JP2687020B2 - Polysilane synthesis method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for synthesizing polysilane, and more specifically, synthesis of polysilane useful as a precursor for SiC fiber, SiC molded body, etc., a polymerization initiator for polystyrene, etc. Regarding the method.

[Prior Art] Conventionally, as a method for synthesizing polysilane, when dichloroorganosilane or the like is used as a starting material, a method of reductive dechlorination and condensation reaction with an alkali metal such as sodium, sodium-potassium alloy or lithium is mainly used. Has been done to.

Another method for synthesizing polysilane is disclosed by E. Hengge et al. In which dichlorodiphenylsilane is mainly used as a starting material and the starting material is electrolyzed in an electrolytic solution containing n-Bu ₄ NCIO ₄ which is a supporting electrolyte. (Journal of Organometallic Chemistry vol.21
2 (1981) P.155-161).

[Problems to be Solved by the Invention] However, in the method of dechlorinating and condensing dichloroorganosilane and the like with an alkali metal, the cost of the obtained polysilane is high because the alkali metal used is expensive.

In addition, since the alkali metal itself is extremely dangerous, it is difficult to handle during the synthesis, which is accompanied by danger.

According to the method of electrolyzing dichlorodiphenylsilane,
Polysilane can be synthesized, but only cyclic octaphenyltetrasilane having a degree of polymerization of 4 was obtained in a yield of 0.5 to 3.0%, and a sufficiently low degree of polymerization and a sufficient yield were obtained. There wasn't.

Further, when dichlorodialkylsilane or dichloroalkylarylsilane is used as the starting material, the target polysilane is not generated at all or only traces are generated, and polysiloxanes other than the target product are generated. It was

Therefore, the present inventors previously electrolyzed at least one of dichloroorganodisilane or trichloroorganodisilane in a dry atmosphere in an electrolytic solution composed of a polar solvent containing a supporting electrolyte, and separated the obtained product. , And proposed a method for synthesizing polysilane which is purified and isolated (Japanese Patent Application No. 63-257360 and Japanese Patent Application Laid-Open No. 2-105825).

However, although this method is a synthetic method that can obtain polysilane in good yield and is simple and inexpensive, it is desired to use expensive metal such as platinum in the electrolytic cell with a diaphragm or an electrode material, and inevitably the secondary metal Improvements have been desired in terms of difficulty in treating the product with chlorine ions.

Further, there is an increasing demand for development of a synthetic method for obtaining a polysilane having a higher degree of polymerization in a high yield.

The present invention has been made in view of the current situation, the object of the present invention, without using a diaphragm, also lightweight, using an inexpensive aluminum electrode or magnesium electrode,
It is an object of the present invention to provide a method for facilitating the treatment of by-produced chlorine ions and for efficiently synthesizing polysilane having a high degree of polymerization and a high yield.

[Means for Solving the Problems] A halogenated organosilicon compound is mixed with a supporting electrolyte, or a polar solvent containing a supporting electrolyte is mixed to prepare an electrolytic solution, and an aluminum or magnesium electrode is used for both the anode and the cathode. The said object was achieved by electrolyzing the used thing in the electrolytic cell which does not use a diaphragm, and electrolyzing while reversing a polarity at a fixed time interval.

In the synthesis method of the present invention, dichloroorganomonosilane is used as a starting material.

The dichloroorganomonosilane is not particularly limited and various ones may be mentioned, but dichlorodialkylsilane such as dichlorodimethylsilane, dichloroalkylarylsilane such as dichloromethylphenylsilane, or dichlorodiarylsilane such as dichlorodiphenylsilane. Is preferred.

The starting material is mixed in the electrolytic solution at a concentration of at least 0.01 mol / l, and is appropriately selected and used according to the electrolysis conditions.

If the concentration is less than the lower limit of the above range, the mixed starting materials are polar solvents or impurities in the supporting electrolyte,
In particular, it is not preferable because it is decomposed by moisture and does not function.

In the synthesis method of the present invention, the electrolytic solution for electrolysis of the starting material is used by mixing the supporting electrolyte with the starting material or by mixing with a polar solvent containing the supporting electrolyte.

The supporting electrolyte used in the present invention must have a wide usable potential range and have a property of not reacting with the starting material or polar solvent used,
Specifically, quaternary ammonium salts such as n-Bu ₄ NBF ₄ and n-Bu ₄ NCl are used, and n-Bu ₄ NCl (tetra-n-butylammonium chloride) is particularly preferable.

Further, as the polar solvent used in the present invention,
It must have a property that it does not react with the starting materials, so protic solvents (alcohols, carboxylic acids, etc.) or water-containing solvents are unsuitable, and the dielectric constant is 10
It is preferable that the above polar solvent, specifically, 1,
2-dimethoxyethane (DME), tetrahydrofuran (TH
F), polar ether solvents such as anisole, hexamethylphosphoramide (HMPA), acetonitrile (AN), dimethylformamide (DMF), dimethylsulfoxide (DMSO), propylene carbonate (PC), etc. A solvent composed of at least one of protic solvents and the like is preferably used, and 1,2-dimethoxyethane is particularly preferable.

For example, when tetra-n-butylammonium chloride is used as a supporting electrolyte and 1,2-dimethoxyethane (DME) is used as a polar solvent, the mixing ratio is about 0.02 at a saturated concentration.
mol / l is preferred.

The electrolytic electrode in the present invention, the anode is made of pure aluminum or an aluminum alloy such as A1050, pure magnesium, or a magnesium alloy such as AZ31, and the cathode is the same material as the anode, which is a conductive material that is stable under electrolysis conditions. And

In the synthesis method of the present invention, electrolysis is performed in a dry atmosphere, and polysilane corresponding to the starting material is obtained in a dissolved and / or precipitated state in the electrolytic solution.

The current density at this time is preferably 0.1 to 1000 mA / cm ₂ , and more preferably 1 to 100 mA / cm ² .

Generally, at a current density lower than the lower limit of the above range, the cathode potential is in the residual current region, so that reduction of the starting material does not occur at all, or even if it does occur, the current efficiency decreases drastically. The reaction (reduction of the solvent and / or supporting electrolyte) is also described, leading to a reduction in current efficiency, and reductive decomposition of polysilane, which is the target product, dissolved in the electrolytic solution occurs, resulting in yield and selectivity. However, both of them are not preferable because the degree of polymerization is reduced.

When a diaphragm is not used in the electrolytic cell as in the present invention, when the anode is a Cl ₂ resistant material (Pt, Ru, etc.), secondary chloride ions are oxidized to Cl ₂ at the anode, and the Cl ₂ Since it is re-reduced to chlorine ions at the cathode, not only the chlorine ions produced as a by-product are not treated, but also the current efficiency is lowered and the electrolytic reduction polymerization itself of the raw material dichloroorganosilane is significantly hindered. Oxidation and chlorination by Cl ₂ generated at the anode also pose a serious problem.

On the other hand, when a normal metal that does not have Cl ₂ resistance (Zn, Cu, etc.) is used for the anode, Cl ₂ is not generated, but it becomes chloride, but metal ions are reduced at the cathode, and chloride ions are treated. Not only does it not only reduce the current efficiency, but also hinder the polymerization of the raw materials.

In the present invention, since an aluminum or magnesium electrode is used for the anode, there is no decrease in current efficiency due to metal deposition in the cathode as described above, and chlorine ion
It can be removed as a precipitate of AlCl ₃ or MgCl ₂ .

That is, in the cathode in the electrolysis in the present invention, (However, R ₁ , R ₂ ; methyl group, phenyl group, alkyl group,
An aryl group and the like are shown. ) Occurs, and the anode is aluminum, With magnesium, The following reaction occurs.

On the other hand, since the oxidation potential of the raw material dichloroorganosilane or the polysilane produced is higher than the oxidation potential of these reactions, the raw material and the product are not decomposed.

Therefore, although the aluminum or magnesium electrode of the anode is consumed as a sacrificial electrode, it is effective in terms of the treatment of by-product chlorine.

On the other hand, both positive and negative electrodes are aluminum or magnesium electrodes, and a fixed time (preferably 0.1 to 10 hours)
By reversing the polarity every time, the electrode adhering surface of the AlCl ₃ or MgCl ₂ layer adhering to the electrode serving as the anode is reduced by the electrode serving as the cathode whose polarity has been reversed, and easily detaches.

Therefore, in addition to the treatment of chlorine as a by-product, the activity of the electrode is continued without lowering, and thus the current efficiency of the electrode reaction in the target reaction is practically not lower.

Further, the temperature condition is preferably −20 to 80 ° C. At this time, the energization amount is preferably 1/10 to 10/1 of the theoretical amount (1 F per 11 mol of C in the starting material), and particularly preferably 0.5 / 1 to 1.5 / 1 of the theoretical amount.

Generally, if the amount is less than the lower limit of the above range, the desired polysilane cannot be obtained satisfactorily, and if the current exceeds the upper limit, the polysilane produced is reductively decomposed, which is not preferable.

As described above, by the above-mentioned electrolysis in the present invention, polysilane such as polydimethylsilane and polymethylphenylsilane can be obtained corresponding to the starting material subjected to the electrolysis.

Further, the degree of polymerization of the obtained polysilane can be adjusted by arbitrarily selecting the electrolysis conditions such as the current density and the amount of energization.

Next, the obtained polysilane is separated and refined from the electrolytic solution after the electrolysis is completed.

The method is not particularly limited, and a suitable method is appropriately selected according to the type of polysilane, the treatment amount, and the like. An example of a preferred method is shown below.

First, if a precipitate is precipitated in the electrolytic solution after completion of electrolysis, it is filtered off, and then the supporting electrolyte is removed from the electrolytic solution. As the method, n-hexane, xylene,
A separation method in which an excess amount of toluene, benzene or the like is added to cause precipitation and filtration, or a separation method by chromatography using a silica gel-CH ₂ Cl ₂ column is used, and the former is particularly preferable.

Then, the electrolytic solution from which the supporting electrolyte has been removed is concentrated by vacuum distillation or the like, and then purified by thin layer chromatography (TLC), column chromatography or the like, if necessary, to obtain an isolated polysilane.

The polysilane obtained in this way is composed of SiC fiber, SiC
It is useful as a precursor for molded articles, a polymerization initiator for polystyrene and the like.

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples.

Example 1 As a supporting electrolyte, 50 ml of 1.2-dimethoxyethane added at a concentration of 0.02 mol / l of tetra-n-butylammonium chloride and 1.2 ml (10 mmol) of dichlorodimethylsilane as a starting material were used as pure Al plates (25 mm × 40 mm). ) Is injected into a beaker-type electrolytic cell with no diaphragm having a cathode and anode, and the theoretical density of 70 mA is set at a current density of 60 mA / cm ² and a temperature of 10 ° C.
% (1350 C) was electrolyzed by reversing the polarity of the electrode every hour.

After completion of electrolysis, the electrolytic solution is filtered with a G4 glass filter,
The precipitate deposited during electrolysis was separated.

The precipitate was washed with methanol, acetone, dilute hydrochloric acid, and distilled water to remove the solvent, supporting salt, aluminum chloride, and low molecular weight product, and then dried under reduced pressure.

The yield of the obtained insoluble polydimethylsilane was 40%, and the current efficiency was 57%.

When the infrared absorption spectrum and the ultraviolet absorption spectrum of the insoluble polydimethylsilane were investigated and analyzed, the degree of polymerization of this insoluble polysilane was equivalent to that of commercially available polydimethylsilane obtained by the sodium condensation method, and the degree of polymerization was 20. Was over.

Example 2 As a supporting electrolyte, 24 ml (200 mmol) of dichlorodimethylsilane to which tetra-n-butylammonium chloride was added so as to have a concentration of 0.05 mol / l was used in the same apparatus as in Example 1 and the polarity of the electrode was the same as in Example 2. Reverse every 30 minutes,
A theoretical amount of 10% electricity was applied (40 mF = 3860C). The product was filtered in a dry atmosphere and purified according to Example 1.

As a result, 0.46 g of insoluble polydimethylsilane having the same degree as in Example 1 was obtained.

 The current efficiency was 40%.

Example 3 Electrolysis was performed according to Example 1 except that dichloromethylphenylsilane was used as the starting material. as a result,
The yield of the soluble chain polymer having a degree of polymerization of about 20 is 50.
%, The current efficiency was 71%.

Example 4 As a supporting electrolyte, 50 ml of 1,2-dimethoxyethane added so that the concentration of tetra-n-butylammonium chloride was 0.02 mol / l, and 1.2 ml (10 mmol) of dichlorodimethylsilane as a starting material were used. (2
The electrode was reversed every 30 minutes using 5 mm × 40 mm), and 70% of the theoretical amount (1350 C) was energized for electrolytic reduction.

After completion of electrolysis, the electrolytic solution is filtered with a G4 glass filter,
The precipitate deposited during electrolysis was separated.

The precipitate was washed with methanol and acetone, dilute hydrochloric acid and distilled water to remove the solvent, supporting salt, magnesium chloride and low molecular weight products.

The yield of the obtained insoluble polydimethylsilane having the same degree of polymerization as in Example 1 was 35%, and the current efficiency was 50%.

[Effects] As described above, according to the present invention, a simple electrolytic cell that does not use a diaphragm is used, and polysilane having a high degree of polymerization can be obtained in good yield. In addition, it is industrially very useful because it does not affect the reaction by the by-product chlorine and has no adverse effect on the equipment and the environment.

Claims (3)

(57) [Claims] 1. A dichloroorganomonosilane as a starting material is mixed with a supporting electrolyte to form an electrolytic solution, and an electrolytic electrode made of pure aluminum, an aluminum alloy, pure magnesium, or a magnesium alloy is used for both an anode and a cathode.
A method for synthesizing polysilane, which comprises performing electrolysis while reversing the polarities of both electrodes at a constant time interval in an electrolytic cell that does not use a diaphragm, and separating and purifying the resulting product. 2. A dichloroorganomonosilane as a starting material is mixed with a polar solvent containing a supporting electrolyte to prepare an electrolytic solution, and an electrolytic electrode made of pure aluminum, aluminum alloy, pure magnesium or magnesium alloy is used for both the anode and the cathode. A method for synthesizing polysilane, characterized in that electrolysis is carried out at a constant time interval while reversing the polarities of both electrodes in an electrolytic cell not using a diaphragm, and the obtained product is separated, purified and isolated. 3. The method for synthesizing a polysilane according to claim 1, wherein the dichloroorganomonosilane is dichlorodimethylsilane, dichloromethylphenylsilane or dichlorodiphenylsilane.