Process for Preparing Epoxy Group-Containing Silanes

The present invention relates to a process for preparing epoxy group-containing silanes. More particularly it relates to a improvement in a process for the preparation of epoxy group-containing alkoxy silanes by hydrosililation of a terminally unsaturated epoxy compound with a hydro-alkoxy silane using a platinum catalyst.

BACKGROUND OF THE INVENTION

Silane coupling agents are compounds having in the molecule an organic functional group and a hydrolizable group reactive with inorganic materials. Since the silane coupling agents are, due to their functional groups. capable of chemically bonding an organic polymer with an inorganic material, such as silica, thereby to remarkably increase the mechanical strength of the organic polymer, a demand of them is increasing as an indispensable material in the development of ultrafashionable composite materials.

Among others, silane coupling agents having an epoxy group in the molecule find wide applications in the fields of electronic materials. Because of very severe requirements for heat resistance and insulating properties in electronic materials, highly pure silane coupling agents having an epoxy group in the molecule are desired in the art.

It is already known in the art that epoxy group-containing alkoxy silanes can be prepared by hydrosililation of a terminally unsaturated epoxy compound with a hydro-alkoxy silane using a platinum catalyst. For example, Japanese Patent Publication No.49-25651 discloses a process wherein 3-glycidoxypropylalkoxysilane is prepared by hydrosililation of allylglycidylether with a hydro-alkoxy silane using as a catalyst a complex of platinum dichloride with an unsaturated ketone such as mesityl oxide. Japanese Patent Publication No.50-24947 discloses a process wherein the reaction of allylglycidylether with a hydro-alkoxy silane is carried out in the presence of a complex of platinum with a beta-diketone such as acetylacetone as a catalyst.

However, there has been a problem in that when a terminally unsaturated epoxy compound is hydrosililated with a hydro alkoxy silane in the presence of a platinum catalyst, in addition to a desired terminally sililated product, an undesired Internally sililated isomer is inevitably produced. For example, when allylglycidylether is hydrosililated with trimethoxysilane using a platinum catalyst, the reaction proceeds as illustrated below, whereby 2-glycidoxyisopropyltrimethoxysilane (undesired isomer, .beta.-isomer) is produced in addition to 3-glycidoxypropyltrimethoxysilane (desired product, .gamma.-isomer). ##STR1##

It is generally very difficult to separate the desired product from the undesired isomer by distillation, since the difference in the boiling point between them is very small. Accordingly, it is desired to provide a process for the preparation of epoxy group-containing alkoxy silanes by which formation of the internally sililated isomer can be suppressed and the desired terminally sililated product can be produced at the highest possible selectivity.

The invention is to solve the above-discussed problem associated with the prior art, and an object of the invention is to provide an improvement in a process for the preparation of epoxy group-containing alkoxy silanes by hydrosililation of a terminally unsaturated epoxy compound with a hydro-alkoxy silane using a platinum catalyst by which formation of the internally sililated isomer can be suppressed and the desired terminally sililated product can be produced at the highest possible selectivity.

It has now been found that if the hydrosililation of a terminally unsaturated epoxy compound with a hydro-alkoxy silane using a platinum catalyst is carried out in the presence of an alcohol, formation of the internally sililated isomer can be suppressed and the desired terminally sililated product can be produced at the highest possible selectivity. Thus, the invention provides an improvement in a process for the preparation of epoxy group-containing alkoxy silanes by hydrosililation of a terminally unsaturated epoxy compound with a hydro-alkoxy silane using a platinum catalyst, which improvement comprises carrying out the hydrosililation in the presence of an alcohol.

The invention will now be described in detail.

Products of the process according to the invention are epoxy group-containing alkoxy silanes. They are useful as silane coupling agents. Among them, particularly useful compounds as epoxy group-containing silane coupling agents are those of the general formula (I)

ti RCH.sub.2 CH.sub.2 SI(OR.sup.1).sub.n R.sup.2.sub.3-n (I)

wherein R is an epoxy-containing organic group free from active hydrogen. R.sup.1 and R.sup.2 each represents alkyl having from 1 to 3 carbon atoms and n is an integer from 1 to 3. Particularly preferred products are compounds of the general formula(I) wherein R is glycidoxymethyl, 3,4-epoxycyclohexyl, oxiranyl, oxiranylphenyl, 3,4-epoxybutyl. oxiranylmethyl, oxiranylethyl and 2-methylglyeidoxymethyl; R.sup.1 and R.sup.2 are selected from the group consisting of methyl and ethyl; and n is 2 or 3.

Any terminally unsaturated epoxy compounds that have heretofore been used for the preparation of epoxy group containing silanes by hydrosililation thereof can be used herein. Those suitable for the preparation of epoxy group-containing alkoxy silanes of the general formula (I) may be represented by the general formula (II)

wherein R is as defined above. Examples of preferred terminally unsaturated epoxy compounds of the general formula (II) include, for example, allylglycidylether, 4 vinylcyclohexene-1-oxide, 3-butadieneoxide, divinylbenzeneoxide, 1,5-hexadieneoxide, 1,4-pentadieneoxide, 3-methyl-1,3-butadiene-1-oxide and allyl(alphamethylglycidyl)ether.

Any hydro-alkoxy silanes having from 1 to 3 alkoxy groups that have heretofore been used for the hydrosililation of terminally unsaturated epoxy compounds can be used herein. Hydro-alkoxy silanes suitable for the preparation of epoxy group-containing alkoxy silanes of the general formula (I) may be represented by the general formula (III)

wherein R.sup.1, R.sup.2 and n are as defined above. Of these. preferred hydro-alkoxy silanes which can be used herein are those of the general formula(III), wherein R.sup.1 and R.sup.2 are selected from the group consisting of methyl and ethyl; and n is 2 or 3. Examples of preferred hydro-alkoxy silanes include. For example, trimethoxysilane. triethoxysilane, methyldimethoxysilane and ethyldiethoxysilane.

Any platinum catalysts that have heretofore been used for the hydrosililation of terminally unsaturated epoxy compounds with hydrosilanes can be used. Preferred platinum catalysts include, for example, hexachloroplatinic acid; complexes of a platinum chloride with an unsaturated ketone such as dichloro(mesityl oxide)platinum(II) and dichloro(methylvinylketone)platinum(II), complexes of a platinum chloride with a beta diketone such as dichloroplatinum(II)acetylacetonate, complexes of a platinum chloride with an olefin such as dichloro(1,5-cyclooctadiene)platinum(II), complexes of a platinum chloride with an amine such as dichlorodiammineplatinum(II) and complexes of a platinum chloride with a phosphine such as dichlorobis(triphenylphosphine)platinum(II).

The amount of the platinum catalyst used may range from 10.sup.-7 to 10.sup.-3 mole, preferably from 10.sup.-6 to 10.sup.-4 mole, per mole of the hydro-alkoxy silane.

Alcohols which can be used herein include, for example, methanol, ethanol, n-propanol, and isopropanol.

For the purpose of the invention it is desirable to use the alcohol in an amount of more than 0.1 mole, preferably from about 0.2 to about 10 moles, more preferably from about 0.5 to about 3.0 moles, per mole of the hydro-alkoxy silanes. With substantially less than about 0.2 mole of the alcohol per mole of the hydro alkoxy silane, the formation of the internally sililated isomer is not satisfactorily suppressed. On the other hand, it is advantageous to avoid use of an excessive amount of the alcohol, or otherwise a side reaction such as noted below may tend to occur.

The alcohol is preferably admixed with the hydroalkoxy silane reactant and the admixture is added to a mixture of the unsaturated epoxy compound reactant and the catalyst under stirring, followed by continuation of the reaction.

Other conditions which can be used herein are the same as have heretofore been used in the preparation of epoxy group containing silanes by hydrosililation of a terminally unsaturated epoxy compound with a hydro-alkoxy silane.

In carrying out the present reaction, the unsaturated epoxy compound may be used in a range from about 0.5to about 2.0 moles, preferably from about 0.7 to 1.3 moles, per mole of the hydro-alkoxy silane. The reaction temperature is normally from ambient temperature to about 100.degree. C., preferably from about 40 to 70.degree. C. The reaction time may normally be from about 0.5 to about 3.0 hours. While the reaction is normally carried out under atmospheric pressure, it may be carried out under elevated pressures.

By the process according to the invention in which a terminally unsaturated epoxy compound is hydrosililated with a hydro-alkoxy silane using a platinum catalyst in the presence of an alcohol, formation of the undesired internally sililated product can be effectively suppressed, and the desired terminally sililated product can be prepared at a selectivity as high as approximately 100%.

While the invention is illustrated by the following examples, the invention is not limited thereto.

A four neck flask equipped with a dropping funnel, a reflux condenser, a stirrer and a thermometer, was charged with 13.7 grams (0 12 mole) of allyglycidylether and 12.mu.l of a 0.1M solution of hexachloroplatinic acid (H.sub.2 PtCl.sub.6.6H .sub.2 O) in isopropyl alcohol (1.2.times.10.sup.-6 mole as platinum). and heated to a temperature of 50.degree. C. under stirring. To the mixture maintained at that temperature under stirring, a mixture of 12.2 grams (0.1mole) of trimethoxysilane and 6.4 grams (0.2 mole) of methanol was dropwise added over a period of 2 hours. The reaction mixture was further maintained at 50.degree. C. under stirring for 1 hour.

At the end of the period, it was revealed by gas chromatography analysis that the desired 3-glycidoxypropyltrimethoxysilane had been obtained at a yield of 90.0% (on a trimethoxysilane basis) and that a yield ratio by weight of the desired product to the internally sililated product was 99.5:0.5

By simple distillation of the reaction mixture, 3-glycidoxypropyltrimethoxysilane of a purity of 99.7% was obtained.

Example 1 was repeated except that methanol was used in an amount of 1.6 grams (0.05 mole) instead of the 6.4 grams (0.2 mole)

Gas chromatography analysis revealed that the desired 3-glycidoxypropyltrimethoxysilane had been obtained at a yield of 91.1% (on a trimethoxysilane basis) and that a yield ratio by weight of the desired product to the internally sililated product was 99.4:0.6.

By simple distillation of the reaction mixture. 3-glycidoxypropyltrimethoxysilane of a purity of 99.6% was obtained.

A four-neck flask equipped with a dropping funnel, a reflux condenser, a stirrer and a thermometer, was charged with 13.7 grams (0.12 mole) of allylglycidylether and 12.mu.l of a 0.1M solution of hexachloroplatinic acid (H.sub.2 PtCl.sub.6, 6H.sub.2 O) in isopropyl alcohol (1.2.times.10.sup.-6 mole as platinum). and heated to a temperature of 80.degree. C. under stirring. To the mixture maintained at that temperature under stirring, a mixture of 16.4 grams (0.1 mole) of triethoxysilane and 4.6 grams (0.1 mole) of ethanol was dropwise added over a period of 2 hours. The reaction mixture was further maintained at 80.degree. C. under stirring for 1 hour.

At the end of the period, it was revealed by gas chromatography analysis that the desired 3-glycidoxypropyltriethoxysilane had been obtained at a yield of 88.2% (on a triethoxysilane basis) and that a yield ratio by weight of the desired product to the internally sililated product was 9.6:0.4.

By simple distillation of the reaction mixture, 3-glycidoxypropyltriethoxysilane of a purity of 99.8% was obtained.

A four-neck flask equipped with a dropping funnel, a reflux condenser, a stirrer and a thermometer, was charged with 13.6 grams (0.11 mole) of 4-vinylcyclohexene-1-oxide and 12.mu.l of a 0.1M solution of hexachloroplatinic acid (H.sub.2 PtCl.sub.6.6H.sub.2 O) in isopropyl alcohol (1.2.times.10.sup.-6 mole as platinum). and heated to a temperature of 50.degree. C. under stirring. To the mixture maintained at that temperature under stirring, a mixture of 12.2 grams (0.1 mole) of trimethoxysilane and 6.4 grams (0.2 mole) of methanol was dropwise added over a period of 2 hours. The reaction mixture was further maintained at 50.degree. C. under stirring for 1 hour.

At the end of the period, it was revealed by gas chromatography analysis that the desired 4-(2-trimethoxysilylethyl)cyclohexene-1-oxide had been obtained at a yield of 99.2% (on a trimethoxysilane basis) and that a yield ratio by weight of the desired product to the internally sililated product was 99.7:0.3

By simple distillation of the reaction mixture, 4-(2-trimethoxysilylethyl)cyclohexene-1-oxide of a purity of 99.9% was obtained.

A four-neck flask equipped with a dropping funnel. a reflux condenser, a stirrer and a thermometer, was charged with 7.7 grams (0.11 mole) of butadiene monooxide and 12.mu.l of a 0.1M solution of hexachloroplatinic acid (H.sub.2 PtCl.sub.6.6H.sub.2 O) in isopropyl alcohol (1.2.times.10.sup.-6 mole as platinum), and heated to a temperature of 50.degree. C. under stirring. To the mixture maintained at that temperature under stirring, a mixture of 12.2 grams (0.1 mole) of trimethoxysilane and 6.4 grams (0.2 mole) of methanol was dropwise added over a period of 2 hours. The reaction mixture was further maintained at 50.degree. C. under stirring for 1 hour.

At the end of the period, it was revealed by gas chromatography analysis that the desired 2-trimethoxysilylethyl oxide had been obtained at a yield of 99.5% (on a trimethoxysilane basis) and that a yield ratio by weight of the desired product to the internally sililated product was 99.6:0.4.

By simple distillation of the reaction mixture, 2-trimethoxysilylethylethylene oxide of a purity of 99.8% was obtained.

A four-neck flask equipped with a dropping funnel, a reflux condenser, a stirrer and a thermometer, was charged with 13.7 grams (0.12 mole) of allylglycidylether and 12.mu.l of a 0.1M solution of a complex of mesityl oxide-platinum dichloride in acetone (1.2.times.10.sup.-6 mole as platinum), and heated to a temperature of 80.degree. C. under stirring. To the mixture maintained at that temperature under stirring, a mixture of 12.2 grams (0.1 mole) of trimethoxysilane and 6.4 grams (0.2 mole) of methanol was dropwise added over a period of 2 hours. The reaction mixture was further maintained at 80.degree. C. under stirring for 1 hour.

At the end of the period, it was revealed by gas chromatography analysis that the desired 3-glycidoxypropyltrimethoxy silane had been obtained at a yield of 90.1%. (on a trimethoxysilane basis) and that a yield ratio by weight of the desired product to the internally sililated product was 99.7:0.3.

By simple distillation of the reaction mixture. 3-glycidoxypropyltrimethoxysilane of a purity of 99.9% was obtained.

A four-neck flask equipped with a dropping funnel, a condenser for collecting a distillate, a stirrer and a thermomether, was charged with 50 grams of finely divided metallic silicon, 1.25 grams of cuprous chloride and 10 ml of dibenzyltoluene, and heated to a temperature of 220.degree. C. under stirring. To the mixture maintained at that temperature under stirring, 300 grams of methanol was dropwise added over a period of 6 hours. The distillate so obtained gas 255 grams in weight, and contained by weight 14.6% of methanol, 64.8% of trimethoxysilane and 30.5% of tetramethoxysilane.

Example 1 was repeated except that the mixture of methanol and trimethoxysilane used in Example 1 was replaced with 22.3 grams of the above distillate (containing 0.1mole of trimethoxysilane and 0.1 mole of methanol).

Gas chromatography analysis revealed that the desired 3-glycidoxypropyltrimethoxysilane had been obtained at a yield of 89.9% (on a trimethoxysilane basis) and that a yield ratio by weight of the desired product to the internally sililated product was 99.3:0.7.

By simple distillation of the reaction mixture, 3-glycidoxypropyltrimethoxysilane of a purity of 99.5% was obtained.

Example 1 was repeated except that the methanol was not used.

Gas chromatography analysis revealed that the desired 3-glycidoxypropyltrimethoxysilane had been obtained at a yield of 90.2% (on a trimethoxysilane basis) and that a yield ratio by weight of the desired product to the internally sililated product was 97.9:2.1.

By simple distillation of the reaction mixture, 3-glycidoxypropyltrimethoxysilane of a purity of 98.0% was obtained.

Example 1 was repeated except that the methanol used in Example 1 was replaced with 6.1 grams of benzene(50% by weight on the basis of the trimethoxysilane used).

Gas chromatography analysis revealed that the desired 3-glycidoxypropyltrimethoxysilane had been obtained at a yield of 90.8% (on a trimethoxysilanebasis) and that a yield ratio by weight of the desired product to the internally sililated product was 98.0:2.0.

By simple distillation of the reaction mixture, 3-glycidoxypropyltrimethoxysilane of a purity of 98.1% was obtained.

Example 3 Was repeated except that the ethanol was not used.

Gas chromatography analysis revealed that the desired 3-glycidoxypropyltriethoxysilane had been obtained at a yield of 89.1% (on a triethoxysilanebasis) and that a yield ratio by weight of the desired product to the internally sililated product was 98.2:1.8.

By simple distillation of the reaction mixture, 3-glycidoxypropyltrimethoxysilane of a purity of 98.3% was obtained.