JP2001288157A - Method of producing 2-cyanoacrylate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of increasing the yield of 2-cyanoacrylate by efficiently removing the high-boiling fraction formed in the reactor of the depolymerization reaction. SOLUTION: When the condensate between cyanoacetate and formaldehyde is depolymerized in the presence of a polymerization inhibitor, the high-boiling fraction that condenses at the temperature higher than the boiling point of 2-cyanoacrylate is re turned to the depolymerization reactor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing 2-cyanoacrylate, which is widely used as a main component of an instant adhesive, and more particularly to an improvement in a depolymerization reaction during a production process.

[0002]

2. Description of the Related Art 2-Cyanoacrylate starts polymerization promptly due to a small amount of water existing near the surface of an adherend,
Almost all adherends made of various materials are adhered in a very short time of about several seconds to several minutes, and the adhesive strength is strong, so it can be used in a wide range of fields such as electricity, electronics, mechanical parts, precision machinery, household goods and medical care. It is used as a main component of instant adhesives in various fields.

As a method for producing 2-cyanoacrylate, a method using cyanoacetate and formaldehyde as raw materials (US Pat. No. 2,721,858: JP-B-35-1030)
No. 9) is widely adopted today as an industrially advantageous method. The manufacturing method includes the following three steps. That is, in the first step, cyanoacetate and formaldehyde are condensed in an organic solvent in the presence of a basic catalyst such as piperidine, and in the second step, the condensate obtained in the first step is reacted with a polymerization inhibitor in the presence of a polymerization inhibitor. In the third step, crude 2-cyanoacrylate obtained by the depolymerization is distilled to obtain purified 2-cyanoacrylate in the presence of a depolymerization catalyst such as diphosphorus oxide, under high-temperature and reduced-pressure conditions. .

However, when the above-described method for producing 2-cyanoacrylate is carried out, a large amount of high-boiling fractions such as 2,4-dicyanoglutaric acid diester are distilled off together with 2-cyanoacrylate in the latter stage of the depolymerization in the second step. Therefore, when trying to increase the yield of crude 2-cyanoacrylate,
The purity of the crude 2-cyanoacrylate will be low. Further, these high-boiling fractions are disclosed in JP-A-60-2047.
As described in No. 52, the action of accelerating the polymerization of 2-cyanoacrylate causes the purity of crude 2-cyanoacrylate to be further reduced. Further, in the third step, when trying to increase the distillation yield of crude 2-cyanoacrylate in order to maintain the yield of purified 2-cyanoacrylate, the higher the purity of crude 2-cyanoacrylate, the larger the boiling point rise, Especially in the latter half of the distillation
Since many impurities distill out with cyanoacrylate,
As a result, there is a problem that the quality of the purified 2-cyanoacrylate is also deteriorated.

As a method for solving these problems, Japanese Patent Application Laid-Open No. 60-204752 discloses a method in which a polymerization inhibitor is used.
Temperature of 50-320 ° C., 0.1-150 mbar (0.
Under a pressure of from 0.01 to 15 kPa), a condensate of cyanoacetate and formaldehyde is depolymerized, and the resulting depolymerized vapor is passed through a temperature zone of 120 to 200 ° C. to separate a high-boiling fraction. A method for obtaining 2-cyanoacrylate in a high yield by passing through a temperature zone of -30 to 50 ° C is disclosed.

However, in this method, the purity of the purified 2-cyanoacrylate can be increased within the range of 120 to 200 ° C. as the temperature zone for separating the high-boiling fraction is lowered. -The yield of cyanoacrylate is reduced. That is, it was difficult to increase the purity while maintaining the yield of 2-cyanoacrylate at a high level. Further, in this method, there is a disadvantage that a high-boiling fraction condensed in a temperature range from the boiling point of 2-cyanoacrylate to less than 120 ° C. still distills out into crude 2-cyanoacrylate.

[0007]

The problem to be solved by the present invention is as follows.
It is an object of the present invention to provide a method for producing a cyanoacrylate, in which a high-boiling-point fraction can be precisely reduced by a simple operation and removed by a simple operation, and a high yield of purified 2-cyanoacrylate can be maintained.

[0008]

Means for Solving the Problems The present inventors have studied diligently the process of fractionally removing a high-boiling fraction condensing at a temperature higher than the boiling point of 2-cyanoacrylate from a fraction produced from a depolymerization reactor. , Even in the process of fractionation of high boiling fractions,
It has been discovered that polymerization of 2-cyanoacrylate is considerably expressed, and as a result, the yield of purified 2-cyanoacrylate is reduced. Further, the present inventors have intensively studied the depolymerizability of a high-boiling fraction containing a 2-cyanoacrylate polymer that has been subjected to shrinkage removal. Found that a large amount of components capable of being re-depolymerized to 2-cyanoacrylate remained, and refluxed the high-boiling fraction containing the 2-cyanoacrylate polymer which had been decomposed and removed to a depolymerization reactor. It has been discovered that the yield of 2-cyanoacrylate can be increased by depolymerizing while performing. Further 2-
Since it is not necessary to strictly separate the cyanoacrylate and the high-boiling fraction at one time, it is not necessary to use a known condensation temperature, for example, 120 to 200 ° C. described in JP-A-60-204752. The inventors have found that the yield and purity of 2-cyanoacrylate can be improved even at a reduced temperature, and have completed the present invention.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The general formula of the 2-cyanoacrylate applied to the present invention is as follows.

[0010]

Embedded image

In the above formula, R is a saturated or unsaturated C 1 -C 20 which may have a halogen atom.
A linear hydrocarbon group, a branched chain hydrocarbon group or a cyclic hydrocarbon group, or an aromatic hydrocarbon group having 1 to 20 carbon atoms which may have a halogen atom is an aromatic hydrocarbon group. Where R
Contains an ether bond, when either or both of the ether-bonded hydrocarbon residual chains have 5 to 20 carbon atoms which may have a halogen atom, are a saturated or unsaturated, linear type. A hydrocarbon group, a branched chain hydrocarbon group or a cyclic hydrocarbon group, or an aromatic group having 5 to 20 carbon atoms which may have a halogen atom.

Specific examples of the 2-cyanoacrylate represented by the above formula include methyl, ethyl, chloroethyl, n-propyl, i-propyl, allyl, propargyl, n-butyl, i-butyl and the like of 2-cyanoacrylic acid. n-pentyl, n-hexyl, amyl, 2-methyl-3-butenyl, 3-methyl-3-butenyl, 2-pentenyl, n-
Hexyl, 6-chlorohexyl, cyclohexyl, phenyl, tetrahydrofurfuryl, 2-hexenyl, 4-
Methyl-pentenyl, 3-methyl-2-cyclohexenyl, norbornyl, heptyl, cyclohexanemethyl,
Cycloheptyl, 1-methyl-cyclohexyl, 2-methyl-cyclohexyl, 3-methyl-cyclohexyl,
2-ethylhexyl, n-octyl, cyclooctyl,
Cyclopentanemethyl, 2,3-dimethylcyclohexyl, n-nonyl, isononyl, oxononyl, n-decyl, isodecyl, n-dodecyl, 2-ethoxyethyl,
2-ethoxy-2-ethoxyethyl, butoxy-ethoxy-ethyl, 2,2,2-trifluoroethyl, hexafluoroisopropyl, lauryl, isotridecyl, myristyl, cetyl, stearyl, oleyl, behenyl,
Hexyldecyl, octyldodecyl, benzyl, chlorophenyl, 2-pentyloxyethyl, 2-hexyloxyethyl, 2-cyclohexyloxyethyl, 2-
Examples thereof include (2-ethylhexyloxy) ethyl and 2-phenoxyethyl, which are used as a main component or a subcomponent of a cyanoacrylate-based instant adhesive.

A method for producing 2-cyanoacrylate using cyanoacetate and formaldehyde as raw materials is described below.
This will be described in more detail below.

1. Condensation Step The condensation step is a step of condensing cyanoacetate and formaldehyde by heating in the presence of a basic catalyst and a solvent to obtain a condensate. The cyanoacetate used in the condensation step corresponds to the product 2-cyanoacrylate, and the formaldehyde is not particularly limited, but specific compounds include formaldehyde gas, formalin aqueous solution, formaldehyde and alcohol. And paraformaldehyde and trioxane. These are used alone or as a mixture, and paraformaldehyde is particularly preferred.

The catalyst used in the condensation step includes known organic basic substances such as piperidine, morpholine, quinoline, isoquinoline, ethylamine, diethylamine, triethylamine, ethanolamine, pyridine acetate, sodium hydroxide, potassium hydroxide and ammonia. And the like. These are used alone or in combination. As the solvent used in the condensation step, toluene,
Xylene, benzene, trichloroethylene, cyclohexane, ethyl acetate, methanol, ethanol, isopropanol, tricresyl phosphate, dioctyl phthalate, diphenylphenyl phosphonate and the like are used, and these are used alone or in combination. The condensate finally obtained in the condensation step of the present invention is subjected to a known suitable pretreatment so that it can be favorably decomposed into 2-cyanoacrylate in the subsequent depolymerization step. As a pretreatment, for example, water contained in the raw material and water generated during the condensation step are removed by azeotropic distillation when a solvent that forms an azeotropic mixture with water is removed, and otherwise distilled off. You.
The catalyst is deactivated using an acidic substance, removed by washing with water, or removed together with a solvent.

2. Depolymerization Step In the depolymerization step, a depolymerization catalyst and a polymerization inhibitor are added to the condensate obtained in the condensation step, and the mixture is depolymerized at a high temperature under reduced pressure to obtain a crude 2
-A step of taking cyanoacrylate as a gas and condensing it. Examples of the depolymerization catalyst used in the depolymerization step include diphosphorus pentoxide, phosphoric acid, polyphosphoric acid, p-toluenesulfonic acid, and the like, and diphosphorus pentoxide is particularly preferred because of its high reactivity. Examples of the polymerization inhibitor used in the depolymerization step include hydroquinone, hydroquinone monomethyl ether, pyrogallol, di-t-butylphenol, and t-butylpyrocatechol, and hydroquinone is particularly preferable. In the depolymerization step, a high-boiling solvent such as tricresyl phosphate, dioctyl phthalate, or diphenylphenyl phosphonate may be added to reduce the viscosity in the reaction vessel during the depolymerization.

3. Distillation Step Subsequently, a distillation operation for removing a trace amount of water remaining in the crude 2-cyanoacrylate and a polymer as an impurity is performed. When using an organic solvent in the distillation, after distilling off these organic solvents, preferably 0.01 to
The crude 2-cyanoacrylate is purified by distillation by heating under a reduced pressure of 1.33 kPa. At the time of the distillation, diphosphorus pentoxide, SO ₂ and paratoluenesulfonic acid, BF ₃ , propane sultone,
It is preferable to add an anionic polymerization inhibitor such as methanesulfonic acid. It is also preferable to add a radical polymerization inhibitor such as hydroquinone, hydroquinone monomethyl ether, and pyrogallol. The crude 2-cyanoacrylate obtained by the depolymerization reaction can be directly led to the distillation step, and the distillation step can be continuously performed simultaneously with the depolymerization reaction.

In order to preserve the purified 2-cyanoacrylate after distillation, it is preferable to add an anionic polymerization inhibitor or a radical polymerization inhibitor of 2-cyanoacrylate. Specific examples of the anionic polymerization inhibitor include SO ₂ , B
Acid gases such as F _3, methanesulfonic acid, hydroxypropyl sulfonic acid, sulfonic acid compounds such as p-toluenesulfonic acid, boron trifluoride ethyl ether, boron trifluoride phenol, boron trifluoride methanol,
Boron trifluoride n-butyl ether, BF ₃ complex such as boron trifluoride acetate, polyphosphoric acid, diphosphorus pentoxide, phosphate compound such as alkyl phosphate, pyromellitic acid, aconitic acid, cyanoacetic acid, capric acid Organic acids and the like can be mentioned, but SO ₂ , BF ₃ , BF ₃ complex, methanesulfonic acid and paratoluenesulfonic acid are particularly preferred. Specific examples of the radical polymerization inhibitor that can be used in the present invention include hydroquinone, hydroquinone monomethyl ether, pyrogallol, di-t-butylphenol, and t-butylpyrocatechol, with hydroquinone being particularly preferred.

The present invention is characterized in that, in the depolymerization step, a high-boiling fraction condensing at a temperature higher than the boiling point of 2-cyanoacrylate is returned from the fraction obtained by the depolymerization to the depolymerization reaction for depolymerization. Is a method for producing 2-cyanoacrylate. The high-boiling fraction can be obtained by separating the 2-cyanoacrylate fraction from the depolymerized fraction, and the separation means is preferably fractionation.

Specifically, a condensate of cyanoacetate and formaldehyde is charged into a reactor provided with a decompressor and a total condenser, and the temperature is gradually increased under reduced pressure. When the temperature inside the reactor reaches a temperature at which the depolymerization reaction starts, gas of 2-cyanoacrylate starts to be emitted, and the temperature inside the reactor is kept higher than the reaction start temperature to continue the depolymerization. The depolymerization pressure is preferably 15 kPa or less, and the temperature is preferably 150 to 320 ° C. If the pressure exceeds 15 kPa, it is necessary to raise the depolymerization temperature, and as a result, an abnormal decomposition reaction tends to occur, and if the temperature is lower than 150 ° C., the depolymerization reaction hardly occurs. It is easy to occur and neither is preferable. On the other hand, the decompressor and the total condenser maintain the temperature at which the gas generated by depolymerization can be condensed. In this case, the temperature of the decompressor becomes 2-
It is preferable that the lower limit be a temperature 10 ° C. higher than the boiling point of the cyanoacrylate and the upper limit be 110 ° C. If the temperature is lower than the lower limit, 2-cyanoacrylate is easily trapped, and if the temperature is higher than the upper limit, a high-boiling fraction is difficult to be trapped, which is not preferable. The temperature of the total contractor is lower than the temperature of the decompressor, but is preferably in the range of -30 to 50C.

The high-boiling fraction in the gas to be depolymerized and distilled off is condensed in a condensing device, and a part or the whole thereof is returned to the depolymerization reactor. In order to increase the yield of 2-cyanoacrylate, it is preferable to return the entire amount. After the high-boiling fraction is once collected, it can be returned to the depolymerization reaction, but the degree of polymerization of the 2-cyanoacrylate polymer present in the high-boiling fraction may increase during the storage. Therefore, it is preferable to depolymerize the high-boiling fraction while refluxing it in the depolymerization reactor. On the other hand, the crude 2-cyanoacrylate that has passed through the decompressor in a gaseous state is condensed and recovered by the entire condenser. At the end of the depolymerization reaction, it is preferable to stop the reflux of the high-boiling fraction to the depolymerization reactor and collect the crude 2-cyanoacrylate when the distilling of the crude 2-cyanoacrylate is reduced or stopped.

In the present invention, in order to increase the purity of the crude 2-cyanoacrylate, a high-boiling fraction condensed at a temperature equal to or higher than the boiling point of 2-cyanoacrylate is reduced from the fraction produced from the depolymerization reactor. However, in the high-boiling fraction fractionally removed, there are still some components that can be re-depolymerized into 2-cyanoacrylate such as a 2-cyanoacrylate polymer. Depolymerizes while refluxing. In this case, a known condensation temperature such as 120 described in JP-A-60-204752 is used.
Needless to say, at a temperature of ~ 200 ° C, if the temperature is at least 10 ° C higher than the boiling point of 2-cyanoacrylate under this pressure, which is a lower decomposition temperature, the yield and purity of crude 2-cyanoacrylate are improved. be able to.

Although the above example describes a batch type depolymerization reaction, the present invention can be applied to a continuous type depolymerization reaction.

[0024]

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. FIG. 1 is a schematic diagram showing a depolymerization reactor and its periphery for explaining the present reaction.

Example 1 A condensate 165 of ethyl cyanoacetate and paraformaldehyde was placed in a 400-liter depolymerization reactor 1 equipped with a stirrer.
kg, and 1.2 kg of diphosphorus pentoxide and 1.8 kg of hydroquinone were added. When the temperature of the reactor was gradually increased under a reduced pressure of 0.3 to 0.8 kPa, the inside of the reactor became 15 kPa.
Around 0 ° C., crude ethyl-2-cyanoacrylate gas began to be emitted, and depolymerization was continued while maintaining the internal temperature at 150 to 200 ° C., while the inside of the decomposer 2 was 90 to 110 ° C.
° C, and the inside of the total contractor 4 was kept at -30 to 10 ° C. The high-boiling fraction in the depolymerized crude ethyl-2-cyanoacrylate gas is condensed by the condensing device, but is not recovered in the high-boiling fraction recovery receiver 6, and the depolymerization reactor reflux pipe is connected. Back to the reactor. On the other hand, the crude ethyl-2-cyanoacrylate that passed through the decompressor in a gaseous state was condensed by the total condenser and collected in the crude 2-cyanoacrylate recovery receiver 5. When the distillation of the crude ethyl-2-cyanoacrylate was stopped, the depolymerization was terminated. During this time, 130.0 kg of crude ethyl-2-cyanoacrylate was obtained (yield: 78.8%). Further, the purity of the obtained crude ethyl-2-cyanoacrylate was 94.5%.

1.3 g of diphosphorus pentoxide and 5 g of hydroquinone per 1 kg of this crude ethyl-2-cyanoacrylate
, And 4% of the first fraction was distilled off.
0.5% of purified ethyl-2-cyanoacrylate was obtained (yield of purified ethyl-2-cyanoacrylate based on a condensate of ethyl cyanoacetate and paraformaldehyde: 71.3%).

Comparative Example 1 In a 400-liter depolymerization reactor 1 equipped with a stirrer, 162.5 kg of the same condensate as in Example 1 was charged, and 1.2 kg of diphosphorus pentoxide and 1.8 kg of hydroquinone were added. When the temperature of the reactor was gradually increased under a reduced pressure of 0.3 to 0.8 kPa, a crude ethyl-2-cyanoacrylate gas began to be emitted from around 150 ° C. inside the reactor, and the internal temperature was lowered. While the depolymerization was continued while keeping the temperature at 150 to 200 ° C, the inside of the decompressor 2 was kept at 120 to 140 ° C, and the inside of the total contractor 4 was kept at -30 to 10 ° C. Depolymerized crude ethyl
The high-boiling fraction in the 2-cyanoacrylate gas is condensed by the condensing device and collected in the high-boiling fraction collection receiver 6. On the other hand, the crude ethyl-2-cyanoacrylate that passed through the decompressor in a gaseous state was condensed by the total condenser and collected in the crude 2-cyanoacrylate recovery receiver 5. Crude ethyl-2-
Depolymerization was terminated when the distilling of the cyanoacrylate and the high-boiling fraction ceased, during which 133.6 kg of crude ethyl-2-cyanoacrylate could be obtained (yield: 82.2%). Also, the obtained crude ethyl-2
The purity of the cyanoacrylate was 87.3%;

1.3 g of diphosphorus pentoxide and 5 g of hydroquinone per 1 kg of this crude ethyl-2-cyanoacrylate
, And 4% of the first fraction was distilled off.
3.3% of a purified product of purified ethyl-2-cyanoacrylate was obtained (yield of purified ethyl-2-cyanoacrylate based on a condensate of ethyl cyanoacetate and paraformaldehyde: 68.5%).

[0029]

According to the present invention, in the production of 2-cyanoacrylate, a high-boiling fraction can be precisely shredded and removed by a simple operation, so that the yield of purified 2-cyanoacrylate can be maintained at a high level. It became possible to improve the purity of crude 2-cyanoacrylate.

[Brief description of the drawings]

FIG. 1 is a process diagram showing a depolymerization reactor and its periphery for explaining the present reaction.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Depolymerization reactor 2 Separator 3 High-boiling fraction depolymerization reactor reflux tube 4 Total condenser 5 Crude 2-cyanoacrylate recovery receiver 6 High-boiling fraction recovery receiver

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshikazu Mori 2-3-1 Fushiki, Takaoka-shi, Toyama F-term (reference) in the Takaoka Plant of Toagosei Co., Ltd. 4H006 AA02 AB99 AD11 BD40 BD52 QN30

Claims (4)

[Claims] In depolymerizing a condensate of cyanoacetate and formaldehyde in the presence of a polymerization inhibitor,
A method for producing 2-cyanoacrylate, comprising returning a high-boiling fraction condensed at a temperature equal to or higher than the boiling point of 2-cyanoacrylate from a fraction obtained by depolymerization to a depolymerization reaction to depolymerize. 2. Depolymerization of a condensate of cyanoacetate and formaldehyde in the presence of a polymerization inhibitor,
2. A high-boiling fraction condensed at a boiling point of 2-cyanoacrylate or higher is fractionated from a fraction obtained by depolymerization, and the fractionated high-boiling fraction is returned to the depolymerization reaction for depolymerization. -A method for producing cyanoacrylate. In depolymerizing a condensate of cyanoacetate and formaldehyde in the presence of a polymerization inhibitor,
From the fraction obtained by depolymerization, the high-boiling fraction condensed at a boiling point of 2-cyanoacrylate or higher is fractionated, and the depolymerized high-boiling fraction is depolymerized while being refluxed to the depolymerization reaction. A method for producing 2-cyanoacrylate. 4. The method according to claim 2, wherein the condensation temperature is a temperature range in which the lower limit is a temperature higher than the boiling point of 2-cyanoacrylate by 10 ° C. and the upper limit is 110 ° C. under the pressure condition of the decompression. Or 3) the method for producing 2-cyanoacrylate.