JPH01261342A - Preparation of bis(trichloromethyl)diphenyl ether - Google Patents

Abstract

PURPOSE:To provide the subject compound useful as a raw material for heat resistant resins, etc., while controlling the generation of by-products, by diluting dimethyldiphenyl ether with an inert solvent, introducing chlorine in the presence of a radical reaction initiator and subsequently starting the irradiation of light to continue the chlorination reaction until the completion of the reaction. CONSTITUTION:Dimethyldiphenyl ether of formula I (the methyl groups are situated at meta or para positions) is diluted with an inert solvent (e.g., carbon tetrachloride or monochlorobenzene) and into the resultant solution chlorine is introduced in the presence of a radical reaction initiator (e.g., benzoyl peroxide). The chlorine is introduced into the solution under the irradiation of light to continue the chlorination reaction until the reaction is accomplished, thereby providing bis(trichloromethyl)diphenyl ether of formula II (the trichloromethyl groups are located at meta or para positions). The objective compound can be produced in high yield and purity and in a short time and is useful as a raw material for polymeric liquid crystals.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing bis(trichloromethyl)diphenyl ether with high purity.

Bis(trichloromethyl)diphenyl ether has a highly reactive trichloromethyl group, and dicarboxylic acids that can be easily derived from it, for example, are very useful compounds as raw materials for heat-resistant resins or polymeric liquid crystals.

(Prior Art) It is well known that the side chains of aromatic compounds having methyl substituents can be selectively chlorinated by radical reactions such as the addition of a radical reaction initiator or light irradiation. This reaction is a sequential reaction, and as chlorine is introduced into the methyl group, the reaction rate decreases significantly. Therefore, when producing trichloromethyl compounds, a strong light source is used as a radical source, and a relatively high temperature is used. It has been necessary to carry out chlorination.

Conventionally, the following method is known as a method for producing bis(trichloromethyl)diphenyl ether.

(1) U.S. Patent No. 3,376,350 for chloromethylating diphenyl ether to produce bis(chloromethyl)diphenyl ether, a method of chlorinating in carbon tetracarbon under irradiation with a solar lamp.

(2) Soviet Patent No. 245061 A method of adding phosphorus pentachloride to dimethyl diphenyl ether and chlorinating it while irradiating it with ultraviolet rays at 110 to 250°C.

(3) Soviet Patent No. 273186 A method of adding an aliphatic nitroester to dimethyl diphenyl ether and heating it to a high temperature for chlorination.

Although not intended for the production of bis(trichloromethyl)diphenyl ether, the following conventional methods are known as using a radical reaction initiator during side chain chlorination of dimethyldiphenyl ether.

(4) JP-A No. 55-89237: A method for obtaining a compound mainly having a dichloromethyl side chain by chlorinating dimethyl diphenyl ether in the coexistence of a nitrogen-containing compound, a sulfur-containing compound, and a radical reaction initiator.

(5) JP-A No. 56-125326: A method for obtaining a compound mainly having dichloromethyl side chains by chlorinating dimethyl diphenyl ether in the coexistence of a sulfur-containing compound and a radical reaction initiator.

(Problems to be Solved by the Invention) Bis(trichloromethyl)diphenyl ether obtained by both methods (1) and (2) of irradiating ultraviolet rays from the initial stage of the reaction and method (3) of high-temperature chlorination is black. is heavily contaminated with tar-like by-products. This is considered to be due to side reactions caused by the benzene ring activated by the ether bond in the molecule (eg, formation of tar-like oligomers due to dehydrochlorination, nuclear chlorination, cyclization reactions, etc.). In the case of the conventional photochlorination method described above, the reaction solution is colored due to the production of tar-like by-products from the beginning of the reaction, so as the reaction progresses, light transmission worsens.
This resulted in a decrease in the reaction rate, an increase in by-products due to dark reactions, and in the worst case scenario, the reaction could not be completed. Moreover, in order to obtain bis(trichloromethyl)diphenyl ether from the reaction solution obtained by these methods, purification means such as distillation or recrystallization are essential.

In addition, the conventional methods (4) and (5) above are mainly aimed at producing compounds having a dichloromethyl side chain, but the method of adding such a third substance However, the problem remains that these substances remain and must be separated and removed.

On the other hand, a method of side chain chlorination using only a radical reaction initiator without the coexistence of a third substance such as the nitrogen-containing compound or sulfur-containing compound is also considered, but this method requires a long time to complete the reaction. The problem is that it requires. Also,
This method has the trouble of having to compensate for the sudden drop in reaction rate in the late stage of the reaction by successive additions of the radical reaction initiator, and the purification process requires that the radical reaction initiator added in large amounts must be separated and removed. There is also the problem of

In general, bis(trichloromethyl)diphenyl ether (i) has a high boiling point and is unstable to heat, (11
) It has a low melting point and is easily soluble in organic solvents, (iii)
It is known that it easily reacts with compounds that have nucleophilic properties, and when the reaction solution obtained by the above conventional method is subjected to a normal purification method, such as distillation, due to the above property (+>), It was inevitable that purification would involve large losses, such as thermal decomposition during distillation, and the solvents that can be used are limited due to (ii> and (iii) above) when purifying by recrystallization. .Also, the above conventional methods (1) to (3)
In this case, there were operational disadvantages such as the fact that the reaction solution was difficult to filter due to tar-like by-products.

(Means for Solving the Problems) The present inventors have developed a method for producing bis(trichloromethyl)diphenyl ether using simple methods such as vacuum concentration of the reaction solution after the reaction without adding purification steps such as distillation or recrystallization. We believe that it is important for industrial production to minimize the side reactions mentioned above in order to obtain high-purity target products through simple operations, and we are focusing on how to suppress the production of nuclear chlorinated products or tar-like byproducts. We conducted a thorough study with a focus on As a result, we found that the chlorination method using a radical reaction initiator is the best method for suppressing the formation of tar-like 01 organisms, and that the formation of tar-like byproducts by light irradiation is most likely to occur at the early stage of the reaction. It has been found that side reactions such as tar-like by-products and nuclear chlorides become less likely to occur as chlorine is introduced into the side chain methyl group. Therefore, dimethyl diphenyl ether, the raw material, was diluted with an inert solvent, first chlorinated in the presence of a radical reaction initiator to introduce chlorine into the side chain, and then light irradiation started to continue chlorination. When a method of completing the reaction was adopted, it was found that the production of tar-like by-products, which is characteristic of the photochlorination method, was not observed, and that the desired product could be produced in high yield and purity in a short time.

That is, the present invention relates to the following general formula (I> (however, the above (
The first step is to dilute the compound represented by the formula I (in which the methyl group is located at the meta or para position) with an inert solvent and introduce chlorine in the presence of a radical reaction initiator, and to introduce chlorine under light irradiation. (However, in the above formula (n), the trichloromethyl group is located at the meta or para position.) This is a method for producing bis(trichloromethyl)diphenyl ether.

The present invention is a method that complementarily combines chlorination using a radical reaction initiator and chlorination using light irradiation,
In particular, the formation of tar-like byproducts, which is a fatal drawback of photochlorination, can be suppressed by using a radical reaction initiator at the beginning of the reaction, and the reaction rate, which decreases as the initiator is consumed in the early stages of the reaction, can be suppressed. It has the effect of being promoted by light irradiation. In other words, in cases where the setting of reaction conditions at the initial stage of the reaction greatly affects the purity of the product, such as in the production method of the target product of the present invention, analysis of the amount of light, the shape of the reaction vessel, etc. is complicated with only photochlorination. Scaling up the device is very difficult due to the addition of a coloring factor, but if a method is adopted in which light irradiation is performed in the final stage of completing the reaction, even if excess chlorine is supplied during light irradiation. However, almost no tar-like by-products or nuclear chloride by-products are observed, and therefore the scale-up of the device can be easily carried out. Although it is possible to carry out the reaction over a long period of time using only a radical reaction initiator, according to the method of the present invention, the reaction can be carried out in the shortest reaction time and with the minimum amount of radical reaction initiator. The decomposition product of the radical reaction initiator in the product has a large boiling point difference with bis(trichloromethyl)diphenyl ether, which is the object of the present invention, and can be easily resolved by simply concentrating under reduced pressure without the need for rectification. It can be easily removed from the reaction mixture.

Specific examples of the compound of formula (I) used in the present invention include 3,3'-dimethyl diphenyl ether; 3.
Examples include compounds in which the methyl group in the formula (I) is located at the meta or para position, such as 1'-dimethyldiphenyl ether and 4,4°-dimethyldiphenyl ether.

Examples of the inert solvent used in the present invention include those inert to chlorination, such as carbon tetrachloride, monochlorobenzene, and dichlorobenzene.

The concentration of raw material dimethyl diphenyl ether during the reaction greatly affects the purity of the product; when the concentration exceeds 10%, the purity of the target product begins to decrease significantly, and when it exceeds 30%, most of it becomes nuclear chloride. It was confirmed that it would happen. Therefore, the amount of solvent used is 1% by weight based on the starting compound of formula (I).
0 times or more, preferably 10 to 50 times, more preferably 1
A range of 3 to 30 times is appropriate.

Examples of the radical reaction initiator used in the present invention include organic perfluorides represented by benzoyl peroxide and azo compounds represented by azobisisobutyronitrile. It is appropriately selected in consideration of the reaction temperature and the half-life of the initiator. The amount of the radical reaction initiator to be added is determined in consideration of not generating excessive chlorine at the initial stage of the reaction and taking into account the optimum amount of chlorine introduced in the first step, but it is usually 0.1 to 0.1 to 100% of the raw material dimethyl diphenyl ether. 10% by weight, preferably in the range of 1 to 5% by weight.

In carrying out the present invention, chlorination in the presence of a radical reaction initiator in the first step involves introducing chlorine into an inert solvent in which the raw material compound is dissolved, so that the chlorination rate of the side chain of the raw material compound is 70%.
% or more, preferably 70 to 90%. In particular, it is preferable to start the second step of chlorination under light irradiation when benzyl protons disappear from the chlorinated raw material compound. The side chain chlorination rate at this stage varies depending on the reaction conditions, but is usually in the range of 75 to 85%. Therefore, the amount of radical reaction initiator added in the first step is such that it does not generate excessive chlorine at the initial stage of the reaction, and also
% or more of chlorine can be introduced. When the amount of chlorine introduced in the first step is less than 70%, the percentage of lower chlorinated compounds (for example, those with methyl and benzyl protons) is high, and the photochlorination in the second step is less than 70%. This is undesirable because it tends to cause side reactions.Also, when the amount of chlorine introduced exceeds 90%, the reaction rate decreases and the reaction takes a long time, and excess chlorine accumulates in the system. An explosive reaction occurs during light irradiation in the second step, which is unfavorable for operation.

The light source used in the second step uses normal ultraviolet rays of about 350 to 500 nm, and preferably uses a high-pressure mercury lamp. As described above, photochlorination in the second step starts when the side chain chlorination rate of the raw material compound is 70% or more.

Although the reaction is carried out batchwise, it is also possible to carry out the reaction continuously in two types, for example, a radical reaction tank in the first step and a photoreaction tank in the second step.

Hydrogen chloride produced by the reaction is known to have a catalytic effect on nuclear chlorination, and when the reaction temperature is low, the solubility of hydrogen chloride increases, resulting in a decrease in product purity. Therefore, the preferred reaction temperature in the first and second steps of the present invention is in the range of 50 to 150°C, particularly at a temperature at which the reaction system gently refluxes.

Alternatively, the reaction may be carried out while introducing an inert gas such as nitrogen gas to drive out hydrogen chloride from the reaction system.

The reaction time varies depending on the rate of chlorine introduction, but is usually in the range of 1 to 30 hours throughout the first and second steps. Particularly at the beginning of the reaction, excessive supply of chlorine will greatly reduce the purity of the product, so the purpose of the initial stage of the reaction is to adjust the amount of chlorine introduced and set the reaction time so as not to discharge excess chlorine outside the system. It is important for manufacturing products with high purity. Further, it is preferable that the chlorine and solvent used are dry. A method is known in which an amide compound or the like is added to the reaction system in order to mask heavy metals that can act as a catalyst for nuclear chlorination, but it is of course possible to add such a masking agent in the present invention. , there is no problem in carrying out the reaction.

Stirring during the reaction is important to prevent localized high concentrations of chlorine, and the method of introducing chlorine etc. depends on the target product II! However, these can be easily determined through experiments etc. in practice.

(Example) Example 1 A reactor equipped with a 100W high-pressure mercury lamp irradiation device was
3,4°-dimethyl diphenyl ether 58.5 (J(
0.29 mol), 915 g of carbon tetrachloride, and 1.8 g of benzoyl peroxide were charged, and the system was heated until it gently refluxed. First, chlorine gas was introduced from the gas introduction tube at a rate of 140 d/min to perform chlorination without lighting the mercury lamp. After about 4 hours, it was confirmed by NMR that the benzyl protons had almost disappeared (the side chain chlorination rate at this point was 83% according to gas chromatography analysis), so a high-pressure mercury lamp was turned on and further chlorine was added under light irradiation. continued to develop. Five hours and 30 minutes after the start of the reaction, the disappearance of benzal protons was confirmed by NMR, so the introduction of chlorine was stopped and the reaction was completed.

Nitrogen gas was introduced into the system to drive out dissolved hydrogen chloride and chlorine gas, and the system was concentrated, and further concentrated under reduced pressure at 80°C and 2 mm 1 lc+ to obtain 120 (l) of a colorless oil. Analysis by gas chromatography revealed that 3. , 4'-bis(trichloromethyl)diphenyl ether in a proportion of 98.5% by weight and a nuclear chloride in a proportion of 1.5% by weight.

Comparative Example 1 3,4'-dimethyldiphenyl ether was placed in a reactor equipped with a 9A 100W high-pressure mercury lamp.

58.5 CI (0.29 mol) and 916 g of ash tetrachloride were charged.

The system was slowly refluxed and chlorine was removed for 140 m under mercury lamp irradiation.
Chlorination was carried out by introducing at a rate of /min.

As the reaction started, the reaction solution gradually turned brown, and the reaction rate decreased significantly in the latter half of the reaction.
After a few minutes, the disappearance of the benzal proton was confirmed by NMR, so the reaction was terminated at this point.

After the reaction, nitrogen gas is introduced to drive out dissolved hydrogen chloride and chlorine gas, and the mixture is concentrated under reduced pressure to form a viscous dark brown oil 12
3g was obtained. When this was analyzed using gas chromatography, it was found that 92.5% of 3,4°-bis(trichloromethyl)diphenyl ether and 3.4% of nuclear chloride (
6)% and other high boiling point substances 4.1% by weight.

Comparative Example 2 3.4°-dimethyldiphenyl ether 58.2g (0
, 29 mol) and 2.9 g of benzoyl peroxide were dissolved in 916 g of carbon tetrachloride, and the system was gently refluxed.

Chlorine was introduced into this at a rate of 140ml/min, and NMR
The reaction was tracked. Eight hours after the start of the reaction, the benzal proton disappeared, so the reaction was terminated.

After the reaction, nitrogen gas is introduced into the system to drive out dissolved hydrogen chloride and chlorine gas, and the mixture is concentrated under reduced pressure to form a pale yellow oil 12.
1g was obtained. When this was analyzed by gas chromatography, it was found that 91.0% by weight of 3,4°-bis(trichloromethyl)diphenyl ether and 3.0% by weight of nuclear chloride were produced.

(Effects of the Invention) The present invention can easily obtain a highly purified target product in a high yield in a short period of time under mild conditions without any equipment or process complexity. The obtained target product can be used as it is as a raw material for heat-resistant resins and polymeric liquid crystals.

Claims (1)

[Claims] Compounds represented by the following general formula (I) ▲Mathematical formulas, chemical formulas, tables, etc.▼(I) (However, in the above formula (I), the methyl group is located at the meta or para position) A general method characterized by comprising a first step of diluting with an inert solvent and introducing chlorine in the presence of a radical reaction initiator, and a second step of introducing chlorine under light irradiation to complete the reaction. Method for producing bis(trichloromethyl) diphenyl ether represented by formula (II) ▲ Numerical formulas, chemical formulas, tables, etc. ▼ (II) (However, in the above formula (II), the trichloromethyl group is located at the meta or para position) .