A new method for synthesizing terephthalamide

Abstract

The invention belongs to the field of chemical synthesis, and discloses a new method for synthesizing terephthalamide. Terephthalic acid and low-melting acid are compounded in an appropriate ratio, and ammonia is introduced for a proper reaction time under a certain temperature and pressure with the participation of an appropriate catalyst, so that both terephthalic acid and the so-called low-melting acid are amidated. The appropriate temperature is controlled and the product is filtered while hot. The filter cake (solid) is terephthalamide, and the filtrate is the corresponding amide generated by the low-melting acid. The filter cake is washed with an appropriate solvent while hot, and vacuum dried at 150°C to obtain high-purity terephthalamide. The combined filtrate (the amide generated by the low-melting acid and the washing liquid generated by the hot-washed filter cake) is cooled, crystallized, filtered, and vacuum dried at 70°C to obtain the amide generated by the low-melting acid. The invention uses the low-melting acid and the corresponding low-melting amide generated as reaction media to promote the terephthalamide reaction.

Description

Technical Field

[0001] The invention belongs to the field of chemical synthesis, and specifically relates to a method for synthesizing terephthalamide. Technical Background

[0002] Terephthalamide is an important chemical intermediate, widely used in synthetic materials, medicines, pesticides and fine organic synthesis.

[0003] In industry, terephthalamide is mainly produced by using terephthalic acid as raw material, and terephthaloyl chloride is obtained by chlorination reaction, and then reacted with ammonia to obtain terephthalamide (CN1422843A; Journal of the American Chemical Society, 2013, 16853.). Commonly used chlorination reagents include thionyl chloride, phosphorus trichloride, phosphorus pentachloride, phosgene, etc. This route has mild reaction conditions, simple operation, and high product yield, but it produces a large amount of chlorine-containing byproducts, a large amount of wastewater discharge, and a high production cost.

[0004] It has been reported that terephthalonitrile can be hydrolyzed at 80°C for 6 hours under the catalysis of iridium complex to obtain 93% terephthalamide (Inorganic Chemistry, 2020, 59 (22): 16582.). This method has a clean process and mild conditions, but the source of terephthalonitrile is limited, and the use of precious metal catalysts is costly. Joshi et al. (Green Chemistry, 2019, 21 (5): 962) reported a method of using dibenzylamine as a raw material and tetrabutylammonium hydroxide as a catalyst, and oxidizing terephthalamide with oxygen at 70°C for 12 hours. This method has mild conditions and a clean process, but the prices of dibenzylamine and catalysts are high, and the cost is high. In general, these methods have mild reaction conditions, but the cost of raw materials is too high and they are not suitable for industrial production.

[0005] The synthesis of terephthalic acid esters by ammonolysis is a cost-effective method. Chinese patent CN113773220 reports that terephthalic acid esters react with ammonia gas in a methanol medium at 80°C for 24 hours to obtain 85% terephthalic acid amide. Some other documents (Shan Yuhua, Petrochemicals, 2004, 33 (1): 51-3; WO2012123328; WO2012014760; Chemistry-AnAsianJ, 2015, 2631-2650) report a method for synthesizing terephthalic acid esters by reacting them with ammonia gas or ammonia water in a solvent under high temperature and high pressure under the action of a catalyst. Such a method has harsh reaction conditions, complex processes, and high equipment requirements, resulting in high production costs.

[0006] In order to reduce production costs and reduce the discharge of three wastes, Chinese patent CN105016939 discloses a method, which is to add an appropriate amount of terephthalic acid into a reactor, and charge ammonia gas with a molar number of 2.6 times that of terephthalic acid, or add ammonium bicarbonate powder with a molar number of ammonium ions with a molar number of 2.8 times that of terephthalic acid, seal the reactor, and react at 305-320°C for 0.5h under stirring conditions to obtain terephthalamide. This method uses cheap raw materials, solvent-free (dry method) high-temperature reaction, which can effectively reduce the discharge of three wastes, but has the disadvantages of high reaction temperature (terephthalic acid sublimes above 300°C), difficulty in high-temperature solid phase operation, and high requirements for equipment. Summary of the invention

[0007] The purpose of the present invention is to provide a new terephthalamide production technology, which produces terephthalamide and low-melting-point amide by co-dissolving amidation, so as to reduce pollutant emissions, reduce production costs, and improve the yield and purity of terephthalamide.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] 1. Compound terephthalic acid with a low melting point acid, introduce ammonia gas to react in the presence of a catalyst at a certain reaction temperature and pressure, so that both terephthalic acid and the so-called low melting point acid are amidated.

[0010] 2. Control the appropriate temperature and filter while hot. The filter cake (solid) is terephthalamide, and the filtrate is the low melting point acid that generates the corresponding amide. Wash the filter cake with a suitable solvent while hot and dry it in vacuum to obtain high-purity terephthalamide.

[0011] 3. The combined filtrate (the amide filtrate generated by the low melting point acid and the washing liquid generated by the hot washing filter cake) is cooled, crystallized, filtered, and vacuum dried to obtain the amide generated by the low melting point acid.

[0012] Furthermore, the low melting point acid refers to an acid with a melting point lower than that of terephthalic acid. The melting point of terephthalic acid is 427°C, so the low melting point acid selected is an acid with a melting point less than 427°C. At the same time, the acid strength of the low melting point acid is also required to be less than that of terephthalic acid, so that the infusible terephthalic acid can preferentially undergo amidation reaction to generate the target product. The acid strength constant PKa of terephthalic acid is 3.5, so the acid strength constant PKa of the low melting point acid is required to be greater than 3.5 (the larger the PKa value, the smaller the corresponding acid strength). For example, suitable low melting point acids can be: isooctanoic acid (melting point -59°C, PKa4.8), oleic acid (melting point 14°C, PKa4.8), glutaric acid (melting point 98°C, PKa4.4), adipic acid (melting point 152°C, PKa4.5), etc.

[0013] Furthermore, the compounding ratio of terephthalic acid to low melting point acid is 1:0.5-1.5 (weight ratio);

[0014] Further, the catalyst is some protonic acid and Lewis acid that can catalyze the amidation reaction of the acid. Suitable ones include: sulfuric acid, phosphoric acid (phosphotungstic acid), zinc compounds (zinc oxide, zinc acetate), tin compounds (stannous oxide, butyl stannoic acid), etc. The amount of the catalyst is 0.05-0.5% of the total weight of terephthalic acid and low melting point acid;

[0015] Furthermore, the amidation reaction temperature is 250-300° C. The amidation reaction pressure refers to the pressure maintained by introducing ammonia gas, which is generally 0.3-0.7 MPa;

[0016] Furthermore, the appropriate time for introducing ammonia gas to react is the time required for both terephthalic acid and the so-called low melting point acid to be amidated, and is generally 6 to 12 hours.

[0017] Further, the hot filtration is performed by controlling the appropriate temperature. The hot filtration temperature depends on the melting point of the corresponding amide generated by the low melting point acid. The appropriate hot filtration temperature is 20 to 50°C higher than the melting point of the corresponding amide generated by the low melting point acid to ensure separation from terephthalamide by filtration. Specifically, the melting point of isooctylamide is 102°C, and the appropriate hot filtration temperature is 122 to 172°C. The melting point of oleic acid amide is 77°C, and the appropriate hot filtration temperature is 97 to 127°C. The melting point of glutaramide is 98°C, and the appropriate hot filtration temperature is 118 to 148°C. The melting point of adipic acid amide is 220°C, and the appropriate hot filtration temperature is 240 to 270°C.

[0018] Further, a suitable solvent is selected to wash the filter cake while it is hot, so as to obtain high-purity terephthalamide. The suitable solvent refers to a substance that can dissolve the corresponding amide generated by the low melting point acid but does not dissolve terephthalamide. These solvents are dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, butyronitrile, etc.

[0019] Furthermore, a suitable solvent is selected to wash the filter cake while hot, and the hot washing of the filter cake refers to washing the filter cake at 100-160° C. Maintaining this temperature range for washing the filter cake allows the solvent to dissolve the amide generated by the low melting point acid well, but not terephthalamide, thereby obtaining high-purity and high-yield terephthalamide.

[0020] Further, the combined filtrate is cooled and crystallized, wherein the crystallization temperature is 30-80°C and the crystallization time is 6-12 hours. The low melting point amide generated by the low melting point acid has a melting point lower than that of terephthalamide.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention uses low melting point acid and the corresponding low melting point amide generated as reaction medium to promote the amidation reaction. In the high temperature co-amidation reaction process, the low melting point acid melts and acts as a reaction medium, so that both terephthalic acid and the so-called low melting point acid are amidated. The generated low melting point acid amide acts as a flow medium for terephthalamide solid particles under high temperature conditions, making the material easy to transport. There is no need to use water, alcohol, or other solvents to serve as reaction medium. It also avoids reacting in a high temperature solid phase (such as CN105016939). The high temperature solid phase has two disadvantages: one is that the reaction is difficult to be uniform, and the other is that the solid phase material is difficult to transport during large-scale production.

[0023] 2. The present invention does not add traditional solvents or media to the reaction system, and there is no discharge of three wastes. This makes the technology of the present invention clean, efficient and low-cost. The material used as a solvent or medium is finally converted into a product. The technology of the present invention provides a new operation mode for the reaction of solid-phase material systems.

[0024] 3. Adding a low melting point weak acid is conducive to producing a higher ammonia concentration in the reaction liquid phase, promoting rapid amidation of terephthalic acid.

[0025] 4. The technology of the present invention uses an acid with a lower acid strength and a much lower melting point as a medium, so that the target product terephthalic acid can be preferentially and completely converted into terephthalamide. The melting point of the generated low-melting-point amide is much lower than the melting point of terephthalamide (greater than 500°C), which makes it easy to separate terephthalamide by hot filtration. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the process for producing terephthalamide and low-melting-point amide by co-solvent amidation. Specific implementation plan

[0027] The present invention is further described below with reference to examples, but is not limited thereto.

[0028] Example 1: Isooctanoic acid as low melting point co-amidation acid

[0029] 1. Add 166g of terephthalic acid (99.8% by mass), 83g of isooctanoic acid (99.5% by mass) and 0.1245g of concentrated sulfuric acid into an autoclave, and replace the air in the autoclave with ammonia. Raise the temperature to 250°C, introduce ammonia, and maintain the ammonia pressure of 0.3MPa for 10 hours to make both terephthalic acid and isooctanoic acid amidated (analyzed by liquid chromatography), then stop introducing ammonia and terminate the reaction.

[0030] 2. After the reaction is completed, the material temperature is reduced to 172°C and filtered while hot. The filter cake (solid) is terephthalamide and the filtrate is isooctanoic acid amide. The filter cake is washed with butyronitrile at 100°C while hot and dried in vacuum at 150°C to obtain 160.7g of terephthalamide with a purity of 99.2% and a yield of 97.4%. The isooctanoic acid amide adhering to the filter cake is washed out by hot butyronitrile and enters the filtrate.

[0031] 3. The combined filtrate (172°C filtrate isooctanoic acid amide and the washing liquid produced by the hot washing filter cake) was cooled to 50°C for crystallization for 12 hours, filtered, and vacuum dried at 70°C to obtain 79.7g of solid isooctanoic acid amide, with a melting point of 100-102°C, a purity of 98.8%, and a yield of 96.0%.

[0032] Example 2: Oleic acid as low melting point co-amidation acid

[0033] 1. Add 166g of terephthalic acid (mass content greater than 99.8%), 166g of oleic acid (mass content 98.0%), and 0.332g of phosphotungstic acid into a high-pressure reactor, and replace the air in the reactor with ammonia. Raise the temperature to 260°C, introduce ammonia, and maintain the ammonia pressure of 0.5MPa for 6 hours to make terephthalic acid and oleic acid amidated (tracked and analyzed by liquid chromatography), then stop introducing ammonia and terminate the reaction.

[0034] 2. After the reaction is completed, the material temperature is lowered to 117°C and filtered while hot. The filter cake (solid) is terephthalamide and the filtrate is oleic acid amide. The filter cake is washed with N-dimethylformamide at 120°C while hot and vacuum dried at 150°C to obtain 161.6g of terephthalamide with a purity of 99.5% and a yield of 98.2%. The oleic acid amide adhering to the filter cake is washed out by hot N-dimethylformamide and enters the filtrate.

[0035] 3. The combined filtrate (117°C filtrate oleic acid amide and the washing liquid produced by the hot washing filter cake) was cooled to 30°C and crystallized for 10 hours, filtered, and vacuum dried at 70°C to obtain 157.9 g of solid oleic acid amide, with a melting point of 75-76°C, a purity of 98.1%, and a yield of 95.6%.

[0036] Example 3: Glutaric acid as low melting point co-amidation acid

[0037] 1. Add 166g of terephthalic acid (mass content greater than 99.8%), 207.5g of glutaric acid (mass content greater than 98.0%) and 1.121g of stannous oxide into an autoclave, replace the air in the autoclave with ammonia, raise the temperature to 280°C, introduce ammonia, maintain the ammonia pressure of 0.6MPa and react for 12 hours to amidate terephthalic acid and glutaric acid (analyzed by liquid chromatography), stop introducing ammonia and terminate the reaction.

[0038] 2. After the reaction is completed, the material temperature is lowered to 128°C and filtered while hot. The filter cake (solid) is terephthalamide and the filtrate is glutaramide. The filter cake is washed with dimethyl sulfoxide at 140°C while hot and dried in vacuum at 150°C to obtain 159.8g of terephthalamide with a purity of 99.6% and a yield of 97.6%. The glutaramide adhering to the filter cake is washed out by hot dimethyl sulfoxide and enters the filtrate.

[0039] 3. The combined filtrate (128°C filtrate glutaramide and washing liquid produced by hot washing filter cake) was cooled to 60°C for crystallization for 8 hours, filtered, and vacuum dried at 70°C to obtain 199.8 g of solid glutaramide, melting point 96-97°C, purity 97.9%, and yield 97.7%.

[0040] Example 4: Adipic acid as a low melting point co-amidation acid

[0041] 1. Add 166g of terephthalic acid (mass content greater than 99.8%), 249g of adipic acid (mass content greater than 99.0%) and 2.075g of zinc acetate into a high-pressure reactor, replace the air in the reactor with ammonia. Raise the temperature to 300°C, introduce ammonia, maintain the ammonia pressure of 0.7MPa and react for 8 hours to make both terephthalic acid and adipic acid amidate (track and analyze with liquid chromatography), stop introducing ammonia and terminate the reaction.

[0042] 2. After the reaction is completed, the material temperature is reduced to 240°C and filtered while hot. The filter cake (solid) is terephthalamide and the filtrate is adipic acid amide. The filter cake is washed with N-methylpyrrolidone at 160°C while hot and vacuum dried at 150°C to obtain 158.8g of terephthalamide with a purity of 99.8% and a yield of 97.0%. The adipic acid amide adhering to the filter cake is washed out by hot N-methylpyrrolidone and enters the filtrate.

[0043] 3. The combined filtrate (240°C filtrate adipamide and washing liquid produced by hot washing filter cake) was cooled to 80°C for crystallization for 6 hours, filtered, and vacuum dried at 70°C to obtain 237.7g of solid adipamide, melting point 216-218°C, purity 98.2%, and yield 96.0%.

[0044] Comparative Example 1: 1,3-malonic acid as low melting point co-amidation acid

[0045] 1. Add 166g of terephthalic acid (content greater than 99.8%), 83g of malonic acid (content greater than 98.5%, melting point 152°C, PKa=2.9), and 0.1245g of concentrated sulfuric acid into a high-pressure reactor, and replace the air in the reactor with ammonia. Raise the temperature to 250°C, introduce ammonia, and maintain the ammonia pressure of 0.3MPa for 5 hours. Malonic acid is completely amidated, but 39.8% of terephthalic acid is still not amidated (tracked and analyzed by liquid chromatography). Continue the reaction for 14 hours until terephthalic acid is completely converted. Stop introducing ammonia and terminate the reaction. React for a total of 19 hours.

[0046] 2. After the reaction is completed, the material temperature is reduced to 220°C and filtered while hot. The filter cake (solid) is terephthalamide, and the filtrate is malonamide (melting point 170°C). The filter cake is washed with N-methylpyrrolidone at 160°C while hot, and vacuum dried at 150°C to obtain 156.4g of terephthalamide, with a purity of 97.3% and a yield of 93.0%. The malonamide adhering to the filter cake is washed out by hot N-methylpyrrolidone and enters the filtrate.

[0047] 3. The combined filtrate (220°C filtrate malonamide and the washing liquid produced by the hot washing filter cake) was cooled to 30°C for crystallization for 12 hours, filtered, and vacuum dried at 70°C to obtain 77.7g of solid malonamide, with a melting point of 167-169°C, a purity of 99.4%, and a yield of 96.3%.

[0048] As can be seen from Comparative Example 1, the disadvantages of using a low melting point acid co-melting amidation reaction with an acid strength relatively higher than that of terephthalic acid are: 1. The amidation reaction of terephthalic acid is significantly slowed down. Because malonic acid, which has a higher acid strength than terephthalic acid, is preferentially converted into amide, the environment of the amidation reaction medium of terephthalic acid changes. In Example 1, terephthalic acid reacts preferentially, and the reaction medium is mainly isooctanoic acid, which easily complexes alkaline ammonia into the liquid phase (i.e., the liquid phase ammonia concentration is high), and reacts with the solid phase strong acid terephthalic acid, so terephthalic acid is completely amidated in a relatively short time. 2. The purity of the amide product of terephthalic acid is low. Since terephthalic acid is basically amidated in the malonic acid amide medium in the late stage of the reaction, the concentration of ammonia in the liquid phase is low, making it difficult for the intermediate product to be completely converted into terephthalamide, resulting in a low yield and purity of the terephthalamide product.

[0049] Comparative Example 2: Method of adding solvent (without adding low melting point acid)

[0050] 166g of terephthalic acid (99.8% by mass), 83g of N,N-dimethylformamide and 0.1245g of concentrated sulfuric acid were added to the autoclave, and the air in the autoclave was replaced with ammonia. The temperature was raised to 250°C, and ammonia was introduced. After maintaining the ammonia pressure of 0.3MPa for 22 hours, the terephthalic acid was completely converted (analyzed by liquid chromatography), and the introduction of ammonia was stopped to terminate the reaction. After the reaction was completed, the material was filtered while hot at 172°C.

[0051] The filter cake was terephthalamide. The filter cake was washed with butyronitrile at 100°C while hot, and dried in vacuo at 150°C to obtain 157.9 g of terephthalamide with a purity of 99.0% and a yield of 95.5%.

[0052] As can be seen from Comparative Example 2, adding a solvent instead of a low melting point acid will affect the yield and purity of phthalamide, with the greatest impact being a significant decrease in the reaction rate (see Example 1). Because the addition of a low melting point weak acid in the example of the present invention is conducive to generating a higher ammonia concentration in the reaction liquid phase, it promotes rapid amidation of terephthalic acid.

Claims

1. A method for synthesizing terephthalamide, characterized in that: Step (1): compounding terephthalic acid and a low melting point acid, adding a catalyst, adjusting the reaction temperature to 250-300°C; introducing ammonia gas, maintaining a certain reaction pressure, so that terephthalic acid and the low melting point acid undergo an amidation reaction; in step (1), the weight ratio of terephthalic acid to the low melting point acid is 1:0.5-1.5; Step (2): filtering while hot after the reaction, collecting the filter cake, washing the filter cake with a solvent while hot, and drying to obtain terephthalamide; and collecting the amide generated by the low melting point acid from the filtrate and the washing liquid; The low melting point acid is one of isooctanoic acid, oleic acid, glutaric acid and adipic acid.

2. The method for synthesizing terephthalamide according to claim 1, characterized in that: The catalyst in step (1) is a protonic acid and / or Lewis acid that can catalyze the amidation reaction of the acid, and the amount of the catalyst used is 0.05-0.5% of the total weight of the terephthalic acid and the low melting point acid.

3. The method for synthesizing terephthalamide according to claim 1, characterized in that: The pressure maintained by introducing ammonia is 0.3~0.7 MPa; the amidation reaction time is 6~12 hours.

4. The method for synthesizing terephthalamide according to claim 1, characterized in that: The temperature of hot filtration in step (2) is 20-50°C higher than the melting point of the corresponding amide generated by the low melting point acid.

5. The method for synthesizing terephthalamide according to claim 1, characterized in that: The washing solvent in step (2) is a solvent that can dissolve the corresponding amide generated by the low melting point acid but does not dissolve terephthalamide.

6. The method for synthesizing terephthalamide according to claim 5, characterized in that: The solvent in step (2) is one or more of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone and butyronitrile.

7. The method for synthesizing terephthalamide according to claim 1, characterized in that: Washing the filter cake while hot means washing at 100~160℃.

8. The method for synthesizing terephthalamide according to claim 1, characterized in that: The amide generated by the low melting point acid is collected from the filtrate and the washing liquid. Specifically, the filtrate is combined with the washing liquid generated by hot washing the filter cake, cooled to 30-80°C for crystallization, filtered, and dried to obtain the amide generated by the low melting point acid.

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