Industrial processes 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). 

This contribution to the broad field of organosilicon chemistry including molecules and materials, marks a very unusual anniversary, the existence of which effectively contradicts a historical statement by the famous organosilicon pioneer F. S. Kipping, who believed 80 years ago that organosilicon chemistry would never gain industrial and commercial importance. Fifty years after the invention of the Miiller-Rochow process, the silicon industry achieved an annual worldwide turnover of US 4.700.000.000. This proves impressively that the basic process - independently developed by R. Muller and E. G. Rochow in 1941/2 - can be considered to be the most important innovation for organosilicon research work in industry and university. 

More than 60 years after its simultaneous discovery by Rochow and Muller, the direct reaction of copper-activated silicon with alkyl chlorides is arguably still the most important industrial process for the preparation of basic organosilanes. An inspiring historic account highlighting the significance of this seminal work has been given by Seyferth.12 A comprehensive review on the subject has been written by Jung and Yoo.13 The most recent work associated with the direct process is concerned with the role of metallic promoters, such as Zn and Cd, as well as mechanistic aspects.14... 

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 ... 

Industrially, however, organosilicon and organotin chlorides axe usually obtained by the direct Rochow process (Section 3.5.2) ... 

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 starting materials for the manufacture of diorganopolysiloxanes are the diorganodi-chlorosilanes. Dimethyldichlorosilane, which is the most important one, is made industrially by the Rochow process from methyl chloride and silicon metal in the presence of a copper catalyst at 250-300 °C. 

The direct reaction process is also called the Rochow process, and methyl-chlorosilane and phenylchlorosilane have been industrially produced by this process [11]. Copper is used as a catalyst. However, the reaction with the single catalyst of copper is not so fast, and the addition of a metal such as Sb, Cd, Al, Zn and Sn or a mixture accelerates the reaction. For example, with a catalyst containing 94.49 wt % Si, 5.00 wt % Cu, 0.50% Zn and 0.001 % Sn, the selectivity of Me2SiCl2 is 80 mole %. In the reaction with methylchloride, the reaction temperature is preferably 300°C and the conversion of silicon is 90-98% [9]. 

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) ... 

Organosilanes, especially dimethyldichlorosilane (M2), are important chemicals used in the silicone industries. The direct reaction of silicon with an organic halide to produce the corresponding organosilanes as a gas-solid-solid catalytic reaction was first disclosed by Rochow [1]. In the reaction, a copper-containing precursor first reacts with silicon particles to form the catalytically active component, which is a copper-silicon alloy, the exact state of which is still under discussion. As the reaction proceeds. Si in the alloy is consumed, which is followed by the release of copper. This copper diffuses into the Si lattice to form new reaction centers until deactivation occurs. The main reaction of the direct process is ... 

The example of the first category is the formation of alkyl- and arylchlorosilanes in the so-called direct process (DP). The process was discovered over 60 years ago by Rochow in the United States, and, independently, by Muller in Germany, and it is still the most important reaction in organosilicon chemistry. In fact, it is at the very basis of the silicone industry, being the primary source of organochlorosilane precursors (mostly methylchlorosilanes, comprising over 90% of the total) in the production of silicone oligomers and polymers. 

A common feature of all these compounds is their tetrahedral structure at the silicon atom which is bound to four oxygen neighbors. A tremendous breakthrough in the history of silicon-based polymers has been achieved by the invention of the Direct Process by Muller and Rochow resulting in the industrial production of methyl chlorosilanes with hydrolytically stable Si-C bonds besides very reactive Si-Cl bonds which serve as building units for a wide variety of polydimethyl siloxanes including silicon fluids, resins, and elastomers. 

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. 

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 silicones industry got its start in the late 1930 s (1,2) and became viable after Rochow s 1940 discovery of the direct process which reacts elemental silicon with MeCl to produce methylchlorosilanes (3,4). This chapter attempts to summarize some of the steps which take place in the process of converting sand into silicones. The vignette chosen for this summary is the production of a platinum-cure, so-called addition cured silicone. This brief review will make use of the M, D shorthand wherein an M group is MojSiO- and a D group is -MojSiO-. Substituents on silicon other than Me are represented with a superscript so that M stands for (H2C=CH)Me2SiO- and DH stands for -(Me)(H)SiO- (5). Figure 1 summarizes the entire process covered in this review. 

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