Methylchlorosilanes Trimethylchlorosilanes

Selectivity of contact mass. Since the most important products in the synthesis of organochlorosilanes are diorganodichlorosilanes, it is natural that the increase of their yield receives much attention. The selective formation of diorganodichlorosilanes when organic chlorine derivatives interact with contact mass is connected with the purity of the reactants, silicon above all. High yield of dimethyldichlorosilane in the direct synthesis of methylchlorosilanes largely depends on the presence of noticeable quantities of aluminum in contact mass. The yield of dimethyldichlorosilane in the presence of aluminum as a rule decreases due to the formation of trimethylchlorosilane in the reaction with pure (semiconductor) silicon in the presence of copper trimethylchlorosilane is virtually not formed. 

Thus, the methylation of dimethyldichlorosilane becomes very significant in the processes of direct synthesis, whereas the total amount of trimethylchlorosilane, which is formed according to the reactions of dis-proportioning and methylation, may reach 60-65%. Thus, in the direct synthesis of methylchlorosilanes the introduction of significant amounts of AI or its compounds into contact mass reduces the yield of dimethyldichlorosilane and respectively increases the yield of trimethylchlorosilane. 

Apart from the main products (dimethyldichlorosilane, methyldichloro-silane, methyltrichlorosilane and trimethylchlorosilane) there are various amounts of such by-products as trichlorosilane, silicon tetrachloride, di-methylchlorosilane and products with a boiling point of more than 70.2°C, i.e. the products of condensation and pyrolysis, which contain fragments like... 

Industrial chlorination of methyltrichlorosilane and trimethylchlorosi-lane is conducted by a similar technique. It should be borne in mind, however, that the chlorination speed of methyl groups greatly depends on the number of methyl radicals in the original methylchlorosilanes. Trimethyl-chlorosilane is the easiest to chlorinate, methyltrichlorosilane is the hardest. For example, the chlorination speed at the transition from dimethyldi-chlorosilane to trimethylchlorosilane increases 9-fold. 

High viscosity (more than 1000 mm2/s) oligomethylsiloxanes can be prepared by the hydrolytic cocondensation of trimethylchlorosilane and tank residue after methylchlorosilane distillation with subsequent partial polycondensation of the obtained products. 

Raw stock tank residue after distilling methylchlorosilanes (40-55% of chlorine, not more than 3% of dimethyldichlorosilane) trimethylchlorosilane (33-45% of chlorine) oil or coke toluene (not less than 98% of the 109.5-111 °C fraction). 

The coating of materials with a water-repellent film has been achieved by use of the methylchlorosilanes. A piece of cotton cloth exposed for a second or two to the vapor of trimethylchlorosilane,... 

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