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143consisting of two octahedra sharing the three chloride ions of one face.' The compound decomposes slowly in air. It is soluble in vater but only very slightly soluble in 12 M hydrochloric acid or ethanol. Its dark green aqueous solutions (absorption maxima a t 462 and 625 mp) oxidize an contact with air.

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The recent development of silicones derived chiefly from the dimethylchlorosilanes prompted us to study the dimethyl and trimethyl chlorosilanes and their fluorination products. The information on these chlorosilanes was, at the time this investigation was carried out, incomplete and in some cases incorrect. Previous investigations in this Laboratory have shown that alkyl chlorosilanes may be fluorinated by antimony trifluoride to yield chlorofluorides and fluorides.3'4•5Methyl trichlorosilane and dimethyl dichlorosilane were not6 reported until 1941 by Gilliam, Liebhafsky, and Winslow.7 Hyde and DeLong8 also prepared dimethyldichlorosilane by means of a Grignard reaction. The preparation and purification of trimethyl chlorosilane had not been described in the literature until after this investigation was completed. Taylor and Walden9 have recently made it by chlorination of trimethylsilane. ExperimentalPreparation and Purification of Dimethyl Dichlorosilane.-The procedure first used in preparing dimethyl dichlorosilane was similar to that used by Gilliam and coworkers.7 Since the boiling points of methyl trichlorosilane and dimethyl dichlorosilane are only four degrees apart, a mixture of these two compounds proved to be very difficult to separate. This difficulty was surmounted in this investigation, by using a ratio of three moles of methylmagnesium bromide (based on the amount of magnesium used) in 1500 ml. ethyl ether to one mole of silicon tetrachloride in 1000 ml. ether. Any methyl trichlorosilane formed was thus converted either to dimethyl dichlorosilane or to trimethyl chlorosilane. These two latter com-

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