that the recovery rate is low, and industrial implementation still has a cost problem.

(Problems to be Solved by the Invention) The present invention aims to provide a method for separating and purifying 2,3-dimethylnaphthalene efficiently and easily with a higher recovery rate than crude 2,3-dimethylnaphthalene. .

(b) Structure of the Invention (Means for Solving Problems) The present inventor has conducted various studies in order to efficiently separate and purify 2,3-dimethylnaphthalene at a higher recovery rate than crude 2,3-dimethylnaphthalene. As a result, when the crude 2,3-dimethylnaphthalene was brought into contact with an amount of methanol insufficient to dissolve all of the dimethylnaphthalene, surprisingly, the purity of 2,3-dimethylnaphthalene significantly increased as an insoluble substance. That is, the present invention has been achieved, and the present invention has been achieved.

That is, the method for purifying crude 2,3-dimethylnaphthalene of the present invention is a method for purifying crude 2,3-dimethylnaphthalene containing other isomers as main impurities.
-Contacting dimethylnaphthalene with an amount of methanol insufficient to dissolve all of the crude 2,3-dimethylnaphthalene dimethylnaphthalene, and increasing the purity of 2,3
-A method characterized by recovering dimethylnaphthalene as an insoluble matter.

Examples of the crude 2,3-dimethylnaphthalene to be the subject of the purification method of the present invention include crude 2,3-dimethylnaphthalene obtained by various methods including the method described above. For example, a method of dehydrogenating a dimethyltetralin mixture obtained by a cyclization reaction of O-xylene and succinic anhydride or a cyclization reaction of O-xylene and 1,4-dichlorobutane, 1,3-dimethylnaphthalene, etc. The crude 2,3-dimethylnaphthalene obtained by various methods such as a method of isomerizing other dimethylnaphthalene isomers or a method of cutting a specific fraction in precision distillation of tar or petroleum is the present invention. Can be used in the method of.

Crude 2,3-dimethylnaphthalene obtained by these methods is 1,2-dimethylnaphthalene, 1,3 as described above.
-Dimethylnaphthalene, 1,4-dimethylnaphthalene,
And 1,6-dimethylnaphthalene are contained, but if the 2,3-dimethylnaphthalene concentration (purity) of the crude 2,3-dimethylnaphthalene is too low, the efficiency of the method of the present invention decreases. Therefore, in such a case, prior to application of the method of the present invention, JP-A-50-154230
The purification method by recrystallization as described in Japanese Patent Publication No. 1994-242242 is applied to increase the purity of 2,3-dimethylnaphthalene to, for example, 6%.
It is desirable to raise it to 0% or more.

The amount of methanol used in the purification method of the present invention is an amount insufficient to dissolve all dimethylnaphthalene in crude 2,3-dimethylnaphthalene, and varies depending on the purity of 2,3-dimethylnaphthalene, but the amount used Is
Normally, the weight ratio is 0.2 with respect to the total amount of dimethylnaphthalene.
The amount is about 5 times, preferably 0.3 to 2 times. The saturated concentration of 2,3-dimethylnaphthalene with respect to methanol is about 3% by weight at room temperature.

Room temperature (normal temperature) is sufficient as the temperature in the contact treatment of crude 2,3-dimethylnaphthalene and methanal in the present invention, and rather it is preferable that the temperature is not so high to improve efficiency. It does not matter if methanol contains some water.

Various methods can be used as the contact treatment operation. For example, a method in which crude 2,3-dimethylnaphthalene is put into methanol at room temperature, stirred and suspended, and a partial extraction treatment is performed, after sprinkling methanol on the crude dimethylnaphthalene and then separating the solution by centrifugation. The so-called suspension washing method is used. In either method, highly purified 2,3-dimethylnaphthalene is obtained as an insoluble material. If the desired purity cannot be obtained in a single treatment,
The process may be repeated as many times as desired.

(Examples, etc.) Hereinafter, examples and comparative examples will be described in more detail.

Examples 1 to 6 In Examples 1, 2, 4 and 6, crude 2,3-dimethylnaphthalene (2,3-body content 71.8%, 1,2-
Body content 21.0%, 1,3-body content 5.1%, 1,
The solids (4-body traces) were mixed with methanol at room temperature at the ratios shown in Table 1, stirred for 30 minutes and then separated, and the residual insoluble matter was separated, dried, and analyzed.
The results are shown in Table 1.

The same treatment was carried out using the insoluble matter obtained in Example 2 in Example 3 and the insoluble matter obtained in Example 4 in Example 5 as crude 2,3-dimethylnaphthalene as a raw material. The results are shown in Table 1.

Comparative Example The same crude 2,3-dimethylnaphthalene as used in Example 1 (1.07 g) was mixed with 10 ml of methanol, heated at a temperature of 60 ° C. to dissolve, and then cooled to 19 ° C. to precipitate crystals. , Separated, dried and analyzed. The results are shown in Table 1.

(c) Effect of the Invention According to the method of the present invention, highly pure 2,3-dimethylnaphthalene can be efficiently obtained with a higher recovery rate than crude 2,3-dimethylnaphthalene.

Claims (1)

[Claims] 1. A crude 2, containing other isomers as main impurities.
The 3-dimethylnaphthalene was contacted with an amount of methanol insufficient to dissolve all of the crude 2,3-dimethylnaphthalene dimethylnaphthalene, and the purity of the 2,3-dimethylnaphthalene was increased.
A method for purifying crude 2,3-dimethylnaphthalene, which comprises recovering 3-dimethylnaphthalene as an insoluble matter.