Low-volatility amine intermediate as well as preparation method and application thereof

Abstract

The invention relates to the technical field of compound preparation, in particular to a low-volatility amine intermediate as well as a preparation method and application thereof.The preparation method of the low-volatility amine intermediate comprises the following steps: S1, adding 4-aminobenzaldehyde and an antioxidant into ethanol, dropwise adding 1, 2, 4-trimethyl-1, 3-pentanedione, and stirring to obtain a mixture A; the preparation method comprises the following steps: adding a 1, 5-naphthylenediamine ethanol solution and a p-toluene sulfonic acid ethanol solution, reacting for 7-9 hours, and carrying out suction filtration, washing and recrystallization to obtain an intermediate A; s2, adding the intermediate A into anhydrous tetrahydrofuran, and stirring to obtain a solution; adding 3-(3, 5-di-tert-butyl-4-hydroxyphenyl) propionic acid, an activating agent and a catalyst into the solution, reacting for 10-15 hours, washing, drying and performing rotary evaporation to obtain an intermediate B; s3, mixing the intermediate A obtained in the step S1 and the intermediate B obtained in the step S2 to obtain the low-volatility amine intermediate. The low-volatility amine intermediate prepared by the invention is applied to curing of epoxy resin, so that the epoxy resin has excellent mechanical properties and oxidation resistance.

Description

Technical Field

[0001] This invention relates to the field of compound preparation technology, specifically to a low-volatility amine intermediate, its preparation method, and its application. Background Technology

[0002] Driven by the growing global awareness of environmental protection, countries are continuously tightening restrictions on VOC (volatile organic compound) emissions. Certification systems such as the EU's REACH and the US EPA impose stringent standards on the toxicity and volatility of chemical materials. Traditional high-volatile amine-based curing agents face application restrictions due to excessive emissions, forcing the industry to develop low-volatile alternatives. Industries such as construction, automotive, and electronics have gradually phased out highly toxic and high-volatile curing agents, shifting towards low-volatile and environmentally friendly products.

[0003] Traditional amine curing agents, such as ethylenediamine and diethylenetriamine, are small-molecule aliphatic amines with low molecular weight and boiling points, exhibiting extremely high volatility at room temperature. These substances not only have a pungent odor but also irritate the skin and respiratory tract, posing a health hazard to construction workers with prolonged exposure. Furthermore, the volatile amines can react with carbon dioxide in the air to form salts, leading to defects such as whitening and spots in the cured coating, affecting the product's appearance and performance. In addition to volatility issues, traditional small-molecule amine curing agents also result in epoxy resins that are brittle after curing, have poor impact resistance, and exhibit inadequate weather resistance.

[0004] Patent CN115108924B discloses an amine intermediate, its preparation method, and its application. The amine intermediate includes N-(2-methoxycyclohexyl)-1,3-propanediamine. The preparation method includes the following steps: 2-methoxycyclohexylamine and acrylonitrile undergo an addition reaction at 10-100°C to generate 3-(2-methoxycyclohexyl)-aminopropionitrile; 3-(2-methoxycyclohexyl)-aminopropionitrile undergoes a hydrogenation reaction at 20-120°C in a hydrogen atmosphere with the aid of a catalyst to obtain the final product. This preparation method is simple and efficient. However, this amine intermediate contains only one primary amine group, and its application in the curing of epoxy resins may lead to a decrease in the overall curing reaction rate.

[0005] Patent CN120247717B discloses a modified amine curing agent and its preparation method, as well as an epoxy resin composite material and its preparation method. This curing agent, through free radical substitution and alkylation reactions, branches C2-C8 alkyl groups to the methylene sites of 4,4'-diaminodiphenylmethane (MDA), forming a molecular structure that combines flexible alkyl chains with rigid benzene rings. Its preparation method includes two steps: MDA reacts with a halogen element under certain reaction conditions to generate a halogenated intermediate, which is then alkylated with a Grignard reagent and purified. Although this curing agent has low volatility, the steric hindrance of the alkyl chain may shield the amine group, affecting its contact with the epoxy group; the flexible chain itself does not participate in crosslinking, diluting the effective crosslinking points per unit volume.

[0006] Therefore, there is an urgent need in the market for a low-volatile amine intermediate that can give epoxy resins excellent mechanical properties at a low cost. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of this invention is to obtain a low-volatile amine intermediate that can give epoxy resin excellent mechanical properties and antioxidant properties while being low in cost.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a low-volatility amine intermediate, which is a composition of intermediate A shown in formula (1) and intermediate B shown in formula (2). Equation (1); Equation (2); Where R is .

[0009] A second aspect of this invention provides a method for preparing a low-volatility amine intermediate, comprising the following steps: S1. Add 4-aminobenzaldehyde and antioxidant to ethanol. Under inert gas protection, add 1,5-naphthyldiamine ethanol solution and p-toluenesulfonic acid ethanol solution dropwise at 20-30℃. Heat to 60-70℃ and reflux for 7-9 hours. Filter immediately, wash, and recrystallize 2-3 times to obtain intermediate A. S2. Add intermediate A obtained in step S1 to anhydrous tetrahydrofuran and stir for 20-30 min to obtain a solution; add 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, activator, and catalyst to the solution, stir at 0-5℃ for 20-30 min under inert gas protection, raise the temperature to 20-30℃ and react for 10-15 h, wash, dry, and rotary evaporate to obtain intermediate B; S3. Mix intermediate A obtained in step S1 and intermediate B obtained in step S2, and stir at 20-30℃ for 3-5 minutes to obtain a low-volatility amine intermediate.

[0010] Preferably, the mass ratio of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid to activator is 1:(0.8-0.85).

[0011] Preferably, the mass ratio of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid to the catalyst is 1:(0.05-0.055).

[0012] The low-volatility amine intermediate prepared in this application has a rigid naphthalene ring structure, a -C=N- structure, and antioxidant groups. Using it in the curing reaction of epoxy resin can result in epoxy resin cured products with excellent mechanical properties and antioxidant properties.

[0013] This application obtains intermediate A containing a naphthalene ring structure by reacting 4-aminobenzaldehyde with 1,5-naphthyldiamine. This intermediate not only has low volatility but also improves the mechanical properties of epoxy resin. Furthermore, by adding an antioxidant during the reaction process, this application can avoid the occurrence of aldehyde oxidation side reactions and improve reaction efficiency. By preferably using ethanol as the reaction solvent, the occurrence of acetal side reactions is reduced.

[0014] In practical applications, this application found that intermediate A is prone to oxidation and discoloration during storage. Using it in the curing reaction of epoxy resin can actually reduce the mechanical properties of the epoxy resin. This may be because the imine bonds in intermediate A are sensitive to light / oxygen, causing oxidation and decomposition reactions during storage, thus affecting its performance. To solve this problem, this application further reacts intermediate A with 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid to introduce an antioxidant group into the structure of intermediate A, obtaining intermediate B. This intermediate B is then compounded with intermediate A to obtain a low-volatility amine intermediate, effectively solving the oxidation problem of intermediate A. Furthermore, this application found that compared to the conventional method of directly adding antioxidants to intermediate B, introducing antioxidant groups into the structure of intermediate A can achieve better performance with a lower amount of antioxidant added.

[0015] In some embodiments, the mass ratio of the 4-aminobenzaldehyde to the antioxidant is 1:(0.005-0.02).

[0016] In some embodiments, the antioxidant is one or more of 2,6-di-tert-butyl-4-methylphenol, antioxidant 1010, antioxidant 1076, and triphenyl phosphite.

[0017] Preferably, the antioxidant is 2,6-di-tert-butyl-4-methylphenol.

[0018] In some embodiments, the concentration of the 1,5-naphthyldiamine ethanol solution is 0.20-0.25 mol / L. -1 .

[0019] In some embodiments, the concentration of the p-toluenesulfonic acid ethanol solution is 0.10-0.15 mol / L. -1 .

[0020] In some embodiments, the ratio of the 4-aminobenzaldehyde to the 1,5-naphthyldiamine ethanol solution is 1 g: (13-17) ml.

[0021] This application avoids excessive condensation caused by excess aldehyde by limiting the ratio of 4-aminobenzaldehyde and 1,5-naphthyldiamine ethanol solution.

[0022] In some embodiments, the ratio of the 4-aminobenzaldehyde to the p-toluenesulfonic acid ethanol solution is 1 g: (2-6) ml.

[0023] In some embodiments, the mass ratio of intermediate A and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid in step S2 is 1:(0.75-0.80).

[0024] In some embodiments, the activator is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride.

[0025] In some embodiments, the catalyst is 4-dimethylaminopyridine and / or 1-hydroxybenzotriazole.

[0026] Preferably, the catalyst is 4-dimethylaminopyridine.

[0027] In some embodiments, the mass ratio of intermediate A to intermediate B in step S3 is 1:(0.15-0.25).

[0028] In some embodiments, the washing conditions in step S2 are washing with saturated sodium bicarbonate; and the drying conditions are drying with anhydrous sodium sulfate.

[0029] A third aspect of the present invention provides the application of a low-volatility amine intermediate in the curing of epoxy resins.

[0030] Compared with the prior art, the present invention has the following beneficial effects: (1) The low-volatility amine intermediate prepared by the present invention has a rigid naphthalene ring structure, -C=N- structure and antioxidant group. Using it in the curing reaction of epoxy resin can make the epoxy resin cured product have excellent mechanical properties and antioxidant properties.

[0031] (2) By adding an antioxidant during the reaction, the present invention avoids the occurrence of aldehyde oxidation side reaction; by using ethanol as the reaction solvent, the occurrence of acetal side reaction is reduced; by limiting the ratio of 4-aminobenzaldehyde and 1,5-naphthyldiamine ethanol solution, excessive condensation caused by excess aldehyde is avoided, thus improving the reaction efficiency.

[0032] (3) In this invention, intermediate A is reacted with 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid to introduce an antioxidant group into the structure of intermediate A to obtain intermediate B, which is then compounded with intermediate A to obtain a low-volatility amine intermediate. This effectively solves the problem of easy oxidation of intermediate A and has a lower cost. Attached Figure Description

[0033] Figure 1 The NMR spectrum of intermediate A obtained in Example 1; Figure 2 The image shows the NMR spectrum of intermediate B obtained in Example 1. Detailed Implementation

[0034] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0035] The compounds and related reagents used in the following examples and comparative examples are all commercially available.

[0036] Example 1 A method for preparing a low-volatility amine intermediate includes the following steps: S1. Add 10g of 4-aminobenzaldehyde and 0.1g of 2,6-di-tert-butyl-4-methylphenol to 50g of anhydrous ethanol. Under nitrogen protection, add 150ml of 0.22mol / L ethanol dropwise at 25℃. -1 A 1,5-naphthyldiamine ethanol solution and 4 ml of 0.12 mol / L... -1 The ethanol solution of p-toluenesulfonic acid was heated to 65°C and refluxed for 8 hours. The mixture was immediately filtered, washed with anhydrous methanol, and recrystallized twice in anhydrous ethanol to obtain intermediate A as shown in formula (1). S2. Add 1g of intermediate A obtained in step S1 to 10g of anhydrous tetrahydrofuran and stir for 25min to obtain a solution; add 0.77g of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 0.64g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and 0.04g of 4-dimethylaminopyridine to the solution, stir at 3℃ for 25min under nitrogen protection, raise the temperature to 25℃ and react for 13h, wash with saturated sodium bicarbonate, dry with anhydrous sodium sulfate, and rotary evaporate at 35℃ to obtain intermediate B as shown in formula (2); S3. Mix 5g of intermediate A obtained in step S1 and 1g of intermediate B obtained in step S2, stir at 25°C for 4 minutes to obtain a low-volatility amine intermediate. Equation (1); Equation (2); Where R is .

[0037] Figure 1 The NMR spectrum of intermediate A; Figure 2 The NMR spectrum of intermediate B.

[0038] Example 2 A method for preparing a low-volatility amine intermediate includes the following steps: S1. Add 10g of 4-aminobenzaldehyde and 0.05g of 2,6-di-tert-butyl-4-methylphenol to 50g of anhydrous ethanol. Under nitrogen protection, add 130ml of 0.25mol / L ethanol dropwise at 20℃. -1 A 1,5-naphthyldiamine ethanol solution and 2 ml of 0.15 mol / L... -1 The ethanol solution of p-toluenesulfonic acid was heated to 60°C and refluxed for 9 hours. The mixture was immediately filtered, washed with anhydrous methanol, and recrystallized twice in anhydrous ethanol to obtain intermediate A. S2. Add 1g of intermediate A obtained in step S1 to 10g of anhydrous tetrahydrofuran and stir for 20min to obtain a solution; add 0.75g of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 0.6g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and 0.041g of 4-dimethylaminopyridine to the solution, stir at 0℃ for 30min under nitrogen protection, raise the temperature to 20℃ and react for 15h, wash with saturated sodium bicarbonate, dry with anhydrous sodium sulfate, and rotary evaporate at 35℃ to obtain intermediate B; S3. Mix 5g of intermediate A obtained in step S1 and 0.75g of intermediate B obtained in step S2, and stir at 20°C for 5 minutes to obtain a low-volatility amine intermediate.

[0039] Example 3 A method for preparing a low-volatility amine intermediate includes the following steps: S1. Add 10g of 4-aminobenzaldehyde and 0.2g of 2,6-di-tert-butyl-4-methylphenol to 50g of anhydrous ethanol. Under nitrogen protection, add 170ml of 0.20mol / L ethanol dropwise at 30℃. -1 A 1,5-naphthyldiamine ethanol solution and 6 ml of 0.10 mol / L... -1 The ethanol solution of p-toluenesulfonic acid was heated to 70°C and refluxed for 7 hours. The mixture was immediately filtered, washed with anhydrous methanol, and recrystallized three times in anhydrous ethanol to obtain intermediate A as shown in formula (1). S2. Add 1g of intermediate A obtained in step S1 to 10g of anhydrous tetrahydrofuran and stir for 25min to obtain a solution; add 0.80g of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 0.68g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and 0.044g of 4-dimethylaminopyridine to the solution, stir at 5℃ for 20min under nitrogen protection, raise the temperature to 30℃ and react for 10h, wash with saturated sodium bicarbonate, dry with anhydrous sodium sulfate, and rotary evaporate at 35℃ to obtain intermediate B as shown in formula (2); S3. Mix 5g of intermediate A obtained in step S1 and 1.25g of intermediate B obtained in step S2, and stir at 30°C for 3 minutes to obtain a low-volatility amine intermediate.

[0040] Example 4 A method for preparing a low-volatility amine intermediate, the specific implementation method is the same as in Example 1, except that the amount of 2,6-di-tert-butyl-4-methylphenol added is 0.03g.

[0041] Example 5 A method for preparing a low-volatility amine intermediate, the specific implementation method is the same as in Example 1, the difference being that 0.22 mol L... -1 The amount of 1,5-naphthyldiamine ethanol solution added was 100 ml.

[0042] Example 6 A method for preparing a low-volatility amine intermediate, the specific implementation method is the same as in Example 1, except that the amount of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid added is 1g.

[0043] Example 7 A method for preparing a low-volatility amine intermediate, the specific implementation method is the same as in Example 1, except that the amount of intermediate B added in step S3 is 1.75g.

[0044] Comparative Example 1 A method for preparing a low-volatility amine intermediate includes the following steps: adding 10g of 4-aminobenzaldehyde and 0.05g of 2,6-di-tert-butyl-4-methylphenol to 50g of anhydrous ethanol, and under nitrogen protection, adding 13ml of 0.25mol / L solution dropwise at 20°C. -1 A 1,5-naphthyldiamine ethanol solution and 2 ml of 0.15 mol / L... -1 The ethanol solution of p-toluenesulfonic acid was heated to 60°C and refluxed for 9 hours. The mixture was immediately filtered, washed with anhydrous methanol, and recrystallized twice in anhydrous ethanol to obtain a low-volatility amine intermediate.

[0045] Comparative Example 2 One amine intermediate is 4,4'-diaminodiphenylmethane.

[0046] Comparative Example 3 One amine intermediate is diethylenetriamine.

[0047] Performance testing The low-volatility amine intermediates obtained in the above embodiments and comparative examples were applied to the curing of epoxy resin E51, and their performance was tested. (1) Low volatility: 100g of epoxy resin E51 and 0.5g of defoamer ACP-1400 were mixed with 100g of amine intermediates obtained in Examples 1-7 at room temperature and stirred for 5 minutes. The mixture was then poured into a preheated mold and cured at 90°C for 2 hours. The temperature was then raised to 140°C and cured for 2 hours. The mixture was then cooled to room temperature to obtain samples 1-7. 100g of epoxy resin E51, 0.5g of defoamer ACP-1400 and 72g of amine intermediate obtained in Comparative Example 1 were mixed and stirred at room temperature for 5 minutes. The mixture was then poured into a preheated mold and cured at 90℃ for 2 hours. The temperature was then raised to 140℃ and cured for 2 hours. The mixture was then cooled to room temperature to obtain sample 8. 100g of epoxy resin E51, 0.5g of defoamer ACP-1400 and 38g of 4,4'-diaminodiphenylmethane were mixed and stirred at room temperature for 5 minutes. The mixture was then poured into a preheated mold and cured at 90℃ for 2 hours. The temperature was then raised to 140℃ and cured for 2 hours. The mixture was then cooled to room temperature to obtain sample 9, which served as comparative example 2. 100g of epoxy resin E51, 0.5g of defoamer ACP-1400 and 16g of diethylenetriamine were mixed and stirred at room temperature for 5 minutes. The mixture was then poured into a preheated mold and cured at 90℃ for 2 hours. The temperature was then raised to 140℃ and cured for 2 hours. The mixture was then cooled to room temperature to obtain sample 10, which served as comparative example 3. During this period, VOC content was tested in accordance with GB / T23985-2009 to characterize low volatility.

[0048] (2) Mechanical properties: The tensile strength and elongation at break of specimens 1-10 were tested using a CMT2000 electronic universal testing machine in accordance with GB / T 1040-2006 standard, with a tensile rate of 5 mm / min.

[0049] The test results are shown in Table 1: Table 1

[0050] As shown in Table 1, the low-volatility amine intermediates in Examples 1-3 of this invention exhibit even lower volatility during the curing process of epoxy resin, and the resulting epoxy resin products possess excellent mechanical properties. A comparison between Example 4 and Example 1 shows that changing the ratio of 4-aminobenzaldehyde and 2,6-di-tert-butyl-4-methylphenol may cause aldehyde condensation side reactions in the system, thus affecting the reaction between 4-aminobenzaldehyde and 1,5-naphthyldiamine, leading to a decrease in the mechanical properties of the epoxy resin product. A comparison between Example 5 and Example 1 shows that changing the ratio of 4-aminobenzaldehyde and 1,5-naphthyldiamine may cause side reactions in the system, reducing the yield of intermediate A and thus affecting subsequent reactions, leading to a decrease in the mechanical properties of the epoxy resin product. A comparison between Example 6 and Example 1... It can be seen that changing the ratio of intermediate A and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid makes the final amine intermediate more susceptible to oxidation and decomposition when exposed to air, thus leading to a decrease in the mechanical properties of the epoxy resin product. A comparison between Example 7 and Example 1 shows that changing the ratio of intermediate A and intermediate B increases the rigidity of the final amine intermediate, thus leading to a decrease in the mechanical properties of the epoxy resin product. A comparison between Comparative Example 1 and Example 1 shows that directly using intermediate A as the curing agent for epoxy resin results in poor mechanical properties and increased volatility due to its susceptibility to oxidation and decomposition. A comparison between Comparative Examples 2 and 3 and Example 1 shows that using conventional amine intermediates as curing agents results in products with poor mechanical properties and high volatility.

[0051] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A low-volatility amine intermediate, characterized in that, A composition of intermediate A as shown in formula (1) and intermediate B as shown in formula (2). Equation (1); Equation (2); Where R is .

2. A method for preparing a low-volatility amine intermediate, characterized in that, Includes the following steps: S1. Add 4-aminobenzaldehyde and antioxidant to ethanol. Under inert gas protection, add 1,5-naphthyldiamine ethanol solution and p-toluenesulfonic acid ethanol solution dropwise at 20-30℃. Heat to 60-70℃ and reflux for 7-9 hours. Filter immediately, wash, and recrystallize 2-3 times to obtain intermediate A. S2. Add intermediate A obtained in step S1 to anhydrous tetrahydrofuran and stir for 20-30 min to obtain a solution; add 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, activator, and catalyst to the solution, stir at 0-5℃ for 20-30 min under inert gas protection, raise the temperature to 20-30℃ and react for 10-15 h, wash, dry, and rotary evaporate to obtain intermediate B; S3. Mix intermediate A obtained in step S1 and intermediate B obtained in step S2, and stir at 20-30℃ for 3-5 minutes to obtain a low-volatility amine intermediate.

3. The method for preparing the low-volatility amine intermediate according to claim 2, characterized in that, The mass ratio of 4-aminobenzaldehyde to the antioxidant is 1:(0.005-0.02).

4. The method for preparing the low-volatility amine intermediate according to claim 2, characterized in that, The antioxidant is one or more of 2,6-di-tert-butyl-4-methylphenol, antioxidant 1010, antioxidant 1076, and triphenyl phosphite.

5. The method for preparing the low-volatility amine intermediate according to claim 2, characterized in that, The concentration of the 1,5-naphthyldiamine ethanol solution is 0.20-0.25 mol / L. -1 .

6. The method for preparing the low-volatility amine intermediate according to claim 2, characterized in that, The concentration of the p-toluenesulfonic acid ethanol solution is 0.10-0.15 mol / L. -1 .

7. The method for preparing the low-volatility amine intermediate according to claim 5, characterized in that, The ratio of the 4-aminobenzaldehyde to the 1,5-naphthyldiamine ethanol solution is 1 g: (13-17) ml.

8. The method for preparing the low-volatility amine intermediate according to claim 2, characterized in that, The mass ratio of intermediate A and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid in step S2 is 1:(0.75-0.80).

9. The method for preparing the low-volatility amine intermediate according to claim 2, characterized in that, The mass ratio of intermediate A to intermediate B in step S3 is 1:(0.15-0.25).

10. The application of a low-volatility amine intermediate according to claim 1 or obtained by the preparation method according to any one of claims 2-9, characterized in that, Used for curing epoxy resins.

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