Method for directionally preparing 2, 6-dichlorotoluene

Abstract

The invention relates to a method for directionally preparing 2, 6-dichlorotoluene, and belongs to the technical field of dichlorotoluene preparation. The catalyst is aluminum trichloride and ferric trichloride composite metal salt ionic liquid, and has higher stability and low hygroscopicity compared with chloroaluminate ionic liquid. The composite ionic liquid reacts with chlorine to generate an aluminum trichloride-based chloride positive ion active intermediate B and an ionic liquid A, the intermediate B and o-chlorotoluene are subjected to electrophilic substitution to generate 2, 6-dichlorotoluene and release aluminum trichloride, and the ionic liquid A and aluminum trichloride form a composite metal salt ionic liquid to complete catalytic circulation. After the composite metal salt ionic liquid is applied to chlorine chlorination with o-chlorotoluene as a raw material, the proportion of 2, 6-dichlorotoluene in a mixed dichlorotoluene product is effectively increased, the content of 2, 6-dichlorotoluene reaches 37% at most, and the catalyst can be repeatedly used.

Description

Technical Field

[0001] The invention relates to a method for directional preparation of 2,6-dichlorotoluene, and belongs to the technical field of dichlorotoluene preparation. Background Art

[0002] At present, 2,6-dichlorotoluene is an important organic raw material intermediate, widely used as a fine chemical intermediate for pesticides, dyes and medicines. 2,6-dichlorotoluene is used as a raw material to synthesize 2,6-dichlorobenzaldehyde and 2,6-dichlorobenzonitrile derivatives, which are used in the pharmaceutical industry to synthesize dicloxacillin sodium, in the pesticide industry to synthesize herbicides dichlorvos and insecticides dichlorvos, and in the dye industry to synthesize the dye acid mordant blue B.

[0003] The synthesis of 2,6-dichlorotoluene in industry usually uses toluene or o-chlorotoluene as the starting material, chlorine gas as the chlorine source, iron powder or Lewis acid such as ferric chloride as the catalyst, and introduces a positioning group on the benzene ring or adds an auxiliary catalyst to obtain the product under appropriate conditions. JP2002154994 A uses toluene as the raw material, antimony pentachloride catalyzes the chlorination reaction, and the selectivity of 2,6-dichlorotoluene is 23.5%. JP2002154995 A uses toluene as the raw material, aluminum chloride catalyzes the chlorination reaction, the catalyst dosage is 10%, and the selectivity of 2,6-dichlorotoluene is 22.4%. EP334025A1 reports a method for synthesizing 2,6-dichlorotoluene by continuous catalytic chlorination using toluene as raw material. While generating 2,6-dichlorotoluene, four other isomers of dichlorotoluene are also generated, namely 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene and 3,4-dichlorotoluene, among which the selectivity of 2,6-dichlorotoluene is very low. Patent CN105481635 A uses o-chlorotoluene as raw material, ferrous sulfide and aluminum chloride as combined catalytic chlorination reaction, and CN105439807 A uses o-chlorotoluene as raw material, manganese and aluminum chloride as combined catalytic chlorination reaction, but neither gives the yield or selectivity of 2,6-dichlorotoluene. These methods have the disadvantages of low selectivity of 2,6-dichlorotoluene and large amount of catalyst. The patent (CN107867969 A) uses C12 as a chlorinating agent, and in the presence of a catalyst chloroaluminate ionic liquid, ortho-chlorotoluene is directed to chlorinate to obtain 2,6-dichlorotoluene. However, the chloroaluminate ionic liquid has the problem of easy water absorption and poor stability.

[0004] In view of the above-mentioned defects, the present invention aims to create a method for directional preparation of 2,6-dichlorotoluene, so as to make it more valuable for industrial utilization. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a method for directional preparation of 2,6-dichlorotoluene.

[0006] The invention discloses a method for directional preparation of 2,6-dichlorotoluene, which uses o-chlorotoluene as a raw material, composite metal salt ionic liquid as a catalyst, and introduces chlorine gas at a certain reaction temperature and reaction time to carry out chlorination reaction to obtain the 2,6-dichlorotoluene.

[0007] Furthermore, the composite metal salt ionic liquid is prepared from alkyl-substituted imidazole chloride and two metal chlorides.

[0008] Furthermore, the alkyl substituted imidazole chloride is 1-butyl-3-methylimidazolium chloride or 1-ethyl-3-methylimidazolium chloride.

[0009] Furthermore, one of the two metal chlorides is aluminum chloride, and the other is ferric chloride.

[0010] Furthermore, the mass ratio of the alkyl-substituted imidazole chloride to the two metal chlorides in the composite metal salt ionic liquid is 1:1 to 1:2.

[0011] Furthermore, the mass ratio of aluminum chloride to ferric chloride in the composite metal salt ionic liquid is 5:1 to 10:1.

[0012] Furthermore, during the chlorination reaction, the amount of the composite metal-based ionic liquid used is 0.05-0.5% of the mass of the o-chlorotoluene solution.

[0013] Furthermore, the reaction temperature of the chlorination reaction is 30-50°C.

[0014] Furthermore, the reaction time of the chlorination reaction is 2 to 6 hours.

[0015] By means of the above scheme, the present invention has at least the following advantages:

[0016] The catalyst of the present invention is a composite metal salt ionic liquid generated by the reaction of alkyl substituted imidazole chloride with two metal chlorides, aluminum chloride and ferric chloride. The composite ionic liquid reacts with chlorine to generate aluminum chloride-based chloride cation active intermediate B and ionic liquid A, and intermediate B then undergoes electrophilic substitution with o-chlorotoluene to generate 2,6-dichlorotoluene and release aluminum chloride, while ionic liquid A and aluminum chloride form a composite metal salt ionic liquid to complete the catalytic cycle. Compared with chloroaluminate ionic liquid, it has higher stability and low hygroscopicity. Compared with simple aluminum chloride and other metal chloride catalysts that need to be hydrolyzed and removed after the reaction, the ionic liquid can be reused many times, reducing the three wastes. After the composite metal salt ionic liquid is applied to chlorine chlorination with o-chlorotoluene as raw material, it effectively increases the proportion of 2,6-dichlorotoluene in the mixed dichlorotoluene product, and the content of 2,6-dichlorotoluene reaches up to 37%. The specific mechanism is as follows:

[0017]

[0018] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show a certain embodiment of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 is a gas chromatogram of the reaction product of Example 1 of the present invention;

[0021] Figure 2 is a gas chromatogram of the reaction product of Example 2 of the present invention;

[0022] Figure 3 It is the gas chromatogram of the reaction product of Example 3 of the present invention. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0024] (1) Preparation of composite metal-based ionic liquid catalysts

[0025] Add 5.00 g of 1-butyl-3-methylimidazolium chloride, 5.03-8.12 g of anhydrous aluminum chloride, and 1.00-1.22 g of anhydrous ferric chloride to a reaction bottle with a venting device, slowly raise the temperature to 120°C under nitrogen flow, and stir and react for 4-6 hours to obtain a dark purple clear solution;

[0026] (2) Directed preparation of 2,6-dichlorotoluene

[0027] Add 30 mL of o-chlorotoluene solution into a reaction bottle with a ventilation device. Under the condition of nitrogen passing, add 150 mg of the above-obtained dark purple clear solution into the reaction bottle. After the addition is completed, slowly pass chlorine into the reaction bottle to react for 3 to 4 hours. During the chlorine passing process, the temperature of the reaction bottle is controlled at 40 to 45°C. During the reaction, samples are taken for gas chromatography monitoring. After the reaction is completed, stirring is stopped, the reaction mixture is allowed to stand, and the upper layer reaction mixture and the lower layer ionic liquid are separated, and the reaction mixture is sampled and analyzed.

[0028] Preparation Example

[0029] Preparation Example 1 of Composite Metal-Based Ionic Liquid Catalyst

[0030] Add 5.00 g of 1-butyl-3-methylimidazolium chloride, 5.03 g of anhydrous aluminum chloride, and 1.00 g of anhydrous ferric chloride to the reaction flask, slowly raise the temperature to 120°C under nitrogen, and keep the temperature for 4 hours to obtain a dark purple clear solution.

[0031] Preparation Example 2 of Composite Metal-Based Ionic Liquid Catalyst

[0032] Add 5.00 g of 1-butyl-3-methylimidazolium chloride, 8.00 g of anhydrous aluminum chloride, and 1.22 g of anhydrous ferric chloride to the reaction flask, slowly raise the temperature to 120°C under nitrogen, and keep the temperature for 4 hours to obtain a dark purple clear solution.

[0033] Example

[0034] Example 1

[0035] Under the condition of nitrogen gas passing, 150 mg of the composite metal-based ionic liquid prepared in Preparation Example 1 was added to the reaction bottle, added to 30 ml of o-chlorotoluene solution, and chlorine was evenly and slowly passed for about 3 hours. The temperature of the chlorination process was controlled at 40-45°C. During the reaction, samples were taken for gas chromatography monitoring. After the reaction was completed, stirring was stopped and the reaction mixture was allowed to stand to separate the upper reaction mixture and the lower ionic liquid. The upper chlorination reaction liquid was analyzed by gas chromatography, and the test results were as follows: the conversion rate of o-chlorotoluene was 56.5%, and among the four dichlorotoluene mixtures generated, 2,6-dichlorotoluene accounted for 36.82%. The specific results are shown in Table 1. The gas chromatogram is shown in Figure 1 .

[0036] Example 2

[0037] The lower layer of ionic liquid after the reaction in Example 1 was added to 30 ml of o-chlorotoluene solution, and chlorine gas was introduced again according to the method in Example 1 for reaction. The upper layer of chlorination reaction liquid was analyzed by gas chromatography, and the test results were as follows: the conversion rate of o-chlorotoluene was 53.74%, and among the four dichlorotoluene mixtures generated, 2,6-dichlorotoluene accounted for 35.79%. The specific results are shown in Table 1. The gas chromatogram is shown in Figure 2 .

[0038] Example 3

[0039] The lower layer of ionic liquid after the reaction in Example 2 was added to 30 ml of o-chlorotoluene solution, and chlorine gas was introduced again according to the method in Example 1. The upper layer of chlorination reaction liquid was analyzed by gas chromatography, and the test results were as follows: the conversion rate of o-chlorotoluene was 57.85%, and among the four dichlorotoluene mixtures generated, 2,6-dichlorotoluene accounted for 35.27%. The specific results are shown in Table 1. The gas chromatogram is shown in Figure 3 .

[0040] Example 4

[0041] Under nitrogen gas flow conditions, 50 mg of the composite metal-based ionic liquid prepared in Preparation Example 1 was added to a reaction bottle, added to 30 ml of o-chlorotoluene solution, and chlorine was evenly and slowly introduced for about 3 hours. The temperature of the chlorination process was controlled at 40-45 ° C. During the reaction, samples were taken for gas chromatography monitoring. After the reaction was completed, stirring was stopped, and the reaction mixture was allowed to stand to separate the upper layer and the lower layer of ionic liquid. The upper layer of chlorination reaction liquid was analyzed by gas chromatography, and the test results were as follows: the conversion rate of o-chlorotoluene was 55.72%, and 2,6-dichlorotoluene accounted for 35.45% of the four dichlorotoluene mixtures generated. The specific results are shown in Table 1.

[0042] Example 5

[0043] Under nitrogen gas flow conditions, 50 mg of the composite metal-based ionic liquid prepared in Preparation Example 2 was added to a reaction bottle, added to 30 ml of o-chlorotoluene solution, and chlorine was evenly and slowly introduced for about 3 hours. The temperature of the chlorination process was controlled at 40-45 ° C. During the reaction, samples were taken for gas chromatography monitoring. After the reaction was completed, stirring was stopped, and the reaction mixture was allowed to stand to separate the upper layer and the lower layer of ionic liquid. The upper layer of chlorination reaction liquid was analyzed by gas chromatography, and the test results were as follows: the conversion rate of o-chlorotoluene was 60.97%, and among the four dichlorotoluene mixtures generated, 2,6-dichlorotoluene accounted for 35.10%, and the specific results are shown in Table 1.

[0044] Comparative Example

[0045] Comparative Example 1

[0046] Add 5.00 g of 1-butyl-3-methylimidazolium chloride and 8.12 g of anhydrous aluminum chloride into the reaction flask, slowly raise the temperature to 120°C under nitrogen, and keep warm for 4 hours to obtain a dark purple clear solution, which is an aluminum chloride-based ionic liquid.

[0047] Under nitrogen gas flow conditions, 300 mg of aluminum chloride-based ionic liquid was added to the reaction bottle, added to 30 ml of o-chlorotoluene solution, and chlorine was evenly and slowly introduced for about 3 hours. The temperature of the chlorination process was controlled at 40-45 ° C. During the reaction, samples were taken for gas chromatography monitoring. After the reaction was completed, stirring was stopped, and the reaction mixture was allowed to stand to separate the upper layer. The upper chlorination reaction liquid was analyzed by gas chromatography, and the test results were as follows: the conversion rate of o-chlorotoluene was 58.56%, and among the four dichlorotoluene mixtures generated, 2,6-dichlorotoluene accounted for 34.90%. The specific results are shown in Table 1.

[0048] Comparative Example 2

[0049] Add 5.00 g of 1-butyl-3-methylimidazolium chloride and 8.12 g of anhydrous aluminum chloride into the reaction flask, slowly raise the temperature to 120°C under nitrogen, and keep warm for 4 hours to obtain a dark purple clear solution, which is a chloroaluminate ionic liquid.

[0050] Under nitrogen gas flow conditions, 100 mg of the aluminum chloride-based ionic liquid was added to a reaction bottle, added to 30 ml of o-chlorotoluene solution, and chlorine was evenly and slowly introduced for about 3 hours. The temperature of the chlorination process was controlled at 40-45°C. During the reaction, samples were taken for gas chromatography monitoring. After the reaction was completed, stirring was stopped, and the reaction mixture was allowed to stand to separate the upper layer. The upper chlorination reaction liquid was analyzed by gas chromatography, and the test results were as follows: the conversion rate of o-chlorotoluene was 56.88%, and among the four dichlorotoluene mixtures generated, 2,6-dichlorotoluene accounted for 26.20%. The specific results are shown in Table 1.

[0051] Table 1 Gas phase analysis results

[0052]

[0053]

[0054] As can be seen from Table 1, in Examples 1-5 of the present invention, aluminum chloride and ferric chloride composite metal ionic liquid are used to catalyze the chlorination of o-chlorotoluene, and the proportion of 2,6-dichlorotoluene in the mixed dichlorotoluene is significantly higher. It can be seen from Examples 1-3 that the ionic liquid can be reused at least three times, and the selectivity of 2,6-dichlorotoluene is not significantly reduced. When the comparative example uses aluminum chloride ionic liquid as the catalyst, the selectivity of 2,6-dichlorotoluene is better when the dosage is large, but lower than that of the composite ionic liquid, and the selectivity is very poor when the dosage is small. This confirms that the present invention

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for directional preparation of 2,6-dichlorotoluene, characterized in that: The product is obtained by taking o-chlorotoluene as raw material and composite metal salt ionic liquid as catalyst and introducing chlorine gas at a certain reaction temperature and reaction time to carry out chlorination reaction.

2. A method for directional preparation of 2,6-dichlorotoluene according to claim 1, characterized in that: The composite metal salt ionic liquid is prepared from alkyl substituted imidazole chloride and two metal chlorides.

3. A method for directional preparation of 2,6-dichlorotoluene according to claim 2, characterized in that: The alkyl substituted imidazole chloride is 1-butyl-3-methylimidazolium chloride or 1-ethyl-3-methylimidazolium chloride.

4. The method for directional preparation of 2,6-dichlorotoluene according to claim 1, characterized in that: One of the two metal chlorides is aluminum chloride, and the other is ferric chloride.

5. The method for directional preparation of 2,6-dichlorotoluene according to claim 1, characterized in that: The mass ratio of the alkyl substituted imidazole chloride to the two metal chlorides in the composite metal salt ionic liquid is 1:1 to 1:

2.

6. The method for directional preparation of 2,6-dichlorotoluene according to claim 1, characterized in that: The mass ratio of aluminum chloride to ferric chloride in the composite metal salt ionic liquid is 5:1 to 10:

1.

7. The method for directional preparation of 2,6-dichlorotoluene according to claim 1, characterized in that: The amount of the composite metal-based ionic liquid used in the chlorination reaction is 0.05-0.5% of the mass of the o-chlorotoluene solution.

8. The method for directional preparation of 2,6-dichlorotoluene according to claim 1, characterized in that: The reaction temperature of the chlorination reaction is 30-50°C.

9. The method for directional preparation of 2,6-dichlorotoluene according to claim 1, characterized in that: The reaction time of the chlorination reaction is 2 to 6 hours.

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