JPH0319226B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing maleimides. More specifically, the present invention relates to a method for producing industrially advantageous maleimides using primary amines and maleic anhydride as raw materials, and in particular, the present invention relates to a method for producing maleimides that are industrially advantageous, and in particular, the primary amines are pretreated with a strong organic or inorganic acid. The present invention relates to a method for obtaining a target maleimide with high selectivity by reacting with an amine salt to form an amine salt and subjecting this to a ring-closing imidization reaction with maleic anhydride. [Prior Art] Methods for producing maleimides have been studied for a long time. The most common method is to produce maleimide by dehydrating maleamic acid using a dehydrating agent such as acetic anhydride, which is also disclosed in US Pat. No. 2,444,536. . That is, it is a method in which maleic anhydride and an amine compound are reacted, and the resulting maleamic acid is dehydrated and ring-closing imidized in the presence of acetic anhydride and sodium acetate. This method requires more than the equivalent amount of expensive acetic anhydride to maleamic acid in the imidization reaction, and also requires a large amount of water to separate and recover the maleimide produced from the liquid after the imidization reaction. Therefore, it has the disadvantage of requiring a large amount of cost to treat a large amount of wastewater containing acetic acid. For these reasons, this method is too expensive to industrially produce imide compounds. Also, as in the specification of Japanese Patent Application Laid-Open No. 53-68770,
A method of reacting maleic anhydride with an amine compound in an organic solvent and carrying out a dehydration ring-closing reaction in the coexistence of an aprotic polar solvent such as dimethylformamide or dimethyl sulfoxide and an acid catalyst without isolating the maleamic acid produced. There is also. However, this method requires a large amount of expensive and toxic aprotic polar solvents such as dimethylformamide, which increases the production cost of maleimide. There are problems such as increased loss due to deterioration of the solvent, and furthermore, it is difficult to remove these aprotic polar solvents from the product maleimide due to their high boiling points. Therefore, it cannot be said that it is an excellent method. Furthermore, as disclosed in Japanese Patent Publication No. 51-40078, solvents such as toluene, xylene, and chlorobenzene having a boiling point of 80°C or higher and chlorosulfonic acid, p-toluenesulfonic acid, and benzenesulfone are used as diluents. There is also a method of carrying out thermal dehydration ring closure with an acid catalyst such as orthophosphoric acid, pyrophosphoric acid, phosphorous acid, etc., and distilling the water produced at this time out of the system by azeotropy with the solvent. Compared to the above two methods, this method not only does not require large amounts of expensive dehydrating agents such as acetic anhydride, but also
It is excellent in that it has a high capacity for separating and recovering the maleimide produced. However, this method uses relatively many expensive acid catalysts such as chlorosulfonic acid, p-toluenesulfonic acid, benzenesulfonic acid, orthophosphoric acid, pyrophosphoric acid, phosphorous acid, etc. The yield is also low and it is not economically satisfactory as an industrial production method. [Problems to be Solved by the Invention] As described above, the currently existing methods for producing maleimides have many problems, none of which are satisfactory for industrial implementation. Thus, an object of the present invention is to provide a method for producing maleimides on an industrial scale in a safe and simple manner at high yield and at low cost. [Means for Solving the Problems] The present inventors have been conducting research on the synthesis reaction of maleimides for a long time. And here is the acid and the first
The inventors discovered that maleimides can be synthesized in a high yield in one step by reacting amine salts produced from amines with maleic anhydride, leading to the completion of the present invention. Generally, according to known methods, the synthesis of maleimides is accomplished by cyclodehydration of maleamic acids obtained by the reaction of primary amines and maleic anhydride. However, since maleamic acids, which are the raw materials for maleimides, are extremely thermally unstable, a rearrangement reaction from cis to trans forms easily occurs during thermal dehydration of maleamic acids, producing fumaramic acids. In addition, in addition to the formation of maleimides due to the intramolecular dehydration reaction of maleamic acids, there are many undesirable side reactions such as intermolecular dehydration reactions, such as dimerization of maleamic acids. The reaction yield for these compounds was very low. In order to suppress such side reactions, attempts have also been made to continuously add maleamic acids to the reaction system to carry out the ring-closing imidization reaction. However, even in this method, the maleamic acids themselves are exposed to high temperatures during ring-closing imidization, so side reactions such as those described above cannot be effectively prevented. As described above, the existing synthesis reactions for maleimides are based on the dehydration ring-closing reaction of maleamic acids, and no matter which method is used, the yield of maleimides is low due to the thermal instability of maleamic acids. There was no way to avoid it. However, the present inventors have discovered that such problems can be solved at once by performing a ring-closing imidization reaction using an amine salt and maleic anhydride. This is because amine salts prepared from primary amines and organic or inorganic acids are completely thermally stable, and maleic anhydride itself is also thermally stable enough to reach its boiling point (202°C). ), it does not change in quality. Thus, even during the ring-closing imidization reaction at a high temperature of 100 to 250°C, these two reaction raw materials are subjected to the reaction with almost no thermal deterioration. In other words, maleimides can be synthesized in good yields with almost no side reactions as described above occurring. Considering that amine salts obtained by the reaction of organic or inorganic acids with primary amines are considered to be chemically stable, this amine salt can be easily converted to maleic anhydride even though the reaction temperature is relatively high. It must be said that it is completely surprising that the reaction produces maleimides in good yield. That is, the present invention involves reacting an amine salt of a primary amine and an organic or inorganic acid at a high temperature in the presence of an organic solvent capable of azeotroping with water, while discharging the water produced from the system together with the organic solvent. ,
This is a method for producing maleimides, which is characterized by carrying out a ring-closing imidization reaction with maleic anhydride. [Function] The most distinctive feature of the present invention is that maleimides are produced in one step by reacting an amine salt obtained by the reaction of a primary amine with an acid with maleic anhydride. The primary amines used in the present invention are listed below. Methylamine, ethylamine, n-propylamine, isopropylamine,
n-butylamine, sec-butylamine, tert-
Butylamine, n-hexylamine, n-dodecylamine, allylamine, benzylamine, cyclohexylamine, aniline, nitroaniline,
These include aminophenol, aminobenzoic acid, anisidine, ethoxyphenylamine, monochloroaniline, dichloroaniline, toluidine, xylidine, ethylaniline, trichloroaniline, tribromoaniline, and the like. In addition, as the inorganic or organic acid, a strong acid with a pKa of 3 or less is preferable, and specifically, sulfuric acid, sulfurous acid,
Sulfuric anhydride, p-toluenesulfonic acid, benzenesulfonic acid, methanesulfonic acid, ethylsulfonic acid, octylsulfonic acid, decanesulfonic acid, chlorobenzenesulfonic acid, phosphoric acid, phosphorous acid, pyrophosphoric acid, metaphosphoric acid, chloroacetic acid, dichloro Acetic acid, trichloroacetic acid, fluoroacetic acid, malonic acid,
Carboxylic acids such as oxalic acid are used. The amounts of acid and amine need only be below the stoichiometric amount in which all of the hydrogen in the acid reacts with primary amines and becomes an amine salt, and does not react with primary amines. There is no problem even if some acid remains. For example, when the acid is a tribasic acid, this acid reacts with a primary amine and can take three forms, monoamine salt, diamine salt, and triamine salt, depending on the amount of each. Therefore, the primary amine and acid Possible forms of the raw material amine salt produced by the reaction include a mixture of a monoamine salt and an acid, a monoamine salt, a mixture of a monoamine salt and a diamine salt, a diamine salt, a mixture of a diamine salt and a triamine salt, and a triamine salt. However, in either case, it can be used as a reaction raw material. The solvent used in the reaction is preferably one that can azeotropically remove the water produced by the reaction with maleic anhydride, is inert, and does not participate in the reaction, such as benzene, toluene, petroleum distillates with a boiling point of 50 to 120°C, xylene, etc. , ethylbenzene, isopropylbenzene, cumene, mesitylene, tert-butylbenzene, pseudocumene, trimethylhexane, octane, tetrachloroethane, nonane, chlorobenzene, ethylcyclohexane, petroleum fraction with a boiling point of 120-170°C, m-dichlorobenzene , sec-butylbenzene, p-dichlorobenzene, decane, p-
Examples include cymene, o-dichlorobenzene, butylbenzene, decahydronaphthalene, tetrahydronaphthalene, dodecane, naphthalene, cyclohexylbenzene, and petroleum fractions with a boiling point of 170 to 250°C. The amount of the solvent to be used is 0.1 to 50 times (volume), preferably 1 to 10 times the amount of the primary amine, in order to conduct the reaction smoothly and satisfy economic conditions. Further, a maleimide having a boiling point suitable for the reaction conditions is selected while taking into account the solubility, price, ease of handling, etc. of the maleimide. Furthermore, when considering the separation of the maleimides from the solvent after the reaction is completed, it may be advantageous to use a low boiling point solvent and carry out the reaction under pressure. Preferred conditions for producing amine salts are selected depending on the physical properties of the primary amines, but they can usually be synthesized by reacting acids and primary amines at a temperature of 100°C or less. . This reaction may be carried out in an inert solvent such as benzene, toluene, xylene, hexane, etc., or may be carried out in water. However, in consideration of the maleimide production process that follows this reaction, it goes without saying that it is preferable to use a solvent that is also used in the next process. In the method of carrying out the present invention, first, an amine salt produced by a reaction between a primary amine and an acid and maleic anhydride are heated in an organic solvent, optionally with a stabilizer added thereto. The higher the temperature, the faster the ring-closing imidization reaction rate and the higher the imidization yield. Therefore, the reaction is usually heated at 100 to 250°C, preferably 130 to 200°C, for 1 to 15 hours, and the water produced by the reaction is distilled out of the system together with the organic solvent, thereby achieving a high yield. maleimides can be produced. Stabilizers include methoxybenzoquinone, p-
Methoxyphenol, phenothiazine, hydroquinone, alkylated diphenylamines, methylene blue, tert-butylcatechol, tert-butylhydroquinone, copper dimethyldithiocarbamate, zinc dimethyldithiocarbamate, copper dibutyldithiocarbamate, copper salicylate, thiodipropionic acid esters, Mercaptobenzimidazole, triphenyl phosphite, alkylphenols, alkyl bisphenols, etc. are used. The effect of these stabilizers is to allow the maleimide produced by the ring-closing imidization reaction to exist stably without deterioration even under the high temperature of the ring-closing imidization reaction. Regarding the amount added, it is 0.005 mol% to 0.5 mol% based on the primary amines, preferably
It is 0.05-0.3 mol%. In a particularly preferred method of implementation, maleic anhydride is fed continuously or semi-continuously at a rate commensurate with the consumption rate of maleic anhydride in the reaction system. Maleic anhydride is supplied in an amount of 0.1 to 0.85 mol per mol of amine salt while discharging the produced water from the system. Since the amine salt as a reaction raw material is not dissolved in the organic solvent used in the present invention, the reaction system is essentially separated into two layers, an organic layer and an amine salt layer. This state is the same during the reaction and at the end of the reaction, and the separation operation is easy. However, after the reaction is complete, the amine component in the amine salt changes to maleimides. Free acid content increases in the amine salt layer. The amount of increase in the acid component at this time is approximately equal to the stoichiometric amount of the maleimides produced. For example, when a diamine salt alone is used as a reaction raw material, the amine salt layer after the ring-closing imidization reaction is a diamine salt and a monoamine salt, or a monoamine salt layer, although this will vary depending on the amount of maleic anhydride used in the reaction. It is a mixture of acid and other substances. Subsequently, when carrying out the next reaction, amine equivalent to the amount of amine consumed in the previous reaction is added to the amine salt layer, and the free acid content is converted into amine salt, thereby converting the amine salt into the initial amount of the previous reaction. Readjust the condition. Thereafter, maleic anhydride is added and the imidization reaction is carried out under the same reaction conditions as in the previous reaction, whereby maleimides can be produced in good yield. The extent to which maleimides are produced from the amine salt depends on the amine salt, maleic anhydride, solvent, reaction temperature, and reaction time, but when performing this reaction repeatedly, only the amount of amine consumed in the reaction can be generated from the amine salt. It is preferable to produce maleimides in high yield by adding them to the layer. More specifically, it is possible to cause most of the amine in the amine salt to react with maleic anhydride, but in order to maintain a stable reaction system and prevent dimerization of the maleimides produced, it is necessary to react with the amine salt. 30-90% of the amines in, preferably 50-70
% with maleic anhydride gives good results. Among the strong acids used, the smaller the pKa value, the higher the dimerization reaction activity of the maleimides produced.
Care should be taken not to exceed the weight percentage. [Examples] The present invention will be explained in more detail by Examples below, but it goes without saying that the present invention is not limited to the scope of these Examples. Example 1 115 g of 85% pure orthophosphoric acid and 100 g of ortho-xylene were placed in a flask equipped with a thermometer, a cooling tube equipped with a water separator, a dropping funnel, and a stirrer, and the internal temperature was adjusted to 90°C. Then, a solution prepared by dissolving 149 g of cyclohexylamine in 500 g of ortho-xylene was added dropwise to this acid solution. At this time, heat was generated, but the internal temperature was kept at 90°C by adjusting the bath temperature. After the addition was completed, a milky white liquid with relatively high viscosity was obtained. Subsequently, 74 g of maleic anhydride was added, and the slurry was heated to 145° C. with stirring to cause a ring-closing imidization reaction. The reaction was allowed to proceed for 5 hours while water produced during the reaction was distilled out of the system together with the solvent.
After the reaction was completed, only the amine salt layer was left in the flask, and only the organic layer was separated from the reaction solution, which had been separated into two layers. The weight of this organic layer was 740g, and the concentration of N-cyclohexylmaleimide in this layer was analyzed by gas chromatography to be 18% by weight.
It was hot. This is N-cyclohexylmaleimide
equivalent to 133.2g (0.74 mol). The amine salt layer weighed 170g. The nitrogen content present in this was determined by elemental analysis to be 5.9% by weight, which corresponded to 71.0g of cyclohexylamine. Thus, 78 g (0.79 mol) of cyclohexylamine was consumed in the reaction.
On the other hand, the amount of N-cyclohexylmaleimide produced was 133.2 g (0.74 mol), which corresponded to 93.7 mol% of the consumed N-cyclohexylamine, and was also consumed by the reaction in the amine salt. It can be seen that the amine content was 52.3%. Next, add 100g of ortho-xylene to the amine salt layer remaining in the flask and bring the internal temperature to 90℃.
Adjusted to. Next, 78 g of cyclohexylamine corresponding to the consumed cyclohexylamine was added together with 500 g of ortho-xylene to form an amine salt. Subsequently, 74 g of maleic anhydride was added, and the mixture was reacted for 5 hours under the same conditions as the previous reaction, and the amount of N-cyclohexylmaleimide produced was measured to be 134.6 g (0.75 mol). This corresponds to 94.9 mol% based on the added cyclohexylamine. The same reaction was repeated and the results shown in Table 1 were obtained. In addition, in the fifth and sixth reactions, 0.2 g of copper dibutyldithiocarbamate was added and reacted when maleic anhydride was added.

[Table] Example 2 Sulfuric acid (98%
%) 100g was added and the internal temperature was adjusted to 50℃. Then, a solution of 73 g of n-butylamine dissolved in 300 g of ethylbenzene was added dropwise. At this time, heat was generated, but the internal temperature was adjusted to 50°C by adjusting the bath temperature. After the reaction was completed, a slightly white and cloudy reaction solution was obtained. Next, add maleic anhydride to this amine salt solution.
After adding 98 g of copper dibutyl dithiocarbamate and 0.05 g of copper dibutyl dithiocarbamate, the slurry liquid was heated to 139°C, and the produced water was distilled out of the system together with ethylbenzene for 10 hours.
Made it react. After the reaction is complete, leave only the amine salt layer in the flask from the reaction solution that has been separated into two layers in the reaction flask, separate only the organic layer, and collect the reaction product liquid.
I gained 430g. The concentration of N-butylmaleimide in this was analyzed by gas chromatography and found to be 19.6% by weight. This is 84.3g (0.55g) of N-butylmaleimide.
moles). In addition, the nitrogen present in 126g of amine salt layer was measured by elemental analysis and was found to be 4.3
% by weight, which corresponds to 28.3 g as n-butylamine component. Therefore, n-butylamine consumed in the reaction was 44.7 g (0.61 mol), while N-butylmaleimide produced was 84.3 g (0.55 mol), which corresponds to 90.2 mol% of the consumed amine. . Subsequently, the amine salt layer remaining in the flask was heated to 50°C, and 300 g of ethylbenzene and 44.7 g of n-butylamine were added to prepare an amine salt solution.
Next, 98 g of maleic anhydride was added, and the reaction was carried out for 10 hours under the same conditions as before, and the amount of N-butylmaleimide produced was measured and found to be 85.1 g (0.56 mol). This is 91.5 for the added n-butylamine.
Corresponds to mol%. Example 3 96 g of methanesulfonic acid was fed into the same reactor used in Example 1 and heated to 50°C. Then, a solution of 99 g of cyclohexylamine dissolved in 500 g of p-cymene was added dropwise to obtain a p-cymene slurry of cyclohexylamine salt of methanesulfonic acid. Subsequently, 100 g of maleic anhydride was added to this slurry, and the slurry liquid was heated to 180° C. while stirring, and the reaction was allowed to proceed for 2 hours while distilling water produced by the reaction out of the system together with the solvent. After the reaction was completed, only the amine salt layer was left in the flask from the reaction solution which had been separated into two layers, and only the organic layer was separated. The weight of this organic layer was 656 g, and the concentration of N-cyclohexylmaleimide in this layer was analyzed by gas chromatography to be 18.5% by weight.
It was hot. This is N-cyclohexylmaleimide
Equivalent to 121.4g. The amine salt layer weighed 126 g. The nitrogen content present in this was determined by elemental analysis to be 3.4% by weight, which corresponds to 30.3g of cyclohexylamine. Therefore, 68.7 g of cyclohexylamine was consumed in the reaction, and 121.4 g of N-cyclohexylmaleimide was produced, which corresponds to 97.8 mol % based on the consumed cyclohexylamine. Next, 69 g of cyclohexylamine was added to the amine salt layer remaining in the flask at 50°C and p-
A mixed solution with 300 g of cymene was added to form an amine salt solution. Next, 100 g of maleic anhydride was added, and the mixture was reacted for 2 hours under the same conditions as the previous reaction, and the amount of N-cyclohexylmaleimide produced was measured and found to be 122.1 g. This is for the added cyclohexylamine
This corresponds to 97.9 mol%. Example 4 115 g of 85% pure orthophosphoric acid and 200 g of toluene were placed in a pressurized vessel equipped with a thermometer, a water separator, a cooling tube, a dropping funnel, and a stirrer, and the internal temperature was adjusted to 30°C. Then, a mixed solution of 62 g of methylamine and 800 g of toluene was added dropwise thereto.
After the dropping was completed, a white liquid with relatively high viscosity was obtained. Subsequently, 200 g of maleic anhydride was added, and the slurry was stirred and heated to 150° C. under a pressure of 2.8 atm. The reaction was allowed to proceed for 3 hours while distilling water produced by the reaction out of the system together with the solvent. After the reaction was completed, the concentration of N-methylmaleimide in the reaction solution was measured and found to be 11.0% by weight. This corresponds to 133.9 g of N-methylmaleimide. Also, the amine salt layer is
It was 121g. The nitrogen content present in this was determined by elemental analysis to be 8.6% by weight, which corresponds to 23g of methylamine. Therefore, this corresponds to 95.9 mol% of the methylamine consumed in the reaction. Next, a mixed solution of 39 g of methylamine and 600 g of toluene was added to the amine salt layer remaining in the reactor to prepare the amine salt layer again. Next, 200 g of maleic anhydride was added, and the reaction was carried out for 3 hours under the same conditions as the previous reaction.
- Methylmaleimide was measured and found to be 133.0g. This corresponds to 95.2 mol% based on the added methylamine.

Claims (1)

[Claims] 1. Water produced by reacting an amine salt produced from a primary amine and an organic and/or inorganic acid at a high temperature in the presence of an organic solvent capable of azeotroping with water, together with the organic solvent. While discharging it out of the system,
A method for producing maleimides, which comprises carrying out a ring-closing imidization reaction with maleic anhydride. 2 The amine salt is obtained by adding a new amine corresponding to the amount of amine consumed by the reaction to the amine salt layer obtained after the completion of the ring-closing imidization reaction, and converting the free acid content into an amine salt. The method according to claim 1, characterized in that: