JPH1192409A - Photochlorination of methylbenzene compounds - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for the photochlorination of a methylbenzene compound, capable of controlling the production of by-products as much as possible and enabling the efficient production of a highly pure trichloromethylbenzene useful for medicines, UV light absorbents and the like by controlling the chlorine concentration of a reaction system to a specific value or smaller in the latter reaction half when the hydrogen atoms in the side methyl group of a methylbenzene is chlorinated by a photochlorination reaction in a specific chlorination degree or larger. SOLUTION: This method for the photo-chlorination of the side chain methyl group of a methylbenzene (preferably toluene, o-xylene or the like) comprises controlling the reaction temperature of the first half of the reaction to 50-150 deg.C and controlling the chlorine concentration of the reaction system and the reaction temperature to <=10.0 g/liter and 100-150 deg.C, respectively, in the latter half giving a chlorination degree of 2.0-2.8. The chlorination degree expresses the degree of chlorine atoms to hydrogen atoms in the chlorinated methyl group. Thereby, the methylbenzene can be chlorinated without using an additive for catching a metal component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for photochlorinating a methyl group of methylbenzenes having a side chain methyl group such as toluene and xylene.

[0002]

2. Description of the Related Art For example, benzotrichloride obtained by photochlorinating the side chain methyl group of toluene is widely used as a raw material for producing pharmaceuticals, ultraviolet absorbers, pesticides, dyes, acid chlorides such as benzoyl chloride and the like. .

As a method for industrially producing such benzotrichloride, generally, a photochlorination reaction in which chlorine acts under light irradiation is employed. Then, in this photochlorination reaction of toluene, benzyl chloride, benzal chloride, and benzotrichloride are mainly generated, but chlorinated nuclei are by-produced in places where light does not reach in the reaction tank, and furthermore, The presence of metal components such as iron, explosive combustion in the gas phase, and a rise in the chlorine concentration in the reaction solution produce high-boiling by-products, which cause the reaction solution to become colored, As a result, the side reaction progresses more and more, and as a result, the yield of benzotrichloride, which is the target substance, or the purity thereof may decrease.

Therefore, as a method for solving such a problem, there is known a method in which the chlorination reaction is stopped in an incomplete state, and the unreacted raw material is recovered by distillation and reused. Requires a distillation operation, and equipment such as a cushion tank for collecting and reusing unreacted substances is also required. It is not always satisfactory.

Further, as another method, for example, a method of adding urea or acid amide to capture the metal component of the reaction system (US Pat. No. 2,695,873), Method for capturing metal components (Japanese Patent Laid-Open No. 51-8 / 1976)
No. 222), a method in which iron in the raw material is removed in advance using urea or a condensate thereof (Japanese Patent Application Laid-Open No. 51-8223), an alkylenepolyamine as a stabilizer is added to a reaction system to prevent nuclear chlorination or the like. Method for suppressing side reaction (Japanese Unexamined Patent Publication No.
No. 208538), a method in which the reactor is improved to improve the gas-liquid contact state between the raw material and chlorine and the light irradiation state (Japanese Patent Application Laid-open No.
-293677 and JP-A-6-298671).

[0006] However, in these methods,
In a method using additives such as urea, acid amide, urea condensate, and alkylene polyamine added for the purpose of capturing metal components or as a stabilizer, the presence of these additives affects the photochlorination reaction. Adversely affect the production of benzotrichloride or the like as the target product and its yield,
After the completion of the reaction, it is necessary to collect and remove these additives, or a step of removing gelled iron is required. However, in the method for improving the gas-liquid contact state and the light irradiation state by improving the reactor, the control system becomes complicated with the improvement of the reactor, and the improvement of these reactors and the control system A large cost is required for the equipment, and a satisfactory effect cannot always be obtained from the viewpoint of suppressing the generation of high-boiling by-products.

[0007]

Therefore, the present inventors add an additive for capturing a metal component in a method for photochlorinating a side chain methyl group of methylbenzenes such as toluene and xylene. Without the need for modification of the reactor with complicated control, the side chain methyl groups of methylbenzenes can be efficiently and completely purified with high purity by photochlorination. As a result of intensive studies on a method capable of chlorinating to a side chain trichloromethyl group by chlorination, a chlorination degree represented by a ratio in which hydrogen atoms in one methyl group are replaced with chlorine atoms is 2.0-2. .8
The generation of by-products starts sharply from a point in time when the value exceeds a certain value in the range, and the generation of this by-product can be suppressed as much as possible by controlling the chlorine concentration of the reaction system to 10 g / liter or less. Heading, the present invention has been completed.

Accordingly, an object of the present invention is to provide a simple method and suppress the generation of by-products as much as possible without using special additives or improving the reactor. Another object of the present invention is to provide a method for photochlorinating methylbenzenes, which can produce the target trichloromethylbenzenes with high purity and high yield.

[0009]

That is, the present invention relates to a method for photochlorinating a side chain methyl group of methylbenzenes, wherein the ratio of hydrogen atoms in one methyl group to chlorine atoms is expressed as a ratio. Photochlorination of methylbenzenes to control the chlorine concentration of the reaction system to 10.0 g / liter or less in the latter half of the reaction when the degree of chlorination to be performed is not less than a predetermined value in the range of 2.0 to 2.8. Is the way.

The present invention also relates to a method for photochlorinating methylbenzenes, wherein the reaction temperature in the first half of the reaction from the start of the reaction is 50 to 150 ° C., and the reaction temperature in the second half of the reaction is 100 to 150 ° C. If the amount of chlorine supplied to the reaction system is relatively high,
From a relatively low value in the range of 2.8, or from a relatively high value in the range of chlorination degree 2.0 to 2.8 when the chlorine supply is relatively low, the reaction This is a method of controlling the chlorine concentration of the reaction system, and further controlling the chlorine concentration of the reaction system by controlling the amount of chlorine supplied to the reaction system.

In the present invention, the methylbenzene used as a raw material may be any compound having a methyl group on a benzene ring, but typically, toluene having one side-chain methyl group or a derivative thereof, O-xylene having two side chain methyl groups, m-xylene, p-
Xylene such as xylene or a mixture thereof, or a derivative thereof, and the like can be given.

In the present invention, 3 in one methyl group
The photochlorination reaction depends on whether the degree of chlorination represented by the ratio of the number of hydrogen atoms replaced by chlorine atoms is less than or equal to a predetermined value in the range of 2.0 to 2.8. Is divided into the first half of the reaction and the second half of the reaction. In the latter half of the reaction, the chlorine concentration of the reaction system is 10.0 g / liter or less, preferably 5.
It is controlled to a range of 0 g / liter or less. When the chlorine concentration of the reaction system in the latter half of the reaction exceeds 10 g / liter, it is difficult to suppress the generation of by-products within a meaningful range. The chlorine concentration is preferably as low as possible from the viewpoint of suppressing the generation of by-products. However, if it is too low, the reaction rate is extremely reduced. Therefore, the chlorine concentration is appropriately determined in consideration of the reaction rate.

The value of the degree of chlorination that distinguishes the photochlorination reaction into the first half and the second half of the reaction can be arbitrarily determined according to the supply rate of chlorine supplied to the reaction system. When the amount of chlorine supplied is relatively high and the reaction rate is high, a relatively low value is set within the range of the chlorination degree of 2.0 to 2.8. Is slow, a relatively high value is set from the range of the chlorination degree of 2.0 to 2.8. The value of the degree of chlorination when this photochlorination reaction is switched from the first half of the reaction to the second half of the reaction varies depending on the type of methylbenzenes used, but a value lower than 2.0 decreases the production rate. If the chlorination degree is set to a value higher than 2.8, the production of by-products may not be suppressed due to an increase in the chlorine concentration in the reaction solution.

For example, methylbenzenes are toluene, and the amount of chlorine supplied to the reaction system from the start of the reaction to the first half of the reaction (the amount of chlorine per hour with respect to the weight of the charged raw material) is 40 to the raw material toluene. ~ 4% by weight / hr
In the case of, the value of the chlorination degree at the time of switching the photochlorination reaction from the first half of the reaction to the second half of the reaction for controlling the chlorine concentration is inversely proportional to the chlorine supply amount, and the chlorination degree is 2.5 to
It is better to determine from the range of 2.8. By setting the value of the degree of chlorination that switches from the first half of the reaction to the second half of the reaction in accordance with the amount of chlorine supplied in this manner, the generation of by-products can be effectively prevented without unnecessarily prolonging the reaction time until the end of the reaction. Can be suppressed.

In the present invention, in order to minimize the formation of by-products in the first half of the reaction from the start of the reaction, the reaction temperature in the first half of the reaction from the start of the reaction is preferably 50 to 150 ° C., more preferably The reaction temperature is preferably from 100 to 150 ° C, and in order to prevent the reaction rate in the latter half of the reaction from extremely lowering, the reaction temperature in the latter half of the reaction is preferably from 100 to 150 ° C. By controlling the reaction temperature in this way, it is possible to prevent the reaction rate from dropping extremely while suppressing the generation of by-products as much as possible, and to efficiently produce high-purity trichloromethylbenzenes in good yield. It can be manufactured in a special way.

The reaction apparatus for carrying out the method of the present invention is not particularly limited, and a conventionally known apparatus can be used as it is, but preferably has a chlorination degree of 2.0. A reaction tank containing a reaction solution of less than a predetermined value in the range of ~ 2.8 and serving as a lower tank in the first half of the reaction;
A reaction in which at least two reaction tanks are connected, each having a reaction tank containing a reaction solution having a chlorination degree of not less than a predetermined value in the range of 2.0 to 2.8 and serving as a higher-order tank in the latter half of the reaction. An apparatus is preferably used. At this time, the chlorine concentration in the reaction system on the higher tank side is controlled to 10.0 g / liter or less, and the exhaust gas from the higher tank side is supplied to the lower tank side, whereby the higher tank is supplied. The unreacted chlorine contained in the exhaust gas on the next tank side is preferably reacted on the lower tank side.

For example, in the case of using a reaction apparatus in which two reaction tanks are connected, one of them is used as a lower tank in the first half of the reaction and the other is used as a higher tank in the second half of the reaction, and the two reaction tanks are used. The operation can be alternately switched between the lower tank and the higher tank.
In the case of using a reactor in which tanks or more reaction tanks are connected in series, it is possible to continuously operate while sequentially switching to a lower tank and a higher tank in accordance with the degree of chlorination that has reached each reaction tank. . By using a reaction apparatus in which a plurality of reaction tanks are connected in this way, the reaction tank operated as a lower tank absorbs chlorine in the exhaust gas, and the chlorine content in the exhaust gas discharged to the outside of the reaction tank. Can be reduced as much as possible.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below based on examples and comparative examples. In the following Examples and Comparative Examples, the chlorination degree of the reactant, the chlorine concentration in the reaction solution (reaction system), and the purity of the product were measured by the following methods, respectively.

[Degree of Chlorination of Reactant] The reactant was sampled from the reactor and subjected to gas chromatographic analysis to determine the sequential product in which three hydrogens in the methyl group were replaced with chlorine in the range of 1 to 3 ( The content percentage by weight is proportionally divided into the chlorination degree of the main component) and calculated.

[Chlorine Concentration in Reaction Solution] 5 g of a reactant was sampled from a reaction vessel, and the reactant was placed in 25 ml of an N / 2 aqueous solution of NaOH, and shaken well for 10 minutes.
I and 10 ml of (1 + 1) acetic acid aqueous solution were added, and N / 1
Using an aqueous solution of Na ₂ S ₂ O _{3 at} 0, titration was performed using the point at which the solution changed from pale yellow to transparent as the end point, and the chlorine concentration was calculated from the iodine consumption (exposed solution measurement JIS K1).
207).

[Purity of product] GC-1 manufactured by Shimadzu Corporation
Using 4A (column: G-205) and chloroparaxylene as an internal standard substance, analysis was carried out by an internal standard method of a gas chromatograph. The analysis value of the internal standard method adopted here was confirmed by a test based on the distillation method of JIS K0066.

Example 1 Two glass-lined light irradiation type reaction tanks A and B equipped with a chlorine injection port, an exhaust port, a reflux condenser, a stirrer, and a jacket are provided side by side. The other reactor B was connected to the chlorine injection port, and each reactor A and B was charged with 2700 liters of toluene, respectively, and both reactors A and B were heated to 50 ° C.

410 k of chlorine from the chlorine inlet of the reaction tank A
g / hr (17.4% by weight of chlorine supplied to toluene)
/ Hr), and the photochlorination reaction of toluene was started under light irradiation with a high-pressure mercury lamp. After the start of the reaction, the reaction temperature of the reaction tank A was maintained at 110 to 130 ° C, and the reaction tank B side was maintained at 80 to 100 ° C. At this stage, both the reaction tanks A and B are operated as lower-order tanks, and the reaction tank B has a role of trapping chlorine contained in the exhaust gas of the reaction tank A.

The degree of chlorination of the reactant in the reaction tank A is measured,
At the time when the chlorination degree was 2.8 (when the reaction tank A became a higher-order tank), the chlorine supply rate was reduced to 100 kg / hr. At this time, the chlorine concentration in the reaction solution in the reaction tank A was 0.5 g.
/ Liter. Thereafter, the photochlorination reaction was continued while maintaining the chlorine concentration in the reaction solution in the reaction vessel A at 0.1 to 5.0 g / liter.

The reaction product in the reaction vessel A was analyzed by gas chromatography analysis, and when the amount of benzal chloride became 0.1% or less, the photochlorination reaction in the reaction vessel A was terminated.
During this time, in the reaction tank A, the chlorine supply rate is gradually reduced from 100 kg / hr to 50 kg / hr, and finally to 15 kg / hr, and the chlorine concentration in the reaction solution in the reaction tank A is reduced to 0.1 to 0.1 kg / hr. It was maintained at 5.0 g / l. At the time of the supply of chlorine of 15 kg / hr, nitrogen gas (N ₂ ) of 5 m ³ / hr was mixed and supplied.

After the reaction in the reaction tank A is completed, the supply of chlorine to the reaction tank A is temporarily stopped, the supply of chlorine to the reaction tank B and the irradiation of light are continued as they are, and 5 m ³ / H
The mixture was cooled to 60 ° C. while blowing nitrogen gas of r, and the reaction product was discharged. Thereafter, 2700 liters of fresh toluene was charged into the reaction vessel A, and the temperature was raised to 50 ° C.

Next, the exhaust port of the reaction tank B was connected to the chlorine injection port of the reaction tank A,
0 kg / hr (amount of chlorine supply to toluene: 17.4% by weight / hr) was supplied, and the photochlorination reaction of toluene was carried out in the same manner as above by reversing the relationship between the reaction tanks A and B. Was.

The reaction product obtained from the reaction vessel A was analyzed by gas chromatography. As a result, 96.0% by weight of benzotrichloride, 0.1% by weight of benzal chloride, and chlorinated nuclei (nuclei of the successive reactants) were obtained. 0.7% by weight of a monochloro body containing one chlorine) and a high-boiling by-product
It was 2% by weight. Further, as a result of analyzing the reaction product obtained from the reaction tank B by gas chromatography, the benzotrichloride 96.
0% by weight, 0.1% by weight of benzal chloride, 0.7% by weight of nuclear chlorinated product, and 3.2% by weight of high-boiling by-product. Further, the reaction product obtained again from the reaction tank A was analyzed by gas chromatography, and as a result, the first reaction tank A was analyzed.
Benzotrichloride, 96.0% by weight, benzal chloride, 0.1% by weight, chlorinated nuclear, 0.7% by weight, and 3.2% by weight of high-boiling by-products.

Example 2 The chlorine concentration in the reaction solution in the higher-order tank was maintained at 1.0 g / liter or less, and finally the chlorine supply was 3 kg / liter.
The operation was performed in the same manner as in Example 1 except that the reaction time was reduced to hr (N ₂ : 5 m ³ / hr).

As a result of analyzing the reaction product obtained from the reaction vessel A by gas chromatography, 98.0% by weight of benzotrichloride, 0.1% by weight of benzal chloride, 0.7% by weight of nuclear chlorinated product, And high-boiling by-products
It was 2% by weight. Moreover, the reaction product obtained from the reaction tank B was analyzed by gas chromatography, and as a result, the result was the same as above.

Example 3 The concentration of chlorine in the reaction solution in the higher-order tank was 0.1 to 7.0 g.
/ L or less, and the operation was carried out in the same manner as in Example 1 except that the chlorine supply rate was finally reduced to 30 kg / hr (N ₂ : 5 m ³ / hr).

As a result of analyzing the reaction product obtained from the reaction vessel A by gas chromatography, 94.0% by weight of benzotrichloride, 0.1% by weight of benzal chloride, 0.7% by weight of nuclear chlorinated product, And high-boiling by-products5.
It was 2% by weight. Moreover, the reaction product obtained from the reaction tank B was analyzed by gas chromatography, and as a result, the result was the same as above.

Comparative Example 1 Using only the reaction vessel A of Example 1, 2700 liters of toluene was charged and heated to 50 ° C., and then 350 kg / hr of chlorine was supplied from the chlorine inlet through a chlorine supply amount of 15.0. Wt% / hr), and the photochlorination reaction of toluene was started under light irradiation with a high-pressure mercury lamp. After the start of the reaction, the reaction temperature of the reaction vessel A was maintained at 110 to 130 ° C., and the photochlorination reaction was continued and terminated until the degree of chlorination of the reactants in the reaction vessel A reached 3.0.

The reaction product obtained from the reaction vessel A was analyzed by gas chromatography. As a result, it was found that benzotrichloride was 88.0% by weight, benzal chloride was 0.1% by weight, nucleated chloride was 0.7% by weight, And high-boiling by-products 1
It was 1.2% by weight.

[0035]

According to the present invention, it is possible to control the chlorine concentration of the reaction system based on the degree of chlorination as much as possible without using special additives or improving the reactor. Generation of by-products can be suppressed, and the target trichloromethylbenzenes can be produced with high purity and high yield.

Claims (6)

[Claims] 1. A method for photochlorinating a side chain methyl group of methylbenzenes, wherein the degree of chlorination represented by the ratio of hydrogen atoms in one methyl group replaced by chlorine atoms is 2.0.
A method for photochlorination of methylbenzenes, wherein the chlorine concentration in the reaction system is controlled to 10.0 g / liter or less in the latter half of the reaction when the reaction value becomes equal to or more than a predetermined value within the range of 2.8 to 2.8. 2. The reaction temperature in the first half of the reaction from the start of the reaction is 50 to 150 ° C., and the reaction temperature in the second half of the reaction is 100 ° C.
The method for photochlorination of methylbenzenes according to claim 1, wherein the temperature is from -150 ° C. 3. When the amount of chlorine supplied to the reaction system is relatively high, a relatively low value in the range of 2.0 to 2.8 is used. The method for photochlorinating methylbenzenes according to claim 1 or 2, wherein the chlorine concentration of the reaction system is controlled as the latter half of the reaction from a relatively high value in the range of chlorination degree 2.0 to 2.8. 4. The method for photochlorination of methylbenzenes according to claim 1, wherein the control of the chlorine concentration in the reaction system is performed by controlling the amount of chlorine supplied to the reaction system. 5. A reaction tank containing a reaction solution having a chlorination degree of less than a predetermined value in a range of 2.0 to 2.8 and serving as a lower tank in the first half of the reaction, and a chlorination degree of 2.0 to 2.8. Using a reaction apparatus having at least two reaction tanks connected to each other and having a reaction liquid containing a reaction solution of a predetermined value or more within the range of 2.8 and serving as a higher-order tank in the latter half of the reaction; The chlorine concentration of the reaction system of 10.0 g /
And controlling the unreacted chlorine contained in the exhaust gas of the higher-order tank in the lower-order tank while supplying the exhaust gas of the higher-order tank to the lower-order tank side. The method for photochlorination of methylbenzenes according to any one of the above. 6. The methylbenzenes are toluene,
The amount of chlorine supplied to the reaction system from the start of the reaction to the first half of the reaction is 40 to 4% by weight / hr based on the amount of the starting toluene. The chlorination degree is 2.5 to 2.
The method for photochlorinating methylbenzenes according to claim 1, wherein the method is determined from the range of 8.