Synthesis Rochow process

Metallurgical grade silicon plays an important role as an alloy constituent in aluminum alloys. Addition of 2-25% improve the casting properties of aluminum in the manufacture of castings for example for engine blocks or cylinder heads. The utilization of metallurgical grade silicon in the manufacture of methylchlorosi lanes and the silicones produced therewith by direct synthesis (Rochow process) is covered in Chapter 4. 

A new approach to understanding the Rochow process synthesis of methylcWorosilanes from CH3 + Cl monolayers on CusSi in vacuum... 

The Rochow Process refers to the synthesis of liquid methylcWorosilanes from metallurgical silicon powder and gaseous methyl cWoride ... 

The synthesis of organosilicones and organosilicone surfactants has been well described elsewhere [36-39] and hence only a brief review is given here. Industrially the manufacture of silicones is performed stepwise via the alkylchlorosilanes, produced through the reaction of elemental silicon with methyl chloride (the Muller—Rochow Process) [40,41]. Inclusion of HC1 and/or H2(g) into the reaction mixture, as in Eq. (1.2), yields CH3HSiCl2, the precursor to the organofunctional silanes, and therefore the silicone surfactants ... 

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). 

Catalytic (Lewis base-induced) disproportionation of tetrachlorodimethyldisilane or dichlorotetramethylsilane is another efficient process to generate oligomeric silanes without formation of solid by-products. - ° The inexpensive starting compounds are obtained as a by-product during the synthesis of chlorosilanes in the Muller-Rochow process. Depending on the molecular structure, that is, the number of chlorine atoms per silicon atom, mixtures of linear or branched polymers form. 

Latest developments concern the quenching of liquid silicon by feeding a jet of molten silicon into water (water granulation) or casting into cooled ingot molds. The material thus produced exhibits an improved reactivity in the synthesis of methylchlorosilanes (Rochow process). 

Silicon tetraalkyl and tetraaryl derivatives (R4Si), as well as alkyl or aryl silicon halides (R SiCl4 , n = 1-3) can be prepared by reaction types 18.38-18.42. Note that variation in stoichiometry provides flexibility in synthesis, although the product specificity may be influenced by steric requirements of the organic substituents. Reaction 18.38 is used industrially (the Rochow process). 

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... 

A direct synthesis of dihalodimethylsilanes 8a-d can be achieved by the reaction of silicon atoms with solid methyl halides 6a-d under concurrent irradiation with UV light (254 nm). Studies in argon matrices at 10 K uncovered all the details of these processes. The basic reactions are now well understood. The crucial step is the radical decay of the primarily formed n-adducts T-5a-d into a methyl radical and the corresponding Si-X radical. Hopefully, these studies can contribute to a better understanding of the decisive steps in the Rochow-Mtiller synthesis. 

Organohalosilanes are industrially produced by direct synthesis from silicon and alkyl- or aryl-halides in the presence of copper or silver catalysts using a process developed by Rochow and Muller in 1941/42. 

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 direct process is also quite versatile and can be fine-tuned to prepare other types of chlorosilanes also. Ethylchlorosilanes could also be similarly prepared analogous to the synthesis of methylchlorosilanes. Preparation of phenylchlorosilanes required a slight modification of the catalyst. Addition of a mixture of HCl and MeCl to silicon affords mixtures of methylchlorosilanes along with MeSiHCU- Simultaneously, along with Rochow, but independently, Richard Mueller in Germany had also come out with a direct process, initially for preparing HSiCls, and later for methylchlorosilanes [7]. 

A process for the synthesis of chloroorganosilanes from elemental silicon and simple alkyl or aryl chlorides in the presence of a catalyst was originally developed in 1945 by Rochow and Patnode [43]. This process was also discovered in Germany during World War II the patent publication appeared several years later [44]. 

The chlorine is obtained back from the hydrolysis process as hydrogen chloride, which is in turn reacted with methanol to give methyl chloride. In a principially closed loop, the methyl chloride is fed back into the Rochow synthesis. 

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