Synthetic method of environment-friendly 5, 6-dimethyl benzimidazole

Abstract

The invention belongs to the technical field of organic chemistry, and mainly relates to preparation of 5, 6-dimethyl benzimidazole, in particular to a synthetic method of environment-friendly 5, 6-dimethyl benzimidazole. According to the method, an environment-friendly organic solvent is adopted to replace a traditional solvent and is combined with a novel catalyst, so that the selectivity and the yield of the reaction are remarkably improved, the use of sulfuric acid is reduced to a great extent, the generation of wastes is reduced to the maximum extent, meanwhile, the catalyst is easy to recycle and reuse, and the reaction cost is reduced. The synthesis method is simple and convenient to operate, mild in condition, environment-friendly and sustainable, has unique advantages and technical progress, has wide market prospects and economic benefits in practical application, and provides a new direction and solution for development of an environment-friendly chemical synthesis technology.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and mainly relates to the preparation of 5,6-dimethylbenzimidazole, and in particular to a method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole. Background Art

[0002] 5,6-Dimethylbenzimidazole is a white crystalline powder. It is an important preliminary raw material for the bio-fermentation synthesis of vitamin B12, so it is also called vitamin B12 precursor.

[0003] The production processes at home and abroad mainly include two routes: one is to use o-xylene as the matrix, through the Friedel-Crafts reaction, to generate 3,4-dimethyl acetone, react with hydroxylamine hydrochloride to generate 3,4-dimethyl acetophenone oxime, and then through Beckmann rearrangement to generate 3,4-dimethylbenzamide, and then through nitration, hydrolysis, and reduction to obtain 4,5-dimethyl-1,2-diphenylamine, and finally condense with formic acid to obtain the final product 5,6-dimethylbenzimidazole. The operating conditions of this technical route are harsh and it is difficult to achieve industrial production; the other is to use 3,4-dimethylaniline as the matrix, and obtain the product through acetylation, nitration, hydrolysis, reduction, and condensation. Although this technology has made some progress, it still has problems such as low product selectivity, large amount of acetic anhydride used in acetylation reaction, large amount of concentrated sulfuric acid used in mixed acid nitration reaction, and large amount of acid-containing wastewater polluting the environment during the production process. Summary of the invention

[0004] In view of the above problems, the present invention proposes a method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole, and the specific operation steps are as follows:

[0005] S1. 5-12 g of anhydrous zinc sulfate, 35-40 g of anhydrous ferric chloride and 20-30 g of manganese sulfate are put into a beaker, 100-160 ml of deionized water is added, and the mixture is stirred at 70-90° C. for 10-20 min. Then, 30-35 g of ammonium bicarbonate is added and the stirring is continued for 10-15 min. The pH value of the solution is adjusted to 7-9 by using NH3·H2O, and then the mixture is allowed to stand for 12-24 h. The obtained precipitate is filtered, washed with deionized water for 3-5 times, dried in an oven for 12 h, and then calcined in a tubular furnace for 1-3 h. The calcination temperature is set to 800-1100° C. to obtain a magnetic carrier. Then, 3-8 g of the magnetic carrier and 2-4 g of zirconium oxychloride are placed in 20-30 ml of deionized water to form a suspension, and NH3·H2O is used to obtain the magnetic carrier. 2O is added to adjust the pH value to 8-9, and then stirred in a water bath for 0.5-1.5h, the water bath temperature is set to 65-75°C, after the stirring is completed, it is allowed to stand at room temperature for 12h, filtered, washed with deionized water for 3-5 times to obtain a precipitate, and the precipitate is soaked in a 0.25-0.8mol / L ammonium thiosulfate solution for 2-5h, and then calcined at 300-500°C for 2-5h to obtain a modified sulfuric acid catalyst A with magnetism; this step prepares a solid acid catalyst with superior performance by organically combining sulfuric acid and zirconium, solves the problem of high corrosion of equipment by liquid acid catalysts such as sulfuric acid in the past, and at the same time, this step uses a manganese-zinc-iron oxide composite as a carrier, which gives the catalyst A a strong magnetism, and simplifies the catalyst recovery operation process and operation cost;

[0006] S2, take 80-120ml of 1,2-dichloroethane and 20-50ml of acetic acid and add them to a beaker, add 3-5g of the catalyst A obtained in step S1, stir for 5-10min, transfer to a microwave reactor after mixing evenly, then slowly add 12.1g of 3,4-dimethylaniline, set the temperature to 40-60°C, the rated power to 700W, react for 1-2h, filter and separate the catalyst, and obtain the product 3,4-dimethylacetanilide after the acetylation reaction; in the prior art, in order to make the acetylation more thorough, excessive acetic anhydride is often used to promote the reaction, resulting in a large amount of acid waste. The step of introducing the catalyst A obtained in step S1 can effectively increase the reaction efficiency, reduce the amount of acid anhydride used, and thus reduce the discharge of acidic wastewater. On the other hand, this step uses dichloromethane as a solvent to promote the dissolution of 3,4-dimethylaniline, further improve the contact between acetic anhydride-catalyst A-3,4-dimethylaniline, and efficiently promote the acetylation process. At the same time, dichloromethane can be directly used as a solvent for subsequent reactions, eliminating the work of solvent replacement in the previous technology. In addition, the microwave synthesis technology used in this step is safe and simple to operate, and the microwave catalysis can effectively shorten the reaction time compared with the previous thermal reaction, and the reaction efficiency is higher;

[0007] S3, when the 3,4-dimethylacetanilide solution obtained in step S2 is cooled to 25-30°C, 20-35ml of acetic anhydride-acetic acid mixture is slowly added, and the addition ratio of the two is 1-1.2:1.5-3, and then stirred at 0°C for 15-30min, after it is fully mixed, 5-8ml of concentrated nitric acid with a mass fraction of 98% is slowly dripped, and after mixing evenly, the water bath reaction temperature is set to 20-50°C, and the reaction is carried out for 3-4h, and then the mixed solution is poured into 20-40ml of ice-water mixture, stirred to precipitate solid nitrate, and the filter cake is collected after suction filtration, and the ice-water mixture is used to wash it repeatedly for 3-5 times to wash away the free acid. After vacuum drying for 12-24h, the nitration crude product can be obtained, and the filtrate and the mixture of the spent acid are stored as solvent circulation liquid for standby use, and then the volume fraction is used for separation. The nitration crude product is crystallized and refined by a deionized water-ethyl acetate-cyclohexane system with a ratio of 3:4-6:2-5 to obtain refined 4,5-dimethyl-2-nitroacetanilide; in the mixed acid nitration process in this step, the mixed solution of step S1 is directly used, which simplifies the operation steps and also reduces the amount of part of the acid serving as the reaction medium. The heat release of the mixed acid is reduced, so that the demand for ice-water mixed solution in the process of precipitating solid nitrate is also greatly reduced, effectively saving energy consumption. On the other hand, in the conventional technology, a mixed solution of sulfuric acid and nitric acid is used for nitration, and the reaction is violent and the amount of concentrated sulfuric acid is large. In this step, acetic anhydride-acetic acid is used instead of concentrated sulfuric acid, which can effectively control the hydrolysis of the acid. At the same time, the purity of the subsequent product is effectively improved by crystallization and refining of the deionized water-ethyl acetate-cyclohexane system;

[0008] S4, 5-15g of the refined 4,5-dimethyl-2-nitroacetanilide obtained in the above step S3 is placed in a round-bottom flask, 30-50ml of a 5%-10% sodium hydroxide solution is added, mixed and stirred for 0.5h, and then equipped with a reflux device for reflux for 1-3h, and the reflux temperature is set to 90-110°C. After the reaction is completed, suction filtration is performed to obtain a red solid product, namely 4,5-dimethyl-2-nitroaniline;

[0009] S5, take 5-10g of 4,5-dimethyl-2-nitroaniline in step S4 and put it into a beaker equipped with a mechanical stirring device, add 2-5g of carbonyl iron powder and 10-20ml of ethyl acetate-methanol (1-2: 1-1.5) mixed solution, stir for 10-20min at a temperature of 30-45°C, then slowly add 15-30ml of 2% TPGS-750-M aqueous solution, continue stirring for 5-10min, then add 3-5g of ammonium chloride, mix well, continue stirring for 4-6h, and wait for the reaction to proceed. After the reaction is complete, the mixture is filtered and washed with ethyl acetate and deionized water for 1-3 times respectively to obtain 4,5-dimethyl-1,2-phenylenediamine. In the prior art, the reaction process must be carried out under the catalysis of hydrogen and precious metal catalysts. This step is carried out by synergistic catalysis with carbonyl iron powder under the nano-micelles composed of TPGS-750, and the reduction amination is carried out without using special high-pressure equipment and hydrogen that is difficult to transport, which effectively reduces the economic cost. At the same time, the carbonyl iron powder in the system can be reused, and the catalyst can be washed with ammonium chloride only to ensure its reaction activity.

[0010] S6. Place 3-7 g of 4,5-dimethyl-1,2-phenylenediamine obtained in step S5 and 2-3 g of anhydrous formic acid in a round-bottom flask, set the temperature to 90-110° C., reflux while stirring, and react for 1.5-2.5 hours. After the reaction is complete, add 1%-5% potassium carbonate solution several times to adjust the pH of the mixed solution to 8, let it stand for 1.5-3 hours, and then filter with a Buchner funnel to obtain a crude product, then put it into 50 ml of an aqueous solution with a mass fraction of 1% activated carbon, set the temperature to 35-50° C., continue stirring for 0.5-1.5 hours, and obtain the final product 5,6-dimethylbenzimidazole by filtration, washing with deionized water and vacuum drying.

[0011] Preferably, the amount of manganese sulfate used in step S1 is 22 g.

[0012] Preferably, the concentration of the ammonium thiosulfate solution in step S1 is 0.4 mol / L.

[0013] Preferably, the amount of 1,2-dichloroethane used in step S2 is 105 ml.

[0014] Preferably, the amount of catalyst A added in step S2 is 3.4 g.

[0015] Preferably, in step S3, the addition ratio of acetic anhydride to acetic acid is 1.2:1.6.

[0016] Preferably, the amount of 2-5g carbonyl iron powder added in step S5 is 3.6g.

[0017] Preferably, the amount of the TPGS-750-M aqueous solution added in step S5 is 24 ml.

[0018] Preferably, the mass concentration of the potassium carbonate solution in step S6 is 5%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. In order to make the acetylation more thorough, the invention introduces catalyst A, which can effectively increase the reaction efficiency, reduce the amount of acid anhydride used, and thus reduce the discharge of acidic wastewater; on the other hand, the solid acid catalyst A prepared by the invention solves the problem of high corrosion of equipment by liquid acid catalysts such as sulfuric acid in the past by organically combining sulfuric acid and zirconium. At the same time, this step uses a manganese-zinc-iron oxide complex as a carrier, which gives the catalyst a strong magnetism and simplifies the catalyst recovery operation process and operating cost;

[0021] 2. The present invention uses dichloromethane as a solvent for both acetylation and nitration, which effectively promotes the dissolution of 3,4-dimethylaniline, simplifies the operation steps, and reduces the consumption of a large amount of chemical solvents. On the other hand, acetic anhydride-acetic acid is used in the nitration process instead of the previous concentrated sulfuric acid, which effectively controls the hydrolysis of the acid and is beneficial to improving the purity of subsequent products.

[0022] 3. The microwave synthesis technology used in this invention is safe and simple to operate. Compared with previous thermal reactions, it has higher reaction efficiency, lower energy consumption and is more environmentally friendly.

[0023] 4. This invention uses nano-micelles composed of TPGS-750 to synergistically catalyze with carbonyl iron powder, and performs reductive amination without using special high-pressure equipment or hydrogen that is difficult to transport, which effectively reduces economic costs. At the same time, the catalyst can be reused after simple washing with ammonium chloride to ensure its reaction activity, which is in line with current sustainable and environmentally friendly strategies. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 It is the process route diagram of the present invention.

[0026] Figure 2 This is a scan of catalyst A in Example 1 of the present invention.

[0027] Figure 3This is a performance evaluation diagram of the cyclic use of catalyst A in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the content of the present invention and are not used to limit the present invention.

[0029] Embodiment 1:

[0030] S1. Take 6g of anhydrous zinc sulfate, 35g of anhydrous ferric chloride and 22g of manganese sulfate into a beaker, add 130ml of deionized water, stir at 70°C for 15min, then add 30g of ammonium bicarbonate and continue stirring for 10min, and adjust the pH of the solution to 7 with NH3·H2O, then let it stand for 12h, filter the obtained precipitate, wash it with deionized water 3 times, dry it in an oven for 24h, and then calcine it in a tubular furnace for 2h, and set the calcination temperature to 1000°C to obtain a magnetic carrier. body, then take 5.5g of magnetic carrier and 2.8g of zirconium oxychloride and place them in 30ml of deionized water to form a suspension, adjust the pH to 9 with NH3·H2O, then stir in a water bath for 0.5h, the water bath temperature is set to 70℃, after stirring, stand at room temperature for 12h, filter and wash with deionized water 3 times to obtain a precipitate, soak it in 0.4mol / L ammonium thiosulfate solution for 3h, and then calcine at 450℃ for 3h to obtain a modified sulfuric acid catalyst A with magnetic properties;

[0031] S2, take 105 ml of 1,2-dichloroethane and 30 ml of acetic acid and add them to a beaker, add 3.4 g of the catalyst A obtained in step S1, stir for 10 min, transfer to a microwave reactor after mixing evenly, then slowly add 12.1 g of 3,4-dimethylaniline, set the temperature to 45 ° C, the rated power to 700 W, react for 1.5 hours, filter and separate the catalyst, and obtain the product 3,4-dimethylacetanilide after the acetylation reaction;

[0032] S3, when the 3,4-dimethylacetanilide solution obtained in step S2 is cooled to 25°C, 35ml of acetic anhydride-acetic acid mixture is slowly added, the addition ratio of the two is 1.2:1.6, and then stirred at 0°C for 15min, after being fully mixed, 6ml of concentrated nitric acid with a mass fraction of 98% is slowly dripped, after mixing evenly, the reaction temperature is set to 20°C, and the reaction is carried out for 4h, and then the mixed solution is poured into 30ml of ice-water mixture, stirred to precipitate solid nitrate, and the filter cake is collected after suction filtration, and the ice-water mixture is used to wash it repeatedly 4 times to wash away the free acid, and the nitration crude product can be obtained after vacuum drying for 24h, and the filtrate and the mixture of the waste acid are stored as a solvent circulation liquid for standby use, and then the nitration crude product is crystallized and refined using a deionized water-ethyl acetate-cyclohexane system with a volume fraction of 3:4:2 to obtain refined 4,5-dimethyl-2-nitroacetanilide;

[0033] S4, put 10g of the refined 4,5-dimethyl-2-nitroacetanilide obtained in the above step S3 into a round-bottom flask, add 30ml of a 5% sodium hydroxide solution by mass, mix and stir for 0.5h, reflux for 2h in a reflux device, and set the reflux temperature to 95°C. After the reaction is completed, filter and obtain a red solid product, which is 4,5-dimethyl-2-nitroaniline;

[0034] S5, take 5.8g of 4,5-dimethyl-2-nitroaniline in step S4 and put it into a beaker equipped with a mechanical stirring device, add 3.6g of carbonyl iron powder and 20ml of ethyl acetate-methanol (1:1.5) mixed solution, stir for 15min at a temperature of 35°C, then slowly add 24ml of TPGS-750-M aqueous solution with a mass fraction of 2%, continue stirring for 10min, then add 4.2g of ammonium chloride, mix well, continue stirring for 4h, filter after the reaction is complete, wash with ethyl acetate and deionized water for 3 times respectively, and you can get 4,5-dimethyl-1,2-phenylenediamine;

[0035] S6. Place 4.5 g of 4,5-dimethyl-1,2-phenylenediamine obtained in step S5 and 2.7 g of anhydrous formic acid in a round-bottom flask, set the temperature to 110°C, reflux while stirring, and react for 2 hours. After the reaction is complete, add 5% potassium carbonate solution several times to adjust the pH of the mixed solution to 8, let it stand for 3 hours, and then filter with a Buchner funnel to obtain a crude product, then put it into 50 ml of an aqueous solution with a mass fraction of 1% activated carbon, set the temperature to 35°C, continue stirring for 1.5 hours, and obtain the final product 5,6-dimethylbenzimidazole by filtration, washing with deionized water and vacuum drying.

[0036] Comparative Example 1: Except that manganese sulfate is not added in step S1, the remaining steps are the same as those in Example 1.

[0037] Comparative Example 2: Except that zirconium oxychloride is not added in step S1, the remaining steps are the same as those in Example 1.

[0038] Comparative Example 3: Except that catalyst A is not added in step S1, the remaining steps are the same as those in Example 1.

[0039] like Figure 1 As shown, the present invention provides an environmentally friendly method for synthesizing 5,6-dimethylbenzimidazole, which can efficiently complete the synthesis of the target product under the efficient catalysis of the catalyst. In Example 1, a magnetic modified sulfuric acid catalyst A was designed and prepared, such as Figure 2 As shown, the average size of the catalyst is 80nm, which is a typical nanostructure, and its surface is rough, which is conducive to reducing mass transfer resistance and increasing the contact between reactants and catalysts. The present invention evaluates the catalytic performance of the catalyst with the yield of 3,4-dimethylacetanilide. As shown in Table 1, the yields of 3,4-dimethylacetanilide in Example 1, Comparative Example 1 and Comparative Example 2 are 99.6%, 80.5% and 60.5% respectively, while the yield of Comparative Example 3 is only 40.2%, because the synergistic effect between the Mn-Zn ferrite and zirconium oxychloride in Example 1 can obtain high-strength acid t-ZrO2, which forms a magnetic solid acid together with fixed high sulfuric acid, and synergistically and efficiently promotes the occurrence of the reaction.

[0040] Table 1

[0041] Group Yield of 3,4-dimethylacetanilide (%) Is it magnetic? Example 1 99.6±0.5 yes Comparative Example 1 80.5±1.0 yes Comparative Example 2 60.5±2.0 yes Comparative Example 3 40.2±0.8 -

[0042] In addition, the present invention also investigates the recycling performance of the catalyst. The recovered catalyst is washed with methanol three times and then dried at 100°C for 24 hours before being used next time. The experimental results show that Figure 3 As shown, after the catalyst was recycled for 4 times, the yield of 3,4-dimethylacetanilide was still maintained above 90%, proving that the catalyst has excellent stability and recycling performance.

[0043] Embodiment 2:

[0044] S1. Take 6g of anhydrous zinc sulfate, 33g of anhydrous ferric chloride and 22g of manganese sulfate and put them into a beaker, add 130ml of deionized water, stir at 70℃ for 15min, then add 30g of ammonium bicarbonate and continue stirring for 10min, and adjust the pH of the solution to 7 with NH3·H2O, then let it stand for 12h, filter the obtained precipitate, wash it with deionized water 3 times, dry it in an oven for 24h, and then calcine it in a tubular furnace for 2h, and set the calcination temperature to 1000℃ to obtain magnetic carrier, then take 5g of the magnetic carrier and 2.8g of zirconium oxychloride and place them in 30ml of deionized water to form a suspension, adjust the pH to 9 with NH3·H2O, then stir in a water bath for 0.5h, the water bath temperature is set to 75°C, after stirring, stand at room temperature for 12h, filter and wash with deionized water 3 times to obtain a precipitate, soak it in a 0.4mol / L ammonium thiosulfate solution for 3h, and then calcine at 450°C for 3h to obtain a modified sulfuric acid catalyst A with magnetic properties;

[0045] S2, take 105 ml of 1,2-dichloroethane and 30 ml of acetic acid and add them to a beaker, add 3.4 g of the catalyst A obtained in step S1, stir for 10 min, transfer to a microwave reactor after mixing evenly, then slowly add 12.1 g of 3,4-dimethylaniline, set the temperature to 45 ° C, the rated power to 700 W, react for 1.5 hours, filter and separate the catalyst, and obtain the product 3,4-dimethylacetanilide after the acetylation reaction;

[0046] S3, when the 3,4-dimethylacetanilide solution obtained in step S2 is cooled to 25°C, 35ml of acetic anhydride-acetic acid mixture is slowly added, the addition ratio of the two is 1.2:1.6, and then stirred at 0°C for 15min, after being fully mixed, 6ml of concentrated nitric acid with a mass fraction of 98% is slowly dripped, after mixing evenly, the reaction temperature is set to 20°C, and the reaction is carried out for 4h, and then the mixed solution is poured into 30ml of ice-water mixture, stirred to precipitate solid nitrate, and the filter cake is collected after suction filtration, and the ice-water mixture is used to wash it repeatedly 4 times to wash away the free acid, and the nitration crude product can be obtained after vacuum drying for 24h, and the filtrate and the mixture of the waste acid are stored as a solvent circulation liquid for standby use, and then the nitration crude product is crystallized and refined using a deionized water-ethyl acetate-cyclohexane system with a volume fraction of 3:4:2 to obtain refined 4,5-dimethyl-2-nitroacetanilide;

[0047] S4, put 10g of the refined 4,5-dimethyl-2-nitroacetanilide obtained in the above step S3 into a round-bottom flask, add 20ml of a 5% sodium hydroxide solution by mass, mix and stir for 0.5h, reflux for 2h in a reflux device, and set the reflux temperature to 95°C. After the reaction is completed, filter and obtain a red solid product, which is 4,5-dimethyl-2-nitroaniline;

[0048] S5, take 5.8g of 4,5-dimethyl-2-nitroaniline in step S4 and put it into a beaker equipped with a mechanical stirring device, add 3.6g of carbonyl iron powder and 20ml of ethyl acetate-methanol (1:1.5) mixed solution, stir for 15min at a temperature of 35°C, then slowly add 24ml of TPGS-750-M aqueous solution with a mass fraction of 2%, continue stirring for 10min, then add 4.2g of ammonium chloride, mix well, continue stirring for 4h, filter after the reaction is complete, wash with ethyl acetate and deionized water for 3 times respectively, and you can get 4,5-dimethyl-1,2-phenylenediamine;

[0049] S6. Place 4.5 g of 4,5-dimethyl-1,2-phenylenediamine obtained in step S5 and 2.7 g of anhydrous formic acid in a round-bottom flask, set the temperature to 110°C, reflux while stirring, and react for 2 hours. After the reaction is complete, add 5% potassium carbonate solution several times to adjust the pH of the mixed solution to 8, let it stand for 3 hours, and then filter with a Buchner funnel to obtain a crude product, then put it into 50 ml of an aqueous solution with a mass fraction of 1% activated carbon, set the temperature to 35°C, continue stirring for 2 hours, and obtain the final product 5,6-dimethylbenzimidazole by filtration, washing with deionized water and vacuum drying.

[0050] Comparative Example 4: The acetic anhydride-acetic acid mixed solution in step S3 is replaced by concentrated sulfuric acid with a mass fraction of 98%, and the remaining steps are the same as those in Example 2.

[0051] In the mixed acid nitration process of Example 2, acetic anhydride-acetic acid mixed solution is used instead of conventional concentrated sulfuric acid to reduce the heat release of the mixed acid. As shown in Table 2, the ice-water mixed solution required in Example 2 is 30 ml, and 70 ml is required in Comparative Example 4, which shows that the use of acetic anhydride-acetic acid mixed solution can greatly reduce the demand for ice-water mixed solution in the process of precipitating solid nitrates, saving energy consumption. On the other hand, the present invention compares the yield and purity of 4,5-dimethyl-2-nitroacetanilide synthesized in Example 2 and Comparative Example 4, wherein the product purity is quantitatively detected by liquid chromatography, the mobile phase is acetonitrile: water, and the flow rate is set to 1.0 mL min -1, UV wavelength 248nm. The experimental results are shown in Table 2. The yield of Example 2 is 89.5% and the purity is 99.8%, indicating that the effects of the acetic anhydride-acetic acid mixture and concentrated sulfuric acid in the nitration process are basically the same. The use of the acetic anhydride-acetic acid mixture does not affect the product quality, but greatly reduces the danger of the reaction, energy consumption and impact on the environment.

[0052] Table 2

[0053]

[0054] Embodiment 3:

[0055] S1. Take 6g of anhydrous zinc sulfate, 35g of anhydrous ferric chloride and 18g of manganese sulfate and put them into a beaker, add 130ml of deionized water, stir at 70℃ for 15min, then add 30g of ammonium bicarbonate and continue stirring for 10min, and adjust the pH of the solution to 7 with NH3·H2O, then let it stand for 12h, filter the obtained precipitate, wash it with deionized water 3 times, dry it in an oven for 24h, and then calcine it in a tubular furnace for 2h, and set the calcination temperature to 1000℃ to obtain a magnetic carrier. body, then take 5.0g of magnetic carrier and 2.5g of zirconium oxychloride and place them in 30ml of deionized water to form a suspension, adjust the pH to 9 with NH3·H2O, then stir in a water bath for 0.5h, the water bath temperature is set to 70℃, after stirring, stand at room temperature for 12h, filter and wash with deionized water 3 times to obtain a precipitate, soak it in 0.4mol / L ammonium thiosulfate solution for 3h, and then calcine at 450℃ for 3h to obtain a modified sulfuric acid catalyst A with magnetic properties;

[0056] S2, take 100 ml of 1,2-dichloroethane and 30 ml of acetic acid and add them to a beaker, add 3.4 g of the catalyst A obtained in step S1, stir for 10 min, transfer to a microwave reactor after mixing evenly, then slowly add 11.2 g of 3,4-dimethylaniline, set the temperature to 45 ° C, the rated power to 700 W, react for 1.5 h, filter and separate the catalyst, and obtain the product 3,4-dimethylacetanilide after the acetylation reaction;

[0057] S3, when the 3,4-dimethylacetanilide solution obtained in step S2 is cooled to 25°C, 35ml of acetic anhydride-acetic acid mixture is slowly added, the addition ratio of the two is 1:1.8, and then stirred at 0°C for 15min, after being fully mixed, 6ml of concentrated nitric acid with a mass fraction of 98% is slowly dripped, after mixing evenly, the reaction temperature is set to 20°C, and the reaction is carried out for 4h, and then the mixed solution is poured into 30ml of ice-water mixture, stirred to precipitate solid nitrate, and the filter cake is collected after suction filtration, and the ice-water mixture is used to wash it repeatedly for 4 times to wash away the free acid, and the nitration crude product can be obtained after vacuum drying for 24h, and the filtrate and the mixture of the waste acid are stored as a solvent circulation liquid for standby use, and then the nitration crude product is crystallized and refined using a deionized water-ethyl acetate-cyclohexane system with a volume fraction of 3:4:2 to obtain refined 4,5-dimethyl-2-nitroacetanilide;

[0058] S4, put 10g of the refined 4,5-dimethyl-2-nitroacetanilide obtained in the above step S3 into a round-bottom flask, add 30ml of a 5% sodium hydroxide solution by mass, mix and stir for 1h, reflux for 2h in a reflux device, and set the reflux temperature to 95°C. After the reaction is completed, filter and obtain a red solid product, which is 4,5-dimethyl-2-nitroaniline;

[0059] S5, take 5.8g of 4,5-dimethyl-2-nitroaniline in step S4 and put it into a beaker equipped with a mechanical stirring device, add 3.6g of carbonyl iron powder and 20ml of ethyl acetate-methanol (1:1.5) mixed solution, stir for 15min at a temperature of 35°C, then slowly add 24ml of TPGS-750-M aqueous solution with a mass fraction of 2%, continue stirring for 10min, then add 4.2g of ammonium chloride, mix well, continue stirring for 4h, filter after the reaction is complete, wash with ethyl acetate and deionized water for 3 times respectively, and you can get 4,5-dimethyl-1,2-phenylenediamine;

[0060] S6. Place 4 g of 4,5-dimethyl-1,2-phenylenediamine obtained in step S5 and 1.8 g of anhydrous formic acid in a round-bottom flask, set the temperature to 100° C., reflux while stirring, and react for 2 hours. After the reaction is complete, add 5% potassium carbonate solution several times to adjust the pH of the mixed solution to 8, let it stand for 3 hours, and then filter with a Buchner funnel to obtain a crude product, then put it into 50 ml of an aqueous solution with a mass fraction of 1% activated carbon, set the temperature to 35° C., continue stirring for 1.5 hours, and obtain the final product 5,6-dimethylbenzimidazole by filtration, washing with deionized water and vacuum drying.

[0061] Comparative Example 5: Except that carbonyl iron powder is not added in step S5, the remaining steps are the same as those in Example 3.

[0062] Comparative Example 6: Except that no TPGS-750-M aqueous solution is added in step S5, the remaining steps are the same as those in Example 3.

[0063] The present invention compares the product yield and product purity of Example 3, Comparative Example 5 and Comparative Example 6. As shown in the experimental data in Table 3, the yield of the product 4,5-dimethyl-1,2-phenylenediamine in the reductive amination reaction of Example 3 is 98.3% and the purity is 99.5%, which further promotes the high yield and high purity of the final product 5,6-dimethylbenzimidazole, which are 96.3% and 99.5%, respectively. In Comparative Example 5 without carbonyl iron powder and Example 6 without TPGS-750-M aqueous solution, 4,5-dimethyl-1,2-phenylenediamine is almost undetectable. -1,2-phenylenediamine, indicating that the reaction basically does not occur. In the previous technology, reductive amination mainly relies on hydrogen and precious metal catalysts, which has caused certain obstacles to the safety and cost of the reaction. The present invention utilizes the synergistic catalysis of TPGS-750 nano-micelles and carbonyl iron powder to achieve high-efficiency and high-quality conversion under low-cost and safe conditions. In addition, the catalyst only needs to be washed with ammonium chloride solution for 3-5 times to achieve active reuse. As shown in Table 4, the catalyst can still maintain a high catalytic effect after being recycled 5 times.

[0064] Table 3

[0065]

[0066] Table 4

[0067]

[0068] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole, characterized in that: The specific steps are as follows: S1. Take 5-12g of anhydrous zinc sulfate, 35-40g of anhydrous ferric chloride and 20-30g of manganese sulfate and put them into a beaker, add 100-160ml of deionized water, stir at 70-90°C for 10-20min, then add 30-35g of ammonium bicarbonate and continue stirring for 10-15min, and adjust the pH of the solution to 7-9 with NH3·H2O, then let it stand for 12-24h, filter the obtained precipitate, wash it with deionized water 3-5 times, dry it in an oven for 12h, and then calcine it in a tubular furnace for 1-3h, and set the calcination temperature to 800-1100°C, that is, A magnetic carrier can be obtained, and then 3-8g of the magnetic carrier and 2-4g of zirconium oxychloride are placed in 20-30ml of deionized water to form a suspension, and the pH is adjusted to 8-9 by using NH3·H2O, and then stirred in a water bath for 0.5-1.5h, and the water bath temperature is set to 65-75°C. After the stirring is completed, it is allowed to stand at room temperature for 12h, filtered, and washed with deionized water 3-5 times to obtain a precipitate, which is soaked in a 0.25-0.8mol / L ammonium thiosulfate solution for 2-5h, and then calcined at 300-500°C for 2-5h to obtain a modified sulfuric acid catalyst A with magnetic properties; S2, take 80-120ml of 1,2-dichloroethane and 20-50ml of acetic acid and add them to a beaker, add 3-5g of the catalyst A obtained in step S1, stir for 5-10min, transfer to a microwave reactor after mixing evenly, then slowly add 12.1g of 3,4-dimethylaniline, set the temperature to 40-60°C, the rated power to 700W, react for 1-2h, filter and separate the catalyst, and obtain the product 3,4-dimethylacetanilide after the acetylation reaction; S3, when the 3,4-dimethylacetanilide solution obtained in step S2 is cooled to 25-30°C, 20-35 ml of acetic anhydride-acetic acid mixture is slowly added, and the addition ratio of the two is 1-1.2:1.5-3, and then stirred at 0°C for 15-30 minutes, after it is fully mixed, 5-8 ml of concentrated nitric acid with a mass fraction of 98% is slowly dripped, and after mixing evenly, the reaction temperature of the water bath is set to 20-50°C, and the reaction is carried out for 3-4 hours, and then the mixed solution is poured into 20- 40 ml of ice-water mixture, stirring to precipitate solid nitrate, collecting the filter cake after suction filtration, repeatedly washing it with ice-water mixture for 3-5 times to wash away free acid, and vacuum drying for 12-24 hours to obtain a nitration crude product, the filtrate and the mixture of the waste acid washed away are stored as solvent circulation liquid for standby use, and then the nitration crude product is crystallized and refined using a deionized water-ethyl acetate-cyclohexane system with a volume fraction of 3:4-6:2-5 to obtain refined 4,5-dimethyl-2-nitroacetanilide; S4, 5-15g of the refined 4,5-dimethyl-2-nitroacetanilide obtained in the above step S3 is placed in a round-bottom flask, 30-50ml of a 5%-10% sodium hydroxide solution is added, mixed and stirred for 0.5h, and then equipped with a reflux device for reflux for 1-3h, and the reflux temperature is set to 90-110°C. After the reaction is completed, suction filtration is performed to obtain a red solid product, namely 4,5-dimethyl-2-nitroaniline; S5, take 5-10g of the 4,5-dimethyl-2-nitroaniline in step S4 and put it into a beaker equipped with a mechanical stirring device, add 2-5g of carbonyl iron powder and 10-20ml of ethyl acetate-methanol (1-2: 1-1.5) mixed solution, stir for 10-20min at a temperature of 30-45°C, then slowly add 15-30ml of 2% TPGS-750-M aqueous solution, continue stirring for 5-10min, then add 3-5g of ammonium chloride, mix well, continue stirring for 4-6h, filter after the reaction is complete, wash with ethyl acetate and deionized water for 1-3 times respectively, and you can get 4,5-dimethyl-1,2-phenylenediamine; S6. Place 3-7 g of 4,5-dimethyl-1,2-phenylenediamine obtained in step S5 and 2-3 g of anhydrous formic acid in a round-bottom flask, set the temperature to 90-110° C., reflux while stirring, and react for 1.5-2.5 hours. After the reaction is complete, add 1%-5% potassium carbonate solution several times to adjust the pH of the mixed solution to 8, let it stand for 1.5-3 hours, and then filter with a Buchner funnel to obtain a crude product, then put it into 50 ml of an aqueous solution with a mass fraction of 1% activated carbon, set the temperature to 35-50° C., continue stirring for 0.5-1.5 hours, and obtain the final product 5,6-dimethylbenzimidazole by filtration, washing with deionized water and vacuum drying.

2. The method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole according to claim 1, characterized in that: The amount of manganese sulfate used in step S1 is 22 g.

3. The method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole according to claim 1, characterized in that: The concentration of the ammonium thiosulfate solution in step S1 is 0.4 mol / L.

4. The method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole according to claim 1, characterized in that: The amount of 1,2-dichloroethane used in step S2 is 105 ml.

5. The method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole according to claim 2, characterized in that: The amount of catalyst A added in step S2 is 3.4 g.

6. A method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole according to claim 1 or 2, characterized in that: In step S3, the addition ratio of acetic anhydride to acetic acid is 1.2:1.

6.

7. The method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole according to claim 3, characterized in that: The amount of 2-5g carbonyl iron powder added in step S5 is 3.8g.

8. A method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole according to claim 5 or 6, characterized in that: The amount of the TPGS-750-M aqueous solution added in step S5 is 24 ml.

9. The method for synthesizing environmentally friendly 5,6-dimethylbenzimidazole according to claim 7, characterized in that: The mass concentration of the potassium carbonate solution in step S6 is 5%.

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