JPH0710798B2 - Method for producing methacrylic acid ester - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a methacrylic acid ester.

Methacrylic acid ester is used as a main component of acrylic resin products, and the polymer obtained by polymerizing these monomers exhibits various different performances depending on the type of alkyl group of the ester. Methyl methacrylate, which is a typical methacrylic acid ester, is transparent and has good gloss, and is excellent in electrical insulation, chemical resistance, and processability. Further, ethyl methacrylate, propyl methacrylate, butyl methacrylate and the like are compounds useful as paints, adhesives, fiber treating agents and the like.

[Conventional technology]

Already, as a method for producing a methacrylic acid ester by dehydrating α-hydroxyisobutyric acid ester, a method using sulfuric acid (JP-A-60-184047), a method using a solid catalyst such as an alkaline earth metal salt (Japanese Patent Publication No. 44-20611, 44-20612, 45
-15724) is known.

[Problems to be solved by the invention]

However, when sulfuric acid is used, decomposition is generally likely to occur, and therefore the yield of the target methacrylic acid ester is low, and in order to increase the yield, it is complicated to adjust the reaction temperature, contact time, etc. Various operations and a large amount of sulfuric acid are required.

Further, when a solid catalyst such as an alkaline earth metal salt is used, there is a drawback that the reaction becomes a gas phase reaction at high temperature.

The use of sodium methoxide or potassium methoxide has been proposed as a catalyst for solving the above-mentioned drawbacks, however, these catalysts also tend to lose their catalytic activity during the reaction, resulting in a large amount of the required catalyst. It has drawbacks.

[Means for solving problems]

The inventors of the present invention have conducted various studies in order to eliminate the drawbacks of using sodium methoxide or potassium methoxide as a catalyst, and as a result, by adding the catalyst to the reaction system over time, a small amount of long catalyst was obtained. The inventors have found that a high catalyst activity can be maintained for a long time and the production of by-products can be suppressed, and the present invention has been completed.

That is, the present invention relates to the general formula (1) (Wherein R represents an alkyl group having 1 to 4 carbon atoms), α-hydroxyisobutyric acid ester is dehydrated to produce a corresponding methacrylic acid ester, and sodium methoxide or potassium methoxide is used as a catalyst. The method for producing a methacrylic acid ester is characterized in that the reaction is carried out while adding side to the reaction system over time.

Hereinafter, the method of the present invention will be described in detail.

Examples of the α-hydroxyisobutyric acid ester used in the method of the present invention include methyl α-hydroxyisobutyrate, ethyl α-hydroxyisobutyrate, n-propyl α-hydroxyisobutyrate, iso-propyl α-hydroxyisobutyrate and α-hydroxyisobutyrate. N-Butyl hydroxyisobutyrate, α-hydroxyisobutyric acid is
o-Butyl and t-butyl α-hydroxyisobutyrate are available, and these α-hydroxyisobutyric acid esters are used as raw materials for the corresponding methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, iso-propyl methacrylate, and methacrylic acid. n-Butyl, iso-butyl methacrylate, t-butyl methacrylate can be produced.

The catalyst used in the method of the present invention is sodium methoxide or potassium methoxide, and although these catalysts have high activity, the activity gradually decreases during the reaction, and the disadvantage that the amount used increases Have Therefore, when the catalyst is used, it is necessary to add it to the reaction system with time to advance the reaction, and the addition method may be either intermittent or continuous. The catalyst can be added in a solid state, but it is preferable to add it after dissolving it in a solvent in order to further increase the activity and reduce the amount used. Methanol is suitable as the solvent.

When these catalysts are used after being dissolved in a solvent, the amount used is α
-0.1-10% by weight to hydroxyisobutyric acid ester
And more preferably 0.5 to 5% by weight. The addition of the catalyst may be continued until the end of the reaction, but if the conversion rate of α-hydroxyisobutyric acid ester reaches 80%, the reaction is completed with the activity of the added catalyst. May end.

In the method of the present invention, the dehydration reaction can be carried out under normal pressure or reduced pressure. The reaction temperature is in the range of 50 to 150 ° C, more preferably 60 to 110 ° C.

The reaction time varies depending on the amount of raw materials used, temperature, amount of catalyst, etc., but is usually 0.5 to 5 hours.

Methacrylic acid ester that is the target product can be obtained by a conventional method such as distillation after the completion of the reaction, but after the water produced during the reaction, the methacrylic acid ester and the added methanol are rapidly and continuously distilled off, A method of purifying by distillation or the like is preferable.

[Operation and effect of the invention]

According to the method of the present invention, it is possible to proceed the reaction under a mild condition in a short time without the need of using a large amount of sulfuric acid or performing the reaction at a high temperature. Further, the catalytic activity is sufficiently higher than that of other catalysts, and the reaction can be allowed to proceed rapidly with a small amount of the catalyst as compared with the case where the catalysts are added all together at the start of the reaction.

Furthermore, the target methacrylic acid ester can be produced in a high yield with almost no generation of by-products such as methacrylic acid.

〔Example〕

 Hereinafter, the method of the present invention will be specifically described with reference to examples.

Example 1 A flask having an inner volume of 500 ml equipped with a stirrer, a thermometer and a fractionation tower was charged with 295 g (2.5 mol) of methyl α-hydroxyisobutyrate and heated at a reaction pressure of 400 mmHg while stirring. When the system became stable, a 28 wt% methanol solution of sodium methoxide as a catalyst was continuously added to the reaction system using a microtube pump. A 28 wt% methanol solution of sodium methoxide was added at a rate of 16 g / hour for 2.5 hours. The total amount of sodium methoxide added was 11.2 g. After the reaction was started, water produced, methyl methacrylate and added methanol were distilled. The reaction was completed in 3 hours, then the pressure was reduced to 60 mmHg and the remaining methyl methacrylate was distilled off.

The by-product generated in the reaction was 13.3 g, which was 4.5% by weight of the charged α-hydroxyisobutyrate.

After completion of the reaction, the distillate was washed with water and then distilled under reduced pressure at 300 mmHg to obtain 190.2 g of the target methyl methacrylate.
The yield based on methyl α-hydroxyisobutyrate was 76%.

Examples 2 to 4 Using the same apparatus as in Example 1 and in the same manner,
Table 1 shows the results of synthesizing corresponding methacrylic acid esters by changing the type of -hydroxyisobutyric acid ester.

Example 5 Using the same apparatus as in Example 1, 295 g (2.5 mol) of methyl α-hydroxyisobutyrate was charged and heated at a reaction pressure of 400 mmHg with stirring. When the inside of the system was stabilized, a 28 wt% methanol solution of potassium methoxide was added as a catalyst at the addition rate of 16 g / hour as in Example 1. The addition time is 3 hours, and the total amount of potassium methoxide added is 13.4 g.
Met. The reaction time was 4 hours.

The by-product produced in the reaction was 6.3% by weight of the charged methyl α-hydroxyisobutyrate.

After completion of the reaction, the distillate was purified in the same manner as in Example 1 to obtain 183.0 g of methyl methacrylate. The yield based on methyl α-hydroxyisobutyrate was 73%.

Claims (1)

[Claims] 1. A general formula (1) (Wherein R represents an alkyl group having 1 to 4 carbon atoms), α-hydroxyisobutyric acid ester is dehydrated to produce a corresponding methacrylic acid ester, and sodium methoxide or potassium methoxide is used as a catalyst. A method for producing a methacrylic acid ester, which comprises reacting while adding side to a reaction system with time.