Process for the preparation of 4-aminophenyl nitrile and polyimides thereof

Abstract

The application provides a preparation method of 4-aminophenyl cyan and a polyimide thereof, and is characterized in that the preparation method of 4-aminophenyl cyan comprises the following steps: Diels-Alder cycloaddition reaction of 1,2-dibromoethylene and methyl sorbate to form a ring; then, an amidation reaction, a Hofmann rearrangement reaction and a Zaitsev elimination reaction are sequentially performed to introduce an amino group; a benzene ring is generated; and an ammoxidation reaction is performed to introduce a cyano group, so that 4-aminophenyl cyan is obtained. The preparation method of 4-aminophenyl cyan provided by the application does not involve toxic cyanogen sodium, toxic cyanogen potassium and other toxic cyanogen reagents, and the reagent is environmentally friendly; the synthesis step has mild conditions, high yield, and no strict equipment requirement. Based on 4-aminophenyl cyan, a cyan-containing diamine and a dianhydride are condensed to prepare a polyimide containing two Schiff base bonds and double cyan groups, which has excellent rigidity, elasticity and heat resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of compound synthesis, and particularly relates to a preparation method of 4-aminobenzonitrile and a polyimide thereof. BACKGROUND

[0002] 4-aminobenzonitrile is a commonly used chemical raw material, and is widely used as a raw material and intermediate of medicines, agrochemicals, dyes and fine chemicals. In the traditional synthesis route of nitrile compounds, most of them involve the use of toxic cyanating reagents such as NaCN, KCN and the like; or CuCN, Zn(CN)2, K4[Fe(CN)6] cyanating reagents produce CN - , which causes catalyst poisoning, incomplete conversion of raw materials; in addition, some methods have the problems of harsh reaction conditions, low yield, poor functional group compatibility, chemical solvent residue, high cost and requirement for equipment, and poor stability and activity of catalysts. The industry has an urgent need for a method for efficiently synthesizing benzonitrile under mild conditions. SUMMARY

[0003] To solve the above problems, the present application provides a preparation method of 4-aminobenzonitrile and a polyimide thereof.

[0004] In one aspect, the present application provides a preparation method of 4-aminobenzonitrile, comprising the following steps:

[0005] (1) Diels-Alder cycloaddition reaction is carried out with 1,2-dibromoethylene and methyl sorbate as raw materials to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-methyl formate;

[0006] (2) 5,6-dibromo-4-methyl-2-cyclohexene-1-methyl formate is reacted with formamide at high temperature in the presence of sodium ethoxide to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide;

[0007] (3) Hofmann rearrangement reaction of 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide occurs in a sodium hypobromite solution of caustic soda to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-amine;

[0008] (4) Zaitsev elimination reaction of 5,6-dibromo-4-methyl-2-cyclohexene-1-amine occurs in an alcohol solution of base under heating to obtain 4-methyl aniline;

[0009] (5) Ammonia oxidation reaction of 4-methyl aniline occurs under palladium catalysis to obtain 4-aminobenzonitrile.

[0010] Further, the step (1) is specifically operated as follows: sorbic acid methyl ester and 1,2-dibromoethylene are dissolved in tetrahydrofuran, heated to reflux at 40-50℃ for 4-10h; stop heating, end reflux, filter the filtrate, add water to liquid-liquid extraction to remove tetrahydrofuran, add ethyl ether to continue extraction, take the extraction phase, remove ethyl ether by rotary evaporation, dry with anhydrous magnesium sulfate, and vacuum dry to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-methyl formate;

[0011] The molar ratio of the sorbic acid methyl ester to the dibromoethylene is 1:(1.01-1.2), and the 1,2-dibromoethylene is a cis structure.

[0012] Further, the step (2) is specifically operated as follows: under nitrogen atmosphere, 5,6-dibromo-4-methyl-2-cyclohexene-1-methyl formate, formamide and sodium ethoxide are mixed in N,N-dimethyl formamide solvent, stirred at 90-100℃ for 2-5h; cool to room temperature, extract with chloroform, rotary evaporate the extract, wash with brine, dry with anhydrous magnesium sulfate, and purify by silica gel column chromatography to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-methyl formamide;

[0013] The molar ratio of the 5,6-dibromo-4-methyl-2-cyclohexene-1-methyl formate, formamide and sodium ethoxide is 2:(6-7):(1-2); the eluent used in column chromatography is n-hexane / ethyl acetate, v:v=1:(3-5).

[0014] Further, the reaction condition of the step (3) is as follows: 5,6-dibromo-4-methyl-2-cyclohexene-1-methyl formamide, 35wt%-50wt% of cold NaOH aqueous solution and sodium hypobromite solution are uniformly mixed, then stirred at constant temperature in an ice-salt bath at-20℃-0℃ for 30-60min; remove the ice-salt bath and wait to restore to room temperature, heat the water bath to 40-50℃ for constant temperature stirring for 2-4h; after cooling to room temperature, decolorize with activated carbon, filter, precipitate the solid with glacial acetic acid, suction filter, wash with water, recrystallize, and vacuum dry to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-amine;

[0015] The concentration of the sodium hypobromite solution is 5wt%-20wt%, which is freshly prepared by adding NaOH aqueous solution into bromine; the molar ratio of the 5,6-dibromo-4-methyl-2-cyclohexene-1-methyl formamide, sodium hypobromite and NaOH is 1:(1-1.5):(6-7.5).

[0016] Further, step (4) is specifically operated as follows: 5,6-dibromo-4-methyl-2-cyclohexen-1-amine is stirred in sodium hydroxide ethanol solution under 71-75℃ water bath heating for 10-20 min; after the reaction is completed, the solution is slightly cooled, dilute hydrochloric acid is added, stirred until the solution pH is 6, water washing is performed, the water layer is taken, excess sodium hydroxide is added to neutralize the solution to pH 8; vacuum distillation is performed, the distillate is cooled to precipitate crystals, and filtration is performed to obtain a solid crude product and a filtrate; the filtrate is taken, sodium chloride is added to saturation, chloroform is used for extraction twice, the crude product is combined with the chloroform extract, rotary evaporation, anhydrous magnesium sulfate drying, and vacuum drying are performed to obtain 4-methylaniline;

[0017] The molar ratio of 5,6-dibromo-4-methyl-2-cyclohexen-1-amine to sodium hydroxide is 1:(2.01-2.2); the concentration of the dilute hydrochloric acid is 0.1-1 mol / L, and the concentration of the sodium hydroxide used for neutralization is 1-3 mol / L.

[0018] Further, the ammonia oxidation condition of step (5) is as follows: 4-methylaniline, tert-butyl nitrite, a palladium catalyst, and N-hydroxyphthalimide (NHPI) are mixed in acetonitrile solvent under a nitrogen atmosphere, and stirred at 70-80℃ for 18-24 h; after the solution is cooled, CH2Cl2 is added for dilution, decolorization, filtration, concentration, and silica gel column chromatography purification to obtain 4-aminobenzonitrile.

[0019] The molar ratio of 4-methylaniline, tert-butyl nitrite, a palladium catalyst, and N-hydroxyphthalimide is 1:(2-3):(0.05-0.1):(0.2-0.3); the palladium catalyst is selected from one of Pd(OAc)2, Pd(OTFA)2, Pd(dba)2, and Pd2(dba)3; and the eluent used for column chromatography is n-hexane / ethyl acetate, v:v=(1-5):(19-15).

[0020] Another aspect of the present application provides a polyimide obtained by polycondensation of a dianhydride and a cyano-containing diamine; the cyano-containing diamine is obtained by synthesis using 4-aminobenzonitrile prepared by the above preparation method as raw material; and the preparation steps of the polyimide include:

[0021] A. 4-aminobenzonitrile, a base reagent, and an end diamino ketone are added to an organic solvent 1 under anhydrous and nitrogen atmosphere, oil bath heating is performed to 85-90℃, water reflux reaction is performed for 6-10 h until no water is generated; after the reaction is completed, cooling is performed, filtration is performed, and the filter cake is washed with acetone for 3-4 times, then the filter cake is taken out, recrystallized with anhydrous ethanol, filtered, and vacuum dried to obtain a cyano-containing diamine.

[0022] The end diamino ketone refers to a ketone compound terminated by two primary amino groups; the molar ratio of the end diamino ketone to 4-aminophenyl cyanide is (1.01-1.2):1; the base reagent is one of triethylamine, sodium carbonate, and potassium carbonate, and the amount used is 2.01-2.05 times the molar amount of 4-aminophenyl cyanide;

[0023] B. Under anhydrous and nitrogen atmosphere, the cyan-containing diamine is dissolved in an organic solvent 2, and the diacid anhydride is added in batches at -10-5°C; the reaction system is stirred at room temperature for 12-18 h to obtain a homogeneous polyamic acid solution with a solid content of 15-30 wt%;

[0024] The molar ratio of the cyan-containing diamine to the diacid anhydride is 1:(0.98-1.02);

[0025] C. The polyamic acid solution is subjected to thermal imidization treatment to obtain polyimide.

[0026] Further, the thermal imidization treatment is as follows: the polyamic acid is diluted with an organic solvent 2, and is subjected to freeze defoaming and nylon cloth filtration to obtain a casting solution with a concentration of 6 wt%-20 wt%; the casting solution is flowed on a clean glass plate, and is treated at 120°C-180°C, 240-280°C for 4-8 h, and finally is kept at 300°C-320°C for 1 h.

[0027] Further, the diacid anhydride is selected from one or more of the following compounds containing two diacid anhydride groups in one molecule: pyromellitic dianhydride, 4,4-biphenyl ether dianhydride, 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, bisphenol A type diether dianhydride, 1,2,4,5-cyclohexane tetra carboxylic dianhydride, 2,3,3',4'-biphenyl tetra carboxylic dianhydride, 3,3',4,4'-biphenyl tetra carboxylic dianhydride, 3,3',4,4'-benzophenone tetra carboxylic dianhydride, 4,4'-oxyphthalic anhydride, 3,3',4,4'-triphenyl ether tetra carboxylic dianhydride, 2,3,3',4'-diphenyl ether tetra carboxylic dianhydride, 3,3',4,4'-diphenyl sulfone tetra carboxylic dianhydride, and derivatives thereof.

[0028] Further, the organic solvent 1 in step A is one or more of dimethyl sulfoxide, tetrahydrofuran, dichloromethane, and ethanol; and the organic solvent 2 in step B comprises one or more of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl pyrrolidone, and dimethyl sulfoxide.

[0029] Various numerical ranges can be disclosed herein. When an applicant discloses or claims any type of range, the applicant's intent is to disclose or claim every possible number that the range can reasonably encompass, including every sub-range between the endpoints of the range, and every combination of sub-ranges, unless otherwise specifically indicated.

[0030] All numerical endpoints of ranges disclosed herein are approximate. As a representative example, Applicants disclose a temperature of "40°C to 50°C" in some embodiments. This range should be interpreted to encompass each of 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, or 50°C within the range of 40°C to 50°C, including any ranges and subranges therebetween.

[0031] In the present application, room temperature is "25°C" unless otherwise specified; the temperature for vacuum drying of the intermediate products and final products of synthesis is 60°C.

[0032] Compared with the prior art, the beneficial effects of the present application are:

[0033] The preparation method of 4-aminophenyl cyanide provided by the present application uses acetonitrile as a cyan source, does not involve toxic cyanide reagents such as sodium cyanide and potassium cyanide, and is environmentally friendly; the conditions of each step are mild, the yield is high, and there is no strict equipment requirement.

[0034] The polyimide provided by the present application contains a Schiff base bond, which can endow the material with elasticity, self-repairing ability, and durable heat resistance; by introducing a cyano group into the polyimide main chain, the intermolecular interaction force is increased, the rigidity and heat resistance of the polymer skeleton are further improved, and it is beneficial to further manufacture terminal materials with strong thermal stability. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows.

[0036] Figure 1 The synthesis route of 4-aminophenyl cyanide provided by the present application.

[0037] Figure 2 The nuclear magnetic resonance spectrum of 4-aminophenyl cyanide obtained in Preparation Example 1. DETAILED DESCRIPTION

[0038] The technical solutions of the present application will be further described in detail below in combination with several preferred embodiments and drawings. The present embodiments are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments. The contents not described in detail in the present application specification belong to the known technology of those skilled in the art. Unless otherwise defined, the experimental materials used in the following examples and comparative examples can be purchased from conventional biochemical reagent companies.

[0039] Preparation Example 1

[0040] According toFigure 1 The preparation method shown prepares 4-aminobenzonitrile:

[0041] (1) In a 250 mL round-bottom flask with a reflux condenser and a magnetic stirrer, 0.2 mol of methyl sorbate was mixed with 40 mL of tetrahydrofuran, and 0.22 mol of cis-1,2-dibromoethylene was added dropwise using a dropping funnel. The mixture was heated to reflux at 50°C for 6 h; the heating was stopped, the reflux was completed, and the filtrate was cooled and extracted with water to remove tetrahydrofuran. The organic phase was further extracted with diethyl ether, and the extract was rotary evaporated to remove diethyl ether, dried over anhydrous magnesium sulfate, and vacuum dried at 60°C to obtain 5,6-dibromo-4-methyl-2-cyclohexen-1-methyl formate with a yield of 85.73%.

[0042] (2) Under a nitrogen atmosphere, 80 mmol of 5,6-dibromo-4-methyl-2-cyclohexen-1-methyl formate, 0.268 mol of formamide, and 60 mmol of sodium ethoxide were sequentially added to 50 mL of N,N-dimethylformamide. After the reaction system was heated to 100°C and kept at this temperature for 2 h, it was cooled to room temperature, extracted with chloroform, rotary evaporated, washed with brine, dried over anhydrous magnesium sulfate, and purified by silica gel column chromatography using n-hexane-ethyl acetate (v:v = 1:5) as the eluent to obtain 5,6-dibromo-4-methyl-2-cyclohexen-1-formamide with a yield of 95.70%.

[0043] (3) Under an ice-salt bath, 75 mmol of bromine was added dropwise to a 250 mL round-bottom flask containing 100 mL of 12.5 wt% NaOH aqueous solution using a dropping funnel while stirring. Fresh sodium hypobromite solution was prepared. While maintaining the ice-salt bath and stirring, 50 mmol of 5,6-dibromo-4-methyl-2-cyclohexen-1-formamide and 0.34 mol of NaOH were mixed to prepare a 50 wt% NaOH aqueous solution, which was then added to the fresh sodium hypobromite solution. The mixture was stirred at -10°C for 50 min. After removing the ice-salt bath and allowing the liquid temperature to return to room temperature, the water bath was heated to 40°C and kept at this temperature for 3 h. After cooling to room temperature, activated carbon was added for decolorization, and the mixture was filtered. The filtrate was acidified with glacial acetic acid to precipitate a solid. The solid was suction filtered, washed with water, recrystallized, and vacuum dried at 60°C to obtain 5,6-dibromo-4-methyl-2-cyclohexen-1-amine with a yield of 67.26%.

[0044] (4) Weigh 32.5 mmol of sodium hydroxide into a 50 mL round-bottom flask, add 20 mL of anhydrous ethanol and shake to dissolve, then add 15 mmol of 5,6-dibromo-4-methyl-2-cyclohexene-1-amine. Stir the reaction mixture in a 75°C water bath for 15 min. After the reaction is complete, add 1 mol / L dilute hydrochloric acid to the solution until the pH is about 6, separate the layers by adding water, and then neutralize the aqueous layer to a pH of about 8 by adding 2 mol / L sodium hydroxide; distill under reduced pressure, add petroleum ether to the collected concentrated solution, and cool to 5°C to precipitate crystals, then filter to obtain the solid crude product and the filtrate; add sodium chloride to the filtrate until it is saturated, extract twice with chloroform, combine the crude product and the extract, and then rotary evaporate, dry over anhydrous magnesium sulfate, and vacuum dry at 60°C to obtain 4-methylaniline crystals with a yield of 95%.

[0045] (5) Under a nitrogen atmosphere, mix 25 mmol of 4-methylaniline with 50 mmol of tert-butyl nitrite, 1.25 mmol of Pd(OAc)2, and 7.5 mmol of N-hydroxyphthalimide in 25 mL of acetonitrile, and stir the mixture at 70°C for 24 h; after the solution cools, dilute it with 100 mL of CH2Cl2, decolorize it with activated carbon, filter it, concentrate it, and then purify it by silica gel column chromatography using n-hexane-ethyl acetate (v:v = 1:8) as the eluent to obtain 4-aminobenzonitrile white solid with a yield of 86.22%.

[0046] The results of its nuclear magnetic resonance hydrogen spectrum (Bruker AVANCE superconducting nuclear magnetic resonance spectrometer, 400 MHz, CDCl3, without internal standard) are shown in Figure 2 .

[0047] Preparation Example 2

[0048] 4-aminobenzonitrile is synthesized as follows:

[0049] (1) In a 100 mL round-bottom flask with a reflux condenser and a magnetic stirrer, add 0.10 mol of methyl sorbate and 40 mL of tetrahydrofuran, then add 0.12 mol of cis-1,2-dibromoethylene dropwise through a dropping funnel, and heat the mixture to reflux at 50°C for 5 h; stop heating, and after the reflux is complete, add water to separate the layers, then add ethyl ether to the organic phase to continue extraction, rotary evaporate the ethyl ether from the extracted phase, dry it over anhydrous magnesium sulfate, and vacuum dry it at 60°C to obtain 5,6-dichloro-4-methyl-2-cyclohexene-1-methylate with a yield of 87.24%.

[0050] (2) Under nitrogen atmosphere, 90 mmol of 5,6-dichloro-4-methyl-2-cyclohexen-1- methyl formate, 0.28 mol of formamide and 72 mmol of sodium ethoxide were sequentially added into 60 mL of N,N-dimethylformamide, and the mixture was stirred at 100°C for 2 h. After cooling to room temperature, the mixture was extracted with chloroform, and the extract was rotary evaporated, washed with brine, dried over anhydrous magnesium sulfate, and finally purified by silica gel chromatography using n-hexane-ethyl acetate (v:v = 1:3) as the eluent to obtain 5,6-dichloro-4-methyl-2-cyclohexen-1-formamide with a yield of 92.70%.

[0051] (3) In a 250 mL round-bottom flask containing 80 mL of 18 wt% NaOH aqueous solution, 67.5 mmol of bromine was added dropwise using a dropping funnel under an ice-salt bath to prepare a fresh sodium hypobromite solution. While maintaining the ice-salt bath and stirring, 45 mmol of 5,6-dibromo-4-methyl-2-cyclohexen-1-formamide and 0.306 mol of NaOH were prepared into a 50 wt% NaOH aqueous solution, which was sequentially added into the fresh sodium hypobromite solution. The mixture was stirred at -10°C for 50 min. After removing the ice-salt bath, the solution was heated to 40°C in a water bath and stirred for 2 h. After cooling to room temperature, activated carbon was added to decolorize the solution, which was then filtered. The solid was obtained by adding glacial acetic acid to the filtrate. After suction filtration, water washing, recrystallization, and vacuum drying at 60°C, 5,6-dibromo-4-methyl-2-cyclohexen-1-amine was obtained with a yield of 69.34%.

[0052] (4) 25 mmol of sodium hydroxide was weighed into a 50 mL round-bottom flask, 15 mL of anhydrous ethanol was added, and the mixture was shaken to dissolve. Then, 12 mmol of 5,6-dibromo-4-methyl-2-cyclohexen-1-amine was added. The reaction mixture was stirred in a 73°C water bath for 10 min. After the reaction was completed, 1 mol / L dilute hydrochloric acid was added to the slightly cooled solution until the pH of the solution was about 6. The solution was partitioned with water, and the aqueous layer was neutralized to a pH of about 8 with 2 mol / L sodium hydroxide. The concentrated solution was collected by vacuum distillation, and petroleum ether was added to the solution to precipitate crystals at 5°C. The solid crude product and the filtrate were obtained by suction filtration. Sodium chloride was added to the filtrate to saturation, and the mixture was extracted twice with chloroform. The crude product and the extract were combined, rotary evaporated, dried over anhydrous magnesium sulfate, and vacuum dried at 60°C to obtain 4-methyl aniline crystals with a yield of 92.8%.

[0053] (5) 20 mmol 4-methylaniline, 45 mmol tert-butyl nitrite, 1.3 mmol Pd(OTFA)2, 6 mmol N-hydroxyphthalimide were mixed in 20 mL acetonitrile under nitrogen atmosphere, and the mixture was stirred at 75 °C for 20 h. After the solution was cooled, 20 mL CH2Cl2was added to dilute the solution, and activated carbon was added to decolorize the solution. After filtration and concentration, the product was purified by silica gel column chromatography using n-hexane-ethyl acetate (v:v = 1:19) as the eluent to obtain 4-aminobenzonitrile as a white solid in a yield of 89.06%.

[0054] Preparation Example 3

[0055] 4-aminobenzonitrile was synthesized as follows:

[0056] (1) 0.25 mol methyl sorbate and 40 mL tetrahydrofuran were sequentially added to a 250 mL round-bottom flask equipped with a reflux condenser and a magnetic stirrer, and 0.27 mol cis-1,2-dibromoethylene was added dropwise to the flask. The mixture was stirred at 50 °C for 8 h. After the heating was stopped and the reflux was completed, the filtrate was cooled and extracted with water. The organic phase was further extracted with diethyl ether, and the extract was dried over anhydrous magnesium sulfate and vacuum dried at 60 °C to obtain 5,6-dichloro-4-methyl-2-cyclohexen-1-methyl formate in a yield of 82.11%.

[0057] (2) 75 mmol 5,6-dichloro-4-methyl-2-cyclohexen-1-methyl formate, 0.24 mol formamide, and 56 mmol sodium ethoxide were sequentially added to 45 mL N,N-dimethylformamide under nitrogen atmosphere, and the reaction system was heated to 100 °C and stirred for 2 h. After the system was cooled to room temperature, the mixture was extracted with chloroform, and the extract was dried over anhydrous magnesium sulfate after being washed with salt water. Finally, the product was purified by silica gel chromatography using n-hexane-ethyl acetate (v:v = 1:4) as the eluent to obtain 5,6-dichloro-4-methyl-2-cyclohexen-1-methyl formamide in a yield of 93.23%.

[0058] (3) Under ice-salt bath, a 250 mL round bottom flask containing 70 mL of 15 wt% NaOH aqueous solution was added 64 mmol of bromine dropwise through a dropping funnel while stirring to prepare a fresh sodium hypobromite solution; while maintaining the ice-salt bath and stirring, 60 mmol of 5,6-dibromo-4-methyl-2-cyclohexen-1 -carboxamide was prepared into a 50 wt% cold NaOH aqueous solution, which was sequentially added into the fresh sodium hypobromite solution, and the mixture was stirred at -10 °C for 60 min; the ice-salt bath was removed, and after the liquid temperature returned to room temperature, the water bath was heated to 40 °C and stirred for 4 h; after cooling to room temperature, activated carbon was added for decolorization, and filtration was performed, and the filtrate was precipitated with glacial acetic acid; the solid was suction filtered, washed with water, recrystallized, and dried at 60 °C under vacuum to obtain 5,6-dibromo-4-methyl-2-cyclohexen-1 -amine with a yield of 69.34%.

[0059] (4) 34 mmol of sodium hydroxide was weighed into a 50 mL round bottom flask, 25 mL of anhydrous ethanol was added and shaken to dissolve, and then 18 mmol of 5,6-dibromo-4-methyl-2-cyclohexen-1 -amine was added. The reaction mixture was stirred in a 75 °C water bath for 20 min. After the reaction was completed, 1 mol / L dilute hydrochloric acid was added to the slightly cooled solution until the solution pH was ~ 6, and water was added to separate the layers, and the aqueous layer was neutralized to pH ~ 8 with 2 mol / L sodium hydroxide; vacuum distillation was performed, petroleum ether was added to the collected concentrated solution, and the temperature was lowered to 5 °C to precipitate crystals, and the solid crude product and filtrate were suction filtered; sodium chloride was added to the filtrate to saturation, and chloroform was extracted twice, and the crude product and extract were combined, rotary evaporated, dried over anhydrous magnesium sulfate, and vacuum dried at 60 °C to obtain 4-methylaniline crystals with a yield of 90.9%.

[0060] (5) Under a nitrogen atmosphere, 24 mmol of 4-methylaniline was uniformly mixed with 54 mmol of tert-butyl nitrite, 1.64 mmol of Pd(OTFA)2, and 7.0 mmol of N-hydroxyphthalimide in 30 mL of acetonitrile solvent, and stirred at 78 °C for 22 h; after the solution was cooled, 30 mL of CH2Cl2was added for dilution, activated carbon was added for decolorization, filtration was performed, and concentrated, and silica gel chromatography was performed with n-hexane-ethyl acetate (v:v = 3:17) as the eluent to obtain 4-aminobenzonitrile white solid with a yield of 87.75%.

[0061] Example 1

[0062] Polyimide 1 was prepared by the following process:

[0063] A. Synthesis of cyanogroup-containing diamine 1: 0.012 mol of 4-aminobenzonitrile obtained in Preparation Example 1 and 0.012 mol of 2,5-diamino-2,5-cyclohexadiene-1,4-dione (CAS No.: 1521-06-8) were dissolved in 20 mL of absolute ethanol, respectively, and the 2,5-diamino-2,5-cyclohexadiene-1,4-dione solution was slowly added to the 4-aminobenzonitrile solution under nitrogen protection, followed by addition of 0.025 mol of triethylamine, and the mixture was heated to 90°C and refluxed for 8 h. The solid was filtered, washed with acetone three times, and the residual organic solvent was removed by rotary evaporation, and the solid was dried at 60°C under vacuum for 48 h to obtain cyanogroup-containing diamine 1 solid, with a yield of 92.34%, and a molecular formula of C 20 H 14 N6, and a molecular structure as follows:

[0064]

[0065] A. Preparation of polyimide 1: 4.0 mmol of cyanogroup-containing diamine 1 was dissolved in 16 mL of absolute DMAc in a 50 mL three-necked flask with a mechanical stirrer, thermometer, and reflux condenser under N2 atmosphere, and dissolved at 0°C; 4.05 mmol of 4,4-biphenyl ether dianhydride was added portionwise, and the reaction mixture was stirred at 0°C under N2 atmosphere for 24 h to obtain a polyamic acid solution with a solid content of about 16 wt%;

[0066] B. 10 mL of DMAc was further added to the polyamic acid solution, and the mixture was frozen and defoamed, and then filtered with a nylon cloth to obtain a casting solution with a concentration of about 10 wt%; the casting solution was cast on a clean glass plate, and treated at 150°C, 240°C, and finally at 320°C for 8 h each time to obtain a polyimide 1 film; the polyimide 1 has the following repeating unit:

[0067]

[0068] Example 2

[0069] Polyimide 2 was prepared by the same steps as in Example 1, except that the 4-aminobenzonitrile used in Step A was obtained in Preparation Example 2, and the terminal diamino ketone used was 3,4-diamino-3-cyclobutene-1,2-dione (CAS No.: 5231-89-0); the obtained cyanogroup-containing diamine 2 has a molecular formula of C 18 H 16 N6, with a yield of 93.41%, and a molecular structure as follows:

[0070]

[0071] The dianhydride raw material used in Step B was pyromellitic dianhydride (CAS No.: 89-32-7), and the aprotic solvent used was DMSO. The polyimide 2 has the following repeating unit:

[0072]

[0073] Example 3

[0074] Polyimide 3 was synthesized using the same steps as in Example 1, except that the 4-aminobenzonitrile used in step A was obtained from Preparation Example 3, the terminal diamino ketone used was 1-(3,4-diaminophenyl)ethyl ketone (CAS No.: 21304-39-2), and the reflux temperature was 85°C; the resulting cyanodiamine 3 had the molecular formula C3. 11 H 14 N4, yield 91.2%, molecular structure is:

[0075]

[0076] The diacid anhydride used in step B is 2,3',4,4'-diphenyl ether tetracarboxylic dianhydride (CAS No.: 50662-95-8), and the aprotic solvent used is NMP. Polyimide 3 has the following repeating units:

[0077]

[0078] Examples 4-5

[0079] Unlike Example 1, in step C, DMAc was used to dilute the polyimide casting solution to a solid content of 6% and 15% respectively.

[0080] Comparative Example 1

[0081] A polyimide is provided, wherein the diamine raw material used is 2,5-diamino-2,5-cyclohexadiene-1,4-dione, and the diacid anhydride used and the preparation process are the same as in Example 1. Polyimide 4 has the following structure:

[0082]

[0083] Comparative Example 2

[0084] A polyimide is provided, wherein the diamine raw material used is 3,4-diamino-3-cyclobutene-1,2-dione, and the diacid anhydride used and the preparation process are the same as in Example 2. Polyimide 5 has the following structure:

[0085]

[0086] Comparative Example 3

[0087] A polyimide, wherein the diamine raw material used is 1,4-diaminobutanone, and the diacid anhydride used and the preparation process are the same as in Example 3. Polyimide 6 has the following structure:

[0088]

[0089] Thermal properties of the polyimide films from Examples 1-5 and Comparative Examples 1-3 were tested:

[0090] The thermal properties of polyimide samples were tested using a NETZSCH DMA 242E dynamic thermomechanical analyzer (Germany). The test temperature ranged from room temperature to 500℃, with a heating rate of 5℃ / min, under a nitrogen atmosphere. The peak temperature of the loss factor test curve was selected as the glass transition temperature (Tg) of the polyimide. g The decomposition temperature of polyimide was tested using a TAQ500 thermogravimetric analyzer. Nitrogen flow rate was 50 mL / min, heating rate was 20 °C / min, and the test range was from room temperature to 800 °C. The thermal performance test results are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] In the table, T g — Glass transition temperature; T 5％ —5% thermal weight loss temperature; T 10％ —10% thermal weight loss temperature; RW / 800℃—Carbon residue at 800℃.

[0095] Table 1 shows that the polyimides in Examples 1-5 exhibit superior thermal properties compared to the comparative examples: T g All exceeded 440℃, T 5％ The temperature range is 568–589℃, and the RW / 800℃ ratio exceeds 60%; while the comparative example T g The values ​​are all less than 400℃, T 5％ Below 500℃, the RW / 800℃ ratio is less than 50%. Data on improved polymer heat resistance and thermal stability indicate that the introduction of cyano groups and Schiff bases enhances the crosslinking network density of the polymer system; the char residue at 800℃ is significantly improved, attributed to the effects of the N flame-retardant element and unsaturated groups such as C=N, cyano groups, and benzene (olefin) rings. Furthermore, Comparative Example 2 exhibits the lowest thermal performance indicators because it has fewer unsaturated carbon rings.

[0096] The mechanical properties of the PI films of Examples 1-5 and Comparative Examples 1-3 were tested:

[0097] The tests were conducted using an Instron Model 5565 universal testing machine, and the samples were cut into standard specimens according to national standards. Tensile properties were tested according to GB / T 2567-2008, with a load of 100 N and a tensile speed of 5 mm / min. Bending properties were tested according to GB / T3356-1999, a standard for testing the bending properties of unidirectional fiber-reinforced plastics, with a sample size of 80 mm × 15 mm × 2 mm, a tensile rate of 2.0 mm / min, and at least five specimens were tested at room temperature. The average value was used to obtain the final specimen's bending strength and bending modulus. Shear properties were tested according to JCT 773-2010, a standard for fiber-reinforced plastics using the short beam method, with a sample size of 20 mm × 10 mm × 2 mm, a tensile rate of 1.0 mm / min, and at least five specimens were tested at room temperature. The average value was used to obtain the final specimen's shear strength. The modulus of each specimen was determined by linearly fitting the elastic portion of the stress-strain curve. The mechanical test data for the film are shown in Table 2.

[0098] Table 2

[0099]

[0100] As shown in Table 2, the mechanical performance of the examples is significantly stronger than that of the comparative examples. The C=N bonds generated by the Schiff base addition reaction are attached to the polyimide backbone, enhancing the toughness of the polymer skeleton, especially improving the bending and shear resistance of the polyimide material. The two strongly polar and electronegative cyano groups present in each repeating unit enhance the intermolecular interaction forces; the rigid cyano groups also increase the rotational energy barrier within the molecular chain, significantly restricting chain mobility and resulting in a marked increase in the mechanical strength of the PI material.

[0101] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all of them.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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

A method for preparing 1,4-aminobenzonitrile, characterized in that, Includes the following steps: (1) 1,2-Dibromoethylene and methyl sorbate were subjected to a Diels-Alder cycloaddition reaction to give methyl 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylate; (2) methyl 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylate was reacted with formamide at high temperature in the presence of sodium ethoxide to give 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide; (3) 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide was reacted with formamide at high temperature in the presence of sodium ethoxide. 5,6-Dibromo-4-methyl-2-cyclohexene-1-carboxamide undergoes a Hofmann rearrangement reaction in sodium hypobromide solution to give 5,6-dibromo-4-methyl-2-cyclohexene-1-amine; (4) 5,6-dibromo-4-methyl-2-cyclohexene-1-amine undergoes a Zaitsev elimination reaction upon heating in an alcoholic solution of alkali to give 4-methylaniline; (5) 4-methylaniline undergoes an ammoxidation reaction under palladium catalysis to give 4-aminobenzonitrile.

2. The method for preparing 4-aminobenzonitrile according to claim 1, characterized in that, Step (1) is specifically performed as follows: methyl sorbate and 1,2-dibromoethylene are dissolved in tetrahydrofuran and heated under reflux at 40-50°C for 4-10 hours; heating is stopped, reflux is completed, the filtrate is cooled, water is added for liquid extraction to remove tetrahydrofuran, the organic phase is taken and added to diethyl ether for further extraction, the extract is removed by rotary evaporation, dried with anhydrous magnesium sulfate, and vacuum dried to obtain methyl 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylate; the molar ratio of methyl sorbate to dibromoethylene is 1:(1.05-1.2); 1,2-dibromoethylene has a cis structure.

3. The method for preparing 4-aminobenzonitrile according to claim 1, characterized in that, The specific operation of step (2) is as follows: under a nitrogen atmosphere, methyl 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylate, formamide and sodium ethoxide are mixed in N,N-dimethylformamide solvent and stirred at a constant temperature of 90-100℃ for 2-5 hours; cooled to room temperature, extracted with chloroform, the extract is rotary evaporated, washed with brine, dried with anhydrous magnesium sulfate, and purified by silica gel column chromatography to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide; the molar ratio of methyl 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylate, formamide and sodium ethoxide is 2:(6-7):(1-2); the eluent used for column chromatography is n-hexane / ethyl acetate, v:v = 1:(3-5).

4. The method for preparing 4-aminobenzonitrile according to claim 1, characterized in that, The reaction conditions for step (3) are as follows: 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide, 35wt% to 50wt% cold NaOH aqueous solution and sodium hypobromide solution are mixed evenly and stirred at a constant temperature of -20℃ to 0℃ in an ice-salt bath for 30 to 60 min; the ice-salt bath is removed and allowed to return to room temperature, and then heated in a water bath to 40 to 50℃ and stirred at a constant temperature for 2 to 4 h; after cooling to room temperature, activated carbon is used for decolorization and filtration, the solid is precipitated with glacial acetic acid, filtered, washed with water, recrystallized and dried under vacuum to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-amine; the concentration of the sodium hypobromide solution is 5wt% to 20wt%, and it is freshly prepared by adding bromine to NaOH aqueous solution; the molar ratio of 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide, sodium hypobromide and NaOH is 1:(1 to 1.5):(6 to 7.5).

5. The method for preparing 4-aminobenzonitrile according to claim 1, characterized in that, Step (4) is as follows: 5,6-Dibromo-4-methyl-2-cyclohexene-1-amine is heated in a sodium hydroxide ethanol solution at 71-75°C and stirred for 10-20 minutes. After the reaction is completed, the solution is cooled slightly and dilute hydrochloric acid is added and stirred until the pH of the solution is ~6. The solution is washed with water and separated. The aqueous layer is taken and excess sodium hydroxide is added to neutralize the solution until the pH is ~8. The solution is distilled under reduced pressure. The distillate is cooled with petroleum ether to crystallize and filtered to obtain a solid crude product and a filtrate. Sodium chloride is added to the filtrate until saturated. The solution is extracted twice with chloroform. The crude product and the extract are combined, evaporated by rotary evaporation, dried with anhydrous magnesium sulfate, and dried under vacuum to obtain 4-methylaniline. The molar ratio of 5,6-dibromo-4-methyl-2-cyclohexene-1-amine to sodium hydroxide is 1:(2.01-2.2). The concentration of the dilute hydrochloric acid is 0.1-1 mol / L, and the concentration of sodium hydroxide used for neutralization is 1-3 mol / L.

6. The method for preparing 4-aminobenzonitrile according to claim 1, characterized in that, The ammonia oxidation conditions in step (5) are as follows: under a nitrogen atmosphere, 4-methylaniline, tert-butyl nitrite, palladium catalyst, and N-hydroxyphthalimide are mixed in acetonitrile solvent and stirred at 70-80℃ for 18-24h; after the solution is cooled, CH2Cl2 is added for dilution, decolorization, filtration, concentration, and column chromatography purification to obtain 4-aminobenzonitrile; the molar ratio of 4-methylaniline, tert-butyl nitrite, palladium catalyst, and N-hydroxyphthalimide is 1:(2-3):(0.05-0.1):(0.2-0.3); the palladium catalyst is selected from one of Pd(OAc)2, Pd(OTFA)2, Pd(dba)2, and Pd2(dba)3; the eluent used for column chromatography is n-hexane / ethyl acetate, v:v = (1-5):(19-15).

7. A polyimide obtained by polycondensation of a diacid anhydride and a cyanodiamine, characterized in that, The cyanodiamine is synthesized from 4-aminobenzonitrile prepared by any one of the preparation methods described in claims 1 to 6; the polyimide is prepared by the following steps: A. Under an anhydrous, nitrogen atmosphere, 4-aminobenzonitrile, terminal diamino ketone, and alkaline reagent are added to organic solvent 1, heated in an oil bath to 85-90°C, and refluxed for 6-10 hours until no water is produced; after completion, the mixture is cooled, filtered, washed with acetone 3-4 times, the filter cake is removed, recrystallized with anhydrous ethanol, filtered, and dried under vacuum to obtain the cyanodiamine; the terminal diamino ketone refers to a ketone compound with two primary amino groups at the end; the ketone-amine molar ratio of the terminal diamino ketone to 4-aminobenzonitrile is (1.01-1.2):1; the alkaline reagent A. The cyanodiamine is one of triethylamine, sodium carbonate, and potassium carbonate, and the amount used is 2.01 to 2.05 times the molar amount of 4-aminobenzonitrile; B. Under an anhydrous and nitrogen atmosphere, the cyanodiamine is dissolved in organic solvent 2, and the diacid anhydride is added in batches at -10 to 5°C; the reaction system is stirred at room temperature for 12 to 18 hours to obtain a homogeneous polyamic acid solution with a solid content of 15 to 30 wt%; the molar ratio of the cyanodiamine to the diacid anhydride is 1:(0.98 to 1.02); C. The polyamic acid solution is subjected to thermal imidization treatment to obtain polyimide, wherein the organic solvent 1 in step A is one or more of dimethyl sulfoxide, tetrahydrofuran, dichloromethane, and ethanol; the organic solvent 2 in step B is one or more of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

8. The polyimide as claimed in claim 7, characterized in that, The thermal imidization treatment is as follows: dilute polyamic acid with organic solvent 2, let it stand and freeze to defoam, filter with nylon cloth to obtain a casting solution with a concentration of 6wt% to 20wt%; cast the casting solution on a clean glass plate and treat it at 120℃ to 180℃ and 240℃ to 280℃ for 4 to 8 hours respectively, and finally keep it at 300℃ to 320℃ for 1 hour.

9. The polyimide according to claim 7, characterized in that, The diacid anhydride is selected from compounds containing two diacid anhydride groups within a molecule, specifically selected from one or more of the following: pyromellitic dianhydride, 4,4-biphenyl ether dianhydride, 4,4'-(hexafluoroisopropene)phthalic anhydride, bisphenol A type diether dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-oxophthalic anhydride, 3,3',4,4'-triphenyl diether tetracarboxylic dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, and 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride.

Images