Fine particle silicon containing surface-bound halogen, a proces

Details Fine particle silicon containing surface-bound halogen, a proces Fine particle silicon containing surface-bound halogen, a proces

1993-10-27

1997-04-08

Lewis, Michael

Organic compounds -- part of the class 532-570 series

Organic compounds

Silicon containing

556472, 423348, C07F 710

Patent

active

056189605

DESCRIPTION:

BRIEF SUMMARY
This invention relates to fine-particle silicon containing surface-bound halogen, more particularly chlorine, to a process for its production by reaction of the silicon surface with silicon tetrahalide and to the use of the fine-particle silicon for the production of organohalosilanes in Rochow's synthesis.
Fine-particle silicon is industrially used in large quantities for the production of organochlorosilanes, more particularly methyl chlorosilanes, by direct reaction with methyl chloride in the presence of copper catalysts and, optionally, other promoters ("Rochow's synthesis", U.S. Pat. No. 2,380,905).
A number of more recent works concentrate on the specific use of trace elements, so-called promoters, in the catalyst system to make the reaction more effective, cf. for example DE-A 3 425 424, EP-A 138 678, EP-A 138 679, DE-A 3 501 085, EP-A 191 502, EP-A 194 214, EP-A 195 728, EP-A 223 447.
Other works are concerned with purity requirements and physical characteristics of silicon suitable for Rochow's synthesis, cf. for example U.S. Pat. No. 3,133,109, U.S. Pat. No. 4,500,724 and EP-A 350 683.
The present invention is based on extensive investigations into the effect which the surface of fine-particle silicon has on Rochow's synthesis. Although silicon reacts relatively sluggishly and hence undergoes hardly any changes in the atmosphere, it passes through stages of high reactivity in the production of fine particles having particle sizes of 20 to 500 .mu.m (depending on the particular reactor system used for Rochow's synthesis). These high-reactivity stages are, for example, freshly broken surfaces where the fine-particle silicon is produced by grinding of coarse-particle silicon or the surface of silicon melt droplets or the already solidified fine-particle silicon at temperatures above about 1,000.degree. C. where the fine-particle silicon is obtained by atomization of a silicon melt.
The reactivity of fine-particle silicon is critically affected by surface reactions with oxygen, atmospheric moisture, carbon dioxide or other constituents of the surrounding atmosphere during the reactive stage.
It has now been found that the reactivity (i.e. reaction rate and selectivity towards the formation of dimethyl dichlorosilane in the reaction with methyl chloride) of fine-particle silicon can be favorably influenced by surface-bound chlorine.
Accordingly, the present invention relates to fine-particle silicon containing surface-bound halogen.
According to the invention, at least every 1,000th and preferably at least every 100th surface atom of the fine-particle silicon should be a halogen atom. At most every second surface atom should be a halogen atom. In a particularly preferred embodiment, the ratio of silicon atoms to halogen atoms is between 3 and 20. The particle diameter of the fine-particle silicon according to the invention is determined by the intended application and is generally between 20 and 500 .mu.m. An average particle diameter of 80 to 200 .mu.m is preferred for use in Rochow's synthesis, the particle size distribution being between 40 and 400 .mu.m.
Although the investigations on which the present invention is based were carried out with a view to the use of the fine-particle silicon in Rochow's synthesis, the fine-particle silicon according to the invention may also be used with advantage in other chemical reactions with silicon providing the surface-bound halogen.
Halogens in the context of the invention are fluorine, chlorine, bromine or iodine. Chlorine is the preferred halogen.
The present invention also relates to a process for producing the fine-particle silicon containing surface-bound halogen.
In its most general form, the process according to the invention for the production of fine-particle silicon containing surface-bound chlorine is characterized in that fine-particle silicon is contacted in reactive form with halogen or gaseous or liquid halogen compounds.
The process is described hereinbelow with reference by way of example to chlorine as the preferred halogen.
Particularly su

REFERENCES:
patent: 4172883 (1979-10-01), Ingle et al.
patent: 4837376 (1989-06-01), Schwirtlich et al.
patent: 5118486 (1992-06-01), Burgie et al.
patent: 5128116 (1992-07-01), Forwald et al.

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