A production process of chlorobromoisocyanuric acid

Abstract

The invention provides a production process of chlorobromoisocyanuric acid, wherein urea is used as a raw material, a pyridine ionic liquid is used as a reaction solvent, cyanuric acid is obtained by reaction, and then chlorobromoisocyanuric acid is obtained through chlorination and bromination steps. The production process of the invention is simple and easy to implement, the raw materials are easily available, the yield is high, the product purity is high, and the production process is green and environmentally friendly, and it is easy to realize industrialization.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, in particular to a production process of chlorobromoisocyanuric acid. Background Art

[0002] Chlorobromoisocyanuric acid, referred to as "Xiaobengling", is an oxidizing disinfectant widely used in water companies, swimming pools, medical facilities, sanitation departments, agriculture, animal husbandry and aquatic products. In agriculture, 50% chlorobromoisocyanuric acid is generally used. As a highly efficient, broad-spectrum, new type of systemic fungicide, it can kill various bacteria, algae, fungi and germs.

[0003] At present, the synthesis process of chlorobromoisocyanuric acid mainly uses cyanuric acid as a raw material, and then undergoes chlorination and bromination reactions to obtain chlorobromoisocyanuric acid.

[0004] CN1337396A reports that bromochloroisocyanuric acid is prepared by using isocyanuric acid as the main raw material through alkali dissolution, chlorination, bromination, rechlorination, filtration and drying, characterized in that isocyanuric acid is dissolved in an aqueous solution or an emulsion of alkali, then chlorine is introduced into the solution or the emulsion at 0-25°C, then liquid bromine is added dropwise, and finally chlorine is introduced for chlorination reaction, and the final pH value of the reaction is controlled between 2-7, so as to obtain a product with a total effective chlorine content of 54-58% and an effective bromine content of 46-49%. CN1389460A reports that potassium hydroxide is subjected to chlorination and bromination reactions at 10-15°C to generate potassium hypochlorite and potassium hypobromite, and potassium hypochlorite and potassium hypobromite react with cyanuric acid at 23-27°C with the catalyst of sodium dodecylbenzenesulfonate to generate potassium chlorobromoisocyanurate. CN1666979A reported that cyanuric acid was mixed with a surfactant to disperse the cyanuric acid into a more uniform suspension, and then chlorinated and brominated. CN102746246A and CN109006862A reported that cyanuric acid was dissolved in a buffer solution with a pH value of 7-9, and then a cuprous ion compound was added as a catalyst, and then bromine and chlorine were directly introduced at a temperature of 10-20°C, and the product was centrifuged and dried to obtain the product chlorobromoisocyanuric acid, with a yield of up to 95%. CN109418275A reported that cyanuric acid was added to triethylamine and then mixed with tetrahydrofuran, and then liquid bromine was slowly added dropwise and chlorine was introduced, and then the obtained solution was subjected to reduced pressure distillation to remove tetrahydrofuran; and then chlorobromoisocyanuric acid was obtained by post-treatment.

[0005] The above method requires the introduction of liquid bromine and chlorine gas during the preparation process, which poses a great safety hazard in industrial production and is not conducive to environmental protection. In addition, the added catalyst requires a separation step, which increases the post-treatment step, and part of the catalyst may remain in the product, affecting the purity of the final product.

[0006] As the main raw material of chlorobromoisocyanuric acid, the currently commonly used synthesis route is the urea thermal decomposition method to produce cyanuric acid. According to the reaction medium, there are mainly three process routes: direct thermal decomposition method, molten salt thermal decomposition method and solvent method.

[0007] Direct pyrolysis refers to directly heating urea without the need for a heating medium, removing ammonia, and pyrolyzing to form cyanuric acid. This method has a simple production process and low investment cost, but there are many difficult problems in the production process. When urea is heated to about 130°C, it will change from a solid to a liquid that is very easy to adhere to the reactor and agitator, resulting in heat transfer obstruction and difficulty in transportation through pipelines, so production is mostly intermittent operation. The product cyanuric acid has a high melting point, and the crude product produced is mostly in block form. The urea is wrapped during the reaction, which affects heat transfer and prolongs the reaction time. In the absence of a heating medium, the heat transfer inside the system is uneven, local overheating is easy, and some products near the wall decompose, thereby reducing the yield. The temperature of the reaction system is high, and the reaction temperature is difficult to control. The generated ammonia escapes quickly, resulting in a large partial pressure of the system, which is easy to form amide by-products with cyanuric acid in the system. Urea sublimation escapes seriously during the heating process. These are the main reasons for the low yield of the direct pyrolysis method. The crude product contains a large amount of amide by-products, which usually need to be boiled under acidic conditions to become a fine product, thus producing a large amount of waste acid.

[0008] The principle of molten salt pyrolysis is that some water-soluble salts can be miscible with urea at high temperature, but not with cyanuric acid, so that the generated cyanuric acid is precipitated from the reaction system. The precipitated cyanuric acid has less contact with the generated ammonia, which reduces the content of amine-derived by-products; cyanuric acid is insoluble in water and can be separated by washing and filtering. The most commonly used salts are generally NH4NO3, NaNO3, KNO3, etc. Both intermittent and continuous production can be achieved; the product purity is high and generally does not require acid washing and refining, which reduces the discharge of three wastes; the urea conversion rate is generally in the range of 60-80%. The molten salt is separated into an aqueous solution, and a large amount of concentrated crystallization is required for recycling, which makes the production process complicated, and the energy consumption is too large, and the loss of molten salt is large, which restricts the promotion and application of this method. US4109089A reported that ammonium nitrate was first used as a molten salt, and nitrogen protection was passed through the reaction system, and the yield reached 88%. Subsequently, molten salts composed of a mixture of sodium nitrate, potassium nitrate, calcium nitrate and ammonium nitrate were used, with the highest yield reaching 75%. Li Mingxin (New Process for Synthesizing Isocyanuric Acid, Liaoning Chemical Industry, 1993 (3), 32-33) used ammonium nitrate as molten salt. After a large number of experiments, the product purity was stabilized at more than 99.0%, and the molten salt recovery rate was 75-85%.

[0009] The solvent method is to use a high-boiling-point inert solvent as a heating medium, heat and polymerize urea in a solvent under stirring conditions, separate the product from the solvent, and then wash the filter cake, dry and other processes to finally obtain a high-purity product. The biggest advantage of this method is that the solvent system evenly disperses urea to reduce the concentration of reactants, the reaction tends to be mild, the partial pressure of ammonia produced is stable and easy to control and absorb, and the contact between ammonia and cyanuric acid is reduced, so that the content of amide impurities is low, the purity of the product is improved, and generally no acid washing and refining is required; secondly, the volatility of urea is reduced, and the yield is increased, generally above 85%; urea is evenly dissolved in the solvent and the heat transfer is uniform, the reaction temperature is easy to control, there is no problem of molten urea sticking to the wall, and the local overheating product decomposition is greatly reduced; and it can be operated continuously. High-boiling-point solvents are expensive and need to be replenished during use. Therefore, the difficulty in promoting this method is to screen cheap and suitable solvents. Solvent systems are roughly divided into single solvents and mixed solvents. The advantage of mixed solvents is that better synthesis conditions can be obtained by changing the solvent ratio, feed ratio, reaction temperature, reaction time, etc., avoiding the problem that a single solvent's boiling point and cyanuric acid solubility are difficult to meet the requirements at the same time. Principles of solvent screening: no reaction with urea and its pyrolysis products; boiling point above the urea pyrolysis temperature; high solubility of urea and pyrolysis intermediates while low solubility of cyanuric acid in them; good thermal stability; cheap and easy to obtain. Oxidative deterioration of solvents often leads to poor product color, which also troubles the application of this method.

[0010] In order to solve the operational difficulties and serious environmental pollution in the current industrial production of cyanuric acid and truly realize clean production, Meng Jishuai et al. (Research on a new green process for synthesizing cyanuric acid by ionic liquid method, Chemical Reagents, 2021, 43 (3), 390-394) reported a new green process technology for generating cyanuric acid by liquid phase urea condensation using ionic liquid as solvent. Using 1-ethyl-3-methylimidazolium tetrafluoroborate as solvent, at an appropriate feed ratio and reaction temperature, the yield of cyanuric acid is more than 70% and the purity is 90%. However, the yield of this method is not high, and a large amount of raw materials need to be wasted, which leads to an increase in the production cost, which is not conducive to industrial production.

[0011] In view of the above problems existing in the current preparation process of chlorobromoisocyanuric acid, it is of great social and economic significance to find a green, environmentally friendly and high-yield preparation process of chlorobromoisocyanuric acid. Summary of the invention

[0012] In order to solve the problems of low yield, low product quality, poor safety of the production process, etc. in the production process of chlorobromoisocyanuric acid in the prior art, the present invention provides a production process of chlorobromoisocyanuric acid, which is simple and easy to operate, has readily available raw materials, high yield, high product purity, and a green and environmentally friendly production process, and is easy to realize industrialization.

[0013] The first aspect of the present invention provides a production process of chlorobromoisocyanuric acid, which comprises the following steps:

[0014] 1) Preparation of cyanuric acid: In the presence of an ionic liquid, urea is used as a raw material, reacted at 150° C.-250° C. with stirring, and cyanuric acid is obtained by post-treatment;

[0015] 2) Preparation of chlorobromoisocyanuric acid: Add cyanuric acid and a surfactant to an aqueous solution to prepare a suspension, then add sodium hypochlorite and sodium hypobromite, adjust the pH value of the solution to 4-6, and react at 5°C-35°C to generate chlorobromoisocyanuric acid;

[0016] The structure of the ionic liquid described in step 1) is as follows:

[0017]

[0018] Wherein, R is selected from C 1 -C1 2 A straight chain or branched alkyl group;

[0019] Y is selected from: NO 3 - , BF 4 - CF 3 CO 2 - , CH 3 SO 4 - , C 2 H 5 SO 4 - or (CN) 2 N - .

[0020] Preferably, the R is selected from C 1 -C 6 A straight chain or branched alkyl group;

[0021] More preferably, R is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, and isobutyl.

[0022] Preferably, Y is selected from NO 3 - , BF 4 - CF 3 CO 2 - .

[0023] Preferably, the ionic liquid is N-ethylpyridinium tetrafluoroborate, N-methylpyridinium nitrate, N-n-propylpyridinium trifluoroacetate, or N-butylpyridinium tetrafluoroborate.

[0024] Preferably, the post-treatment step of step 1) comprises: filtering the reaction solution and washing the filter cake with water; combining the filtrate and the washing solution, and distilling under reduced pressure to obtain an ionic liquid that can be recycled; and drying the filter cake to obtain cyanuric acid.

[0025] Preferably, the reaction temperature of step 1) is 160°C-220°C, more preferably 180°C-200°C.

[0026] Preferably, the reaction time of step 1) is 1-8 hours, more preferably 3-5 hours.

[0027] Preferably, in step 1), the feed mass ratio of urea to ionic liquid is 1:2 to 1:6; more preferably 1:3 to 1:4.

[0028] Preferably, the surfactant in step 2) is selected from sodium laurate, sodium oleate, sodium stearate, and sodium dodecylbenzene sulfonate.

[0029] Preferably, the reaction temperature of step 2) is 15°C-30°C.

[0030] Preferably, in step 2), the molar ratio of cyanuric acid to sodium hypochlorite and sodium hypobromite is 1:(1-2):(1-2)

[0031] Preferably, in step 2), the pH value is adjusted by adding an acid, and the acid is selected from acetic acid, hydrochloric acid and sulfuric acid.

[0032] In the process of preparing cyanuric acid by liquid phase method in the prior art, solvent is usually added as reaction medium. Commonly used organic solvents such as cyclohexanol, nitrobenzene, etc. are volatile and toxic, which can easily have adverse effects on the environment and human health, and high boiling point solvents such as cyclopentane are expensive. With the development of green chemistry, researchers are committed to reducing and eliminating pollution at the source, so it is crucial to use green and recyclable solvents. Ionic liquids are increasingly recognized as a regulatable green solvent. They have low melting points and vapor pressures and are a high-quality green alternative to volatile organic solvents. At the same time, ionic liquids have good solubility. Meng Jishuai et al. (Research on a New Green Process for Synthesizing Cyanuric Acid by Ionic Liquids, Chemical Reagents, 2021, 43 (3), 390-394) used a series of imidazole ionic liquids as a new solvent for synthesizing cyanuric acid. It can dissolve urea well under high temperature conditions, has high heat transfer efficiency, low energy consumption, recyclability, and is green and environmentally friendly. However, the effect of imidazole ionic liquid as solvent in the document is not good, wherein the yield of 1-butyl-3-methylimidazolium tetrafluoroborate is only 79.41%, and the purity is only 90.16%, which is significantly lower than other solvents, limiting its application in industrial production. The inventors have found through a large number of experiments that using pyridine ionic liquid as a reaction solvent not only has the function of green environmental protection, but also can greatly improve the yield of the reaction and the purity of the product.

[0033] In addition, in the step of preparing chlorobromoisocyanuric acid, the present invention selects water as a solvent, which is cheap, green and pollution-free, and avoids the use of other solvents, which are expensive and difficult to recover. Since cyanuric acid is not very soluble in water at a relatively low temperature, it usually forms a suspension. If the particles of the suspension are too large, it is not conducive to the subsequent chlorination and bromination reactions. Therefore, the present invention selects to add a surfactant to the reaction solution, so that cyanuric acid is more evenly dispersed in water, thereby improving the yield of the chlorination and bromination reactions.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) In the step of preparing cyanuric acid, pyridine ionic liquid is used as a solvent, which is green and environmentally friendly, and the yield and purity of the product are greatly improved;

[0036] 2) In the step of preparing chlorobromoisocyanuric acid, a surfactant is added to make the cyanuric acid more evenly dispersed in water, thereby improving the yield of chlorination and bromination reactions;

[0037] 3) The ionic liquid of the present invention is easy to recycle and can be reused, which reduces the production cost and is more environmentally friendly;

[0038] 4) The production process of the present invention is simple, the raw materials are cheap and readily available, and it is suitable for industrial production. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Example 1 Preparation of ionic liquid

[0041] In a 1000ml three-necked flask, add 109g bromoacetic acid and 79g pyridine, stir and react at 105-115°C for 2 hours, then add 110g sodium tetrafluoroborate and continue stirring for 3 hours. After the reaction is completed, add 200mL water, stir well, let stand and filter, wash the ionic liquid phase with 200mL water × 3, and dry to obtain N-ethylpyridinium tetrafluoroborate ionic liquid.

[0042] Referring to the above similar methods, N-methylpyridine nitrate, N-n-propylpyridine trifluoroacetate, and N-butylpyridine tetrafluoroborate ionic liquids were prepared respectively.

[0043] Example 2 Effect of different ionic liquids on the reaction

[0044] In a 100mL three-necked flask with a reflux condenser and magnetic stirring, add 60g of ionic liquid, heat and stir to 140℃, slowly add 18g of urea, continue to heat to 190℃, react for 4 hours, stop heating, wait for the reaction liquid to cool to room temperature, add water to dissolve, filter, wash the filter cake with deionized water 3 times; combine the filtrate and washing liquid, distill under reduced pressure to obtain ionic liquid, which can be recycled; dry the filter cake in a vacuum drying oven to obtain cyanuric acid. The reaction results are shown in the following table:

[0045]

[0046] Example 3 Effect of reaction temperature on reaction

[0047] In a 100mL three-necked flask with a reflux condenser and magnetic stirring, add 60g of N-ethylpyridinium tetrafluoroborate ionic liquid, heat and stir to 140°C, slowly add 18g of urea, continue to heat to the reaction temperature, react for 4 hours, stop heating, wait for the reaction liquid to cool to room temperature, add water to dissolve, filter, wash the filter cake with deionized water 3 times; combine the filtrate and the washing liquid, distill under reduced pressure to obtain an ionic liquid, which can be recycled; dry the filter cake in a vacuum drying oven to obtain cyanuric acid. The reaction results are shown in the following table:

[0048] Reaction temperature / ℃ Yield / % purity / % 170 78.5 80.2 180 89.4 94.9 190 90.3 95.4 200 88.4 96.2 210 75.5 92.0

[0049] As can be seen from the above table, the more suitable temperature for the present invention is 180-200° C. When the temperature is too low, the raw material reaction is incomplete, resulting in a lower yield and low product purity; when the temperature is too high, the urea sublimation speed is too fast, which will reduce the reaction yield.

[0050] Example 4 Effect of Feed Ratio on Reaction

[0051] In a 100mL three-necked flask with a reflux condenser and magnetic stirring, add a certain amount of N-ethylpyridinium tetrafluoroborate ionic liquid, heat and stir to 140°C, slowly add 18g of urea, continue to heat to 190°C, react for 4 hours, stop heating, wait for the reaction liquid to cool to room temperature, add water to dissolve, filter, wash the filter cake with deionized water 3 times; combine the filtrate and the washing liquid, distill under reduced pressure to obtain an ionic liquid, which can be recycled; dry the filter cake in a vacuum drying oven to obtain cyanuric acid. The reaction results are shown in the following table:

[0052]

[0053] Example 5 Preparation of chlorobromoisocyanuric acid

[0054] Add 600 mL of water to a three-necked flask, then add 129 g of cyanuric acid and 7 g of a surfactant, stir and mix evenly to prepare a cyanuric acid suspension. Then add 74.5 g (1 mol) of sodium hypochlorite and 119 g (1 mol) of sodium hypobromite to the suspension, adjust the pH of the solution to 5-6 with dilute hydrochloric acid, and react for 3 hours at 10-20 ° C. After the reaction is completed, the reaction solution is centrifuged and filtered, the filter cake is washed with cold water, the filter cake is dried, and chlorobromoisocyanuric acid is obtained. The reaction results are shown in the following table:

[0055]

[0056]

[0057] It can be seen from the above table that adding surfactants in chlorination and bromination reactions can greatly improve the yield and purity of the products.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A production process of chlorobromoisocyanuric acid, comprising the following steps: 1) Preparation of cyanuric acid: In the presence of an ionic liquid, urea is used as a raw material, reacted at 150° C.-250° C. with stirring, and cyanuric acid is obtained by post-treatment; 2) Preparation of chlorobromoisocyanuric acid: Add cyanuric acid and a surfactant to an aqueous solution to prepare a suspension, then add sodium hypochlorite and sodium hypobromite, adjust the pH value of the solution to 4-6, and react at 5°C-35°C to generate chlorobromoisocyanuric acid; The ionic liquid in step 1) is selected from N-ethylpyridinium tetrafluoroborate, N-methylpyridinium nitrate, N-n-propylpyridinium trifluoroacetate, and N-butylpyridinium tetrafluoroborate.

2. The production process according to claim 1, characterized in that: The post-treatment step of step 1) includes: filtering the reaction solution and washing the filter cake with water; combining the filtrate and the washing solution, and performing reduced pressure distillation to obtain an ionic liquid that can be recycled; and drying the filter cake to obtain cyanuric acid.

3. The production process according to claim 1, characterized in that: The reaction temperature of step 1) is 160° C.-220° C.; the reaction time of step 1) is 1-8 hours; and the feed mass ratio of urea to ionic liquid in step 1) is 1:2 to 1:

6.

4. The production process according to claim 3, characterized in that: The reaction temperature of step 1) is 180° C.-200° C.; the reaction time of step 1) is 3-5 hours; and the feed mass ratio of urea to ionic liquid in step 1) is 1:3 to 1:

4.

5. The production process according to claim 1, characterized in that: The surfactant in step 2) is selected from sodium laurate, sodium oleate, sodium stearate, and sodium dodecylbenzene sulfonate.

6. The production process according to claim 1, characterized in that: The reaction temperature of step 2) is 15°C-30°C.

7. The production process according to claim 1, characterized in that: In step 2), the molar ratio of cyanuric acid to sodium hypochlorite and sodium hypobromite is 1:(1-2):(1-2).

8. The production process according to claim 1, characterized in that: In step 2), the pH value is adjusted by adding an acid, wherein the acid is selected from acetic acid, hydrochloric acid and sulfuric acid.

Images