Process for preparing silicon hydrides

Details Process for preparing silicon hydrides Process for preparing silicon hydrides

1983-03-08

1985-09-17

Cooper, Jack

Chemistry of inorganic compounds

Silicon or compound thereof

Binary compound

556474, C01B 3304

Patent

active

045420050

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a process for the preparation of silicon hydrides, particularly monosilane, disilane and derivatives thereof with high yield and reduced amount of by-products.


BACKGROUND OF THE ART

It has been conventionally known to prepare monosilane, disilane or derivatives thereof by using an alkyl aluminum hydride. For example, in Japanese patent application Publication No. 36-517, British Pat. No. 823,483, German Pat. Nos. 1,055,511 and 1,117,090, there is disclosed a process for preparing a silicon hydride by the reduction of a silicon halide with sodium hydride in the presence of an alkyl aluminum hydride. In this known process, it is sodium hydride that serves as reducing agent for the silicon halide, and the alkyl aluminum hydride is added in such a small amount as 0.1-30% so that it serves only as an activating agent.
Another process for the reduction of a silicon halide is disclosed in French Pat. No. 1,499,032, in which the reducing agent consists of an alkyl aluminum hydride only.
These processes, however, are not yet satisfactory in that the yield of end products is lower and high quality is not obtained.
From the industrial standpoint, it is more advantageous to utilize an alkyl aluminum hydride in the form of a mixture of said alkyl aluminum hydride and a trialkyl aluminum rather than as pure alkyl aluminum hydride, since such a mixture is commercially available at a low price. However, when the reduction of a silicon halide is conducted using such a mixture of alkyl aluminum hydride and trialkyl aluminum, there is an extremely low yield of a silicon hydride, together with a large amount of by-produced silicon halide hydride, for example, monochlorosilane SiH.sub.3 Cl, which is probably produced because of insufficient reduction of the silicon halide. In addition, there is produced a large amount of ethane as by-product.
An object of the present invention is to provide a process for the preparation of silicon hydrides with improved yield and reduced amount of by-products without lowering the activity of alkyl aluminum hydride by using a mixture of an alkyl aluminum hydride and a trialkyl aluminum which is easily available as the reducing agent for silicon halides.


DISCLOSURE OF THE INVENTION

In accordance with the present invention there is provided a process for the preparation of silicon hydrides by reducing a silicon compound with a mixture of an alkyl aluminum hydride and a trialkyl aluminum, which comprises adding preliminarily into said mixture an aluminum halide compound in an amount sufficient for converting at least 90 mol percent of the trialkyl aluminum to a dialkyl aluminum monohalide prior to the reduction reaction.
Surprisingly, it has been found that when adding a specified amount of the aluminum halide compound to the mixture of alkyl aluminum hydride and trialkyl aluminum prior to the reduction of the silicon compound, silicon hydrides of high yield are obtained without reducing the activity of alkyl aluminum hydride and by-producing of silicon halide hydride and ethane is extremely reduced.


BEST MODE FOR CARRYING OUT THE INVENTION

The starting silicon compound which may be used in the present invention is a compound of the formula Si.sub.n X.sub.2n+2 in which n is an integer equal to or larger than 1 and the X's may be the same or different and represent halogen atoms, hydrogen atoms, alkoxy groups, alkyl groups, aryl groups or vinyl groups, the case of all X's being hydrogen atoms being excluded. The larger n becomes, the more difficult it is to handle such silicon compound and therefore to work the present invention.
Typical groups or atoms as X include methyl group, ethyl group, propyl group, n-butyl group, iso-butyl group, pentyl group, vinyl group, phenyl group, p-methylphenyl group, methoxy group, ethoxy group and halogen atoms such as chlorine and bromine. As the preferred compound falling within the above-mentioned general formula for use in the present invention there are included such compounds as silicon tetrachloride,

REFERENCES:
patent: 3099672 (1963-07-01), Cooper et al.
patent: 3496206 (1970-02-01), Berger

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