WO2010091975A1

WO2010091975A1 - Method for producing cyano acrylates esters

Info

Publication number: WO2010091975A1
Application number: PCT/EP2010/051225
Authority: WO
Inventors: Carsten Friese; Lars Zander
Original assignee: Henkel Ag & Co. Kgaa
Priority date: 2009-02-13
Filing date: 2010-02-02
Publication date: 2010-08-19
Also published as: DE102009000861A1

Abstract

The invention relates to a method for producing cyanoacrylate esters, essentially using a transesterification reaction, wherein the transesterification reaction is carried out in the presence of a transesterification catalyst, comprising at least one acid with a pk value of ≤ 5 and at least one metal catalyst.

Description

Process for the preparation of cyanoacrylates

The present invention relates to a process for the preparation of cyanoacrylic acid esters. The process is essentially based on a transesterification reaction, wherein the transesterification reaction is carried out in the presence of a transesterification catalyst which comprises at least one acid having a pks value ≦ 5 and at least one metal catalyst.

Cyanacrylic acid ester polymerizable adhesive compositions have found wide use in both industrial and medical applications because of their ease of use, as well as the high rate of cure and strength of the resulting adhesive bond. It is known that monomeric forms of cyanoacrylates are extremely reactive and rapidly polymise in the presence of even minute amounts of a polymerization initiator, including airborne or surface moisture. The polymerization is initiated by anions, free radicals, zwitterions or ion pairs. Once the polymerization has been started, the cure speed can be very high. Polymeric adhesive compositions based on cyanoacrylic acid esters have therefore proved to be attractive solutions, for example, in the bonding of plastics, rubbers, glass, metals, wood and also biological tissues.

As disclosed in US Pat. No. 6,667,031, the conventional synthesis of mono-cyanoacrylic acid esters is based on a Knoevennagel condensation in which cyanoacetate is reacted with formaldehyde. The resulting prepolymer is depolymerized at high temperatures of 150 to over 200 ⁰ C by thermal cracking, the separation of the monomers formed from the reaction solution is usually carried out by distillation. The thermal depolymerization succeeds only if this process takes place in the presence of stabilizers or mixtures of stabilizers, the both a radical and an anionic repolymerization of the monomers formed under the reaction conditions described can be prevented.

Stabilizers that prevent anionic repolymerization are usually, but not exclusively, Lewis acids, such as sulfur dioxide, nitric oxide or boron trifluoride or inorganic or organic Brønsted acids, especially those having a pKa ≤ 5, such as sulfuric acid, phosphoric acid or organic sulfonic acids ,

Often, the very high concentration of stabilizers used in the process results in the removal of some of the stabilizer by the removal of the monomer from the reaction solution by distillation. The resulting sometimes very high residual concentration of the stabilizer in the distilled Cyanacrylatmonomer leads to overstabilization, especially in low-demanding cyanoacrylic acid esters, whereby the rate of polymerization is reduced.

The preparation of Biscyanacrylaten has long been known and can be done as follows:

Analogously to the Knoevenagel condensation described above, formaldehyde and biscyanacetates are reacted. This results in a crosslinked polymer, which can hardly be thermally depolymerized.

Furthermore, the preparation of Biscyanacrylaten done in a retro-Diels-Alder reaction. For example, as described in U.S. Patent 3,975,422, a monofunctional cyanoacrylate having dienes is first blocked. The blocked monofunctional cyanoacrylate is saponified to the free acid. From the corresponding acid chloride, the ester is then prepared with a diol. After the biscyanoacrylate has been replaced by maleic anhydride, the pure biscyanoacrylate is finally obtained after repeated recrystallization from benzene. This production route thus comprises 5 stages and is therefore uneconomical. An alternative possibility for the preparation of Biscyanacrylaten is taught in European Patent EP 0764148 B1.

The biscyanoacrylates are obtained by reaction of 2-cyanoacrylic acid or its alkyl ester with diols, the reaction preferably being carried out in the presence of sulfonic acids as catalyst in solution. The biscyanoacrylates are then isolated by fractional crystallization.

A disadvantage of this method has been found that relatively high amounts of sulfonic acids must be used to achieve an effective esterification or transesterification reaction. A complete separation of the sulfonic acids from the product obtained is often difficult, which is to observe a noticeable reduction in the rate of polymerization of the particular monomer, especially in the case of overly expensive biscyanoacrylates, since the said sulfonic acids act as anionic polymerization inhibitors.

The aim of the present invention was therefore the development of an effective process for the preparation of mono-, bis- and / or Multicyanacyrlsäureestern in high purity using as small amounts of anionic polymerization inhibitors.

The solution according to the invention can be found in the claims. It consists essentially in the transesterification of mono-cyanoacrylic acid esters with monohydric and / or polyhydric alcohols in the presence of a transesterification catalyst comprising at least one acid having a pks value ≦ 5 and additionally at least one metal catalyst. By using the at least one metal catalyst, it is possible to significantly minimize the amount of acids, in particular acids with a pks value ≤ 5 compared to conventional methods.

The present invention therefore provides a process for preparing at least one cyanoacrylic acid ester of the general formula (I), comprising the steps:

Formula (I) a) transesterification of at least one 2-cyanoacrylic acid ester of the general formula (II),

Formula (II) where R ^{1 is} a branched or unbranched alkyl radical having 1 to 6 C atoms, with at least one alcohol of the general formula (III)

[ ^{H "} Hn ^R formula (III) in the presence of a transesterification catalyst comprising at least one acid having a pks value ≦ 5 and at least one metal catalyst and b) isolating the cyanoacrylic acid ester of the general formula (I) obtained in step a), where n is a is integer from 1 to 6 and R is an n-valent radical comprising 1 to 100 carbon atoms.

For the purposes of the present invention, an n-valent radical R is an n-valent organic radical having 1 to 100 carbon atoms which, starting from the cyanoacrylic acid ester of the general formula (I) or alcohol of the general formula (III), is replaced by the homolytic one Cleavage of n carbon-oxygen bonds is formally formed.

The term of the n-valent radical will be explained in more detail below using the example of the trivalent alcohol TMP (n = 3):

The formal homolytic cleavage of the three C-OH bonds in the TMP molecule gives rise to a 3-valent organic radical in the context of the present invention.

Depending on the alcohol used, both mono-cyanoacrylic acid esters and also higher cyanoacrylic acid esters can be prepared by the process according to the invention.

In a preferred embodiment of the process according to the invention, the cyanoacrylic acid ester of the general formula (I) is therefore prepared from monocyan cyanoacrylates of the general formula (Ia)

Formula (Ia) and / or from Biscyanacrylsäureestern of the general formula (Ib)

Formula (Ib) and / or from triscyanoacrylic esters of the general formula (Ic)

Formula (Ic) selected, wherein radical R is as defined above. In a preferred embodiment of the process according to the invention, the radical R in formula (I), formula (Ia), formula (Ib), formula (Ic) and / or formula (III) comprises a C3 to Cioo chain, preferably a C ₅ to C70 chain and in particular a C ₁₀ to C ₅₀ chain, which is interrupted by at least one oxygen atom. The rest R can be linear, branched or cyclic.

In particular, radicals R which have at least one polyethylene glycol and / or at least one polypropylene glycol unit are preferred.

In a further embodiment of the process according to the invention, the radical R in formula (I), formula (Ia), formula (Ib), formula (Ic) and / or formula (III) comprises 3 to 18, in particular 4, 8, 10 and / or 12 directly connected C atoms. The remainder R can likewise be linear, branched or cyclic.

The radical R may furthermore contain an aromatic group or, in addition to hydrogen and carbon atoms, also comprise at least one heteroatom, for example selected from halogen, oxygen and / or nitrogen atoms.

In the case of the alcohols of the general formula (III)

[ ^H -Hn ^R formula (III) are monohydric to hexahydric alcohols (n = 1-6), with mono-, di- and / or trihydric alcohols being preferred. From these alcohols, the above-shown mono-cyanoacrylic acid esters of the general formula (Ia), the Biscyanacrylsäureester of the general formula (Ib) and the Triscyanacrylsäureester of the general formula (Ic) are easily representable.

The alcohols used in the process according to the invention are preferably primary or secondary alcohols, primary alcohols being preferred since these have a higher reactivity in the transesterification reaction exhibit. In general, any mixtures of different alcohols can be used.

The alcohol of the general formula (III) used in the process according to the invention is selected in a preferred embodiment of the present invention from compounds of the general formula (IIIa) R ² COO (CH ₂ CH ₂ O) _m H formula (IIIa) in which R ² CO is a linear or branched acyl radical having 12 to 22 carbon atoms and m is a number from 5 to 30 and preferably 15 to 25. Typical examples are adducts of ethylene oxide with lauric acid, isotridecanoic acid, myristic acid, palmitic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, petroselinic acid, linoleic acid, linolenic acid, elaeostearic acid, arachidic acid, gadoleic acid, behenic acid and erucic acid and their technical mixtures, for example in the pressure cracking of natural fats and oils or in the reduction of aldehydes from Roelen's oxosynthesis. Preferably, addition products of ethylene oxide are used to fatty acids having 16 to 18 carbon atoms.

Further preferred alcohols are preferably selected from methylglycol, methyldiglycol, hexanediol, octanediol, decanediol dodecanediol, glycerol and / or trimethylolpropane and / or from any desired mixtures thereof.

In the process according to the invention, the alcohols of the formula (III) are reacted with at least one 2-cyanoacrylic acid ester of the general formula (II)

R ¹

Formula (II) wherein R ^{1 is} a branched or un branched AI kylrest having 1 to 6 carbon atoms. For the purposes of the present invention, methyl-2-cyanoacrylic acid esters or ethyl-cyanoacrylic acid esters are preferred 2-cyanoacrylic acid esters, since the alcohol methanol or ethanol formed in the transesterification reaction can be easily removed. It is also possible to use mixtures of different 2-cyanoacrylic acid esters in the process according to the invention, with mixtures of methyl-2-cyanoacrylic acid ester or ethyl-2-cyanoic acid acrylic ester being preferred.

The at least one 2-cyanoacrylic acid ester of the general formula (II) is preferably used in excess in the process according to the invention. The molar ratio of 2-cyanoacrylic acid ester to the alcohol of the general formula (III) is preferably at least 2.0: 1, 0 .. In particular, the molar ratio of 2-cyanoacrylic acid ester to the alcohol of the general formula (III) is between 2.0: 1 , 0 and 10.0: 1, 0, preferably between 2.1; : 1, 0 and 2.5: 1, 0, with a ratio of 2.2: 1, 0 being particularly preferred.

The transesterification is carried out according to the process of the invention in the presence of a transesterification catalyst comprising at least one acid having a pks value ≦ 5 and at least one metal catalyst.

The pks value of the at least one acid is determined in aqueous solution at 25.degree. C., it also being easy for the person skilled in the art to derive the pKa values of acids from the corresponding literature. A compilation of different pKs values can be found, for example, in Holleman-Wiberg, Lehrbuch der anorganischen Chemie, 101st edition, pp. 237-238 and the literature cited therein.

Preferred acids are distinguished by a pKs value ≦ 4, in particular by a pKs value ≦ 3 or ≦ 2, and particularly preferably by a pKs value ≦ 1. The technically appropriate lower limit of the pKs value of At least one acid is present at a value of -20, with particular preference being given to acids which have a pKa value> -16.

In a particularly preferred embodiment of the process according to the invention, the acid having a pks value ≦ 5 is a sulfonic acid of the general formula (IV)

Formula (IV) wherein R ^{2 is} a presumptive substituted aryl group or a fluoro-substituted alkyl group.

Preferably, R ² in formula (IV) is a trifluoromethane group or a group of general formula (V),

Formula (V) wherein R ^{3 represents} a methyl, methoxy, ethyl, ethoxy, n-propyl, / propyl or n-butyl group, and especially a methyl group.

As already described above, the at least one acid having a pKa value ≦ 5 has a stabilizing effect on the cyanoacrylic acid ester produced in the process according to the invention, since the acid prevents anionic polymerization of the cyanoacrylic acid ester. If large amounts of the corresponding acid are used in the transesterification reaction, overstabilization of just less reactive cyanoacrylic acid esters can occur since complete removal of the acid from the product obtained is often difficult.

It is therefore particularly advantageous to limit the amount of acid used with a pKs value ≦ 5, which is why, in a particularly preferred embodiment of the process according to the invention, the at least one acid having a pks value ≦ 5 in an amount of 0.0001 to 0, 75% by weight, preferably from 0.001 to 0.5 wt .-% and in particular from 0.01 to 0.2 wt .-%, each based on the total amount of the 2-cyanoacrylic acid ester of the general formula (II), is present. In particular, the proportion of the at least one acid having a pKa value ≦ 5, based on the total amount of the 2-cyanoacrylic acid ester of the general formula (II), should be below 0.25% by weight, in order to overstabilize the product produced in the process according to the invention avoid.

The transesterification catalyst used in the process according to the invention comprises, in addition to the at least one acid having a pKa ≦ 5, at least one metal catalyst which is suitable for catalyzing the transesterification reaction. Preferred metal catalysts are, for example, metal alkoxides and / or metal acetylacetonates.

In general, tin catalysts, chromium catalysts, titanium catalysts, zirconium catalysts and / or lithium catalysts and / or any desired mixtures thereof are also preferred metal catalysts in the context of the process according to the invention.

Suitable metal catalysts from the group of tin catalysts are dialkyltin dicarboxylates, such as dibutyltin dicarboxylates, in particular dibutyltin diacetate, dibutyltin dilaurate, dibutyltin diisoctoate, dibutyltin maleate and mixed dibutyltin dicarboxylates, especially with longer-chain fatty acid residues, dioctyltin dicarboxylates, in particular dioctyltin dilaurate, trialkyltin alkoxides, such as. For example, tributyltin oxide, monoalkyltin compounds such as Monobutylzinndihydroxychlorid and monobutyltin dioxide, tin salts such as tin acetate, tin oxalate, and tin chloride, tin oxides such. B. SnO.

Further suitable metal catalysts from the group of titanium catalysts are monomeric and polymeric titanates and titanium chelates such as tetraisopropyl orthotitanate, tetrapropyl orthotitanate, tetraethyl orthotitanate, tetrabutyl orthotitanate, tetraisobutyl orthotitanate, 2-ethylhexyl titanate, Stearyltitanat, Kresyltitanat, titanium acetylacetonate, triethanolamine titanate, octylene glycol titanate, Isostearyltitanat, Zitronensäurediethylestertitanat and from the group of zirconium catalysts, zirconates and zirconium chelates such as tetrapropyl zirconate, tetraisopropyl zirconate, tetrabutyl zirconate, Triethanolaminzirkonat, Zitronensäurediethylesterzirkonat, zirconium (IV) - acetylacetonate and lithium catalysts such as lithium salts, lithium alkoxides, and aluminum (III), chromium (III), iron (III), cobalt (II), nickel (II) and zinc (II) acetylacetonate.

Preference is given to dibutyltin diacetate, mixed dibutyltin dicarboxylates with longer-chain fatty acid esters, dioctyltin dilaurate,

Monobutyltin dihydroxy chloride, monobutyltin dioxide, tin acetate, tin oxalate, stannous chloride, tetraisopropyl orthotitanate, tetrapropyl orthotitanate, tetraethyl orthotitanate, tetrabutyl orthotitanate, tetrapropyl zirconate, as well as lithium salts and alkoxides and acetylacetonates mentioned above.

Particularly preferred are dibutyltin diacetate, tetraisopropyl orthotitanate and / or tetraethyl orthotitanate.

The at least one metal catalyst is preferably present in amounts of from 0.01 to 10% by weight, preferably from 0.1 to 5% by weight and in particular from 1 to 3% by weight, depending on the reactivity of the individual reactants and the reaction conditions selected .-%, in each case based on the total amount of the 2-cyanoacrylic acid ester of the general formula (II) used.

It is particularly preferred that the transesterification catalyst used in the process according to the invention comprises a trifluoromethanesulfonic acid as acid with a pks value ≦ 5 and at least one titanium catalyst as metal catalyst or consists of these components. It is particularly advantageous if the trifluoromethanesulfonic acid in an amount of 0.001 to 0.2 wt .-% and / or the titanium catalyst in an amount of 0.01 up to 3% by weight, based in each case on the total amount of 2-

Cyanacrylsäureesters of the general formula (II), is present.

In this context, suitable titanium catalysts are described above.

The process according to the invention is preferably carried out in the presence of at least one radical polymerization inhibitor, the required amount of which can easily be determined by a person skilled in the art. Suitable free-radical polymerization inhibitors are, for example, phenol compounds such as hydroquinone, hydroquinone monomethyl ether, butylated hydroxyanisole (BHA), 2,6-di-tert-butyl-4-methylphenol (BHT), t-butylcatequinone, catechol and p-methoxyphenol. Mixtures of said radical polymerization inhibitors can also be used. A particularly preferred radical polymerization inhibitor in the context of the present invention is butylated hydroxyanisole (BHA) and / or hydroquinone monomethyl ether.

Furthermore, the process according to the invention is preferably carried out in the presence of a gaseous acid at 22 ° C., in particular a Lewis acid, the acid being selected, for example, from sulfur dioxide and / or boron trifluoride.

The transesterification can be carried out at atmospheric pressure, but also at reduced or overpressure from 0.001 to 200 bar. The cleaved in the transesterification alcohol is preferably distilled off continuously or after completion of the reaction, wherein the reaction in a suitable solvent, such as toluene, xylene or toluene / xylene mixtures can be carried out. The process according to the invention is preferably carried out with the aid of a distillation column having a high separation efficiency.

The cyanoacrylic acid ester of the general formula (I) obtained by the process according to the invention can be obtained in a highly pure form, in particular by Distillation or crystallization can be isolated, with product purities of greater than 98% can be achieved.

The cyanoacrylate esters prepared by the present process can be used for bonding components, in particular for bonding electrical and / or electronic components, and for producing medical adhesives for treating surgically cut or traumatically torn tissue.

embodiments

Representation of a Monocyanacrylats

In a three-necked flask 91, 3 g (1, 2 mol) of absolute methylene glycol, 1, 3 g of hydroquinone monomethyl ether, 1, 3 g of tetraisopropyl orthotitanate and 0.1 g of trifluoromethanesulfonic presented and slowly covered with SO2. Subsequently, 125 g (1 mol) of ethyl cyanoacrylate are added and the mixture heated to 125 ⁰ C, the ethanol formed is transmitted by a set at 8O ⁰ C dephlegmator. After completion of the ethanol release (control by determination of the refractive index), the reaction mixture is fractionally distilled. At a temperature between 110-152 ⁰ C (0.06 mbar) 146 g Methylglykolcyanacrylat be obtained in a purity of 98%.

Preparation of a Biscyanacrylats

Add 1, 10-decanediol (348 mg, 2 mmol) and hydroquinone (5 mg, 0.045 mmol) in absolute toluene (25 mL). The mixture is treated at 7O ⁰ C with a solution of ethyl cyanoacrylate (1, 001 g, 1 ml, 8 mmol) in absolute toluene (3 ml). Subsequently, tetraisopropyl orthotitanate (13.5 mg, 14 μl, 0.625 mmol) and trifluoromethanesulfonic acid (1, 35 mg, 0.8 μl, 0.009 mmol) are added. The mixture is heated at reflux for 5 h. The toluene / ethanol mixture is then removed azeotropically slowly (about 17 ml). After cooling, the residue is filtered off and the eluate (about 7 ml) is diluted with the same amount of heptane. At a temperature of -2O ⁰ C, the biscyanoacrylate slowly precipitates as a white powder in a yield of 50%.

Claims

claims

1) Process for the preparation of at least one cyanoacrylic acid ester of the general formula (I), comprising the steps:

2) A method according to claim 1, characterized in that the cyanoacrylic acid ester of the general formula (I) is selected from mono- cyanoacrylic acid ester of the general formula (Ia)

Formula (Ia) and / or from Biscyanacrylsäureester of the general formula (Ib)

Formula (Ib) and / or triscyanacrylsäureester of the general formula (Ic),

Formula (Ic) wherein the radical R comprises 1 to 100 carbon atoms.

3) Method according to claim 1 and / or 2, characterized in that the radical R in formula (I), formula (Ia), formula (Ib), formula (Ic) and / or formula (III) a C3 to Cioo chain which is interrupted by at least one oxygen atom.

4) Method according to claim 1 and / or 2, characterized in that the radical R in formula (I), formula (Ia), formula (Ib), formula (Ic) and / or formula 3 to 18 directly connected carbon atoms includes.

5) Method according to at least one of claims 1 to 4, characterized in that the 2-cyanoacrylic acid ester of the general formula (II) is selected from the group consisting of methyl 2-cyanoacrylic acid ester and ethyl 2-cyanoacrylic.

6) Method according to at least one of claims 1 to 5, characterized in that the at least one organic acid having a pks value ≤ 5 is a sulfonic acid of the general formula (IV),

Formula (IV) wherein R ^{2 is} an optionally substituted aryl group or a fluoro-substituted alkyl group.

7) Method according to at least one of claims 1 to 6, characterized in that the at least one acid having a pks value ≤ 5 in an amount of 0.0001 to 0.75 wt .-%, based on the total amount of 2- Cyanacrylsäureesters of the general formula (II), is present.

8) Method according to at least one of claims 1 to 7, characterized in that the at least one metal catalyst is selected from the group of tin catalysts, chromium catalysts,

Titanium catalysts, zirconium catalysts and / or lithium catalysts.

9) Method according to at least one of claims 1 to 7, characterized in that the at least one metal catalyst is selected from the group of metal alkoxides and / or Metallacetylacetonate.

10) Method according to at least one of claims 1 to 9, characterized in that the at least one metal catalyst in an amount of 0.01 to 10 wt .-%, based on the total amount of the 2-cyanoacrylic acid ester of the general formula (II), is present ,

11) Method according to at least one of claims 1 to 8 and 10, characterized in that the transesterification catalyst comprises trifluoromethanesulfonic acid as acid with a pks value ≤ 5 and at least one titanium catalyst as a metal catalyst or consists of these components.

12) Method according to claim 12, characterized in that the trifluoromethanesulfonic acid in an amount of 0.001 to 0.2 wt .-% and / or the titanium catalyst in an amount of 0.01 to 3 wt .-%, each based on the Total amount of the 2-cyanoacrylic acid ester of the general formula (II), is present. 13) Method according to at least one of claims 1 to 12, characterized in that the method is carried out in the presence of at least one radical polymerization inhibitor and / or at least one gaseous acid.

14) Method according to at least one of claims 1 to 13, characterized in that the isolation of the at least one Cyyanacrylsäureesters according to formula (I) by distillation or crystallization.