CN108299457B - A kind of preparation method of the tetracarboxylic dianhydride of bicyclic structure - Google Patents

Abstract

The invention discloses a preparation method of tetracarboxylic dianhydride with a bicyclic structure, belonging to the field of fine chemical preparation methods. The main technical scheme is that phthalic acid is used as an initial raw material, and the bicyclo-tetracarboxylic dianhydride with a full-exterior structure is synthesized through five-step reactions of electrolytic reduction, 1, 4-addition, methyl esterification reaction, hydrogenation reduction, ester exchange dehydration ring closure and the like. Compared with the traditional preparation process, the method has the advantages of few operation steps, mild reaction conditions, high yield and the like, and is suitable for large-scale industrial production.

Description

A kind of preparation method of the tetracarboxylic dianhydride of bicyclic structure

technical field

The invention belongs to the field of preparation methods of fine chemicals, in particular to a preparation method of bicyclic tetracarboxylic dianhydride.

Background technique

Since Du Pont applied for the world's first patent on polyimide (PI) in the 1950s, this type of material has been known for its excellent heat resistance, insulation and dielectric properties, mechanical and mechanical properties, resistance to Chemical properties and other advantages have been widely used. The early polyimides were mainly synthesized from aromatic dianhydrides and aromatic diamine monomers. Such aromatic PIs are easily affected by the π electron cloud and easily form charge transfer complexes between electron donors and acceptors ( CTC), resulting in darker color and poor light transmission performance of PI materials. At the same time, due to the influence of large π bonds, such PI materials are insoluble and infusible, with high molding temperature and difficulty in recycling. It is difficult to meet high-performance PI materials in specific fields For this reason, the synthesis of alicyclic and semi-alicyclic PI materials through the synthesis of alicyclic dianhydrides has received extensive attention.

In the original study, as reported by T M and T Kurosaki in "Macromolecules" 1997, 30(4): 993-1000, mainly bicyclo[2.2.2]oct-7-ene-2,3,5,6- Tetracarboxylic dianhydride, an unsaturated dianhydride containing carbon-carbon double bonds, is a PI material prepared by reacting this dianhydride monomer with different diamines. It is found that the thermal stability of the PI material is poor, such as in a nitrogen atmosphere. At temperatures above 360°C, thermal decomposition occurs. It is further proved that this unsaturated dianhydride monomer is prone to 1,4-addition reverse reaction at high temperature (greater than 350°C), see reaction formula 1.

In order to improve the thermal stability of PI materials, an attempt has been made to hydrogenate the unsaturated dianhydride to obtain a saturated dianhydride to solve the above problems. T M and T Kurosaki et al. tried to combine bicyclo[2.2.2]oct-7-ene-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid-2,3:5 ,6-dianhydride direct hydrogenation reduction to obtain bicyclo[2.2.2]octane-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid-2,3:5,6 - dianhydride, but without success. Since the catalytic hydrogenation reaction is a two-phase reaction, the reactants are all carried out on the surface of the catalyst, and the above-mentioned dianhydride monomer has poor solubility, and the common low-boiling point solvent is almost insoluble, making the hydrogenation reduction reaction difficult to carry out. Although the high boiling point solvent can dissolve a small amount of the above dianhydride, the hydrogen absorption effect of the high boiling point solvent is poor, and at the same time, it may be caused by the bicyclo[2.2. The π electron cloud in the carbon-carbon double bond is affected by four carbonyl groups, and its steric hindrance is large. Combining these two points, the hydrogenation reduction reaction is also difficult to carry out in a high-boiling solvent.

According to the report of T Matsumoto and T Kurosaki in "Reactive & Functional Polymers" 1996, 30(1): 55-59, and Japanese Patent JP2008100979A, a synthetic bicyclo[2.2.2]octane-2,3,5,6- For the preparation method of tetracarboxylic dianhydride, see Reaction Formula 2. In this scheme, during the reaction of (±)-trans-1,2-dihydrophthalic acid dimethyl ester (2) and fumaric acid dimethyl ester, due to (±)-trans-1,2-dihydrogen Due to the influence of two ester groups, dimethyl phthalate (2) has poor reactivity, so a higher reaction temperature (>180° C.) is required to make the reaction proceed smoothly. Bicyclo[2.2.2]octane-2-exo, 3-endo, 5-exo, 6-exo-tetracarboxylic acid tetramethyl ester (4) was hydrolyzed under different conditions, and finally different configurations were obtained The dianhydride, hydrolyzed under alkaline conditions, will eventually yield a bicyclo[2.2.2]octane-2-endo, 3-endo, 5-exo, 6-exo-tetracarboxylic acid-2, 3:5,6-dianhydride (6a), hydrolyzed under acidic conditions, will eventually give a bicyclo[2.2.2]octane-2-endo, 3-endo, 5-exo, 6-exo -Tetracarboxylic acid-2,3:5,6-dianhydride (6b), but the dianhydride of this configuration like 6a has a lower melting point, and the PI synthesized from it has relatively poor thermal stability, so it needs to be like 6b. It is a dianhydride monomer with an all-exterior structure, while 4 is difficult to hydrolyze under acidic conditions, the reaction time is long (>18h), and the yield of the final synthesized 6b is too low.

SUMMARY OF THE INVENTION

In order to overcome the above difficulties, the present invention provides a bicyclo[2.2.2]octane-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid-2,3:5,6 -The preparation method of dianhydride, see Reaction formula 3. The raw materials used in the invention are cheap, the reaction conditions are mild, and the reaction is rapid, and only one kind of bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride with an all-exterior structure is obtained, and the yield is Significantly improved (yield > 93%), and at the same time, the by-product of methyl alkyl acid was obtained, and the atom utilization rate was high.

Preparation of bicyclo[2.2.2]octane-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid-2,3:5,6-dianhydride of the present invention The process method of the method comprises the following steps:

1) Preparation of (±)-trans-1,2-dihydrophthalic acid: the mixed solution composed of phthalic acid, dilute acid and organic solvent is placed in an electrolytic cell with a diaphragm, a lead electrode is used, and the electrolysis temperature is 20 ℃～80℃, the current density is controlled at 100～600A/m ² , (±)-trans-1,2-dihydrophthalic acid is generated by electrolytic reduction, and the reacted electrolyte is distilled under reduced pressure to separate out a white solid, which is filtered and removed. Recrystallized from ionized water and dried in vacuo to obtain a white solid with a yield of about 90%; mp: 212℃～213℃; 1H NMRδ(DMSO-d6): 3.53 (2H, CH), 5.81 (2H, =CH-), 6.00 (2H, -CH=), 12.73 (2H, COOH).

2) Preparation of bicyclo[2.2.2]oct-7-ene-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid-2,3:5,6-dianhydride : Place the white solid and maleic anhydride prepared in 1) in a reaction device with a condenser, in a nitrogen atmosphere, use acetic anhydride or propionic anhydride as a solvent and a dehydrating agent, heat up to 70 ℃ ~ 85 ℃ raw materials dissolve, continue to heat up To 85 ℃～140 ℃, react for 0.5～3 hours, the reaction process continuously separates out white solid, filtration, acetone washing, vacuum drying obtains white solid powder, the yield is about 85%; mp: 351 ℃～352 ℃; ¹ H NMRδ( _DMSO -d6): 3.48 (2H, CH), 3.61 (4H, CH), 6.38 (2H, -CH=CH-).

3) Preparation of bicyclo[2.2.2]oct-7-ene-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid tetramethyl ester: white powder prepared in 2) , methanol solvent and concentrated sulfuric acid are placed in a reaction device with a condenser, the reaction temperature is 30 ℃ ~ 70 ℃ to the reflux state, and the reaction is carried out for 3 to 7 hours. After the reaction is completed, white needle-like crystals are precipitated by cooling and crystallization, and the yield is filtered and vacuum-dried. About 97%; mp: 130℃～132℃; ¹ H NMRδ(DMSO-d ₆ ): 3.07 (2H, CH), 3.22 (4H, CH), 3.48 (12H, CH ₃ ), 6.14 (2H, -CH) =CH-).

4) Preparation of bicyclo[2.2.2]octane-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid tetramethyl ester: white needle-like crystals prepared in 3), Methanol or ethanol solvent and 5% palladium-carbon catalyst are placed in a 500ml high-pressure reaction kettle, the air in the reaction kettle is replaced by hydrogen (three times), the hydrogen pressure in the reaction kettle is 2MPa～5MPa, the reaction temperature is 60 ℃～120 ℃, and the reaction time is 6 ~12 hours, after the reaction is completed, use diatomaceous earth to filter to palladium-carbon catalyst, and then cool down under reduced pressure distillation to separate out white granular crystals, filter and vacuum dry, and the yield is about 85%; mp: 150 ° C ~ 152 ° C; ¹ H NMRδ ( _DMSO -d6): 1.48 (4H, _CH2 ), 2.30 (2H, CH), 3.12 (4H, CH), 3.56 (12H, _CH3 ).

5) Preparation of bicyclo[2.2.2]octane-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid-2,3:5,6-dianhydride: 4 ) prepared white granular crystals, the alkyl acid and concentrated sulfuric acid are placed in a reactor with a piercing fractionation column, the reaction temperature is 80 ° C ~ 130 ° C, and the reaction is carried out for 1 to 3 hours, and white powder solids are continuously precipitated during the reaction process. Vacuum drying, while distilling out low fraction by-products, the yield is about 96%; mp: 389℃～391℃; ¹ H NMRδ (DMSO-d ₆ ): 1.37 (4H, CH ₂ ), 2.47 (2H, CH), 3.52 (4H, CH).

Further, the electrolysis temperature described in the step (1) of the present invention is 20°C to 50°C, and the current density is 200 to 500 A/m ² .

Further, the reaction temperature described in step (2) of the present invention is 80°C to 120°C.

Further, the catalytic amount of the concentrated sulfuric acid described in the step (3) of the present invention is 2% to 5% of the total mass of the raw materials, and the reaction temperature of the methyl esterification is 50°C to 70°C.

Further, the reaction temperature of the hydrogenation reaction described in step 4) of the present invention is 80 ° C ~ 120 ° C, the catalytic amount of 5% palladium carbon accounts for 2% ~ 10% of the total mass of the raw materials, and the hydrogen pressure in the reactor is 4MPa～5MPa.

Further, the alkyl acid solvent described in step 5) of the present invention can be selected from one or more of formic acid, acetic acid and propionic acid.

Further, the molar ratio of the raw materials described in step 5) of the present invention and the concentrated sulfuric acid is 1:0.5-1:1, and the reaction temperature is 100°C-130°C.

Detailed ways

In order to further illustrate the specific process of the preparation process of bicyclic alkene tetracarboxylic dianhydride in this scheme, the specific experimental scheme is listed below, but this scheme is not limited to the specific numbers listed in the experimental case, and the scheme of mass enlargement or reduction of the same ratio It also belongs to the content of the experimental case disclosure.

Example 1

Cathode plate: Pb; length 100mm, width 40mm, thickness 2mm.

Anode plate: Pb; length 80mm, width 40mm, thickness 2mm.

Catholyte: 300 ml of 5% _H2SO4 in water, ₂₀₀ ml of dioxane, 40 g (240 mmol) of phthalic acid.

Anolyte: ₅ % _H2SO4 aqueous solution, the liquid level is the same as that of the catholyte.

Diaphragm: N324 cation exchange membrane

Current density: 200A/m ²

Reaction temperature: 30°C

HPLC detected the reaction progress, and the reaction was finished after 17 hours. After the reaction solution was decompressed and distilled out a part of the solvent, a white solid was precipitated by cooling crystallization, suction filtration, washed with distilled water 1 to 2 times, filtered and dried in vacuo to obtain 36.84g product, yield 91 %, and the purity detected by HPLC was 99.6%.

36.84g (220mmol) (±)-trans-1,2-dihydrophthalic acid, 21.48g (220mmol) maleic anhydride, 60g acetic anhydride were placed in a reaction device with a condenser, in a nitrogen atmosphere The raw material was dissolved after warming up to 70°C, and the temperature was continued to rise to 120°C. Magnetic stirring. After half an hour, white solids were continuously precipitated in the reaction solution. Powder, 85% yield.

46.27 g (190 mmol) of bicyclo[2.2.2]oct-7-ene-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid-2,3:5,6- Dianhydride, 9.25g (90mmol) concentrated sulfuric acid, 140g methanol were placed in a reaction device with a condenser, the temperature was raised to reflux temperature, magnetic stirring was performed, the reaction progress was detected by TLC dot plate, the reaction was completed after 5 hours, and white needles were precipitated by cooling crystallization. 61.67 g of product were obtained by suction filtration and vacuum drying, and the yield was 97%.

61.67g (180mmol) bicyclo[2.2.2]oct-7-ene-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid tetramethyl ester, 3g (1.41mmol) 5% palladium carbon and 180g methanol were placed in a 500ml autoclave, the air in the reactor was replaced by hydrogen (2 to 3 times), the hydrogen pressure in the reactor was 5MPa, the temperature was raised to 100°C and the reaction was started, mechanical stirring, TLC spotting The reaction process was detected, the reaction was finished after 6 hours, the palladium carbon in the solution was filtered out with diatomaceous earth, after a part of methanol solvent was distilled off under reduced pressure, white granular crystals were separated out by cooling crystallization, suction filtration, and vacuum drying to obtain 54.78g product, the yield was 88%.

54.78g (160mmol) bicyclo[2.2.2]octane-2-exterior, 3-exterior, 5-exterior, 6-exterior-tetracarboxylic acid tetramethyl ester, 16.5g (160 mmol) concentrated sulfuric acid, 160 g of acetic acid was placed in a reactor with a piercing fractionation column, and the temperature was raised to 120 ° C to start the reaction, and magnetic stirring was performed. After half an hour, a white solid was continuously precipitated in the reaction solution, and the low-cut fraction methyl acetate at 55 ° C was collected, 1 After 1 hour, the reaction was stopped, filtered with suction, washed with acetic acid for 1 to 2 times, and dried in vacuo to obtain 38.47 g of white powder with a yield of 94%. .

Example 2

Cathode plate: Pb; length 100mm, width 40mm, thickness 2mm.

Anode plate: Pb; length 80mm, width 40mm, thickness 2mm.

Catholyte: 250 ml 10% aqueous _H2SO4 , ₂₅₀ ml isopropanol, 60 g (360 mmol) phthalic acid.

Anolyte: ₁₀ % _H2SO4 aqueous solution, the liquid level is the same as that of the catholyte.

Diaphragm: N324 cation exchange membrane

Current density: 300A/m ²

Reaction temperature: 25°C

HPLC detected the reaction progress, and the reaction was finished after 17 hours. After the reaction solution was decompressed and distilled out a part of the solvent, a white solid was precipitated by cooling crystallization, suction filtration, washed with distilled water 1 to 2 times, filtered and dried in vacuo to obtain 54.05g of product, with a yield of 89 %, and the purity detected by HPLC was 99.6%.

54.05g (320mmol) (±)-trans-1,2-dihydrophthalic acid, 31.52g (320mmol) maleic anhydride, 160g acetic anhydride were placed in a reaction device with a condenser, in a nitrogen atmosphere After warming up to 70°C, the raw materials were dissolved, and the temperature was continued to rise to 80°C. Magnetic stirring was performed. After 1 hour, white solids were continuously precipitated in the reaction solution. After 3 hours, the reaction stopped. Powder, 88% yield.

70.20 g (283 mmol) of bicyclo[2.2.2]oct-7-ene-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid-2,3:5,6- Dianhydride, 14.04g (151mmol) of concentrated sulfuric acid and 220g of methanol were placed in a reaction device with a condenser, heated to reflux temperature, magnetically stirred, and the reaction progress was detected by TLC dot plate, the reaction was completed after 5 hours, and white needles were precipitated by cooling crystallization 93.37g of product was obtained by suction filtration and vacuum drying, and the yield was 97%.

93.37g (274mmol) bicyclo[2.2.2]oct-7-ene-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid tetramethyl ester, 2.8g (1.31mmol ) 5% palladium carbon, 270g methanol are placed in the 500ml autoclave, hydrogen replaces the air in the reactor (replacement 2 to 3 times), the hydrogen pressure in the reactor is 5MPa, is warming up to 120 ℃ and starts to react, mechanical stirring, TLC point The reaction process was detected by the plate, and hydrogen was supplemented 3 times during the reaction. After 10 hours, the reaction was completed. The palladium carbon in the solution was filtered out with diatomaceous earth. Drying gave 81.71 g of product, a yield of 87%.

81.71g (239mmol) bicyclo[2.2.2]octane-2-exterior, 3-exterior, 5-exterior, 6-exterior-tetracarboxylic acid tetramethyl ester, 36.9g (358mmol) concentrated sulfuric acid, 240 g of formic acid was placed in a reactor with a piercing fractionation column, and the temperature was raised to 100 ° C to start the reaction, and magnetic stirring was performed. After 1 hour, a white solid was continuously precipitated in the reaction solution, and the low-cut fraction methyl formate at 30 ° C was collected, 2 The reaction was stopped after one hour, suction filtered, washed with acetic acid for 1 to 2 times, and vacuum-dried to obtain 54.34 g of white powder with a yield of 91%. .

Example 3

Cathode plate: Pb; length 100mm, width 40mm, thickness 2mm.

Anode plate: Pb; length 80mm, width 40mm, thickness 2mm.

Catholyte: 400 ml 15% aqueous _H2SO4 , ₂₀₀ ml DMF, 80 g (480 mmol) phthalic acid.

Anolyte: ₁₅ % _H2SO4 aqueous solution, the liquid level is the same as that of the catholyte.

Diaphragm: N324 cation exchange membrane

Current density: 400A/m ²

Reaction temperature: 50°C

HPLC detected the reaction progress, and the reaction finished after 17 hours. After the reaction solution was decompressed and distilled out a part of the solvent, a white solid was precipitated by cooling crystallization, suction filtration, washed with distilled water 1 to 2 times, filtered and dried in vacuo to obtain 75.30 g of product, yield 93 %, and the purity detected by HPLC was 99.8%.

75.30 g (448 mmol) (±)-trans-1,2-dihydrophthalic acid, 43.91 g (448 mmol) maleic anhydride, 220 g acetic anhydride were placed in a reaction device with a condenser, in a nitrogen atmosphere The raw material was dissolved after warming up to 70°C, continued to be heated to 140°C under reflux, magnetic stirring, after 10 minutes, white solids were continuously precipitated in the reaction solution, the reaction stopped after half an hour, suction filtration, acetone washing 1 to 2 times, and vacuum drying to obtain 86.69 g white powder, the yield is 78%.

86.69 g (350 mmol) of bicyclo[2.2.2]oct-7-ene-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid-2,3:5,6- Dianhydride, 13g (140mmol) of concentrated sulfuric acid and 250g of methanol were placed in a reaction device with a condenser, heated to reflux temperature, magnetically stirred, and the progress of the reaction was detected by TLC dot plate. The crystals were filtered with suction and dried under vacuum to obtain 114.12 g of the product with a yield of 96%.

114.12g (335mmol) bicyclo[2.2.2]oct-7-ene-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid tetramethyl ester, 11.4g (5.36mmol) ) 5% palladium carbon, 230g ethanol are placed in the 500ml autoclave, hydrogen replaces the air in the reactor (replacement 2 to 3 times), the hydrogen pressure in the reactor is 5MPa, is warming up to 110 ℃ and starts to react, mechanical stirring, TLC point The reaction process was detected by the plate, and hydrogen was supplemented 5 times during the reaction. After 3 hours, the reaction was completed. The palladium carbon in the solution was filtered out with diatomaceous earth. Drying gave 103.31 g of product with a yield of 90%.

103.31g (300mmol) bicyclo[2.2.2]octane-2-exterior, 3-exterior, 5-exterior, 6-exterior-tetracarboxylic acid tetramethyl ester, 15.56g (150mmol) concentrated sulfuric acid, 200g propionic acid was placed in a reactor with a piercing fractionation column, and the temperature was raised to 130 ° C to start the reaction, magnetic stirring, and after half an hour, a white solid was continuously precipitated in the reaction solution, and the low-cut fraction methyl propionate at 78 ° C was collected. , the reaction was stopped after 1 hour, suction filtration, washed with acetic acid 1 to 2 times, and vacuum-dried to obtain 72.48 g of white powder with a yield of 96%. The mass of the low-cut colorless liquid was 98.9 g with a yield of 93%. 98.9%.

Claims (4)

1. a preparation method of the tetracarboxylic dianhydride of bicyclic structure, the method is characterized in that comprising the following steps: 1) The mixed solution composed of phthalic acid, dilute acid and organic solvent is placed in an electrolytic cell with a diaphragm, and a lead electrode is used for electrolytic reduction to generate (±)-trans-1,2-dihydrophthalic acid. The product is a racemic mixture of two different isomers, 1S, 2S and 1R, 2R; Wherein, the dilute acid is an aqueous sulfuric acid solution with a mass fraction of 5% to 20%; 2) In a nitrogen atmosphere, using acetic anhydride or propionic anhydride as solvent and dehydrating agent, (±)-trans-1,2-dihydrophthalic acid reacts with maleic anhydride to form a bicyclic with a full external structure [2.2 .2] Oct-7-ene-2,3,5,6-tetracarboxylic dianhydride; the reaction temperature is 60℃～140℃; 3) Using methanol as a solvent and concentrated sulfuric acid as a catalyst, the bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride methyl ester prepared in step 2) was prepared to form bicyclo[2.2.2]oct-7-ene-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid tetramethyl ester; Wherein, the consumption of concentrated sulfuric acid is 1%～10% of the total mass of raw materials, and the reaction temperature of methyl esterification is 30℃～70℃; 4) In the autoclave, methanol was used as a solvent, 5% palladium carbon was used as a catalyst, and the bicyclo[2.2.2]oct-7-ene-2-exterior, 3-exterior, and 5-exterior prepared in step 3) were used. Type, 6-exo-tetracarboxylic acid tetramethyl ester hydrogenation reduction, the reaction generates bicyclo[2.2.2]octane-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic Tetramethyl acid; 5) In the fractionation reactor, alkyl acid is used as solvent, concentrated sulfuric acid is used as catalyst and dehydrating agent, and the bicyclo[2.2.2]octane-2-exo, 3-exo, and 5-exo prepared in step 4) are used. Type, 6-exo-tetracarboxylic acid tetramethyl ester exchange, dehydration ring closure to generate bicyclo[2.2.2]octane-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic Acid-2,3:5,6-dianhydride, and at the same time fractional distillation of methyl alkyl acid as a low fraction; Wherein, the alkyl acid solvent is one or more of formic acid, acetic acid, propionic acid, n-butyric acid and tert-butyric acid; bicyclo[2.2.2]octane-2-exterior, 3-exterior, The molar ratio of 5-exo, 6-exo-tetramethyl tetracarboxylate and concentrated sulfuric acid is 1:0.5～1:2, and the reaction temperature is 80℃～130℃; The tetracarboxylic dianhydride with the bicyclic structure is the product of step 5) bicyclo[2.2.2]octane-2-exo, 3-exo, 5-exo, 6-exo-tetracarboxylic acid- 2,3:5,6-dianhydride, its structural formula is,

2 . The preparation method according to claim 1 , wherein, in step 1), the electrolysis temperature is 20° C.˜80° C., and the current density is 100˜600 A/m ² . 3. preparation method according to claim 1 is characterized in that, in step 1), organic solvent is dioxane, tetrahydrofuran, isopropanol, methanol, ethanol, dimethyl formamide, dimethyl ethyl alcohol One or more of the amides. 4. preparation method according to claim 1, is characterized in that, in step 4), the reaction temperature of hydrogenation reaction is 60 ℃～120 ℃, and the consumption of 5% palladium carbon accounts for 2%～20% of raw material gross mass %, the hydrogen pressure in the reaction kettle is 2MPa～5MPa.