Methylchlorosilanes, manufacture

The polymers described in this chapter are derived from the residue of the manufacture of methylchlorosilanes by the direct process. Approximately 10% of the reaction product of methylchlorosilane manufacture is a residue (called the direct-process residue) (2). The fraction of direct-process residue boiling between 150 and 160 °C consists primarily of 1,2-dimethyltetra-chlorodisilane and 1,1,2-trimethyltrichlorodisilane (3). 

The contamination of methylchlorosilanes with products of steel corrosion (iron peroxides) sharply retards liquid phase chlorination. The yield of monochlorosubstitutes is reduced, whereas the yield of di- and polychloro-substitutes and the quantity of the unreacted methylchlorosilane increase. To prevent the corrosion products from entering the reactor, the chlorine line (from the rotameter to bubbler 7) and the valve before the bubbler are manufactured from vinyplast. Besides, the line connecting condenser 8 with the further section of the diversion communication is given a U-shape. 

The possible toxicity of methylchlorosilanes and of all the silicone resins, oils, and elastomers is naturally a matter of concern in their manufacture and use. The methylchlorosilanes hydrolyze immediately they are inhaled and so have the odor and effect of hydrogen chloride at all low concentrations they cause no ill effects. Four years experience on the part of a group of laboratory workers has not revealed a single instance of toxic effect, either acute or chronic, from the inhalation of methylchlorosilanes. Fluoroscopic examination has revealed no deposits in the lungs, nor have the individuals in the group suffered any other disorder that could be attributed to silicon or its compounds. It must be concluded that there is no accumulation of organosilicon substances in the body that can be detected over this interval of time. 

Manufacture of methylchlorosilanes from Si + CH3CI with a copper catalyst... 

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... 

The F3 cyclic species is obtained through hydrolysis of the corresponding silane, methyl(3,3,3-trifluoropropyl)dichlorosilane. This silane is the hydrosilylation adduct of 3,3,3-trifluoropropene and methyldichlorosilane, CH3HSiCl2, a minor product of the Rochow-Muller direct process for manufacturing methylchlorosilanes. The hydrosilylation reaction is catalyzed with transition metal complexes of platinum or rhodium such as Speier s catalyst and hexachloroplatinic acid in isopropanol. The reaction conditions are very similar to those employed with unfluorinated reagents, complicated only by the fact that 3,3,3-trifluoropropene is a gas. 

Compared to the Grignard process, the direct process is not very versatile. In practice, it is satisfactory for the manufacture of only methyl- and phenylchloro-silanes. (For the latter, silver is the preferred catalyst and a reaction temperature of about 400°C is used.) When the process is used for other chlorosilanes, yields are unacceptably low. However, methylchlorosilanes are the chlorosilanes most widely used in the manufacture of commercial silicones and the direct process has become the dominant process. 

The industrial manufacture of siloxanes has its beginnings with pure silicon, which is pulverized and allowed to react with methyl chloride in a pressurized fluid bed reactor in the presence of a copper catalyst. Under carefully controlled conditions, this reaction yields a mixture of methylchlorosilanes in which di-methyIdichlorosilane predominates ... 

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