A preparation process of dehydrothio-p-toluidine

Abstract

The present application relates to the field of chemical synthesis technology, and specifically discloses a preparation process of dehydrogenated thio-p-toluidine. A preparation process of dehydrogenated thio-p-toluidine, comprising the following steps: S1. raw material p-toluidine and sulfur are heated to liquid state respectively, and an alkali catalyst is added to the sulphur liquid; S2. at a temperature of 165-170 ° C, p-toluidine liquid and sulphur liquid are sprayed simultaneously into a mixer from different inlets, and a reaction product is obtained under the action of an alkali catalyst; S3. as the step S2 is carried out, the reaction product formed by the reaction is crystallized and filtered to obtain a filter cake and a filtrate, and the filter cake is washed and dried to obtain dehydrogenated thio-p-toluidine. The preparation process of the present application prepares dehydrogenated thio-p-toluidine, and the yield can reach 86.6wt%-87.7wt%, and the purity can reach 96.3wt%-96.7wt%, and the dehydrogenated thio-p-toluidine produced not only has a high yield, but also has a high purity.

Description

Technical Field

[0001] The present application relates to the technical field of chemical synthesis, and more specifically, to a preparation process of dehydrothio-p-toluidine. Background Art

[0002] Dehydrothio-p-toluidine, also known as 2-(4-aminophenyl)-6-methylbenzothiazole, is an important organic intermediate and is widely used in the synthesis of monosulfonic acid, disulfonic acid and other dyes.

[0003] At present, the preparation of dehydrothio-p-toluidine is mainly completed by the "one-pot method" of a reaction tank with stirring, in which p-methylaniline and elemental sulfur are melted and reacted at 180-225°C in a reaction tank under base catalysis for 20-24 hours, and the elemental sulfur reacts with the amino group on p-methylaniline and the methyl group on another p-methylaniline molecule to obtain dehydrothio-p-toluidine.

[0004] With respect to the above-mentioned related technologies, the applicant has found that during the reaction process, there are still active amino groups and methyl groups on the benzene ring structure of the generated product dehydrothio-p-toluidine molecule, so it continues to react with the unreacted elemental sulfur at high temperature to form a viscous polymer, which seriously hinders the diffusion and mass transfer process of the reactants, resulting in a long reaction time, a large number of by-products, and difficulty in separating the product, which directly leads to a low product yield. Summary of the invention

[0005] In order to improve the yield of dehydrothio-p-toluidine, the present application provides a preparation process of dehydrothio-p-toluidine.

[0006] In the first aspect, the present application provides a preparation process of dehydrothio-p-toluidine, which adopts the following technical scheme:

[0007] A preparation process of dehydrothio-p-toluidine comprises the following steps:

[0008] S1. The raw materials p-toluidine and sulfur are heated to liquid state to obtain p-toluidine liquid and sulfur liquid; and the base catalyst is added to the sulfur liquid;

[0009] S2. At a temperature of 165-170° C., p-toluidine liquid and sulfur liquid are simultaneously sprayed into the mixer from different inlets, and the p-toluidine liquid and sulfur liquid are respectively formed into mist and collide with the mixture, and react under the action of an alkali catalyst to obtain a reaction product;

[0010] S3. As step S2 is carried out, the reaction product formed by the reaction is crystallized and filtered to obtain a filter cake and a filtrate. The filter cake is washed and dried to obtain dehydrothio-p-toluidine.

[0011] The reaction equation is:

[0012]

[0013] By adopting the above technical solution, the p-toluidine and sulfur raw materials are first heated to liquid, and then the two reaction liquids are mixed by a spraying method, such as using a Venturi reactor to spray and mix the two liquid materials. The mist-like reaction liquid can increase the contact area between the reactants, so that the reactants are fully contacted, the mass transfer efficiency between the reactants is improved, and the reactants are fully reacted, which can effectively improve the yield of the generated dehydrogenated thio-p-toluidine. In addition, the p-toluidine liquid and the sulfur liquid can also collide multiple times during the spray mixing process. During the collision process, the flow direction of the reaction liquid is changed, the agitation is increased, and the mixing degree between the reactants is further improved, and the reactants are fully reacted. As the reaction of p-toluidine and sulfur proceeds, the generated reactants include not only the target product dehydrogenated p-toluidine thiosulfate but also unreacted p-toluidine and sulfur. By timely crystallizing and precipitating the generated dehydrogenated p-toluidine thiosulfate and separating it from the reaction system, it is possible to effectively prevent the active amino groups and methyl groups on the generated dehydrogenated p-toluidine from continuing to participate in the reaction, effectively prevent the formation of dark viscous polymers, reduce the generation of waste residues, and ensure that more reaction raw materials participate in the reaction. The reduction of by-products is conducive to further improving the yield of the target product dehydrogenated p-toluidine thiosulfate.

[0014] The alkaline catalyst can be a mixture of one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide, which provides an alkaline environment for the reaction.

[0015] Preferably, the injection feeding rate of the p-toluidine liquid is 315-320 g / min; the injection feeding rate of the sulfur liquid is 185-190 g / min.

[0016] By adopting the above technical scheme, the injection feeding speed of the liquid reactant is limited within the scope of the present application, which can ensure that the overall reaction rate is guaranteed while the raw materials are fully contacted; if the injection feeding speed is too fast, it may cause part of the sprayed reactant to fall before it has time to contact with another reactant, which will affect the adequacy of the mixing of the reactants and reduce the yield of the product; if the injection feeding speed is too slow, the overall reaction rate will be reduced and the reaction time will be prolonged.

[0017] Preferably, the crystallization temperature is 135-140°C.

[0018] By adopting the above technical scheme, the crystallization precipitation temperature can be any temperature of 135-140° C., such as 135° C., 138° C., 140° C., etc.; at this crystallization temperature, dehydrogenated p-toluidine can be precipitated more completely, ensuring that dehydrogenated p-toluidine is more completely separated from the reaction system, reducing the probability of continued reaction between dehydrogenated p-toluidine and sulfur in the system, and ensuring the yield of dehydrogenated p-toluidine.

[0019] Preferably, the filtrate is refluxed back into the mixer for pipeline circulation reaction.

[0020] By adopting the above technical scheme, the filtrate contains unreacted p-toluidine and sulfur. The filtrate is added into the reaction system again, so that the p-toluidine and sulfur in the filtrate can participate in the reaction again, so that the raw materials are fully utilized, more dehydrogenated p-toluidine is synthesized, and the yield of dehydrogenated p-toluidine is further improved.

[0021] Preferably, the filtrate is heated to 165-170° C. before entering into the circulation reaction.

[0022] By adopting the above technical scheme, the filtrate is first heated to the reaction temperature before entering the reaction system, which can avoid the influence of the filtrate on the temperature of the reaction system after entering the reaction system, ensure the normal progress of the reaction, and help to improve the yield of dehydrothio-p-toluidine.

[0023] Preferably, the mass ratio of p-toluidine to sulfur is (1.6-1.7):1.

[0024] By adopting the above technical scheme, the mass ratio of p-toluidine to sulfur is any ratio of (1.6-1.7):1, such as 1.6:1, 1.7:1, etc.; the ratio of p-toluidine to sulfur is limited to ensure full utilization of p-toluidine and reduce waste of sulfur, thereby maximizing resource utilization.

[0025] Preferably, the by-product hydrogen sulfide gas generated in step S2 is subjected to alkali absorption treatment.

[0026] Preferably, the alkali is a 30 wt%-40 wt% aqueous solution of sodium hydroxide.

[0027] By adopting the above technical solution, the reaction by-product hydrogen sulfide is absorbed by alkali to generate solid sodium hydrosulfide, which can not only reduce the pollution of hydrogen sulfide to the environment, but also allow hydrogen sulfide to be reused, which is in line with the concept of green development.

[0028] In a second aspect, the present application provides a dehydrogenated thio-p-toluidine, using the following technical solution:

[0029] A dehydrothio-p-toluidine is prepared by any of the above-mentioned preparation processes of dehydrothio-p-toluidine.

[0030] In summary, this application has the following beneficial effects:

[0031] 1. The present application adopts the method of first heating p-toluidine and sulfur raw materials to liquid, and then mixing the two reaction liquids by a spraying method to react and prepare dehydrogenated p-toluidine, so that the mist reactants are fully in contact, increasing the mass transfer efficiency between the reactants, and separating the reaction product dehydrogenated p-toluidine from the reaction system as the reaction proceeds, effectively avoiding the active amino group and methyl on the generated dehydrogenated p-toluidine from continuing to react with sulfur, while ensuring that more reaction raw materials participate in the reaction, and improving the yield of dehydrogenated p-toluidine; and also effectively preventing the formation of dark viscous polymers, reducing the generation of waste residues, and improving the purity of dehydrogenated p-toluidine. The yield of dehydrogenated p-toluidine can reach 86.6wt%-87.7wt%, and the purity can reach 96.3wt%-96.7 wt%. The produced dehydrogenated p-toluidine has not only a high yield but also a high purity.

[0032] 2. In the present application, it is preferred to introduce the filtrate after separation of dehydrothio-p-toluidine during the reaction into the reaction system again for reaction, so as to make full use of the reactants and further improve the yield of dehydrothio-p-toluidine. DETAILED DESCRIPTION

[0033] The present application is further described in detail below in conjunction with embodiments.

[0034] raw material

[0035] The raw materials in the examples of this application can be obtained from the market:

[0036] p-Toluidine, chemically pure;

[0037] Sulfur, chemically pure;

[0038] The base catalyst was sodium carbonate, chemically pure. Example

[0039] Example 1

[0040] A dehydrothio-p-toluidine, the preparation method of which is as follows:

[0041] S1. Preparation of liquid raw materials

[0042] 1) Add 21.4 kg of p-toluidine into reaction tank A and heat to liquid at 140°C to obtain p-toluidine liquid;

[0043] 2) 12.8 kg of sulfur and 0.032 kg of sodium carbonate alkali catalyst were added to reaction tank B and heated at 170°C until the sulfur was liquid to obtain liquid sulfur;

[0044] S2. Injection reaction

[0045] The circulation pipeline is heated to 165°C, so that the p-toluidine liquid in the reaction tank A enters the A port of the venturi jet reactor through the circulation pipeline, and the sulfur liquid in the reaction tank B enters the B port of the venturi jet reactor. The p-toluidine liquid at the A port of the venturi jet reactor is sprayed at a rate of 315 g / min, and the sulfur liquid at the B port of the venturi jet reactor is sprayed at a rate of 185 g / min, so that the p-toluidine liquid and the sulfur liquid collide and mix to perform a chemical reaction to obtain a reaction product; the reaction is completed in 70 minutes;

[0046] S3. Separation and purification

[0047] As the reaction proceeds, the reactant is crystallized at 135° C. to obtain a filtrate and a filter cake; the filter cakes are collected, and after the reaction is completed, all the filter cakes are mixed, washed twice with clean water, and then filtered and dried to obtain dehydrothio-p-toluidine;

[0048] S4. By-product treatment

[0049] The hydrogen sulfide gas generated during the reaction was passed into a 40 wt% sodium hydroxide aqueous solution spray tower for absorption, and the formed slurry was filtered through crystallization, and the filter cake was dried to obtain a block by-product sodium hydrosulfide.

[0050] Example 2

[0051] Different from Example 1, in step S2 of Example 2, the circulation pipeline is heated to 170°C.

[0052] Example 3

[0053] Different from Example 2, in step S2 of Example 3, the p-toluidine liquid at port A of the Venturi jet reactor is jetted at a rate of 320 g / min, and the sulfur liquid at port B of the Venturi jet reactor is jetted at a rate of 190 g / min.

[0054] Example 4

[0055] Different from Example 3, the crystallization temperature in Example 4 is 140°C.

[0056] Example 5

[0057] A dehydrothio-p-toluidine, the preparation method of which is as follows:

[0058] S1. Preparation of liquid raw materials

[0059] Same as Example 3;

[0060] S2. Injection reaction

[0061] Same as Example 3;

[0062] S3. Separation and purification

[0063] Same as Example 3;

[0064] S4. Reflux of filtrate

[0065] The filtrate obtained in S3 is refluxed to the A port of the Venturi jet reactor through a circulation pipeline heated to 170°C to participate in the reaction until the reaction is completed;

[0066] S5. By-product treatment

[0067] Same as Example 3.

[0068] Comparative Example

[0069] Comparative Example 1

[0070] Different from Example 1, in step S2 of Comparative Example 1, the circulation pipeline is heated to 200°C.

[0071] Comparative Example 2

[0072] Different from Example 1, in step S2 of Comparative Example 2, the circulation pipeline is heated to 120°C.

[0073] A dehydrothio-p-toluidine, the preparation method of which is as follows:

[0074] 21.4 kg of p-toluidine, 12.8 kg of sulfur and 0.032 kg of sodium carbonate alkali catalyst were added to a stirred reactor, and the reaction was carried out at 200° C. The reaction was completed after 22 hours. The obtained reaction product was crystallized at 135° C. to obtain a filter cake. The filter cake was washed twice with clean water, and then filtered and dried to obtain dehydrothio-p-toluidine.

[0075] Performance testing

[0076] Detection method / test method

[0077] The dehydrothio-p-toluidine obtained in the examples and comparative examples was weighed and the yield was calculated. The purity of the dehydrothio-p-toluidine obtained was then analyzed by conventional HPLC, as shown in Table 1.

[0078] Table 1 Performance test results

[0079] Yield / wt% Purity / wt% Example 1 86.6 96.3 Example 2 86.9 96.6 Example 3 86.8 96.5 Example 4 86.8 96.3 Example 5 87.7 96.6 Comparative Example 1 86.5 96.4 Comparative Example 2 84.6 96.2 Comparative Example 3 55.2 85.4

[0080] In combination with Examples 1-5 and Table 1, it can be seen that the process for preparing dehydrogenated p-toluidine by the present application has a yield of dehydrogenated p-toluidine of 86.6wt%-87.7wt% and a purity of 96.3wt% or more. The preparation process of the present application not only has a high yield of dehydrogenated p-toluidine, but also has a high yield of dehydrogenated p-toluidine and a high overall benefit.

[0081] Combining Examples 1-2 with Comparative Examples 1-2, and in combination with Table 1, it can be seen that the temperature of the reactants in Example 2 is higher than that in Example 1, and the yield of dehydrogenated p-toluidine in Example 2 is slightly higher than that in Example 1. The reaction temperature in Comparative Example 1 is higher than that in the present application, and the yield of dehydrogenated p-toluidine in Comparative Example 1 and Example 1 is not much different; the reaction temperature in Comparative Example 2 is lower than the temperature specified in the present application, and the yield in Comparative Example 2 decreases, which may be because the reaction temperature in Comparative Example 2 cannot maintain a good molten state of the reaction liquid, resulting in incomplete reaction of the reactants. This shows that the molten state of the reactants can be maintained within the temperature specified in the present application, which can allow the reaction to proceed normally; the yield of dehydrogenated p-toluidine will not increase when the reaction is higher than the specified temperature of the present application, but will cause a waste of heat.

[0082] Combined with Comparative Example 2, the traditional "one-pot method" was used in Comparative Example 2, and the yield of dehydrothio-p-toluidine in Comparative Example 2 was significantly lower than that in Example 1, and the purity of the obtained dehydrothio-p-toluidine was also significantly lower than that in Example 1. This shows that the preparation process of the present application can not only improve the yield of dehydrothio-p-toluidine, but also improve the purity of dehydrothio-p-toluidine. This may be because in the traditional "one-pot method", during the reaction, the generated product dehydrothio-p-toluidine still has active amino groups and methyl groups on the ring structure, and continues to react with unreacted sulfur at high temperature to form a viscous polymer, which seriously hinders the diffusion and mass transfer process of the reactants, thereby reducing the yield of dehydrothio-p-toluidine; and many by-products are generated, and the by-products and dehydrothio-p-toluidine cannot be completely separated, resulting in low purity of dehydrothio-p-toluidine. In the present application, timely removal of dehydrothio-p-toluidine from the reaction system can effectively improve the yield and purity of dehydrothio-p-toluidine; this may be because timely separation of the generated dehydrothio-p-toluidine from the reaction system can effectively prevent the active amino group and methyl group on the generated dehydrothio-p-toluidine from continuing to react with sulfur, while ensuring that more reaction raw materials participate in the reaction, further improving the yield of dehydrothio-p-toluidine; and it also effectively prevents the formation of dark viscous polymers, reduces the generation of waste residues, and improves the purity of dehydrothio-p-toluidine.

[0083] In addition, it can be seen that the reaction temperature in Example 1 is 165°C and the reaction time is 70 min; the reaction temperature in Comparative Example 3 is 200°C and the reaction time is 22 h. In the present application, not only the reaction temperature is low, but also the reaction rate is significantly higher than that in Comparative Example 3, which effectively improves the production efficiency.

[0084] Combining Example 1 with Example 5 and Table 1, it can be seen that in Example 5, the filtrate after separating dehydrothio-p-toluidine during the reaction process is reintroduced into the reaction system, and the yield of dehydrothio-p-toluidine in Example 5 is higher than that in Example 1, which shows that the reuse of the filtrate can improve the yield of dehydrothio-p-toluidine; this may be because the filtrate contains unreacted p-toluidine and sulfur, and the filtrate is added to the reaction system again, so that the p-toluidine and sulfur in the filtrate can participate in the reaction again, so that the raw materials are fully utilized.

[0085] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A process for preparing dehydrothio-p-toluidine, characterized in that: The following steps are involved: S1. The raw materials p-toluidine and sulfur are heated to liquid state to obtain p-toluidine liquid and sulfur liquid; and the base catalyst is added to the sulfur liquid; S2. At a temperature of 165-170° C., p-toluidine liquid and sulfur liquid are simultaneously sprayed into the mixer from different inlets, and the p-toluidine liquid and sulfur liquid are respectively formed into mist and collide with the mixture, and react under the action of an alkali catalyst to obtain a reaction product; S3. As the step S2 is carried out, the reaction product formed by the reaction is crystallized and filtered to obtain a filter cake and a filtrate, and the filter cake is washed and dried to obtain dehydrogenated thiotoluidine; The mixer is a Venturi jet reactor; the jet feeding rate of the p-toluidine liquid is 315-320 g / min; the jet feeding rate of the sulfur liquid is 185-190 g / min; the mass ratio of p-toluidine to sulfur is (1.6-1.7):1; The crystallization temperature is 135-140°C; The filtrate is heated and refluxed into the mixer for pipeline circulation reaction; the filtrate is heated to 165-170° C. and then enters the circulation reaction.

2. A process for preparing dehydrothio-p-toluidine according to claim 1, characterized in that: The hydrogen sulfide gas generated as a byproduct in step S2 is subjected to alkali absorption treatment.