Chloroorganosilanes from a Direct Process

SiCU + LiAlH4 SiH4 + LiCI + AICI3 SiCU + 4ROH - Si(OR 4 + 4HC1 

A process for the synthesis of chloroorganosilanes from elemental silicon and simple alkyl or aryl chlorides in the presence of a catalyst was originally developed in 1945 by Rochow and Patnode [43]. This process was also discovered in Germany during World War II the patent publication appeared several years later [44]. 

The direct process is used mainly for the production of dichlorodimethylsilane (Eq.2.8). 

The yield of this reaction decreases rapidly at temperatures above 300 C, but it is also minimal below 250 °C. The synthesis must therefore be carried out at 250-350 °C. This is accomplished by heating the mixture first to a higher temperature and then allowing it slowly to cool. Local superheating effects and inactivity of the silicon/catalyst surface can be avoided by continuous stirring. 

In the absence of a catalyst, silicon reacts with methylchloride only at 350-550° the products are tetrachlorosilane and trichloromethylsilane [45]. The catalyst for the direct process is always copper in some cases co-catalysts are added. The greatest catalytic efficiency is obtained when the amount of copper is 10 % of the amount of silicon. This decreases the activation energy from 185 kJ/mol to 63 kJ/mol [46]. 

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