Preparation method of N-methyldiphenylamine

Abstract

The invention provides a preparation method of N-methyl diphenylamine. The preparation method of the N-methyl diphenylamine comprises the following steps: enabling diphenylamine and tetramethylammonium hydroxide to react to generate the N-methyl diphenylamine; wherein the mass ratio of the diphenylamine to the tetramethylammonium hydroxide is 1: (1-10). According to the method, tetramethylammonium hydroxide is adopted as a methylation reagent source to react with diphenylamine, no catalyst needs to be used, the process is simple, the conversion rate and yield are high, the resource utilization rate is high, and the prepared N-methyldiphenylamine is high in purity.

Description

Technical Field

[0001] The present invention relates to the field of organic synthesis, and particularly relates to a method for preparing N-methyl diphenylamine. Background Art

[0002] N-methyl diphenylamine, also known as diphenylmethylamine, is mainly used in industries such as pesticides, printing and dyeing, and chemical intermediates.

[0003] Currently, the methods for preparing N-methyl diphenylamine disclosed in the prior art are mainly divided into five types. The first type uses methylaniline and halobenzene as raw materials, such as patent documents CN111377964A and CN106892945A, but this method has many reaction steps and low yield. The second type uses diphenylamine and methylation reagents (such as dimethyl sulfate, methylmagnesium, methyllithium) as raw materials, such as patent documents WO2023172667A2, WO2018002958A1, CN107118587A, but dimethyl sulfate, a methylation reagent, is a highly toxic raw material with high pollution; reagents such as methylmagnesium and methyllithium have harsh reaction conditions, requiring anhydrous and anaerobic conditions. The third type uses diphenylamine and formaldehyde as raw materials, such as patent document JP06072968A, but the reaction catalyst for this method is a noble metal catalyst, which is expensive, has poor recyclability, and low yield. The fourth type uses diphenylamine and methanol as raw materials, such as patent document CN116425638A, but the reaction catalyst for this method is a composite catalyst of magnesium oxide, aluminum oxide, and cobalt oxide, which is difficult to prepare and has high cost. The fifth type uses diphenylamine and formic acid as raw materials, such as patent document CN106892826A, but the reaction solvent for this method is phenylsilane, and the use of this solvent requires being away from oxygen and moisture. At the same time, this method uses a platinum-based catalyst, with high reaction conditions requirements and high cost.

[0004] Therefore, there is an urgent need for a new method for preparing N-methyl diphenylamine with low production cost, simple process, high yield, and environmental friendliness. Summary of the Invention

[0005] In order to overcome the technical defects in the prior art for preparing N-methyl diphenylamine, such as high production cost, complex process, low yield, and large environmental pollution, the present invention provides a method for preparing N-methyl diphenylamine. By using tetramethylammonium hydroxide as the source of methylation reagent and reacting with diphenylamine under the action of a polar solvent, the present invention does not require the use of any catalyst, has a simple process, high conversion rate and yield, high resource utilization rate, and the prepared N-methyl diphenylamine has high purity.

[0006] The first aspect of the present invention provides a method for preparing N-methyl diphenylamine, which comprises the following steps:

[0007] React diphenylamine with tetramethylammonium hydroxide to produce N-methyldiphenylamine; wherein, the mass ratio of diphenylamine to tetramethylammonium hydroxide is 1:(1 - 10).

[0008] In one or more embodiments, the mass ratio of the diphenylamine to the tetramethylammonium hydroxide is 1:(1 - 6), preferably 1:(1 - 3).

[0009] In one or more embodiments, the reaction is carried out in a solvent, and the mass ratio of the diphenylamine to the solvent is 1:(1 - 10), preferably 1:(1 - 6), more preferably 1:(1 - 3).

[0010] In one or more embodiments, the tetramethylammonium hydroxide is added to the reaction system in the form of an aqueous solution, and the mass concentration of the tetramethylammonium hydroxide in the aqueous solution is 1% - 99%, preferably 20% - 50%, more preferably 25% - 40%.

[0011] In one or more embodiments, the reaction is carried out in a polar solvent, and the polar solvent is preferably selected from one or more of dimethyl sulfoxide, N-methylpyrrolidone, γ-butyrolactone, N,N-dimethylacetamide, N,N-dimethylformamide, and ethylene glycol.

[0012] In one or more embodiments, the temperature of the reaction is 100 - 250 °C, preferably 150 - 200 °C, more preferably 180 - 200 °C.

[0013] In one or more embodiments, the method includes the following steps: dropwise add tetramethylammonium hydroxide to diphenylamine for reaction to produce N-methyldiphenylamine.

[0014] In one or more embodiments, the method includes the following steps:

[0015] (1) Mix diphenylamine and a part of the solvent to obtain a first mixed solution; mix tetramethylammonium hydroxide or its aqueous solution and the remaining solvent to obtain a second mixed solution;

[0016] (2) Dropwise add the second mixed solution to the first mixed solution for reaction.

[0017] In one or more embodiments, the dropping rate is 50 - 500 g / h, preferably 100 - 300 g / h.

[0018] In one or more embodiments, after the reaction, post-treatment is further included, and the steps of the post-treatment include: subjecting the reaction solution after the reaction to atmospheric distillation, first vacuum distillation, and second vacuum distillation in sequence, and the bottom liquid obtained after the second vacuum distillation is the N-methyldiphenylamine.

[0019] In one or more embodiments, the temperature of the atmospheric distillation is 65 - 85 °C.

[0020] In one or more embodiments, the temperature of the first vacuum distillation is 100 - 110 °C.

[0021] In one or more embodiments, the temperature of the second vacuum distillation is 150 - 180 °C. Detailed implementation manners

[0022] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and expressions mentioned herein. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meanings understood by those skilled in the art for the present invention. In case of conflicts, the definitions in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall in no way limit the scope of the present invention, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0024] In this article, terms such as "comprising", "including", "containing" and similar terms cover the meanings of "consisting essentially of" and "consisting of". For example, when it is disclosed herein that "A comprises B and C", it should be considered that "A consists essentially of B and C" and "A consists of B and C" have been disclosed herein.

[0025] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub - ranges and individual numerical values (including integers and fractions) within the range.

[0026] In this article, unless otherwise specified, percentages refer to mass percentages and ratios refer to mass ratios.

[0027] In this article, when describing embodiments or examples, it should be understood that they are not used to limit the present invention to these embodiments or examples. On the contrary, all alternatives, improvements and equivalents of the methods and materials described in the present invention can be covered within the scope defined by the claims.

[0028] In this text, for the sake of brevity of description, not all possible combinations of all technical features in each implementation or embodiment are described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation or embodiment can be combined arbitrarily, and all possible combinations should be considered as the scope described in this specification.

[0029] The present invention provides a method for preparing N-methyl diphenylamine, which comprises the following steps: reacting diphenylamine with tetramethylammonium hydroxide to produce N-methyl diphenylamine; wherein, the mass ratio of diphenylamine to tetramethylammonium hydroxide is 1:(1 - 10), preferably 1:(1 - 6), more preferably 1:(1 - 3), for example 1:1, 1:3, 1:5, 1:8, 1:9.

[0030] The inventors found in the research that using tetramethylammonium hydroxide as the source of methylation reagent to react with diphenylamine requires no catalyst, the reaction can be carried out under normal pressure, no side reactions occur, the yield and conversion rate are high, the selectivity is high, and the solvent and by-products after the reaction can be recycled, greatly reducing the reaction cost.

[0031] Using tetramethylammonium hydroxide as the source of methylation reagent, its raw material is preferably added to the reaction system in the form of an aqueous solution, and the mass concentration of tetramethylammonium hydroxide in the aqueous solution can be 1% - 99%, preferably 20% - 50%, more preferably 25% - 40%, for example 25%, 30%, 45%, 60%, 80%, 95%.

[0032] The reaction temperature applicable to the present invention can be 100 - 250 °C, preferably 150 - 200 °C, more preferably 180 - 200 °C, for example 120 °C, 130 °C, 160 °C, 190 °C, 210 °C, 240 °C.

[0033] In some preferred embodiments, the reaction of diphenylamine and tetramethylammonium hydroxide is carried out in a solvent. The solvent is preferably a polar solvent. The mass ratio of diphenylamine to the solvent is preferably 1:(1 - 10), more preferably 1:(1 - 6), particularly 1:(1 - 3), for example 1:2, 1:3, 1:4.3, 1:5, 1:8.

[0034] In the present invention, the step of reacting diphenylamine and tetramethylammonium hydroxide may include adding tetramethylammonium hydroxide dropwise to diphenylamine for reaction. Before the dropwise addition, tetramethylammonium hydroxide and diphenylamine can be first mixed with the solvent respectively and then reacted.

[0035] In some preferred embodiments, the method for preparing N-methyl diphenylamine comprises the following steps:

[0036] (1) Mix diphenylamine with a portion of the solvent to obtain a first mixed solution; mix tetramethylammonium hydroxide solution with the remaining solvent to obtain a second mixed solution; the order of preparing the first mixed solution and the second mixed solution is not sequential.

[0037] (2) Dropwise add the second mixed solution to the first mixed solution for reaction.

[0038] Wherein, the sum of the masses of the portion of the solvent and the remaining solvent is the total mass of the solvent. The mass ratio of the portion of the solvent to the remaining solvent can be 1:(0.5 - 1.5), for example, 1:0.58, 1:1, 1:1.2, 1:4.

[0039] Wherein, the dropping rate can be 50 - 500 g / h, preferably 100 - 300 g / h, for example, 80 g / h, 106 g / h, 118 g / h, 120 g / h, 150 g / h, 200 g / h, 250 g / h, 275.1 g / h, 288.6 g / h, 290 g / h, 350 g / h, 450 g / h. The dropping method can be to slowly dropwise add the second mixed solution into the container containing the first mixed solution using a peristaltic pump.

[0040] Wherein, the dropping time can be 1 - 10 h, preferably 1 - 8 h, most preferably 1 - 6 h, for example, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 9 h.

[0041] Wherein, the reaction temperature can be 100 - 250 °C, preferably 150 - 200 °C, more preferably 180 - 200 °C, for example, 110 °C, 130 °C, 140 °C, 160 °C, 170 °C, 190 °C.

[0042] Wherein, the reaction completion time can be until the second mixed solution is completely dropwise added.

[0043] In some preferred embodiments, after the reaction is completed, post-treatment is further included. The steps of post-treatment include: subjecting the reaction solution after the reaction is completed to atmospheric distillation, first vacuum distillation, and second vacuum distillation in sequence.

[0044] The purpose of atmospheric distillation is to remove methanol generated by the decomposition of tetramethylammonium hydroxide in the reaction system. The temperature of atmospheric distillation can be 65 - 85 °C, for example, 70 °C, 80 °C, 82 °C. In the reaction, a portion of tetramethylammonium hydroxide will decompose to generate trimethylamine and methanol.

[0045] The purpose of the first vacuum distillation is to remove the water generated in the reaction system. The temperature of the first vacuum distillation can be 100 - 110 °C, for example, 100 °C, 105 °C, 108 °C.

[0046] The purpose of the second vacuum distillation is to remove the polar solvent in the reaction system. The temperature of the second vacuum distillation can be 150 - 180 °C, such as 155 °C, 160 °C, 165 °C, 168 °C, 170 °C, 175 °C, 178 °C.

[0047] After the second vacuum distillation, the bottom liquid obtained is the finished product of N - methyl diphenylamine.

[0048] The reaction formula of the present invention is as follows:

[0049]

[0050] After tetramethylammonium hydroxide reacts with diphenylamine under the action of a polar solvent, it decomposes into trimethylamine. The trimethylamine tail gas generated by the reaction can be absorbed by an acidic solution. Examples of the acidic solution include but are not limited to hydrochloric acid, sulfuric acid, nitric acid, acetic acid, phosphoric acid solution, etc. The concentration of the hydrochloric acid solution can be 18 - 50 wt%, such as 20 wt%, 30 wt%, 40 wt%, 50 wt%.

[0051] The present invention includes N - methyl diphenylamine prepared by a preparation method of N - methyl diphenylamine according to any embodiment herein. The finished product of N - methyl diphenylamine prepared by the present invention is light yellow, and the purity is preferably 99.5 - 99.8%.

[0052] Advantages of the present invention:

[0053] By using tetramethylammonium hydroxide as the source of methylation reagent and reacting with diphenylamine, the present invention does not require the use of any catalyst, greatly reducing the cost; the reaction conditions can be under normal pressure without high - temperature and high - pressure conditions; the conversion rate is high, the yield is high (up to 94.8% - 98.1%), there are basically no side reactions, the resource utilization rate is high, and the post - treatment process is simple. The N - methyl diphenylamine product prepared by the preparation method of the present invention has a high purity (up to 99.5% - 99.8%). Tetramethylammonium hydroxide belongs to a green chemical product. After participating in the reaction in the reaction system, it decomposes into trimethylamine without residue and does not need to be treated separately, reducing the post - treatment operation process and being environmentally friendly. By - products such as water, solvent, and trimethylamine can be reused.

[0054] The present invention develops a new way to prepare N - methyl diphenylamine, greatly reducing the cost, being highly feasible for large - scale production, greatly promoting the development and utilization of this chemical product, and having a good market prospect for the research on its new synthesis route.

[0055] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the present invention. The methods, reagents, and materials used in the embodiments are conventional methods, reagents, and materials in the art unless otherwise specified. The raw material compounds in the embodiments can all be obtained through commercial channels.

[0056] Purity detection: The gas chromatography detection method was adopted, and the analytical instrument was Agilent gas chromatograph 6820; the chromatographic column was Agilent HP-5 gas chromatograph; the detector was FID (hydrogen flame ionization detector); the injection port mode was split; the injection port temperature was 280 °C; among them, the operating conditions are shown in Table 1 below:

[0057] Table 1. Operating conditions for purity detection

[0058] Heating rate (°C / min) Column temperature (°C) Retention time (min) Initial - 90 0 Gradient 1 15 270 0 Gradient 2 1 280 5

[0059] Example 1

[0060] S1. Under a nitrogen atmosphere, 84.6 g (0.5 mol) of diphenylamine and 85.0 g of the polar solvent N-methylpyrrolidone were put into a 500 mL four-necked flask to obtain a first mixed solution, and the temperature was raised to 190 °C. Then, a second mixed solution composed of 338.4 g of a 25% aqueous solution of tetramethylammonium hydroxide and 85.0 g of N-methylpyrrolidone was slowly added dropwise to the reaction system with a peristaltic pump. At 190 °C, the addition was completed within 4 h, and the dropping rate was 105.85 g / h; the reaction continued until the second mixed solution was added dropwise, and the trimethylamine tail gas was absorbed with a 20 wt% hydrochloric acid solution.

[0061] S2. The reaction solution after the reaction was kept warm for 0.5 h, and the temperature was lowered to 80 °C. A small amount of methanol in the reaction system was removed by atmospheric distillation (part of the tetramethylammonium hydroxide will decompose to form trimethylamine and methanol). Then the temperature was raised to 100 °C, and water in the reaction system was removed by the first vacuum distillation. Finally, the temperature was raised to 170 °C, and N-methylpyrrolidone in the reaction system was removed by the second vacuum distillation. The bottom liquid obtained was the finished product of N-methyldiphenylamine, and 90.1 g of a light yellow finished product was obtained, with a yield of 98.1% and a product purity of 99.8%. The calculation method of the yield is the mass of the actually obtained N-methyldiphenylamine / the theoretical mass of N-methyldiphenylamine. The yield calculation formula for this example is 90.1 * 99.8% / (0.5 * 183.249) = 98.1%.

[0062] Example 2

[0063] S1. Under a nitrogen atmosphere, 126.9 g (0.75 mol) of diphenylamine and 340 g of the polar solvent dimethyl sulfoxide were added to a 2000 mL four-necked flask to obtain a first mixed solution, and the temperature was raised to 180 °C. Then, a second mixed solution composed of 507.6 g of a 25% by mass aqueous solution of tetramethylammonium hydroxide and 200 g of dimethyl sulfoxide was slowly added dropwise to the reaction system using a peristaltic pump. At 190 °C, the addition was completed within 6 h, and the dropping rate was 117.9 g / h. The reaction continued until the second mixed solution was completely added dropwise, and the trimethylamine tail gas was absorbed with a 50 wt% sulfuric acid solution.

[0064] S2. The reaction solution after the reaction was kept warm for 0.5 h, and the temperature was lowered to 80 °C. A small amount of methanol in the reaction system was removed by atmospheric distillation. Then, the temperature was raised to 100 °C, and water in the reaction system was removed by the first vacuum distillation. Finally, the temperature was raised to 150 °C, and dimethyl sulfoxide in the reaction system was removed by the second vacuum distillation. The resulting bottom liquid was the finished product of N-methyl diphenylamine. 132.8 g of a light yellow finished product was obtained, with a yield of 96.3% and a product purity of 99.7%.

[0065] Example 3

[0066] S1. Under a nitrogen atmosphere, 84.6 g (0.5 mol) of diphenylamine and 85.0 g of the polar solvent N-methylpyrrolidone were added to a 500 mL four-necked flask to obtain a first mixed solution, and the temperature was raised to 190 °C. Then, a second mixed solution composed of 1015.2 g of a 25% by mass aqueous solution of tetramethylammonium hydroxide and 85.0 g of N-methylpyrrolidone was slowly added dropwise to the reaction system using a peristaltic pump. At 190 °C, the addition was completed within 4 h, and the dropping rate was 275.1 g / h. The reaction continued until the second mixed solution was completely added dropwise, and the trimethylamine tail gas was absorbed with a 30 wt% hydrochloric acid solution.

[0067] S2. The reaction solution after the reaction was kept warm for 0.5 h, and the temperature was lowered to 80 °C. A small amount of methanol in the reaction system was removed by atmospheric distillation. Then, the temperature was raised to 100 °C, and water in the reaction system was removed by the first vacuum distillation. Finally, the temperature was raised to 170 °C, and N-methylpyrrolidone in the reaction system was removed by the second vacuum distillation. The resulting bottom liquid was the finished product of N-methyl diphenylamine. 89.2 g of a light yellow finished product was obtained, with a yield of 96.9% and a product purity of 99.5%.

[0068] Example 4

[0069] S1. Under a nitrogen atmosphere, 42.3 g (0.25 mol) of diphenylamine and 43 g of the polar solvent dimethyl sulfoxide were added to a 2000 mL four-necked flask to obtain a first mixed solution, and the temperature was raised to 180 °C. Then, a second mixed solution composed of 1692.0 g of a 25% aqueous solution of tetramethylammonium hydroxide and 42.3 g of dimethyl sulfoxide was slowly added dropwise to the reaction system using a peristaltic pump. At 190 °C, the addition was completed within 6 h, and the dropping rate was 288.6 g / h. The reaction continued until the second mixed solution was completely added dropwise, and the trimethylamine tail gas was absorbed with a 40 wt% sulfuric acid solution.

[0070] S2. The reaction solution after the reaction was kept warm for 0.5 h, and then the temperature was lowered to 80 °C. A small amount of methanol in the reaction system was removed by distillation under atmospheric pressure. Then the temperature was raised to 100 °C, and water in the reaction system was removed by the first vacuum distillation. Finally, the temperature was raised to 150 °C, and dimethyl sulfoxide in the reaction system was removed by the second vacuum distillation. The resulting bottom liquid was the finished product of N-methyl diphenylamine. 43.6 g of a light yellow finished product was obtained, with a yield of 94.8% and a product purity of 99.6%.

[0071] Comparative Example 1

[0072] S1. Under a nitrogen atmosphere, 42.3 g (0.25 mol) of diphenylamine and 43 g of dimethyl sulfoxide were added to a 1000 mL four-necked flask, and the temperature was lowered to 0 °C. Then, 6.5 g (0.27 mol) of sodium hydride was added to the system in batches, and the reaction was kept warm at 0 °C for 1 h. Then, 39 g (0.275 mol) of methyl iodide was added dropwise to the system, and the addition was completed within 0.5 h, and the dropping rate was 72 g / h. The reaction continued until the methyl iodide was completely added dropwise. The hydrogen iodide tail gas was absorbed with a 30 wt% sodium hydroxide solution.

[0073] S2. The reaction solution was kept warm overnight at 25 °C, then 100 g of water was added to the reaction solution for quenching, and it was stirred at 25 °C for 1 h. Then, 500 g of ethyl acetate was added for organic phase extraction. The obtained organic phase was first heated to 100 °C, and ethyl acetate was removed under atmospheric pressure. Then, the temperature was raised to 180 °C, and a small amount of dimethyl sulfoxide remaining in the extraction was removed by vacuum distillation. The resulting bottom liquid was the finished product of N-methyl diphenylamine. 33.6 g of a light brown finished product was obtained, with a yield of 71.4% and a product purity of 97.4%.

Claims

1. A method for preparing N-methyl diphenylamine, characterized in that, It includes the following steps: React diphenylamine with tetramethylammonium hydroxide to produce N-methyldiphenylamine; wherein, the mass ratio of diphenylamine to tetramethylammonium hydroxide is 1:(1-10).

2. The preparation method of N-methyl diphenylamine according to claim 1, characterized in that, The mass ratio of the diphenylamine to the tetramethylammonium hydroxide is 1:(1-6), preferably 1:(1-3).

3. The preparation method of N-methyl diphenylamine according to claim 1, characterized in that, The reaction is carried out in a solvent, and the mass ratio of the diphenylamine to the solvent is 1:(1-10), preferably 1:(1-6), more preferably 1:(1-3).

4. The preparation method of N-methyl diphenylamine according to claim 1, characterized in that The method satisfies one or more of the following characteristics: The tetramethylammonium hydroxide is added to the reaction system in the form of an aqueous solution, and the mass concentration of tetramethylammonium hydroxide in the aqueous solution is 1%-99%, preferably 20%-50%, more preferably 25%-40%; The reaction is carried out in a polar solvent, and the polar solvent is preferably selected from one or more of dimethyl sulfoxide, N-methylpyrrolidone, γ-butyrolactone, N,N-dimethylacetamide, N,N-dimethylformamide, and ethylene glycol.

5. The preparation method of N-methyl diphenylamine according to claim 1, characterized in that, The temperature of the reaction is 100-250°C, preferably 150-200°C, more preferably 180-200°C.

6. The preparation method of N-methyl diphenylamine according to claim 1, characterized in that, The method includes the following steps: Dropwise add tetramethylammonium hydroxide to diphenylamine for reaction to produce N-methyldiphenylamine.

7. The preparation method of N-methyl diphenylamine according to claim 6, characterized in that, The method includes the following steps: (1) Mix diphenylamine and part of the solvent to obtain a first mixed solution; mix tetramethylammonium hydroxide or its aqueous solution and the remaining solvent to obtain a second mixed solution; (2) Dropwise add the second mixed solution to the first mixed solution for reaction.

8. The preparation method of N-methyl diphenylamine according to claim 7, characterized in that, The dropping rate is 50-500 g / h, preferably 100-300 g / h.

9. The preparation method of N-methyl diphenylamine according to claim 1, characterized in that, After the reaction, post-treatment is further included, and the steps of the post-treatment include: subjecting the reaction solution after the reaction to atmospheric distillation, first vacuum distillation, and second vacuum distillation in sequence, and the bottom liquid obtained after the second vacuum distillation is the N-methyldiphenylamine.

10. The preparation method of N-methyl diphenylamine according to claim 9, characterized in that, The method has one or more of the following characteristics: The temperature of the atmospheric distillation is 65-85°C; The temperature of the first vacuum distillation is 100-110°C; The temperature of the second vacuum distillation is 150-180°C.

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