JPH0246014B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing 2,6-dihaloalkylbenzene represented by the following general formula.

(In the formula, R ₁ represents an alkyl group, X ₁ and
Each X ₂ represents the same or different halogen atom. ) These compounds include, for example, 2,6-dihaloalkylbenzenes such as 2,6-dichlorotoluene, 2,6-dichloroethylbenzene, 2-chloro-6-bromotoluene, and 2-chloro-6-bromoisopropylbenzene. . Generally, the alkyl group as R ₁ has 1 to 18 carbon atoms, but there is no particular restriction on the number of carbon atoms, and the halogen atoms as X ₁ and X ₂ include fluorine, chlorine,
Contains bromine or iodine.

Among these compounds, various synthetic methods have been studied to date for the production of 2,6-dichlorotoluene, and the main method is to synthesize 2,6-dichlorotoluene from 6-chloro-2-nitrotoluene to 6-chloro-2-amino. A method of producing via toluene; a method of chlorinating para-toluenesulfonic acid or para-toluenesulfonic acid chloride and then desulfonating it (for example, Japanese Patent Publication No. 40-12615, Japanese Patent Publication No. 40-17372); reacting isobutylene with toluene; , 4-tert-butyltoluene and 2-tert-butyltoluene are obtained, and 4-tert-butyl-2,6-dichlorotoluene is obtained by reacting 4-tert-butyltoluene obtained by rectification with chlorine. Methods such as the synthesis of 2,6-dichlorotoluene by dealkylation using sulfuric acid (Japanese Patent Publication No. 39084/1984) are known, but all of these conventional methods require a large number of reaction stages and are complicated. However, since it is difficult to separate the products at each reaction stage, the yield and purity of the target product are poor.

In addition, 2,6
-The synthesis method for dihaloalkylbenzene is not well known, and the desired 2,6-dihaloalkylbenzene cannot be obtained effectively.

In view of the drawbacks of the conventional methods described above, the present invention provides a simple method for producing 2,6-dihaloalkylbenzene that can easily and inexpensively obtain a target product with extremely high yield and high purity. It is something.

To explain in more detail, for example, as a first step, a 4-4-- having a tertiary alkyl group such as a tertiary butyl group or a tertiary amyl group at the para position and a halogen at the 2 position
By introducing a halogen gas such as chlorine or bromine into tertiary alkyl-2-haloalkylbenzene or the like in the presence of a Friedel-Crafts catalyst, 4- Tertiary alkyl-2,6-dihaloalkylbenzene is obtained [formula (1)].

(In the formula, R ₂ represents a tertiary alkyl group.
R ₁ represents an alkyl group, and X, X ₁ and X ₂ represent halogen. ) Next, as a subsequent step, 2-haloalkyl bene is added to the 4-tertiary alkyl compound in which the 2 and 6 positions are halogenated obtained in the halogenation reaction in the first step, and the tertiary alkyl bene is added in the presence of a Friedel-Crafts catalyst. By transalkylating the group, the desired 2,6-dihaloalkylbenzene can be obtained with high selectivity and high yield [formula (2)]. In addition, the 4-tertiaryalkyl-2-haloalkylbenzene produced as a by-product in the transalkylation reaction in the latter stage is recycled as a starting material in the halogenation reaction in the first stage, so the reaction yield is low except for some loss of recycled raw material. This is close to a quantitative value, and in the method of the present invention, the desired 2,6-dihaloalkylbenzene can be obtained by externally supplying halogen and orthohaloalkylbenzene as raw materials. Generally, tertiary alkyl groups as _R2 include those having 4 to 15 carbon atoms, especially 4 or 5 carbon atoms.

The first stage halogenation reaction in the method of the present invention is
Anhydrous ferric chloride, anhydrous aluminum chloride, anhydrous antimony trichloride, anhydrous antimony pentachloride, or iodine is added to 4-tertiaryalkyl-2-haloalkylbenzene as a catalyst, and 0 to 70
This is accomplished by blowing in a halogen gas such as chlorine or bromine at a temperature of 10°C. In order to avoid the formation of trohalo compounds, the reaction needs to be carried out at a relatively low temperature, and it is also important to control the conversion rate by using a smaller equivalent amount of halogen gas than the theoretical amount relative to the raw material.

When introducing fluorine gas, the reaction proceeds explosively, so it is recommended to dilute it with a large excess of inert gas, such as nitrogen or helium, and to use a solvent such as acetonitrile to smoothly remove the reaction heat. good.

The halogenated reaction product obtained in this way is purified by rectification after removing the catalyst.
The 2,6-dihaloalkylbenzene is separated and sent to the subsequent process. The unreacted raw materials recovered at this time are returned to the halogenation reaction in the previous stage. In the present invention, since 4-tertiaryalkyl-2-halobenzene is used, there are extremely few by-products of 2,5-dihalo and trihalo other than the target 2,6-dihalo, so the halogenation reaction product can be directly transferred to the next transalkylation step without being rectified.

In the latter step of the transalkylation in the method of the present invention, a large excess of 2-haloalkylbenzene, equal to or more than the same mole, preferably 2 moles or more, is added to the 4-tertiaryalkyl-2,6-dihaloalkylbenzene, and anhydrous chloride is added as a catalyst. The reaction is carried out in the presence of a Friedel-Crafts catalyst such as ferric iron, anhydrous aluminum chloride, anhydrous antimony trichloride, anhydrous antimony pentachloride, etc., with thorough stirring at room temperature to 100° C. for 1 hour to 12 hours. This transalkylation reaction gives the desired 2,6-dihaloalkylbenzene in extremely high yield, often close to quantitative yield.

After removing the catalyst from the reaction product by washing with water, the oil phase is distilled to obtain the target product, 2,6-dihaloalkylbenzene, and on the other hand, 4-tertiary alkyl-2-haloalkylbenzene is obtained as a by-product. , these by-products can be recycled to the previous halogenation step.

Since the reaction product is used repeatedly in some cases, the reaction product is distilled under reduced pressure at a temperature of 80°C or lower without removing the catalyst, and unreacted 2-haloalkylbenzene is recovered. After the desired 2,6-dihaloalkylbenzene is obtained by rectification, the by-product 4-tertiaryalkyl-2-haloalkylbenzene and catalyst remaining as a residue can be recycled directly to the chlorination process, which is extremely advantageous. It is.

According to the later transalkylation reaction in the method of the present invention, tertiary alkyl groups enter the para position of 2-haloalkylbenzene with extremely high selectivity, and very few enter the ortho position. This selectivity is even better than that of haloalkylbenzenes which do not have a halogen in the ortho position.

The 4-tertiary alkyl 2-haloalkylbenzene, which is the starting material for the first-stage halogenation reaction in the method of the present invention, is produced as a by-product along with the target product in the second-stage reaction (2) as described above, and is recycled to the first-stage reaction (1). However, the insufficient amount can be easily obtained by alkylating a tertiary olefin such as isobutene or isoamylene with 2-haloalkylbenzene in the presence of a Friedel-Crafts catalyst [formula (3)] .

As a catalyst for this alkylation reaction, anhydrous ferric chloride, anhydrous aluminum chloride, anhydrous antimony pentachloride or iodine is used, and the reaction is carried out from 0 to
The reaction is carried out at a low temperature of 30°C, and the reaction product containing a tertiary alkyl group in the ortho position is removed by rectification under reduced pressure to obtain a pure compound having a 4-tertiary alkyl group in the para position. Since the raw material contains a halogen in advance at the 2-position, there is little production of products containing a tertiary alkyl group at the ortho-position.

Although ortho-tertiary alkylated products are not preferred products in the process of the present invention, the orientation of the tertiary alkyl group in the ortho position is the lowest among Friedel-Crafts catalysts when anhydrous ferric chloride is used. The orthotertiary alkylated product removed by fractional distillation can also be converted into the para-form by thermal transformation. However, since this alkylation reaction is only carried out to fill the slight shortage of 4-tertiary alkylated material in the recycled raw material in the method of the present invention, the raw material loss due to the production of ortho-tertiary alkylated product is The overall yield is often not significantly affected. This method is similar to the method of tertiary alkylation of toluene with isobutylene, fractional distillation to separate only the para isomer, chlorination, and dealkylation, as seen in the known method of Japanese Patent Publication No. 46-39084. This is an essentially different point.
In addition, the reaction conditions for the subsequent transalkylation reaction in the method of the present invention are extremely mild;
Although the yield is high, it differs from the harsh reaction using sulfuric acid as seen in such known process dealkylation reactions.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 (Synthesis of 2,6-dichlorotoluene from orthochlorotoluene, Part 1) [Chlorination step] 4-tert-butyl-2-chlorotoluene
Anhydrous ferric chloride 10 was added to 384.2 g, kept at 50°C, and 142 g of chlorine was blown into the reactor. Hydrogen chloride gas produced by the reaction was introduced into water and recovered as hydrochloric acid. The amount of HCl recovered was 72.5g. The reaction product liquid was directly fed into the next transalkylation step without separating the catalyst.

[Transalkylation process]

Add 2000 g of orthochlorotoluene and 400 g of anhydrous ferric chloride to the product obtained in the chlorination step, and heat at 70°C.
I kept it for 4 hours while stirring it. Next, the reaction product was subjected to fractional distillation under reduced pressure without separating the catalyst so that the bottom temperature did not exceed 75°C. First, 1746 g of unreacted orthochlorotoluene was recovered, and then 2,6 g of unreacted orthochlorotoluene was recovered.
-321g of dichlorotoluene distillate was obtained. Purity is 98.5
It was %. The yield calculated from the reacted chlorine is
The yield was 98.2%, and the yield was 97.8% based on the consumed orthochlorotoluene.

The residue was directly chlorinated in the same manner as above, and then orthochlorotoluene was added and the same transalkylation step was carried out, but the yield and purity of the 2,6-dichlorotoluene produced were remained unchanged.

Example 2 (Synthesis of 2,6-dichlorotoluene from orthochlorotoluene, Part 2) [Chlorination step] 4-tertiary amyl-2-chlorotoluene
10 g of anhydrous ferric chloride was added to 413.7 g, and 142 g of chlorine was introduced at 50°C. The generated hydrogen chloride gas was treated in the same manner as in Examples 1 and 2, and the amount of HCl generated was 73g.
It was hot. The reaction product was directly passed on to the next step in the same manner as in Example 2.

4-tertiary amyl-2- used in this process
Chlortoluene was prepared as follows. Isoamylene (2-
700 g of a mixture of methylbutene-1 and 2-methylbutene-2 was reacted at 10°C in the presence of 100 g of anhydrous aluminum chloride, and the product was washed with water and the oil phase was fractionated to obtain 4-tert-amyl-2-chlorotoluene.
Obtained 1670g. The purity was 99%.

[Transalkylation process]

2000 g of orthochlorotoluene and 400 g of anhydrous ferric chloride were added to the liquid product obtained in the chlorination step, and the mixture was stirred and reacted at 70° C. for 7 hours. Next, the reaction product is fractionated under reduced pressure while maintaining the bottom temperature not to exceed 80°C, and the reaction product is distilled into orthochlorotoluene.
1740g was collected. Then, 319 g of 2,6-dichlorotoluene fraction was obtained. Its purity was 99%.
The yield was 98% based on chlorine and 95.4% based on consumed orthochlorotoluene.

Example 3 (from orthochlorotoluene -2-chlor6-
Synthesis of bromotoluene) [Bromation step] 4-tert-butyl-2-chlorotoluene
10 g of anhydrous ferric chloride was added to 384.2 g, and 159.8 g of bromine was introduced in the same manner as in Example 2.

[Transalkylation process]

2000 g of orthochlorotoluene and 400 g of anhydrous ferric chloride were added to the reaction product of the bromination step and treated in the same manner as in Example 2 to obtain 409 g of 2-chloro-6-bromotoluene, the purity of which was 98.5%. 1745g of orthochlorotoluene was recovered.

The yield was 98.1% based on bromine and 97.7% based on orthochlorotoluene.

Claims (1)

[Claims] 1 2,6-dihalide obtained by halogenating 4-tertiaryalkyl-2-haloalkylbenzene in the presence of a Friedel-Crafts catalyst,
A method for producing 2,6-dihaloalkylbenzene, which comprises transalkylating it by bringing it into contact with 2-haloalkylbenzene.