Methyl chloride direct reaction with silicon

Alternatives to the methyl chloride direct process have been reviewed (31). Processes to make phenyl and ethyl silicones have employed direct-process chemistry. Phenyl chloride has been used in place of methyl chloride to make phenylchlorosHanes (15). In addition, phenylchlorosilanes are produced by the reaction of benzene, HSiCl, and BCl (17,31). EthylsiUcones have been made primarily in the CIS, where the direct process is carried out with ethyl chloride in place of methyl chloride (32). Vinyl chloride can also be used in the direct process to produce vinylchlorosilanes (31). Alternative methods for making vinylchlorosilanes include reaction of vinyl chloride with HSiCl or the platinum-catalyzed hydrosilylation of acetylene with HSiCl. ... 

Method of synthesis the direct reaction between silicon metal and methyl chloride in a fluid bed reactor yields a complex mixture of methyl chlorosilanes the chlorosilanes are distilled or purified, and the primary product - dimethyidichlorosilane, (CH3)2SiCl2 - is reacted with water (hydrolysis) to give poly(dimethylsiloxane) oligomers (Me SiOJ. ... 

The direct reaction of methyl chloride with silicon metal is the foundation stone of the worldwide silicone industry352. In corporate laboratories over the years, the reaction has been carefully engineered to provide the maximum amount of the desired product, dimethyldichlorosilane. Despite the industrial importance of the direct reaction, and the great amount of research devoted to it, its mechanism is still obscure353. Recently, however, a model has been suggested in which silicon in silylene form provides the crucial intermediate. 

After more than fifty years of industrial use, the direct reaction of methyl chloride with silicon, which underlies the entire silicone industry, is not understood. Promising recent experiments on this process are likely to be continued, and should at least settle the question of the nature of the intermediates. Are silylenes important in the process, either in the gas phase or at the silicon surface ... 

If ethylchlorosilanes are desired, they may be made by the direct method by the vapor-phase reaction of ethyl chloride with silicon at 300° C., using 10 per cent of copper as catalyst.8 The reactions follow the general plan indicated in the flow sheet for the corresponding methyl compounds (Fig. 2). 

Although the direct reaction of elemental silicon with methyl chloride shown in Eq. (3) looks simple, it is a complicated reaction and gives many kinds of byproducts.7,8 The yield of methylchlorosilane obtained from the direct reaction varies, and depends upon the reaction conditions such as temperature, pressure, flow rate of reactants, and other processing conditions including particle size and impurities of elemental silicon, catalyst, promoter, reactor type, etc.7... 

The direct reaction of elemental silicon with methyl chloride in the presence of copper affords dimethyldichlorosilane as the major product... 

Many studies on the direct reaction of methyl chloride with silicon-copper contact mass and other metal promoters added to the silicon-copper contact mass have focused on the reaction mechanisms.7,8 The reaction rate and the selectivity for dimethyldichlorosilane in this direct synthesis are influenced by metal additives, known as promoters, in low concentration. Aluminum, antimony, arsenic, bismuth, mercury, phosphorus, phosphine compounds34 and their metal complexes,35,36 Zinc,37 39 tin38-40 etc. are known to have beneficial effects as promoters for dimethyldichlorosilane formation.7,8 Promoters are not themselves good catalysts for the direct reaction at temperatures < 350 °C,6,8 but require the presence of copper to be effective. When zinc metal or zinc compounds (0.03-0.75 wt%) were added to silicon-copper contact mass, the reaction rate was potentiated and the selectivity of dimethyldichlorosilane was enhanced further.34 These materials are described as structural promoters because they alter the surface enrichment of silicon, increase the electron density of the surface of the catalyst modify the crystal structure of the copper-silicon solid phase, and affect the absorption of methyl chloride on the catalyst surface and the activation energy for the formation of dimethyldichlorosilane.38,39 Cadmium is also a structural promoter for this reaction, but cadmium presents serious toxicity problems in industrial use on a large scale.41,42 Other metals such as arsenic, mercury, etc. are also restricted because of such toxicity problems. In the direct reaction of methyl chloride, tin in... 

The reaction of elemental silicon with a 1 2.5 mixture of /so-propyl chloride and hydrogen chloride using 0.17 wt% NiCl2(dppb) as a promoter at 220 °C gave fso-propyldichlorosilane and /so-propyltrichlorosilane in 55 and 2% yields (based on /so-propyl chloride used), respectively. Zinc, known as a good promoter for the direct reaction of methyl chloride, was found to be an inhibitor in this reaction in addition to being an accelerator... 

The formation of the expected 2,4,6-trisilaalkanes 2 can be explained by the 2 1 reaction of (chloromethyl)silanes 1 and elemental silicon. The byproducts, 1,3-disilaalkanes 3, were obtained from the reaction of (chloromethyl)silane reactant 1 and hydrogen chloride (or chlorine) with the same silicon atom, as methyldichlorosilane (or methyltrichlorosilane) was obtained from the methyl chloride reaction. This result indicates that some of the (chloromethyl)silane reactant decomposed under the reaction conditions and acted as a chlorine or hydrogen chloride source. In the direct reaction of (chloromethyl)dimethylchlorosilane (lc), a significant amount of starting material was recovered at temperatures below 300 °C, but the reaction went to completion above 320 °C. 2,6-Dimethyl-2,4,4,6-tetra-chloro-2,4,6-trisilaheptane (2c) was obtained in much higher yields than 3-methyl-l,l,l,3-tetrachloro-l,3-disilabutane (3c) at reaction temperatures ranging from 280 to 320 °C, but the ratio of both compounds reversed above 340 °C. 

Zinc inhibited and cadmium promoted this particular reaction, consistent with the results observed for the direct reaction of elemental silicon with a mixture of alkyl chloride and hydrogen chloride, described above. In addition to allylchlorosilanes, several other compounds were also produced as minor products, including the following 2-methyl-1,1,4,4-tetrachloro-l,4-disilabutane 1,1,5,5-tetrachloro-1,5-disilapentane and 3-(dichlorosilyl)-1,1,5,5-tetrachloro-1,5-disilapentane. 

Recent studies on the direct reaction of elemental silicon with alkyl chlorides such as methyl chloride, activated alkyl chlorides, polychloro-methanes, (chloromethyl)silanes, (dichloromethyl)silanes, etc. are summarized in this review. In the direct reaction of elemental silicon with activated alkyl chlorides and polychloromethanes, the decomposition of the reactants can be suppressed and the production of polymeric carbosilanes reduced by adding hydrogen chloride to the reactants. These reactions provide a variety of new organosilicon compounds containing Si-H and Si- Cl functionalities, which should find considerable application in the silicone industry. 

Silylenes Divalent, dicoordinate silicon compounds, are the silicon coimterparts to the carbenes well known in organic chemistry. Since silylenes are frequent intermediates in both thermal and photochemical reactions, their importance in organosilicon chemistry is great [1]. There is recent evidence that even the direct reaction of methyl chloride with silicon, the foundation stone of the worldwide silicone industry, may proceed through the formation of silylene intermediates [2]. 

The earliest commercial syntheses of silicone materials were also carried out by reactions of Grignard reagents with SiCU, followed by hydrolysis of the dichlorosilanes. This route has now been displaced by the direct reaction between methyl chloride and silicon to give methylchlorosilanes, described more fully in Section 4.1. Silicones were first introduced commercially in the late 1930s and production has increased continuously since that time. 

A cornerstone of the modem silicone industry is the direct reaction of methyl chloride with sihcon, discovered in the early 1940s by E. G. Rochow in the United States and independently by R. Muller in Germany.The direct reaction, carried out by all basic producers of silicones, is done in a fluidized bed reactor using finely divided silicon with particle size 30-300 pm, at about 300 °C. In spite of decades of research in many laboratories, the exact course of the reaction is not yet known. 

Direct synthesis is the reaction of alkyl or aryl chloride and silicon in the presence of a proper catalyst. Mostly, methyl chloride is snbjected to the reaction at 250 350 °C in a flnid bed with fine particles of silicon mixed with a copper catalyst (eqnation 2). ... 

The Rochow Process. Rochow found that alkyl and aryl halides react directly with silicon when their vapors contacted silicon at elevated temperatures to produce complex mixtures of organosilicon halides. The reaction is promoted by a wide variety of metals from both the main group and the transition series, but the most efficient catalyst is copper. The most studied reaction of this type is the reaction between methyl chloride and silicon to give dimethyldichlorosilane and methyltrichlorosilane. Dimethyldichloro-silane is major feedstock silane for methylsilicon polymers. 

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... 

Transition metals have already established a prominent role in synthetic silicon chemistry [1 - 5]. This is well illustrated by the Direct Process, which is a copper-mediated combination of elemental silicon and methyl chloride to produce methylchlorosilanes, and primarily dimethyldichlorosilane. This process is practiced on a large, worldwide scale, and is the basis for the silicones industry [6]. Other transition metal-catalyzed reactions that have proven to be synthetically usefiil include hydrosilation [7], silane alcdiolysis [8], and additions of Si-Si bonds to alkenes [9]. However, transition metal catalysis still holds considerable promise for enabling the production of new silicon-based compounds and materials. For example, transition metal-based catalysts may promote the direct conversion of elemental silicon to organosilanes via reactions with organic compounds such as ethers. In addition, they may play a strong role in the future... 

The direct, copper catalyzed reaction of methyl chlorid with silicon, the Direct Process , is the most important reaction for the production of methylsilicon intermediates. A similar reaction with hydrogen chloride yields trichlorosilane, which in turn is the basis for trifiinctional intermediates and also for polycrystalline silicon, the raw material for the semiconductor industry. This Direct Process has been practiced for fifty years and much progress has been made by many towards understanding and optimizing the process, but much still remains to be learned about this complex series of heterogeneous reactions. 

Silicon is reacted with methyl chloride by a process discovered by Mueller Rochow over fifty years ago. This Direct Process gives a mixture of mono-, di-, trimethyl chlorosilanes together with small amounts of polysilanes, but normally the reaction is operated to maximize the yield of dimethyldichlorsilane. 

Methylchlorosilanes are used in the manufacture of a variety of resins, elastomers, and silicone oils. They are produced as a mixture of chlorosilanes, mainly dimethyldichlorosilane, by the reaction between silicon and methyl chloride by a direct route discovered independently by Rochow (1945) and Muller (1950). In this route, metallic copper, with or without promoters, is used to accelerate the reactions. The form of copper is important and depends on its preparation and association with the silicon phase. The whole system of solids comprising silicon metal, copper... 

Direct Process. The preparation of organosilanes by the direct process, first reported in 1945, is the primary method used commercially (142,143). Organosilanes in the United States, France, Germany, Japan, and the CIS are prepared by this method, including CH SiHC, (CH3)2SiHCl, and CTRSiHCL. Those materials are utilized as polymers and reactive intermediates. The synthesis involves the reaction of alkyl halides, eg, methyl and ethyl chloride, with silicon metal or silicon alloys in a fluidized bed at 250—450°C ... 

Methylsilyl chloride has acquired considerable industrial importance as a precursor for the preparation of silicon it is prepared directly by reaction of methyl chloride with silicon in the presence of copper as catalyst at high temperatures.317 Details for direct synthesis of methylsilyl chlorides have been given by Rochow.318 The main product is dichloro(dimethyl)silane in accordance with a reaction 2CH3C1 + Si - (CH3)2SiCl2, but trichloro(methyl)-silane, trimethylsilyl chloride, tetramethylsilane, silicon tetrachloride, and other products are also formed. 

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