JPS5912642B2 - Method for side chain chlorination of aromatic compounds - Google Patents

Description

Detailed Description of the Invention The present invention effectively chlorinates the side chain of an aromatic compound having a lower alkyl group as a side chain, such as toluene or xylene, using chlorine. It relates to an improved method for applying the invention.

This type of chlorination reaction is generally carried out by introducing chlorine into the liquid phase reaction system in a glass reaction vessel while irradiating it with light. The presence of the component is undesirable.

If impurity metal components are present, the reaction solution may become colored during the chlorination reaction, impairing light transmission, and as a result, side reactions take priority and nuclear chlorides and dehydrochlorination condensates, etc. This results in a decrease in the purity and yield of the desired product, the side chain chlorinated product. The impurity metal components present in the reaction system are considered to be those derived from the reactor material and those mixed in the aromatic compound to be chlorinated and chlorine.

For those derived from reactor materials, by using corrosion-resistant materials and thoroughly cleaning them before use, it is possible to prevent metal components from entering the reaction system to some extent, and chlorine is normally used as a gas. By filtering this chlorine gas, it is possible to remove as much of the metal components as possible15. However, regarding metal components mixed in aromatic compounds, especially iron, it is almost impossible to obtain industrial standard products that do not contain iron, and therefore, as long as these aromatic compounds are used, It is extremely difficult to prevent the impurity metal component 20 from being mixed in. For the reasons mentioned above, in the conventionally developed side chain chlorination methods, techniques have been devised to mainly reduce or eliminate the influence of impurity metal components mixed into the reaction system on the chlorination reaction. A method (US Pat. No. 2,695,873) in which urea, acid amide, etc. are present in the reaction system is known.
However, in this method, the added urea etc. decomposes during the chlorination reaction and produces a white sticky gum-like substance, which adheres to the walls of the reaction vessel, the light source 30 lamp cover, etc., and prevents the transmission of light. In addition, it may be difficult to separate and remove the target product from these additives after the reaction is completed. This invention enables an effective side chain chlorination reaction by removing metal components contained in the aromatic compound to be chlorinated in advance before the chlorination reaction without mixing them into the reaction system. The purpose of this work is to provide a method for chlorinating the side chains of aromatic compounds in a manner that can proceed in a consistent manner.

That is, when chlorinating the side chain of an aromatic compound having a lower alkyl group in the side chain, this invention performs a pretreatment consisting of contacting the aromatic compound with urea or a condensate thereof, and then chlorinates the aromatic compound. This is a method for side chain chlorination of aromatic compounds.

Examples of aromatic compounds to be subjected to side chain chlorination according to the present invention include toluene, xylene, and ethylbenzene.

As mentioned above, when these aromatic compounds are obtained and used on an industrial scale, it is impossible to completely eliminate the contamination of metal components, especially iron. It is undesirable for benzene to be mixed as an impurity into these aromatic compounds. This is because if this is mixed in, the chlorination of the side chain will be hindered and it will be difficult to complete the chlorination of the side chain, resulting in a decrease in both the purity and yield of the final product.
In addition to urea, urea or its condensate used as a treatment agent in the pretreatment of aromatic compounds in the present invention includes biuret and triuret.

Further, the shape of these materials can be selected as appropriate, such as powder or granules. When carrying out this invention, prior to side chain chlorination of the aromatic compound, the aromatic compound to be side chain chlorinated is brought into contact with a treatment agent to substantially remove impurity metal components contained in the aromatic compound. Remove.

The contact method is to use the treatment agent as a fixed bed and flow the aromatic compound through this fixed bed, or to directly introduce the treatment agent into the aromatic compound and disperse and suspend it.
Methods such as over-separation can actually be adopted industrially. However, since the pretreatment in this invention requires simply bringing the treatment agent and the aromatic compound into contact, any method that can bring the two into contact can be employed. The contact temperature may be room temperature, and the contact time is 20 seconds to 2 minutes to reduce the amount of ferric chloride in the aromatic compound from 10 ppm to 1.
1! ) m or less. The pretreated aromatic compound thus obtained is then side-chain chlorinated. This side chain chlorination can be carried out by a conventional method, for example, the pretreated aromatic compound is placed in a glass reaction vessel, and chlorine is introduced into the reaction vessel while irradiated with light to allow the chlorination reaction to proceed. . As chlorine, crude chlorine gas or dehydrated chlorine gas generated from an electrolytic tank, or liquid chlorine can be used. As the light source, sunlight, discharge lamps, incandescent lamps, etc. can be used, and indium lamps, high-pressure mercury lamps, ultra-high-output mercury lamps, etc. are particularly advantageous industrially. The temperature of the chlorination reaction may be any temperature from room temperature to the boiling point of the reaction solution, but
The temperature is preferably 0°C or higher. The reaction time varies depending on the degree of chlorination, but is usually about 10 minutes to 100 hours. It has been conventionally known that a catalyst is generally added to the reaction system during a side chain chlorination reaction, but a catalyst can also be added in the present invention if necessary. After removing dissolved chlorine, hydrogen chloride, etc. from the obtained reaction-completed liquid, the desired reaction product is recovered and purified by operations such as filtration, distillation, and crystallization, as necessary. As is clear from the above description, according to the present invention, impurity metal components contained in aromatic compounds to be side-chain chlorinated can be effectively removed by a simple and quick operation prior to the chlorination reaction. Therefore, in the subsequent side chain chlorination, the reaction can proceed without the influence of impurity metal components, so that the desired product can be obtained in high yield and high purity. In addition, in this invention, since a metal component scavenger such as urea is not added to the chlorination reaction system, urea decomposition products generated when urea is added to the chlorination reaction system can be removed from the reactor wall, light source lamp cover, etc. Since there is no adhesion to the surface or the accompanying obstruction of light transmission, side chain chlorination can be carried out very simply and advantageously in practice.

The present invention will be further explained below with reference to Examples. Example 1 After adding 5 y of biuret powder to 500 y of toluene containing 10 ppm of ferric chloride and stirring, the biuret was mixed with ▲
It was removed by over-separation.

The remaining amount of ferric chloride in toluene obtained as F5 liquid is 0.
．． It was 3 ppm or less. Ferric chloride was determined by absorbance measurement using the orthophenanthroline color method. 184.3 tons of the above biuret-treated toluene was charged into a 500 ml glass reactor equipped with a thermometer, a chlorine suction pipe, and a reflux condenser that also served as an exhaust gas, and the reaction temperature was maintained at 90 to 100°C, and the reaction temperature was 400 to 500 mμ. Chlorine was introduced while irradiating wavelength light at 150 W/d. Even when chlorine was introduced at a rate of 157 y/min for 4 hours, the reaction solution was hardly colored (Hazen color number according to JIS K69Ol-1968 was 20), and the purity of trichlorotoluene, the target reaction product, was determined by gas chromatography analysis. According to 99
．． It was 90%. For comparison, toluene without biuret treatment was chlorinated using the same reactor and reaction conditions as above, and the purity of the desired reaction product was 99.
Although the concentration was 5%, the reaction solution was markedly colored and had a concentration of 500 Hazen or more.

For further comparison, 20Tr19 of urea was added to toluene 184,37 containing 10ppm of ferric chloride without biuret treatment, and chlorination was carried out using the same reactor and reaction conditions as above. Although there was almost no coloration (Hazen color number is 20), urea or its decomposition products adhered to the reaction wall, contaminated the reactor, and impeded light transmission.

Because of this, the reaction was not completed and the purity of trichlorotoluene was 9.
It became 8.4%. Example 2 Diameter 3.5cm. 100ml of crystalline urea in a glass cylinder of
paraxylene containing 10 ppm of ferric chloride was passed through this at a speed of 50 m/min.

On the other hand, two 500 m1 glass reactors equipped with a thermometer, a chlorine blowing pipe, and a reflux condenser that also serves as exhaust were connected in series, and each was filled with the above-mentioned urea-filtered paraxylene 2.
127 (2m01) each, and the reaction solution temperature was set to 110
While maintaining the temperature at ~130°C and irradiating with light in the same manner as in Example 1, chlorine was introduced into the first tank at a rate of 3 mol/hour for 5 hours. 1st
The exhaust gas from the tank was introduced into the second tank. Furthermore, under the same conditions as above, chlorine gas was added to only the second tank at a rate of 3 mol/hour.
A period of time was introduced to complete side chain chlorination in the second tank. Second
The degree of coloration of the reaction-completed liquid in the tank was low and was 160. Further, as a result of analyzing this liquid by gas chromatography, the purified product obtained was α・α・α・α″・α7・α5-hexachlorparaxylene, and the purity was 93.7%. Therefore, when paraxylene containing 10 ppm of ferric chloride was used without urea treatment in the same reactor and reaction conditions as above, the reaction solution was significantly colored from the beginning of the reaction and the reaction could not be completed. For another comparison, paraxylene 2127 containing 10 ppm of ferric chloride without urea treatment was charged into the same two reactors installed in series as above, and urea 20W19 was added to each.
When chlorination was carried out under the same reaction conditions as above, urea or its decomposition products adhered to the walls of the reactor, contaminating the reactor and blocking light transmission.

Claims (1)

[Claims] 1. When chlorinating the side chain of an aromatic compound having a lower alkyl group in the side chain, the aromatic compound is pretreated by bringing it into contact with urea or a condensate thereof, and then chlorination is carried out. A method for side chain chlorination of aromatic compounds.