JPS5846496B2 - Method for preventing popcorn polymerization of α,β-unsaturated carboxylic acid esters - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing popcorn polymerization of α,β-unsaturated carboxylic acid esters.

When producing an α,β-unsaturated carboxylic acid ester, such as an acrylic ester or a methacrylic ester, the ester is obtained by reacting acrylic acid or methacrylic acid with an alcohol or an epoxy compound, or by transesterification.

It is known that these α,β-unsaturated carboxylic acid esters are easily polymerized, and polymerization often occurs due to heat, light, etc. during the manufacturing process, storage, and transportation.

In particular, acrylic esters or methacrylic esters that have functional groups such as halogens, hydroxyl groups, epoxy groups, or alkoxyl groups in their ester groups are highly polymerizable and have a three-dimensional structure under heating conditions such as in distillation and concentration processes. Insoluble polymer (popcorn polymer) forms rapidly.

Such polymers are more likely to form in the gas phase than in the liquid phase of the system, and once formed, they will continue to grow explosively in both the gas and liquid phases no matter what polymerization inhibitor is added, causing damage to evaporation towers, piping, etc. It can become blocked and even spontaneously ignite due to the heat of polymerization.

In addition, popcorn polymerization generally occurs violently when the temperature exceeds 100°C, and popcorn polymerization tends to occur in common steel or stainless steel manufacturing equipment, especially in the protrusions of the equipment or on uneven metal surfaces. However, the boiling point of the ester The cost is relatively high, and the material of the manufacturing equipment is mainly stainless steel, making it increasingly difficult to prevent popcorn polymerization.

Hydroquinone, hydroquinone monomethyl ether, phenothiazine, paraphenylenediamine, metal copper salts, etc. have been known as conventional polymerization inhibitors.
It has little effect on preventing popcorn polymerization.

Furthermore, nitroso compounds, which are known to be effective in preventing popcorn polymerization, are less effective at high temperatures of 100° C. or higher, and require high concentrations, and also cause coloring of products.

In order to overcome the above-mentioned problems, the present inventors have conducted intensive research on a new polymerization prevention method, and have found that the N-oxyl compound has an extremely remarkable effect on preventing popcorn polymerization of α,β-unsaturated carboxylic acid esters. The present inventors have discovered that the present invention exhibits the following properties and does not cause any coloring phenomenon to the product, and has completed the present invention.

The gist is that in the production process of α,β-unsaturated carboxylic esters, especially acrylic esters or methacrylic esters, one or more compounds of the group consisting of N-oxyl compounds represented by the following general formula (1) are used. The present invention relates to a method for preventing popcorn polymerization by adding it to α,β-unsaturated carboxylic acid esters.

(In the formula, Rlt R2t R3t R4 is an alkyl group,
or R,, R, or Rs t R4 taken together with the carbon atom to which they are bonded represent a CH2- or -CH2CHCH2 group, and R7
represents an alkyl group or a phenyl group.

) These popcorn polymerization inhibitors (hereinafter referred to as the polymerization inhibitors of the present invention).

) easily dissolves in α,β-unsaturated carboxylic acid esters and is stable even at high temperatures of 100°C or higher, so if it is selected according to the boiling point of the target ester, it can dissolve in both gas and liquid phases over a wide temperature range. It shows a sufficient effect of preventing popcorn polymerization.

The amount of the polymerization inhibitor of the present invention added is smaller than that of a commonly used polymerization inhibitor, and is in the range of 1 to 11,000 pp, preferably 5 to 1,100 pp, based on the α,β-unsaturated carboxylic acid ester.

Further, there is no problem in using the polymerization inhibitor of the present invention in combination, and a synergistic effect may be exhibited in some cases.

The method of adding the polymerization inhibitor of the present invention is that the required amount is added to the raw material in advance in the manufacturing process, especially the distillation/concentration process, or it can be added from the top or bottom of the distillation column, making it easy to handle. be.

The α,β-unsaturated carboxylic acid ester that is the object of the present invention is an ester having a functional group such as a halogen, a hydroxyl group, an epoxy group, or an alkoxyl group in the ester group.

For example, 2-chloroethyl acrylate, 2-chloroethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, ethylene glycol diacrylate,
Ethylene glycol dimethacrylate, glycidyl acrylate, glycidyl methacrylate, methyl glycidyl acrylate, methyl glycidyl methacrylate, 2
-Ethoxyethyl acrylate, 2-ethoxyethyl methacrylate, carpitol acrylate, carpitol methacrylate, tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate,
Examples include benzyl acrylate, benzyl methacrylate, allyl acrylate, allyl methacrylate, pentyl acrylate, and pentyl methacrylate, but are not limited to specific examples.

In the present invention, N-oxyl compounds that exhibit remarkable effects on preventing popcorn polymerization include, for example, 2゜2.4,4-tetramethylazetidine-1-oxyl, 2,2-dimethyl-4,4-dipropylazetidine -1-oxyl, 2
, 2,5,5-tetramethylpyrrolidine-1-oxyl, 2,2,5゜5-tetramethyl-3-oxopyrrolidine-1-oxyl, 2,2,6,6-tetramethylpiperidine-1-oxyl , 6-aza-7,7-dimethyl-spiro(4t5)decane-6-oxyl, 2.2,6,
6-tetramethyl-4-acetoxypiperidine-1-oxyl, 2,2,6,6-kedormethyl-4-benzoyloxypiperidine-1-oxyl, and the like.

In addition, the popcorn polymerization prevention method according to the present invention does not cause coloring of the product and does not cause any trouble in subsequent handling.

If the polymerization inhibitor of the present invention is added to the α,β-unsaturated carboxylic acid ester in this way, popcorn polymerization will not occur during the production, so the range of production operations will be widened, reducing the need for production equipment, ensuring safe operation, and Its effects, such as improved product yield and quality, are immeasurable.

Next, the present invention will be explained based on Examples, but the present invention is not limited by the Examples.

Example 1 A Raschig ring packed column with a reflux condenser was attached to a 300 mJ glass flask, and 50 ppm of 2,2,5,5-tetramethyl-3 was added to 2-hydroxyethyl acrylate.
-Oxopyrrolidine-1-oxyl added solution 20
0 g was charged into a flask, and the mixture was refluxed under reduced pressure conditions such that the temperature inside the flask reached 100°C.

Even after 4 hours had passed, no popcorn polymer was observed.

On the other hand, when 200 ppm of hydroquinone was added, a popcorn polymer was generated in the light column after 20 minutes, and the light distillation system was blocked after 40 minutes.

Example 2 Using the same equipment and operation as in Example-1, 20 ppm of 2,
When a solution containing 2,6,6-tetramethyl-4-acetoxypiperidine-1-oxyl was refluxed at 100°C, no popcorn polymer was observed to occur even after 8 hours.

In contrast, 20% of hydroquinone monomethyl ether
When 0 ppm was added, popcorn polymers were generated in the packed tower after 1 hour.

Example 3 Using the same equipment and operation as in Example-1, a solution of 2-chloroethyl acrylate to which 50 ppm of 2,2-dimethyl-4,4-dipropylacetidine-1-oxyl was added was heated at 100°C. When the mixture was refluxed under the following conditions, no popcorn polymer was observed to occur even after 4 hours.

In contrast, 20% of hydroquinone monomethyl ether
When 0 ppm of nitrosobenzene was added, polymerization occurred after 30 minutes, and when 100 ppm of nitrosobenzene was added, popcorn polymerization occurred in the packed column after 1.5 hours.

Example 4 Using the same equipment and operation as in Example-1, 100 ppm of 2,2,5 was added to glycidyl methacrylate.
, 5-tetramethylpyrrolidine-1=oxyl was refluxed at 100°C, and no popcorn polymer was observed even after 4 hours had passed.

On the other hand, when 500 ppm of hydroquinone is added, it polymerizes after 30 minutes and 300 ppm of phenothiazine is added.
When pm was added, polymerization occurred after 7 minutes, and when 250 ppm of N-nitrosodiphenylamine was added, popcorn polymerization occurred after 2 hours, and the distillation system was rapidly clogged.

Example 5 When distilling reacted and washed crude tetrahydrofurfuryl acrylate using a 5M stainless steel batch distiller,
50 ppm of 6-aza-7,7-dimethyl-spiro[4,5]decane-6-oxyl was added dropwise to tetrahydrofurfuryl acrylate from the top of the distillation column to give 1101 u.
The residue was distilled off under reduced pressure of H over 10 hours.

After distillation, the still was disassembled and examined, and no popcorn polymers were found.

On the other hand, when 200 ppm of hydroquinone was dropped from the top of the distillation column, popcorn polymerization occurred 30 minutes after the start of distillation, and after 2 hours the distillation system was clogged, forcing the distillation to be stopped.

Claims (1)

[Scope of Claims] 1 α,β-unsaturated carboxylic acid ester with the following general formula (
α characterized by adding a member or a plurality of compounds of the group consisting of N-oxyl compounds represented by 1)
, a method for inhibiting popcorn polymerization of β-unsaturated carboxylic acid esters. (In the formula, R1, R2, Ra t R4 represent an alkyl group, or R1, R2 or R3, R, together with the carbon atom to which they are bonded, represent a CH2- or -CH2CHCH2 group, and R7
represents an alkyl group or a phenyl group. )