JPH04128264A - Purification of n-substituted maleimide - Google Patents

Abstract

PURPOSE:To obtain an N-substituted maleimide having excellent heat stability in storing, transporting and flaking by washing a solution of N-substituted maleimide in an organic solvent with an aqueous solution of mineral so as pH of water layer after washing to be in a specific range. CONSTITUTION:An aqueous solution of N-substituted maleimide in an organic solvent is washed with an aqueous solution of mineral acid (e.g. aqueous solution of hydrochloric acid, sulfuric acid or phosphoric acid) so as pH of water layer after washing to be <=0.5. The amount of the aqueous solution of mineral acid is >=0.1 pt.wt., preferably 0.1-10 pts.wt. to N-substituted maleimide and the temperature in washing is preferably in a range of 0-80 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a purification method for obtaining N-substituted maleimide having excellent thermal stability.

N-substituted maleimide is used as a raw material for heat-resistant resins (for example, JP-A-63-61926, JP-A-61-2768).
07 Publication), and in recent years, as raw materials for optical materials (for example, JP-A-63-90520, JP-A-63-25).
6647), and is further used as a raw material for agricultural medicines.

[Problems to be solved by conventional technology and invention] N-7
It is known that converted maleimide has an active double bond, tends to generate impurities or color due to polymerization reactions, etc., and has problems with thermal stability during storage and transportation.

Therefore, there is a method of adding an N-ff substituted maleimide polymerization inhibitor (Japanese Patent Application Laid-Open No. 143911/1982), a method of preparing an acrylonitrile solution of N-substituted maleimide and adding a polymerization inhibitor (Japanese Patent Application Laid-open No. 126167/1989). ) etc. are disclosed.

In addition, N-substituted maleimide is irritating to the human body, and if inhaled in fine powder, it will irritate the nasal passages and throat, causing coughing and sneezing, and if left in contact with the skin, it will cause inflammation and other undesirable properties. has.

Therefore, it is preferable to use N-substituted maleimide in the form of flakes instead of powder, but this requires heating and melting the N-substituted maleimide and applying it to a flaker, which results in stable storage at room temperature. Thermal stability, which is even better than the properties, is required, and the existing method of adding a polymerization inhibitor has not been sufficient.

On the other hand, the purification method is considered to be an important factor regarding the stability of NJt-converted mashimaleimide.

Conventionally, the method for purifying N-substituted maleimides is to inject the reaction solution into a large amount of cold water, filter out the precipitated crystals, and wash the crystals with an even larger amount of water or organic solvent (Orga
nic 5ynthesis, Co11. Vol.
V.

944 (1973) ), a method in which the organic layer is separated after neutralization and washing with a dilute aqueous sodium carbonate solution, and the solvent is removed (Japanese Patent Publication No. 1983-46394), and after the reaction, acid treatment with a strong acid such as sulfuric acid A method of converting the by-product into a resin, distributing it, and washing it with water (Japanese Patent Application Laid-Open No. 61-22065,
JP-A No. 61-204166), a method of washing with a dilute aqueous alkali solution, washing with water again, distilling off the solvent, and recrystallizing from an alcoholic solvent (JP-A No. 60-100554); A method of distilling after washing with an acid aqueous solution (Japanese Unexamined Patent Publication No. 1-216969), a method of distilling in the coexistence of phosphorous oxygen acids (Japanese Unexamined Patent Publication No. 1-216970), etc. are known.

However, these purification methods are aimed at improving the extraction yield and purity of N-substituted maleimide,
The thermal stability of the N-substituted maleimide product itself was insufficient and required the addition of the above-mentioned polymerization inhibitor.

An object of the present invention is to provide a purification method for obtaining an N-substituted maleimide that has excellent thermal stability during storage, transportation, and flaking.

[Means to solve the problem]

As a result of intensive research into improving the thermal stability of N-substituted maleimides, the present inventors found that trace amounts of basic substances remaining in the product N-substituted maleimide significantly lowered the thermal stability. It has been found that an N-substituted maleimide having an amine value of 0.01 or less, defined as the number of hydrogen chloride required to titrate 1 g of maleimide with hydrochloric acid in a chloroform-ethanol mixed solvent, has good thermal stability.

Furthermore, N-substituted maleimide with an amine value of 0.01 or less can be obtained by washing the organic solvent solution of N-substituted maleimide with a mineral acid aqueous solution such that the pn of the aqueous layer after washing is less than 0.5. The present inventors have discovered that the present invention is possible and have completed the present invention.

That is, in the purification of an N-fi-substituted maleimide organic solvent solution by washing with an aqueous mineral acid solution, the present invention improves the pH of the aqueous layer after washing.
This is a method for purifying N-substituted maleimide, which is characterized by washing with an aqueous mineral acid solution in which the N-substituted maleimide is less than 0.5.

Specifically, the ~-substituted maleimides that can be used in the purification method of the present invention include N-phenylmaleimide, N-(3-methylphenyl)maleimide, N-(4-methoxyphenyl)maleimide, N-(4-acetoxyphenyl)maleimide, and N-(4-acetoxyphenyl)maleimide. phenyl)maleimide, N-(3-nitrophenyl)maleimide, N-
(4-(methoxycarbonyl)phenylmaleimide, N
-(4-hydroxyphenyl)maleimide, N-(4-
dodecylphenyl)maleimide, N(3,5-dichlorophenyl)maleimide, N-(2,6-cyphthylphenyl)maleimide, N-isobutylmaleimide, N-cyclohexylmaleimide, N,N'-(13-phenylene) -Bismaleimide, N,N'-(1,4-naphthylene)-bismaleimide, N,N'-(4,4'-diphenyl)-bismaleimide, N,N'-(4,4'-diphenyl ether) -Bismaleimide, N,N'-(4,4
'-diphenylmethane)-bismaleimide, N,N'-
[4,4"-(2,2'-diphenylpropane)]-bismaleimide, N,N(4,4'-diphenylthioether)-bismaleimide, N,N'-(4,4"-diphenyldisulfide) -Bismaleimide, N, N'-(4
,4'-diphenylsulfone)-bismaleimide, N,
Examples include, but are not limited to, N'-(3,3'-hensiphenone)-bismaleimide.

Furthermore, the purification method of the present invention can be carried out by any method such as thermally or chemically dehydrating and ring-closing the corresponding N-l-substituted maleimide, or dehydrochloridizing the corresponding N-substituted chlorosuccinimide by reacting with a base. It is also effective against N-substituted maleimides prepared by
Since the base used often remains in substituted maleimides, the purification method of the present invention is particularly effective.

The organic solvent used in the present invention may be any organic solvent as long as it is inert to the N-substituted maleimide and separates into two layers from water in a state in which the N-substituted maleimide is dissolved. , aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as benzene, toluene and xylene, halogenated hydrocarbons such as chlorobenzene and dichloroethane, ethers such as diethyl ether and tetrahydrofuran, ethyl acetate and butyl acetate, etc. Examples include esters.

Examples of the mineral acid aqueous solution used in the purification method of the present invention include aqueous solutions such as hydrochloric acid, sulfuric acid, and phosphoric acid, and the pH of the aqueous layer after washing the N-fl substituted maleimide organic solvent fIj solution is 0.
．． The amount and concentration of the aqueous mineral acid solution are selected to be less than 5. Alternatively, water may be first added to a solution of the N-substituted maleimide in an organic solvent, and a mineral acid may be added such that the pH of the aqueous layer is less than 0.5.

If the pH of the aqueous layer after washing is 0.5 or higher, the removal of basic substances in the N-fi-converted mamarimide will be insufficient, and the amine value will be 0.5. If it becomes higher than OL, the thermal stability of the product will deteriorate, and polymerization and coloring may occur.

In addition, if the pH of the aqueous layer after washing is less than 0, N
- Polymerized or hydrolyzed products of substituted maleimides may be formed in small amounts as insoluble matter, and the p of the aqueous layer is 0 or more.
．． More preferably, it is less than 5.

The amount of the aqueous mineral acid solution is preferably 0.1 parts by weight or more, preferably 0.1-10 parts by weight, based on the N-substituted maleimide. If it is less than 0.1 part by weight, the cleaning effect will not be sufficient even if pn is less than 0.5, and if it is more than 10 parts by weight, there will be no difference in the cleaning effect and the wastewater treatment of the cleaning liquid will be burdensome.

The temperature during cleaning with an aqueous mineral acid solution is selected within the range from OoC to the boiling point of the solvent, taking into consideration the solubility of N-substituted maleimide in organic solvents. Since this is easy to occur, it is preferable to carry out the process at a temperature in the range of 0 to 80°C.

Isolation of the N-substituted maleimide from an organic solvent solution of the N-substituted maleimide washed with an aqueous mineral acid solution according to the present invention may be performed by a simple operation of removing the organic solvent under reduced pressure after washing with water.
You may add recrystallization or distillation operation from the required number.
The N-substituted maleimide thus obtained exhibits sufficient thermal stability during heating and melting for flaking, storage and transportation, but the thermal stability can be further improved by adding a known polymerization inhibitor such as an alkyl-substituted phenol. In some cases.

〔Example〕

Hereinafter, the present invention will be explained in detail using Reference Examples, Examples, and Comparative Examples, but the present invention is not limited only to the Examples.

Reference Example 1 105 g of N-phenylchlorosuccinimide was suspended in a mixed solution of 450 g of toluene and 100 g of water, and 55-6
50 g of triethylamine was added dropwise over 12 hours while stirring at 0° C. After the addition, stirring was continued at 60° C. for 2 hours, and the organic layer was separated to obtain a toluene solution of 86.7 g of N-phenylmaleimide.

Example 1 50g of water was added to the toluene solution obtained in Reference Example 1, and 40~
While stirring at 50° C., 10% sulfuric acid was added until ρ11 of the aqueous layer became 0.4. 14g of 10% sulfuric acid was required.
Met. The organic layer was separated and further washed three times with 50 g of water.

When the organic layer was concentrated under reduced pressure, N-phenylmaleimide 84
．． 9 g (98% yield) was obtained as a non-reddish yellow solid. The amine value of this N-phenylmaleimide is 0.
Purity by liquid chromatography is 99.8
%, and the extinction index of 530- measured as a 10% acrylonitrile solution in an 11 glass cell at room temperature is o, o
It was os. This tophenylmaleimide was dissolved under nitrogen for 10
Table 1 shows the purity determined by liquid chromatography after heating at 0°C for 24 hours, the extinction index of 530-, and the changes observed by visual observation, and there were no changes before and after heating.

Examples 2 to 3 The amount of 10% sulfuric acid in Example 1 was increased, the pH of the aqueous layer after washing with sulfuric acid was adjusted to O, and 14g of 98% sulfuric acid was added to 10% sulfuric acid.
N-phenylmaleimide was obtained in the same manner except that the pH was adjusted to less than 100 ml. However, when the pH was less than 0, a trace amount of insoluble matter was formed, so the solution was filtered through a 1μ filter before separation. These N-phenylmaleimides were subjected to the same heating test as in Example 1 and the results are shown in Table 1, but there was no change before and after heating.

Examples 4 to 14 The N-phenylmaleimide in Example 1 was replaced with various N-substituted maleimides, and the p)I of the aqueous layer after washing with sulfuric acid was 0.
The process was carried out in the same manner as in Example I, except that a value of less than 5 was selected as appropriate. The various N-substituted maleimides obtained were subjected to the same heating test as in Example 1, and the results are shown in Table 1, and there was almost no change before and after heating.

Comparative Examples 1 to 3 The pH of the aqueous layer after washing with sulfuric acid in Example 1 was set to 0.5.2.
．． N-7 enylmaleimide was obtained by the same treatment except that the respective values were adjusted to 3.5. The results of the same heating test as in Example 1 are shown in Table 1, and a decrease in purity and reddish coloration were observed due to heating.

Comparative Examples 4 to 14 The same treatment as in Example 4 was carried out except that 111 in the aqueous layer after washing with sulfuric acid was appropriately selected to be 0.5 or more. The various N-phenylmaleimides obtained were subjected to the same heating test as in Example 1, and the results are shown in Table 1, but a decrease in purity and reddish coloration were observed upon heating.

Comparative Example 15 2,6-dit was added to the N-phenylmaleimide obtained in Comparative Example 2.
IQOppm of ar t-butyl-p-cresol was added as a polymerization inhibitor, and the same heating test as in Example 1 was conducted. As shown in Table 1, a slight improvement in stability was observed, but it was not sufficient.

Example 15 50 g of N-phenylmaleimide obtained in Example 1 was
Distillation was carried out at a bath temperature of °C and a pressure of 9 snHg'7' for 1 hour to obtain 49.1 g of N-phenylmaleimide. At this time, the remaining amount in the still was 0.9 g. The fraction was subjected to a heating test in the same manner as in Example 1, and the results are shown in Table 1, but there was no change before and after heating.

Comparative Example 16 50 g of N-phenylmaleimide obtained in Comparative Example 2 was
Distilled for 1 hour at a bath temperature of °C and a pressure of 9 sdg.
．． 3 g of N-phenylmaleimide was obtained. At this time, the remaining amount in the still was 1.7 g. The fraction was subjected to a heating test in the same manner as in Example 1, and the results are shown in Table 1, but a decrease in purity and reddish coloring due to heating were observed.

Reference example 2 Anhydrous? L/inic acid 107.8 g, xylene 4oo1
11. Dimethylformamide 25-1 and 5.0 g of pl-luenesulfonic acid were charged and dissolved by heating with stirring.

Next, 93.1 g of aniline was added dropwise over 1 hour, and the mixture was refluxed for 2 hours. During this time, the produced water was removed from a water separator.

The amount of N-phenylmaleimide in the xylene solution thus obtained was 166.5 g (yield: 96.1%).

Example 16 A xylene solution of N-phenylmaleimide obtained in Reference Example 2 was heated to 50°C and diluted with 6% sodium chloride water for 200 hours.
g was added for washing, and the aqueous layer was separated. Next, after adding 50 g of water, 5% sulfuric acid was added dropwise while stirring to bring the ρ11 of the aqueous layer to 0.
．． 4 and washed. Subsequently, after washing three times with 50 g of water, it was concentrated under reduced pressure to obtain 165.2 g of N-phenylmaleimide.
I got it.

A heating test similar to that in Example 1 was conducted and the results shown in Table 1 were obtained, but the changes before and after heating were slight.

Comparative Example I7 The xylene solution of N-phenylmaleimide obtained in Reference Example 2 was mixed with 200 g of a 6% aqueous sodium carbonate solution at 50°C.
was added for washing, and the aqueous layer was separated. Next, 150 g of a dilute aqueous sulfuric acid solution adjusted to 1112 was added for washing, and the aqueous layer was separated. The aqueous layer at this time had a pH of 2.9.

Then, after washing three times with 50 g of water, the mixture was concentrated under reduced pressure to obtain 165.4 g of N-phenylmaleimide.

A heating test similar to that in Example 1 was conducted, and the results shown in Table 1 were obtained. There was a significant decrease in purity and reddish coloring before and after heating.

[Effects of the Invention] The purification method of the present invention allows N to be produced with excellent thermal stability, with less deterioration in purity and reddish coloring during storage and transportation, and even during flaking.
-fi-converted mamaleimide is obtained.

Claims (1)

[Claims] 1. In purification of an organic solvent solution of N-substituted maleimide with an aqueous mineral acid solution, washing at 0 to 80°C with an aqueous mineral acid solution such that the pH of the aqueous layer after washing is less than 0.5. A method for purifying N-substituted maleimide, the method comprising: 2. The purification method according to claim 1, wherein the pH of the aqueous layer is 0 or more and less than 0.5. 3. The purification method according to claim 1, wherein the N-substituted maleimide is an N-substituted maleimide produced by dehydrochlorination reaction of N-substituted chlorosuccinimide with a base. 4. Amine value of N-substituted maleimide after purification is 0.01
The purification method according to claim 1, wherein: 5. The amount of mineral acid aqueous solution is 0.1 per N-substituted maleimide.
The purification method according to claim 1, wherein the amount is 10 parts by weight.