JPH0686424B2 - Method for producing N-phenylmaleimide - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing N-phenylmaleimide in which by-products of impurities are effectively prevented and the yield is remarkably improved.

(Prior Art and Problems Thereof) A method of reacting maleic anhydride with aniline to produce phenylmaleimide is conventionally known.

This conventionally known production method is one in which equimolar amounts of maleic anhydride and aniline are used to carry out a condensation reaction. However, a compound obtained by adding aniline to N-phenylmaleimide, that is, N-phenyl- (2-anilino) succinimide However, there is a problem in that the yield of the target phenylmaleimide is low because a large amount of impurities that are difficult to remove are produced as a by-product.

Therefore, the present invention, in the production of N-phenylmaleimide,
The technical problem is to effectively suppress the by-product of impurities that are difficult to remove, such as N-phenyl- (2-anilino) succinimide, and improve the yield of the target N-phenylmaleimide.

(Means for Solving the Problems) In order to achieve the above-mentioned technical objects, the present invention comprises the steps of (A) charging each raw material when producing N-phenylmaleimide by condensing maleic anhydride and phenylamine The amount is represented by the following formula A / BC ≧ 1.05 (1) where A is the number of moles of maleic anhydride charged, B is the number of moles of phenylamine, and C is the number of moles of acidic catalyst. The condensation reaction is carried out under satisfactory conditions, and (B) after completion of the reaction, the reaction system is washed with water in the pH range of 6.5 to 7.5 to extract and remove the residual catalyst.

(Operation) According to the present invention, the condensation reaction is performed under the condition that the charged amount of each reactant satisfies the above formula (1).
As shown in Examples described later, by-products of difficult-to-remove impurities such as N-phenyl- (2-anilino) succinimide are effectively suppressed, and accordingly, the yield of the target N-phenylmaleimide is significantly increased. It will improve.

That is, in the conventional production method, the amounts of the maleic anhydride and phenylamine charged were equimolar, but in consideration of the extremely small amount of the acidic catalyst used, the anhydride in the present invention was used. It will be appreciated that the charge of maleic acid is in excess of that of phenylamine.

Therefore, according to the present invention, almost all of the charged phenylamine is subjected to the desired condensation reaction with maleic anhydride, resulting in a side reaction of phenylamine.
It effectively suppresses the generation of difficult-to-remove impurities such as N-phenyl- (2-anilino) succinimide.

Further, according to the present invention, after completion of the condensation reaction, the pH is adjusted to 6.5 to 7.
It is also important to wash the reaction system with water to extract and remove the residual catalyst in the range of 5, especially 6.7 to 7.3.

That is, if the washing treatment is carried out on the alkaline side beyond the above range, the produced N-phenylmaleimide is decomposed, and another impurity that is difficult to separate, that is, fumaranilic acid, is produced as a by-product. Further, if the water washing treatment is carried out on the acidic side of the above range, the acid is insufficiently removed, and this acid is concentrated in the distillation still during the subsequent distillation operation, causing the loss of polymerization of N-phenylmaleimide. Becomes

(Effects and Effects) Thus, according to the present invention, it is possible to effectively prevent the by-product of impurities and obtain N-phenylmaleimide in a high yield.

The obtained N-phenylmaleimide is provided for use as, for example, a heat-resistant thermosetting resin raw material.

(Preferred embodiment of the invention) In the production method of the present invention, maleic anhydride and phenylamine are condensed in the presence of an acidic catalyst, followed by washing with water to extract and remove the residual catalyst, followed by distillation separation operation. To obtain N-phenylmaleimide.

Condensation reaction step The condensation reaction is carried out by dissolving or dispersing maleic anhydride, phenylamine and an acidic catalyst in a predetermined solvent and heating under reflux.

As the phenylamine, aniline, o-, m-, or p-substituted aniline such as toluidine and cumidine can be used.

In the present invention, as described above, the condensation reaction is performed so that the charged amount of each raw material substance satisfies A / BC> 1.05, but it is particularly preferable that A / BC <1.2. (In the above formula, A, B, and C respectively represent the molar amounts of maleic anhydride, phenylamine, and acidic catalyst charged.) That is, if the charged amount of maleic anhydride becomes excessive, it may occur due to recovery loss and the like. Not desirable.

The amount of the acidic catalyst used is preferably in the range of 0.5 to 5% by weight based on the total amount of maleic anhydride and N-phenylamine. If the amount of catalyst is less than 0.5% by weight, the desired catalytic effect cannot be obtained, and even if it is used in excess of 5% by weight, a certain amount of effect cannot be obtained, which is economically disadvantageous. In addition, the removal of the residual catalyst becomes troublesome.

As an acidic catalyst, inorganic acid such as sulfuric acid, hydrochloric acid, phosphoric acid p-
Organic acids such as toluenesulfonic acid can be used, but they may be in the form of salts with phenylamine.

The heating under reflux is carried out after the maleic anhydride, phenylamine and acidic catalyst are dissolved or dispersed in the solvent, but the solution obtained by dissolving or dispersing maleic anhydride and the acidic catalyst in the solvent is heated under reflux and this system is used. Alternatively, a method in which a liquid obtained by dissolving or dispersing phenylamine in a solvent is added dropwise may be adopted.

It is generally preferred that the amount of solvent is 2 to 10 times, especially 4 to 6 times the total amount of each raw material. As a solvent,
Hydrocarbons having a boiling point of 120 ° C. to 180 ° C., halogenated hydrocarbons, and other aprotic polar solvents can be used.

The reaction temperature is usually in the range of 100 to 180 ° C, particularly 120 ° C to 160 ° C, and the pressure is preferably atmospheric pressure or reduced pressure.

The reaction time is generally in the range of 2 to 10 hours, especially 5 to 6 hours.

Water Washing Process After the completion of the condensation reaction, this reaction system is subjected to a water washing process.

In this water washing treatment, an aqueous system having a pH of 6.5 to 7.5, particularly 6.7 to 7.3, is circulated and supplied to the reaction system to extract and remove the residual acidic catalyst and excess unreacted maleic anhydride.

Since the pH of this aqueous system gradually rises with the circulation supply, an alkali such as Na ₂ CO _{3 is} appropriately added to control the pH. In this case, it is desirable that the accumulated concentration of salts such as Na ₂ CO ₄ in the circulating liquid is 15 to 20% by weight.

Distillation Separation Step After washing with water, the oil phase containing N-phenylmaleimide is subjected to a distillation operation to separate the solvent and the like to obtain the desired N-phenylmaleimide.

In the present invention, since the amount of each raw material charged is adjusted so as to satisfy certain conditions, N-phenyl-
Since the by-products of substances that are difficult to separate by distillation, such as (2-anilino) succinimide, are effectively suppressed, the target N-phenylmaleimide can be easily obtained by a distillation operation.

For example, as will be apparent from the examples described below, according to the production method of the present invention, the yield of the target N-phenylmaleimide is 90 mol% or more, which is extremely high. Here, the yield of N-phenylmaleimide is a value expressed based on the amount of aniline charged.

At the time of the above-mentioned distillation separation, it is preferable to add a polymerization inhibitor to the oil phase to be distilled to prevent the polymerization loss of N-phenylmaleimide.

As the polymerization inhibitor to be used, those known per se such as 2,5-ditert-butylhydroquinone and 4-tert-butylcatechol can be used in a per se known amount.

Example 1 Maleic anhydride 51.5 g (0.525 mol), sulfuric acid 2.5 g (0.026
Mol) and 400 g of mixed xylenes were charged into a 1 round bottom flask equipped with a stirrer, a funnel, a reflux condenser and a water separator. The heating of the contents of the flask was started, and when the solvent started to be refluxed, the addition of a separately prepared solution of 46.5 g (0.5 mol) of aniline dissolved in 100 g of mixed xylene was started. After dropping for about 6 hours, post-reaction was carried out for 30 minutes after the dropping was completed. Distillation of water produced by the reaction was observed while the aniline solution was added dropwise. The total amount of water produced in the water separator was 9.1 g. After the completion of all reactions, the solvent insoluble matter contained in the reaction mixture was separated. The amount of insoluble matter was about 3.3 g.
The reaction product solution obtained by removing this insoluble matter was led to an extraction neutralizer. The extraction neutralizer is composed of a raw material tank, a raw material supply pump, a rotating disk type countercurrent extractor (extractor liquid holdup 300 ml, 6 actual stages), a neutralizing tank with a pH controller and a water phase circulation pump.

The reaction product solution was charged into the raw material tank, and was supplied to the lower part of the extractor by a raw material supply pump at a flow rate of 300 ml / hr. A 20% -Na ₂ SO ₄ aqueous solution (pH 6.8) was supplied to the upper part of the extractor at a flow rate of 600 ml / hr. The extraction machine disk was rotated to perform the extraction operation. The aqueous phase discharged by extracting the acid catalyst, unreacted maleic acid and maleic anhydride contained in the reaction product solution was led to a neutralization tank, and neutralized to pH 7 with 13% -NaOH aqueous solution.
The neutralized aqueous phase was recycled to the extractor. A part of the product discharged from the upper part of the extractor was collected and batch-washed with distilled water using a separating funnel, but no change in pH of the aqueous phase was observed. The whole amount of the reaction product solution was treated for 2 hours and a half, and 150 ml of xylene was further fed to wash out the holdup in the system.

After adding 0.09 g of 2,4-di-tert-butylhydroquinone to the reaction product solution from which the acid catalyst was removed, the solvent xylene was distilled off by a rotary evaporator, and a concentrate containing N-phenylmaleimide as a main component 87.5 g Got A molecular distillation apparatus (manufactured by Shinko Faudler) using the concentrate as a distillation raw material
Thin film distillation was performed using. 82.1 g of distillate output was obtained under the conditions of 6 mmHg and 170 ° C. (outer wall temperature). As a result of analyzing the distillate by liquid chromatography, contamination with N-phenyl- (2-anilino) succinimide as an impurity was not found.

The total yield for the theoretical amount of N-phenylmaleimide produced is
It was 94.9 mol%.

Comparative Example 1 Example 1 was repeated except that in the condensation reaction of maleic anhydride and aniline, the charged amount of maleic anhydride was 49.0 g (0.5 mol) and the amount of aniline in the aniline solution to be dropped was 55.9 g (0.60 mol). I went the same way. After completion of the condensation reaction, the amount of the solvent-insoluble matter separated was 13.0 g.

The amount of distillate obtained by the final distillation operation was 60.6 g, and contained 0.2% of the impurity N-phenyl- (2-anilino) succinimide.

The total yield of N-phenylmaleimide based on the theoretical production is 70.
It was mol%.

Comparative Example 2 The reaction product solution obtained by conducting the condensation reaction under the same conditions as in Example 1 was directly neutralized with a 0.5% -NaOH aqueous solution. A final distillate was obtained by the same post-treatment method as in Example 1, and the amount of the distillate was 74.4 g. This contained 0.18% of N-phenyl- (2-anilino) succinimide.

The overall yield of N-phenylmaleimide was 85.8 mol%.

Example 2 In Example 1, the charged amount of maleic anhydride was 49.0 g.
Condensation reaction extraction neutralization was performed in the same manner as in Example 1 except that the content was changed to (0.50 mol). As a result of liquid chromatography analysis of the reaction product solution at this stage, the yield of N-phenylmaleimide was 93 mol%.

To the solution of the reaction product, 0.09 g of 2,5-di-tert-butylhydroquinone was added and the solvent was distilled off to obtain 86.5 g of a concentrate.

The concentrate was transferred to a 300 ml distillation flask and subjected to simple distillation under the conditions of 6 mmHg and 140 ° C. After cutting off the previous fraction such as xylene and unreacted aniline remaining in the concentrate, the main fraction of N-phenylmaleimide was collected. The main fraction obtained over 1 hour and 30 minutes was 76.4 g. The overall yield of N-phenylmaleimide was 88.3 mol%.

Comparative Example 3 The procedure of Example 2 was repeated, except that 2,5-di-tert-butylhydroquinone was not added to the distillation raw material. The main fraction obtained in the final simple distillation operation was 6
The total yield of N-phenylmaleimide was 79.0 mol%.

Claims (1)

[Claims] 1. A method for producing N-phenylmaleimide by subjecting maleic anhydride and aniline to a condensation reaction in the presence of an acidic catalyst, wherein the amount of each raw material charged is represented by the following formula: A / BC ≧ 1.05 , A is the number of moles of maleic anhydride charged, B is the number of moles of aniline, and C is the number of moles of acid catalyst charged. The condensation reaction is carried out so that the pH is 6.
A production method characterized in that the reaction system is washed with water in the range of 5 to 7.5 to extract and remove the residual catalyst.