JPH0345051B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the use of a new cocatalyst which provides extremely high selectivity, particularly towards the para position, in the production of nuclear chlorinated toluene by chlorination of toluene. The production of nuclear chlorinated toluene by chlorination of toluene has been well known and is of great industrial importance. This chlorination reaction is usually carried out in the presence of a Lewis acid catalyst such as antimony chloride, ferric chloride, or aluminum chloride, and produces monochlorinated products, polychlorinated products, and their positional isomers, depending on the conditions. This is accompanied by the formation of benzyl chloride. Under the production conditions of monochlorotoluene, the main product is o-chlorotoluene (hereinafter
(abbreviated as OCT) and p-chlorotoluene (hereinafter abbreviated as PCT), and may contain small amounts of m-chlorotoluene (hereinafter abbreviated as MCT), dichlorotoluene, benzyl chloride, etc. as by-products. be. Of the main products OCT and PCT, OCT has relatively little utility value, whereas PCT has wide utility value as a raw material for industrial chemicals, agricultural chemicals, and pharmaceuticals, and is one of the extremely important industrial products. It is one. Therefore, when producing monochlorotoluene, it is economically important to increase the production ratio of PCT and OCT, that is, the ratio of PCT to monochlorotoluene by even 0.5%, and for this purpose, chlorination has traditionally been Much effort has been put into the selection of conditions and catalysts. For example, U.S. Patent No. 3000975 describes titanium,
A method using chlorinated tin and zirconium as a catalyst (PCT/OCT=23/75) was published in U.S. Patent No. 3226447.
A method using a catalyst consisting of a combination of iron, aluminum, or antimony halides and an organic sulfur compound such as mercaptoacetic acid (PCT/OCT=
31.5/38.0) are listed. Furthermore, Dutch patent application No. 6511488 describes _a catalyst system of FeCl ₃ and S ₂ Cl ₂ , U.S. Pat _.
A catalyst using an inorganic sulfur compound such as CS ₂ ZnS as a co-catalyst is described, and French Patent No. 1491144 describes a catalyst using a Lewis acid catalyst and an organic sulfur compound such as selenium or thiophene or dimethylthiophene, each of which has been improved. It shows the effect of In addition, JP-A No. 50-34009 describes a catalyst system that combines selenium or selenium halides or oxides with iron (PCT/monochlorotoluene = 52.1-52.6%), and JP-A No. 52-19631 In the issue, a catalyst consisting of a Lewis acid and thianthrene as a promoter (PCT/monochlorotoluene = 50.5%) was published in JP-A-52
-19630 also contains a catalyst using polychlorothianthrene as a cocatalyst (PCT/monochlorotoluene = 55.9%);
No. 53-87323 also discloses a catalyst using a thianthrene compound having an electron-withdrawing substituent and an electron-donating substituent as a cocatalyst (PCT/monochlorotoluene=
56-59%) described. Furthermore, in JP-A-56-5139, 2-, 3-, 7
Phenoxatine compounds having a hydrogen atom, an electron-withdrawing group, or an electron-donating group at the - and 8-positions are disclosed. According to the above method, the improvement effect of increasing the production ratio of PCT and OCT is certainly recognized. However, some of these catalysts do not improve the production ratio as much as expected, are expensive and unsuitable from an industrial standpoint, are difficult to synthesize co-catalysts, and have low yields. These include those that are difficult to obtain, and even if the selectivity of PCT is high, it is difficult to employ them industrially. It is an object of the present invention to provide an improved method for carrying out the direct nuclear chlorination of toluene. That is, in producing monochlorotoluene,
The object of the present invention is to provide an industrially advantageous method for producing PCT by using a cocatalyst with extremely high para-selectivity. The present inventors have already filed a patent application No. 55-01350 for a method for producing nuclear chlorinated toluene using alkyl-substituted and unsubstituted halogenated phenoxatine compounds as promoters, but as a result of further intensive research, It was discovered that a phenoxatin compound synthesized from a specific diphenyl ether, or a chlorinated phenoxatin compound obtained by further chlorination, has cocatalytic ability with specific high para-selectivity, especially in low-temperature reactions. I've reached it. That is, the present invention provides a method for nuclear chlorination of toluene using a Lewis acid as a catalyst, using the general formula (In the formula, R represents a methyl group at the 1st and/or 3rd position, m represents an integer of 0 to 2, X represents a chlorine atom when m is 0, and a hydrogen atom when m is 1 to 2. A method for nuclear chlorination of toluene, characterized in that a chlorinated phenoxatine compound having a total substituted chlorine number of 1.4 to 3.5 obtained by chlorinating a phenoxatine compound represented by This is what we provide. The main catalyst used in the present invention is a Lewis acid, and generally known catalysts can be used. It also includes those that form a Lewis acid during a chlorination reaction or exhibit that function. Examples include common elemental antimony, iron, and halides, oxyhalides, oxides, sulfides, carbonyl compounds, and organometallic compounds of antimony, iron, aluminum, tin, titanium, and the like. Typical examples include antimony trichloride, antimony pentachloride, antimony trioxide, acitimony oxychloride, ferric chloride, iron sulfide, aluminum chloride, and tin tetrachloride, especially antimony trichloride, antimony pentachloride, and tin chloride. Ferric iron and the like are most preferred. Specifically, the phenoxatin compounds before chlorination used in the method of the present invention include 6,9-dimethyl-2,8-dichlorophenoxatin, 3,6,9
-trimethyl-8-chlorophenoxatin, and 1,3,6,9-tetramethyl-8-chlorophenoxatin. Also among these
When m of the R _n group is 1, that is, 3-methyl, 1,6,9-trimethyl-8-chlorophenoxatin, in which the methyl group is at the peri-position of S, is produced during the cyclization reaction with sulfur. However, this compound can also be used in the present invention. An example of a general method for producing phenoxatin compounds as cocatalysts is 2-chloro-
2-chloro-5- obtained by brominating p-xylene
Bromo-p-xylene, Experimental Chemistry Course Volume 19
p. 182, or Chemical Abstracts Vol. 65, 10530f (1966)
The 2,5,
3'-Trimethyl-4-chlorodiphenyl ether is separated by vacuum distillation. Subsequently, using this as a raw material, it was reacted with sulfur or sulfur chloride using aluminum chloride as a catalyst, according to the method described in Organic Syntheses.Col.Vol. 2, page 485. 1,6,9-trimethyl-8-chlorophenoxatin or 3,6,9-trimethyl-8-chlorophenoxatin can be synthesized. To further chlorinate the phenoxatin compound, the reaction is carried out in the presence of a Lewis acid catalyst using an inert solvent such as nitrobenzene, if necessary. The Lewis acid catalyst is used in the range of 0.001 to 5% based on the phenoxatin compound, and the equivalent or slight excess of chlorine required for the desired degree of chlorination is used at a temperature of 50° to 150°C, preferably 70° to 120°C. By introducing the compound under a temperature range, a chlorinated phenoxatin compound having a desired degree of chlorination can be synthesized. By further chlorinating in this manner, it is possible to impart a cocatalyst ability that is even better than that of the phenoxatin compound before chlorination. The conditions that the phenoxatine compound should have before chlorination according to the present invention are 6,9-dimethyl-
A methyl group is added to the 1st and/or 3rd position of 8-chlorophenoxatin, or 2 if there is no methyl group.
Only by having a chlorine atom in this position does it exhibit excellent cocatalytic ability with para-selectivity. The total number of substituted chlorines in chlorinated phenoxatin is 1.4~
The effect is significant in the range of 3.5. There is no problem even if it is a mixture of different numbers of total substituted chlorine, that is, different degrees of chlorination. When the number of total substituted chlorine is 3.7 or more, the effect decreases significantly. The amounts of the main catalyst and cocatalyst used can vary within a considerable range. The amount of main catalyst Lewis acid used is about 0.005% to about 5% by weight based on toluene.
The weight ratio of co-catalyst to main catalyst used is 0.05:
Although it can be used in the range of 1 to 20:1, from the viewpoint of improving the PCT production ratio and economical aspects, the main catalyst is about 0.01% to about 1% by weight based on toluene, and the weight ratio of co-catalyst to main catalyst is 0.2. :1 to 5:1
It is preferable to use it in When chlorinating using the main catalyst and co-catalyst of the present invention, the reaction temperature can be from 0° C. or lower to the boiling point or lower. However, in general, the temperature range is between 0°C and 80°C, and since the cocatalyst of the present invention has a characteristic of exhibiting high selectivity at the para position, especially at low temperatures, the temperature between 0°C and 80°C is selected.
Preferably it is carried out at 40°C. In the method of the present invention, the reaction system can be carried out under reduced pressure or pressurized system, but it is preferably carried out under approximately atmospheric pressure. Although it can be carried out in the presence of a solvent, there is no particular need for the presence of a solvent. Further, it can be carried out either batchwise or continuously. According to the method of the present invention, the production ratio of PCT to OCT is well over 1.1. In terms of the production ratio of PCT to monochlorotoluene, unprecedentedly good results can be obtained, ranging from 55% to over 60% depending on the conditions. Furthermore, if the promoter of the present invention is used, PCT,
The production of by-products other than OCT, such as MCT, is small, and the by-product of benzyl chloride is also very small, and depending on the conditions, it can be almost eliminated. The cocatalyst can also be produced by a known easy method, and the cocatalyst of the present invention is suitable for industrially producing PCT efficiently and is of extremely high value. The present invention will be explained below with reference to Examples. In the examples, parts indicate parts by weight unless otherwise specified. Reference Example 1 Synthesis of 2-chloro-5-bromo-p-xylene 2-chloro-p-
400 parts of xylene (bp 183-184°C) and 2 parts of anhydrous aluminum chloride were charged, and 360 parts of bromine was added dropwise over 5 hours at 35-60°C to react. Water was added to the reaction solution to remove the catalyst by washing with water, and then the oil layer was cooled. Filter the precipitated crystals, wash with methanol, and use mp60.
2-chloro-5-bromo-p-xylene at ~64°C
Obtained 377 copies. Reference Example 2 Synthesis of 2,5,3'-trimethyl-4-chlorodiphenyl ether In a 300 ml four-necked flask equipped with a reflux condenser, thermometer, and stirrer, a reaction product of 45 parts of m-cresol and caustic potash was added. 80 parts of 2-chloro-5-bromo-p-xylene obtained in Reference Example 1, 2 parts of potassium iodide, and 0.5 part of copper powder were charged and reacted at 170 to 200°C for 10 hours.
After this, 100ml of toluene was added to the reaction solution and filtered.
After removing insoluble matter, the oil layer was washed once each with dilute aqueous caustic soda solution and water, and after separation, it was distilled under reduced pressure.
58 parts of a fraction of 2,5,3'-trimethyl-4-chlorodiphenyl ether were obtained at 163-170°C/4 mmHg. Reference Example 3 Synthesis of 3,6,9-trimethyl-8-chlorophenoxatin A dropping funnel was attached to the above four-necked flask.
40 parts of 5,3'-trimethyl-4-chlorodiphenyl ether and 2 parts of granular aluminum chloride were charged, and 15.2 parts of sulfur chloride was added dropwise at 50 to 90°C over about 3 hours. After the reaction was completed, 100 ml of water and 80 ml of dichloroethane were added to the reaction solution, and only the dissolved dichloroethane was collected. Dichloroethane was distilled off, and the viscous 3,6,9-trimethyl-8-chlorophenoxatin was concentrated under reduced pressure. I got a assembled product. Reference Example 4 Synthesis of chlorinated 3,6,9-trimethyl-8-chlorophenoxatin Crude phenoxatin compound obtained in Reference Example 3 above
Pour 30 parts into the four-necked flask equipped with a chlorine introduction tube instead of the dropping funnel, add 36 parts of nitrobenzene and 0.5 parts of antimony pentachloride, and bring the internal temperature to 90.
Chlorination with different degrees of chlorination 3,6,9-
Trimethyl-8-chlorophenoxatin (hereinafter referred to as chlorinated 3,6,9-trimethyl-8-chloro-PX)
) was synthesized. After aerating the chlorination reaction solution with nitrogen gas, a small amount of toluene and a large amount of methanol were added, and the precipitated crystals were filtered, dried, and used as a promoter. In addition, all samples were subjected to another cleaning treatment to sufficiently remove inorganic substances, and each sample was subjected to chlorine analysis to calculate the average chlorine content. Examples 1 and 2 For the chlorination reaction of toluene, a reactor equipped with a glass container having a diameter of 40 mm and a length of 500 mm and equipped with a thermometer, a reflux condenser, and a chlorine blowing tube was used. The amount of toluene charged was 460 ml, the main catalyst was antimony trichloride 500 ppm, and the co-catalyst was the chlorinated 3,6,9- obtained in Reference Example 4.
Add 500 ppm of trimethyl-8-chloro-PX,
Chlorination was carried out at a chlorine injection rate of 1.2 parts/min. The results are shown in Table 1. Examples 1 and 2 are examples in which the average chlorine content of the phenoxatin compound was changed in Reference Example 4, and the reaction liquid compositions in the table below are values quantitatively analyzed by gas chromatography. The average chlorine content refers to the total number of substituted chlorine, and is the average value determined from the chlorine analysis of Reference Example 4. The production rate of m-chlorotoluene, which is difficult to separate from PCT, was quantified under different analysis conditions, and in the case of Example 2, it was about 0.4% relative to PCT.
Furthermore, in Example 2, the amount of benzyl chloride produced in the reaction solution was below the detection limit. Comparative Examples 1 to 5 Various different phenoxatin compounds were synthesized according to the methods described in Reference Examples 1 to 4, and these compounds were further chlorinated. Comparative Examples 1 to 5 were used to compare the cocatalyst ability of the compounds with the cocatalyst of the present invention. 3 in Table 1. In addition, the results using 2,3,7,8-tetrachlorophenoxatin and 3-methyl-2,7,8-trichlorophenoxatin as cocatalysts are shown in Table 1 as Comparative Examples 4 and 5. . The conditions for chlorinating toluene were the same as in Examples 1 and 2. The structure and physical properties of the substituted diphenyl ether used as a raw material are also shown in Table 1.

【table】

[Table] From Table 1, from the comparison of Examples 1 and 2 and Comparative Examples 1 to 3, the necessity of the 6,9-dimethyl-8-chloro substituent and the X that should be included in conjunction with it
It can be seen that the effects vary significantly depending on the presence or absence of the -, R- groups, their positions, and the total number of substituted chlorine groups. Furthermore, from comparison with Comparative Examples 4 and 5, it is clear that the paraselectivity in toluene chlorination is surprisingly improved compared to known cocatalysts. Examples 3 to 6 According to Reference Examples 1 to 4, 2,5-dimethyl-4,
4'-dichlorodiphenyl ether and 2,5,
3′,5′-tetramethyl-4-chlorodiphenyl ether was synthesized, and 6,9-dimethyl-2,8
-dichlorophenoxatin, and 1,3,6,
9-tetramethyl-8-chlorophenoxatin was obtained, and these were further chlorinated and used as a co-catalyst. Table 2 shows the results of chlorinating toluene in the same manner as in Examples 1 and 2. Comparative Example 6 Chlorinated 1, 3,
9-trimethyl-8-chloro-PX from Reference Example 1~
Table 2 shows the results of chlorinating toluene in the same manner as in Examples 1 and 2.

【table】

[Table] From the comparison between Example 5 and Comparative Example 6, it can be seen that the selectivity of PCT varies greatly depending on the presence or absence of the substituent defined in the present invention, such as the methyl group at the 6-position. It was found from Examples 3 and 4 that the cocatalyst of the present invention was more effective in low-temperature chlorination, and from Example 6 that the phenoxatin compound showed a high level of paraselectivity even in the form of a mixture. Examples 7 to 10 Chlorinated 3,6,9-trimethyl-8 obtained by synthesizing 3,6,9-trimethyl-8-chlorophenoxatin and subsequently chlorinating it according to Reference Examples 1 to 4
Toluene was chlorinated in the same manner as in Examples 1 and 2, except that -chloro-PX was used as a promoter and the amount, average chlorine content, type of main catalyst, and reaction temperature were changed. These results are shown in Table 3. Comparative Examples 7 to 9 Chlorinated 3-methyl-PX was synthesized from 3-methyl diphenyl ether according to Reference Examples 1 to 4,
For comparison with Examples 7, 8, and 10, toluene was chlorinated in substantially the same manner as in Examples 7, 8, and 10. These results are also listed in Table 3.

[Table] From the results in Table 3, it can be seen that the promoter of the present invention is
It can be seen that better results were obtained than in the example of No.-013050, and that the selectivity of PCT was significantly improved, especially under the chlorination conditions of the low-temperature reaction.

Claims (1)

[Claims] 1. In the nuclear chlorination of toluene using a Lewis acid as a catalyst, the general formula (In the formula, R represents a methyl group at the 1st and/or 3rd position, m represents an integer of 0 to 2, X represents a chlorine atom when m is 0, and a hydrogen atom when m is 1 to 2. A method for nuclear chlorination of toluene, characterized in that a chlorinated phenoxatin compound having a total substituted chlorine number of 1.4 to 3.5 obtained by chlorinating a phenoxatin compound represented by the following formula is used as a cocatalyst.