JPH06128222A - Production of maleimide - Google Patents

Abstract

PURPOSE:To produce a maleimide in high yield by heating a maleinamic ester and carrying out alcohol removal reaction to form a ring closure imide while distilling away a formed alcohol and a maleimide. CONSTITUTION:A maleinamic ester of the formula (R is 1-8C alkyl) is heated, alcohol removal reaction is carried out while distilling away an alcohol and a maleimide formed in the reaction out of the reaction system so that reaction between the formed maleimide and the maleinamic ester of the raw material is prevented and polymerization reaction of maleimide is suppressed to give a corresponding high-purity N-nonsubstituted maleimide in high yield and economically. Maleimide, for example, is required to have heat resistance. Maleimide is useful as an intermediate raw material for medicine and agricultural chemical besides raw material for synthetic resin. Since the alcohol removal reaction by this method is readily advanced, maleimide is obtained more efficiently than using a dehydrating agent. Since a specific purifying process is not required, manufacturing cost can extremely be reduced.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing maleimide, and more specifically, to produce N-unsubstituted maleimide which is a high yield, high purity and economically compatible with N-unsubstituted maleamic acid ester as a starting material. On how to do. The maleamic acid ester and maleimide in the present invention mean N-unsubstituted maleamic acid ester and N-unsubstituted maleimide, respectively. Maleimide is a compound useful as an intermediate raw material for medicines, agricultural chemicals, etc. in addition to, for example, a raw material of a synthetic resin required to have heat resistance.

Many methods are known for the production of maleimides. For example, US Pat. No. 3,899,50
No. 9 describes a continuous recycle production method in which maleic acid or mixed maleic acid of hydrocarbon and ammonia are reacted in the gas phase in the presence of a dehydration catalyst. European Patent No. 82620 discloses a production method by ammoxidation of 1,3-butadiene and ammonia in the presence of an oxidation catalyst composed of a variable valence metal oxide, and JP-A-60-188367 discloses. , A method for producing succinimide by oxidative dehydrogenation in the presence of a specific catalyst is described. However, all of these methods have drawbacks such as low yield, complicated operation, and high cost. A method is also known in which maleic anhydride is reacted with furan, cyclopentadiene or the like to form a Diels-Alder adduct, which is treated with ammonia to be converted into an imide compound and further thermally decomposed to obtain a maleimide. However, this method has complicated steps and is not suitable for industrial practice. The most general method for producing maleimide is a method in which a maleamic acid is dehydrated and cyclized with a dehydrating agent. For example, German Patent No. 1
Japanese Patent No. 934791 discloses a method for producing maleimide using orthophosphoric acid as a dehydrating agent. However, this method has drawbacks such as low yield. In the method described in JP-A-50-126659,
Acetyl chloride, benzoyl chloride, thionyl chloride, phosphorus pentoxide, etc. are used as dehydrating agents, but all of these dehydrating agents have high reactivity with water, and therefore are difficult to handle and have strong corrosiveness. Therefore, this method has low workability,
Equipment cost is also high and not suitable for industrial implementation. Japanese Unexamined Patent Publication No. 64-7148 discloses a method for producing maleimide using cyanuric chloride as a dehydrating agent and N, N-dimethylformamide as a solvent. However, since this method uses expensive and toxic cyanuric chloride and dimethylformamide, it cannot be said to be suitable for industrial practice. In addition, since aprotic polar solvents such as dimethylformamide have a high boiling point, it is difficult to separate and remove them from the product maleimide. On the other hand, regarding the method for producing an N-substituted maleimide derivative, for example, in JP-A-62-215563, a maleic acid monoester is reacted with an isocyanate compound to form a maleamic acid monoester, and then a high vacuum is produced. There is disclosed a method for producing an N-substituted maleimide by subjecting this to a dealcoholization reaction by heating to cause ring-closing imidization under conditions. However, according to this method, the raw material isocyanate compound is relatively expensive, and when the dealcoholization reaction is carried out, 10 to ³ to 1 is used.
Since a high vacuum of 0 to ⁵ mmHg is required, enormous cost is required for facility investment such as a high-performance vacuum pump and its accompanying equipment in order to realize such a vacuum condition. This is a completely disadvantageous method. In addition,
In this method, during the dealcoholization reaction of maleamic acid monoester, the alcohol produced is coagulated and separated by a trap, while the N-substituted maleimide compound of the reaction product is dispersed as a precipitate by dispersing the reaction solution in water. (See Example 1 of the same publication). In addition, JP-A-3-1183
No. 62 discloses a method for producing an N-substituted maleimide by subjecting an N-substituted maleamic acid monoester to ring-closing imidation by dealcoholation reaction in the presence of an acid catalyst and superheated steam. However, this method has a disadvantage in that it is economically disadvantageous as compared with the method of carrying out dealcoholization reaction by simply heating in that superheated steam is used.
This method can be performed in either a batch system or a continuous system. In the case of a batch system, a mixture of a maleamic acid ester and an acid catalyst is introduced into a reactor, and superheated steam is contacted with the mixture to carry out a dealcoholization reaction. (See page 5, upper left column of the same publication). Further, according to the continuous method, the reaction mixture is taken out from the reaction vessel together with water vapor and cooled to obtain the produced N-substituted maleimide (see Example 1 of the same publication). Further, in JP-A-3-173866, an N-substituted maleinamic acid monoester, an acid catalyst and a mixture of an inert solvent and an alcohol are heated to carry out a ring-closing imidation by a dealcoholization reaction to carry out an N-substituted. A method of making a maleimide is disclosed. In this method, a dealcoholization reaction is carried out under reflux with heating and stirring, and then the reaction liquid is cooled to first separate an aqueous layer (acid catalyst) and then an N-substituted maleimide from an organic layer. (See Example 1 of the same publication). Further, in JP-A-3-184956, N-substituted maleamic acid esters are reacted with alcohol in the presence of an acid catalyst to esterify the N-substituted maleamic acid esters thus obtained in an inert solvent. Is a method for producing an N-substituted maleimide by heating in the presence of an acid catalyst to carry out a dealcoholization reaction, in which a polymerization inhibitor is added to the reaction system particularly in the ring-closure imidization step by dealcoholization reaction. Disclosed is a method for producing N-substituted maleimides. In the ring-closure imidization step by this method, the amount of the solvent in the reaction system is kept constant by azeotropically removing the produced alcohol together with the solvent using the solvent, and successively supplementing the reduced solvent (6th publication of the publication). (See bottom right column of page). Further, the reaction solution is cooled and then washed with water to first separate the aqueous layer (acid catalyst) and then the N-substituted maleimide from the organic layer (see Example 1 of the same publication). Furthermore, JP-A-4-221365
The publication discloses a method for producing an N-substituted maleimide in which a N-substituted maleamic acid monoester is subjected to ring-closure imidization in a solvent in the presence of a catalyst comprising an alkali metal salt of an inorganic acid and / or an organic acid. There is. In this method, the reaction is carried out at room temperature (25 ° C.), after the reaction is completed, the catalyst is separated by filtration, and the N-substituted maleimide is separated from the resulting reaction solution (see Example 1 of the same publication).

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The inventors of the present invention have described a method for producing an N-substituted maleamic acid ester and an N-substituted maleimide described in JP-A-4-221365, etc., to produce a maleamic acid ester and a maleimide. However, when compared with the yields of the N-substituted maleamic acid ester and the N-substituted maleimide described in these publications, the results were remarkably low. According to the research conducted by the present inventors, it has been found that there are various causes for the above result. For example, since the solubility of the starting material, maleamic acid, in the solvent used for the esterification reaction is extremely low, the esterification reaction has to be carried out in a slurry state, and as a result, the yield of the maleamic acid ester is significantly increased. It will be low. When the imidization reaction is further continued, the reaction system is still in a slurry state and the reaction practically does not proceed. Therefore, the yield of the obtained maleimide is several mol% with respect to the maleic acid as a starting material. It will be nothing more. Further, maleimide has higher reactivity than N-substituted maleimide, and facilitates a polymerization reaction based on the maleimide double bond or an addition reaction based on an active hydrogen atom bonded to a nitrogen atom in the reaction system. It causes it to change in quality immediately. Furthermore, the amide group of the maleamic acid ester has one active hydrogen atom more than the amide group of the N-substituted maleamic acid ester, and therefore has a different chemical property. As a result, the maleic acid ester and the maleimide formed are different from each other. Side reactions tend to occur such that the reaction easily occurs. Especially in the presence of excess acid catalyst, the proportion of these side reactions increases significantly. In short, the chemical properties of the N-substituted maleamic acid ester and the maleic acid ester, and the chemical properties of the N-substituted maleimide and the maleimide are significantly different, in other words, the amide group of the maleamic acid ester is bound to each other. 1 hydrogen
Depending on whether the number is 2 or 1, and whether the atom bonded to the nitrogen atom of the imide ring is a hydrogen atom or a carbon atom, the chemical properties of the N-substituted compound and the N-unsubstituted compound. It is completely different, and it is no exaggeration to say that they are completely different compounds, and it was found that the known method for producing an N-substituted maleimide cannot be directly applied to the production of maleimide. An object of the present invention is to solve the above problems and provide a method for producing a corresponding maleimide in a high yield by ring-closing imidation by dealcoholization reaction of a maleamic acid ester by heating.

Means for Solving the Problems As a result of intensive studies to solve the above problems, the inventors of the present invention promptly identified a maleimide as a reaction product and a maleamic acid ester as a raw material in a reaction system. Separation, that is, by carrying out a dealcoholization reaction while distilling the alcohol and maleimide produced by the reaction out of the reaction system, the reaction between the maleimide product and the maleamic acid ester as a raw material is prevented, and the maleimide It has been found that it is possible to suppress the polymerization reaction of and the maleimide which is the target compound can be obtained in high yield, and the present invention has been completed based on this finding. That is, the invention has the general formula (1):

[Chemical 2] (In the formula, R represents an alkyl group having 1 to 8 carbon atoms), the maleic acid ester represented by the formula (1) is heated, and an alcohol produced when the corresponding maleimide is produced by ring-closing imidation by dealcoholization reaction and A method for producing a maleimide, which comprises carrying out a dealcoholization reaction while distilling the maleimide out of the reaction system. Hereinafter, the present invention will be described in detail. In the above general formula (1), R has 1 carbon atom.
To 8 are straight-chain or branched alkyl groups, and specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group,
Examples thereof include a tert-butyl group, an amyl group, a sec-amyl group, an isoamyl group, an n-hexyl group, an isohexyl group, an n-heptyl group, an n-octyl group and a 2-ethylhexyl group. Specific examples of the maleamic acid ester represented by the general formula (1) used in the present invention include maleic acid methyl ester, maleamic acid ethyl ester, maleamic acid n-propyl ester, maleamic acid isopropyl ester, Maleamic acid n-butyl ester, maleamic acid isobutyl ester, maleamic acid sec-butyl ester, maleamic acid tert-butyl ester, maleamic acid amyl ester, maleamic acid sec-amyl ester, maleamic acid isoamyl ester, Maleamic acid n-hexyl ester,
Examples thereof include maleic acid isohexyl ester, maleamic acid n-heptyl ester, maleamic acid n-octyl ester, and maleic acid 2-ethylhexyl ester. These maleamic acid esters can be easily prepared from alcohol and maleamic acid by a known method. In the present invention, when a maleimide ester of the general formula (1) is subjected to ring-closure imidation by a dealcoholization reaction by heating to produce a corresponding maleimide, the produced alcohol and maleimide are distilled out of the reaction system immediately after the production. It is characterized by carrying out a dealcoholization reaction, but for that purpose the maleic acid ester as a starting material is scarcely distilled, and the dealcoholization reaction is carried out at the operating pressure and temperature at which the alcohol and maleimide produced are mainly distilled. Should be done. That is, in general, the boiling point of each compound decreases in the order of maleamic acid ester, maleimide and alcohol, so that the dealcoholization reaction proceeds efficiently at the operating pressure and temperature of the reaction system, and the maleic acid is not less than the boiling point of maleimide. It may be adjusted so as to be not higher than the boiling point of the amic acid ester. The operating pressure and temperature of the reaction system are
The maleic acid ester of the general formula (1), which is the starting material, differs depending on the type of the maleamic acid ester and cannot be specified unconditionally, but the operating pressure is usually 500 to 1 mmHg, and particularly 300 to 3 m.
The range of mHg, the reaction temperature is 20 ~ 200 ℃, especially 7
It is preferably in the range of 0 to 180 ° C. The reaction time is
In the above operating pressure and temperature range, usually 1 to 5
It's about time. In the present invention, the target maleimide can be produced in a particularly high yield by selecting the operating pressure and temperature such that the produced alcohol and maleimide do not substantially exist in the reaction system. When the operating pressure of the reaction system is higher than the above range or the operating temperature is lower than the above range, the dealcoholization reaction does not proceed sufficiently, and the produced alcohol and maleimide are distilled out of the reaction system. However, the maleimide and the maleamic acid ester may react in the reaction system. Also, the operating temperature is too high than the above range,
If the operating pressure is lower than the above range, a side reaction may occur to significantly reduce the purity of the target compound, maleimide, or the starting material, maleamic acid ester, may be distilled out of the reaction system. There is also. The dealcoholization reaction in the present invention proceeds by heating, but a catalyst may be used to increase the reaction rate. As this catalyst, any catalyst can be used as long as it is a catalyst used for dealcoholization reaction. As a specific example,
Inert inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, carbonic acid and phosphoric acid and their metal salts, organic acids such as acetic acid, maleic acid, fumaric acid, succinic acid and phthalic acid and their metal salts or their acid components Examples thereof include those supported on various carriers and acidic ion exchange resins. Further, in the dealcoholization reaction of the present invention, a polymerization inhibitor may be used. As this polymerization inhibitor, any of those generally used as a polymerization inhibitor can be used. Specific examples include phenol, methoxyphenol, tert-butylcatechol, hydroquinone, tert-butylhydroquinone, dilauryl thiodipropionate, distearyl thiodipropionate, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, zinc dibutyldithiocarbamate, Nickel dibutyldithiocarbamate, copper dibutyldithiocarbamate, sodium salicylate,
Examples thereof include phenyl salicylate, phenothiazine, 2-mercaptobenzimidazole and triphenylphosphite. In the present invention, alcohol and maleimide are distilled out of the reaction system as reaction products, but these reaction products can be collected by a conventionally known method such as cooling. At this time, if the alcohol and the maleimide are separated and collected, the subsequent separation and purification steps become unnecessary, so it is preferable to divide and collect the reaction product.

EXAMPLES The present invention will be described in more detail below with reference to examples. Example 1 A vacuum distillation apparatus equipped with a 500 ml flask was charged with 129.0 g (1.0 mol) of maleic acid methyl ester and 0.1 g of copper dibutyldithiocarbamate, and the reaction temperature was 150 ° C. and the operating pressure was 15 mmHg. A dealcoholization reaction was performed. The distillate was introduced into a receiver kept at 80 ° C. and collected to obtain 64.2 g of a white solid. When this white solid was analyzed by nuclear magnetic resonance analysis (NMR analysis), it was confirmed to be maleimide. Furthermore, the content of maleimide in the white solid was measured by gas chromatography and found to be 99.5 mol% or more. Therefore, 65.9 mol% relative to maleic acid methyl ester
Maleimide was obtained with a yield of. Examples 2 to 5 In Example 1, the dealcoholization reaction of maleic acid methyl ester was carried out in the same manner as in Example 1 except that the reaction temperature, the operating pressure, and the presence or absence of the catalyst were changed. The results are shown in Table 1.

[Table 1] Note: (1) Strongly acidic ion exchange resin (DI, manufactured by Mitsubishi Kasei Co., Ltd.)
AION-PK216), amount used 7.2 g (2) Silica carrier (Fuji Devison Co., Ltd., 150 μ)
Orthophosphoric acid 33% supported on m), usage amount 2.0 g Comparative Example 1 According to the method for producing an N-substituted maleimide from an N-substituted maleamic acid described in JP-A-3-184956, maleimide acid to maleimide is used. Was manufactured. In a 500 ml four-necked flask equipped with a thermometer, a cooling pipe equipped with a water separator, a toluene supply pipe and a stirrer, 23.0 g (0.2 mol) of maleamic acid, 180 ml of toluene,
55.3 g (0.6 mol) of isobutyl alcohol and 2.0 ml of concentrated sulfuric acid were charged, and the reaction temperature was kept at 80 ° C. by heating and stirring to reduce the pressure, and water produced by the reaction was distilled out of the system together with toluene. While carrying out the esterification reaction for 1 hour. At this time, the reaction solution was in a slurry form. Then, the reduced pressure was released, and 0.1 g of p-methoxyphenol was added to the flask while still at 80 ° C. When heating is started again under normal pressure, toluene is supplied into the flask at a rate of 180 ml / h from the toluene supply pipe from the time when the toluene starts to reflux, and 180
The toluene was extracted at a rate of ml / h. At this time, the reaction system was in the form of a slurry, and there was some solid mass. After completion of the reaction, filtration was carried out and the solid collected by filtration was analyzed by high performance liquid chromatography to give 3.2 mol% maleimide. As a result of analyzing the organic layer by gas chromatography, the maleimide was 6.0 mol%. Was obtained. The yield of maleimide based on the maleamic acid used as the starting material was only 9.2 mol%. Comparative Example 2 Maleimide was produced from maleamic acid ester according to the method for producing N-substituted maleimide from N-substituted maleamic acid monoester described in JP-A-3-173866. In a 200 ml three-necked flask equipped with a thermometer, a cooling tube equipped with a water separator, and a stirrer, 12.9 g (0.1 mol) of maleic acid methyl ester, 90 ml of toluene, 32.0 g of methyl alcohol (1.0 mol).
Mol) and 1.0 ml of concentrated sulfuric acid, and the mixture was heated and stirred under reflux for 3 hours to carry out dealcoholization reaction. After the reaction was completed, the reaction solution was analyzed by high performance liquid chromatography to measure the amount of maleimide produced. The yield was only 10.0 mol% based on the maleamic acid methyl ester used as the starting material for maleimide. Comparative Example 3 Maleimide was produced from maleic acid ester according to the method for producing N-substituted maleimide from N-substituted maleamic acid ester described in JP-A-4-221365. To a 200 ml three-necked flask equipped with a thermometer, a condenser equipped with a water separator and a stirrer was added 12.9 g (0.1 mol) of maleic acid methyl ester, 90 ml of methyl alcohol and 0.8 g of sodium carbonate, The dealcoholization reaction was carried out by continuing stirring at room temperature (25 ° C.) for 3 hours. After the reaction was completed, the catalyst was removed by filtration.
Next, the reaction solution was analyzed by high performance liquid chromatography to measure the amount of maleimide produced. The yield was only 27.9 mol% based on the maleic acid methyl ester used as the starting material for maleimide.

According to the method of the present invention, the reactivity is high,
Since the dealcoholization reaction is carried out while distilling maleimide as a reaction product out of the reaction system, the reaction between maleimide acid ester as a starting material and maleimide, the side reaction such as polymerization of maleimide itself is suppressed, and the maleimide has a high yield. Can be manufactured at a rate. Since the dealcoholization reaction in the present invention proceeds extremely easily as compared with the conventionally known cyclodehydration reaction using a dehydrating agent, according to the method of the present invention, maleimide can be produced more efficiently than in the conventional method using a dehydrating agent. can do. The maleimide obtained by the method of the present invention has a very high purity and does not require a special purification step, so that it is possible to significantly reduce the production cost. Therefore, according to the method of the present invention, the low cost is achieved. A maleimide can be produced with.

Claims (1)

[Claims] 1. General formula (1): (In the formula, R represents an alkyl group having 1 to 8 carbon atoms), the maleic acid ester represented by the formula (1) is heated, and an alcohol produced when the corresponding maleimide is produced by ring-closing imidation by dealcoholization reaction and A method for producing a maleimide, which comprises carrying out a dealcoholization reaction while distilling the maleimide out of the reaction system.