Silicones direct process

V. SILICON DIRECT PROCESS REACTIONS WITH REAGENTS OTHER... 

A key report investigated a variety of substrates in their reaction with silicon in an effort to find evidence for silylene intermediates during the silicon direct process reaction. When silicon, copper and methanol were reacted as described above but in the presence of alkenes, alkyldimethoxysilanes and (MeO SiH were formed95-97. The use of allyl propyl ether instead of alkenes gave allyldimethoxysilane, with 38% selectivity. These results and the reaction of silicon with MeCl in the presence of butadiene to give silacyclopent-3-enes indicates intermediate formation of silylenes. 

Two groups have made minor breakthroughs in the non-halogen direct process. In 1978 Malek, Speier and coworkers reported the reaction between dimethyl ether and silicon . Prior to their work there were some attempts to employ dimethyl ether as a substrate. Rochow and Zuckeiman disputed one claim . Later Newton and Rochow discussed the difficulty of using dimethyl ether in a direct process . Malek s and Speier s work showed that when silicon was reacted with MeOMe in the presence of metal catalysts and MeBr, 64.4% Me2Si(OMe)2 could be obtained. The silicon (150 g, 98%, 0.44% Fe, 0.26% Al, 0.058% Ca, 0.005% Sn, 0.04% Mn, 0.032% Ti, 0.051% V, 0.002% B, 0.014% Cr, 0.05% Zn and 0.002% Pb) was ground with steel balls to 2.7 microns for 16 h with Cu powder (12 g). One-hundred parts of silicon, 3.3 parts of copper, 0.3 part of iron, 0.43 part of aluminum and 0.13 part of calcium were combined in an autoclave and MeOMe and MeBr were added (mole ratio of Si MeOMe MeBr 100 350 1) and then heated for 20 h at 258 °C. While this process was not entirely halogen-free, it was the most successful ether silicon direct process to date. 

Silicon—Carbon Bond-Forming Reactions. After the Rochow-MbUer direct process, the hydro silylation reaction (139),... 

Synthesis of Silicone Monomers and Intermediates. Another important reaction for the formation of Si—C bonds, in addition to the direct process and the Grignard reaction, is hydrosdylation (eq. 3), which is used for the formation of monomers for producing a wide range of organomodified sihcones and for cross-linking sihcone polymers (8,52—58). Formation of ether and ester bonds at sihcon is important for the manufacture of curable sihcone materials. Alcoholysis of the Si—Cl bond (eq. 4) is a method for forming silyl ethers. HCl removal is typically accomphshed by the addition of tertiary amines or by using NaOR in place of R OH to form NaCl. 

Silicones, an important item of commerce, are widely available commercially (9,494). The principal manufacturers of silicone operate direct-process reactors to produce dimethyl dichi orosilane and, ultimately, polydimethyl siloxane. Typical plants produce more than 450 t per year. The siUcone industry is a global enterprise in the 1990s, with principal producers in the United States (Dow Coming, GE, and OSi), Europe (Wacker Chemie, Hbls, Rhc ne-Poulenc, and Bayer), and Southeast Asia (Shin-Etsu, Toshiba SiUcones, and Dow Coming, Japan). Table 15 Hsts the approximate sales of the principal producers for 1991. 

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 ... 

Reaction (2) was also studied using the different catalysts. Before exposure to CH3CI, the contact masses were subject to XRD analysis. In the XRD patterns of the catalysts with higher activities for the Rochow direct process, the XRD peaks of the Cu-containing species were weaker and broader when normalized to the silicon peaks (silicon was used in excess). This suggests that some undetectable species were formed and the catalytic species were well-dispersed. This agrees well with the view of Lieske and co-workers [5]. 

The reactivity and product selectivity increase as dispersing agents were introduced. Simultaneously, a higher silicon conversion was also obtained. A higher silicon conversion will decrease the burden of waste disposal. Therefore, this study provides a convenient and economical way for the preparation of highly effective CuCl catalyst that can be used in practical production using the direct process. 

Highly active CuCl catalysts for the direct process of methylchlorosilane synthesis were prepared by reducing Cu with a sodium sulfite solution in the presence of dispersing agents. Several well-known dispersants, e.g. SDBS, were used in this study. When SDBS was used, a catalyst in the form of small flakes was obtained that gave the best performance in reactivity, product selectivity and silicon conversion. This provides a convenient way to prepare the CuCl catalyst for use in industrial production. 

Direct particle interception, in depth filtration theory, 11 339 Direct potentiometry, 9 582—585 Direct printing, 9 218 Direct process, silicone synthesis via,... 

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 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. 

Lewis, L. N. Recent Advances in the Direct Process. In The Chemistry of Organic Silicon Compounds Rappoport, Z., Apeloig, Y., Eds. Wiley Sussex, 1998 Vol. 2, Part 2, Chapter 26, pp 1581-1597. 

It is likely that more silicon-carbon bonds are produced by the hydrosilylation of olefins than by any other method except the direct process. This deceptively simple addition of an Si-H bond to a C-C multiple bond can be promoted by a variety of means, but transition metal catalysis is by far the most significant. Two relatively old catalysts, H2PtCl6 ( Speier s catalyst ) and Pt2(Me2ViSiOSiMe2Vi)3 ( Karstedt s catalyst ), remain the most effective, and the remarkable rates and turnover numbers observed in these systems are among the most impressive in all of organometallic chemistry. The bulk of the literature on hydrosilylation falls outside the scope of this review, and readers are directed to the comprehensive work on hydrosilylation edited by Marciniec.93... 

This review attempts to summarize the published literature and information in patents from the 1980s to the present. The effect of promoters will be discussed first because it was the understanding of their function which led to a quasi-second revolution in the area of the Direct Process. The second area discussed will be the effect of silicon morphology on selectivity and yield. The third area of this review will focus on mechanistic studies aimed at understanding the fundamental chemical and physical effects in the Direct Process. The fourth area of review will be the use of substrates other than MeCl in the Direct Process. Finally, a discussion will be presented on the recovery and use of by-products from MCS, previously considered waste products. 

C. The Effect of Oxygen in Silicon Metal Used in the Direct Process... 

There are many examples of the direct reaction of silicon with ethyl chloride, vinyl chloride and chlorobenzene1. Vinyl and allylchlorosilanes76 were first made via a direct process in 1945 as were phenylchlorosilanes77. Jung s group has recently extended the direct reaction of silicon with a variety of substrates including allyl chloride78. Silicon... 

This relatively complicated reaction has been replaced by the so-called Direct Process or Rochow Process, 12,16,22 which starts from elemental silicon. It is illustrated by the reaction... 

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