Patent Description:
Silane coupling agents are compounds including both a moiety which is reactive with inorganic matter (i.e. silicon-bonded hydrolysable group) and another moiety which is fully reactive with and soluble in organic matter, within their molecule. They are widely used as a resin modifier.

Among these, silane coupling agents having a ketimine structure are under study as modifiers for conjugated diene copolymers (Patent Document <NUM>).

The ketimine structure-bearing organosilicon compounds, however, have poor storage stability and turn to active hydrogen-containing organosilicon compounds with elapse of time, which can adversely affect a composition having the relevant compound admixed.

It is thus desired to improve the storage stability of ketimine structure-bearing organosilicon compounds. <CIT> discloses organosilicon compounds with a ketimine structure.

An object of the invention, which has been made under the above-mentioned circumstances, is to provide a method for preparing a ketimine structure-bearing organosilicon compound which is improved in storage stability.

Making extensive investigations to attain the above object, the inventors have found that a ketimine structure-bearing organosilicon compound having good storage stability can be obtained by reducing the chlorine content. The invention is predicated on this finding.

The preparation method of the invention is successful in forming a ketimine structure-bearing organosilicon compound having good storage stability.

The invention provides a method for preparing a ketimine structure-bearing organosilicon compound, specifically a method for preparing a ketimine structure-bearing organosilicon compound having the following general formula (<NUM>), the method comprising the following steps (I) and (II), characterized in that the chlorine content is reduced to less than <NUM> ppm by weight based on the ketimine structure-bearing organosilicon compound.

In the formulae, R<NUM> is each independently a C<NUM>-C<NUM> alkyl or C<NUM>-C<NUM> aryl group, R<NUM> is each independently a C<NUM>-C<NUM> alkyl or C<NUM>-C<NUM> aryl group, and R<NUM> and R<NUM> are each independently hydrogen or a C<NUM>-C<NUM> alkyl or C<NUM>-C<NUM> aryl group.

The C<NUM>-C<NUM> alkyl group may be straight, branched or cyclic, and examples thereof include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl.

Examples of the C<NUM>-C<NUM> aryl group include phenyl, α-naphthyl, and β-naphthyl.

Of these, R<NUM> and R<NUM> are preferably selected from straight alkyl groups, with methyl and ethyl being more preferred.

R<NUM> and R<NUM> are preferably selected from hydrogen and C<NUM>-C<NUM> alkyl groups, more preferably methyl, ethyl, n-propyl, n-butyl, and isobutyl, even more preferably methyl and isobutyl, with a combination of methyl and isobutyl being most preferred.

The subscript n is an integer of <NUM> to <NUM>, preferably <NUM> or <NUM>, and more preferably <NUM>.

The subscript m is an integer of <NUM> to <NUM>, preferably <NUM> or <NUM>, and more preferably <NUM>.

In the invention, organosilicon compounds having the following formulae (<NUM>) and (<NUM>) are preferred. <CHM>
Herein R<NUM> and n are as defined above, Me is methyl, and Et is ethyl.

Examples of the amino-containing organosilicon compound having formula (<NUM>) used in step (I) include <NUM>-aminopropyltrimethoxysilane, <NUM>-aminopropyldimethoxymethylsilane, and <NUM>-aminopropyltriethoxysilane.

Examples of the carbonyl compound having formula (<NUM>) include dimethyl ketone, methyl ethyl ketone, methyl isobutyl ketone, acetaldehyde, benzaldehyde, and propionaldehyde.

In step (I), the reaction of the amino-containing organosilicon compound with the carbonyl compound is preferably performed under such conditions that the carbonyl compound is in excess in molar ratio.

Although the reaction takes place in a solventless system, a solvent may be used. Suitable solvents include hydrocarbon solvents such as pentane, hexane, cyclohexane, heptane, isooctane, benzene, toluene, and xylene. These solvents may be used alone or in admixture of two or more. Of these, toluene is preferred.

In step (I), the water formed by reaction of the amino-containing organosilicon compound with the carbonyl compound must be removed from the reaction system.

Although the method of water removal is not particularly limited, the water is preferably distilled off by refluxing the carbonyl compound in excess in the system or the solvent by means of a Dean-Stark setup or the like.

The reaction temperature is not particularly limited as long as water can be distilled off. Preferred reaction temperature is <NUM> to <NUM>.

Since the ketimine structure-bearing organosilicon compound having formula (<NUM>) is improved in storage stability by reducing the chlorine content thereof, treatment for reducing the chlorine content is performed as step (II) in the invention.

The treatment used herein for reducing the chlorine content is not particularly limited. Exemplary treatments include purification by distilling, addition of alkali metal alkoxides, and adsorption by inorganic adsorbents. In the invention, these treatments may be performed alone or in combination of two or more. A step including adsorption treatment by an inorganic adsorbent is preferred.

Suitable inorganic adsorbents used for reducing the chlorine content include silica, aluminum hydroxide, hydrotalcite, magnesium silicate, aluminum silicate, aluminum oxide, magnesium oxide, and solid solutions of aluminum oxide and magnesium oxide, which may be used alone or in combination of two or more.

The inorganic adsorbents are commercially available, for example, as Kyoward series (Kyoward <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>) from Kyowa Chemical Industry Co. Of these, Kyoward <NUM> which is a synthetic hydrotalcite (Mg<NUM>Al<NUM>(OH)<NUM>CO<NUM>·mH<NUM>O) is especially preferred from the aspect of treatment efficiency.

The inorganic adsorbent is preferably used in an amount of <NUM> to <NUM> parts by weight, more preferably <NUM> to <NUM> part by weight based on <NUM> parts by weight of the organosilicon compound having formula (<NUM>) from the aspects of high treatment efficiency and easy removal of the inorganic adsorbent after treatment.

Independent of whether the preparation method of the invention starts with either of steps (I) and (II), there is obtained a ketimine structure-bearing organosilicon compound having good storage stability as intended in the invention. Preferably step (I) precedes because the order from step (I) to step (II) is effective for reducing the reaction time of step (I).

When step (II) precedes, at least one of the amino-containing organosilicon compound of formula (<NUM>) and the compound of formula (<NUM>) to be used as reactants in step (I) may be treated for reducing the chlorine content. The treatment of the compound of formula (<NUM>) is preferred.

If the chlorine content after reduction is <NUM> ppmw or more, the organosilicon compound of formula (<NUM>) has poor storage stability. In the case of an organosilicon compound having the formula (<NUM>), for example, organosilicon compounds of the formulae (<NUM>) to (<NUM>) form with a lapse of time.

With this in mind, the preparation method of the invention involves step (II) of reducing the chlorine content of the final ketimine structure-bearing organosilicon compound to less than <NUM> ppmw for thereby improving the storage stability of the compound. Step (II) may be repeated plural times until the chlorine content is reduced below <NUM> ppmw.

For the purpose of further improving the storage stability, the compound having formula (<NUM>) is preferably purified by distillation to a purity of at least <NUM>%.

Examples and Comparative Examples are given below for further illustrating the invention although the invention is not limited thereto.

The chlorine content was measured by the following method.

After <NUM> of each of the samples obtained in Examples and Comparative Examples or <NUM>-aminopropyltrimethoxysilane, <NUM> of toluene and <NUM> of deionized water were mixed, stirring was continued for <NUM> hour. The water layer was taken out. The concentration of water-soluble chloride ions in the water layer was measured by ion chromatography under the following conditions and reported as the chlorine content.

A <NUM>-L separable flask equipped with a stirrer, reflux condenser, dropping funnel, and thermometer was charged with <NUM>,<NUM> (<NUM> moles) of methyl isobutyl ketone. To the flask, <NUM> (<NUM> moles) of <NUM>-aminopropyltrimethoxysilane having a chlorine content of <NUM> ppm was added dropwise at an internal temperature of <NUM>-<NUM> over <NUM> hour. Stirring was continued for <NUM> hours at <NUM>. During dropwise addition and aging, the water formed was removed by refluxing with the methyl isobutyl ketone. On analysis by gas chromatography, the disappearance of the peaks assigned to <NUM>-aminopropyltrimethoxysilane was observed. After aging, there was obtained <NUM>,<NUM> of a pale yellow clear liquid (step (I)).

Then, <NUM> (<NUM> part by weight) of Kyoward <NUM> (Kyowa Chemical Industry Co. , the same hereinafter) was added to the resulting solution, which was stirred in a nitrogen atmosphere at room temperature for <NUM> hours. The Kyoward <NUM> was then removed from the solution by filtration under pressure (step (II)). The solution was purified by distillation under conditions of <NUM> Torr (wherein 1Torr = <NUM> Pa) and <NUM>, yielding <NUM> of a colorless clear liquid. On <NUM>H-NMR analysis, the liquid was identified to be an organosilicon compound having the above formula (<NUM>).

An organosilicon compound having formula (<NUM>) was prepared as in Example <NUM> except for using the same parts by weight of Kyoward <NUM> instead of Kyoward <NUM>.

A <NUM>-L separable flask equipped with a stirrer was charged with <NUM> of <NUM>-aminopropyltrimethoxysilane having a chlorine content of <NUM> ppm and <NUM> (<NUM> part by weight) of Kyoward <NUM>. The contents were stirred in a nitrogen atmosphere at room temperature for <NUM> hours and then filtered under pressure to remove the Kyoward <NUM> from the <NUM>-aminopropyltrimethoxysilane (step (II)). It was confirmed that the chlorine content was less than <NUM> ppm.

A <NUM>-L separable flask equipped with a stirrer, reflux condenser, dropping funnel, and thermometer was charged with <NUM>,<NUM> (<NUM> moles) of methyl isobutyl ketone. To the flask, <NUM> (<NUM> moles) of the above <NUM>-aminopropyltrimethoxysilane was added dropwise at an internal temperature of <NUM>-<NUM> over <NUM> hour. Stirring was continued for <NUM> hours at <NUM>. During dropwise addition and aging, the water formed was removed by refluxing with the methyl isobutyl ketone. On analysis by gas chromatography, the disappearance of the peaks assigned to <NUM>-aminopropyltrimethoxysilane was observed. After aging, there was obtained <NUM>,<NUM> of a pale yellow clear liquid (step (I)).

The solution was purified by distillation under conditions of <NUM> Torr (wherein <NUM> Torr = <NUM> Pa) and <NUM>. yielding <NUM> of a colorless clear liquid. On <NUM>H-NMR analysis, the liquid was identified to be an organosilicon compound having formula (<NUM>).

An organosilicon compound having formula (<NUM>) was prepared as in Example <NUM> except that step (II) of using Kyoward <NUM> was omitted.

A <NUM>-L separable flask equipped with a stirrer, reflux condenser, dropping funnel, and thermometer was charged with <NUM>,<NUM> (<NUM> moles) of methyl isobutyl ketone. To the flask, <NUM> (<NUM> moles) of <NUM>-aminopropyltriethoxysilane having a chlorine content of <NUM> ppm was added dropwise at an internal temperature of <NUM>-<NUM> over <NUM> hour. Stirring was continued for <NUM> hours at <NUM>. During dropwise addition and aging, the water formed was removed by refluxing with the methyl isobutyl ketone. On analysis by gas chromatography, the disappearance of the peaks assigned to <NUM>-aminopropyltriethoxysilane was observed. After aging, there was obtained <NUM>,<NUM> of a pale yellow clear liquid (step (I)).

Then, <NUM> (<NUM> part by weight) of Kyoward <NUM> was added to the resulting solution, which was stirred in a nitrogen atmosphere at room temperature for <NUM> hours. The Kyoward <NUM> was then removed from the solution by filtration under pressure (step (II)).

The solution was purified by distillation under conditions of <NUM> Torr (wherein <NUM> Torr = <NUM> Pa) and <NUM>. yielding <NUM> of a colorless clear liquid. On <NUM>H-NMR analysis, the liquid was identified to be an organosilicon compound having the above formula (<NUM>).

A <NUM>-L separable flask equipped with a stirrer was charged with <NUM> of <NUM>-aminopropyltriethoxysilane having a chlorine content of <NUM> ppm and <NUM> (<NUM> part by weight) of Kyoward <NUM>. The contents were stirred in a nitrogen atmosphere at room temperature for <NUM> hours and then filtered under pressure to remove the Kyoward <NUM> from the <NUM>-aminopropyltriethoxysilane (step (II)).

A <NUM>-L separable flask equipped with a stirrer, reflux condenser, dropping funnel, and thermometer was charged with <NUM>,<NUM> (<NUM> moles) of methyl isobutyl ketone. To the flask, <NUM> (<NUM> moles) of the above <NUM>-aminopropyltriethoxysilane was added dropwise at an internal temperature of <NUM>-<NUM> over <NUM> hour. Stirring was continued for <NUM> hours at <NUM>. During dropwise addition and aging, the water formed was removed by refluxing with the methyl isobutyl ketone. On analysis by gas chromatography, the disappearance of the peaks assigned to <NUM>-aminopropyltriethoxysilane was observed. After aging, there was obtained <NUM>,<NUM> of a pale yellow clear liquid (step (I)).

The solution was purified by distillation under conditions of <NUM> Torr (wherein <NUM> Torr = <NUM> Pa) and <NUM>, yielding <NUM> of a colorless clear liquid. On <NUM>H-NMR analysis, the liquid was identified to be an organosilicon compound having formula (<NUM>).

The organosilicon compounds obtained in Examples and Comparative Examples were measured for a chlorine content by the above-mentioned method. The results are shown in Table <NUM>.

Closed containers were filled with the organosilicon compounds obtained in Examples and Comparative Examples and stored at <NUM>. The purity immediately after purification by distilling and after <NUM> months of storage was measured by gas chromatography under the following conditions. The results are also shown in Table <NUM>.

Claim 1:
A method for preparing an organosilicon compound having a ketimine structure, represented by the following formula (<NUM>):
<CHM>
wherein each R<NUM> independently is a C<NUM>-C<NUM> alkyl or C<NUM>-C<NUM> aryl group, each R<NUM> independently is a C<NUM>-C<NUM> alkyl or C<NUM>-C<NUM> aryl group, R<NUM> and R<NUM> are each independently hydrogen or a C<NUM>-C<NUM> alkyl or C<NUM>-C<NUM> aryl group, n is an integer of <NUM> to <NUM>, and m is an integer of <NUM> to <NUM>, said method comprising the steps of:
(I) reacting an amino-containing organosilicon compound having the following formula (<NUM>) with a carbonyl compound having the following formula (<NUM>):
<CHM>
<CHM>
wherein R<NUM>, R<NUM>, R<NUM>, R<NUM>, n, and m are as defined above, and
(II) reducing a chlorine content,
the chlorine content being reduced to less than <NUM> ppm by weight based on the organosilicon compound having formula (<NUM>).