JPS6372632A - Production of alpha,alpha'-dichloroxylene - Google Patents

Abstract

PURPOSE:To obtain the titled substance in high selectivity, by reacting xylene with chlorine under irradiation of light or using a radical generator by a batch or semibatch method while keeping the concentration of alpha-monochloroxylene within a specific range. CONSTITUTION:Xylene is reacted with chlorine under irradiation with light or using a radical generator, e.g. a peroxide based or azo based radical generator, etc., to give the titled substance. In the process, the reaction is carried out while keeping the concentration of alpha-monochloroxylene in the reaction system at 60-90mol% by a batch or semibatch method. The alpha-monochloroxylene and unreacted xylene are separated from the column top by distillation of the reaction solution and recycled to the reaction system to enhance the yield of the aimed substance. The concentration of the alpha-monochloroxylene in the reaction solution is adjusted by the amount of the above-mentioned recycle and the amount of the raw material xylene fed from the outside of the system.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing α,α'-dichloroxylene. More specifically, the present invention relates to a method of chlorinating xylene in a batch or semi-batch process to produce α,α''-dichloroxylene.

(Prior Art) α, α°-dichloroxylene is a general term for compounds containing three types of isomers: p-unit, m-unit, and 〇-unit.

Since this compound has one reactive chlorine atom in each side chain methyl group, it is useful as an intermediate raw material. Can be converted. However, when xylene is chlorinated to produce α, α”-dichloroxylene, there are various problems.
In addition to , α′ -dichloroxylene, various side chain chlorinated products with different degrees of chlorination or nuclear chlorinated products directly chlorinated to the aromatic nucleus are produced as by-products, and the target products, α, α°
-It was difficult to obtain dichloroxylene with high selectivity. Various attempts have been made to solve this problem, but they are still not sufficient.

For example, in Japanese Patent Publication No. 57-25009, xylene is reacted with chlorine molecules under irradiation with light, the reaction solution is retained, and the distillate containing unreacted xylene and α-chloroxylene is circulated to the reaction system. When α,α′-dichloroxylene is continuously produced, α,α′-dichloroxylene in the reaction system is 5 to 25 mol%, and tetrachloroxylene and higher chlorinated products are 5 mol% or less. A continuous method for producing α,α°-dichloroxylene is proposed, which is characterized by carrying out a chlorination reaction so that the following results are obtained. However, although there is a large amount of low-boiling xylene and α-monochloroxylene that is reused, the selectivity of α,α′-dichloroxylene is not high.

Furthermore, in JP-A-53-65830, when producing a dihalogen derivative in which two methyl groups of an alkyl aromatic hydrocarbon are each halogenated, UV-containing light is irradiated in the liquid phase in the presence or absence of a solvent. The alkyl aromatic hydrocarbon is then reacted with a halogen to form a hydrogen halide and the dihalogen derivative, and then the dihalogen derivative precipitated as a solid is separated, and the unreacted alkyl aromatic hydrocarbon and the dihalogen are separated. It is characterized in that monohalogen derivatives and polyhalogenated derivatives other than the derivatives are recycled to the halogenation reaction step. However, in this case as well, α, α is not satisfactory in terms of selectivity of dihalogen derivatives.

-The reality is that there is no method for producing dichloroxylene with high selectivity.

(Problems to be Solved by the Invention) The purpose of the present invention is to minimize the generation of side chain chlorinated products with different degrees of chlorination and nuclear chlorinated products in which aromatic nuclei are directly chlorinated, which is the above-mentioned problem. , α, α.

- To provide a manufacturing method for obtaining dichloroxylene with high selectivity.

(Means for Solving the Problems) The inventors of the present invention made extensive studies to achieve the above object, and were finally defeated by the present invention.

That is, the present invention provides for producing α,α°-dichloroxylene by reacting xylene and chlorine under irradiation with light or using a radical generator, and the fl1 reaction system is a batch type or semi-patch type, and (2) Always keep the concentration of α-monochloroxylene in the reaction system from 60 mol% to 90 mol%.
α, which is characterized by reacting as follows:
This is a method for producing α°-dichloroxylene.

The present invention will be explained in more detail below.

The xylene referred to in the present invention is 0-xylene, m-xylene, or p-xylene. Also α.

α゛-Dichloroxylene is α,α′-dichloro-〇-xylene or α,α°-dichloro-m-xylene or α,α′-dichloro-p-xylene.

Further, α-monochloroxylene is α-monochloro〇-xylene, α-monochloro m-xylene, or α-monochloro p-xylene.

α,α°-dichloroxylene according to the present invention can be produced by reacting chlorine on xylene in the liquid phase under irradiation with light or in the presence of a peroxide radical generator or an azo radical generator. . In this case, the light is
Ultraviolet-containing light is used, emitted from light sources commonly used in this field, such as natural light, mercury lamps, hydrogen discharge tubes, flash discharge lamps, etc. Typical examples of the peroxide radical generator include benzoyl peroxide and acetyl peroxide, but any peroxide radical generator commonly used in this field can be used.

Typical examples of the azo radical generator include azobisisobutyronitrile and azotriphenylmethane, but any azo radical generator commonly used in this field can be used.

Normally, to chlorinate xylene in a liquid phase, a solvent may or may not be used, and in the present invention, depending on the conditions, a solvent may or may not be necessary. For example, depending on the reaction conditions, if xylene is solid, it is preferable to use a solvent and conduct the reaction in a liquid phase.
As the solvent, carbon tetrachloride, chloroform, hexachloroethane, tetrachloroethane, etc. can be used.

In addition, the reaction temperature can be arbitrarily selected, usually from 0°C to below the boiling point of xylene, or when using a solvent, below the boiling point of the solvent, but in the case of chlorination of p-xylene, crystals tend to precipitate at low temperatures. Therefore, it is desirable to carry out the chlorination at a temperature at which crystals do not precipitate.Also, when m-xylene is chlorinated, nuclear chlorides tend to form at low temperatures, so the temperature is usually 40°C.
It is desirable to carry out the test at temperatures above ℃.

Further, chlorine may be supplied alone, but may be used in combination with an inert gas such as nitrogen.

In the chlorination reaction, α-monochloroxylene is formed by xylene and side chain chlorinated products of xylene &! : The reaction is carried out in the presence of 60 mol% or more and 90 mol% or less, based on 1, at all times during the reaction.
If α-monochloroxylene is less than 60 mol χ, α
, the selectivity of α′-dichloroxylene is not sufficient,
Moreover, if it exceeds 90 mol %, the amount of low-boiling components reused in the reaction system, ie, xylene and α-monochloroxylene, increases, which is not preferable as a method for producing α,α'-dichloroxylene.

In the present invention, unreacted xylene and α-monochloroxylene are reused in order to produce α,α′-dichloroxylene at a high yield compared to xylene.Normally, the reaction liquid is introduced into a distillation column, and the boiling point is Low unreacted xylene and α-monochloroxylene are distilled out from the top of the column, separated from other components, and then recycled back to the reaction system. It is adjusted by the liquid amount of α-monochloroxylene and unreacted xylene and the amount of raw material xylene newly supplied from outside the system.

The chlorination reaction in the present invention is characterized in that it is carried out in a hatch type or semi-batch type. In the batch type or semi-batch type, chlorine is supplied after xylene and α-monochloroxylene are charged into the reaction system in advance, and xylene and/or α-monochloroxylene are not supplied from outside the system while chlorine is being supplied. means. When a chlorination reaction is carried out in a batch or semi-batch manner, the amount of α-monochloroxylene in the reaction solution increases as chlorine is supplied compared to it (initial charge amount) before chlorine supply. The amount of α-monochloroxylene can always be kept above the initial charge amount. However, if chlorine is further supplied, the amount of α-monochloroxylene decreases, so it is possible to supply chlorine up to the same amount as the initial charge.

Normally, the amount of α-monochloroxylene at the end of the reaction is determined by the amount of chlorine supplied, so if the amount of chlorine to be supplied is determined before the chlorination reaction, the amount of α-monochloroxylene will always be greater than the initial charge amount, making it a high choice. α1 α゛-dichloroxylene is obtained at a ratio of α1 α′-dichloroxylene.

When the chlorination reaction is carried out in a batch or semi-batch manner, the concentration of α-monochloroxylene in the reaction solution when chlorine is supplied can be maintained at a higher concentration than in a continuous reaction. The conversion rate to xylene color α, α′ - dichloroxylene increases, and α, α′
-Dichloroxylene can be produced.

As for the method of removing α,α′-dichloroxylene from the chlorination reaction finished liquid, conventional (known methods) can be used. For example, in the case of distillation, it is possible to use a xylene, α-monochloroxylene, and α,α-dichloroxylene are cut from the top of the column, and α has a higher boiling point than α,α′-dichloroxylene.

α, α′-trichloroxylene, etc. can be extracted from the bottom of the column.
, α°-dichloroxylene is obtained.

Further, α,α-dichloroxylene may be recycled to the reaction system together with xylene and α-monochloroxylene. In this case, it becomes a polychlorinated product in the chlorination reaction and is removed from the bottom of the column. Of course, it is also possible to extract only α, α-dichloroxylene. In addition, highly pure α,α'-trichloroxylene can also be fractionated using the crystallization method.

(Example) The present invention will be explained below with reference to Examples.

Examples 1 to 5 Comparative Examples 1 to 2 A mercury lamp irradiation type photoreactor made of glass with a volume of 1) and equipped with a jacket, a reflux condenser, a stirrer, and a chlorine gas inlet was equipped with the following materials as shown in Table 1. After charging the raw materials in the ratio shown in Table 1, chlorine is blown in under the conditions shown in Table 1 while stirring.
The chlorination reaction was carried out while controlling the temperature by sending cold water into the jacket. Various chlorinated substances in the reaction solution were analyzed by gas chromatography. Results first
In all cases shown in the table, almost no chlorine was observed in the gas discharged from the reactor.

Comparative Example 3 In the same reactor as in Examples 1 to 5, a continuous chlorination reaction was carried out by installing a reaction liquid extraction nozzle at a site with a volume of 1) 500 liters from the bottom.

First, the reactor was filled with p-xylene, and p-xylene was supplied at a rate of 10.6 g/min, α-chloro-p-xylene at 21.1 g/min, and chlorine at a rate of 14.1 g/min. did. The chlorination reaction was carried out at 60°C by sending cold water to Jijima Kenoto while stirring. At the time when 5 times the volume of the 0 reaction was flowed, the reaction solution was sampled.
Various chlorinated substances in the reaction solution were analyzed by gas chromatography. The results are shown in Table 1. It should be noted that almost no chlorine was observed in the gas discharged from the reactor.

(Effect of the invention) The manufacturing method according to the present invention has tJa
<, α, α° -Dichloroxylene can be obtained with high selectivity, and it is an industrially excellent method.

Claims (1)

[Claims] 1) When producing α,α'-dichloroxylene by reacting xylene and chlorine under irradiation with light or using a radical generator, (1) the reaction system is a batch type or semi-batch type, and ( 2) A method for producing α,α'-dichloroxylene, characterized in that the reaction is carried out while the concentration of α-monochloroxylene in the reaction system is always maintained at 60 mol% or more and 90 mol% or less.