Preparation method of 4-aminobenzonitrile and polyimide of 4-aminobenzonitrile

Abstract

The invention provides a preparation method of 4-aminobenzonitrile and polyimide thereof, and is characterized in that the preparation method of 4-aminobenzonitrile comprises the following steps: 1, 2-dibromoethylene and methyl sorbate are subjected to a Diels-Alder cycloaddition reaction to form a ring; then sequentially carrying out amidation reaction and Hofmann rearrangement reaction to introduce amino groups; and carrying out Zaitsev elimination reaction to obtain a benzene ring, and carrying out ammoxidation reaction to introduce cyano groups to obtain 4-cyanophenyl. The preparation method of 4-aminobenzonitrile provided by the invention does not involve toxic cyanation reagents such as toxic sodium cyanide and potassium cyanide, and the reagents are environment-friendly; and the synthesis step conditions are mild, the yield is high, and no harsh equipment requirement exists. Polyimide containing two Schiff base bonds and dicyano groups at the same time is prepared through condensation of cyano-containing diamine synthesized on the basis of 4-aminobenzonitrile and dianhydride, and the polyimide has excellent rigidity, elasticity and heat resistance.

Description

Technical Field

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

[0002] 4-Aminobenzonitrile is a commonly used chemical raw material, widely used as a raw material and intermediate for medicines, agricultural chemicals, dyes and fine chemicals. Currently, most of the traditional synthetic routes of nitrile compounds involve the use of highly toxic cyanation reagents such as NaCN and KCN; or cyanation reagents such as CuCN, Zn(CN)2, K4[Fe(CN)6] to produce CN - , resulting in catalyst poisoning and incomplete raw material conversion; in addition, some methods have the disadvantages of harsh reaction conditions, low yield, poor functional group compatibility, residual chemical solvents, high cost and equipment requirements, and poor catalyst stability and activity. The industry is in urgent need of methods for efficiently synthesizing benzonitrile under mild conditions. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a preparation method of 4-aminobenzonitrile and its polyimide.

[0004] The present invention provides a method for preparing 4-aminobenzonitrile, comprising the following steps:

[0005] (1) 1,2-dibromoethylene and methyl sorbate are used as raw materials to undergo a Diels-Alder cycloaddition reaction to obtain methyl 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylate;

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

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

[0008] (4) 5,6-dibromo-4-methyl-2-cyclohexene-1-amine is heated in an alkali alcohol solution to undergo a Zaitsev elimination reaction to give 4-methylaniline;

[0009] (5) 4-Methylaniline undergoes ammoxidation reaction under palladium catalysis to obtain 4-aminobenzonitrile.

[0010] Furthermore, the specific operation of step (1) is as follows: methyl sorbate and 1,2-dibromoethylene are dissolved in tetrahydrofuran, and heated to reflux at 40-50° C. for 4-10 hours; heating is stopped, reflux ends, the filtrate is cooled, water is added, and tetrahydrofuran is removed by liquid extraction, ether is added to the organic phase for further extraction, the extract phase is taken by rotary evaporation to remove ether, dried over anhydrous magnesium sulfate, and vacuum dried to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester;

[0011] The molar ratio of methyl sorbate to vinyl dibromide is 1:(1.01-1.2), and 1,2-vinyl dibromide is a cis structure.

[0012] Furthermore, the specific operation of step (2) is: under a nitrogen atmosphere, 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester, formamide and sodium ethoxide are mixed in N,N-dimethylformamide solvent, and stirred at a constant temperature of 90-100° C. for 2-5 hours; cooled to room temperature, extracted with chloroform, and the extract was rotary evaporated, washed with brine, dried over anhydrous magnesium sulfate, and purified by silica gel column chromatography to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide;

[0013] The molar ratio of 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester, 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).

[0014] Furthermore, the reaction conditions of step (3) are as follows: 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide, 35 wt% to 50 wt% cold NaOH aqueous solution and sodium hypobromite solution are mixed uniformly and stirred at a constant temperature of -20°C to 0°C in an ice salt bath for 30 to 60 minutes; the ice salt bath is removed and the temperature is restored to room temperature, and a water bath is heated to 40 to 50°C and stirred at a constant temperature for 2 to 4 hours; after cooling to room temperature, the mixture is decolorized with activated carbon, filtered, and the solid is precipitated with glacial acetic acid, filtered, washed with water, recrystallized, and dried in vacuo to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-amine;

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

[0016] Furthermore, the specific operation of step (4) is as follows: 5,6-dibromo-4-methyl-2-cyclohexene-1-amine is stirred in a sodium hydroxide ethanol solution under heating in a water bath at 71-75° C. for 10-20 min; after the reaction is completed, the solution is slightly cooled, diluted hydrochloric acid is added, and stirred until the solution pH is about 6, the separated liquid is washed with water, and the water layer is neutralized by adding excess sodium hydroxide to the solution pH about 8; vacuum distillation is performed, petroleum ether is added to the distillate to cool and crystallize, and suction filtration is performed to obtain a solid crude product and a filtrate; sodium chloride is added to the filtrate to saturation, and the filtrate is extracted twice with chloroform, the crude product and the chloroform extract are combined, rotary evaporation, drying over anhydrous magnesium sulfate, and vacuum drying are performed to obtain 4-methylaniline;

[0017] The molar ratio of the 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 the sodium hydroxide used for neutralization is 1-3 mol / L.

[0018] Furthermore, the ammoxidation conditions in step (5) are as follows: 4-methylaniline is mixed with tert-butyl nitrite, a palladium catalyst, and N-hydroxyphthalimide (NHPI) in an acetonitrile solvent under a nitrogen atmosphere, and stirred at 70 to 80° C. for 18 to 24 hours; after the solution is cooled, CH2Cl2 is added to dilute it, decolorize, filter, concentrate, and purify by silica gel column chromatography to obtain 4-aminobenzonitrile;

[0019] 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).

[0020] Another aspect of the present invention provides a polyimide obtained by polycondensation of a dibasic acid anhydride and a cyano group-containing diamine; the cyano group-containing diamine is synthesized using 4-aminobenzonitrile prepared by the above-mentioned preparation method as a raw material; the preparation steps of the polyimide include:

[0021] A. In an anhydrous, nitrogen atmosphere, 4-aminobenzonitrile, an alkali reagent and a terminal diamino ketone are added to an organic solvent 1, heated in an oil bath to 85-90°C, and refluxed for 6-10 hours until no water is produced; after the reaction, the mixture is cooled, filtered, rinsed with acetone 3-4 times, and the filter cake is taken out, recrystallized with anhydrous ethanol, filtered, and vacuum dried to obtain a cyano diamine;

[0022] The terminal diamino ketone refers to a ketone compound terminated with two primary amino groups; the molar ratio of the terminal diamino ketone to 4-aminobenzonitrile is (1.01-1.2):1; the alkaline 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-aminobenzonitrile;

[0023] B. In anhydrous nitrogen atmosphere, dissolve the cyano diamine in organic solvent 2, and add the dibasic acid anhydride in batches at -10 to 5°C; stir the reaction system at room temperature for 12 to 18 hours to obtain a homogeneous polyamic acid solution with a solid content of 15 to 30 wt%;

[0024] The molar ratio of the cyano group-containing diamine to the dibasic acid anhydride is 1:(0.98-1.02);

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

[0026] Furthermore, the thermal imidization treatment is as follows: diluting the polyamic acid with an organic solvent 2, standing and freezing to defoam, filtering with nylon cloth to obtain a casting liquid with a concentration of 6wt% to 20wt%; casting the casting liquid on a clean glass plate, treating at 120°C to 180°C and 240°C to 280°C for 4 to 8h, respectively, and finally keeping warm at 300°C to 320°C for 1h.

[0027] Further, the dibasic acid anhydride is selected from a compound containing two dibasic acid anhydride groups in one molecule, specifically selected from one or more of pyromellitic anhydride, 4,4-biphenyl ether anhydride, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, bisphenol A type diether anhydride, 1,2,4,5-cyclohexanetetracarboxylic anhydride, 2,3,3',4'-biphenyltetracarboxylic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 3,3',4,4'-benzophenonetetracarboxylic anhydride, 4,4'-oxyphthalic anhydride, 3,3',4,4'-triphenylbis(ether) tetracarboxylic anhydride, 2,3,3',4'-diphenyl ether tetracarboxylic anhydride, 3,3',4,4'-diphenyl sulfonetetracarboxylic anhydride and derivatives thereof.

[0028] Furthermore, 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 comprises one or more of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0029] Various numerical ranges may be disclosed herein. When applicants disclose or claim any type of range, applicants intend to disclose or claim individually every possible number that the range can reasonably encompass, including the endpoints of the range and any subranges and combinations of subranges encompassed therein, unless otherwise indicated.

[0030] All numerical endpoints of the ranges disclosed herein are approximate. As a representative example, the applicant discloses in some embodiments that the temperature is "40°C to 50°C". This range should be interpreted as covering 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 in the range of 40°C to 50°C, including any ranges and sub-ranges between these values.

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

[0032] Compared with the prior art, the present invention has the following beneficial effects:

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

[0034] The polyimide provided by the present invention contains Schiff base bonds, which can give the material elasticity and self-repairing ability as well as durable heat resistance; by introducing cyano groups into the polyimide main chain, the intermolecular interaction force is increased, and the rigidity and heat resistance of the polymer skeleton are further improved, which is conducive to further making a terminal material with strong thermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0036] Figure 1 The invention provides a synthetic route for 4-aminobenzonitrile.

[0037] Figure 2 This is the H NMR spectrum of 4-aminobenzonitrile obtained in Preparation Example 1. DETAILED DESCRIPTION

[0038] The technical scheme of the present invention is further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. This embodiment is implemented under the premise of the technical scheme of the invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments. The contents not described in detail in the specification of the present invention belong to the known technology of professionals and technicians in this field. Unless otherwise defined, the experimental materials used in the following embodiments and comparative examples can be purchased by conventional biochemical reagent companies.

[0039] Preparation Example 1

[0040] according to Figure 1 The preparation method shown is used to prepare 4-aminobenzonitrile:

[0041] (1) In a 250 mL round-bottom flask equipped with a reflux condenser and a magnetic stirrer, 0.2 mol of methyl sorbate and 40 mL of tetrahydrofuran were added in sequence and mixed, and 0.22 mol of cis-1,2-dibromoethylene was added using a dropping funnel and stirred evenly. The mixture was heated to reflux at 50°C for 6 h; the heating was stopped, the reflux ended, the filtrate was cooled, water was added to separate and extract to remove tetrahydrofuran, ether was added to the organic phase to continue extraction, the extract phase was rotary evaporated to remove ether, dried over anhydrous magnesium sulfate, and vacuum dried at 60°C to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester, with a yield of 85.73%.

[0042] (2) In a nitrogen atmosphere, 80 mmol of 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester, 0.268 mol of formamide and 60 mmol of sodium ethoxide were added in sequence to 50 mL of N,N-dimethylformamide, and the mixture was heated to 100° C. and stirred at the constant temperature for 2 h; the mixture was cooled to room temperature, extracted with chloroform, and the extract was rotary evaporated, washed with brine, and dried over anhydrous magnesium sulfate. The extract was 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-cyclohexene-1-carboxamide in a yield of 95.70%.

[0043] (3) In an ice-salt bath, 75 mmol of bromine was added dropwise to a 250 mL round-bottom flask containing 100 mL of a 12.5 wt% NaOH aqueous solution using a dropping funnel and stirring to prepare a fresh sodium hypobromite solution; while maintaining an ice-salt bath and stirring state, 50 mmol of 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide and 0.34 mol of NaOH were prepared into a 50 wt% cold NaOH aqueous solution, which was added to the freshly prepared sodium hypobromite solution in sequence and mixed, and the mixture was stirred at -10°C for 50 min; the ice-salt bath was removed, and after the liquid temperature returned to room temperature, it was heated to 40°C in a water bath and stirred at a constant temperature for 3 h; after cooling to room temperature, activated carbon was added for decolorization, and the mixture was filtered, and the filtrate was taken and glacial acetic acid was used to precipitate a solid; suction filtration was performed, the solid was washed with water, recrystallized, and vacuum dried at 60°C to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-amine with a yield of 67.26%.

[0044] (4) Weigh 32.5mmol sodium hydroxide into a 50mL round-bottom flask, add 20mL anhydrous ethanol and shake to dissolve, then add 15mmol 5,6-dibromo-4-methyl-2-cyclohexene-1-amine. The reaction mixture is stirred in a 75℃ water bath for 15min. After the reaction is completed, the solution is slightly cooled and 1mol / L dilute hydrochloric acid is added to the solution until the pH value of the solution is ~6. Water is added for separation and extraction. The aqueous layer is neutralized by adding 2mol / L sodium hydroxide to the solution until the pH value of the solution is ~8; vacuum distillation is performed, petroleum ether is added to the collected concentrated solution, the temperature is lowered to 5℃ for crystallization, and suction filtration is performed to obtain a solid crude product and a filtrate; sodium chloride is added to the filtrate until saturated, and chloroform is used for extraction twice. The crude product and the extract are combined, rotary evaporated, dried over anhydrous magnesium sulfate, and vacuum dried at 60℃ to obtain 4-methylaniline crystals with a yield of 95%.

[0045] (5) Under nitrogen atmosphere, 25 mmol of 4-methylaniline, 50 mmol of tert-butyl nitrite, 1.25 mmol of Pd(OAc)2, and 7.5 mmol of N-hydroxyphthalimide were mixed uniformly in 25 mL of acetonitrile solvent, and the mixture was stirred at 70° C. for 24 h. After the solution was cooled, 100 mL of CH2Cl2 was added for dilution, activated carbon was added for decolorization, the mixture was filtered, and the mixture was concentrated. The mixture was purified by silica gel column chromatography using n-hexane-ethyl acetate (v:v=1:8) as the eluent to obtain 4-aminobenzonitrile as a white solid in a yield of 86.22%.

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

[0047] Preparation Example 2

[0048] The synthesis of 4-aminobenzonitrile was carried out as follows:

[0049] (1) In a 100 mL round-bottom flask equipped with a reflux condenser and a magnetic stirrer, 0.10 mol of methyl sorbate and 40 mL of tetrahydrofuran were added in sequence and mixed, and 0.12 mol of cis-1,2-dibromoethylene was added through a dropping funnel, and the mixture was heated to reflux at 50° C. for 5 h; the heating was stopped and the reflux ended, and water was added to the solution to cool and extract the tetrahydrofuran, and ether was added to the organic phase to continue extraction, and the extract phase was rotary evaporated to remove the ether, dried over anhydrous magnesium sulfate, and dried under vacuum at 60° C. to obtain 5,6-dichloro-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester, with a yield of 87.24%.

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

[0051] (3) In an ice-salt bath, 67.5 mmol of bromine was added dropwise to 80 mL of 18 wt% NaOH aqueous solution in a 250 mL round-bottom flask using a dropping funnel and stirred to prepare a fresh sodium hypobromite solution; while maintaining the ice-salt bath and stirring state, 45 mmol of 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide and 0.306 mol of NaOH were prepared into a 50 wt% cold NaOH aqueous solution, and the solution was added to the freshly prepared sodium hypobromite solution in sequence and mixed, and the mixture was stirred at -10°C for 50 min; the ice-salt bath was removed, and after the liquid temperature returned to room temperature, the solution was heated in a water bath to 40°C and stirred at a constant temperature for 2 h; after cooling to room temperature, activated carbon was added for decolorization, and the solution was filtered, and the filtrate was taken and precipitated with glacial acetic acid to obtain a solid; the solid was filtered, washed with water, recrystallized, and dried in a vacuum at 60°C to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-amine with a yield of 69.34%.

[0052] (4) Weigh 25 mmol of sodium hydroxide into a 50 mL round-bottom flask, add 15 mL of anhydrous ethanol and shake to dissolve, then add 12 mmol of 5,6-dibromo-4-methyl-2-cyclohexene-1-amine. The reaction mixture is stirred in a 73°C water bath for 10 min. After the reaction is completed, the solution is slightly cooled and 1 mol / L of dilute hydrochloric acid is added to the solution until the pH value of the solution is about 6. Water is added to separate the solution, and 2 mol / L of sodium hydroxide is added to the water layer to neutralize the solution until the pH value of the solution is about 8; vacuum distillation is performed, petroleum ether is added to the collected concentrated solution, the temperature is lowered to 5°C for crystallization, and suction filtration is performed to obtain a solid crude product and a filtrate; sodium chloride is added to the filtrate until saturated, and it is extracted twice with chloroform. The crude product and the extract are combined, rotary evaporated, dried over anhydrous magnesium sulfate, and vacuum dried at 60°C to obtain 4-methylaniline crystals with a yield of 92.8%.

[0053] (5) Under nitrogen atmosphere, 20 mmol of 4-methylaniline, 45 mmol of tert-butyl nitrite, 1.3 mmol of Pd(OTFA)2, and 6 mmol of N-hydroxyphthalimide were mixed uniformly in 20 mL of acetonitrile solvent, and the mixture was stirred at 75° C. for 20 h. After the solution was cooled, 20 mL of CH2Cl2 was added for dilution, activated carbon was added for decolorization, the solution was filtered, and the solution was concentrated. The solution 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] The synthesis of 4-aminobenzonitrile was carried out as follows:

[0056] (1) In a 250 mL round-bottom flask equipped with a reflux condenser and a magnetic stirrer, 0.25 mol of methyl sorbate and 40 mL of tetrahydrofuran were added in sequence and mixed, 0.27 mol of cis-1,2-dibromoethylene was added to the dropping funnel and mixed evenly, and then heated to reflux at 50° C. for 8 h; the heating was stopped and the reflux ended, and the filtrate was cooled, water was added to separate and extracted, and ether was added to the organic phase to continue extraction, and the extract phase was rotary evaporated to remove ether, dried over anhydrous magnesium sulfate, and dried in a vacuum at 60° C. to obtain 5,6-dichloro-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester, with a yield of 82.11%.

[0057] (2) Under nitrogen atmosphere, 75 mmol of 5,6-dichloro-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester, 0.24 mol of formamide and 56 mmol of sodium ethoxide were added in sequence to 45 mL of N,N-dimethylformamide. After mixing evenly, the reaction system was heated to 100° C. and stirred at the constant temperature for 2 h. After cooling to room temperature, the mixture was extracted with chloroform, the extract was rotary evaporated, washed with brine, and dried over anhydrous magnesium sulfate. Finally, the extract 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-cyclohexene-1-carboxamide in a yield of 93.23%.

[0058] (3) In an ice-salt bath, 64 mmol of bromine was added dropwise to a 250 mL round-bottom flask containing 70 mL of a 15 wt% NaOH aqueous solution using a dropping funnel and stirring to prepare a fresh sodium hypobromite solution; while maintaining an ice-salt bath and stirring, 60 mmol of 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide and 0.408 mol of NaOH were prepared into a 50 wt% cold NaOH aqueous solution, which was added to the freshly prepared sodium hypobromite solution in sequence and mixed, 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, it was heated in a water bath to 40°C and stirred at a constant temperature for 4 h; after cooling to room temperature, activated carbon was added for decolorization, filtration was performed, and the filtrate was taken and glacial acetic acid was used to precipitate a solid; suction filtration was performed, the solid was washed with water, recrystallized, and vacuum dried at 60°C to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-amine with a yield of 69.34%.

[0059] (4) Weigh 34 mmol of sodium hydroxide into a 50 mL round-bottom flask, add 25 mL of anhydrous ethanol and shake to dissolve, then add 18 mmol of 5,6-dibromo-4-methyl-2-cyclohexene-1-amine. The reaction mixture is stirred in a 75°C water bath for 20 min. After the reaction is completed, the solution is slightly cooled and 1 mol / L of dilute hydrochloric acid is added to the solution until the pH value of the solution is about 6. Water is added to separate the solution, and 2 mol / L of sodium hydroxide is added to the water layer to neutralize the solution until the pH value of the solution is about 8; vacuum distillation is performed, petroleum ether is added to the collected concentrated solution, the temperature is lowered to 5°C for crystallization, and suction filtration is performed to obtain a solid crude product and a filtrate; sodium chloride is added to the filtrate until saturated, and it is extracted twice with chloroform. The crude product and the extract are 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 nitrogen atmosphere, 24 mmol of 4-methylaniline, 54 mmol of tert-butyl nitrite, 1.64 mmol of Pd(OTFA)2, and 7.0 mmol of N-hydroxyphthalimide were mixed in 30 mL of acetonitrile solvent and stirred at 78°C for 22 h. After the solution was cooled, 30 mL of CH2Cl2 was added for dilution, activated carbon was added for decolorization, the solution was filtered, and concentrated. The solution was purified by silica gel chromatography using n-hexane-ethyl acetate (v:v=3:17) as the eluent to obtain 4-aminobenzonitrile as a white solid with a yield of 87.75%.

[0061] Example 1

[0062] Polyimide 1, the preparation process of which includes:

[0063] A. Synthesis of cyano 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 anhydrous ethanol, and the 2,5-diamino-2,5-cyclohexadiene-1,4-dione solution was slowly added to the 4-aminobenzonitrile solution under nitrogen protection, and then 0.025 mol of triethylamine was added, and the temperature was raised to 90° C. and refluxed for 8 h; filtered, the solid was washed with acetone three times, and the residual organic solvent was removed by rotary evaporation. The solid was vacuum dried at 60° C. for 48 h to obtain a cyano diamine 1 solid with a yield of 92.34%. The molecular formula is C 20 H 14 N6, molecular structure is as follows:

[0064]

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

[0066] B. 10 mL of DMAc was added to the polyamic acid solution, and the solution was allowed to stand for freezing and defoaming, and filtered through nylon cloth to obtain a casting solution of about 10 wt %. The casting solution was cast on a clean glass plate, and treated at 150° C. and 240° C. for 8 h, respectively, and finally kept at 320° C. for 1 h to obtain a polyimide 1 film. The polyimide 1 has the following repeating units:

[0067]

[0068] Example 2

[0069] The synthesis steps of polyimide 2 are the same as those of Example 1, except that: the 4-aminobenzonitrile used in step A is obtained from Preparation Example 2, the terminal diaminoketone used is 3,4-diamino-3-cyclobutene-1,2-dione (CAS No.: 5231-89-0); the molecular formula of the obtained cyano-containing diamine 2 is C 18 H 16 N6, the yield is 93.41%, the molecular structure is as follows:

[0070]

[0071] The dibasic anhydride raw material used in step B is pyromellitic anhydride (CAS No.: 89-32-7), and the aprotic solvent used is DMSO. Polyimide 2 has the following repeating units:

[0072]

[0073] Example 3

[0074] The synthesis steps of polyimide 3 are the same as those of Example 1, except that: the 4-aminobenzonitrile used in step A is obtained from Preparation Example 3, the terminal diaminoketone raw material used is 1-(3,4-diaminophenyl)ethanone (CAS No.: 21304-39-2), and the reflux temperature is 85°C; the molecular formula of the obtained cyano diamine 3 is C 11 H 14 N4, yield 91.2%, molecular structure:

[0075]

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

[0077]

[0078] Embodiment 4-5

[0079] The difference from Example 1 is that in step C, DMAc is used to dilute the polyimide casting solution to 6% and 15% solid content respectively.

[0080] Comparative Example 1

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

[0082]

[0083] Comparative Example 2

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

[0085]

[0086] Comparative Example 3

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

[0088]

[0089] Thermal performance tests were performed on the polyimide films of Examples 1 to 5 and Comparative Examples 1 to 3:

[0090] The thermal properties and tests of polyimide samples were carried out using a German NETZSCH DMA 242E dynamic thermal mechanical analyzer. The test temperature was from room temperature to 500°C, the heating rate was 5°C / min, and the test was carried out in a nitrogen atmosphere. The peak temperature of the loss factor test curve was selected as the glass transition temperature (T g ). The decomposition temperature of polyimide was tested on a TAQ500 thermogravimetric analyzer. The nitrogen flow rate was 50 mL / min, the 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 rate at 800℃.

[0095] From Table 1, the polyimides of Examples 1 to 5 exhibit better thermal properties than the comparative example: T g All exceeded 440℃, T 5％ The range is 568~589℃, and RW / 800℃ is more than 60%; while the comparative example T g The values ​​are all less than 400℃, T 5％ The heat resistance and thermal stability of the polymer are improved by less than 500℃, and RW / 800℃ is less than 50%. The data on the improvement of the heat resistance and thermal stability of the polymer show that the introduction of cyano group and Schiff base can enhance the cross-linking network density of the polymer system; the residual carbon rate at 800℃ is significantly improved, which is attributed to the effect of N flame retardant elements and unsaturated groups such as C=N, cyano group and benzene (ene) ring. In addition, the thermal performance index of comparative example 2 is the lowest because it has fewer unsaturated carbon rings.

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

[0097] The test was conducted using an Instron Model 5565 universal testing machine and cut into standard specimens according to the national standard. The tensile properties were based on GB / T 2567-2008, with a load of 100N and a tensile speed of 5mm / min; the bending properties were based on the national standard GB / T3356-1999 unidirectional fiber reinforced plastic bending properties test method, with a test sample size of 80mm×15mm×2mm, a tensile rate of 2.0mm / min, and 5 or more specimens tested at room temperature, and the average value was used to obtain the bending strength and bending modulus of the final specimen; the shear properties were based on the national standard JCT 773-2010 fiber reinforced plastic short beam method, with a test sample size of 20mm×10mm×2mm, a tensile rate of 1.0mm / min, and 5 or more specimens tested at room temperature, and the average value was used to obtain the shear strength of the final specimen. The modulus of each specimen was determined by linearly fitting the elastic part of the stress-strain curve. The mechanical test data of the film are shown in Table 2.

[0098] Table 2

[0099]

[0100] From Table 2, the mechanical performance of the embodiment is significantly stronger than that of the comparative example. The C=N bond generated by the Schiff base addition reaction is connected to the polyimide main chain, which enhances the toughness of the polymer skeleton, especially improves the bending and shear resistance of the polyimide material. The two highly polar and electronegative cyano groups in each repeating unit enhance the intermolecular interaction force; the rigid cyano group also increases the energy barrier for rotation within the molecular chain, greatly restricts the chain mobility, and significantly enhances 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 with reference to the aforementioned embodiments, and obtained relatively ideal results.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. The preparation method of 4-aminobenzonitrile is characterized in that: The following steps are involved: (1) 1,2-dibromoethylene and methyl sorbate are used as raw materials to undergo a Diels-Alder cycloaddition reaction to obtain methyl 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylate; (2) 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester reacts with formamide at high temperature in the presence of sodium ethoxide to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide; (3) 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide undergoes Hofmann rearrangement reaction in a caustic soda solution of sodium hypobromite to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-amine; (4) 5,6-dibromo-4-methyl-2-cyclohexene-1-amine is heated in an alkali alcohol solution to undergo a Zaitsev elimination reaction to give 4-methylaniline; (5) 4-Methylaniline undergoes ammoxidation reaction under palladium catalysis to obtain 4-aminobenzonitrile.

2. The method for preparing 4-aminobenzonitrile according to claim 1, wherein The specific operation of step (1) is as follows: methyl sorbate and 1,2-dibromoethylene are dissolved in tetrahydrofuran, and heated to reflux at 40-50° C. for 4-10 hours; the heating is stopped, the reflux ends, the filtrate is cooled, water is added, and the tetrahydrofuran is removed by split extraction, and ether is added to the organic phase for further extraction, the extract phase is rotary evaporated to remove ether, dried over anhydrous magnesium sulfate, and vacuum dried to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester; The molar ratio of methyl sorbate to vinyl dibromide is 1:(1.05-1.2); 1,2-vinyl dibromide is a cis structure.

3. The method for preparing 4-aminobenzonitrile according to claim 1, wherein The specific operation of step (2) is as follows: under a nitrogen atmosphere, 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester, formamide and sodium ethoxide are mixed in N,N-dimethylformamide solvent, and stirred at a constant temperature of 90-100° C. for 2-5 hours; cooled to room temperature, extracted with chloroform, and the extract was rotary evaporated, washed with brine, dried over 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 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxylic acid methyl ester, 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, wherein The reaction conditions of step (3) are as follows: 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide, 35 wt% to 50 wt% cold NaOH aqueous solution and sodium hypobromite solution are uniformly mixed and then stirred at a constant temperature of -20°C to 0°C in an ice salt bath for 30 to 60 minutes; the ice salt bath is removed and the temperature is restored to room temperature, and then heated in a water bath to 40 to 50°C and stirred at a constant temperature for 2 to 4 hours; after cooling to room temperature, activated carbon is used for decolorization, filtration is performed, and solids are precipitated with glacial acetic acid, suction filtered, washed with water, recrystallized, and vacuum dried to obtain 5,6-dibromo-4-methyl-2-cyclohexene-1-amine; The sodium hypobromite solution has a concentration of 5wt% to 20wt% and is freshly prepared by adding bromine to a NaOH aqueous solution; the molar ratio of 5,6-dibromo-4-methyl-2-cyclohexene-1-carboxamide, sodium hypobromite and NaOH is 1:(1-1.5):(6-7.5).

5. The method for preparing 4-aminobenzonitrile according to claim 1, wherein The specific operation of step (4) is as follows: 5,6-dibromo-4-methyl-2-cyclohexene-1-amine is stirred in a sodium hydroxide ethanol solution under heating in a water bath at 71-75° C. for 10-20 min; after the reaction is completed, the solution is slightly cooled, diluted hydrochloric acid is added, and stirred until the solution pH is about 6, the separated liquid is washed with water, and the water layer is neutralized by adding excess sodium hydroxide to the solution pH about 8; distillation under reduced pressure, petroleum ether is added to the distillate to cool and crystallize, and suction filtration is performed to obtain a solid crude product and a filtrate; sodium chloride is added to the filtrate until saturated, and the filtrate is extracted twice with chloroform, the crude product and the extract are combined, rotary evaporation, drying over anhydrous magnesium sulfate, and vacuum drying to obtain 4-methylaniline; The molar ratio of the 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 the sodium hydroxide used for neutralization is 1-3 mol / L.

6. The method for preparing 4-aminobenzonitrile according to claim 1, wherein The ammoxidation conditions in step (5) are as follows: 4-methylaniline, tert-butyl nitrite, palladium catalyst, and N-hydroxyphthalimide are mixed in an acetonitrile solvent under a nitrogen atmosphere, and stirred at 70 to 80° C. for 18 to 24 hours; after the solution is cooled, CH2Cl2 is added to dilute, decolorize, filter, concentrate, and purify by column chromatography 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 dibasic acid anhydride and a cyano group-containing diamine, characterized in that: The cyano group-containing diamine is synthesized by using 4-aminobenzonitrile prepared by the preparation method according to any one of claims 1 to 6 as a raw material; the preparation steps of the polyimide include: A. In an anhydrous, nitrogen atmosphere, 4-aminobenzonitrile, terminal diaminoketone and alkaline reagent are added to organic solvent 1, heated to 85-90°C in an oil bath, and refluxed for 6-10 hours until no water is produced; after the reaction, cool and filter, rinse with acetone 3-4 times, take out the filter cake, recrystallize with anhydrous ethanol, filter, and vacuum dry to obtain cyano diamine; The terminal diamino ketone refers to a ketone compound terminated with two primary amino groups; the molar ratio of the terminal diamino ketone to 4-aminobenzonitrile is (1.01-1.2):1; the alkaline 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-aminobenzonitrile; B. In anhydrous nitrogen atmosphere, dissolve the cyano diamine in organic solvent 2, and add the dibasic acid anhydride in batches at -10 to 5°C; stir the reaction system 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 cyano group-containing diamine to the dibasic acid anhydride is 1:(0.98-1.02); C. The polyamic acid solution is subjected to thermal imidization treatment to obtain polyimide.

8. The polyimide according to claim 7, characterized in that The thermal imidization treatment is as follows: diluting polyamic acid with an organic solvent 2, standing and freezing to defoam, filtering with nylon cloth to obtain a casting solution with a concentration of 6wt% to 20wt%; casting the casting solution on a clean glass plate, treating at 120°C to 180°C and 240°C to 280°C for 4 to 8h, respectively, and finally keeping warm at 300°C to 320°C for 1h.

9. The polyimide according to claim 7, characterized in that The dibasic acid anhydride is selected from a compound containing two dibasic acid anhydride groups in one molecule, specifically selected from one or more of pyromellitic anhydride, 4,4-biphenyl ether anhydride, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, bisphenol A type diether anhydride, 1,2,4,5-cyclohexanetetracarboxylic anhydride, 2,3,3',4'-biphenyltetracarboxylic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 3,3',4,4'-benzophenonetetracarboxylic anhydride, 4,4'-oxyphthalic anhydride, 3,3',4,4'-triphenyl bisether tetracarboxylic anhydride, 2,3,3',4'-diphenyl ether tetracarboxylic anhydride, 3,3',4,4'-diphenyl sulfone tetracarboxylic anhydride and derivatives thereof.

10. The polyimide according to claim 7, 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 comprises one or more of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

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