JPS5918378B2 - Method for inhibiting polymerization of acrylic acid or methacrylic acid or their esters - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention prevents polymerization and precipitation of solids in systems involving heating of acrylic acid and methacrylic acid and their esters, that is, reaction systems and distillation systems, and prevents them from being mixed into products. This invention relates to a method for inhibiting polymerization that does not cause coloring.

In the production of acrylic acid and methacrylic acid and their esters, it is known to use hydroxy compounds such as phenol and quinone, carboxy compounds such as tannic acid, amine compounds, sulfur compounds, etc. as polymerization inhibitors. .

However, depending on the types of acids and esters targeted, these known methods for inhibiting polymerization may have a small polymerization inhibiting effect and require large doses, or may be mixed into products during purification processes such as distillation. This causes inconveniences such as coloring and a delay in the start of polymerization during product use.

In addition, when hydrolyzing acrylonitrile or methacrylic acid amide in the presence of sulfuric acid, amine inhibitors act effectively and are often used, but some of these become sulfates, for example in distillation columns. Concentrate and precipitate at the bottom,
This may cause operational troubles.

Furthermore, a method for preserving dimethylaminoethyl acrylate using phenothiazine is known, but the polymerization inhibiting effect of this phenothiazine is not satisfactory in reaction systems and distillation systems that involve heating, and furthermore, in reaction systems and distillation systems that involve heating, In this case, the phenothiazine not only mixes into the product and causes coloration, but also delays the initiation of polymerization during use of the product, which is undesirable.

In view of the disadvantages of these known polymerization inhibitor methods, the present inventors have conducted intensive research and found that a specific nuclear substituted product of phenothiazine has extremely excellent overall performance.
The invention has been completed.

That is, the present invention relates to the production of acrylic acid or methacrylic acid or esters thereof by reaction of the corresponding nitrile or acid amide with water or alcohol, or transesterification reaction of the corresponding ester with alcohol, or crude reaction. When separating by distillation from the product liquid, the general formula (in the table, R represents hydrogen or a methyl group, and M.n represents an integer from 0 to 2, respectively).

However, it is selected so as to satisfy m+n≧1. ) is a method for inhibiting polymerization of acrylic acid or methacrylic acid or their esters, which is characterized by making a phenothiazine compound represented by the following formula exist in a reaction system or a distillation system.

Examples of compounds corresponding to these general formulas used as polymerization inhibitors in the present invention include 3-(α-methylbenzyl)phenothiazine, 1-(d-methylbenzyl)phenothiazine, and 3,7-bis( α-Methylbenzyl)phenothiazine 3-(d-d-dimethylbenzyl)phenothiazine, 1-(α・d-dimethylbenzyl)phenothiazine, 3●7-bis(d・α-dimethylbenzyl)phenothiazine, 3-(d- d-dimethylbenzyl)
-7-(α-methylbenzylphenothiazine, 1-(
It is represented by α-methylbenzyl)-9-(α·α-dimethylbenzyl)phenothiazine.

These compounds can be prepared by, for example, a method of reacting a phenothiazine with an aromatic substituted alkenyl hydrocarbon in the presence of a Friedel-Crafts catalyst as described in Japanese Patent Publication No. 19088/1988, and a method described in Japanese Patent Application Publication No. 51-22742. It can be produced by a method in which an aromatic secondary amine and an aromatic substituted alkenyl hydrocarbon are reacted in the presence of a Friedelkraff catalyst, and then the reactant is reacted with sulfur.

In addition, when producing by these methods, M, . Although a mixture of compounds with different n may be obtained, this mixture may be used as an X polymerization inhibitor without isolating each compound.

The amount of the polymerization inhibitor added cannot be determined in general depending on the usage conditions, but it is 0.0001 to 0.01 part per 1 part by weight of the acid or ester that exists or is to be synthesized.
Particularly suitable is 0.0005 to 0.005 part.

The method of the present invention is effective for acrylic acid and methacrylic acid and their esters, and the esters include methyl acrylate, ethyl acrylate,
Examples include butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, glycidyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, glycidyl methacrylate, and the like.

The polymerization inhibitor used in the present invention is a high boiling point substance and non-sublimable, and when it is present during distillation purification, it inhibits polymerization at the bottom of the distillation pot or distillation column, but it does not affect the products that are vaporized components. It will not be mixed in. However, since polymerization in the vapor phase or product fraction is not inhibited, an inhibitor with a high volatile content may be added to the distillate, or
Alternatively, it is preferable to deal with this by adding it to the distillation system ~ According to the present invention, polymerization during reaction and distillation is effectively inhibited, and at the same time it is concentrated during distillation and precipitates solid matter, causing operational inconvenience. It never occurs.

Furthermore, since the polymerization inhibitor is a high boiling point substance, it does not mix into the distillate and color the product or delay the start of polymerization when the product is used. This will be explained in more detail below using Examples and Comparative Examples.

In addition, in Examples and Comparative Examples, all parts indicate parts by weight. Synthesis Example 1 Phenothiazine 1997 (1 mol), toluol 120
208 t (2 mol) of styrene was added dropwise to a mixture of 0 ml and boron trifluoride phenol complex salt 67 at a temperature of 80 to 85° C. over 1 hour, and the mixture was stirred at the same temperature for 4 hours.

The reaction solution was then washed with water and toluol was completely distilled off to obtain an amber product 4067 with a melting point of 48-76°C.
The main components of the product are bis(α-methylbenzyl)phenothiazine and (d-methylbenzyl)phenothiazine. Synthesis Example 2 Diphenylamine 1697 (1 mol), xylene 250
ml and boron trifluoride phenol complex 67 as a catalyst were mixed, stirred and heated to reach a temperature of 120 to 130°C, and then styrene 2087 was added dropwise to react over about 6 hours.

After the reaction, the reaction mixture was washed with water to remove the catalyst, and xylene was distilled off to obtain 360 tons of yellowish brown oil. Adding 64 tons of sulfur (2 tile atoms) and 2 tons of iodine to the oil,
The mixture was heated to 00° C. and stirred until the generation of hydrogen sulfide stopped, yielding a yellow-brown resinous material 390y. The softening point of the resin material is 6
It was 5℃. The product is bis(α-methylbenzyl)
The main ingredient is phenothiazine.

Synthesis example 3 Phenothiazine 1997 (1 mol), toluol 120
α in a mixture of 0ml and boron trifluoride phenol complex salt 67
-Methylstyrene 236y (2 mol) at a temperature of 80-85
The mixture was added dropwise at 1 hour at 0.degree. C., and stirred at the same temperature for 4 hours.

Next, this reaction solution was washed with water, and toluene was distilled off to obtain 350 tons of white powder (melting point: 130-133 °C). This product was recrystallized from perchlorethylene and had a melting point of 135.
．． 265 tons of white scaly crystals (60.2%
Yield) was obtained. The product is bis(d.α-dimethylbenzyl)phenothiazine. Synthesis Example 4 In Synthesis Example 2, a-methylstyrene 2367 was used instead of styrene, and the reaction was carried out in the same manner as in Synthesis Example 2.
A yellow-green resinous material 3507 was obtained.

The softening point of the resin-like material is 40°C, and its main component is (α
・d-dimethylbenzyl)phenothiazine and bis(α
-α-dimethylbenzyl)phenothiazine. Example 1 0.0% of the product of Synthesis Example 1 was added to a mixture of 95 parts of methacrylic acid amide synthesized from 100 parts of acetone cyanohydrin and 185 parts of sulfuric acid, and 188 parts of sulfuric acid and others.
After adding 1 part of water and 105 parts of water, 110 parts of
The mixture was heated and stirred at ~115°C for 2 hours.

After cooling to room temperature, the mixture was allowed to stand and separated into an organic layer and an aqueous layer.

An emulsified layer containing a polymer existed at the interface between the organic layer and the aqueous layer, and the amount was 10 parts after standing for 5 minutes, but reduced to 2 parts after standing for 30 minutes. Ta.

/)'-X, the emulsified layer and aqueous layer were discharged from the system.
The amount of polymer contained in the emulsified layer is very small (compared to the organic layer 0).
．． 5wt%) The liquid separation operation was carried out smoothly. Moreover, the water layer was hardly colored, which indicates that almost no polymerization inhibitor was contained in the water layer. organic layer 10
0 parts contains 93 parts of methacrylic acid, which is converted into 8 parts.
0-100 Hgabs, purified in a batch distiller under reduced pressure.

Although 90 parts of methacrylic acid was distilled out, no solid matter was precipitated in the distillation residue.

Furthermore, the obtained fraction had no coloration at all, and the degree of coloration did not increase even after storage for more than one month. Further, the thermal stability test result of the organic layer was that the polymerization time at 105° C. was 100 hours or more.

Comparative Example 1 To 283 parts of a methacrylic amide mixture synthesized in the same manner as in Example 1, 0.1 part of phenylpistolidine was added to hydrolyze the methacrylic amide.

The hydrolysis conditions were exactly the same as in Example 1. After cooling and standing, 1% of polymerized suspended matter was formed at the interface between the organic layer and the aqueous layer based on the organic layer.

Although the liquid separation operation was accompanied by some difficulties, it was possible to perform it. The aqueous layer liquid took on a brown color, indicating that some of the polymerization inhibitor had mixed into the aqueous layer. 100 parts of the organic layer contained 92 parts of methacrylic acid.

The organic layer thus obtained was heated to 80 to 1001 mHg.
ABS was fractionally distilled under reduced pressure.

When 75 parts of methacrylic acid was distilled out of the distillate, the viscosity of the distillation residue increased and solid matter precipitated. The thermal stability test result of the organic layer was 16 hours in polymerization time at 105°C.

Comparative Example 2 When 0.1 part of phenothiazine was added in place of phenylpistoloidine under exactly the same conditions as Comparative Example 1,
The emulsified layer present at the interface between the organic layer and the aqueous layer was 25 parts after standing for 5 minutes, and was finally reduced to 4 parts after standing for 3 hours.

The polymer contained in this emulsified layer was 1.0 wt% relative to the organic layer, and 99 parts of the organic layer contained 91 parts of methacrylic acid. In addition, during distillation purification, coloring of the fraction and precipitation of solid matter in the evaporation residue were observed. Example 2 0.0% of the product of Synthesis Example 1 was added to a mixture of 95 parts of methacrylic acid amide synthesized from 100 parts of acetone cyanohydrin and 185 parts of sulfuric acid, and 188 parts of sulfuric acid and others.
Add 1 part of methanol and add 60ff1) of methanol. After adding 34 parts of water, the mixture was heated and stirred at 80° C. for 4 hours.

After cooling and standing, the aqueous layer and emulsified layer were discharged from the system, and the organic layer was distilled. At the time of liquid separation, almost no emulsified layer containing the polymer was observed at the interface between the organic layer and the aqueous layer, and the liquid separation operation was easily performed.

When 120 parts of the organic layer was distilled, the distillation rate was 95%, and the distillate contained 108 parts of methyl methacrylate.

No precipitation of solid matter was observed in the residue after distillation.
Further, no coloration of the distillate was observed.

Example 3 0.4 part of the product of Synthesis Example 2 was dissolved in 100 parts of acrylonitrile, and this was combined with 203 parts of sulfuric acid, 100 parts of water,
95 parts of ethanol were mixed and heated in a reactor equipped with a reflux condenser.

After heating and stirring at 110°C for 4 hours, the mixture was cooled and left to stand, and the aqueous layer and emulsified layer were separated and discharged from the system.

190 parts of the organic layer was distilled under reduced pressure of 200 mmHgabs.

In order to prevent polymerization of the distillation line and the distillate, 0.2 part of hydroquinone was added to the organic layer, and a portion of this was distilled off.

During separation of the crude reaction solution, an emulsified layer containing some polymer was observed at the interface between the organic layer and the aqueous layer, but this did not interfere with the separation operation.

Almost no polymerization was observed during distillation of the organic layer, and some solid matter was observed in the pot after 175 parts of ethyl acrylate had been distilled out of the distillate, but this did not interfere with the distillation operation. .

Comparative example 3 Ethyl acrylate was synthesized in exactly the same manner as in Example 3.

Phenylbisaniline was added as a polymerization inhibitor in an amount equivalent to 4000 ppm based on acrylonitrile. When the crude reaction solution was separated, an emulsified layer containing a slightly larger amount of polymer than in Example 3 was observed at the interface between the organic layer and the aqueous layer, but the separation operation was possible.

0.2 parts of hydroquinone was added to 190 parts of the organic layer, and 20 parts of
01111Hgabs, distillation was performed under reduced pressure.

When 103 parts of ethyl acrylate was distilled out, the inside of the pot was polymerized. In addition, a large amount of sulfate, a polymerization inhibitor, precipitated in the pot. Example 4 400 parts of methyl methacrylate, 178 parts of dimethylaminoethanol, 6.4 parts of dibutyltin oxide, and 0.4 parts of the product of Synthesis Example 2 as a polymerization inhibitor were added to give 105 to 1
The reaction was carried out at 50°C for 4 hours.

The generated methanol was extracted from the system as an azeotrope with methyl methacrylate. First, from 491 parts of the crude reaction solution (containing 170 parts of methyl methacrylate and 314 parts of dimethylaminoethyl methacrylate) after completion of the synthesis, unreacted methyl methacrylate was heated to 230 mmHgabs. was distilled and recovered under reduced pressure, and then 10m7! 299 parts of dimethylaminoethyl methacrylate was distilled off under reduced pressure using LHgabs. During each of the above operations, no polymer formation was observed;
This example demonstrated that the substance of the present invention exhibits excellent performance as a polymerization inhibitor for acrylic acid and methacrylic acid esters containing amino groups.

Example 5 The same procedure as in Example 4 was carried out except that 0.4 part of the product of Synthesis Example 3 was used as a polymerization inhibitor.

As a result, no polymerization was observed during each operation, and dimethylaminoethyl methacrylate was obtained without any problems.

Example 6 The same procedure as in Example 2 was carried out except that 0.1 part of the product of Synthesis Example 4 was used as a polymerization inhibitor.

As a result, no polymerization was observed during each operation, and no coloring of the fractions was observed.

Claims (1)

[Claims] 1. When producing acrylic acid or methacrylic acid or their esters by the reaction of the corresponding nitrile or acid amide with water or alcohol, or the transesterification reaction of the corresponding ester with alcohol, or When separating by distillation from the crude reaction product liquid, there are general formulas ▲mathematical formulas, chemical formulas, tables, etc.▼ (In the table, R represents hydrogen or a methyl group, m and n are 0 to 2
Each represents an integer. However, it is selected so as to satisfy m+n≧1. 1. A method for inhibiting polymerization of acrylic acid or methacrylic acid or esters thereof, which comprises making a phenothiazine compound represented by ) exist in a reaction system or a distillation system.