CN116120189A - Preparation method of liquid aromatic amine curing agent containing secondary amino groups and primary amino groups - Google Patents

Abstract

The invention discloses a method for preparing aromatic diamine by using o-chloroaniline and N-ethylaniline as aromatic monoamine raw materials and reacting with paraformaldehyde in hydrochloric acid aqueous solution. The synthetic process has good environmental protection, and the obtained novel aromatic diamine contains primary amino and secondary amino with mild reaction activity, has light color and liquid state at normal temperature, and can be used as a curing agent component in various two-component polyurethane systems.

Description

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

Technical Field

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

Background

Chain extenders are important auxiliaries for elastomeric polyurethane materials and can be used directly as curing agents or for formulating the curing agent components. The aromatic amine chain extender/curing agent contains benzene rings, so that the modulus and heat resistance of polyurethane can be improved; and the ureido generated by the reaction of the amino group and isocyanate can form a stronger hydrogen bond; the reaction of the amine curing agent and the isocyanate prepolymer is not easy to be interfered by moisture in the air. These factors give polyurethane elastomers excellent in strength, abrasion resistance, heat resistance, high elasticity, etc. The physical form and reactivity of the chain extender/curing agent are closely related to operability, and aromatic amine curing agents which are mild in reactivity and liquid are welcomed by those skilled in the art of cast polyurethane and the like.

However, the variety of the aromatic diamine chain extender with medium reactivity on the market is few, and the research on the variety is not reported. The report about the synthesis of liquid aromatic diamine, namely, the authors of the 'liquid MOCA synthesis and the application of the liquid MOCA in polyurethane elastomer' in the 'master graduation paper' take mixed amine and formaldehyde as raw materials to synthesize a series of aromatic diamine samples, specifically, o-chloroaniline (OCA) is taken as a first aromatic monoamine raw material (accounting for more than 50% of the mixed amine), aniline is taken as a second monoamine, and 2,5-, 2, 6-dichloroaniline is taken as third monoamine and fourth monoamine in partial formula, so that a plurality of liquid and solid aromatic diamine samples are obtained; it has been found that, in a system using o-chloroaniline and aniline as main reaction materials, 3' -dichloro-4, 4' -diaminodiphenylmethane (MOCA) and 4,4' -diaminodiphenylmethane (MDA) which are symmetrical in molecular structure and crystalline are produced, and that a substance having a large amount of an asymmetrical molecular structure in the product is advantageous for obtaining a liquid product at room temperature. The Chinese patent application No. 200810010746.5 discloses a production method of 3-chloro-3 '-ethyl-4, 4' -diaminodiphenyl methane, which has the reaction time of 15-20 hours and adopts high vacuum high-temperature distillation to collect 205-235 ℃ fractional stage target product. The prior researches report that aniline and o-ethylaniline with higher activity are used as monoamines except OCA in mixed amine, the primary amino activity of the monoamines is higher, and the prepared aromatic diamine has high activity, so that the aromatic diamine has fast reaction with an aromatic polyisocyanate prepolymer, has short operation time, can only be used in the fields of epoxy resin, reaction injection molding polyurethane urea and the like, and has little application in the polyurethane industry.

Commercially available liquid aromatic diamine chain extender bis (sec-butylamino) diphenylmethane (MDBA, unilink4200 or Wanalink 6200) is generally obtained by reacting 4,4' -diaminodiphenylmethane (MDA) with methyl ethyl ketone to obtain ketimine and simultaneously carrying out catalytic hydrogenation, wherein primary amino groups of MDA with high reactivity are converted into secondary amino groups with certain steric hindrance, so that the reactivity is reduced, and the product is in a liquid state. However, the preparation of the chain extender requires reaction under high pressure conditions.

Disclosure of Invention

In view of the above, the present invention aims to overcome the shortcomings of the prior art and provide a method for preparing a liquid polyurethane curing agent with moderate reactivity and asymmetric molecular structure aromatic diamine as a main component at normal pressure, namely a method for preparing a liquid aromatic amine curing agent with secondary amino groups and primary amino groups.

In order to achieve the aim, the technical scheme adopted by the invention is that o-chloroaniline and N-ethylaniline (the mixture of two monoamines is simply called as mixed amine) with medium reactivity are condensed with paraformaldehyde under the acidic condition, and the o-chloroaniline and the N-ethylaniline are connected through a methylene bridge to synthesize an aromatic amine polyurethane curing agent containing aromatic diamine with an asymmetric molecular structure, namely 3-chloro-4-amino-4' -ethylamino-diphenylmethane.

The reaction formula for synthesizing the main product 3-chloro-4-amino-4' -ethylamino-diphenyl methane is as follows:

in addition, the synthetic products also comprise symmetrical molecular structure products MOCA and 4,4' -di (ethylamino) diphenylmethane formed by condensing o-chloroaniline and N-ethylaniline with formaldehyde respectively, and a small amount of products such as tri-benzene ring triamine. Wherein the 3-chloro-4-amino-4 '-ethylaminodiphenylmethane, 4' -di (ethylamino) diphenylmethane and the triamine product are all liquid when stored separately at room temperature, while the MOCA is solid, and if the MOCA content is high, a part of the MOCA will crystallize out, so the MOCA content in the product mixture needs to be controlled; because the cost of N-ethylaniline is higher than that of o-chloroaniline, the balance between the cost and the application form (normal temperature liquid state) needs to be obtained.

In order to obtain a liquid product which is stable in storage, and taking into account the differences in cost and reactivity between the o-chloroaniline and the N-ethylaniline, the MOCA content in the product mixture is reduced, and the molar ratio of the o-chloroaniline to the N-ethylaniline is controlled to be 1:0.6-2. If the amount of N-ethylaniline is increased, the cost increases although the product obtained is in the liquid state; if the o-chloroaniline ratio in the mixed amine is increased, the MOCA content in the product mixture is high, crystallization is easy to generate when the product mixture is cooled to room temperature, and the obtained product is pasty or low-melting-point solid.

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 kept acidic, and the molar ratio of the hydrochloric acid to the mixed amine is controlled to be (1.05-1.30) to 1. If the amount of hydrochloric acid is so low that the aqueous ammonium salt solution is neutral or alkaline, the reaction cannot proceed; if the amount of hydrochloric acid is increased beyond the above range, the yield is not increased significantly or the reaction time is shortened, but more neutralizing agent is consumed, resulting in waste and an increase in the post-treatment amount.

Because the aqueous formaldehyde solution reacts with aniline derivatives faster than paraformaldehyde, the reaction with paraformaldehyde is smoother, and paraformaldehyde is used as a formaldehyde source in the invention. The common formaldehyde aqueous solution contains 8% -15% of methanol as a stabilizer for preventing formaldehyde from polymerizing and crystallizing. Compared with the formaldehyde aqueous solution, the paraformaldehyde is used as a formaldehyde source, the reaction system does not contain methanol, and the method is also beneficial to wastewater treatment. Paraformaldehyde is an oligomer of formaldehyde, has high purity, and is slowly decomposed into single-molecule formaldehyde in an acidic medium to participate in the reaction. Thus, in the case of the following formulation, formaldehyde (molecular weight 30 g/mol) is still used as metering unit for its use, for example 30g of paraformaldehyde corresponds to 30g (1 mol) of pure formaldehyde.

The molar ratio of formaldehyde to mixed amine is controlled in the range of (0.4-0.5) to 1. If the formaldehyde consumption is low, the aromatic monoamine residue is more after the reaction is finished, and the efficiency of the reaction vessel is reduced; if formaldehyde is excessive, the polyfunctional product content in the product increases, resulting in an increase in viscosity.

The aromatic amine raw material and product can be oxidized in a small amount if contacting oxygen in the reaction process, the color is darkened, in order to eliminate the dissolved oxygen in the raw material medium and prevent the oxidation in the reaction and post-treatment process, the invention uses a small amount of organic discoloration inhibitor, including one of hydrazine hydrate, hydroxylamine hydrochloride, hydroxylamine, N-dibenzyl hydroxylamine and the like, the dosage is 0.2-1.0 percent of aromatic amine, and a small amount of discoloration inhibitor is respectively added into the reaction system in the initial stage and the post-treatment stage of the reaction. Compared with ferrous and stannous inorganic salts used in certain processes, the organic discoloration inhibitor can be decomposed at high temperature and is easy to remove, and pollution of divalent and polyvalent metal ions to polyurethane curing agent products can be reduced.

After the condensation reaction (methylene) is finished, the hydrochloric acid is neutralized by sodium hydroxide aqueous solution, wherein the molar ratio of the sodium hydroxide to the hydrochloric acid is about 1:1, and the pH value of the neutralized aqueous solution is preferably in a weak alkaline state and is in a range of 8-10.

The synthesis process comprises the following steps:

(1) Hydrochloric acid, a discoloration inhibitor and a small amount of water are added into a reaction vessel, o-chloroaniline and N-ethylaniline are added under stirring at the temperature of 20-40 ℃ to form an aqueous solution of ammonium salt at the temperature of 40-50 ℃.

(2) Reacting under nitrogen protection, adding paraformaldehyde powder into mixed amine hydrochloride aqueous solution at 45-60 ℃ in 2-3 batches, finishing the adding within 1 hour at the reaction temperature of 50-70 ℃, slowly dissolving the solid powder, heating to 80 ℃ within 1-2 hours after finishing adding the paraformaldehyde, and then reacting for 3-4 hours at 80-90 ℃ to obtain a crude product taking the asymmetric aromatic diamine as a main component.

(3) Cooling to about 50 ℃, adding sodium hydroxide aqueous solution (liquid alkali) for neutralization until the pH value is about 8-10, standing, separating and removing the lower inorganic salt aqueous solution, washing an organic layer with a small amount of hot water for 2 times, removing the residual inorganic salt in the organic phase, adding a small amount of discoloration inhibitor, distilling out excessive unreacted o-chloroaniline and N-ethylaniline through vacuum distillation, and reusing the mixture in the synthesis process. The product was a pale yellow transparent liquid.

The main component of the product is an aromatic diamine mixture, and the product contains a small amount of isomers and a small amount of triamine, which is generally within 10%, because the functionality of the components is not lower than 2, the application of the components as a polyurethane chain extender and a curing agent is not affected, and the diamine and a small amount of triamine in the product mixture are not required to be separated by a high-vacuum high-temperature distillation method and the like.

The aqueous phase containing sodium chloride contains trace aromatic amine, and can be extracted by using a small amount of butyl acetate or toluene; the aqueous solution produced by washing the aromatic amine product is also extracted with the above water-insoluble solvent, and then distilled to separate, and the accumulated small amount of aromatic amine raw material can be recovered and reused after analyzing the content thereof, i.e., added as raw material in reproduction. Butyl acetate or toluene is distilled and recovered for reuse. The sodium chloride obtained by evaporating the aqueous phase can be used as industrial salt. The synthesis process of the invention is more environment-friendly than the traditional synthesis process of methylenedianiline derivatives.

The liquid aromatic secondary amine is mainly used as a chain extender or a curing agent of polyurethane and polyurea systems, is liquid, is convenient to use, and can be used for producing casting polyurethane elastomer by a low-temperature process, and room-temperature-curing double-component polyurethane CASE materials, including polyurethane waterproof paint, polyurethane plastic runway double-component glue, double-component room-temperature-curing adhesive, sealant/pouring sealant and the like.

Detailed Description

The following detailed description of the preferred embodiments of the present invention will be provided in connection with.

Example 1

Adding 80g of water, 134g of hydrochloric acid with the concentration of 30% and 0.5g of hydrazine hydrate with the concentration of 50% into a 500mL four-port reaction bottle provided with a stirrer, a thermometer, a reflux condenser and a dropping funnel, adding 77g of o-chloroaniline and 48.5g of N-ethylaniline under the protection of nitrogen and stirring, adding 13.5g of paraformaldehyde in 3 batches every 20 minutes at 45-60 ℃ after stirring uniformly, then slowly heating to 70 ℃ within 1 hour (the paraformaldehyde is basically dissolved), heating to 80 ℃ within 1 hour, then reacting for 3 hours at 85 ℃, and cooling;

142g of 31% sodium hydroxide solution is added, the mixture is stirred and cooled to 40 ℃, the mixture is stood and layered, the organic phase (oil phase) is respectively washed 2 times with 20g of 50 ℃ hot water, 0.1g of hydroxylamine is added, then reduced pressure distillation is carried out, a small amount of unreacted N-ethylaniline, o-chloroaniline and water are distilled out, and the mixture is cooled to obtain 108.9g of dry anhydrous pale yellow liquid product. The yield was 92.4% based on formaldehyde, and it was found by HPLC analysis that 3-chloro-4-amino-4 ' -ethylaminodiphenylmethane was about 45.9%, 3' -dichloro-4, 4' -diaminodiphenylmethane was about 29.7%, bis (N-ethylamino) diphenylmethane was about 14.3%, trifunctional arylamine compound was about 10.1%, and amine equivalent was about 130.4. The liquid state is still obtained after the mixture is placed at 25 ℃ for 1 month.

About 21g of the two aromatic monoamines are recovered by reduced pressure distillation and water phase extraction, the o-chloroaniline is about 64% and the N-ethylaniline is about 36% as detected by gas chromatography.

Example 2

180g of water and 233g of 30% hydrochloric acid are added into a 1000mL four-port reaction bottle, 1.1g of hydroxylamine hydrochloride is added, after uniform stirring, 103g of o-chloroaniline and 97g of N-ethylaniline (the total amount of the o-chloroaniline and the N-ethylaniline is aromatic monoamine) are added under the protection of nitrogen and stirring, 24g of paraformaldehyde is added every 10 minutes at 45-60 ℃, then the temperature is slowly increased to 70 ℃ within 1 hour, then the temperature is increased to 80 ℃ within 1 hour, then the reaction is carried out for 3.5 hours at 80 ℃, and the reaction product is cooled to about 50 ℃;

250g of 31% sodium hydroxide solution is added, the mixture is stirred and cooled to 40 ℃, the mixture is stood for layering, the organic phase (oil phase) is respectively washed 2 times by 25g of 50 ℃ hot water, 0.1g of hydroxylamine is added, then reduced pressure distillation is carried out, a small amount of unreacted N-ethylaniline, o-chloroaniline and water are distilled out, and the mixture is cooled to obtain 190.5g of dry anhydrous pale yellow liquid product. About 91.3% yield as formaldehyde, about 51.5% 3-chloro-4-amino-4 ' -ethylaminodiphenylmethane, about 20.1% 3,3' -dichloro-4, 4' -diaminodiphenylmethane, about 19.1% bis (N-ethylamino) diphenylmethane, about 9.7% other diamines and triamines, and about 131.2 amine equivalents as determined by high performance liquid chromatography. The solution was still in a liquid state after 3 months at 25 ℃.

Example 3

180g of water and 192g of 30% hydrochloric acid are added into a 1000mL four-port reaction bottle, 1.5g of 50% hydrazine hydrate aqueous solution is added, 77g of o-chloroaniline and 109.1g of N-ethylaniline are added under the protection of nitrogen and stirring, 18g of paraformaldehyde is added every 15 minutes at 45-60 ℃ after uniform stirring, then the temperature is slowly raised to 85 ℃ within 1.5 hours, then the reaction is carried out for 3.5 hours at 85-90 ℃, and the reaction is cooled to about 50 ℃;

220g of 31% sodium hydroxide solution is added, stirred uniformly and cooled to 40 ℃, the mixture is stood for layering, the organic phase (oil phase) is distilled by steam, and free monoamine is distilled out for the next synthesis. Washing with 40g of 50 ℃ hot water, adding 0.2g of hydroxylamine into the oil phase, then decompressing and dehydrating at-0.095 MPa multiplied by 100 ℃, and cooling to obtain 147.8g of pale yellow liquid product. About 95% yield based on formaldehyde, wherein about 50.3% 3-chloro-4-amino-4 ' -ethylaminodiphenylmethane, about 11.4% 3,3' -dichloro-4, 4' -diaminodiphenylmethane, about 29.9% bis (N-ethylamino) diphenylmethane content, about 8.4% triamine, etc., and about 130 amine equivalent. The solution was still in a liquid state after 3 months at 25 ℃.

Example 4

Using a procedure and process conditions similar to example 1, using a 1000mL three-necked flask, 180g of water, 63.8g of o-chloroaniline, 121.2g of N-ethylaniline, 20.3g of paraformaldehyde, 210g of 30% hydrochloric acid, 230g of 31% sodium hydroxide solution, 0.3g of first hydroxylamine and 0.1g of second hydroxylamine. The work-up gives 163g of a pale yellow to yellow liquid product. About 93.1% yield based on formaldehyde, wherein about 44.8% of 3-chloro-4-amino-4 ' -ethylaminodiphenylmethane, about 8.9% of 3,3' -dichloro-4, 4' -diaminodiphenylmethane, about 38.5% of bis (N-ethylamino) diphenylmethane, about 7.8% of triamine, etc., and about 129.3% of amine equivalents. The solution was still in a liquid state after 3 months at 25 ℃.

Example 5

Using a procedure and process conditions similar to example 2, the amount of o-chloroaniline was 89.3g, the amount of N-ethylaniline was 106g, paraformaldehyde was 23.6g,30% hydrochloric acid 249g, and 31% sodium hydroxide solution 268g, other starting materials were the same as in example 2. Work-up gives 188.2g of a pale yellow liquid product. About 92% yield based on formaldehyde, wherein about 50.8% of 3-chloro-4-amino-4 ' -ethylaminodiphenylmethane, about 15.7% of 3,3' -dichloro-4, 4' -diaminodiphenylmethane, about 24.1% of bis (N-ethylamino) diphenylmethane, about 9.4% of triamine and the like, and about 129.9 amine equivalent. The solution was still in a liquid state after 3 months at 25 ℃.

Comparative example 1

The procedure and process conditions similar to those used in example 4 were employed, except that the amount of o-chloroaniline was 127.6g and the amount of N-ethylaniline was 60.6g, and the other starting materials were the same as in example 4. Work-up gives 163.5g of the product as a pale yellow liquid. The yield was about 91.9% based on formaldehyde, wherein 3-chloro-4-amino-4 ' -ethylaminodiphenylmethane was about 43.2%, 3' -dichloro-4, 4' -diaminodiphenylmethane was about 37.8%, bis (N-ethylamino) diphenylmethane was about 9.8%, triamine and the like was about 9.2%, and amine equivalent was about 131.5. The paste starts to be changed into paste after being placed at 25 ℃ for 2 days, and has no fluidity after 7 days.

Comparative example 2

The starting materials and process conditions used in this example were essentially the same as in example 2, except that no discoloration inhibitor was added, yielding 191.1g of a brown liquid product which remained liquid after 3 months.

The above embodiments are provided to illustrate 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 the same, and are not intended to limit the scope of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be construed to be included in the scope of the present invention.

Claims (7)

1. A preparation method of a liquid aromatic amine curing agent containing secondary amino groups and primary amino groups is characterized by comprising the following steps: mixing o-chloroaniline and N-ethylaniline as aromatic monoamine material, condensation reaction with formaldehyde in the presence of color change inhibitor and inorganic acid catalyst, and post-treatment to obtain liquid target product.

2. The method for preparing the secondary amino group and primary amino group-containing liquid aromatic amine curing agent according to claim 1, wherein the method comprises the following steps: the molar ratio of the o-chloroaniline to the N-ethylaniline is 1:0.6-2.

3. The method for preparing the secondary amino group and primary amino group-containing liquid aromatic amine curing agent according to claim 1, wherein the method comprises the following steps: the inorganic acid is hydrochloric acid; dissolving a water-insoluble mixed amine with hydrochloric acid to form an aqueous solution of an ammonium salt; the mol ratio of the hydrochloric acid to the mixed amine is (1.05-1.30) to 1.

4. The method for preparing the secondary amino group and primary amino group-containing liquid aromatic amine curing agent according to claim 1, wherein the method comprises the following steps: the paraformaldehyde is used as formaldehyde source, and the molar ratio of formaldehyde to mixed amine is (0.4-0.5) to 1.

5. The method for preparing the secondary amino group and primary amino group-containing liquid aromatic amine curing agent according to claim 1, wherein the method comprises the following steps: and adding a small amount of organic discoloration inhibitor in the initial reaction stage and the post-treatment process to eliminate the discoloration problem of the aromatic amine caused by dissolved oxygen and oxygen, wherein the discoloration inhibitor is a mixture formed by one or more of hydrazine hydrate, hydroxylamine hydrochloride, hydroxylamine and N, N-dibenzyl hydroxylamine, and the dosage of the discoloration inhibitor is 0.2-1.0% of the mass of the mixed amine.

6. The method for preparing the secondary amino group and primary amino group-containing liquid aromatic amine curing agent according to claim 1, wherein the process steps and the reaction conditions are as follows:

(1) Neutralizing and dissolving the mixed amine with hydrochloric acid to form a mixed amine hydrochloride aqueous solution, wherein the temperature is controlled below 50 ℃;

(2) Under the protection of nitrogen, adding paraformaldehyde for condensation reaction, controlling the reaction temperature at 50-90 ℃, and raising the temperature stepwise according to the sequence of low temperature and high temperature, wherein the reaction time is 3-8 hours;

(3) And adding sodium hydroxide aqueous solution to a pH value of 8-10 after the reaction is finished, standing until the liquid is layered after the neutralization reaction is finished, washing an organic phase with water, vacuumizing, collecting unreacted o-chloroaniline and N-ethylaniline, vacuumizing, and removing water to obtain a light-colored viscous liquid product.

7. The method for producing a secondary amino group-and primary amino group-containing liquid aromatic amine curing agent according to claim 1 or 6, wherein: the mixed amine obtained by distillation in the post-treatment process and the mixed amine obtained by extraction and separation in the water phase can be used as reaction raw materials; the sodium chloride obtained after the water phase is evaporated can be recycled as industrial salt, and the synthesis process is environment-friendly.