Rochow process mechanism

The proposed silylene mechanism gives an explanation for the high selectivity of (CH3)2SiCl2 formation in the "Direct Synthesis" of methylchlorosilanes (Miiller-Rochow process). Via an oxidative addition of CH3CI to methylsilylenes on the surface of a Cu/Si catalyst, (CH3)3SiCl2 is produced in a kinetically controlled process (Scheme 2). 

Of special interest are molecules possessing n electrons only in combination with o bonds. The reactions of silicon atoms with target molecules of this type are relevant for the understanding of the Rochow-MUller (R.-M.) synthesis [2]. In a recent essay Seyferth describes the enormous importance of this direct synthesis of dichlorodimethylsilane by reaction of a silicon/copper alloy with methyl chloride [3]. At the same time he points out that even today, more than 60 years after its discovery in 1940, the mechanism of this process is still not fully understood. It was our hope... 

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 reaction mechanism is not clarified yet. Older proposals by Hurd and Rochow, Bazant, Klebansky, Fikhtengolts and Voorhoeve, or Golubtsov are today replaced by the silylene mechanism [6], which provides a good explanation for the products obtained in the Direct Process. 

The reaction mechanism of the copper catalyzed reactions is probably a radical chain process like that proposed by Rochow for the direct synthesis of organo-silicon compounds ... 

Silicon alloyed with a copper catalyst and promoter substances reacts with methyl chloride (at temperatures around 300 °C) to give a mixture of methylchlorosilanes in the industrial direct synthesis. Dimethyldichlorosilane represents the most important target in this process. Since Rochow [1] and Mtiller [2] discovered this direct synthesis route for the silicon-promoter-catalyst system, many investigations were done to increase the activity as well as the selectivity and to clarify the mechanism. Zinc, tin, and phosphorus, beside other substances, were found to give effects [3-6]. The goal of this research work is to find out whether there are relationships between the electronic effect of phosphorus, tin, boron, or indium doping of silicon and its reactivity as well as selectivity in direct synthesis. Characterization of the electronic state of the variously doped silicon relies on photo-EMF measurements. 

The great industrial process for the production of alkylchlorosilanes is the heterogeneous Rochow-Muller process whose mechanism remains somewhat obscure. Essentially dialkyldichlorosilanes are produced in the mixture RnSiCl4 n(n = 1-4) ... 

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