JPH06100534A - Production of bismaleimide - Google Patents

Abstract

PURPOSE:To obtain a high-purity bismaleimide in an easily separable and recoverable state in high yield by carrying out the dehydrative cyclization reaction of bismaleamic acid in the absence of an acid catalyst and an acid dehydration agent at a temperature lower than the temperature capable of suppressing the formation of by-product. CONSTITUTION:Bismaleamic acid obtained by reacting maleic anhydride with a diamine is subjected to dehydrative cyclization in the presence of a lower alcohol (especially preferably methanol) and a tertiary amine [preferably tri(1-10C alkyl)amine, especially triethylamine) at 0-40 deg.C (preferably 0-25 deg.C) using a carbodiimide (e.g. dicyclohexylcarbodiimide) as a dehydration agent to obtain a bismaleimide. Preferably, the amount of the carbodiimide is 2-10mol (especially 2-3mol), that of the lower alcohol is >=0.001mol and the tertiary amine is 0.01-50mol (especially 0.01-5mol) based on 1mol of bismaleamic acid.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing high-purity bismaleimide in high yield.

[0002]

Bismaleimide, alone or in combination with other monomers, forms a thermosetting product having excellent heat resistance and dimensional stability. In particular, this cured product does not show a significant decrease in mechanical strength and physical properties even at a high temperature of about 300 ° C. Therefore, the composite material of this cured product and glass fiber or carbon fiber is lightweight, has high strength, and has super heat resistance. Therefore, it is attracting attention as a highly reliable heat-resistant material for various members such as around aircraft or automobile engines.

The production of bismaleimide is carried out by reacting maleic anhydride with a diamine to synthesize bismaleamic acid in the first step, and then producing bismaleamide acid by dehydration ring closure to synthesize bismaleimide in the second step. It is produced by a two-step reaction, and usually the first and second steps are continuously performed.

Usually, the first-step reaction proceeds quantitatively, and in the conventional method, it is carried out at room temperature to 50 ° C. or lower. Next, the reaction in the second step is carried out by removing the condensed water while suppressing the formation of by-products.

As a method of removing the condensed water, a method of distilling the condensed water together with a solvent in the presence or absence of an acid catalyst is disclosed in, for example, JP-A-57-159764. However, this method requires a long reaction time at a high temperature, and a side reaction occurs due to the high temperature.
Moreover, there is a drawback that the yield of bismaleimide is low.

There is also a method of using a dehydrating agent such as acetic anhydride as in USP 3,018,290, but this method uses a large amount of water when separating and collecting the bismaleimide produced from the reaction solution after maleimidation. Therefore, there is a drawback in that a large amount of waste liquid containing acetic acid is produced, and it requires a great deal of cost to render it pollution-free. Furthermore, the yield and purity of bismaleimide are low.

When an acid is used as a dehydrating agent or a catalyst as in the above-mentioned conventional method, it is unavoidable that the acid remains in the produced bismaleimide.
This residual acid has an unfavorable effect on the curing reaction when curing the bismaleimide. Although the curing reaction mechanism of bismaleimide is complicated, in addition to the addition reaction by the carbon-carbon double bond derived from maleic anhydride as the main reaction, there is an addition reaction with the diamine used during curing, but the residual acid is It hinders the latter addition reaction and causes insufficient curing, resulting in a decrease in heat resistance of the cured product.

Further, JP-A-4-198166 and JP-A-4-198167 also propose a method in which an acid catalyst is not used in the production of bismaleimide in order to avoid such problems.

However, also in this method, the dehydration cyclization reaction for imidization of maleamic acid is carried out at a high temperature of 140 ° C. in order to azeotropically separate the condensed water produced. Under such a high temperature, a complicated side reaction progresses in addition to the desired reaction, and when a cured product is formed, the production of by-products that deteriorate the heat resistance increases.

As described above, the conventionally proposed method for producing a bismaleimide has many problems and is not satisfactory for industrial implementation.

[0011]

SUMMARY OF THE INVENTION Under the above circumstances, the present invention can be satisfied without using an acid catalyst or an acid dehydrating agent at a lower temperature that can suppress the by-products of the dehydration cyclization reaction of bismaleamic acid. It is an object of the present invention to provide a novel production method which can be carried out at a reaction rate that is possible, which is easy to separate and recover the produced bismaleimide, and which can obtain bismaleimide in high purity and high yield. .

[0012]

Means for Solving the Problems The inventors of the present invention have been earnestly researching to cyclize bismaleamic acid synthesized by maleic anhydride and diamine at low temperature in a short time, and surprisingly, carbodiimide It was found that the cyclization by the method proceeds in a solvent only in the coexistence of a lower alcohol and a tertiary amine, and a high-purity bismaleimide can be obtained in a high yield, and the present invention has been completed.

That is, according to the present invention, (1) a method for producing a bismaleimide which comprises dehydrating and ring-closing a bismaleamic acid with a carbodiimide in the presence of a lower alcohol and a tertiary amine, and (2) maleic anhydride and a diamine. And a bismaleamidic acid obtained by reacting with and a carbodiimide for dehydration ring closure in the coexistence of a lower alcohol and a tertiary amine.

Bismaleamic acid is synthesized by a known method from maleic anhydride and diamine.

The diamine is represented by the formula (3) H ₂ N—R′—NH ₂ (3) (wherein R ″ represents a divalent organic group).

As the divalent organic group in the formula (3),
An aliphatic group, an aromatic group, an alicyclic group, a heterocyclic group, or a group of a combination thereof, or those containing oxygen, sulfur, or -CO.
-, - SO -, - SO 2 -, - CONH-,

[0017]

[Chemical 1]

(Wherein R ³ and R ⁴ represent hydrogen or a C _1-3 alkyl group) and the like are included. These groups may be substituted with a halogen group, an alkoxy group or the like.

However, preferred among these are those having an aromatic group which may be substituted. For example,

[0020]

[Chemical 2]

(In the formula, R ⁵ represents hydrogen or a C _1-3 alkyl group)

[0022]

[Chemical 3]

(In the formula, R ⁶ represents a C _1-3 alkylene group)

[0024]

[Chemical 4]

{Where A is

[0026]

[Chemical 5]

(Wherein R ⁷ and R ⁸ represent hydrogen or a C _1-3 alkyl group),

[0028]

[Chemical 6]

(In the formula, R ⁹ and R ¹⁰ represent hydrogen or a C _1-3 alkyl group), —O—, —CO—, —SO—, —SO
_2- indicates -CONH-} and the like.

A preferred specific example is 4,4 '.
-Diaminobenzophenone, 2,2-bis (4-aminophenyl) propane, bis (4-aminophenyl) sulfone, bis (4-aminophenyl) ether, bis (3
-Chloro-4-aminophenyl) methane, (3-aminophenyl-4'-aminophenyl) methane, bis (3-
Aminophenyl) methane, bis (4-aminophenyl)
Examples include methane, 4-methyl-m-phenylenediamine, p- or m-xylylenediamine, p- or m-phenylenediamine.

In the production of bismaleamic acid, the amount of maleic anhydride to be used is 1 to 10 times, preferably 1.5 to 5 times, and more preferably 2 to 3 times the mol of the diamine. is there.

In the present invention, it is also possible to produce bismaleamic acid from maleic anhydride and diamine, and subsequently dehydrate and ring-close the bismaleamic acid to produce bismaleimide.
Also, the bismaleimide can be produced by separating the former step of producing bismaleamic acid and the latter step of dehydration ring closure of bismaleamic acid.

In the present invention, the dehydration ring-closing reaction of bismaleamic acid uses carbodiimide as a dehydrating agent.

In the conventional method, an acid catalyst such as acetic anhydride is used as a dehydrating agent, but this method requires a large amount of water when separating and recovering the bismaleimide produced from the reaction solution after maleimidation. Therefore, there is a drawback that a large amount of waste water containing an acid such as acetic acid is produced, and it takes a great deal of cost to render it pollution-free.

On the other hand, when carbodiimide is used as a dehydrating agent, water is not used when separating and recovering the produced bismaleimide, and an acid which requires neutralization after the reaction is not generated. From this point of view, the method for producing the bismaleimide according to the present invention is very simple and economical as compared with the conventional method.

The carbodiimide used in the present invention has the formula (4) R ₁ -N = C = N-R ₂ (4) (wherein R ₁ and R ₂ are hydrogen or a C _1-8 hydrocarbon group). Shown).

Examples of the C _1-8 hydrocarbon group in the formula (4) include methyl, ethyl, n-propyl, isopropyl and n.
-Butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isoamyl, tert-amyl,
alkyl groups such as n-hexyl, isohexyl, n-heptyl, n-octyl; cyclopropyl, cyclobutyl,
Examples thereof include cycloalkyl groups such as cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl; aromatic groups such as phenyl, benzyl, phenethyl, toluyl and xylyl.

Further, these hydrocarbon groups may be substituted with a group inert to this reaction. Examples thereof include C _1-3 alkoxy groups and halogens.

Examples of particularly preferable carbodiimides include dicyclohexylcarbodiimide, diphenylcarbodiimide, dimethylcarbodiimide, diethylcarbodiimide, di-p-toluylcarbodiimide and the like.

The amount of the carbodide used is 2 to 10 mol, preferably 2 to 5 mol, per 1 mol of bismaleamic acid.
Mol, and more preferably 2-3 mol.

The lower alcohol used in the present invention may be either a monoalcohol or a polyhydric alcohol as long as it is an alcohol containing 5 or less carbon atoms. For example, methanol, ethanol, propanol, isopropanol, butanol, Isobutanol, secondary butanol,
Examples include tert-butanol, amyl alcohols, ethylene glycol, glycerin and the like. A particularly preferred lower alcohol is methanol.

The amount of the lower alcohol used is not particularly limited as long as it is 0.001 mol or more per 1 mol of bismaleamic acid, and the lower alcohol itself may be used as a solvent.

The tertiary amine used in the present invention includes
For example, trimethylamine, triethylamine, tri-n
-Trialkylamines having an alkyl group having 1 to 10 carbon atoms such as butylamine, N, N-dimethylbenzylamine, N, N-diethylbenzylamine and other N,
N-dialkylbenzylamines and amines having a bicyclo structure such as diazabicyclo [2.2.2] octane and 1,8-diazabicyclo [5.4.0] 7-undecene can be used. A particularly preferred tertiary amine is triethylamine.

The amount of the tertiary amine used is 0.01 to 50 mol, preferably 0.01 to 10 mol, and more preferably 0.01 to 5 mol, per 1 mol of bismaleamic acid.

The solvent used in the present invention is not particularly limited as long as it is a non-aqueous solvent. However, since the reaction intermediate bismaleamic acid has a low solubility in general organic solvents, this bismaleamic acid can be used. Solvents that are soluble are preferred. For example, alcohols such as methanol, ethanol and isopropyl alcohol, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, ethers such as diethyl ether and dioxane, dichloromethane, 1,
2-dichloroethane, halogenated hydrocarbons such as p-dichlorobenzene, N, N-dimethylformamide, N,
N-dimethylacetamide, dimethyl sulfoxide, N
Examples thereof include polar solvents such as aprotic polar solvents such as -methyl-2-pyrrolidone.

The amount of the solvent used in the present invention is 1 to 1 part by weight of the total amount of maleic anhydride and diamine.
100 parts by weight, or 1 to 100 parts by weight with respect to 1 part by weight of bismaleamic acid.

As described above, in the present invention, the former step of producing bismaleamic acid from maleic anhydride and diamine and the latter step of producing bismaleimide by dehydration ring closure of bismaleamic acid are involved. Can be continuously carried out, or both steps can be separated to produce bismaleimide using separately prepared bismaleamic acid as a starting material. In the latter case, of course, the method for producing bismaleamic acid is not limited.

In the present invention, it is important to use carbodiimide as a dehydrating agent in the coexistence of a lower alcohol and a tertiary amine in the subsequent imidization reaction. These three are indispensable, and bismaleimide cannot be obtained without any of these. This reaction is
It can be made to proceed in a range of 0 to 40 ° C., preferably 0 to 25 ° C., without particular heating, under gentle stirring for 1 to 3 hours. The ability to carry out the reaction at such low temperatures is one of the important advantages of the present invention. At such a low temperature, formation of by-products such as isoimide can be suppressed,
The yield can be increased, and when the target bismaleimide is used as a curable resin, the heat resistance, which is a characteristic of this resin, can be further increased.

After completion of the reaction, the bismaleimide can be easily separated and recovered as follows. That is, the reaction mixture is concentrated by removing the solvent, ethyl acetate is added to this concentrated liquid to precipitate carbodiimide hydrate, and this is separated by filtration. The solvent can be further removed from the filtrate and dried to obtain a high-purity product bismaleimide.

As described above, in the present invention, the water released during the imidization is hydrated and trapped by the carbodiimide, and the hydrate can be easily precipitated and separated from the reaction system. Further, since an acid dehydrating agent or an acid catalyst is not used in the reaction, water is not required for separation / collection or washing of the produced bismaleimide, therefore, without being troubled by the problem of treating wastewater containing an acid, High-purity bismaleimide can be obtained from the reaction mixture by a simple operation.

The bismaleimide obtained according to the present invention does not contain an acid which inhibits the curing reaction. In addition, the present invention can carry out the imidization reaction at a low reaction temperature of 0 to 40 ° C. with a sufficient reaction rate, so that by-products can be suppressed and heat resistance and the like are reduced when bismaleimide is used as a cured product. Very few by-products such as isoimide are produced.

As described above, the bismaleimide obtained according to the present invention is not only high in purity, but also does not contain any impurities which are particularly problematic, or the amount thereof is extremely small.

[0053]

The present invention will be described in more detail with reference to the following examples.

Example 1 (Production of bismaleamic acid) 10.8 g of maleic anhydride
(0.11 mol), 100 g of 1,2-dichloroethane
It was then dissolved in the mixture and placed in a 300 ml four-necked flask equipped with a condenser, a thermometer, a dropping funnel and a stirrer.

At room temperature and with stirring, bis (4
A solution of 9.9 g (0.05 mol) of -aminophenyl) methane in 20 g of 1,2-dichloromethane was added to about 20.
The mixture was added dropwise over minutes, and stirring was continued for 15 minutes as it was to synthesize bismaleamic acid.

(Production of bismaleimide) After the completion of dropping, 23.8 g of dicyclohexylcarbodiimide was continuously obtained.
(0.115 mol), triethylamine 2.0 g (0.
02 mol) and 3.2 g (0.1 mol) of methanol were added, the mixture was cooled to 5 ° C., and stirring was continued for 3 hours.

Next, 100 g of ethyl acetate was added dropwise to the concentrated solution from which the solvent had been removed under reduced pressure, and the deposited precipitate was filtered, and then the solvent was removed under reduced pressure again to give bis (4-maleimidophenyl) methane 17. 2 g was obtained.

The yield was 96% in terms of bis (4-aminophenyl) methane, the purity was 95%, and the melting point was 157 ° C. The NMR chart is shown in FIG.

Example 2 19.7 g of phenyl bis (4-maleamic acid) methane
(0.05 mol) together with 150 g of 1,2-dichloroethane, 300 ml equipped with a cooling pipe, a thermometer and a stirrer
It was put in a 3-necked flask and dissolved.

Then dicyclohexylcarbodiimide 2
3.8 g (0.115 mol), triethylamine 2.0
g (0.02 mol) and 3.2 g (0.1 mol) of methanol were added, the mixture was cooled to 5 ° C., and stirring was continued for 3 hours.

Then, the same purification as in Example 1 was carried out to obtain 17.5 g of bis (4-maleimidophenyl) methane.

Yield 98%, purity 97%, melting point 15
It was 9 ° C.

Example 3 The same as Example 2 except that 1,2-dichloroethane was changed to methanol.

As a result, 17.0 g of bis (4-maleimidophenyl) methane was obtained. Yield 95%, Purity 9
The melting point was 4% and the melting point was 155 ° C.

Comparative Example 1 The procedure of Example 2 was repeated except that neither methanol nor triethylamine was added. As a result, generation of bis (4-maleimidophenyl) methane was not seen.

Comparative Example 2 The procedure of Example 2 was repeated except that methanol was not added. As a result, bis (4-maleimidophenyl)
No formation of methane was seen. The compound obtained was similar to that of Comparative Example 1.

Comparative Example 3 The same procedure as in Example 2 was carried out except that triethylamine was not added. As a result, generation of bis (4-maleimidophenyl) methane was not seen. The compound obtained was similar to that of Comparative Example 1.

Comparative Example 4 The procedure of Example 2 was repeated except that dicyclohexylcarbodiimide was not added. As a result, generation of bis (4-maleimidophenyl) methane was not seen. The compound obtained was bismaleamic acid.

[0069]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, the dehydration cyclization reaction of bismaleamic acid can be carried out at a low temperature which does not require heating, so that the formation of undesired by-products can be suppressed, Bismaleimide can be obtained with high purity and high yield. In addition, the eliminated water can be immediately hydrated and captured by galvodiimide without using an acid dehydrating agent or an acid catalyst during the cyclization reaction, and this hydrate can be easily operated after the reaction is completed. Since it can be precipitated and separated from the reaction mixture, the separation and recovery of the bismaleimide product are very easy, and washing with water is unnecessary. In this respect, the present invention is advantageous over conventional methods that require the use of water for separation / recovery or purification, which involves the problem of wastewater treatment.

Therefore, according to the present invention, because of low energy consumption and simplification of the process, the cost is low and the acid is not contained.
It is possible to obtain high quality bismaleimide having a low content of by-products such as isoimide.

Claims (9)

[Claims] 1. A method for producing a bismaleimide, which comprises subjecting a bismaleamic acid to a dehydration ring closure with a carbodiimide in the presence of a lower alcohol and a tertiary amine. 2. A carbodiimide is a compound represented by the formula (1) R ₁ —N═C═N—R ₂ (1) (wherein R ₁ and R ₂ represent hydrogen or a hydrocarbon group). The method for producing a bismaleimide according to claim 1. 3. The method for producing a bismaleimide according to claim 2, wherein R ₁ and R ₂ are hydrocarbon groups having 1 to 8 carbon atoms. 4. The method for producing a bismaleimide according to claim 1, wherein the lower alcohol has 1 to 6 carbon atoms. 5. The method for producing a bismaleimide according to claim _{1, wherein the} tertiary amine is tri-C _1-10 alkylamine. 6. The bismaleamic acid is represented by the formula (2) HOOC—CH═CH—CONH—R′—NHCO—CH═CH—COOH (2) (wherein R ′ represents a divalent organic group). The method for producing a bismaleimide according to claims 1 to 5. 7. A carbodiimide in an amount of 2 to 10 moles and a lower alcohol in an amount of 0.0 to 1 mole of bismaleamic acid.
The method for producing a bismaleimide according to claims 1 to 6, wherein the amount is 0.01 mol or more and 0.01 to 50 mol of a tertiary amine. 8. A method for producing a bismaleimide, which comprises reacting maleic anhydride with a diamine and subjecting the obtained bismaleamic acid to dehydration ring closure by the method according to any one of claims 1 to 7. 9. The method for producing a bismaleimide according to claim 8, wherein 1 to 10 mol of maleic anhydride is used with respect to 1 mol of diamine.