Reactions of Silicon with Chloromethanes

Subsequent to the papers by E. G. Rochow [45 a] and R. Muller [45 b] on the direct synthesis of methylchlorosilanes, Patnode and Schiessler in an U.S.-Patent as early 

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Summary The Direct Process discovered by Rochow and Muller around 1940 is the basic reaction used to produce methylchlorosilanes, which are the monomeric intermediates used for production of silicones. An understanding of the elementary reactions, the nature of active sites and the action of promotors does not nearly come close to the performance level of the industrial process and the economic importance. The silylene-mechanism is a useful model to understand the complex product mixture from the reaction of silicon with chloromethane. 

The Direct Process is the reaction of silicon with chloromethane to form methylchlorosilanes (Eq.l). This reaction is unique, in that it is the only solid-catalyzed gas-solid reaction applied in the chemical industry. The Direct Process was first discovered by Rochow [1] and independently Muller [2] around 1940. 

The copper-catalyzed reaction of silicon with chloromethane leads to a complex mixture of various monomeric and dimeric methylchlorosilanes termed crude silane. 

Copper is believed to form a CusSi-phase in the active sites [7]. The CusSi-phase facilitates the reaction of silicon with chloromethane, the silicon is much more reactive than in silicon metal itself... 

Using the same reaction procedure described in the direct reaction of elemental silicon with methylene chloride or chloroform, the reaction of elemental silicon with a gaseous mixture of tetrachloromethane and hydrogen chloride afforded no tetrakis(chlorosilyl)methane instead, tris(chlorosilyl)methanes and bis(chlorosilyl)methanes were obtained, which were the same products derived from the reactions of chloroform and methylene chloride, respectively. This result may be rationalized by the decomposition of tetrachloromethane to chloroform and methylene chloride on the silicon-copper contact mass during the reaction, followed by reaction with elemental silicon to afford the products or by the decomposition reaction of partial silylated chloromethane intermediates.16... 

Chloromethane can be produced by either chlorination of methane or reaction of methanol with hydrogen chloride. In an integrated production of silicones hydrogen chloride obtained by hydrolysis of methylchlorosilanes is recycled to the Direct Process via a chloromethane synthesis. The losses are compensated by make-up chloromethane or hydrogenchloride. Impurities, tike water, methanol, dimethyl ether or oxygen, must be kept at as low a level as possible. 

The reaction of chloroform with silicon/copper is also possible. The tris(trichlorosilyl)methane produced in this way can be transformed by means of chlorination into tris(trichlorosilyl)chloromethane, which in turn can react with silicon/copper to form the carbasilacyclic compound ],l,3.3-tetrachloro-2,2,4.4-tetrakis(trichlorosilyl)- ,3-disilacyclobutane [183] (m.p. 275-278 C Eq. 3.69) ... 

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