Preparation of chlorinated methylchlorosilanes

The chlorination of methylchlorosilanes is realised by free chlorine in the liquid or gaseous phase. The reaction takes place by the radical chain mechanism its initiators (substances capable of generating free radicals) can be peroxides (benzoyl, kumyl, etc.), the dinitrile of 2,2 -azobis(isobutyric) acid, fluorine, 60Co y-rays, as well as UV rays. 

The chlorination of methylchlorosilanes with UV rays happens readily and forms a whole range of chlorinated methylchlorosilanes. For example, apart from chloromethyltrichlorosilane CIO FSiCF the reaction also forms dimethyltrichlorosilane Cl2CHSiCI3 and trimethyltrichlorosilane Cl3CSiCl3  

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. 

For a satisfactory yield of the most valuable product, monochloride, the chlorination should be carried out at a large excess of methylchlorosilanes. Flowever, the photochemical process has some considerable disadvantages, which make it harder to use in industry. The disadvantages include  

It is more practical to chlorinate organochlorosilanes with the help of initiators. The use of radical initiators (the dinitrile of 2,2 -azobis(isobutyric) acid, etc.) allows to carry out the chlorination reaction in the dark. This chlorination method is known in the literature as the dark technique. 

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