Hydrogenation reduction process of 4-chloro-2, 5-dimethoxyaniline

Abstract

The invention provides a hydrogenation reduction process of 4-chloro-2, 5-dimethoxyaniline, which comprises the following steps: S1, with 4-chloro-2, 5-dimethoxynitrobenzene as a raw material and a noble metal catalyst as a reaction system catalyst, introducing hydrogen for reaction in the presence of an additive, an anti-dechlorination assistant and a solvent; and S2, after the reaction is finished, carrying out nitrogen pressure filtration on the reaction liquid, separating and purifying the filtrate to obtain the product 4-chloro-2, 5-dimethoxyaniline, and recycling the noble metal catalyst. According to the method disclosed by the invention, the raw material conversion rate is greater than 99.99%, the selectivity of 4-chloro-2, 5-methoxyaniline is greater than 99%, the dechlorination impurity content is less than 0.05%, and the catalyst can be continuously applied mechanically for more than 100 times in a reaction kettle and keeps stable reaction activity and selectivity by applying the method disclosed by the invention.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic hydrogenation, and in particular to a hydrogenation reduction process of 4-chloro-2,5-dimethoxyaniline. Background Art

[0002] 4-Chloro-2,5-dimethoxyaniline (2,5-Dimethoxy-4-chloroaniline) is an important intermediate used in the production of pesticides and azo pigments. It is mainly used as an intermediate for various yellow azo organic pigments and various red azo organic pigments. Its downstream azo pigments account for a large proportion of the pigment and dye industry, and the market demand for it has increased year by year.

[0003] CN112079734B relates to a method for preparing 4-chloro-2,5-dimethoxyaniline. Using copper chloride as a catalyst, the reaction is conducted at 95°C for 8 hours while oxygen is introduced into a 9N hydrochloric acid solution. However, the selectivity is poor, at only 95%. Furthermore, the high-temperature hydrochloric acid system is equipment-unfriendly, making it unsuitable for industrialization. CN110698353B relates to a method for preparing 4-chloro-2,5-dimethoxyaniline. Using supported nickel as a catalyst, the reaction is conducted with hydrazine hydrate. Both hydrazine hydrate and nickel are hazardous chemicals. This process generates a large amount of wastewater, and residual heavy metal nickel ions remain in the product, which is inconsistent with green chemistry principles. Furthermore, industrial production of this process requires strict temperature control, otherwise it is prone to uncontrolled explosion. CN106045864A discloses a production process for preparing 4-chloro-2,5-dimethoxyaniline using a hydrazine hydrate catalytic reduction method. The process involves preparing a catalyst by drying and crushing a homemade Fe(OH)3 clay; an ethanol solvent, 4-nitro-2,5-dimethoxychlorobenzene, and the catalyst are sequentially added to a reactor, and a hydrazine hydrate solution is added dropwise at a uniform rate to obtain a product. The residue catalyst filtered from the solution is then reused. However, the catalyst in this patent can only be reused twice, which is costly in the long term. CN105949069A relates to a method for producing 4-chloro-2,5-dimethoxyaniline by continuous hydrogenation. This method suffers from backmixing issues, requiring at least three reactors for complete reaction, resulting in low reactor efficiency and a catalyst dosage of 1%-3% of the raw material, resulting in high catalyst costs.

[0004] Based on this, it is necessary to develop a hydrogenation reduction process for 4-chloro-2,5-dimethoxyaniline to facilitate industrial production. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a hydrogenation reduction process for 4-chloro-2,5-dimethoxyaniline. The process is equipment-friendly, conforms to the principles of green chemistry, and the catalyst can be recycled more than 100 times, with high kettle efficiency and low catalyst cost. The obtained product has high conversion rate and selectivity, and the catalyst has strong recycling performance, which is economical and efficient.

[0006] To achieve the above object, the technical solution of the present invention is as follows: In one aspect, the present invention provides a hydrogenation reduction process for 4-chloro-2,5-dimethoxyaniline (Formula (II)), comprising: S1: Using 4-chloro-2,5-dimethoxynitrobenzene (Formula (I)) as a raw material and a noble metal catalyst as a catalyst in the reaction system, hydrogen is introduced in the presence of an additive, an anti-dechlorination aid, and a solvent to carry out the reaction; S2: After the reaction is completed, the reaction liquid is filtered through nitrogen pressure, and the filtrate is purified by vacuum distillation to obtain the product 4-chloro-2,5-dimethoxyaniline, and the precious metal catalyst is recycled.

[0007] The reaction process is shown below: .

[0008] Furthermore, the noble metal catalyst is a platinum-carbon catalyst or a palladium-carbon catalyst, preferably a platinum-carbon catalyst.

[0009] Furthermore, the metal loading in the noble metal catalyst is 0.5% to 5%, preferably 1% to 2%.

[0010] Furthermore, the mass ratio of the 4-chloro-2,5-dimethoxynitrobenzene to the noble metal catalyst is 1:(0.0004-0.01), preferably 1:(0.003-0.005).

[0011] Furthermore, the solvent is selected from at least one of methanol, ethanol, isopropanol, water, and toluene. Preferably, the solvent is ethanol, or a mixture of methanol and toluene (the volume ratio of the two is 1:1).

[0012] Furthermore, the mass ratio of the 4-chloro-2,5-dimethoxynitrobenzene to the solvent is 1:(1-10), preferably 1:(3.33-6.67).

[0013] Furthermore, the additive is at least one of sodium hydroxide, potassium hydroxide, ammonia, triethylamine, and 1,8-diazabicycloundec-7-ene, preferably sodium hydroxide or triethylamine. The additive promotes the reaction while also dechlorinating and absorbing the generated hydrogen chloride, achieving rational resource utilization. The additive creates alkaline reaction conditions. Without additives, the reaction is excessive, leading to dechlorination. The hydrogen chloride generated by dechlorination reacts with water to form hydrochloric acid, which is corrosive and can corrode the stainless steel autoclave, damaging the autoclave and stirring. Under alkaline conditions, the generated hydrogen chloride is neutralized into salt, preventing damage to the autoclave.

[0014] Furthermore, the mass ratio of the 4-chloro-2,5-dimethoxynitrobenzene to the additive is 1:(0.01-0.1), preferably 1:(0.02-0.05).

[0015] Furthermore, the anti-dechlorination auxiliary agent is at least one of ethylenediamine, dicyandiamide, cyclohexylamine, and cyclohexanediamine, preferably ethylenediamine or dicyandiamide. The present invention suppresses the dechlorination reaction by adding an anti-dechlorination auxiliary agent to the reaction system, thereby improving the selectivity of the reaction. The anti-dechlorination auxiliary agent will adhere to the surface of the catalyst in the reaction system, modify the catalyst surface, and form a layer of "proton exchange membrane", which prevents the direct contact of the halogen-containing nitroaromatic reactant with the precious metal surface, and also induces an effective non-contact hydrogenation mechanism mediated by protons and electrons. In this process, the auxiliary agent layer acts as a "proton exchange membrane", allowing hydrogen molecules to penetrate and be activated into electrons and protons at the platinum-auxiliary agent interface. With the generation of separated protons and electrons, the nitro group with strong electrophilicity can be hydrogenated by electron transfer and then proton transfer, a process promoted by the hydrogen bond network formed by the protonated auxiliary agent. This unique mechanism makes it highly directional in the nitro hydrogenation reaction, and does not produce side reactions, reducing the production of dechlorination by-products.

[0016] Furthermore, the mass ratio of the 4-chloro-2,5-dimethoxynitrobenzene to the anti-dechlorination auxiliary agent is 1:(0.001-0.05), preferably 1:(0.005-0.01).

[0017] Furthermore, the method is carried out in a high-pressure reactor, and after the reaction is completed, the reaction liquid is nitrogen-filtered and then transported to a separation unit via a pump.

[0018] Furthermore, the reaction temperature of the method is 60-100°C, preferably 60-85°C.

[0019] Furthermore, the reaction pressure of the method is 0.4-1.0 MPa, preferably 0.5-0.8 MPa.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The invention provides a hydrogenation reduction process for 4-chloro-2,5-dimethoxyaniline. The obtained product has high conversion rate and selectivity, and the catalyst has strong recycling performance, is economical and efficient.

[0021] The present invention achieves efficient and green production of 4-chloro-2,5-methoxyaniline by optimizing process conditions (reaction conditions and catalyst performance), significantly improving production efficiency and product quality.

[0022] The present invention effectively improves the yield and purity of the target product, reduces the generation of dechlorination by-products, and is more friendly to production equipment by precisely controlling key parameters such as reaction temperature, pressure, auxiliary agent dosage, additive dosage and catalyst loading.

[0023] The 4-chloro-2,5-methoxyaniline prepared by the method of the present invention has the advantages of good selectivity, high yield, short reaction time, excellent finished product appearance, environmental friendliness and safety, high efficiency and low cost, and is particularly suitable for industrial scale-up application. It is expected to overcome the limitations of existing technologies and promote the sustainable development of the 4-chloro-2,5-methoxyaniline industry.

[0024] The method of the present invention achieves a raw material conversion rate of greater than 99.99%, a 4-chloro-2,5-methoxyaniline selectivity of greater than 99%, and a dechlorinated impurity content of less than 0.05%. In addition, the method of the present invention enables the catalyst to be continuously applied in a reactor for more than 100 times while maintaining stable reaction activity and selectivity. DETAILED DESCRIPTION

[0025] The following content provides different embodiments or examples so that those skilled in the art can implement accordingly with reference to the description text. Of course, these are merely examples and are not intended to limit the present invention. The endpoints and any value of the scope disclosed in the present invention are not limited to this accurate scope or value, and these scopes or values ​​should be interpreted as comprising values ​​close to these scopes or values. For numerical ranges, between the endpoint values ​​of each scope, between the endpoint values ​​of each scope and a separate point value, and between the separate point value, can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered as specifically disclosed in this article.

[0026] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. Throughout this specification, the schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0027] Example 1 Under nitrogen, 50g of 4-chloro-2,5-methoxynitrobenzene, 180g of ethanol, 0.2g of 1% platinum-on-carbon catalyst (dry value), 1g of triethylamine, and 0.25g of dicyandiamide were placed in a reactor. Stirring was initiated, and the atmosphere was purged with nitrogen followed by hydrogen. The reaction was carried out at 80°C and 0.8 MPa for 1 hour and 30 minutes. After completion, the reaction was filtered through nitrogen pressure to obtain a 4-chloro-2,5-methoxyaniline solution, which was then pumped to the next separation unit. The catalyst was retained in the reactor for further use. The product and hydrogen mixture was cooled and separated by gas-liquid separation to obtain 4-chloro-2,5-dimethoxyaniline. Sampling and analysis showed a 100% raw material conversion, a 99.44% selectivity for the target product, and 0.02% of the chlorinated impurities were removed.

[0028] Example 2 The difference from Example 1 is that this example is a catalyst replication, the first batch of catalyst dosage is 0.2g, and each replication is performed with 0.02g of catalyst added. The replication data are shown in Table 1 below:

[0029] As can be seen from Table 1, the catalyst used in the present invention can be recycled for more than 100 times in the reaction, and has high conversion rate and selectivity for catalyzing 4-chloro-2,5-methoxynitrobenzene.

[0030] Example 3 The difference from Example 1 is that the reaction solvent and dosage were screened, and the other reaction conditions remained unchanged. The conversion rate and selectivity results are shown in Table 2 below.

[0031] Table 2 Reaction results of different solvents and catalytic dosages

[0032] From the results in Table 2 and Example 1, it can be seen that ethanol has the best effect, while the selectivity of the other solvents is slightly worse. When the proportion of solvent is too high, the reaction solution is diluted, and within the same reaction time, the product conversion rate and selectivity are reduced.

[0033] Example 4 The difference from Example 1 is that the type and amount of catalyst were screened, and the other reaction conditions remained unchanged. The conversion rate and selectivity results are shown in Table 3 below.

[0034] Table 3 Reaction results of different catalysts and dosages

[0035] As can be seen from the results in Table 3 and Example 1, a low catalyst dosage, within the same reaction time, affects the reaction conversion rate. Considering catalyst cost, the optimal mass ratio of 4-chloro-2,5-methoxynitrobenzene to the precious metal catalyst is 1:0.003-1:0.005 on a dry basis. Furthermore, compared to other catalysts, the preparation method of the present invention combined with a platinum-on-carbon catalyst produces the best results.

[0036] Example 5 The difference from Example 1 is that the additives and their amounts were screened, and the other reaction conditions remained unchanged. The conversion rate and selectivity results are shown in Table 4 below.

[0037] Table 4 Reaction results of different additives and dosages

[0038] Note: “-” means the corresponding component was not added.

[0039] The results in Table 4 show that the use of different additives has a certain impact on product conversion and dechlorinated impurities. Using different additive dosages has little effect on reaction conversion, but selectivity varies. Reactions without additives exhibit poor conversion and selectivity, and high impurity levels.

[0040] Example 6 The difference from Example 1 is that the reaction temperature and pressure are screened, and the other reaction conditions remain unchanged. The conversion rate and selectivity results are shown in Table 5 below.

[0041] Table 5 Reaction results catalyzed under different reaction conditions

[0042] It can be seen from the results of Table 5 and Example 1 that using a reaction temperature that is too high or too low has some effect on the conversion rate, changes the selectivity, and also affects the dechlorination of impurities; using different hydrogen pressures has a certain effect on the reaction conversion rate.

[0043] Example 7 The difference from Example 1 is that the anti-dechlorination additive is different, and the other reaction conditions remain unchanged. The conversion rate and selectivity results are shown in Table 6 below.

[0044] Table 6 Reaction results catalyzed by different anti-dechlorination additives

[0045] Note: “-” means the corresponding component was not added.

[0046] It can be seen from the results in Table 6 that different types of anti-dechlorination additives are applicable to the method of the present invention, and the conversion rate and selectivity are relatively good. Without the anti-dechlorination additive, the dechlorination by-products increase, and the conversion rate and selectivity are also affected.

[0047] Although the above embodiments have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concepts. Therefore, the above descriptions are merely embodiments of the present invention and do not limit the scope of patent protection of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the scope of patent protection of the present invention.

Claims

1. A hydrogenation reduction process for 4-chloro-2,5-dimethoxyaniline, characterized in that: include: S1: Using 4-chloro-2,5-dimethoxynitrobenzene as raw material and a noble metal catalyst as a catalyst in the reaction system, hydrogen is introduced in the presence of additives, an anti-dechlorination aid and a solvent to carry out the reaction; S2: After the reaction is completed, the reaction solution is filtered through nitrogen pressure, and the filtrate is separated and purified to obtain the product 4-chloro-2,5-dimethoxyaniline, and the noble metal catalyst is recycled; The anti-dechlorination auxiliary agent is at least one of ethylenediamine, dicyandiamide, cyclohexylamine and cyclohexanediamine.

2. The hydrogenation reduction process according to claim 1, wherein The noble metal catalyst is a platinum-carbon catalyst or a palladium-carbon catalyst, The metal loading in the noble metal catalyst is 0.5% to 5%, preferably 1% to 2%.

3. The hydrogenation reduction process according to claim 1, wherein The mass ratio of the 4-chloro-2,5-dimethoxynitrobenzene to the noble metal catalyst is 1:(0.0004-0.01), preferably 1:(0.003-0.005).

4. The hydrogenation reduction process according to claim 1, wherein The solvent is selected from at least one of methanol, ethanol, isopropanol, water, and toluene; The mass ratio of the 4-chloro-2,5-dimethoxynitrobenzene to the solvent is 1:(1-10), preferably 1:(3.33-6.67).

5. The hydrogenation reduction process according to claim 1, wherein: The additive is at least one of sodium hydroxide, potassium hydroxide, ammonia water, triethylamine, and 1,8-diazabicycloundec-7-ene, preferably sodium hydroxide or triethylamine.

6. The hydrogenation reduction process according to claim 1, characterized in that: The mass ratio of the 4-chloro-2,5-dimethoxynitrobenzene to the additive is 1:(0.01-0.1), preferably 1:(0.02-0.05).

7. The hydrogenation reduction process according to claim 1, characterized in that: The mass ratio of the 4-chloro-2,5-dimethoxynitrobenzene to the anti-dechlorination auxiliary agent is 1:(0.001-0.05), preferably 1:(0.005-0.01).

8. The hydrogenation reduction process according to claim 1, wherein: The method is carried out in a high-pressure reactor. After the reaction is completed, the reaction liquid is nitrogen-filtered and then transported to a separation unit via a pump.

9. The hydrogenation reduction process according to claim 1, characterized in that: The reaction temperature of the method is 60-100°C, preferably 60-85°C.

10. The hydrogenation reduction process according to claim 1, characterized in that: The reaction pressure of the method is 0.4-1.0 MPa, preferably 0.5-0.8 MPa.

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