A method for synthesizing 4-toluidine-2-sulfonic acid

Abstract

This invention discloses a method for synthesizing 4-toluidine-2-sulfonic acid. The method includes: (1) dissolving p-toluidine in a solvent to obtain a p-toluidine solution; (2) adding sulfuric acid dropwise to the p-toluidine solution, and obtaining a slurry after a salt-forming reaction; (3) filtering the slurry and taking the filter cake; (4) sulfonating the filter cake to obtain 4B acid. In this invention, the salt-forming reaction occurs in a solvent, and the salt particles are very fine. However, after the salt-forming reaction, the filtrate needs to be filtered out, and only the filter cake is retained for the sulfonation reaction. At this time, there is very little solvent in the sulfonation reaction system, which will not affect the system temperature rise and saves the solvent removal time after the sulfonation reaction. At the same time, the fine salt particles ensure that the sulfonation reaction is carried out fully and that there is no serious carbonization, thus ensuring the purity and quality of the product. Since the impurities in the p-toluidine raw material are removed in step (3), the purity requirement of the p-toluidine raw material is reduced.

Description

Technical Field

[0001] This invention belongs to the field of chemistry, specifically relating to a method for synthesizing 4-toluidine-2-sulfonic acid. Background Technology

[0002] 4-Toluidine-2-sulfonic acid is a dye intermediate. Coupled with 2,3-acid, it can produce Pigment Red 6B and Lissole Red BK; coupled with 2-naphthol, it can produce Pigment Yellow Brilliant Red BL. These pigments are widely used in coloring inks, plastics, rubber, wires and cables, and daily chemical products.

[0003] The synthesis of 4-toluidine-2-sulfonic acid typically uses p-toluidine and sulfuric acid as raw materials, and currently there are two synthesis processes: the high-temperature baking and transposition method and the solvent method. The high-temperature baking and transposition method involves first adding a small amount of water to p-toluidine with a purity of 99.5% or higher, heating to dissolve the p-toluidine, then adding a measured amount of sulfuric acid dropwise. The mixture is then kept at 120-130℃ for 1-3 hours to react and generate an acidic sulfate. Subsequently, the mixture is dehydrated under reduced pressure and baked at 180-230℃ for 3-4 hours to convert the acidic sulfate into stable 4-toluidine-2-sulfonic acid through intramolecular rearrangement.

[0004] The solvent method involves first adding sufficient solvent to p-toluidine with a purity of 99.5% or higher, heating to dissolve the p-toluidine, then adding a measured amount of sulfuric acid dropwise, followed by holding at 120-130℃ for 1-3 hours to form a salt, and finally holding at 180-190℃ for 3-4 hours under reduced pressure to induce a sulfonation reaction, and finally removing the solvent (requiring at least 8 hours) to obtain 4-toluidine-2-sulfonic acid.

[0005] High-temperature baking and solvent methods each have their advantages and disadvantages: (1) The material obtained after dehydration under reduced pressure in the high-temperature baking method is in the form of lumps or large particles. During the sulfonation reaction in the high-temperature baking method, not only can the interior of the lumps or large particles not be fully sulfonated, but the exterior of the lumps or large particles is in contact with the heat source for a long time, resulting in carbonization of the product. This results in the final 4-toluidine-2-sulfonic acid product having insufficient purity and poor quality. (2) Although the solvent method has a solvent to protect the product from carbonization, the presence of the solvent not only leads to slow heating, but also requires a long desolventization process after the sulfonation reaction is completed, which takes too long. (3) Both the high-temperature baking and solvent methods require the purity of p-toluidine raw material to reach more than 99.5%, resulting in higher raw material costs. Summary of the Invention

[0006] The purpose of this invention is to provide a method for synthesizing 4-toluidine-2-sulfonic acid, which has relatively low requirements for the purity of p-toluidine raw materials, and shortens the time consumption while ensuring product purity.

[0007] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0008] A method for synthesizing 4-toluidine-2-sulfonic acid, the method comprising the following steps:

[0009] (1) Dissolve p-toluidine in a solvent to obtain a p-toluidine solution;

[0010] (2) Add sulfuric acid dropwise to the p-toluidine solution, and obtain the slurry after the salt formation reaction;

[0011] (3) Filter the slurry and collect the filter cake;

[0012] (4) The filter cake is subjected to sulfonation to obtain the 4-toluidine-2-sulfonic acid.

[0013] This invention organically combines the existing high-temperature baking and displacement method with the solvent method. Steps (1) and (2) are the same as the solvent method, in which a salt-forming reaction occurs in the solvent, resulting in very fine salt particles in the slurry. However, in this invention, the filtrate needs to be filtered out after the salt-forming reaction, and only the filter cake (i.e., the salt particles) is retained to enter the next step of the sulfonation reaction. At this time, there is very little solvent in the sulfonation reaction system, which will not affect the temperature rise of the system on the one hand, and greatly saves the solvent removal time after the sulfonation reaction on the other hand. At the same time, the fine salt particles ensure that the sulfonation reaction is carried out fully and that there is no serious carbonization, thus ensuring the purity and quality of the product.

[0014] Since most of the impurities in the p-toluidine raw material are present in the filtrate, they will be removed in step (3). Therefore, the purity requirements of the p-toluidine raw material are not high in this invention, as long as it is not less than 98%.

[0015] Preferably, in step (1) of the above-described method for synthesizing 4-toluidine-2-sulfonic acid, the solvent is selected from C2-C7 alcohol solvents. Such solvents are more effective at dissolving impurities in the p-toluidine raw material.

[0016] As a further preferred embodiment, in step (1) of the above-mentioned method for synthesizing 4-toluidine-2-sulfonic acid, the solvent is selected from at least one of isopropanol, propanol, and n-butanol.

[0017] Preferably, in step (2) of the above-mentioned method for synthesizing 4-toluidine-2-sulfonic acid, the molar ratio of p-toluidine to sulfuric acid is 1:(1-1.05).

[0018] Preferably, in step (2) of the above-mentioned method for synthesizing 4-toluidine-2-sulfonic acid, the salt formation reaction is carried out at 60-100°C for 1-3 h.

[0019] Preferably, in step (3) of the above-mentioned method for synthesizing 4-toluidine-2-sulfonic acid, the slurry is subjected to vacuum filtration. Vacuum filtration results in faster filtration speed, drier filter cake, and more thorough solid-liquid separation.

[0020] Preferably, in step (3) of the above-mentioned method for synthesizing 4-toluidine-2-sulfonic acid, the filter cake is washed with a solvent to effectively remove impurities from the p-toluidine raw material.

[0021] Preferably, in step (3) of the above-mentioned method for synthesizing 4-toluidine-2-sulfonic acid, the sulfonation reaction is carried out at 180-190°C for 3-4 h.

[0022] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0023] 1. This invention organically combines the existing high-temperature baking and displacement method with the solvent method. Steps (1) and (2) are the same as the solvent method, in which a salt-forming reaction occurs in the solvent, making the salt particles in the slurry very fine. However, in this invention, after the salt-forming reaction is completed, the filtrate needs to be filtered out, and only the filter cake (i.e., the salt particles) is retained to enter the next step of the sulfonation reaction. At this time, there is very little solvent in the sulfonation reaction system, which will not affect the temperature rise of the system on the one hand, and greatly saves the solvent removal time after the sulfonation reaction on the other hand. At the same time, the fine salt particles ensure that the sulfonation reaction is carried out fully and that there is no serious carbonization, thus ensuring the purity and quality of the product.

[0024] 2. In this invention, since most of the impurities in the p-toluidine raw material are present in the filtrate, they will be removed in step (3). Therefore, this invention does not have high requirements for the purity of the p-toluidine raw material, as long as it is not lower than 98%.

[0025] 3. The reaction time of the synthesis method of the present invention is comparable to that of the conventional high-temperature baking and transposition method, while the product quality is comparable to or even better than that of the conventional solvent method. It combines the advantages of both methods and has broad application prospects. Detailed Implementation

[0026] The following examples illustrate the technical solution of the present invention in a more detailed manner.

[0027] Example 1

[0028] This embodiment describes a method for synthesizing 4-toluidine-2-sulfonic acid, which includes the following steps:

[0029] (1) Dissolve p-toluidine in a solvent to obtain a p-toluidine solution;

[0030] Specifically, 50g of 99% p-toluidine and 150g of isopropanol were added to a 500ml three-necked flask, heated to 40℃ and stirred to dissolve, thus obtaining a p-toluidine solution.

[0031] (2) Add sulfuric acid dropwise to the p-toluidine solution, and obtain the slurry after the salt formation reaction;

[0032] Specifically, 46.3g of 98% concentrated sulfuric acid was slowly added dropwise using a constant pressure funnel over a period of 30 minutes. The temperature inside the vessel was then raised to 70°C using a heating mantle and maintained for 2 hours to obtain the filter slurry.

[0033] (3) Filter the slurry and collect the filter cake;

[0034] Specifically, the filter cake was filtered out using a Buchner funnel and then rinsed twice with 50g of isopropanol.

[0035] (4) The filter cake is subjected to a sulfonation reaction to obtain 4-toluidine-2-sulfonic acid of this embodiment;

[0036] Specifically, the filter cake was transferred to a 500ml flask, heated and stirred in an oil bath to 180°C for baking, and the exhaust gas was depressurized to -0.08Mpa using a vacuum pump to dehydrate it. The reaction was kept at this temperature for 3 hours to obtain 4-toluidine-2-sulfonic acid of this embodiment.

[0037] In this example, 83.5 g of 4-toluidine-2-sulfonic acid was prepared. The sample analysis showed that the whiteness was 75, the amino value was 98.37%, and the purity was 99.32% according to liquid chromatography.

[0038] Example 2

[0039] This embodiment describes a method for synthesizing 4-toluidine-2-sulfonic acid, which includes the following steps:

[0040] (1) Dissolve p-toluidine in a solvent to obtain a p-toluidine solution;

[0041] Specifically, 50g of 98% p-toluidine and 100g of propanol were added to a 500ml three-necked flask, heated to 40℃ and stirred to dissolve, thus obtaining a p-toluidine solution;

[0042] (2) Add sulfuric acid dropwise to the p-toluidine solution, and obtain the slurry after the salt formation reaction;

[0043] Specifically, 45.8g of 98% concentrated sulfuric acid was slowly added dropwise using a constant pressure funnel over a period of 30 minutes. The temperature inside the vessel was then raised to 80°C using a heating mantle and maintained for 2 hours to obtain the filter slurry.

[0044] (3) Filter the slurry and collect the filter cake;

[0045] Specifically, the filter cake was filtered out using a Buchner funnel and then rinsed with 50g of propanol.

[0046] (4) The filter cake is subjected to a sulfonation reaction to obtain 4-toluidine-2-sulfonic acid of this embodiment;

[0047] Specifically, the filter cake was transferred to a 500ml flask, heated and stirred in an oil bath to 190°C for baking, and the exhaust gas was depressurized to -0.09Mpa using a vacuum pump to dehydrate it. The reaction was kept at this temperature for 3 hours to obtain 4-toluidine-2-sulfonic acid of this embodiment.

[0048] In this example, 82.9 g of 4-toluidine-2-sulfonic acid was prepared. The sample analysis showed that the whiteness was 77, the amino value was 98.41%, and the purity was 99.28% according to liquid chromatography.

[0049] Example 3

[0050] This embodiment describes a method for synthesizing 4-toluidine-2-sulfonic acid, which includes the following steps:

[0051] (1) Dissolve p-toluidine in a solvent to obtain a p-toluidine solution;

[0052] Specifically, 50g of 99.5% p-toluidine and 100g of n-butanol were added to a 500ml three-necked flask, heated to 40℃ and stirred to dissolve, thus obtaining a p-toluidine solution;

[0053] (2) Add sulfuric acid dropwise to the p-toluidine solution, and obtain the slurry after the salt formation reaction;

[0054] Specifically, 46.7g of 98% concentrated sulfuric acid was slowly added dropwise using a constant pressure funnel over a period of 30 minutes. The temperature inside the vessel was then raised to 90°C using a heating mantle and maintained for 2 hours to obtain the filter slurry.

[0055] (3) Filter the slurry and collect the filter cake;

[0056] Specifically, the filter cake was filtered out using a Buchner funnel and then rinsed twice with 50g of n-butanol.

[0057] (4) The filter cake is subjected to a sulfonation reaction to obtain 4-toluidine-2-sulfonic acid of this embodiment;

[0058] Specifically, the filter cake was transferred to a 500ml flask, heated and stirred in an oil bath to 190°C for baking, and the exhaust gas was depressurized to -0.08Mpa using a vacuum pump for dehydration. The reaction was maintained at this temperature for 4 hours to obtain 4-toluidine-2-sulfonic acid of this embodiment.

[0059] In this example, 84.8 g of 4-toluidine-2-sulfonic acid was prepared. The sample analysis showed that the whiteness was 73, the amino value was 98.53%, and the purity was 99.46% according to liquid chromatography.

[0060] Comparative Example 1 Solvent Method

[0061] This comparative example describes a method for synthesizing 4-toluidine-2-sulfonic acid, comprising: adding 50g of 99.5% p-toluidine and 150g of trichlorobenzene to a 500ml three-necked flask, heating to 40℃ and stirring to dissolve, slowly adding 46.5g of 98% concentrated sulfuric acid dropwise using a constant pressure funnel over 30min, raising the temperature to 120℃ using a heating mantle and maintaining the temperature for 2h; heating and stirring in an oil bath to 190℃ for baking, depressurizing the tail gas to -0.08MPa using a vacuum pump for dehydration, and maintaining the temperature for 4h; and removing the solvent after the reaction (taking 8h).

[0062] In this comparative example, 85g of 4-toluidine-2-sulfonic acid was prepared. The sample analysis showed that the whiteness was 70, the amino value was 98.63%, and the purity was 99.26% according to liquid chromatography.

[0063] Comparative Example 2: High-Temperature Baking Transposition Method

[0064] This comparative example describes a method for synthesizing 4-toluidine-2-sulfonic acid, comprising: adding 50g of 99.5% p-toluidine and 20g of water to a 500ml three-necked flask, heating to 40℃ and stirring to dissolve, slowly adding 46.5g of 98% concentrated sulfuric acid dropwise using a constant pressure funnel over a period of 30min, raising the temperature to 120℃ using a heating mantle and maintaining the temperature for 2h; heating and stirring in an oil bath to 190℃ for baking, dehydrating the tail gas by reducing the pressure to -0.08MPa using a vacuum pump, and maintaining the reaction temperature for 4h.

[0065] In this comparative example, 84.7 g of 4-toluidine-2-sulfonic acid was prepared. The sample analysis showed that the whiteness was 40, the amino value was 98.25%, and the purity was 99.01% according to liquid chromatography.

Claims

1. A method for synthesizing 4-toluidine-2-sulfonic acid, characterized in that, The steps are as follows: (1) Dissolve p-toluidine in a solvent to obtain a p-toluidine solution; (2) Add sulfuric acid dropwise to the p-toluidine solution, and obtain the slurry after the salt formation reaction; (3) Filter the slurry and collect the filter cake; (4) The filter cake is subjected to sulfonation to obtain the 4-toluidine-2-sulfonic acid.

2. The method for synthesizing 4-toluidine-2-sulfonic acid as described in claim 1, characterized in that, In step (1), the purity of p-toluidine is not less than 98%.

3. The method for synthesizing 4-toluidine-2-sulfonic acid as described in claim 1, characterized in that, In step (1), the solvent is selected from C2-C7 alcohol solvents.

4. The method for synthesizing 4-toluidine-2-sulfonic acid as described in claim 1, characterized in that, In step (1), the solvent is selected from at least one of isopropanol, propanol, and n-butanol.

5. The method for synthesizing 4-toluidine-2-sulfonic acid as described in claim 1, characterized in that, In step (2), the molar ratio of p-toluidine to sulfuric acid is 1:(1-1.05).

6. The method for synthesizing 4-toluidine-2-sulfonic acid as described in claim 1, characterized in that, In step (2), the salt formation reaction is carried out at 60-100℃ for 1-3 h.

7. The method for synthesizing 4-toluidine-2-sulfonic acid as described in claim 1, characterized in that, In step (3), the slurry is filtered.

8. The method for synthesizing 4-toluidine-2-sulfonic acid as described in claim 1, characterized in that, In step (3), the filter cake is washed with a solvent.

9. The method for synthesizing 4-toluidine-2-sulfonic acid as described in claim 1, characterized in that, In step (4), the sulfonation reaction is carried out at 180-190°C for 3-4 hours.