JPH03261763A - Method for preventing polymerization of maleimides - Google Patents

Abstract

PURPOSE:To efficiently prevent polymerization of maleimides without coloring maleimides by using a specific phosphorus compound as a polymerization inhibitor. CONSTITUTION:For example, in a process for obtaining maleimides from maleic anhydride and amines, process for purifying crude maleimides by distillation, etc., polymerization of maleimides is prevented using at least one kind of phosphorus compound selected from a group consisting of phosphoric acid esters (e.g. ethyl diethyl phosphonoacetate or ethyl acid phosphate), phosphate [e.g. triphenyl phosphite or tris(nonylphenyl) phosphite] and phosphoric acid amides (e.g. hexamethylphosphoric triamide) as a polymerization inhibitor. The phosphorus compound is used at an amount of 0.0001-5wt.% preferably 0.001-1wt.% based on the raw material or maleimides.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for preventing polymerization of maleimides. Specifically, the present invention is a method for inhibiting the polymerization of maleimides using a specific phosphorus compound as a polymerization inhibitor, such as a process of producing maleimides from maleic anhydride and amines, and purifying crude maleimides by distillation or the like. The purpose of the present invention is to provide a method of significantly preventing the polymerization of maleimides by using this specific polymerization inhibitor in processes such as storing or transporting maleimides.

[Prior Art] Maleimides are extremely unstable compounds that easily cause polymerization reactions due to their molecular structure. Therefore, various methods have been proposed to inhibit polymerization in the process of producing maleimides from maleic anhydride and amines, the process of purifying crude maleimides, and the like. For example, during the production of maleimides, in order to prevent polymerization of maleimides during the reaction, maleamic acid is heat-treated under reduced pressure, and the generated maleimides are quickly distilled out of the reaction system. is published in 1977-
It is disclosed in Japanese Patent No. 27974. Also, JP-A-53
Publication No. 137956 discloses that maleimides are produced by previously adding hydrogen halide to the double bonds of maleic anhydride as a raw material to eliminate the polymerization reactivity of the double bonds, and then reacting with amines for dehydration and ring closure. A method is disclosed. However, none of these methods has disclosed a method for producing maleimides in good yield by preventing polymerization of maleimides.

Furthermore, methods for purifying crude maleimides with as little heat as possible have been disclosed, for example, in JP-A-58-96066 and JP-A-60-100.
No. 554, etc., purification is carried out by recrystallization at a relatively low temperature using a solvent such as methanol, toluene, or isopropanol.

However, even if purified under these conditions, polymerization will proceed while the maleimide is being stored, rendering it almost useless as a commercial product.

For example, if a maleimide homopolymer is contained in a maleimide, for example, if this maleimide and styrene or styrene and acrylonitrile are copolymerized, this copolymer contains a maleimide. Because the homopolymer is included, the heat resistance and strength are not as high as expected, and because the maleimide homopolymer is insoluble in the monomer, the appearance, especially the transparency, of the copolymer becomes extremely poor. This will greatly reduce the commercial value of the copolymer.

[Problem to be solved by the invention] As described above, although preventing the polymerization of maleimide compounds during manufacturing, purification, and transportation processes is a very important issue, there is no effective method for preventing polymerization. Very few proposals have been made so far.

SUMMARY OF THE INVENTION In view of the current situation, an object of the present invention is to provide a polymerization prevention method that effectively prevents the polymerization of maleimides without coloring the maleimides themselves.

[Means for Solving the Problems] In order to achieve the above object, the present inventors have made intensive studies and found that by using a specific phosphorus compound as a polymerization inhibitor, maleimides themselves can be prevented from being colored. They discovered that polymerization can be efficiently prevented and completed the present invention.

That is, the present invention provides a method for polymerization of maleimides, characterized in that at least one phosphorus compound selected from the group consisting of phosphoric acid esters, phosphorous acid esters, and phosphoric acid amides is used as a polymerization inhibitor. Regarding prevention methods.

The present invention will be explained in detail below.

Phosphate esters used in the present invention include ethyl diethyl phosphonoacetate, ethyl acid phosphate, β-chloroethyl acid phosphate, butyl acid phosphate, butyl pyrophosphate, butoxyethyl acid phosphate, and 2-ethylhexyl acid phosphate. , di(2-ethylhexyl) phosphate, ethylene glycol acid phosphate,
(2-hydroxyethyl) methacrylate acid phosphate, tris(2-chloroethyl) phosphate,
Examples include tris(dichloropropyl) phosphate, octyldichloropropyl phosphate, phenyldichloropropyl phosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, tricresyl phosphate, triphenyl phosphate, and the like.

In addition, the phosphite esters used in the present invention include triphenyl phosphite, tris(nonylphenyl) phosphite, triethyl phosphite, tris(2
-ethylhexyl) phosphite, tridecyl phosphite, tris(tridecyl) phosphite, tristearyl phosphite, diphenyl mono(2-ethylhexyl) phosphite, diphenyl monodecyl phosphite, diphenyl monotridecyl phosphite, dilauryl hydrogen phosphite phyto, dilauryl hydrogen phosphite, diphenyl hydrogen phosphite, tetraphenyl dipropylene glycol phosphite, tetraphenyltetra(tridecyl)pentaerythritol tetraphosphite, tetra(tridecyl)-4,4
-isopropylidene diphenyl phosphite, trilauryl trithiophosphite, bis(tridecyl)pentaerythritol diphosphite, bis(nonylphenyl)pentaerythritol diphosphite, distearyl pentaerythritol diphosphite, tris(2,4
- ditertiarybutylphenyl) phosphite, water-soluble bisphenol A/bentaerythritol phosphite polymer, hydrogenated I-sphenol A/phosphite polymer, and the like.

Further, examples of the phosphoric acid amide used in the present invention include hexamethylphosphoric triamide and the like.

Among the above phosphorus compounds, in the present invention, compounds selected from the group consisting of tris(2-chloroethyl) phosphate, trisnonylphenyl phosphite, tristearyl phosphite, distearyl pentaerythritol diphosphite, and hexamethylphosphoric triamide are used. At least one selected type can be suitably used.

Compared with p-methoxyphenol, hydroquinone, etc., which are generally used as polymerization inhibitors, the phosphorus compound specified by the present invention has a very high polymerization inhibitory effect on maleimides, as is clear from the Examples and Comparative Examples described below. A significant difference can be seen.

Examples of maleimides to which the polymerization prevention method of the present invention can be applied include maleimide, N-methylmaleimide, N-ethylmaleimide, N-hexylmaleimide, N-octylmaleimide, N-dodecylmaleimide, N-benzylmaleimide, N- Cyclohexylmaleimide, N-phenylmaleimide, N-nitrophenylmaleimide, N-
Methoxyphenylmaleimide, N-methylphenylmaleimide, N-carboxyphenylmaleimide, N-hydroxyphenylmaleimide, N-chlorophenylmaleimide, N-dimethylphenylmaleimide, N-dichlorophenylmaleimide, N-bromophenylmaleimide,
Examples include N-dibromophenylmaleimide, N-)lichlorophenylmaleimide, N-1libromophenylmaleimide, and solutions containing one or more of these, such as acrylonitrile, styrene, maleic anhydride, (meth) Examples include solutions of acrylic esters and mixed solutions thereof, but are not limited thereto.

The phosphorus compound specified by the present invention can be used in any step in the maleimide production process, such as in the raw material, during the amidation reaction, during the imidization reaction, during purification, during storage, and during transportation, and is excellent. Provides a polymerization prevention effect. In particular, when maleimides are stored for a long period of time, they can be stored stably without causing changes in the hue of the maleimides.

The amount of the phosphorus compound specified by the present invention depends on the temperature of each step,
Although it is determined appropriately depending on time, pressure, gas phase composition, liquid phase composition, etc., it is generally 0.0001 to 5% by weight, preferably 0.001 to 5% by weight based on the raw material or maleimide.
It is used in an amount of 1% by weight. Further, the phosphorus compound specified by the present invention can also be used in combination with other polymerization inhibitors, such as hydroquinone and p-methoxyphenol.

Furthermore, regarding the addition method, these polymerization inhibitors may be added as they are in liquid or powder form, or may be added after being dissolved in a solvent, raw material, etc.

[Example] Hereinafter, the present invention will be explained in more detail based on Examples.

Examples 1 to 12 and Comparative Examples 1 to 7 Maleimides and polymerization inhibitors were sealed in test tubes by changing various conditions such as the type of maleimide, the type of polymerization inhibitor, and the amount added. It was placed in an oil bath and heated for 3 hours. At this time, nitrogen gas was introduced into the gas phase portion of the sealed tube. After heating for 3 hours, the sealed tube was taken out from the oil bath, the maleimides in the sealed tube were cooled and crushed, and the purity was determined by analysis using high performance liquid chromatography.The results are shown in Table 1 below. I got it.

Example 13 Yellow N-phenylmaleimide 1 with a purity of 99.8% by weight
kg and 0.1 g of distearyl pentaerythritol diphosphite were heated from the outer shell part in a stainless steel container having a diameter of 10 CI, 11% and a height of 20 cm and equipped with a heating shell to bring the internal temperature to 100°C. At this time, N-phenylmaleimide was a yellow liquid.

Note that the gas phase part of the container was replaced with nitrogen gas.

When kept in this state for 30 days, the color of N-phenylmaleimide after 30 days remained the same as the initial color.
Analysis of this product by high performance liquid chromatography revealed that the purity was 99.6% by weight, with almost no change.

Claims (1)

[Claims] 1. Maleimides characterized in that at least one phosphorus compound selected from the group consisting of phosphoric acid esters, phosphorous acid esters, and phosphoric acid amides is used as a polymerization inhibitor. A method for preventing polymerization. 2. The phosphorus compound is at least one selected from the group consisting of tris(2-chloroethyl) phosphate, trisnonylphenyl phosphite, tristearyl phosphite, distearyl pentaerythritol diphosphite, and hexamethylphosphoric triamide. 2. The method of claim 1.