Higher Silicon Chlorides

Silicon bromide, Si2Br6, 2 98 (See also Silicon tetrabromide) Silicon chlorides, higher, 1 42 Si2Cl6, 1 42 Si,Cl, 1 44... 

In order to prevent the decomposition of the higher chlorides of silicon, it is very important that only a small part of the reaction tube should be heated at a time. When the chlorine is first passed through the reaction tube, the temperature of the heating coil is about 250°C. when the reaction is well started, it is lowered to about 150°C. The best rate of flow of chlorine is less than two bubbles per second. Under these conditions, in about 12 or 14 days, all the calcium-silicon will be used up, and about 700 ml. of liquid silicon chlorides will be collected. 

This reaction again affords another opportunity for preparing higher silicon chlorides, for example ... 

A similar interpretation may be based upon the results of Schwarz and coworkers580 581>. These authors hydrolyzed higher silicon chlorides and found solid white polymeric compounds in which the original Si-Si framework is retained. An irregular network containing Si-O-Si bond systems is also formed, so that the earlier postulated structural formulas are certainly incorrect. 

A 16 membered ring carbodiimide is obtained in the reaction of Me2SiCl2 with cyanamide." In addition to the tetramer, oligomers with n = 2 to 7 are detected. Also, higher oligomeric carbodiimides are formed in the reaction of alkyl- and dialkyl silicon chlorides with cyanamide in the presence of pyridine." Also, from bis(trimethylsilyl)carbodiimide and silicon tetrachloride in the presence of pyridine, the silicon polycarbodiimide 34 is obtained." ... 

Higher chlorides, Si2Cle to Si6Cl,4 (highly branched - some cyclic) are formed from SiCU plus Si or a silicide or by amine catalysed disproportionations of Si2Cl,5, etc. Partial hydrolysis gives oxide chlorides, e.g. CUSiOSiCla. SiCU is used for preparation of silicones. 

As shown in Table XIV, the reactivity of (trichloromethyl)silanes varied depending upon the substituent on silicon. The reactivity and yields of (trichloromethyl)-methyldichlorosilanes were slightly higher than those of (trichloroinethyl)tri-chlorosilanes in the aluminum chloride-catalyzed alkylation as similarly observed in the alkylations with (ai-chloroalkyl)silanes and (dichloroalkyl)silanes. The electron-donating methyl group on the silicon facilitates the alkylation more than the electron-withdrawing chlorine. The minor products, (diphenylmethyl)chloro-silanes, were presumably derived from the decomposition of (triphenylmethyl)-chlorosilanes. 

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