JP2949150B1 - Method for producing cyclohexyl methacrylate - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To produce cyclohexyl methacrylate,
While maintaining catalytic activity, it effectively suppresses the formation of insoluble three-dimensional polymers during purification. SOLUTION: Transesterification of methyl methacrylate and cyclohexanol is carried out in the presence of anhydrous lithium hydroxide catalyst. At this time, the water content in the system is maintained at 1000 ppm or less. In particular, the water content of industrial cyclohexanol is adjusted to 1.8 to 2.0% in order to prevent coagulation, and it is preferable to dehydrate it beforehand. The reaction solution obtained by the above reaction is purified by a distillation column in which N-nitrosophenylhydroxylamine salt is present in a solid phase in a gas phase,
Polymerization of cyclohexyl methacrylate in a reaction solution is efficiently suppressed, and formation of an insoluble three-dimensional polymer is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing cyclohexyl methacrylate, and more particularly to a method for producing cyclohexyl methacrylate by transesterifying methyl methacrylate and cyclohexanol in the presence of lithium hydroxide.

[0002]

2. Description of the Related Art Conventionally, it has been known that in transesterification of methyl methacrylate and alcohol, cyclohexanol is used as an alcohol raw material and lithium hydroxide is used as a catalyst (Japanese Patent Application Laid-Open No. 54-61117, Japanese Patent Application Laid-Open No. No. 2-101043).

[0003] Lithium hydroxide includes other known catalysts, for example, organic acids such as organic sulfonic acids, alkali metal hydroxides such as potassium hydroxide and calcium hydroxide, and alkali metals such as sodium methoxide. Compared with alkoxide catalyst, side reaction and generation of polymer are less,
Since there is no need to wash with water since the corrosiveness and their removal after the reaction can be easily performed by filtration or the like, there is an advantage that there is no waste water problem.

[0004] In Example 3 of JP-A-2-101043, a combination of methyl methacrylate, cyclohexanol and lithium hydroxide is specified. From the viewpoint of maintaining the catalytic activity, it is said that the use of dried lithium hydroxide is desirable. It is also said that the water content of air or oxygen blown into the system is preferably 1000 ppm or less.

However, cyclohexanol as an alcohol raw material is different from other general alcohol raw materials,
In the anhydrous state, it has the property of being easily solidified. For this reason, during industrial production, taking into account solidification during storage and transportation,
It is usual to add about 1.8 to 2.0% of water. As mentioned above, even if dry lithium hydroxide is used as a catalyst and air or oxygen having a water content of 1000 ppm or less is blown, as long as industrial cyclohexanol is used as a raw material in industrial practice, water derived from cyclohexanol causes It is inevitable that the water content will increase.

On the other hand, since the obtained reaction solution of cyclohexyl methacrylate contains a large amount of impurities, a high molecular weight polymer cannot be obtained as it is, and it is usual to purify it by means such as distillation. However, cyclohexyl methacrylate is rich in polymerizability, and an insoluble polymer having a three-dimensional structure is rapidly generated under heating conditions in the distillation purification step. In particular, the insoluble polymer is easily generated in the gas phase in the distillation system, which may obstruct the distillation tower, piping, etc., causing operation failure, and also reduces the yield of cyclohexyl methacrylate. As polymerization inhibitors for similar compounds including cyclohexyl methacrylate, in addition to hydroquinone, hydroquinone monomethyl ether, paraphenylenediamine, phenothiazine and the like, N-nitrosamines, especially N-nitrosophenylhydroxylamine salts (hereinafter, “cuperons”) (Japanese Patent Application Laid-Open Nos. 63-126853 and 64-42462).
No.).

[0007] Cuprons are excellent polymerization inhibitors. However, according to the findings of the present inventors, the polymerization inhibition effect of cuperons themselves is surprisingly small, and the radical catching action during decomposition and the polymerization inhibiting action of decomposed products are observed. Is presumed to effectively suppress the polymerization of cyclohexyl methacrylate.
Accordingly, the invention described in JP-A-63-126853, in which cupperones are dissolved in a substance to be distilled and supplied to a distillation column, and the invention described in JP-A-64-42462, in which cuprons dissolved in glycols are supplied to a distillation column. In the invention described in the publication, a sufficient polymerization inhibitory effect cannot be expected. Suppose JP-A-64-4
Even if the invention described in No. 2462 is applied to the distillation of cyclohexyl methacrylate, when a cuperone is dissolved and used, due to a difference in the stability of each of the cuperons, a certain product may be dissolved before being supplied to the distillation column. Decomposition may progress in solution, or some substances may not be sufficiently decomposed while they are in the column and may flow down as they are, decomposing in the gas phase of the distillation column where polymerization is most likely to occur. The polymerization inhibiting effect obtained by the above is not sufficiently exhibited.

[0008]

DISCLOSURE OF THE INVENTION The present invention has solved the above-mentioned problems, and at the time of transesterification between methyl methacrylate and cyclohexanol, maintains the catalytic activity of lithium hydroxide in a good state to achieve high yield. It is an object of the present invention to provide a process for producing cyclohexyl methacrylate at a high rate and effectively suppressing the generation of an insoluble polymer based on the polymerization of cyclohexyl methacrylate during purification of the obtained reaction solution.

[0009]

The process for producing cyclohexyl methacrylate of the present invention which has achieved the above objects is as follows.

(1) Methyl methacrylate and cyclohexanol are
In the presence of anhydrous lithium hydroxide catalyst, the water content in the
The transesterification was carried out while maintaining the concentration below 00 ppm, and the resulting reaction solution
In a distillation column, with a polymerization inhibitor N-nitrosophenylhydroxyl.
For purification in the presence of a silamine salt, N-nitro
Sophenylhydroxylamine salt in gas phase in distillation column
A process for producing cyclohexyl methacrylate, characterized by being present as a solid . (2) Solid N-nitrosophenylhydroxylamine
2. The method for producing cyclohexyl methacrylate according to claim 1, wherein the salt is in a slurry state . (3) Solid N-nitrosophenylhydroxylamine
The resin salt is a resin molded product mainly composed of phenolic resin,
Wherein said fat foam or resin coating film
The method for producing cyclohexyl methacrylate according to claim 1 .

In the present invention, when the methyl methacrylate and cyclohexanol are transesterified in the presence of an anhydrous lithium hydroxide catalyst, the water content in the system is 1000 pp.
m or less.

If the water content exceeds 1000 ppm, the catalytic activity of lithium hydroxide drops sharply, the reaction time becomes longer, the reaction is not completed, and the yield of cyclohexyl methacrylate decreases. The cause of the deterioration of the catalytic activity of lithium hydroxide is presumed to be that anhydrous lithium hydroxide changes to a monohydrate having weak catalytic activity. In addition, when water is present in the system, the hydrolysis of lithium hydroxide and the raw material methyl methacrylate and the target product, cyclohexyl methacrylate, is promoted, and lithium hydroxide is converted to lithium methacrylate having no catalytic activity. I do. This lithium methacrylate also has extremely poor filterability, and causes various troubles.

The method for maintaining the water content in the reaction system is not particularly limited, but it is preferable that each of the raw materials to be used is previously dried or dehydrated. In particular, since the water content of industrial cyclohexanol is adjusted to 1.8 to 2.0% to prevent coagulation as described above, it is effective to previously dehydrate it.

The reaction solution obtained by the above method is purified by a distillation column in which cuprons are present as a solid in the gas phase.
The polymerization of cyclohexyl methacrylate in the reaction solution can be efficiently suppressed. The reason is not always clear,
It is presumed that the presence of a solid in the gaseous phase effectively combines the radical catching action at the time of decomposing couperones and the action of inhibiting the decomposition product from polymerization as described above.

In the present invention, an industrial raw material is used as the raw material methyl methacrylate. On the other hand, a pure reagent can be used as the raw material cyclohexanol, but industrially containing 1.8 to 2.0% of water is used industrially to prevent coagulation. It is desirable that the industrial raw material cyclohexanol be dehydrated in advance. The dehydration treatment is performed by, for example, adding the solvent that forms an azeotrope with water as it is, or distilling off the water under reduced pressure or normal pressure, to obtain a water content of 1000 ppm or less, preferably 5 ppm or less.
The content is set to 00 ppm or less. The amount of methyl methacrylate charged to dehydrated cyclohexanol is about 1.2 to 10 equivalents, preferably about 1.2 to 5.0 equivalents.

The anhydrous lithium hydroxide used for the catalyst includes:
A commercially available product may be used, or a monohydrate of lithium hydroxide may be heated and dried to be used as an anhydride. A constant temperature dryer or a blast heating dryer may be used for heating and drying the monohydrate. The end point of the drying can be confirmed by a loss on drying when the monohydrate becomes an anhydride of about 42%. The amount of lithium hydroxide used is preferably about 0.1 to 5% by weight, more preferably 0.3 to 2% by weight, based on cyclohexanol. Lithium hydroxide is charged at once at the start of the reaction. When divided and charged, there is almost no catalytic effect of the added amount. This is presumably because, as the reaction progresses, lithium hydroxide as a catalyst and lithium methacrylate as a by-product are partially dissolved in the reaction solution, and additional lithium hydroxide is hardly dissolved in the reaction solution.

The method for removing water from the reaction system in the present invention is not particularly limited, but it is practical to dehydrate each raw material in advance as described above, but it is necessary to form an azeotropic mixture with water. The water in the system may be azeotropically removed using a solvent or methyl methacrylate.

In the reaction, a polymerization inhibitor is usually used. As the polymerization inhibitor, for example, hydroquinone, hydroquinone monomethyl ether, di-t-butylhydroxytoluene, phenothiazine, N-N'-dinaphthyl-p-phenylenediamine, oxygen, a polymerization inhibitor such as cuperone alone or in combination. Can be used. In particular, an ammonium salt of N-nitrosophenylhydroxylamine (hereinafter referred to as "cuperone") is charged together with cyclohexanol, and the reaction is carried out while blowing oxygen into the reaction system. Hydroquinone monomethyl ether methyl methacrylate is introduced into the distillation column. A method of continuously adding a solution is effective for preventing polymerization.

The reaction temperature of the transesterification is usually 50
To 150 ° C, preferably 80 to 120 ° C. If the temperature is too low, the reaction time will be long and the production efficiency will be poor. If the temperature is too high, there is a risk that a polymer is formed. The reaction time is 1 to 15 hours, preferably 3 to 8 hours. The reaction may be performed under normal pressure, but it is desirable to reduce the pressure in order to facilitate the removal of generated methanol or to appropriately control the reaction temperature. The reaction proceeds while the produced methanol is distilled out of the system as an azeotrope together with methyl methacrylate or the solvent used using a distillation apparatus. At that time, the reflux ratio may be adjusted so that the top temperature is near the azeotropic temperature of methanol and methyl methacrylate or the solvent used.

The reaction solution after the reaction may be filtered and distilled by a conventional method, but a filtration aid may be used at the time of filtration. Further, when the distillation is performed using a distillation column in which clopenes are present in a solid state in the gas phase, polymerization in the purification step is extremely effectively suppressed. As clopenes, aluminum salts of N-nitrosophenylhydroxylamine, ethanolamine salts of N-nitrosophenylhydroxylamine and the like can be used in addition to cupron. Among them, cuperone has extremely low solubility in cyclohexyl methacrylate, is most suitable for being supplied in a solid state to the gas phase of a distillation apparatus, is excellent in the effect of suppressing insoluble polymers, and is easily available.

In the vapor phase section of the distillation apparatus in which solid clopenes are present in the present invention, the packed column in which packing such as Raschig rings of the distillation column is disposed, or the tray column section in which the tray is disposed, is provided. Most effective. The amount of couperones in the gas phase is about 0.5 to 5000 ppm, preferably about 1 to 1000 ppm, more preferably about 3 to 100 ppm.
ppm. When the amount is too small, the effect of inhibiting the polymerization of cyclohexyl methacrylate is insufficient, and an insoluble polymer is easily generated. On the other hand, if it is excessive, it may not only be economically disadvantageous but also cause coloring of the distillate.

The method of applying solid couperones to the gas phase of the distillation apparatus is not particularly limited. In the case of couperone, since the solubility in cyclohexyl methacrylate is extremely small as described above, the slurries are added to cyclohexyl methacrylate. It is desirable to disperse and apply.
The application location may be from one or a plurality of locations in the packed tower and the shelf, and the application may be continuous or discontinuous.

As another application method, it is also possible to immobilize cuprons in a resin molded body having an arbitrary shape such as a phenol resin and to dispose the resin molded body in the packed tower or the tray column. . For example, if the resin molded body is put in a detachable wire mesh or a porous container through which gas or liquid can pass, it can be easily replaced according to the consumption of cuprons, and the operability is excellent. Further, the respective salts of the cuperons are mixed with a phenol resin, a resin curing agent, a solvent, etc. to obtain a composition, and the obtained composition is impregnated into a porous filler such as a ceramic such as a Raschig ring in a packed tower, It can be applied and cured or dried to form and fix a coating film inside and on the surface of the filler.

In the present invention, cuperons can be used separately or in combination with other polymerization inhibitors such as hydroquinone, hydroquinone monomethyl ether, paraphenylenediamine, phenothiazine and the like at the time of distillation.

[0025]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0026]

Example 1 A 2-L four-necked flask equipped with a rectification tower, a fractionating head, a cooling pipe, a gas introduction pipe, a stirrer, and a thermometer was charged with 900 g (9 mol) of the raw material methyl methacrylate and the cyclodextrin as a raw material. 450 g (4.5 mol) of hexanol, 3.0 g of anhydrous lithium hydroxide and 0.6 g of cupron were charged. The water content after charging the raw materials was 300 ppm. While introducing nitrogen gas containing 7% by volume of oxygen into the reactor at a rate of 2 ml / min, the pressure in the system was adjusted to 450 mmHg, and heating and stirring were performed. From the top of the rectification column, a methyl methacrylate solution in which 1% by weight of hydroquinone monomethyl ether was dissolved was continuously added at a flow rate of 3 ml / hour during the reaction. The degree of reduced pressure was adjusted so that the reaction temperature became 90 to 100 ° C., and was finally 200 mmHg.
After the reflux was started, methanol produced by the reflux apparatus was reacted with methyl methacrylate while azeotropically distilling off. Six hours after the start of reflux, in gas chromatography,
When the peak area of the starting material cyclohexanol became 0.3% of the total peak area of cyclohexanol and the product cyclohexyl methacrylate, the transesterification reaction was terminated. The reaction solution was cooled to 40 ° C., and “KC Floc W-50S” (trade name) manufactured by Nippon Filter Paper Co., Ltd.
g, and the mixture was stirred and mixed, and then filtered using a filter paper (No. 2, manufactured by Advantech Co., Ltd., diameter 9 cm) with a suction filter. The filtration time was 1 minute and 30 seconds.

The filtrate was charged into a 2 L four-necked flask equipped with a rectification tower, a fractionating head, a condenser, a stirrer, and a thermometer, and was subjected to distillation. From the top of the rectification column, 1 ml at 3 ml / h during distillation
A solution of cyclohexyl methacrylate in which weight percent hydroquinone monomethyl ether was dissolved was continuously added.
In addition, from the start to the end of distillation, once every two hours,
1 mg of cuperone was slurried with 1 g of cyclohexyl methacrylate in which 1% by weight of hydroquinone monomethyl ether was dissolved, and added to the top of the distillation column. After removing an excess of the initial distillate mainly composed of methyl methacrylate, the mixture is rectified at a reflux ratio of 1, 20 g of a middle distillate composed mainly of cyclohexyl methacrylate, and 730 g of the objective cyclohexyl methacrylate at 64-65 ° C./2 mmHg. Was obtained as a mainstay. The purity of the main fraction was 99.6% (area ratio). After completion of the distillation, no insoluble polymer was found in the rectification column.

[0028]

Example 2 A transesterification reaction was carried out in the same manner as in Example 1 except that industrial cyclohexanol having a water content of 1.8% was used as a raw material cyclohexanol and the water content was adjusted to 1000 ppm by dehydration beforehand. Was.
The water content in the system after charging the raw materials was 850 ppm. About 8 hours after the start of reflux, the peak area of the starting material cyclohexanol was 0.9% with respect to the total area of cyclohexanol and the product cyclohexyl methacrylate in gas chromatography, and the transesterification reaction was completed.
The reaction solution was cooled to 40 ° C. and filtered as in Example 1, and the filtration time was 7 minutes. The filtrate was distilled in the same manner as in Example 1 to obtain 40 g of a middle distillate mainly composed of cyclohexyl methacrylate and 707 g of the intended cyclohexyl methacrylate as a main distillate. The purity of the main run is 99.6
% (Area ratio). After completion of the distillation, no insoluble polymer was found in the rectification column.

[0029]

Example 3 12 g of phenol novolak, 3 g of hexamethylenetetramine and 1 g of cuperone were uniformly mixed.
After crushing and heating at 80 ° C. for 1 hour, 120
Cured at ℃ for 1 hour. As a result, a phenol resin foam having a foaming ratio of 9 times was obtained. Under the same conditions as in Example 1, 1 g of the above-obtained phenolic resin foam (divided into about 0.5 mm) instead of using a slurry containing cupperon is uniformly held in a packed tower. In the same manner as in Example 1, distillation was carried out, and 18 g of a middle distillate containing cyclohexyl methacrylate as a main component, and 64 to 65 ° C./2
728 g of the desired cyclohexyl methacrylate in mmHg
Was obtained as a mainstay. The purity of main dome is 99.6% (area ratio)
Met. After completion of the distillation, no insoluble polymer was found in the rectification column.

[0030]

Example 4 10 g of phenol novolak, 3 g of hexamethylenetetramine and 0.1 g of cuperone were dissolved in 10 g of acetone and 15 g of methanol. This resin solution was applied and impregnated into 305 g of Raschig rings by a dipping method. Then, acetone and methanol were removed by a rotary evaporator to obtain a coating-coated Raschig ring, which was heated in an oven at 120 ° C. for 1 hour. Then, under the same conditions as in Example 1, instead of using the slurry containing cuperon, 150 g of the coating-coated Raschig ring obtained above was packed in a packed tower, and distillation was carried out in the same manner as in Example 1 to obtain methacrylic acid. 20 g of a middle distillate mainly composed of cyclohexyl, and 64-65 ° C./2
727 g of the desired cyclohexyl methacrylate in mmHg
Was obtained as a mainstay. The purity of the main dome is 99.5% (area ratio)
Met. After completion of the distillation, no insoluble polymer was found in the rectification column.

[0031]

Example 5 Instead of cuperone used in Example 3, N
-The same procedure as in Example 3 was carried out except that an aluminum salt of nitrosophenylhydroxylamine was used, and 17 g of a middle distillate containing cyclohexyl methacrylate as a main component, and the desired cyclohexyl methacrylate at 64 to 65 ° C / 2 mmHg. 730 g were obtained as the main fraction. The purity of the main fraction was 99.6% (area ratio). After the distillation was completed, no insoluble polymer was found in the rectification column.

[0032]

Example 6 Instead of cuperone used in Example 4, N was used.
-The same procedure as in Example 4 was carried out except that an ethanolamine salt of nitrosophenylhydroxylamine was used, and 22 g of a middle distillate containing cyclohexyl methacrylate as a main component,
Also, 724 g of the intended cyclohexyl methacrylate was obtained as a main fraction at 64 to 65 ° C./2 mmHg, and the purity of the main fraction was 99.7% (area ratio). After the distillation,
No insoluble polymer was found in the rectification column.

[0033]

Comparative Example 1 The reaction was carried out in the same manner as in Example 1 except that the water content was adjusted to 3000 ppm as the raw material cyclohexanol. The water content in the system after charging the raw materials is 1150ppm
Met. Approximately 8 hours after the start of the reflux, the production of methanol was no longer observed, and the reaction was terminated. In gas chromatography, the peak area of the starting material cyclohexanol was 8.5% based on the total area of cyclohexanol and the product cyclohexyl methacrylate. The reaction solution was cooled to 40 ° C. and filtered as in Example 1,
Filtration was not possible on the way.

[0034]

Comparative Example 2 Instead of using the slurry of cuperone used in Example 1, a cyclohexyl methacrylate solution in which 1% by weight of hydroquinone monomethyl ether was dissolved was continuously fed from the top of the column at a rate of 0.1 ml / min. Except for this, the procedure was the same as in Example 1. Around the time of switching from the middle distillate to the main distillate, the pressure difference in the distillation column increased, and insoluble polymer was generated in the upper part and the middle part of the column, and the upper part of the column was in a closed state.

[0035]

COMPARATIVE EXAMPLE 3 Instead of using the cuperon slurry used in Example 1, a solution of cyclohexyl methacrylate in which 1% by weight of phenothiazine was dissolved was 0.1 m from the top of the tower.
The same procedure as in Example 1 was carried out except that the feed was continuously carried out at 1 / min. During the main distillation, the pressure difference in the distillation column increased, and insoluble polymer was generated in the upper part and middle part of the column. The upper part of the tower was closed.

[0036]

Comparative Example 4 In Example 1, 0.1% by weight of couperone was added to the reaction filtrate before distillation, and instead of using a slurry of couperone, cyclohexyl methacrylate in which 1% by weight of hydroquinone monomethyl ether was dissolved was used. The procedure was performed in the same manner as in Example 1 except that the solution was continuously fed from the top of the tower at 0.1 ml / min. During the main distillation, the pressure difference in the distillation column increased, and insoluble polymer was generated in the upper part and middle part of the column, and the upper part of the column was in a closed state.

[0037]

COMPARATIVE EXAMPLE 5 Instead of using the cuperon slurry used in Example 1, a cyclohexyl methacrylate solution in which 1% by weight of an aluminum salt of N-nitrosophenylhydroxylamine was dissolved was added at a rate of 0.1 ml / min from the top of the tower. Except for feeding continuously, the same procedure as in Example 1 was carried out. During the main distillation, the pressure difference in the distillation column increased, and an insoluble polymer was generated in the middle part of the column.

[0038]

According to the present invention, in producing cyclohexyl methacrylate by transesterification between methyl methacrylate and cyclohexanol, water in the system is reduced to 100%.
By adjusting the water content of 0 ppm or less, particularly the industrial raw material cyclohexanol to 1000 ppm or less, the catalytic activity of lithium hydroxide is maintained, cyclohexyl methacrylate is obtained in a high yield, and the obtained transesterification reaction is performed. In the subsequent distillation and purification of the liquid, by applying couperones in a substantially solid state to the gas phase of the distillation column, the polymerization of cyclohexyl methacrylate is effectively suppressed, and clogging of the apparatus due to generation of insoluble polymer, etc. , And an integrated industrial production system for cyclohexyl methacrylate has been made possible.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI // C07B 61/00 300 C07B 61/00 300 (56) References JP-A-2-101042 (JP, A) JP-A-49 -125315 (JP, A) JP-A-10-195022 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C07C 69/54 C07C 67/03 C07C 67/54 C07C 67/62

Claims (3)

(57) [Claims] The method according to claim 1] methyl methacrylate and cyclohexanol, in the presence of anhydrous lithium hydroxide catalyst, and transesterification while maintaining the water content in the system to 1000ppm or less, the resulting
The reaction solution is passed through a distillation column, and the polymerization inhibitor N-nitrosophenyl
In purifying in the presence of droxylamine salt, N-
Nitrosophenylhydroxylamine salt is removed from the gas in the distillation column.
A process for producing cyclohexyl methacrylate, characterized in that it is present as a solid in the phase . 2. Solid N-nitrosophenylhydroxy
The method for producing cyclohexyl methacrylate according to claim 1 , wherein the ruamine salt is in a slurry state . 3. Solid N-nitrosophenylhydroxy
Luamine salt is a resin molding whose main component is phenolic resin
The method for producing cyclohexyl methacrylate according to claim 1, wherein the method is a body, a resin foam, or a resin coating film .