Preparation method of 2, 4-dinitrotoluene

Abstract

The invention relates to a preparation method of 2, 4-dinitrotoluene, and belongs to the technical field of organic synthesis. Comprising the following steps: dissolving toluene in a solvent, dropwise adding a fuming nitric acid solution diluted by using the solvent under the catalysis of concentrated sulfuric acid, and reacting to obtain 2, 4-dinitrotoluene; wherein the molar feeding ratio of the toluene to the fuming nitric acid is 1: (2.1-2.2); the solvent is one of dichloromethane, trichloromethane or dichloroethane. According to the method, fuming nitric acid with the same molar weight is dissolved in the solvent for dilution and then added into methylbenzene for reaction, so that the feeding amount of a nitrating agent can be effectively controlled, and generation of tri-nitration products is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a method for preparing 2,4-dinitrotoluene. Background Art

[0002] 2,4-Dinitrotoluene is an organic compound with the chemical formula C7H6N2O4. It is a light yellow crystalline powder, slightly soluble in water, ethanol, and ether, and easily soluble in benzene and acetone. It is mainly used in organic synthesis.

[0003] At present, the industrial method for preparing 2,4-dinitrotoluene is mainly based on the two-stage nitration method, that is, using toluene as raw material, first preparing a nitration product, and then performing a two-stage nitration to prepare 2,4-dinitrotoluene. The nitration methods are mainly divided into the following categories: 1. Nitration with concentrated nitric acid This type of nitration often requires the use of many times excess nitric acid, which must be utilized or recovered, thus limiting its practical application.

[0004] 2. Homogeneous nitration in concentrated sulfuric acid medium When the nitrated substance or the nitration product is solid at the reaction temperature, the nitrated substance is often dissolved in a large amount of concentrated sulfuric acid, and then a mixture of sulfuric acid and nitric acid is added for nitration. This method only requires a small amount of excess nitric acid and generally has a high yield, but the disadvantage is that the amount of sulfuric acid used is too large.

[0005] 3. Heterogeneous mixed acid nitration When both the nitrified substance and the nitration product are liquid at the reaction temperature, heterogeneous mixed acid nitration is often used. Through strong stirring, the organic phase is dispersed into the acid phase to complete the nitration reaction. This nitration method has many advantages and is currently the most commonly used and important nitration method in industry.

[0006] However, the above methods all have the problem that the product is over-nitrated during the nitration process, resulting in a trinitration product; at the same time, the content of 2,6-dinitrotoluene in the dinitration product is relatively high, which affects the purity of the final product. Summary of the invention

[0007] In view of the problems that trinitration products are easily generated when preparing 2,4-dinitrotoluene by the existing nitration method and the content of isomers is high after purification, the present invention provides a method for preparing 2,4-dinitrotoluene to solve the above problems. The present invention can effectively control the feeding amount of the nitrating agent and avoid the generation of trinitration products by dissolving an equimolar amount of fuming nitric acid in a solvent and diluting the solvent, and then adding the fuming nitric acid into toluene for reaction.

[0008] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing 2,4-dinitrotoluene, comprising dissolving toluene in a solvent, and dropwise adding a fuming nitric acid solution diluted with the solvent under the catalysis of concentrated sulfuric acid to react, so as to obtain 2,4-dinitrotoluene; wherein the molar feed ratio of toluene to fuming nitric acid is 1:(2.1-2.2); and the solvent is one of dichloromethane, chloroform or dichloroethane.

[0009] Further, the specific steps are as follows: (1) Dissolve toluene in a solvent, then add concentrated sulfuric acid, stir and cool to -10~0℃ for later use; (2) Take fuming nitric acid, add solvent to dilute it, stir it evenly, then drip it into the solution in step (1), and after the dripping is complete, bring it to reflux; (3) After the mononitration product disappears as monitored by TLC, the temperature is cooled to room temperature, 5% sodium carbonate aqueous solution is added and stirred, the mixture is allowed to stand for separation, and the organic phase is concentrated under reduced pressure to obtain 2,4-dinitrotoluene.

[0010] Furthermore, the amount of solvent used to dilute the fuming nitric acid is 3-5 ml / ml based on the amount of fuming nitric acid, and the amount of concentrated sulfuric acid used is 0.08-0.12 g / g based on the amount of toluene.

[0011] Furthermore, the amount of solvent used in step (1) is 3-5 ml / g based on the amount of toluene.

[0012] In a second aspect, the present invention also provides a method for refining 2,4-dinitrotoluene, comprising the following steps: after the organic phase is concentrated under reduced pressure to obtain a viscous substance, ethanol is added, heated until it becomes clear, then the temperature is reduced to 50-55°C, water is slowly added, and the temperature is kept warm; after solids are precipitated, the temperature is further reduced to 10-15°C, and 2,4-dinitrotoluene is obtained by solid-liquid separation.

[0013] Furthermore, the amount of ethanol used is 4-8 g / g based on the amount of toluene fed; and the amount of water used is 0.5-1 g / g based on the amount of toluene fed.

[0014] Furthermore, during the heat preservation process, if no solid is precipitated, 2,4-dinitrotoluene seed crystals are added in an amount of 0.5 wt% to 0.8 wt% based on the toluene feed amount.

[0015] Furthermore, the temperature is cooled by a gradient cooling method, and the cooling rate is 8-10°C / h.

[0016] The beneficial effects of the present invention are: The preparation and purification method of 2,4-dinitrotoluene provided by the present invention can effectively control the feeding amount of the nitrating agent and avoid the generation of trinitration products by dissolving an equimolar amount of fuming nitric acid in a solvent and diluting it, and then adding it into toluene for reaction. The present invention also provides a purification method of 2,4-dinitrotoluene, which adopts a specific ratio of ethanol aqueous solution, crystallization at a specific temperature and gradient cooling to effectively remove isomers in the crude product. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0018] Example 1 A method for preparing 2,4-dinitrotoluene, comprising the following steps: (1) Take 92g of toluene and dissolve it in 400ml of chloroform; then add 9.2g of concentrated sulfuric acid, stir evenly, and cool to -10~-5℃.

[0019] (2) Take 90 ml of fuming nitric acid, add 400 ml of cold chloroform, mix well and slowly drip into the chloroform solution of toluene in step (1), and control the temperature of the reaction system to -10~0°C. After the dripping is completed, the reaction system is heated to reflux.

[0020] (3) TLC monitoring of 2-nitrotoluene and 4-nitrotoluene disappears and drops to 20-25°C. Add 500ml of 5% sodium carbonate aqueous solution to the reaction system, and pay attention to the generation of gas during stirring and washing; let the liquid stand for separation, wash the organic phase once with 500ml of water, dry it with anhydrous sodium sulfate, filter it, and distill it under reduced pressure until the system is a viscous solid-liquid mixture. Sample HPLC detection shows that the content of 2,4-dinitrotoluene is 87.96% (area normalized), the content of 2,6-dinitrotoluene is 11.41% (area normalized), and the content of 2,4,6-trinitrotoluene is 0.12% (area normalized).

[0021] (4) Add 460 g of anhydrous ethanol to the concentrate, heat to reflux and dissolve, then cool to 55°C, slowly add 46 g of water, no solid precipitates after the addition, keep warm and stir, solid gradually precipitates after about 20 min, keep warm for 10 min, then slowly cool at a rate of 10°C / h until the temperature drops to 10-15°C; keep warm for 30 min, filter, rinse the filter cake with 95% ethanol, and dry to obtain 151.2 g of 2,4-dinitrotoluene, with a yield of 83.1%; HPLC purity was 99.61% (area normalized), 2,6-dinitrotoluene content was 0.34% (area normalized), and 2,4,6-trinitrotoluene was not detected.

[0022] Example 2 A method for preparing 2,4-dinitrotoluene, comprising the following steps: (1) Take 92g of toluene and dissolve it in 400ml of dichloromethane; then add 9.2g of concentrated sulfuric acid, stir evenly, and cool to -10~-5℃.

[0023] (2) Take 91 ml of fuming nitric acid, add 400 ml of cold dichloromethane, mix well and slowly drip into the dichloromethane solution of toluene in step (1), and control the temperature of the reaction system to -10~0°C. After the addition is completed, the reaction system is heated to reflux.

[0024] (3) TLC monitoring shows that 2-nitrotoluene and 4-nitrotoluene disappear and the temperature drops to 20-25°C. Add 500ml of 5% sodium carbonate aqueous solution to the reaction system, and pay attention to the generation of gas during stirring and washing; let the mixture stand for separation, wash the organic phase once with 500ml of water, dry it with anhydrous sodium sulfate, filter it, and distill it under reduced pressure until the system is a viscous solid-liquid mixture. Samples were taken for HPLC detection, and the content of 2,4-dinitrotoluene was 85.37% (area normalized), the content of 2,6-dinitrotoluene was 12.18% (area normalized), and the content of 2,4,6-trinitrotoluene was 1.67% (area normalized). Due to the low boiling point of dichloromethane, the reaction rate is reduced, the reaction time is prolonged, and the content of trinitration products increases.

[0025] (4) 460 g of anhydrous ethanol was added to the concentrate, and the mixture was heated to reflux and dissolved. The mixture was then cooled to 55°C and 46 g of water was slowly added. No solid was precipitated after the addition. The mixture was stirred for 30 min and no solid was precipitated. 0.5 g of 2,4-dinitrotoluene was added and the mixture was stirred for 30 min. Solid was precipitated. The mixture was stirred for 10 min and the temperature was slowly reduced at a rate of 10°C / h until the temperature reached 10-15°C. The mixture was filtered after 30 min of heating. The filter cake was rinsed with 95% ethanol and dried to obtain 141.4 g of 2,4-dinitrotoluene with a yield of 77.7%. The purity was 99.46% (area normalized) according to HPLC. The content of 2,6-dinitrotoluene was 0.47% (area normalized) and no 2,4,6-trinitrotoluene was detected.

[0026] Example 3 A method for preparing 2,4-dinitrotoluene, comprising the following steps: (1) Take 92g of toluene and dissolve it in 400ml of dichloroethane; then add 9.2g of concentrated sulfuric acid, stir evenly, and cool to -10~-5℃.

[0027] (2) Take 90 ml of fuming nitric acid, add 400 ml of cold dichloroethane, mix well and then slowly drip into the dichloroethane solution of toluene in step (1), and control the temperature of the reaction system to -10~0°C. After the dripping is completed, the reaction system is heated to reflux.

[0028] (3) TLC monitoring of 2-nitrotoluene and 4-nitrotoluene disappears and drops to 20-25°C. Add 500ml of 5% sodium carbonate aqueous solution to the reaction system, and pay attention to the generation of gas during stirring and washing; let the liquid stand for separation, wash the organic phase once with 500ml of water, dry it with anhydrous sodium sulfate, filter it, and distill it under reduced pressure until the system is a viscous solid-liquid mixture. Sample HPLC detection, 2,4-dinitrotoluene content is 87.63% (area normalized), 2,6-dinitrotoluene content is 11.46% (area normalized), 2,4,6-trinitrotoluene content is 0.15% (area normalized).

[0029] (4) Add 460 g of anhydrous ethanol to the concentrate, heat to reflux and dissolve, then cool to 55°C, slowly add 46 g of water, no solid precipitates after the addition, keep warm and stir, solid gradually precipitates after about 15 minutes, keep warm for 10 minutes, then slowly cool at a rate of 10°C / h until the temperature drops to 10-15°C; keep warm for 30 minutes and filter, rinse the filter cake with 95% ethanol, and dry to obtain 151.5 g of 2,4-dinitrotoluene, with a yield of 83.2%; HPLC purity was 99.55% (area normalized), 2,6-dinitrotoluene content was 0.36% (area normalized), and 2,4,6-trinitrotoluene was not detected.

[0030] Example 4 A method for preparing 2,4-dinitrotoluene, comprising the following steps: (1) Take 5.0 kg of toluene and dissolve it in 25 L of chloroform; then add 500 g of concentrated sulfuric acid, stir evenly, and cool to -10~-5°C.

[0031] (2) Take 7.32 kg of fuming nitric acid, add 25 L of cold chloroform, mix well and slowly add to the chloroform solution of toluene in step (1), and control the temperature of the reaction system to -10~0°C. After the addition is completed, the reaction system is heated to reflux.

[0032] (3) TLC monitoring shows that 2-nitrotoluene and 4-nitrotoluene disappear and the temperature drops to 20-25°C. Add 40L of 5% sodium carbonate aqueous solution to the reaction system, and pay attention to the generation of gas during stirring and washing; let the liquid stand for separation, wash the organic phase once with 40L of water, dry it with anhydrous sodium sulfate, filter it, and distill it under reduced pressure until the system is a viscous solid-liquid mixture. Samples were taken for HPLC detection, and the content of 2,4-dinitrotoluene was 87.44% (area normalized), the content of 2,6-dinitrotoluene was 11.62% (area normalized), and the content of 2,4,6-trinitrotoluene was 0.19% (area normalized).

[0033] (4) Add 20 kg of anhydrous ethanol to the concentrate, heat to reflux and dissolve, then cool to 55°C, slowly add 2.5 kg of water, no solid precipitates after the addition, keep warm and stir, solid gradually precipitates after about 15 minutes, keep warm for 10 minutes, then slowly cool at a rate of 10°C / h until the temperature drops to 10-15°C; keep warm for 30 minutes and filter, rinse the filter cake with 95% ethanol, and dry to obtain 8.2 kg of 2,4-dinitrotoluene, with a yield of 83.0%; HPLC purity was 99.57% (area normalized), 2,6-dinitrotoluene content was 0.34% (area normalized), and 2,4,6-trinitrotoluene was not detected.

[0034] Example 5 A method for preparing 2,4-dinitrotoluene, comprising the following steps: (1) Take 20.0 kg of toluene and dissolve it in 100 L of chloroform; then add 2.0 kg of concentrated sulfuric acid, stir evenly, and cool to -10~-5°C.

[0035] (2) Take 29 kg of fuming nitric acid, add 100 L of cold chloroform, mix well and then slowly add to the chloroform solution of toluene in step (1), and control the temperature of the reaction system to -10~0°C. After the addition is completed, the reaction system is heated to reflux.

[0036] (3) TLC monitoring shows that 2-nitrotoluene and 4-nitrotoluene disappear and the temperature drops to 20-25°C. Add 170L of 5% sodium carbonate aqueous solution to the reaction system, and pay attention to the generation of gas during stirring and washing; let the liquid stand for separation, wash the organic phase once with 150L of water, dry it with anhydrous sodium sulfate, filter it, and distill it under reduced pressure until the system is a viscous solid-liquid mixture. Samples were taken for HPLC detection, and the content of 2,4-dinitrotoluene was 87.50% (area normalized), the content of 2,6-dinitrotoluene was 11.54% (area normalized), and the content of 2,4,6-trinitrotoluene was 0.21% (area normalized).

[0037] (4) Add 80 kg of anhydrous ethanol to the concentrate, heat to reflux and dissolve, then cool to 55°C, slowly add 10 kg of water, no solid precipitates after the addition, keep warm and stir, solid gradually precipitates after about 25 minutes, keep warm for 10 minutes, then slowly cool at a rate of 10°C / h until the temperature drops to 10-15°C; keep warm for 30 minutes and filter, rinse the filter cake with 95% ethanol, and dry to obtain 32.9 kg of 2,4-dinitrotoluene, with a yield of 83.3%; HPLC purity was 99.60% (area normalized), 2,6-dinitrotoluene content was 0.33% (area normalized), and 2,4,6-trinitrotoluene was not detected.

[0038] It can be seen from Examples 1 to 5 that as the reaction scale is expanded, the product yield and purity are not affected, and the preparation process of the present invention is stable.

[0039] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A method for preparing 2,4-dinitrotoluene, characterized in that: Toluene is dissolved in a solvent, and under the catalysis of concentrated sulfuric acid, a fuming nitric acid solution diluted with a solvent is added dropwise to react to obtain 2,4-dinitrotoluene; wherein the molar feed ratio of toluene to fuming nitric acid is 1:(2.1-2.2); and the solvent is one of dichloromethane, chloroform or dichloroethane.

2. A method for preparing 2,4-dinitrotoluene as claimed in claim 1, characterized in that: The specific steps are as follows: (1) Dissolve toluene in a solvent, then add concentrated sulfuric acid, stir and cool to -10~0℃ for later use; (2) Take fuming nitric acid, add solvent to dilute it, stir it evenly, then drip it into the solution in step (1), and after the dripping is complete, bring it to reflux; (3) After the mononitration product disappears as monitored by TLC, the temperature is cooled to room temperature, 5% sodium carbonate aqueous solution is added and stirred, the mixture is allowed to stand for separation, and the organic phase is concentrated under reduced pressure to obtain 2,4-dinitrotoluene.

3. A method for preparing 2,4-dinitrotoluene as claimed in claim 2, characterized in that: The amount of solvent used in step (1) is 3-5 ml / g based on the amount of toluene.

4. A method for preparing 2,4-dinitrotoluene as claimed in claim 2, characterized in that: The amount of solvent used to dilute the fuming nitric acid is 3-5 ml / ml based on the amount of fuming nitric acid, and the amount of concentrated sulfuric acid used is 0.08-0.12 g / g based on the amount of toluene.

5. A method for preparing 2,4-dinitrotoluene as claimed in claim 1, characterized in that: The preparation method of 2,4-dinitrotoluene also includes a refining method, and the specific steps are as follows: after the organic phase is concentrated under reduced pressure to obtain a viscous substance, ethanol is added, heated until it becomes clear, then the temperature is lowered to 50-55°C, water is added, and the temperature is kept warm; after solids are precipitated, the temperature is further lowered to 10-15°C, and 2,4-dinitrotoluene is obtained by solid-liquid separation.

6. A method for preparing 2,4-dinitrotoluene as claimed in claim 5, characterized in that: The amount of ethanol used is 4-8 g / g based on the amount of toluene added; the amount of water used is 0.5-1 g / g based on the amount of toluene added.

7. The method for preparing 2,4-dinitrotoluene as claimed in claim 5, characterized in that: During the heat preservation process, 2,4-dinitrotoluene seed crystals are added in an amount of 0.5wt% to 0.8wt% based on the toluene feed amount.

8. A method for preparing 2,4-dinitrotoluene as claimed in claim 5, characterized in that: The temperature is cooled by gradient cooling method, and the cooling rate is 8~10℃ / h.