JPH0319224B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for producing maleimide. Specifically, the present invention relates to a method for producing maleimide, which is said to be thermally unstable, at low temperatures and in high yield. The maleimide targeted by the present invention is a photosensitive resin,
It is a compound useful as a raw material for heat-resistant resins, medicines, and agricultural chemicals. <Prior Art> A method for producing maleimide from maleamic acid has been known for a long time. In other words, there are methods in which maleic anhydride and amines are reacted, and the resulting maleamic acid is dehydrated and ring-closed in the presence of a dehydrating agent such as acetic anhydride to imidize it, or this maleamic acid is reacted with an acid in an organic solvent. This method involves dehydration and ring closure at high temperatures using a catalyst, and azeotropically removing the generated water with an organic solvent. However, these methods have the following drawbacks. First of all, the method of imidizing acetic anhydride as a dehydrating agent requires expensive acetic anhydride in an amount equivalent to or more than maleamic acid, and it is difficult to recover the by-product acetic acid as acetic anhydride. Therefore, it is not an industrially advantageous method. In addition, a method of azeotropically distilling the water produced during the thermal dehydration ring-closing reaction with the solvent using an acid catalyst such as sulfuric acid, phosphoric acid, or p-toluenesulfonic acid in a solvent and distilling it out of the system while imidizing the water is the above-mentioned acetic anhydride. It has the advantage that it does not require large amounts of expensive dehydrating agents compared to methods that use dehydration, but the high reaction temperature in the reaction process of imidization by heating dehydration produces many side reaction products, making separation and purification difficult. The disadvantage is that the yield is accordingly low. More specifically, in the specifications of JP-A-53-68770 and JP-A-60-109562, maleic anhydride and an amine compound are reacted in a molar ratio of 1.0 to 1.5 in an organic solvent. A method has been proposed in which maleamic acid is imidized by azeotropic dehydration ring closure of water produced in the presence of a polar solvent such as dimethyl sulfoxide or dimethyl formamide and an acid catalyst. Maleimide, N-
It can be recognized that this is an effective method for producing aromatic maleimides such as chlorophenylmaleimide. However, thermally unstable N-alkylmaleimides produce a large amount of side reaction products during the dehydration ring-closing reaction, which not only results in poor yields but also makes separation and purification difficult, making operations complicated. The drawback was found that it was not possible to obtain Furthermore, since it is difficult to recover the polar solvent used in these methods, they cannot be said to be advantageous as industrial production methods. <Means> In view of this situation, the present inventors conducted intensive research and found that as a method for producing maleimides, the dehydration ring-closing imidization reaction of maleamic acid was carried out in the presence of maleic acid in an organic solvent at a reaction temperature of 100 to 150°C. We have found a method that allows the reaction to be carried out industrially at lower temperatures than conventional methods, preferably in the range of 110°C to 140°C. Thus, by the method of the present invention, high purity maleimides can be easily produced with fewer side reaction products and simple purification. The maleamic acid used as a raw material in the present invention is represented by the general formula [). ([) In the formula, R is an alkyl group having 1 to 20 carbon atoms, an alkenyl group, or a phenyl group, and these are branched chains or a methyl group, ethyl group, propyl group,
It may have a substituent such as halogen. ) This maleamic acid is produced almost quantitatively from the corresponding amines and maleic anhydride. The amines used as raw materials for the maleamic acid used in the present invention are represented by _RNH2 , and this R
is an alkyl group or phenyl group having 1 to 20 carbon atoms, and specific examples include when R is an alkyl group; methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, sec-butylamine, tert-butylamine, Examples include alkylamines such as n-hexylamine, n-octylamine, n-dodecylamine, n-hexadecylamine, n-octadecylamine, and cyclohexyl; when R is an alkenyl group; dodecenylamine, tetradecenylamine, Hexadecenylamine, when R is a phenyl group; aniline, orthochloroaniline, methacryloylaniline, parachloroaniline, orthomethylaniline, metamethylaniline, paramethylaniline, orthomethoxyaniline, metamethoxyaniline, paramethoxyaniline, etc. Can be mentioned. In the present invention, particularly excellent effects are achieved when amines in which R has an alkyl group are used as raw materials. The organic solvent used in the present invention may be an inert solvent that does not participate in the reaction, and specific examples include aromatic solvents such as benzene, toluene, xylene, ethylbenzene, chlorobenzene, mesitylene, cumene, pseudocumene, and p-cymene. A system solvent, a polar solvent such as dimethyl sulfoxide, dimethylacetamide, dimethylformamide, N-methylpyrrolidone, hexamethylphosphoramide, etc., and more preferably maleic anhydride in a molten state can be used as the solvent. The amount of these solvents used is 1 to 20 times, preferably 2 to 5 times the weight of maleamic acid. The reaction in the method of the present invention is carried out at 100-150°C, preferably 110-140°C, for 1-10 hours, preferably 3-6 hours.
This is carried out by stirring under reflux for a period of time and under pressure or atmospheric pressure. When the reaction temperature is below 100°C, the reaction rate is slow, and when it is above 150°C, side reaction products increase and maleic acid, which should be effective in the reaction, is rearranged to fumaric acid, losing reaction activity and reducing the yield. After the reaction is complete, the produced water that coexists in the product is distilled off, but maleic acid also becomes anhydrous.The maleic anhydride present is distilled off under reduced pressure, and this maleic anhydride is recycled and reused as a raw material. be done. The reaction product thus obtained is filtered to remove side reaction products, and the resulting solution is purified by a conventional method such as distillation or recrystallization. The advantages of the present invention compared to conventional methods are that the dehydrating agent, acid catalyst,
There is no need to add polar solvents, metal salts, stabilizers, etc., and the water produced during the reaction is not forcibly removed from the system by azeotropic dehydration, etc., making the reaction operation simple and achieving high yields and high purity. Maleimides are produced. Of course, in the present invention, known acid catalysts as dehydrating agents, stabilizers, and promoters can be used in combination. For example, acetic anhydride, acetic acid, sulfuric acid, sulfuric anhydride,
p-Toluenesulfonic acid, orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, benzenesulfonic acid, and as stabilizers methoxybenzoquinone, hydroquinone, phenothiazine, dimethyldithiocarbamate, 2,4-dimethyl-6-tert-butylphenol, p- Tert-butylcatechol and the like can be used in combination with metal salts such as zinc, chromium, cobalt, nickel, etc. as promoters. In the present invention, the imidization ring-closing reaction is carried out in the above-mentioned solvent at a temperature in the range of 100 to 150°C, with at least 0.05 molar amount of maleic acid shared with respect to the starting maleamic acid. This maleic acid is a hydrated form of maleic anhydride, and has been found to increase the reaction rate of the imidization ring-closing reaction of raw maleamic acid and to have the effect of stabilizing the maleimide produced.
That is, maleic acid coexisting at the start of the imidization ring-closing reaction takes in by-product water while carrying out the imidization ring-closing reaction, allowing the reaction to proceed without forcibly discharging the produced water from the reaction system. It has an effect. Of course, after the reaction is completed, the produced water may be removed by adding an azeotropic solvent, and as water is lost from the reaction system, maleic acid is also anhydrified to form maleic anhydride. Furthermore, this anhydrous maleic anhydride can be easily distilled off from the reaction system, making it easy to purify the maleimide produced. As a concrete process for carrying out the method of the present invention, the following method is possible. (i) Only maleic anhydride is used as a solvent, and the necessary amount of water is added thereto to coexist with maleic acid in an amount of 0.05 mole or more relative to the raw material maleamic acid to carry out the imidization ring-closing reaction. (ii) Perform the reaction in (i) above by adding a stabilizer, an acid catalyst, or a cocatalyst. (iii) An aromatic hydrocarbon or a polar solvent is used as a solvent, and a necessary amount of maleic acid is allowed to coexist with the solvent to carry out the imidization ring-closing reaction. (iv) In (iii), a stabilizer, an acid catalyst or a co-catalyst is added to carry out the reaction. (v) In (i) above, aromatic hydrocarbons and polar solvents are also used as solvents to carry out the reaction. (vi) In (ii) above, aromatic hydrocarbons and polar solvents are also used as solvents to carry out the reaction. The method of the present invention will be explained in more detail below using Examples and Comparative Examples. Example 1 147.1 g (1.5 mol) of maleic anhydride and 400 g of ortho-xylene were charged into a 1000 ml four-necked flask equipped with a thermometer, reflux condenser and stirrer, and heated and dissolved at 55° C. with stirring. This was added to n-octylamine (purity
98%) was added thereto and reacted at 65°C for 1 hour. Next, water was added so that the malein distribution in the system was 0.10 mol, and the temperature was raised to 120°C, and the azeotropic water was allowed to react for 6 hours under reflux. The maleic acid content in the system finally reached 0.67 mol. After the reaction was completed, reaction product water and unreacted maleic anhydride (including dehydrated maleic acid) were distilled off under reduced pressure. Insoluble side-reactants in the reaction product thus obtained were filtered, the liquid was washed and separated, and ortho-xylene was distilled off under reduced pressure, resulting in 108.3 g of n-
Light brown crystals of octylmaleimide were obtained. As a result of gas chromatograph analysis using 2-ethylanthraquinone as an internal standard, the purity was 88.0%, which was 75.9 mol% based on the raw material n-octylamine.
Corresponds to the yield. Examples 2 to 8 and Comparative Examples 1 to 2 In Example 1, the molar ratio of maleic anhydride and amine compound, maleimidization reaction temperature and time,
N-alkylmaleimide compounds were synthesized in the same manner as in Example 1 except that the types of amine compounds were changed. In addition, the maleic acid concentration at the start of the reaction is 0.15 to 0.20 relative to the raw material maleamic acid.
The amount was adjusted within the molar range. The results are shown in Table 1.

[Table] Example 8 Using the same reactor as used in Example 1, 147.1 g (1.5 mol) of maleic anhydride and 400 g of ortho-xylene were added.
was charged and heated and dissolved at 60°C while stirring. In this
-Octylamine (98% purity) 77.5g (0.6mol)
was added and reacted at 70°C for 1 hour, and then orthophosphoric acid (purity 90
%) 6g and dimethylsulfamide 18ml zinc acetate
0.05g and 0.08g of methoquinone were added. Next, the maleic acid content in the mixed liquid is
Water was added to the mixture to make it 0.1 times the mole, the temperature was raised to 130°C, and the reaction was carried out under total reflux for 5 hours. At the end of the reaction, the reaction solution contained 0.62 mol of maleic acid. After the reaction, reaction product water and unreacted maleic anhydride (including that produced by dehydration of maleic acid) were distilled off under reduced pressure. Insoluble side-reactants in the reaction product thus obtained were filtered, the liquid was washed with water, ortho-xylene was distilled off under reduced pressure, and 115.5 g of n
- Light brown crystals of octylmaleimide were obtained. As a result of gas chromatography analysis, the purity was 87.5%.
This corresponds to a yield of 80.5% based on the raw material n-octylamine. Comparative Example 3 Maleic anhydride was added to a 1000 ml four-necked flask equipped with a thermometer, a water separator, a condenser, and a stirrer.
147.1g (1.5 mol) and 400g of ortho-xylene were charged and heated and dissolved at 55°C with stirring. Add to this 79.1g of n-octylamine (98% purity)
(0.6 mol) was added and reacted at 70°C for 1 hour. then
The temperature was raised to 130°C and the reaction was carried out for 5 hours. The water produced by the reaction was azeotropically distilled off together with ortho-xylene. Thereafter, in the same manner as in Example 1, 80.1 g of n-octylmaleimide was obtained. The purity determined by gas chromatography was 55.0%, corresponding to a yield of 35.1% based on the raw material n-octylamine. Comparative Example 4 Maleic anhydride was added to a 1000 ml four-necked flask equipped with a thermometer, a water separator, a condenser, and a stirrer.
Add 98g (1 mol) and 400g of toluene and heat to 55°C with stirring.
The mixture was heated and dissolved. 79.1 g (0.6 mol) of n-octylamine (purity 98%) was added to this and reacted at 70°C for 1 hour. Subsequently, 28 g (0.15 mol) of p-toluenesulfonic acid, p-toluenesulfonic acid, n
-0.03 mol of octylamine and 15 g of dimethyl sulfoxide were added, the temperature was raised to 120°C, and the reaction was carried out for 5 hours. Water produced during the reaction was distilled off together with toluene. Thereafter, 95.5 g of n-octylmaleimide was obtained by the same operation as in Example 1. The purity determined by gas chromatography was 68.2%, corresponding to a yield of 51.8% based on the raw material n-octylamine.

Claims (1)

[Claims] 1. When producing the corresponding maleimide from the maleamic acid represented by the general formula [], in the presence of at least 0.05 molar amount of maleic acid relative to the maleamic acid, in an organic solvent at 100 to 150°C. A method for producing maleimide, which comprises subjecting the maleamic acid to a ring-closing imidization reaction at a temperature within a range. ([In the formula, R is an alkyl group having 1 to 20 carbon atoms, an alkenyl group, or a phenyl group, and these are branched chains or a methyl group, an ethyl group, a propyl group,
It may have a substituent such as halogen. )