Method for recrystallizing formamidine hydriodate

Abstract

The invention discloses a method for recrystallizing formamidine hydriodate, which comprises the following steps of: dissolving a formamidine hydriodate crude product prepared by adopting a rotary evaporation method under a certain condition by taking an alkali solution as a good solvent for recrystallization to prepare a saturated solution, and further cooling the saturated solution to separate out formamidine hydriodate crystals. According to the method, residual acidic substances in the formamidine hydriodate crude product subjected to rotary evaporation are removed, and the problem that the product purity is reduced due to the fact that acidic impurities are easily included in formamidine hydriodate crystals in the recrystallization process is solved. Compared with a traditional recrystallization process for preparing the high-purity formamidine hydriodate, the method has the advantages that the recrystallization frequency is reduced, the process time is effectively shortened, the process cost is reduced, and industrial production of the formamidine hydriodate is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of perovskite photovoltaic cell precursor materials, and particularly relates to a method for recrystallizing formamidine hydroiodide. Background Art

[0002] Perovskite photovoltaic technology is currently in a stage of rapid industrial development, and the demand for precursor materials for perovskite photovoltaic cells is increasing day by day. Formamidine hydroiodide is one of the core precursor materials for perovskite photovoltaic cells. At present, the "rotary evaporation-recrystallization" process route is generally used for preparation. The recrystallization process is a key step in the preparation of high-quality formamidine hydroiodide. Since the rotary evaporation process cannot completely remove the by-product acetic acid and excess hydroiodic acid, the crude product obtained often has more residual acidic impurities, and the larger the single batch output, the more obvious this phenomenon is, which puts higher requirements on the recrystallization process. In order to obtain high-purity formamidine hydroiodide crystals, it is necessary to carry out multiple recrystallization processes and repeatedly purify the product to achieve the effect of completely removing acidic impurities. This not only increases the complexity of the process, but also the impurity removal effect is not ideal, which brings great difficulties to industrial production. Therefore, optimizing the recrystallization process of formamidine hydroiodide and improving the quality of formamidine hydroiodide products are of great significance to designing a process route suitable for the industrial production of formamidine hydroiodide. Summary of the invention

[0003] The invention aims to provide a method for recrystallizing formamidine hydroiodide, aiming to efficiently remove acidic impurities in a crude formamidine hydroiodide product during the recrystallization process, thereby avoiding the problem that the acidic impurities are easily contained in formamidine hydroiodide crystals, and obtaining high-purity formamidine hydroiodide crystals through primary crystallization.

[0004] To achieve the above object, the present invention optimizes the recrystallization solvent, adopts an alkaline solution and controls the pH of the crystallization mother liquor to complete the recrystallization process, which specifically includes the following steps:

[0005] (1) directly mixing formamidine acetate and hydroiodic acid, and stirring the mixture at 20 to 50° C. for 6 to 8 hours to obtain a clear reaction solution;

[0006] (2) filtering the reaction solution obtained in step (1), and then performing rotary evaporation at a vacuum degree of -0.095 MPa and a temperature of 80 to 120° C. to remove a large amount of by-products acetic acid and water, and collecting the crude product of formamidine hydroiodide after the solvent is completely evaporated;

[0007] (3) preparing an alkaline solution of a certain concentration at room temperature, using deionized water as a solvent of the alkaline solution;

[0008] (4) Add the alkali solution prepared in step (3) dropwise to the crude product collected in step (2), and stir and dissolve it at a rotation speed of 400 rpm / min at room temperature. Control the pH of the alkali solution by adding deionized water to completely dissolve the crude product and obtain a clear and transparent solution;

[0009] (5) Evaporate the solution obtained in step (4) at normal pressure at 70-80 °C until the solution is saturated;

[0010] (6) Recrystallize the saturated solution obtained in step (5) by cooling to obtain a slurry of formamidine hydroiodide;

[0011] (7) Filter the slurry obtained in step (6), wash the solid 3 times with ether, and then place it in a vacuum drying oven. Dry it for 24 h under the conditions of a temperature of 30-40 °C and a vacuum degree of -0.095 MPa to obtain formamidine hydroiodide crystals.

[0012] Preferably, the molar ratio of hydroiodic acid to formamidine acetate in step (1) is 1.02-1.05 to ensure that hydroiodic acid is in excess and the reaction proceeds fully. The chemical equation of this reaction is as follows:

[0013] [NH 2 CH=NH 2 + CH 3 COOˉ+HI→[NH 2 CH=NH 2 + Iˉ+CH 3 COOH

[0014] Preferably, the alkali used in step (3) includes one or more of ammonia water, sodium hydroxide, potassium hydroxide, and sodium carbonate.

[0015] Preferably, the concentration of the alkali solution prepared in step (3) is 0.001-0.1 mol / L. The inventor found that the concentration of the alkali solution plays a key role in removing acidic impurities. Too low a concentration results in poor impurity removal effect, and trace acidic impurities will still remain in the mother liquor. Too high a concentration can completely remove acidic impurities, but excessive alkali remaining in the mother liquor is likely to precipitate with the precipitation of formamidine hydroiodide crystals, resulting in a decrease in product purity.

[0016] ​​Preferably, in step (4), the pH of the alkali solution is controlled to be 8-10. The inventor found that the pH of the crystallization mother liquor affects the crystallization effect of formamidine hydroiodide, and controlling the pH of the recrystallization process is the key to obtaining high-quality formamidine hydroiodide. Too low pH indicates poor removal effect of acidic impurities, and trace acidic impurities are easily occluded in the product. Too high pH not only leads to poor particle size uniformity of the product, but also easily precipitates alkaline impurities, affecting the product purity. Therefore, recrystallization of the mother liquor within a suitable pH range not only ensures the complete removal of acidic impurities, but also avoids the introduction of excessive alkaline substances, and ensures good particle size uniformity of the product.

[0017] Preferably, in step (6), the cooling rate of the recrystallization process is 0.5-1 °C / min, the cooling end temperature is 3-5 °C, and the holding time at the cooling end temperature is 12-16 h. The inventor found that the cooling rate is the key parameter for controlling the particle size of formamidine hydroiodide crystals. Too low cooling rate results in an increase in crystal particle size and an increase in process time; too high cooling rate causes explosive precipitation of crystals, easily leading to occlusion of impurities in the mother liquor and reducing the purity of formamidine hydroiodide crystals. The cooling end temperature and the holding time determine the yield of formamidine hydroiodide crystals, and a suitable range can obtain a higher yield. Description of the Drawings

[0018] Figure 1 is the morphology diagram of formamidine hydroiodide crystals under 500 times of scanning electron microscope in Example 1. Detailed Description of the Invention

[0019] The present invention will be further described in detail below with reference to the drawings, examples and comparative examples. It can be understood that the specific examples described herein are only used to explain the present invention, rather than limiting the present invention.

[0020] Example 1:

[0021] (1) 52.1 g of formamidine acetate and hydroiodic acid were mixed in a beaker and stirred at 20 °C for 6 h. According to the molar ratio of formamidine acetate to hydroiodic acid of 1.04, the amount of 55 wt% concentration of hydroiodic acid required was 71.6 mL.

[0022] (2) The reaction solution obtained in step (1) was filtered and the solvent was evaporated to dryness on a rotary evaporator. The temperature during rotary evaporation was 80 °C and the vacuum degree was -0.095 MPa. After the solvent was completely evaporated, the crude product of formamidine hydroiodide was collected.

[0023] (3) At room temperature, 12 mg of sodium hydroxide and 11.2 mg of potassium hydroxide were added to 500 mL of deionized water to prepare a 0.001 mol / L alkali solution.

[0024] (4) Add 376 mL of the alkali solution prepared in step (3) dropwise to the crude product collected in step (2), while stirring and dissolving at a speed of 400 rpm / min at room temperature. Add 33 mL of deionized water to control the pH of the alkali solution to 8, and at the same time completely dissolve the crude product to obtain a clear and transparent solution.

[0025] (5) Evaporate the solution obtained in step (4) at normal pressure at 70 °C for 0.5 h until the solution is saturated.

[0026] (6) Cool the saturated solution obtained in step (5) at a rate of 0.5 °C / min until the temperature drops to 3 °C, and then keep it for 12 h. After completion, obtain the crystal slurry of formamidine hydroiodide.

[0027] (7) Filter the crystal slurry obtained in step (6), wash the solid with ether 3 times, and then put it into a vacuum drying oven. Dry it at a temperature of 30 °C and a vacuum degree of -0.095 MPa for 24 h to obtain formamidine hydroiodide crystals.

[0028] The appearance diagram of the formamidine hydroiodide crystals obtained by the recrystallization process under 500 times magnification of a scanning electron microscope is as Figure 1 shown. It can be seen that the crystals are short rod-shaped, with a smooth surface, good particle size uniformity, and good crystallization quality.

[0029] Example 2:

[0030] (1) Mix 83.3 g of formamidine acetate and hydroiodic acid in a beaker, and stir and react at 50 °C for 8 h. According to the molar ratio of formamidine acetate to hydroiodic acid of 1.05, the amount of 55 wt% concentrated hydroiodic acid required is 115.6 mL.

[0031] (2) Filter the reaction solution obtained in step (1), and evaporate the solvent on a rotary evaporator. The temperature during rotary evaporation is 120 °C, and the vacuum degree is -0.095 MPa. After the solvent is completely evaporated, collect the crude product of formamidine hydroiodide.

[0032] (3) At room temperature, add 5.8 g of 30% ammonia water solution and 3.2 g of sodium carbonate to 800 mL of deionized water to prepare a 0.1 mol / L alkali solution.

[0033] (4) Add 542 mL of the alkali solution prepared in step (3) dropwise to the crude product collected in step (2), while stirring and dissolving at a speed of 400 rpm / min at room temperature. Add 124 mL of deionized water to control the pH of the alkali solution to 10, and at the same time completely dissolve the crude product to obtain a clear and transparent solution.

[0034] (5) Evaporate the solution obtained in step (4) at normal pressure at 80 °C for 0.2 h until the solution is saturated.

[0035] (6) Cool down the saturated solution obtained in step (5) at a rate of 1 °C / min until the temperature drops to 5 °C, then hold for 24 h. After completion, a slurry of formamidine hydroiodide is obtained.

[0036] (7) Filter the slurry obtained in step (6), wash the solid with ether three times, and then place it in a vacuum drying oven. Dry it for 24 h under the conditions of a temperature of 40 °C and a vacuum degree of -0.095 MPa to obtain formamidine hydroiodide crystals.

[0037] Comparative Example 1:

[0038] (1) Mix 52.1 g of formamidine acetate with hydroiodic acid in a beaker and stir and react at 20 °C for 6 h. According to the molar ratio of formamidine acetate to hydroiodic acid of 1.04, the amount of 55 wt% concentrated hydroiodic acid required is 71.6 mL.

[0039] (2) Filter the reaction solution obtained in step (1), and evaporate the solvent on a rotary evaporator. The temperature during rotary evaporation is 80 °C and the vacuum degree is -0.095 MPa. After the solvent is completely evaporated, collect the crude product of formamidine hydroiodide.

[0040] (3) Add 200 mL of absolute ethanol to the crude product collected in step (2), and stir at 70 °C at a speed of 400 rpm / min until the solid is completely dissolved to obtain a saturated solution.

[0041] (4) Cool down the saturated solution obtained in step (3) at a rate of 0.5 °C / min until the temperature drops to -5 °C, then hold for 12 h. After completion, a slurry of formamidine hydroiodide is obtained, and the slurry is filtered to obtain formamidine hydroiodide crystals.

[0042] (5) Repeat steps (3) and (4) twice.

[0043] (6) Wash the crystals obtained in step (5) with ether three times, and then place them in a vacuum drying oven. Dry them for 24 h under the conditions of a temperature of 30 °C and a vacuum degree of -0.095 MPa to obtain formamidine hydroiodide crystals.

[0044] Comparative Example 2:

[0045] The difference between this comparative example and Comparative Example 1 is that the number of recrystallizations is reduced to 1 time. The specific operation steps are as follows:

[0046] (1) Mix 52.1 g of formamidine acetate with hydroiodic acid in a beaker and stir and react at 20 °C for 6 h. According to the molar ratio of formamidine acetate to hydroiodic acid of 1.04, the amount of 55 wt% concentrated hydroiodic acid required is 71.6 mL.

[0047] (2) Filter the reaction solution obtained in step (1) and evaporate the solvent on a rotary evaporator. The temperature during rotary evaporation is 80 °C and the vacuum degree is -0.095 MPa. After the solvent is completely evaporated, collect the crude formamidine hydroiodide product.

[0048] (3) Add 200 mL of absolute ethanol to the crude product collected in step (2) and stir at 70 °C at a speed of 400 rpm / min until the solid is completely dissolved to obtain a saturated solution.

[0049] (4) Cool the saturated solution obtained in step (3) at a rate of 0.5 °C / min until the temperature drops to -5 °C, and then maintain it for 12 h. After completion, obtain the crystal slurry of formamidine hydroiodide and filter the crystal slurry to obtain formamidine hydroiodide crystals.

[0050] (5) Wash the crystals obtained in step (4) with ether three times and then put them into a vacuum drying oven. Dry them for 24 h under the conditions of a temperature of 30 °C and a vacuum degree of -0.095 MPa to obtain formamidine hydroiodide crystals.

[0051] The purity of the formamidine hydroiodide crystals prepared in the examples and comparative examples and the pH of the aqueous solution of the formamidine hydroiodide crystals are shown in Table 1:

[0052] Table 1

[0053] sample Example 1 Example 2 Comparative Example 1 Comparative Example 2 pH 7.5 7.2 6.5 5.3 purity 99.9％ 99.8％ 99.2％ 98％

[0054] It can be seen that the pH of the aqueous solution of the formamidine hydroiodide crystals prepared in the examples of the present invention is greater than 7, showing neutrality, and the purity of the formamidine hydroiodide crystals can reach 99.9%, indicating that the acidic impurities in the product have been completely removed after one recrystallization with an alkaline solution, and the quality of the product has been improved. While the pH of the aqueous solution of the formamidine hydroiodide crystals prepared in the comparative examples is less than 7, showing weak acidity, and the purity of the formamidine hydroiodide crystals is low, indicating that the traditional recrystallization process has a poor effect on removing acidic impurities, and in order to ensure the removal of acidic impurities, it is necessary to carry out multiple recrystallizations to improve the product purity.

Claims

1. A method for recrystallizing formamidine hydroiodide, characterized in that: The following steps are involved: (1) directly mixing formamidine acetate and hydroiodic acid, and stirring the mixture at 20 to 50° C. for 6 to 8 hours to obtain a clear reaction solution; (2) filtering the reaction solution obtained in step (1), and then performing rotary evaporation at a vacuum degree of -0.095 MPa and a temperature of 80 to 120° C. to remove a large amount of by-products acetic acid and water, and collecting the crude product of formamidine hydroiodide after the solvent is completely evaporated; (3) preparing an alkaline solution of a certain concentration at room temperature, using deionized water as a solvent of the alkaline solution; (4) adding the alkaline solution prepared in step (3) dropwise to the crude product collected in step (2), stirring and dissolving at a speed of 400 rpm / min at room temperature, controlling the pH of the alkaline solution by adding deionized water, and dissolving the crude product completely to obtain a clear and transparent solution; (5) evaporating the solution obtained in step (4) at 70-80° C. under normal pressure until the solution is saturated; (6) recrystallizing the saturated solution obtained in step (5) by cooling, and obtaining a crystal slurry of formamidine hydroiodide after completion; (7) The slurry obtained in step (6) was filtered, and the solid was washed with ether three times and then placed in a vacuum drying oven, and dried for 24 hours at a temperature of 30 to 40° C. and a vacuum degree of −0.095 MPa to obtain formamidine hydroiodide crystals.

2. The method according to claim 1, characterized in that In step (1), the molar ratio of hydroiodic acid to formamidine acetate is 1.02 to 1.

05.

3. The method according to claim 1, characterized in that The alkali used in step (3) includes one or more of ammonia water, sodium hydroxide, potassium hydroxide and sodium carbonate.

4. The method according to claim 1, characterized in that The concentration of the alkaline solution prepared in step (3) is 0.001 to 0.1 mol / L.

5. The method according to claim 1, characterized in that In step (4), the pH of the alkaline solution is controlled to be 8-10.

6. The method according to claim 1, characterized in that The cooling rate of the recrystallization process in step (6) is 0.5-1°C / min, the cooling end temperature is 3-5°C, and the holding time at the cooling end temperature is 12-16h.

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