JP2632977B2 - Method for producing unsaturated carboxylic acid-2-isocyanatoalkyl ester - Google Patents

Description

The present invention relates to an improved production of an unsaturated isocyanatoalkyl carboxylate represented by the general formula [I], which is useful as an intermediate for various syntheses. About the law.

[Wherein, R represents a hydrogen atom, a lower alkyl group, a phenyl group,
Or a vinyl group, and R ¹ , R ² , and R ³ each independently represent a hydrogen atom or a lower alkyl group. [Problems to be Solved by the Prior Art and the Invention] The compound represented by the general formula [I], which is an object of the present invention, is a bifunctional monomer having a double bond and an isocyanate group in one molecule, Useful as various synthetic intermediates,
A typical example is (meth) acrylic acid-2
-Isocyanatoethyl ester and cinnamic acid-2-isocyanatoethyl ester.

The production of unsaturated carboxylic acid isocyanatoalkyl esters is carried out by cold phosgenation of 2-alkenyl-2-oxazolines. (UK Patent No. 1,252,099
This reaction is usually carried out in a water-insoluble solvent such as dichloromethane or toluene in the presence of an aqueous alkali solution such as sodium hydroxide. .

For example, Dieter Arlt in British Patent No. 1,252,099 reacts by mixing 2-isopropenyl-2-oxazoline and phosgene, each dissolved in dichloromethane, and sodium hydroxide, dissolved in water. Accordingly, a method for producing methacrylic acid-2-isocyanatoethyl ester is disclosed.
Kenneth Allen Burdett disclosed the same reaction in JP-A-54-5921 by reacting 2-isopropenyl-2-oxazoline and sodium hydroxide with phosgene dissolved in dichloromethane, respectively. Has been done.

This method is an excellent method that is energy-saving and safe, but (1) the product is very easily polymerized, and the yield when isolated as a high-purity product tends to be low.
(2) It is difficult to effectively and effectively remove the generated hydrogen chloride,
Not preferred in terms of product quality. There are problems such as.

That is, in these reactions, the reaction solution after completion of the reaction is divided into two phases. Of these, the organic phase is washed with a basic aqueous solution and water, the solvent is removed by distillation, and then the desired product is formed by distillation under reduced pressure. Isocyanate alkyl carboxylate is isolated. At this time, the yield of the target product may be lower than usual and the chlorine content in the product may be higher, but in such a case, the bottom after distillation is very viscous. Also, in the gas chromatogram of the liquid after distilling off the solvent, although the impurity peak is small, the purity of the target product is low, so that a considerable amount of polymer is formed. it is conceivable that.

Since the unsaturated carboxylic acid isocyanatoalkyl ester is very easily polymerized, a polymer is always produced as a by-product during the reaction, but the amount varies depending on slight fluctuations in the reaction conditions.

In general, when still a small amount of the target product is still contained in the still residue after distillation, in order to increase the yield, it is often mixed with the crude product and recycled to the distillation column. However, in the case of this reaction product, surprisingly, even if it was recycled, the yield did not increase, but rather the tendency to decrease was observed.

On the other hand, apart from this method, a method of producing by reacting an unsaturated carboxylic acid aminoalkyl ester with phosgene (U.S. Pat. No. 2,821,544), a method via an unsaturated carboxylic acid uretanoalkyl ester (U.S. Pat.
No. 516) has also been disclosed. These methods have a problem that the yield is low for industrial implementation, but even if this is solved, the reaction solution after the reaction contains a considerable amount of polymers and basic compounds. This is the same as in the above-described method, and involves the same problem with respect to the isolation of the desired product.

[Means for solving the problem]

The present inventors have conducted intensive studies in order to solve such a problem, and as a result, the unsaturated carboxylic acid-
It has been found that when a polymer of 2-isocyanatoalkyl ester is present in the reaction solution, the viscosity of the reaction solution increases, making it difficult to isolate the target component and also has an action of accelerating the polymerization.

Further, since this polymer is difficult to use as a solvent in a solvent such as n-hexane, for example, by replacing the solvent of the reaction solution with these poor solvents, the produced polymer can be easily removed by phase separation. They have found that they can do this and have completed the present invention.

That is, in the present invention, after the synthetic reaction of the unsaturated carboxylic acid-2-isocyanatoalkyl ester, the solvent of the organic phase containing the target reaction product is replaced with a poor solvent for the polymer of the ester to remove the polymer. Accordingly, the present invention provides a method for improving the yield and quality of unsaturated carboxylic acid-2-isocyanatoalkyl ester.

In the present invention, the poor solvent for the polymer is difficult to dissolve the polymer under conditions of normal temperature and normal pressure, and sufficiently dissolves the objective unsaturated carboxylic acid-2-isocyanatoalkyl ester. A solvent having a sufficiently large boiling point difference from the ester, specifically, a non-polar organic solvent, for example, a paraffinic solvent such as n-hexane, n-heptane, cyclohexane, or alkylcyclohexane is used.

In order to replace the solvent during the reaction with a poor solvent for these polymers, a method in which the solvent is concentrated by evaporation and then a poor solvent may be added, or when the reaction solvent has a low boiling point such as dichloromethane, a poor solvent may be used. After adding the solvent, the reaction solvent may be driven off by distillation.

When the polymer is replaced by a poor solvent, the polymer is phase-separated. This is removed, and the remaining liquid is washed with a basic aqueous solution and then with water.

First, a 5-20% aqueous solution of a basic aqueous solution, such as sodium hydroxide or sodium hydrogen carbonate, is used.
Add about 1/2 to 1 volume (volume), stir, allow to stand, and separate into two phases. This operation is desirably repeated two or three times. Thereafter, the same amount of water is added and the mixture is stirred, allowed to stand, and separated into two phases.

The organic phase is taken and dehydrated using a dehydrating agent such as anhydrous sodium sulfate, anhydrous calcium chloride or the like, or water is removed by utilizing the azeotrope of water and a solvent. Thereafter, the solvent is removed by distillation, and then the desired product is obtained by distillation under reduced pressure.

Thus, after removing the polymer in advance, washing,
When distillation is performed, both the removal rate of chlorine and the distillation yield are improved.

〔Example〕

Next, the method of the present invention will be described more specifically with reference to representative examples.

Example 1 375 g of a dichloromethane solution containing 8% of 2-isopropenyl-2-oxazoline, 400 g of a dichloromethane solution containing 10% of phosgene, and 500 g of an aqueous solution containing 10% of sodium hydroxide were simultaneously placed at a temperature of 0 ° C. At a rate that allows it to be kept in the reactor with a stirrer. After completion of the dropwise addition, the stirring was stopped and the mixture was allowed to stand for a while to separate the two phases, and the oil phase was extracted. The aqueous phase was added with 200 ml of dichloromethane, shaken for 5 minutes, and allowed to stand to separate the two phases, and the oil phase was extracted.
Combined with the oil phase extracted earlier. Dichloromethane was removed by distillation under a slight reduced pressure (about distilling at a liquid temperature of 40 ° C.). Then, 500 ml of n-hexane was added and the mixture was allowed to stand to separate into two layers. The lower phase was extracted and n-hexane 250m
After adding l, the mixture was shaken, and allowed to stand. Then, the mixture was separated into two phases again. The upper phase was taken and combined with the upper phase.

This was washed twice with 5% sodium bicarbonate water and twice with water, and then transferred to a distillation apparatus. First, n-hexane was removed under a slight reduced pressure, and then reduced to 5 mmHg to reduce the methacrylic acid as a fraction at 71 to 73 ° C. 34.5 g of -2-isocyanatoethyl ester was obtained. The chlorine content in this was 0.15%.

Comparative Example 1 The same experiment as in Example 1 was performed, but the dichloromethane solution was directly washed with 5% sodium bicarbonate water and water and distilled without using n-hexane. As a result, the yield of methacrylic acid-2-isocyanatoethyl ester as a fraction at 71 to 73 ° C./5 mmHg was 25 g, and the chlorine content therein was 0.45%.

Example 2 97 g of ethanolamine hydrochloride, 250 ml of toluene and
Take 0.3 g of anthraquinone in a reactor equipped with a stirrer,
Was heated. To this, 119 g of crotonic acid chloride was added dropwise at a rate such that the temperature was between 70 and 100 ° C.,
After that, the reaction was carried out for 2 hours under nitrogen. Phosgene was blown into the solution under reflux until the solution became transparent. (About 3
It took time. After blowing out excess phosgene by blowing nitrogen gas, about 220 ml of toluene was distilled off under reduced pressure of 100 Torr. 250 ml of n-hexane was added thereto, stirred, and allowed to stand. Separate both phases, and add n-hexane to the lower phase.
When 250 ml was added and shaken, the mixture was separated into two phases again. The lower phase was extracted, and the upper phase was combined with the upper phase. When this was washed and distilled in the same manner as in Example 1, 97 to 10
86 g of crotonic acid-2-isocyanatoethyl ester was obtained as a fraction at 1 ° C./9 mmHg.

Comparative Example 2 After performing the same reaction as in Example 2, washing and distillation without replacing the solvent with n-hexane, the amount of crotonic acid 2-isocyanatoethyl ester obtained was only 51 g, A dark brown viscous liquid (including solids) remained as a residue.

〔The invention's effect〕

According to the present invention, in a process for producing an unsaturated carboxylic acid-2-isocyanatoalkyl ester from 2-alkenyl-2-oxazoline or unsaturated carboxylic acid-2-aminoethyl ester and phosgene, the yield of the compound is reduced. While improving the product, it becomes easy to obtain a product having a low chlorine content.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinya Matsuhira 1-26-1, Hamamatsucho, Minato-ku, Tokyo Showa Rhodia Chemical Co., Ltd.

Claims (1)

(57) [Claims] 1. A process for producing an unsaturated carboxylic acid-2-isocyanatoalkyl ester by reacting 2-alkenyl-2-oxazoline or an aminoalkylsteryl unsaturated carboxylate with phosgene, comprising the steps of:
After replacing the solvent of the organic phase containing the target product with a poor solvent for the polymer of the ester to remove the polymer, the polymer is washed with a basic aqueous solution, and the mixture is washed with a basic aqueous solution of 2-isocyanatoalkyl carboxylate. Method for producing ester.