A continuous method for preparing high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate

Abstract

A continuous method for preparing high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate includes: dissolving 2,6-diamino-3,5-dinitropyridine in a 35% aqueous phosphoric acid solution, adding 5% Pd / C catalyst, and performing a hydrogenation reaction. After the reaction is completed, the Pd / C catalyst is filtered off to obtain an aqueous solution of 2,3,5,6-tetraaminopyridine phosphoric acid; adding the aqueous solution of 2,3,5,6-tetraaminopyridine phosphoric acid to a reaction solution prepared by mixing 2,5-dihydroxyterephthalic acid and NaOH aqueous solution; after the addition is complete, adding more aqueous phosphoric acid solution to adjust the pH value to 4-5; and then cooling, filtering, and drying to obtain high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate (TD salt). The method of this invention can effectively shorten the preparation route of TD salt, avoid the precipitation of 2,3,5,6-tetraaminopyridine from the phosphoric acid aqueous solution into hydrochloride, and does not require the addition of reducing agent during the preparation process, further preventing oxidation, improving yield and purity, and is suitable for continuous large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-performance poly(2,5-dihydroxy-1,4-phenylene pyridobisimidazole) PIPD fiber, in particular to a continuous preparation method of high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate. BACKGROUND

[0002] Poly(2,5-dihydroxy-1,4-phenylene pyridobisimidazole) PIPD fiber is a high-performance fiber developed by Akzo Nobel Laboratory in the Netherlands, which has excellent properties such as high strength, high modulus, high temperature resistance, and flame resistance. In addition, due to the presence of hydroxyl groups in the polymer main chain structure, a hydrogen bond network can be formed in the radial direction of the fiber, giving the fiber axial compression performance comparable to carbon fiber, the best among organic fibers. Therefore, it has broad application prospects in the fields of national defense and military industry.

[0003] Currently, there are two main methods for preparing PIPD polymer. The first method is to use monomer 2,3,5,6-tetraaminopyridine hydrochloride and monomer 2,5-dihydroxy-terephthalic acid, with polyphosphoric acid as the solution, tin powder as the initiator, and phosphorus pentoxide as the water absorber, to condense at 180℃. The reaction equation is as follows:

[0004]

[0005] However, this method takes a long time and the obtained polymer has a low molecular weight, which is difficult to meet the molding needs of high-performance fibers. The second method is to first prepare 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate by neutralizing the two monomers (2,3,5,6-tetraaminopyridine hydrochloride and 2,5-dihydroxy-terephthalic acid), and then condensing 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate in polyphosphoric acid. The reaction equation is as follows:

[0006]

[0007] This method has a short reaction time and does not need to go through the process of removing hydrochloric acid before polymerization. The molar ratio of the two monomers can be maximized to 1:1 during the polymerization process, so the obtained polymer has a high molecular weight and a narrow molecular weight distribution. However, 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate and its precursor TAP hydrochloride are easily oxidized in air, so controlling the purity of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate and 2,3,5,6-tetraaminopyridine hydrochloride is the key to using this method to prepare high-molecular-weight PIPD polymer.

[0008] The preparation process of 2,3,5,6-tetraaminopyridine hydrochloride at present is starting from 2,6-diaminopyridine, obtaining 2,6-diamino-4,5-dinitropyridine through sulfation and nitration, obtaining 2,3,5,6-tetraaminopyridine phosphoric acid aqueous solution through Pd / C high-pressure hydrogenation, finally using hydrochloric acid to prepare 2,3,5,6-tetraaminopyridine hydrochloride, adding tetrahydrofuran to precipitate 2,3,5,6-tetraaminopyridine hydrochloride crystal. The preparation of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalic acid salt is dissolving the prepared 2,3,5,6-tetraaminopyridine hydrochloride in water, adding the prepared 2,5-dihydroxy-terephthalic acid alkaline aqueous solution (usually selecting NaOH or KOH), then adding phosphoric acid aqueous solution to adjust the pH to 4-5, obtaining 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalic acid salt precipitate, then filtering, washing with water and drying to finally obtain 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalic acid salt. As shown in the following formula:

[0009]

[0010] In order to meet the requirement of high molecular weight of polymer for PIPD fiber forming, the purity control of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalic acid salt and 2,3,5,6-tetraaminopyridine hydrochloride before polymerization is the core. The conventional experience considers that separating high-purity 2,3,5,6-tetraaminopyridine hydrochloride and transferring it to a new reaction system can effectively reduce the occurrence of side reactions and thus improve the purity and yield of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalic acid salt. Usually, after filtering to remove Pd / C from the monomer 2,3,5,6-tetraaminopyridine phosphoric acid aqueous solution prepared by high-pressure hydrogenation reduction, hydrochloric acid is added, and then 2,3,5,6-tetraaminopyridine hydrochloride is separated from the aqueous phase by adding a poor solvent THF. The 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalic acid salt is prepared by neutralizing the 2,3,5,6-tetraaminopyridine hydrochloride separated by acid precipitation with another monomer 2,5-dihydroxy-terephthalic acid alkaline aqueous solution. Separating high-purity 2,3,5,6-tetraaminopyridine hydrochloride is a conventional idea for obtaining highly pure 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalic acid salt.

[0011] The above process for preparing 2,3,5,6-tetraaminopyridine hydrochloride has the following three defects:

[0012] 1) In order to obtain high-purity 2,3,5,6-tetraaminopyridine monomer, hydrochloric acid and tetrahydrofuran are used to precipitate 2,3,5,6-tetraaminopyridine hydrochloride. The 2,3,5,6-tetraaminopyridine hydrochloride obtained by filtration and drying is then transferred to a new reaction flask to prepare the final 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate. This process increases the use of hydrochloric acid and THF, which increases the solvent cost in the preparation of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate. Moreover, 2,3,5,6-tetraaminopyridine hydrochloride has good water solubility. Although hydrochloride crystals can be obtained by precipitation with poor solvents, some 2,3,5,6-tetraaminopyridine hydrochloride will still dissolve in the mother liquor and cannot precipitate, inevitably causing material loss. There are significant losses in terms of both solvent cost and actual product yield.

[0013] 2) 2,3,5,6-Tetraaminopyridine hydrochloride is hygroscopic and easily oxidized to black in air. Deteriorated 2,3,5,6-tetraaminopyridine hydrochloride will lead to lower purity and yield of the prepared 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, ultimately affecting the molecular weight of the PIPD polymer. The method reported in the current literature of first preparing 2,3,5,6-tetraaminopyridine hydrochloride and then transferring the material to prepare 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate increases the probability of 2,3,5,6-tetraaminopyridine hydrochloride being exposed to oxygen and deteriorating during the material transfer process. This will affect the yield and purity of the subsequent 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, ultimately resulting in a low molecular weight of the obtained PIPD polymer.

[0014] 3) This method of preparing 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate by precipitating and then dissolving 2,3,5,6-tetraaminopyridine via hydrochloride is complicated in its preparation steps and requires high water and oxygen content. Ultimately, this results in high material, equipment, and time costs for the production of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, making it difficult to achieve large-scale, continuous production of high-purity, high-yield 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate. Summary of the Invention

[0015] Based on this, the present invention provides a continuous preparation method for high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, to solve the technical problems of long process routes, low overall yield and easy oxidation of raw materials in existing methods for preparing 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate.

[0016] To achieve the above objectives, the present invention provides a continuous method for preparing high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, comprising the following steps:

[0017] S1. Under an anaerobic environment, 2,6-diamino-3,5-dinitropyridine was dissolved in a 35% aqueous solution of phosphoric acid, and 5% of Pd / C catalyst was added. After hydrogenation, the Pd / C catalyst was filtered off after the reaction was completed to obtain an aqueous solution of 2,3,5,6-tetraaminopyridine phosphoric acid.

[0018] S2. Under anaerobic conditions, an aqueous solution of 2,3,5,6-tetraaminopyridine phosphoric acid is added to a reaction solution prepared by mixing 2,5-dihydroxy-terephthalic acid and NaOH aqueous solution. The molar ratio of 2,5-dihydroxy-terephthalic acid to NaOH is controlled at 1:3.5-1:5, and the molar ratio of 2,5-dihydroxy-terephthalic acid to 2,6-diamino-3,5-dinitropyridine from step 3 is controlled at 1.05:1-1.2:1. After the addition is complete, an aqueous solution of phosphoric acid is added to adjust the pH value to 4-5. After cooling, filtration, and drying, high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate is obtained.

[0019] As a further preferred technical solution of the present invention, in step S1, the ratio of 2,6-diamino-3,5-dinitropyridine to phosphoric acid aqueous solution is controlled at 40g:200mL-80g:200mL, and the mass ratio of Pd / C catalyst to 2,6-diamino-3,5-dinitropyridine is controlled at 5:100-10:100.

[0020] As a further preferred technical solution of the present invention, in step S1, the hydrogenation reaction temperature is controlled at 50-80℃ and the reaction time is controlled at 5-8h.

[0021] As a further preferred technical solution of the present invention, in step S1, the hydrogen pressure of the hydrogenation reaction is controlled within 0.3-1.0 MPa.

[0022] As a further preferred technical solution of the present invention, in step S2, the concentration of the NaOH aqueous solution is controlled at 40g:300mL-50g:400mL.

[0023] As a further preferred technical solution of the present invention, in step S2, the reaction temperature is controlled at 10-50℃ and the reaction time is controlled at 1-2h.

[0024] As a further preferred embodiment of the present invention, the 2,6-diamino-3,5-dinitropyridine is prepared by the following steps:

[0025] 2,6-Diaminopyridine was dissolved in ethanol, sulfuric acid was added dropwise and stirred to react, and the mixture was cooled, filtered, and dried to obtain pyridine hydrochloride.

[0026] The obtained pyridine hydrochloride was dissolved in fuming sulfuric acid, and fuming nitric acid was added dropwise to react. Then, ice water was added to precipitate the precipitate. After filtration and drying, 2,6-diamino-4,5-dinitropyridine was obtained.

[0027] As a further preferred embodiment of the present invention, the molar ratio of 2,6-diaminopyridine to sulfuric acid is 1:2-1:4, the reaction temperature is 10-60℃, and the reaction time is controlled at 2-4h.

[0028] As a further preferred technical solution of the present invention, the ratio of pyridine hydrochloride to fuming sulfuric acid is controlled at 80g:200mL-120g:200mL, the reaction temperature is controlled at 0-20℃, and the reaction time is controlled at 2-3h.

[0029] The continuous preparation method of high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate of the present invention, using the above-mentioned technical solution, can achieve the following beneficial effects:

[0030] The method of this invention can effectively shorten the preparation route of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, avoiding the steps of first preparing 2,3,5,6-tetraaminopyridine from an aqueous phosphoric acid solution to form hydrochloride, and then dissolving it in an aqueous solution to prepare 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate. Furthermore, no reducing agent is added during the preparation process, further preventing the oxidation of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate. This method improves the yield and purity of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, making it more suitable for continuous, large-scale preparation of high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, and providing a reliable guarantee for the preparation of high molecular weight PIPD polymers. Attached Figure Description

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0032] Figure 1 This is a flowchart illustrating the preparation process of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate in Example 1 of the present invention.

[0033] Figure 2 The image shows the physical sample of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate prepared in Example 1 of this invention.

[0034] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0035] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0036] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0037] Example 1

[0038] This invention provides a continuous method for preparing high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, the preparation process of which is described in the following article. Figure 1 As shown.

[0039] Step 1: Take a 500mL three-necked flask, add 200g of 2,6-diaminopyridine and 350mL of anhydrous ethanol, heat to 50℃, stir for 0.5h until completely dissolved, then add 48mL of concentrated sulfuric acid dropwise using a constant pressure dropping funnel. After the addition is complete, continue stirring for 1h, cool to room temperature, filter, wash with ethanol, and dry in a vacuum oven to obtain 278.2g of sulfate, with a yield of 96%.

[0040] Step 2: Take a 1000mL three-necked flask, add 500mL of fuming sulfuric acid, add the sulfate prepared above in batches, stir vigorously, and after the solution becomes clear, add fuming nitric acid (154mL) dropwise. The reaction temperature is always controlled below 10℃. After the addition is complete, continue the reaction for 1 hour. Then, quickly pour the reaction solution into ice water to precipitate the precipitate. Filter, wash the filter cake with dilute ammonia and water in sequence, and dry to obtain 332g of 2,6-diamino-3,5-dinitropyridine (yield 95%).

[0041] Step 3: Add 50g of 2,6-diamino-3,5-dinitropyridine, 3.5g of 10% Pd / C catalyst, and 350mL of 30% phosphoric acid aqueous solution to a 1L autoclave. After purging with nitrogen, add H2 to 0.8MPa and react at 50℃ until no more H2 is consumed. The entire reaction lasts approximately 5 hours. After the reaction is complete, connect a short PTFE hose to the bottom outlet of the autoclave and then to a self-made sealed filter device. Connect this filter to a 1L three-necked flask. Filter the resulting 2,3,5,6-tetraaminopyridine phosphoric acid aqueous solution (removing Pd / C) through the N2 at the top of the autoclave and collect it in the three-necked flask. The resulting 2,3,5,6-tetraaminopyridine phosphoric acid aqueous solution is colorless and transparent and is used as reaction solution 1 for later use.

[0042] Step 4: Take another 1L three-necked flask, add 40.08g of NaOH, purge with nitrogen three times, then add 300mL of deoxygenated water. After complete dissolution, add 49.6g of 2,5-dihydroxy-terephthalic acid (the molar ratio of 2,5-dihydroxy-terephthalic acid to 3,5,6-tetraaminopyridine hydrochloric acid is 1:1.1) in batches. The system will turn reddish-brown. After complete dissolution, heat to 50℃ to prepare reaction solution 2. Connect the three-necked flask containing reaction solution 1 to the three-necked flask containing reaction solution 2 using a flexible silicone tube. Slowly and steadily pump reaction solution 1 into reaction solution 2 using a peristaltic pump. 2. During the high-speed stirring process, pale yellow and light green solids were formed during the dropwise addition of reaction solution 2. After reaction solution 1 was completely pumped out, 30 mL of phosphoric acid aqueous solution (30% by mass, prepared with deoxygenated water) was added to the system to adjust the pH value of the reaction system to 4-5. The mixture was then filtered under nitrogen atmosphere to obtain a light green filter cake of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate. After washing with ethanol, the cake was vacuum dried for 24 hours to obtain 76.6 g of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate (e.g., ...). Figure 2 (As shown in Table 1), the yield was 95%. The purity of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate was obtained by elemental analysis, as shown in Table 1. The experimentally obtained proportions of each element had an error of less than 0.5% compared with the theoretical values.

[0043] Table 1

[0044] C(％) H(％) O(％) N(％) Theoretical value 43.95 4.82 31.52 19.71 Test value 43.90 4.86 30.95 20.29

[0045] Comparative Example 1

[0046] Comparative Example 1 uses a traditional process and serves as a comparison experiment with Example 1. The specific implementation method is the same as that of Example 1, except for steps three and four, as detailed below:

[0047] In step three, after the high-pressure hydrogenation is completed, the reaction solution is taken out of the reactor and filtered to remove Pd / C. Then, 350 mL of hydrochloric acid and 200 mL of tetrahydrofuran are added, and pale yellow crystals precipitate out. After the addition is completed, the solution is rapidly filtered under a nitrogen atmosphere and dried under vacuum to obtain 40.8 g of light brown 2,3,5,6-tetraaminopyridine hydrochloride solid, with a yield of 61%.

[0048] In step four, 40.8 g of 2,3,5,6-tetraaminopyridine hydrochloride was dissolved in 150 mL of deoxygenated water to prepare reaction solution 1. Reaction solution 1, prepared from 2,3,5,6-tetraaminopyridine hydrochloride, appeared yellowish-green, indicating that the 2,3,5,6-tetraaminopyridine hydrochloride underwent slight oxidation during the transfer process due to oxidation by water and oxygen in the air. Reaction solution 2 was prepared by mixing 30.5 g of 2,5-dihydroxyterephthalic acid and 24.6 g of NaOH, with 200 mL of deoxygenated water used to dissolve the NaOH. Reaction solution 1 was then added to reaction solution 2. After this process, 22 mL of a phosphoric acid aqueous solution (30% by mass, prepared with deoxygenated water) was added to the system to adjust the pH to 4-5. The final mass of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate obtained was 42 g, with a yield of 81%. The purity was characterized by elemental analysis, and the proportions of each element had an error of about five percent compared to the theoretical value.

[0049] Comparative experiments show that, after high-pressure hydrogenation of the same mass of 2,6-diamino-3,5-dinitropyridine (50g), the present invention, without the addition of hydrochloric acid for precipitation, ultimately yields 76.6g of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, with a yield of 95%. The final purity of the product, as characterized by elemental analysis, has an error of less than 0.5% in the proportion of each element. The traditional process, which involves precipitation with hydrochloric acid, yields 42g of 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate, with a yield of 81%. The purity of the product, as characterized by elemental analysis, has an error of approximately 5% in the proportion of each element. Furthermore, hydrochloric acid and THF are used in this process. Therefore, the technical solution of the present invention has significant advantages in terms of material cost, product yield, and purity.

[0050] Traditional techniques, from a design perspective, require obtaining high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate (2,3,5,6-tetraaminopyridine hydrochloride first. This can only be achieved through separation via hydrochloric acid precipitation. Therefore, separation followed by preparation is the conventional approach. The invention we aim to protect breaks with this conventional approach, maximizing the utilization of the prepared 2,3,5,6-tetraaminopyridine without separation or precipitation. By controlling the amount of 2,5-dihydroxyterephthalic acid and the reaction temperature, we achieve the continuous preparation of high-purity 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate.

[0051] Example 2:

[0052] The specific method is the same as in Example 1, except that the amount of 2,5-dihydroxyterephthalic acid in step four is reduced to 47.37g (ensuring a molar ratio of 2,5-dihydroxyterephthalic acid to 2,3,5,6-tetraaminopyridine of 1:1.05), and the amount of NaOH is increased to 40.1g (ensuring a molar ratio of 2,5-dihydroxyterephthalic acid to NaOH of 1:4). The obtained 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate is pale yellow, with a total amount of 73.4g and a yield of 91%. The elemental ratios obtained by elemental analysis have an error of less than 0.5% compared with the theoretical values.

[0053] Example 3

[0054] The specific method is the same as in Example 1, except that the amount of 2,5-dihydroxyterephthalic acid in step four is increased to 54.14 g (to ensure that the molar ratio of 2,5-dihydroxyterephthalic acid to 2,3,5,6-tetraaminopyridine is 1:1.2), and the amount of NaOH is increased to 43.75 g (to ensure that the molar ratio of 2,5-dihydroxyterephthalic acid to NaOH is 1:4). The obtained 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate is pale yellow, with a total amount of 75 g and a yield of 93%. The elemental ratios obtained by elemental analysis have an error of less than 0.5% compared with the theoretical values.

[0055] Example 4

[0056] The specific method is the same as in Example 1, except that the reaction temperature in step four is lowered to 25°C. The resulting 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate is pale yellow, with a total weight of 78 g and a yield of 96.7%. The elemental proportions obtained through elemental analysis have an error of less than 0.5% compared to the theoretical values. This indicates that a lower temperature in the acid-base reaction helps to reduce the effect of exothermic reactions and obtain a higher yield. The preferred reaction temperature in step four is 10-25°C.

[0057] Example 5

[0058] The specific method is the same as in Example 1, except that the amount of NaOH in step four is increased to 60.1 g. The resulting 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate is grayish-yellow, with a total amount of 71.3 g and a yield of 88.4%. This indicates that increasing the amount of base used to dissolve 2,5-dihydroxyterephthalic acid (the molar ratio of DHTA to NaOH is 1:6) leads to a significant decrease in the overall yield. Preferably, the molar ratio of 2,5-dihydroxyterephthalic acid to NaOH is controlled between 1:3.5 and 1:5.

[0059] Example 6

[0060] The specific method is the same as in Example 1, except that the value of the phosphoric acid aqueous solution in step four is increased to 50 mL. The obtained 2,3,5,6-tetraaminopyridine-2,5-dihydroxyterephthalate is grayish-yellow, with a total amount of 72 g and a yield of 89.3%. This indicates that adjusting the pH of the mother liquor to be more acidic (less than 4) significantly reduces the overall yield.

[0061] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for continuous production of high purity 2, 3, 5, 6-tetraaminopyridine-2, 5-dihydroxyterephthalic acid salt, characterized by, The method comprises the following steps: S1, in an oxygen-free environment, 2, 6-diamino-3, 5-dinitropyridine is dissolved in a 20-35% phosphoric acid aqueous solution, 5-10% Pd / C catalyst is added, hydrogenation reaction is carried out, and after the reaction is completed, the Pd / C catalyst is filtered out to obtain a 2, 3, 5, 6-tetraaminopyridine phosphoric acid aqueous solution; S2, in an oxygen-free environment, the 2, 3, 5, 6-tetraaminopyridine phosphoric acid aqueous solution is added to a reaction solution prepared by mixing 2, 5-dihydroxy-terephthalic acid and a NaOH aqueous solution, the molar ratio of 2, 5-dihydroxy-terephthalic acid to NaOH is controlled to be 1:3.5-1:6, and the molar ratio of 2, 5-dihydroxy-terephthalic acid to 2, 6-diamino-3, 5-dinitropyridine in step 1 is controlled to be 1.05:1-1.1:1; after the feeding is completed, the pH value is adjusted to 4-5 by adding a phosphoric acid aqueous solution, and then cooling, filtering and drying are carried out to obtain high-purity 2, 3, 5, 6-tetraaminopyridine-2, 5-dihydroxy terephthalate; In step S2, the reaction temperature is controlled at 10-50 o C.

2. The method for continuously preparing high purity 2, 3, 5, 6-tetraaminopyridine-2, 5-dihydroxyterephthalic acid salt according to claim 1, characterized by, In step S1, the ratio of 2, 6-diamino-3, 5-dinitropyridine to the phosphoric acid aqueous solution is controlled to be 40g:200mL-80g:200mL, and the mass ratio of Pd / C catalyst to 2, 6-diamino-3, 5-dinitropyridine is controlled to be 5:100-10:

100.

3. The method for continuously preparing high purity 2, 3, 5, 6-tetraaminopyridine-2, 5-dihydroxyterephthalic acid salt according to claim 1, characterized by, In step S1, the hydrogenation reaction temperature is controlled at 50-80 o C, and the reaction time is controlled at 5-8h.

4. The method for continuously preparing high purity 2, 3, 5, 6-tetraaminopyridine-2, 5-dihydroxyterephthalic acid salt according to claim 1, characterized by, In step S1, the initial pressure of hydrogen in the hydrogenation reaction is controlled to be 0.3-1.0 Mpa.

5. The method for continuously preparing high purity 2, 3, 5, 6-tetraaminopyridine-2, 5-dihydroxyterephthalic acid salt according to claim 1, characterized by, In step S2, the concentration of the NaOH aqueous solution is controlled to be 40g:300mL-50g:400mL.

6. The method for continuously preparing high purity 2, 3, 5, 6-tetraaminopyridine-2, 5-dihydroxyterephthalic acid salt according to claim 1, characterized by, In step S2, the reaction time is controlled to be 1-2 h.

7. The process for the continuous preparation of high purity 2, 3, 5, 6-tetraaminopyridine- 2, 5-dihydroxyterephthalic acid salt according to any one of claims 1-6, characterized in that, The 2, 6-diamino-3, 5-dinitropyridine is prepared by the following steps: 2, 6-diaminopyridine is dissolved in ethanol, sulfuric acid is added dropwise, stirring reaction is carried out, cooling, suction filtration and drying are carried out to obtain pyridine hydrochloride; The obtained pyridine hydrochloride is dissolved in fuming sulfuric acid, fuming nitric acid is added dropwise for reaction, and then ice water is added for sedimentation and precipitation, and then filtering, drying are carried out to obtain 2, 6-diamino-4, 5-dinitropyridine.

8. The method for continuously producing high-purity 2, 3, 5, 6-tetraaminopyridine-2, 5-dihydroxyterephthalic acid salt according to claim 7, characterized by, The molar ratio of the 2,6-diaminopyridine to sulfuric acid is 1:2-1:4, the reaction temperature is 10-60 o C, and the reaction time is controlled at 2-4 h.

9. The method for continuously producing high-purity 2, 3, 5, 6-tetraaminopyridine-2, 5-dihydroxyterephthalic acid salt according to claim 7, characterized by, The ratio of the pyridine hydrochloride to fuming sulfuric acid is controlled at 80g:200mL-120g:200mL, the reaction temperature is controlled at 0-20 o C, and the reaction time is controlled at 2-3h.

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