Cianoacrilato

Method for producing purified 2-cyanoacrylate


The present invention relates to a method for producing a purified 2-cyanoacrylate, which is widely used as a main component of an instant adhesive and, in particular, to an improvement in a purification step of the production process.

BACKGROUND ART

A 2-cyanoacrylate is generally produced by condensation of a cyanoacetate and formaldehydein an organic solvent, followed by depolymerization of the polymer thus obtained at high temperature and reduced pressure. A crude 2-cyanoacrylateobtained here generally has low purity, poor adhesion performance, poor stability, etc., and it is therefore further distilled to give a purified 2-cyanoacrylate.

With regard to distillation and purification of a 2-cyanoacrylate, a method is known inwhich, in order to prevent polymerization of the 2-cyanoacrylate, an anionic polymerization inhibitor such as diphosphorus pentoxide, phosphoric acid, orparatoluenesulfonic acid, and a radical polymerization inhibitor such as hydroquinone, catechol, or pyrogallol are added to a crude 2-cyanoacrylate, which is then subjected to distillation at reduced pressure while heating.

Furthermore,JP-A-1-135754 (JP-A denotes a Japanese unexamined patent application publication) proposes a method in which distillation is carried out while continuously and countercurrently adding a polymerization inhibitor from an upper part ofa distillation column.

Moreover, U.S. Pat. No. 2,794,788 discloses a method in which distillation is carried out under a flow of an acidic gas such as SO2, BF3, HF, or CO2,for the purpose of inhibiting polymerization of a 2-cyanoacrylate in adistillate system.

Furthermore, JP-A-4-124168 proposes a method in which distillation is carried out without using the above-mentioned acidic gas but instead using a polymerization inhibitor such as a BF3 ether complex salt or a BF3 carboxylic acidcomplex salt.

DISCLOSURE OF INVENTION

However, even if theabove-mentioned polymerization inhibitor such as diphosphorus pentoxide or hydroquinone, or the polymerization inhibitor such as a BF3 ether complex salt or a BF3 carboxylic acid complex salt is used, there is stillthe problem that the 2-cyanoacrylate easily polymerizes in the distillate system.

Furthermore, with regard to the method in which distillation is carried out under a flow of an acidic gas such asSO2, BF3, HF, or CO2, since a 2-cyanoacrylate thus obtained contains a large amount of acidic gas, it is necessary toremove this acidic gas by degassing, etc. Moreover, since these acidic gases are discharged as exhaust gas, removal equipment is necessary, and there are problems in terms of the operation and the environment.

It is an object of the present invention to solve the above-mentionedproblems, that is, to provide a method that, unlike the case in which an acidic gas is used, does not have problems in terms of the operation and the environment, and that cancontinuously prevent a 2-cyanoacrylate from polymerizing in the distillate system when distilling the 2-cyanoacrylate.

As a result of an intensive investigation in order to attain this object by the present inventors intoa method of preventing polymerization of a 2-cyanoacrylate in the distillate system when distilling it, the present invention has beenaccomplished. That is, the present invention is a method for producing a purified 2-cyanoacrylate by distilling a crude 2-cyanoacrylate in the presence of a polymerization inhibitor, characterized in that a polymerization inhibitor having a boilingpoint at normalpressure of within ±12° C. of the boiling point at normal pressure of the purified 2-cyanoacrylate is used as the polymerization inhibitor.

BEST MODE FOR CARRYING OUT THE INVENTION

The present inventors have found that the polymerization inhibitor used in JP-A-1-135754 has a boiling point that is higher than the boiling point of ethyl 2-cyanoacrylate by more than 12° C., and when a...