JP3475780B2 - Method for producing 2-cyanoacrylate - Google Patents

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 instant adhesives, and more particularly to improvement of depolymerization reaction during the production process.

[0002]

2. Description of the Related Art 2-Cyanoacrylate rapidly initiates polymerization due to a small amount of water present near the surface of an adherend,
Almost all adherends made of various materials except some inert materials such as polyethylene and polypropylene are adhered in a very short time of several seconds to several minutes, and the adhesive force is also strong, so electrical, electronic, mechanical Parts, precision machinery, household items,
It is used as the main component of instant adhesives in a wide range of fields such as medicine.

As a method for producing 2-cyanoacrylate, a method using cyanoacetate and formaldehyde as raw materials (USP 2721858: JP-B-35-10309).
No.) 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, in the second step, the condensate obtained in the first step in the presence of a polymerization inhibitor, In the presence of a depolymerization catalyst such as diphosphorus pentoxide, depolymerization is performed under high temperature and reduced pressure conditions, and in the third step, crude 2-cyanoacrylate obtained by depolymerization is distilled to obtain purified 2-cyanoacrylate. is there.

Regarding the above-mentioned method for producing 2-cyanoacrylate, batch production has hitherto been taken, but since this method has poor production efficiency, various continuous methods have been studied. However, since the depolymerization process must be performed at a high temperature for a long time, it was difficult to make it continuous. Further, in the depolymerization step, although the reaction rate was high at the initial stage of the reaction, there was a problem that the reaction rate gradually decreased. Further, a serious problem in this step is that during the reaction at high temperature and for a long time as described above, a large amount of by-products are generated as a result of incomplete depolymerization of the condensate of cyanoacetate and formaldehyde. . The production of these by-products reduces the yield of the product 2-cyanoacrylate. Furthermore, a part of the by-product remains in the depolymerization reactor as a large amount of tar-like and coke-like residues after the reaction is completed. If the residue remains in the reactor, the heat transfer and the mixing of the reaction solution become incomplete, so that there is also a problem that the reaction yield of the next depolymerization batch is reduced.

In order to prevent this, it was necessary to wash the depolymerization reactor very carefully after each reaction. Therefore, the cost is high for cleaning, and the productivity is extremely low in this step because the cleaning is required every depolymerization reaction and the reactor cannot be used during the cleaning. On the other hand, it was also studied to increase the size of the depolymerization reaction batch, but this method was not economical because the residue was further increased and the product yield was lowered.

As a method for solving these problems, JP-A-47-16420 discloses that in the presence of a polymerization inhibitor, depolymerization is carried out at a temperature of 150 to 230 in an extruder equipped with a degassing device.
A method of continuously depolymerizing a 2-cyanoacrylate condensate containing no heat medium at a temperature of 0.5 to 230 mmHg and at a temperature of 0.5 to 230 mmHg is disclosed. Further, JP-A-46-7573 discloses a method in which a mixture of a 2-cyanoacrylate condensate, a polymerization inhibitor and a heating medium is introduced into a thin film evaporator to carry out continuous depolymerization. These methods are
Since the reaction mixture in the depolymerization zone can be easily and quickly brought to the desired temperature, there is almost no generation of by-products, the yield of the product is improved, and depolymerization for the purpose of cleaning the depolymerization apparatus is performed. It has a feature that the interruption of the process can be avoided.

However, these methods require special expensive equipment, and it is difficult to control the temperature and the pressure, and it is difficult to carry out them industrially.

In the method for producing 2-cyanoacrylate, the depolymerization step is the rate-determining step of the production, and there is a strong demand for a method capable of suppressing the generation of by-products during the reaction and allowing the reaction to be semi-continuous. .

[0009]

[Means for Solving the Problems] The present inventors diligently studied the relationship between the depolymerization conditions and the amount of by-products (residues) that reduce the yield of the product and force frequent cleaning of the reactor. As a result, the change in the concentration of the depolymerization catalyst in the reaction solution that occurs while continuing the depolymerization reaction causes the generation of the residue, and by keeping the concentration constant during the reaction, the residue The present inventors have completed the present invention by discovering a totally unexpected fact that the occurrence is suppressed.

Further, as a result of studying a method of keeping the catalyst concentration in such a reaction solution constant and carrying out semi-continuous depolymerization, the present inventors have found that the depolymerization reactor causes coarse reaction due to the progress of the depolymerization reaction. By supplying the 2-cyanoacrylate condensate containing no depolymerization catalyst by the amount of the discharged 2-cyanoacrylate monomer and decreasing the amount of the reaction liquid, the catalyst concentration in the reactor can be kept substantially constant. This has led to the completion of the present invention.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The 2-cyanoacrylate applied to the present invention is represented by the following general formula.

[0012]

CH ₂ = C (CN) COOR

In the above formula, R is a saturated or unsaturated C1-20 carbon atom which may have a halogen atom,
It is a linear or branched chain hydrocarbon group, a saturated or unsaturated cyclic hydrocarbon group, or an aromatic group. However, in the case where R contains an ether group, the number of carbon atoms which may have a halogen atom in any of the remaining chains bonded by the ether group is 5
To 20 saturated or unsaturated, linear or branched chain hydrocarbon groups, saturated or unsaturated cyclic hydrocarbon groups, and aromatic groups.

Specific examples of the 2-cyanoacrylate represented by the above formula include methyl, ethyl, chloroethyl, n-propyl, i-propyl, allyl, propargyl, n-butyl and i-butyl of 2-cyanoacrylate. 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 instant adhesive.

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

1. Condensation step The condensation step is a step in which cyanoacetate and formaldehyde are heated and condensed in the presence of a basic catalyst and a solvent to obtain a condensate. Cyanoacetate used in the condensation step corresponds to the product 2-cyanoacrylate, and formaldehyde is not particularly limited, but specific compounds include formaldehyde gas, formalin aqueous solution, formaldehyde and alcohol. Reaction products, paraformaldehyde, trioxane, etc., which may be used alone or in combination, and paraformaldehyde is particularly preferable.

The catalyst used in the condensation step is a known organic basic substance such as piperidine, morpholine, quinoline, isoquinoline, ethylamine, diethylamine, triethylamine, ethanolamine, pyridine acetate, sodium hydroxide, potassium hydroxide or ammonia. Inorganic basic substances, such as these, may be 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, diphenyl phenyl phosphonate, etc. are mentioned, and these are used individually or in mixture. The condensate finally obtained in the condensation step of the present invention is subjected to a known and suitable pretreatment so that it is well decomposed into 2-cyanoacrylate in the subsequent depolymerization step. As a pretreatment, for example, water contained in the raw material or water generated in the condensation step is removed azeotropically when a solvent that forms an azeotropic mixture with water is used, and is distilled off if not. It
The catalyst is deactivated by using an acidic substance, washed with water, or removed together with the 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, depolymerization is performed at high temperature under reduced pressure, and a crude monomer of 2-cyanoacrylate is taken out as a gas,
This is the step of condensing this. As the depolymerization catalyst used in the depolymerization step, there are diphosphorus pentoxide, phosphoric acid, polyphosphoric acid, paratoluenesulfonic acid and the like, and diphosphorus pentoxide is particularly preferable because of its high reactivity. Examples of the polymerization inhibitor used in the depolymerization step include hydroquinone, hydroquinone monomethyl ether, pyrogallol, di-t-butylphenol, t-butylpyrocatechol and the like, and hydroquinone is particularly preferable. Further, in the depolymerization step, a high boiling point solvent such as tricresyl phosphate, dioctyl phthalate or diphenylphenylphosphonate may be added in order to reduce the viscosity in the reaction vessel during depolymerization.

3. Distillation Step Subsequently, a distillation operation is carried out in order to remove a trace amount of water remaining in the crude monomer of 2-cyanoacrylate, a polymer such as an impurity, and the like. When an organic solvent is used in the distillation, after distilling off these organic solvents, 0.1 to 10 m
The 2-cyanoacrylate is purified by distillation by heating under reduced pressure of mHg. At the time of distillation, it is preferable to add anionic polymerization inhibitors such as diphosphorus pentoxide, SO ₂ , paratoluene sulfonic acid, BF ₃ , propane sultone and methane sulfonic acid to 2-cyanoacrylate on the kettle side. preferable. It is also preferable to add a radical polymerization inhibitor such as hydroquinone, hydroquinone monomethyl ether or pyrogallol. It is also possible to introduce the crude monomer of 2-cyanoacrylate obtained by the depolymerization reaction as it is into the distillation step and continuously perform the distillation step simultaneously with the depolymerization reaction.

In order to store the purified 2-cyanoacrylate after distillation, it is advisable 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 gas such as F ₃ , sulfonic acid compounds such as methanesulfonic acid, hydroxypropylsulfonic acid, paratoluenesulfonic acid, boron trifluoride ethyl ether, boron trifluoride phenol, boron trifluoride methanol,
BF ₃ complex such as boron trifluoride n-butyl ether, acetic acid boron trifluoride, phosphoric acid compound such as polyphosphoric acid, phosphorus pentoxide, alkyl phosphate, pyromellitic acid, aconitic acid, cyanoacetic acid, organic acid such as capric acid Etc., but SO ₂ , BF ₃ , BF ₃ complex, methanesulfonic acid, and paratoluenesulfonic acid are particularly preferable. Specific examples of the radical polymerization inhibitor usable in the present invention include hydroquinone, hydroquinone monomethyl ether, pyrogallol, di-t-butylphenol, and t.
-Butylpyrocatechol and the like, and hydroquinone is particularly preferable.

The present invention is characterized in that in the depolymerization step, a depolymerization reactor having a stirrer is used to carry out the depolymerization reaction while keeping the concentration of the depolymerization catalyst in the reaction solution constant. . The crude monomer of 2-cyanoacrylate produced with the progress of the depolymerization reaction is discharged out of the system. As a result, the reaction liquid decreases and the concentration of the depolymerization catalyst relatively increases, which deviates from the optimum value of the reaction, resulting in the generation of by-products and a decrease in the reaction rate. In order to prevent this, the present invention is characterized in that the depolymerization catalyst concentration in the reactor is kept constant at an optimum value.

There are various concrete methods for keeping the depolymerization catalyst concentration constant, but the amount of the reaction liquid in the depolymerization reactor was kept constant for the condensate of cyanoacetate and formaldehyde containing no depolymerization catalyst. As described above, it is preferable to carry out the depolymerization reaction while continuously supplying it to the reactor because it is simple and the reaction can be performed semicontinuously. In order to keep the amount of the reaction solution constant, for example, a method of measuring the weight of the reactor itself, a method of using the amount of the substance distilled off from the reactor as a guide, or the like is used. However, in a reactor equipped with an ordinary stirring device, the liquid level and the liquid level are linked, so the liquid level of the depolymerization reactor is kept constant by measuring the liquid level with a liquid level gauge. The method of performing depolymerization while supplying the condensate so as to maintain the above temperature is a more simple and more preferable method although the accuracy is somewhat lowered.

Not only when the depolymerization catalyst is not contained in the condensate, but also when the depolymerization catalyst is deactivated or 2
-A case where a small amount of a depolymerization catalyst is contained for the purpose of supplementing the catalyst distilled along with the crude monomer of cyanoacrylate is also included in the present invention. When the condensate supplied to the reactor is heated in advance, the temperature of the depolymerization reaction is kept constant, so that a higher quality crude 2-cyanoacrylate monomer can be efficiently obtained. More preferable.

As another method, there is a method of appropriately discharging the reaction solution having an increased depolymerization catalyst concentration and supplying a condensate containing no depolymerization catalyst instead. Is not preferable because the yield of the product deteriorates. Further, instead of keeping the liquid level constant, there is also a method of supplying the condensate while appropriately detecting the depolymerization catalyst concentration in the reaction liquid, which allows the depolymerization reaction to be carried out under more preferable conditions. Although the generation of organisms can be suppressed, it has a drawback that the work becomes complicated.

In the depolymerization reaction, the preferable range of the concentration of the depolymerization catalyst in the reaction solution varies depending on the kind of the catalyst used, but in the case of a phosphorus-containing compound, it is 1 to 50 g in terms of diphosphorus pentoxide. / Liter range.

[0026]

In the depolymerization reaction of 2-cyanoacrylate, the generation of the residue requiring washing is caused by the change in the concentration of the depolymerization catalyst present in the reaction solution at the time of depolymerization. By keeping the catalyst concentration constant during the reaction, generation of residue is suppressed.

[0027]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1 1.2 liters of ethyl acetate and 480 g of paraformaldehyde were placed in a 4 liter glass reactor equipped with a stirrer, condenser and Dane-Stark water separator.
(14.7 mol), ethyl cyanoacetate 1700 g (1
(4.7 mol) and 1.2 ml of piperidine were added, and the temperature was raised and the reaction was carried out under the azeotropic temperature of ethyl acetate and water. Ethyl acetate in the distillate was separated from water by a water separator and then returned to the reactor. After reacting for 16 hours to remove the theoretical dehydrated amount of water and returning to room temperature, a brown transparent viscous liquid was obtained. When ethyl acetate was distilled off under reduced pressure,
A condensate of a brown viscous liquid was obtained inside the reactor.

300 g of the above-mentioned condensate was charged into a 1-liter glass reactor equipped with a stirrer and a condenser and stirred well while heating to 50 ° C., and diphosphorus pentaoxide 4 was added.
g and 3 g of hydroquinone were added. Catalyst concentration is 13g /
It is a liter. When the temperature of the reactor was gradually raised under a reduced pressure of 2 to 3 mmHg, a crude monomer of ethyl-2-cyanoacrylate began to distill around the temperature of 150 ° C inside the reactor, and the internal temperature was increased to 150 to While continuing the depolymerization while maintaining the temperature at 200 ° C., 150 to 200 of the condensate containing no catalyst was added so that the height of the liquid surface of the reactor was constant.
Depolymerization was continued by continuously adding while heating to ℃. After 830 g of the condensate was continuously added, depolymerization was completed when no more distillate was obtained. During this period, 1060 g of crude ethyl-2 was added.
-Cyanoacrylate could be obtained (Yield: 94
% (Raw material basis)). The residue left at the bottom of the reactor is 5
It was 0 g.

1.3 kg of diphosphorus pentaoxide and 5 g of hydroquinone per 1 kg of this crude ethyl-2-cyanoacrylate
Was distilled in addition, it is possible to obtain a fraction of 80% ethyl 2-cyanoacrylate distilled product, further SO ₂ 20pp
m and hydroquinone 1000 ppm were added to obtain a purity of 99.
A 6% ethyl-2-cyanoacrylate purified product was obtained.

Comparative Example 1 The condensate 3 was placed in a 1 liter glass reactor equipped with a stirrer, a condenser and a Dane-Stark type water separator.
00 g was charged and stirred well while heating at 50 ° C., and 4 g of phosphorus pentoxide and 3 g of hydroquinone were added. The catalyst concentration is 13 g / l. 2-3 mmHg in the reactor
When the temperature inside the reactor was gradually raised to 150 ° C., a crude monomer of ethyl-2-cyanoacrylate began to distill around the inside temperature of 150 ° C.
Depolymerization was continued while the temperature was kept at 00 ° C, and the depolymerization reaction was terminated when distillation was stopped. During this period, 270 g of crude ethyl-2-cyanoacrylate could be obtained (yield: 90% (raw material basis)). The residue left on the bottom of the reactor was 25 g.

Except that the reactor was used as it was without washing,
When the depolymerization reaction was performed in the same manner as in Comparative Example 1, the yield of crude ethyl-2-cyanoacrylate (raw material mol basis) was lowered to 85%.

[0033]

INDUSTRIAL APPLICABILITY According to the present invention, in the production of 2-cyanoacrylate, the depolymerization step can be carried out semi-continuously while maintaining a high reaction rate for a long period of time with a simple operation, and is carried out after depolymerization. Since the number of times the depolymerization reactor is washed can be significantly reduced, the productivity in this step can be greatly improved. Furthermore, the yield of the product α-cyanoacrylate can be improved and the quality can be improved.

Claims (2)

(57) [Claims] 1. A method for producing 2-cyanoacrylate by depolymerizing a condensate of cyanoacetate and formaldehyde, the reaction in a depolymerization reactor having a stirrer.
Method for producing a 2-cyanoacrylate which is characterized in that the depolymerization depolymerization reaction kept constant concentration during the reaction of the catalyst in the liquid. 2. A condensate of cyanoacetate containing no depolymerization catalyst and formaldehyde is continuously supplied to the reactor so that the amount of the reaction liquid in the depolymerization reactor having a stirrer can be kept constant. A method for producing 2-cyanoacrylate, which comprises carrying out a depolymerization reaction while carrying out.