Preparation method of a liquid aromatic amine curing agent containing secondary amino group and primary amino group

Abstract

The present invention discloses a method for preparing aromatic diamines by reacting o-chloroaniline and N-ethylaniline together as aromatic monoamine raw materials with paraformaldehyde in an aqueous hydrochloric acid solution. This synthesis process has good environmental protection. The obtained novel aromatic diamines contain primary and secondary amino groups with mild reaction activity, are light in color, are liquid at room temperature, and can be used as curing agent components in various two-component polyurethane systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic chemical synthesis, and relates to a preparation method of a polyurethane curing agent containing an aromatic diamine with an asymmetric molecular structure, and in particular to a preparation method of a liquid aromatic amine curing agent containing a secondary amino group and a primary amino group. Background Art

[0002] Chain extenders are important auxiliaries for elastic polyurethane materials and can be directly used as curing agents or used to prepare curing agent components. Aromatic amine chain extenders / curing agents contain benzene rings, which can improve the modulus and heat resistance of polyurethanes; moreover, the urea groups formed by the reaction of amino groups with isocyanates can form strong hydrogen bonds; the reaction of amine curing agents with isocyanate prepolymers is not easily interfered by moisture in the air. These factors endow polyurethane elastomers with excellent properties such as strength, wear resistance, heat resistance, and high elasticity. The physical form and reactivity of chain extenders / curing agents are closely related to operability, and aromatic amine curing agents with mild reactivity and in liquid state are popular among industry insiders in fields such as cast polyurethane.

[0003] However, there are few varieties of aromatic diamine chain extenders with medium reactivity on the current market, and there are not many research reports in this regard. Regarding the reports on the synthesis of liquid aromatic diamines, the author of the master's thesis "Synthesis of Liquid MOCA and Its Application in Polyurethane Elastomers" condensed and synthesized a series of aromatic diamine samples using mixed amines and formaldehyde as raw materials. Specifically, o-chloroaniline (OCA) was used as the first aromatic monoamine raw material (accounting for more than 50% of the mixed amines), aniline was used as the second monoamine, and 2,5- and 2,6-dichloroaniline were used as the third and fourth monoamines in some formulations to obtain several liquid and solid aromatic diamine samples; it was found that for the system with o-chloroaniline and aniline as the main reaction raw materials, since symmetric and crystalline products 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA) and 4,4'-diaminodiphenylmethane (MDA) would be formed, the presence of more substances with asymmetric molecular structures in the products was beneficial for obtaining liquid products at room temperature. The Chinese invention patent with the application number 200810010746.5 discloses a production method of 3-chloro-3'-ethyl-4,4'-diaminodiphenylmethane. The reaction time of this method is 15 to 20 hours, and high-vacuum high-temperature distillation is used to collect the target product in the distillate fraction of 205 to 235°C. The above-mentioned existing research reports use highly reactive aniline and o-ethylaniline as monoamines other than OCA in the mixed amines. The primary amino groups of these monoamines have high activity, and the prepared aromatic diamines have high activity, making their reaction with aromatic polyisocyanate prepolymers fast and the operation time short. They can only be used in fields such as epoxy resins and reaction injection molding polyurethane ureas and are not widely used in the polyurethane industry.

[0004] The commercially available medium- and low-reactivity liquid aromatic diamine chain extender bis(sec-butylamino) diphenyl methane (MDBA, Unilink4200 or Wanalink6200) is generally obtained by reacting 4,4'-diaminodiphenyl methane (MDA) with methyl ethyl ketone to obtain a ketimine and simultaneously carrying out catalytic hydrogenation, converting the primary amino group of highly reactive MDA into a secondary amino group with a certain steric hindrance, thereby reducing the reactivity, and the product is liquid. However, the preparation process of this chain extender requires a reaction under high-pressure conditions. SUMMARY OF THE INVENTION

[0005] In view of this, the object of the present invention is to overcome the deficiencies of the prior art and provide a method for preparing a liquid polyurethane curing agent mainly composed of an aromatic diamine with a medium reactivity and an asymmetric molecular structure under normal pressure, that is, to provide a method for preparing a liquid aromatic amine curing agent containing secondary amino groups and primary amino groups.

[0006] To achieve the above object, the technical solution adopted in the present invention is to condense medium-reactivity o-chloroaniline and N-ethylaniline (a mixture of two monoamines is simply referred to as "mixed amine") together with paraformaldehyde under acidic conditions. The o-chloroaniline and N-ethylaniline are connected by a methylene bridge to synthesize an aromatic diamine with an asymmetric molecular structure - 3-chloro-4-amino-4'-ethylaminodiphenyl methane, an aromatic amine polyurethane curing agent.

[0007] The reaction formula for synthesizing the main product 3-chloro-4-amino-4'-ethylaminodiphenyl methane is as follows:

[0008]

[0009] In addition, in the synthesis product, there are also symmetry molecular structure products MOCA and 4,4'-bis(ethylamino)diphenyl methane formed by the condensation of o-chloroaniline and N-ethylaniline with formaldehyde respectively, and a small amount of products such as triphenyl ring triamine. Among them, 3-chloro-4-amino-4'-ethylaminodiphenyl methane, 4,4'-bis(ethylamino)diphenyl methane and the triamine product are all liquid when stored alone at room temperature, while MOCA is solid. If the content of MOCA is high, a part of it will crystallize out, so the content of MOCA in the product mixture needs to be controlled; and because the cost of N-ethylaniline is higher than that of o-chloroaniline, a balance between cost and application form (liquid at room temperature) needs to be achieved.

[0010] In order to obtain a liquid product with stable storage, considering the cost and the difference in reactivity between o-chloroaniline and N-ethylaniline, and to reduce the content of MOCA in the product mixture, the molar ratio of o-chloroaniline to N-ethylaniline is controlled at 1:(0.6 - 2). If the amount of N-ethylaniline increases, although the resulting product is liquid, the cost increases; if the proportion of o-chloroaniline in the mixed amine increases, the content of MOCA in the product mixture is high, and crystallization is likely to occur when cooled to room temperature, and the resulting product is paste-like or a solid with a low melting point.

[0011] In order to better dissolve or uniformly disperse the hydrophobic aromatic organic mixed amine raw material in water, hydrochloric acid is used as a catalyst and a salifying agent, and the reaction system is maintained acidic. The molar ratio of hydrochloric acid to the mixed amine is controlled at (1.05 - 1.30):1. If the amount of hydrochloric acid is so low that the ammonium salt aqueous solution is neutral or alkaline, the reaction cannot proceed; if the amount of hydrochloric acid increases beyond the above range, the yield will not increase significantly or the reaction time will not be shortened. On the contrary, more neutralizing agent will be consumed, resulting in waste and an increase in the amount of post-treatment.

[0012] Since the reaction of aqueous formaldehyde solution with aniline derivatives is faster than that of paraformaldehyde, and the reaction with paraformaldehyde is more stable, paraformaldehyde is used as the formaldehyde source in the present invention. Commonly used aqueous formaldehyde solution contains 8% - 15% methanol as a stabilizer to prevent the polymerization and crystallization of formaldehyde. Compared with using aqueous formaldehyde solution, when paraformaldehyde is used as the formaldehyde source, there is no methanol in the reaction system, which is also beneficial for wastewater treatment. Paraformaldehyde is an oligomer of formaldehyde with high purity. It slowly decomposes into monomolecular formaldehyde in an acidic medium and participates in the reaction. Therefore, when measuring the dosage in the following formula, formaldehyde (molecular weight 30 g / mol) is still used as the measurement unit for its dosage. For example, 30 g of paraformaldehyde is equivalent to 30 g (1 mol) of pure formaldehyde.

[0013] The molar ratio of formaldehyde to the mixed amine is controlled in the range of (0.4 - 0.5):1. If the amount of formaldehyde is low, there will be a lot of aromatic monoamine residue after the reaction, and the efficiency of the reaction vessel will be reduced; if formaldehyde is in excess, the content of polyfunctional products in the product increases, resulting in an increase in viscosity.

[0014] If the aromatic amine raw material and the product come into contact with oxygen during the reaction process, a small amount will be oxidized and the color will become darker. In order to remove the dissolved oxygen in the raw material medium and prevent oxidation during the reaction and post-treatment processes, the present invention uses a small amount of organic color-changing inhibitors, including one of hydrazine hydrate, hydroxylamine hydrochloride, hydroxylamine, N,N-dibenzylhydroxylamine, etc. The dosage is 0.2% - 1.0% of the aromatic amine. A small amount of color-changing inhibitor is added to the reaction system at the initial stage of the reaction and the post-treatment stage respectively. Compared with the ferrous and stannous inorganic salts used in some processes, these organic color-changing inhibitors can be decomposed at high temperature and are easily removed, which can reduce the pollution of divalent and polyvalent metal ions to the polyurethane curing agent product.

[0015] After the condensation reaction (methylenation) is completed, neutralize hydrochloric acid with an aqueous sodium hydroxide solution. The molar ratio of sodium hydroxide to hydrochloric acid is about 1:1, and it is advisable that the aqueous solution after neutralization is weakly alkaline, with a pH value range of 8-10.

[0016] The synthesis process of the present invention is as follows:

[0017] (1) Add hydrochloric acid, a color change inhibitor and a small amount of water into a reaction vessel. While stirring at 20-40 °C, add o-chloroaniline and N-ethylaniline to make an aqueous solution of ammonium salt at 40-50 °C.

[0018] (2) React under nitrogen protection. Add paraformaldehyde powder in 2-3 batches to the aqueous solution of mixed amine hydrochloride at 45-60 °C, and add it all within 1 hour at a reaction temperature between 50-70 °C. It can be seen that the solid powder slowly dissolves. After adding paraformaldehyde, raise the temperature to 80 °C within 1-2 hours, and then react at 80-90 °C for 3-4 hours to obtain a crude product mainly composed of asymmetric aromatic diamine.

[0019] (3) Cool to about 50 °C, add an aqueous sodium hydroxide solution (caustic soda) for neutralization until the pH value is about 8-10. Let it stand and separate to remove the lower layer of inorganic salt aqueous solution. The organic layer is first washed twice with a small amount of hot water to remove the residual inorganic salts in the organic phase. Then a small amount of color change inhibitor can be added, and the excess unreacted o-chloroaniline and N-ethylaniline are distilled out by vacuum distillation and can be recycled for reuse in the next synthesis. The product is a light yellow transparent liquid.

[0020] The main component in the product is a mixture of aromatic diamines, and it also contains a small amount of isomers and triphenyl ring products, generally within 10%. Since the functionality of these components is not less than 2, it does not affect its application as a polyurethane chain extender and curing agent, and there is no need to separate the diamine and a small amount of triamine products in the product mixture by methods such as high-vacuum high-temperature distillation.

[0021] The aqueous phase containing sodium chloride contains trace amounts of aromatic amines, which can be extracted with a small amount of butyl acetate or toluene; the aqueous solution produced by washing the aromatic amine product is also extracted with the above-mentioned water-insoluble solvents, and then separated by distillation. The small amount of aromatic amine raw materials accumulated can be recycled after analyzing their content, that is, added as raw materials during reproduction. Butyl acetate or toluene is distilled and recycled for reuse. The sodium chloride obtained by evaporating the aqueous phase can be used as industrial salt. The synthesis process of the present invention is more environmentally friendly than the traditional synthesis process of methylene diphenylamine derivatives.

[0022] This type of liquid aromatic secondary diamine is mainly used as a chain extender or curing agent in polyurethane and polyurea systems. Because it is a liquid, it is convenient to use and can be used in the production of cast polyurethane elastomers by low-temperature processes, as well as in two-component polyurethane CASE materials cured at room temperature, including polyurethane waterproof coatings, two-component glues for polyurethane plastic tracks, two-component room-temperature curing adhesives, and sealants / potting compounds, etc. Detailed implementation mode

[0023] The preferred implementation modes of the present invention will be described in detail below.

[0024] Example 1

[0025] 80 g of water and 134 g of 30% hydrochloric acid were added to a 500 mL four-necked reaction flask equipped with a stirrer, a thermometer, a reflux condenser, and a dropping funnel. 0.5 g of 50% hydrazine hydrate was added. Under nitrogen protection and stirring, 77 g of o-chloroaniline and 48.5 g of N-ethylaniline were added. After stirring evenly, 13.5 g of paraformaldehyde was added in 3 batches every 20 minutes at 45 - 60 °C. Then, the temperature was slowly raised to 70 °C within 1 hour (the paraformaldehyde had basically dissolved), and then raised to 80 °C within 1 hour. Then, the reaction was carried out at 85 °C for 3 hours and cooled;

[0026] 142 g of 31% sodium hydroxide solution was added, and the mixture was cooled to 40 °C under stirring, allowed to stand for liquid separation, and the organic phase (oil phase) was washed twice with 20 g of hot water at 50 °C. 0.1 g of hydroxylamine was added, and then vacuum distillation was carried out. A small amount of unreacted N-ethylaniline, o-chloroaniline, and water were distilled off. After cooling, 108.9 g of a dry and anhydrous light yellow liquid product was obtained. The yield based on formaldehyde was 92.4%. By high-performance liquid chromatography analysis, it was measured that 3-chloro-4-amino-4'-ethylaminodiphenylmethane was about 45.9%, 3,3'-dichloro-4,4'-diaminodiphenylmethane was about 29.7%, the content of bis(N-ethylamino)diphenylmethane was about 14.3%, and the trifunctional aromatic amine compound, etc., was about 10.1%. The amine equivalent was about 130.4. It remained liquid after being placed at 25 °C for 1 month.

[0027] A total of about 21 g of two aromatic monoamines recovered by vacuum distillation and water phase extraction were recovered. By gas chromatography detection, o-chloroaniline accounted for about 64% and N-ethylaniline accounted for about 36%.

[0028] Example 2

[0029] Add 180 g of water and 233 g of 30% hydrochloric acid to a 1000 mL four-necked reaction flask. Add 1.1 g of hydroxylamine hydrochloride. After stirring evenly, under nitrogen protection and stirring, add 103 g of o-chloroaniline and 97 g of N-ethylaniline (the total amount of o-chloroaniline and N-ethylaniline is the aromatic monoamine). Add 24 g of paraformaldehyde in 6 portions at intervals of 10 minutes at 45 - 60 °C. Then slowly heat up to 70 °C within 1 hour, and then heat up to 80 °C within 1 hour. Then react at 80 °C for 3.5 hours and cool to about 50 °C;

[0030] Add 250 g of 31% sodium hydroxide solution, cool to 40 °C under stirring, let it stand for liquid separation. Wash the organic phase (oil phase) twice with 25 g of hot water at 50 °C, add 0.1 g of hydroxylamine, and then distill under reduced pressure to distill out a small amount of unreacted N-ethylaniline, o-chloroaniline and water. After cooling, obtain 190.5 g of a dry and water-free light yellow liquid product. The yield based on formaldehyde is about 91.3%. By high performance liquid chromatography analysis, it is found that 3-chloro-4-amino-4'-ethylaminodiphenylmethane is about 51.5%, 3,3'-dichloro-4,4'-diaminodiphenylmethane is about 20.1%, the content of bis(N-ethylamino)diphenylmethane is about 19.1%, other diamines and triamines are about 9.7%, and the amine equivalent is about 131.2. It remains liquid after being placed at 25 °C for 3 months.

[0031] Example 3

[0032] Add 180 g of water and 192 g of 30% hydrochloric acid to a 1000 mL four-necked reaction flask. Add 1.5 g of 50% hydrazine hydrate aqueous solution. Under nitrogen protection and stirring, add 77 g of o-chloroaniline and 109.1 g of N-ethylaniline. After stirring evenly, add 18 g of paraformaldehyde in 5 portions at intervals of 15 minutes at 45 - 60 °C. Then slowly heat up to 85 °C within 1.5 hours, and then react at 85 - 90 °C for 3.5 hours and cool to about 50 °C;

[0033] Add 220 g of 31% sodium hydroxide solution, stir evenly and cool to 40 °C, let it stand for liquid separation. Perform steam distillation on the organic phase (oil phase) to distill out the free monoamine for the next synthesis. Wash with 40 g of hot water at 50 °C. Add 0.2 g of hydroxylamine to the oil phase, and then remove water under reduced pressure at -0.095 MPa × 100 °C. After cooling, obtain 147.8 g of a light yellow liquid product. The yield based on formaldehyde is about 95%. Among them, 3-chloro-4-amino-4'-ethylaminodiphenylmethane is about 50.3%, 3,3'-dichloro-4,4'-diaminodiphenylmethane is about 11.4%, the content of bis(N-ethylamino)diphenylmethane is about 29.9%, triamines, etc. are about 8.4%, and the amine equivalent is about 130. It remains liquid after being placed at 25 °C for 3 months.

[0034] Example 4

[0035] Using similar steps and process conditions as in Example 1, a 1000 mL three-necked flask was used, with 180 g of water, 63.8 g of o-chloroaniline, 121.2 g of N-ethylaniline, 20.3 g of paraformaldehyde, 210 g of 30% hydrochloric acid, 230 g of 31% sodium hydroxide solution, 0.3 g of hydroxylamine for the first time, and 0.1 g of hydroxylamine for the second time. After post-treatment, 163 g of a light yellow to yellow liquid product was obtained. The yield based on formaldehyde was approximately 93.1%, among which 3-chloro-4-amino-4'-ethylaminodiphenylmethane was approximately 44.8%, 3,3'-dichloro-4,4'-diaminodiphenylmethane was approximately 8.9%, the content of bis(N-ethylamino)diphenylmethane was approximately 38.5%, triamine, etc. was approximately 7.8%, and the amine equivalent was approximately 129.3. It remained liquid after being placed at 25°C for 3 months.

[0036] Example 5

[0037] Using similar steps and process conditions as in Example 2, the amount of o-chloroaniline used was 89.3 g, the amount of N-ethylaniline used was 106 g, the amount of paraformaldehyde was 23.6 g, the amount of 30% hydrochloric acid was 249 g, the amount of 31% sodium hydroxide solution was 268 g, and other raw materials were the same as in Example 2. After post-treatment, 188.2 g of a light yellow liquid product was obtained. The yield based on formaldehyde was approximately 92%, among which 3-chloro-4-amino-4'-ethylaminodiphenylmethane was approximately 50.8%, 3,3'-dichloro-4,4'-diaminodiphenylmethane was approximately 15.7%, the content of bis(N-ethylamino)diphenylmethane was approximately 24.1%, triamine, etc. was approximately 9.4%, and the amine equivalent was approximately 129.9. It remained liquid after being placed at 25°C for 3 months.

[0038] Comparative Example 1

[0039] Using similar steps and process conditions as in Example 4, the difference was that the amount of o-chloroaniline used was 127.6 g and the amount of N-ethylaniline used was 60.6 g, and other raw materials were the same as in Example 4. After post-treatment, 163.5 g of a light yellow liquid product was obtained. The yield based on formaldehyde was approximately 91.9%, among which 3-chloro-4-amino-4'-ethylaminodiphenylmethane was approximately 43.2%, 3,3'-dichloro-4,4'-diaminodiphenylmethane was approximately 37.8%, the content of bis(N-ethylamino)diphenylmethane was approximately 9.8%, triamine, etc. was approximately 9.2%, and the amine equivalent was approximately 131.5. It started to become paste-like after being placed at 25°C for 2 days and had no fluid state after 7 days.

[0040] Comparative Example 2

[0041] In this example, the raw materials and process conditions used were basically the same as in Example 2, except that no discoloration inhibitor was added, and 191.1 g of a brown liquid product was obtained, which remained liquid after being placed for 3 months.

[0042] The above embodiments are only used to illustrate the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. However, it should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of a liquid aromatic amine curing agent containing secondary amino groups and primary amino groups, characterized in that: Using o-chloroaniline and N-ethylaniline mixed as the aromatic monoamine raw material, a condensation reaction is carried out with formaldehyde in the presence of a discoloration inhibitor and an inorganic acid catalyst, and the liquid target product is obtained after post-treatment; A small amount of organic discoloration inhibitor is added in the initial stage of the reaction and during the post-treatment process to eliminate the discoloration problem of aromatic amines caused by dissolved oxygen and oxygen. The discoloration inhibitor is one selected from hydrazine hydrate, hydroxylamine hydrochloride, hydroxylamine and N,N-dibenzylhydroxylamine, and the dosage is 0.2% - 1.0% of the mass of the mixed amine; The molar ratio of o-chloroaniline to N-ethylaniline is 1∶(0.6 - 2); using paraformaldehyde as the formaldehyde source, the molar ratio of formaldehyde to the mixed amine is (0.4 - 0.5)∶1, and the mixed amine is a mixture of o-chloroaniline and N-ethylaniline.

2. The preparation method of the liquid aromatic amine curing agent containing secondary amino group and primary amino group according to claim 1, wherein: The inorganic acid is hydrochloric acid; the water-insoluble mixed amine is dissolved with hydrochloric acid to form an aqueous solution of ammonium salt; the molar ratio of hydrochloric acid to the mixed amine ranges from (1.05 - 1.30)∶1.

3. The preparation method of the liquid aromatic amine curing agent containing secondary amino group and primary amino group according to claim 1, characterized in that, The process steps and reaction conditions are as follows: (1)The temperature for neutralizing and dissolving the mixed amine with hydrochloric acid to form an aqueous solution of mixed amine hydrochloride is controlled below 50°C; (2)Under nitrogen protection, paraformaldehyde is added for the condensation reaction. The reaction temperature is controlled at 50 - 90°C, and the temperature is increased step by step in the order of first low temperature and then high temperature. The reaction time is 3 - 8 hours; (3)After the reaction is completed, an aqueous sodium hydroxide solution is added to adjust the pH value to 8 - 10. After the neutralization reaction is completed, the mixture is allowed to stand for liquid separation. The organic phase is washed with water and then evacuated to collect the unreacted o-chloroaniline and N-ethylaniline, and at the same time, the water is removed by evacuation to obtain a light-colored viscous liquid product.

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