CS269846B1 - Process for preparing N-phenylmaleinimide and substituted derivatives thereof - Google Patents

Abstract

The preparation of N-phenylmaleimide and its substituted derivatives consists in reacting a mixture of N-phenylmaleamic acid or its substituted derivative, acetic anhydride and an organic tertiary base at a temperature of 20 °C to 80 °C and, after the reaction is complete, isolating the product by filtration after diluting the reaction mixture with water.

Description

The invention relates to a method for preparing N-phenylmaleimide and its substituted derivatives by cyclization of N-phenylmaleamic acid, or their derivatives. The obtained substances of general formula I in which B denotes H, Cl, SO ₃ H(Na), COOH, OCH^Og or CH ₃ , find application in the rubber and plastics industry as modifiers for the preparation of heat-resistant polymers, in the preparation of some insecticides, herbicides and fungicides, as adhesives increasing the adhesion of some textile fibers to natural and synthetic rubbers, as crosslinking agents improving the useful properties of some polymers or as raw materials in the pharmaceutical industry.

The methods used so far for the preparation of N-phenylmaleimides consist in the cyclization of N-phenylmaleamic acids with a mixture of alkali salts of fatty acids and anhydrides of lower fatty acids; manganese, lithium or cobalt salts have also been proposed as catalysts for the cyclization. Magnesium or nickel salts have also been used together with triethylamine in a mixture with acetic anhydride. Methods for removing water during the cyclization by azeotropic distillation with toluene or by the addition of anhydrous alkali salts of fatty acids in the presence of a solvent are also described.

The disadvantage of the existing methods is the use of relatively expensive catalysts or solvents and, above all, the difficulties in isolating the resulting products. None of the mentioned methods has solved the issue of disposal of waste filtrates, which due to the presence of heavy metal ions cannot be cleaned simply by passing them through a biological treatment station.

It has now been found that the above disadvantages of the previously known processes are solved by the present invention. The subject is a method for preparing N-phenylmaleimides or substituted derivatives of the above formula, which consists in that a mixture of 1 mole of N-phenylmaleamic acid or its substituted derivative, 2 to 6 moles of acetic anhydride and 0.1 to 2 moles of an organic tertiary base is allowed to react at a temperature of 20 °C to 80 °C and after the reaction is complete, the product is isolated by filtration after diluting the reaction mixture with water. The method can also be carried out in such a way that the isolation of the product is carried out by filtration only after neutralization of the reaction mixture with an alkaline solution or carbonate and the filtrate obtained can be advantageously used for the preparation of sodium acetate, which has a wide range of uses in chemistry.

The advantage of the above procedure lies in its simplicity, low technical and thus economic complexity. In contrast to known procedures, wastewater can be easily used, which is also non-toxic, which is advantageous primarily from an ecological point of view. The method of using neutralized filtrates, which are discarded during product isolation, is also advantageous, because in this way it is possible to achieve approximately 80% utilization of the acetic anhydride entering the reaction. In the existing procedures, these wastes cannot be used well enough and are disposed of as waste.

As organic tertiary bases for cyclization, for example, tri-n-butylamine, pyridine, triethylamine, triethanolamine, N-methylpiperidine, or other available substances can be used. In practical use, no fundamental difference in the effect on the course of the reaction was found, which could indicate a greater advantage of using any of them. The advantage can only be decided on the basis of their availability, price ratio, or toxicity.

The method using neutralization of the reaction mixture for the production of the by-product - sodium acetate has the advantage that the reaction mixture does not have to be diluted as much, because the salinity of the resulting solution is sufficient to exclude all the product. Sodium acetate can then be obtained by crystallization from the separated mother liquors, or a saturated solution of sodium acetate can be directly used in other chemical productions, in which the pH of the aqueous medium is adjusted. This is most often the case in conventional dyeing productions. For neutralization, it is then essentially the same,

CS 269 846 Bl whether sodium hydroxide or carbonate solutions are used.

The amount of acetic anhydride for cyclization is always higher than the theoretical amount. The amount must always be chosen to be sufficient to dilute the reaction mixture enough to make it stirrable. A device with good stirring capability then requires a smaller amount of acetic anhydride for cyclization.

The following examples describe the reaction. The parts given are by weight.

Example 1

300 parts of acetic anhydride and 50 parts of pyridine are introduced into the reactor. 191 parts of N-phenylmaleamic acid are introduced into the mixture. The resulting suspension is heated to 60 °C for 3 hours with stirring and after this time it is poured into 7,500 parts of cold water. The precipitated product is suctioned off with suction and washed with 500 parts of warm water. After drying, 150 parts of N-phenylmaleimide are obtained in the form of yellow needles with a melting point of 90 °C, which can be recrystallized from ethanol.

Example 2

205 parts of N-4-tolylmaleamic acid are added to a mixture of 280 parts of acetic anhydride and 100 parts of triethylamine and the resulting suspension is heated for 2.5 hours at a temperature of 55 °C. After the reaction is complete, the mixture is diluted by adding 5,000 parts of cold water. The precipitated product is suction filtered, washed with water until the acidity is lost and dried. The yield of N-4-tolylmaleimide in the form of a yellow powder is 145 parts. The melting point of the product after recrystallization from ethanol is 150 °C.

Example 3

N-2-tolylmaleimide can also be prepared in the same manner as in Example 2 with a yield of 135 parts. The light yellow powder has a melting point of 72°C after recrystallization.

Example 4

350 parts of acetic anhydride and 130 parts of tri-n-butylamine are introduced into the reactor. 236 parts of N-4-nitrophenylmaleamic acid are added to the resulting mixture with stirring and the suspension is heated to a temperature of 60 °C for 6 hours with stirring. After the reaction is complete, the mixture in the reactor is not diluted by adding 5,500 parts of cold water and the precipitated product is separated by filtration. The resulting N-4-nitrophenylmaleimide in the form of bright yellow needles weighs 130 parts after drying. The pure substance has a melting point of 166 °C.

Example 5

In the same manner as in Example 5, N-3-nitrophenylmaleimide (yellow needles, melting point 125 °C) and N-2-nitrophenylmaleimide (also deep yellow needles, melting point 130 °C) can also be prepared in yields of about 125 parts.

Claims (2)

SUBJECT OF THE INVENTION 1. A process for the preparation of N-phenylmaleimide or its substituted derivatives of general formula I, in which B represents H, Cl, SO₂, H₃Na), COOH, OCH₂, NO₂ and CH₂, cyclization of N-phenylmaleamic acid or its substituted derivatives, characterized in that a mixture of 1 mole of N-phenylmaleamic acid or its substituted derivative, 2 to 6 moles of acetic anhydride and 0.1 to 2 moles of organic tertiary base is allowed to react at a temperature of 20 °C to 80 °C and after completion of the reaction the product is isolated by filtration after dilution of the reaction mixture CS 269 846 Bl with water. 2. The method according to item 1, characterized in that the isolation of the product is carried out by filtration after neutralization of the reaction mixture with an alkali hydroxide or carbonate solution.