Preparation of chlorinated methylphenyldichlorosilanes

When organochlorosilane molecules have at the same time alkyl and aryl groups, there is a possibility of controlled chlorination of these compounds. The determining factors are the conditions of the reaction, the type of the catalyst and the type of the chlorinating agent. 

when methylphenyldichlorosilane is chlorinated in the presence of radical initiators (the dinitrile of 2,2 -azobis(isobutyric) acid, etc.), only the methal radical is chlorinated, while the phenyl radical is untouched. 

The technology of methylphenyldichlorosilane chlorination is similar to that of methylchlorosilanes. The main difference is that the radical chlorination of methylphenyldichlorosilane occurs at a sufficient speed at higher temperatures (100-110°C), than in the case of methylchlorosilanes (60-70°C). At lower temperature (50-70 °C) the chlorination of methylphenyldichlorosilane is slow, and at higher temperatures (140-150 °C) the bond Si—Caik is destroyed. This difference in the conditions for methylphenyldichlorosilane chlorination seems to be caused by spatial difficulties due to the presence of the phenyl radical. 

The technological diagram of the production of phenyl(chloromethyl)dichlorosilane is similar to the diagram given in Fig. 19. In this process, similar to methylchlorosilane chlorination, in order to maximise the yield of phenyl(chloromethyl)dichlorosilane, the original methylphenyldichlorosilane should have a low conversion degree otherwise, the process forms a great amount of products of a deeper chlorination. 

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