Halogen Derivatives of Silicopentane and Silicohexane

The chlorinated derivatives Si₅Cl₁₂ and Si₆Cl₁₄ have been isolated by Besson and Fournier from among the products of the action of the silent electric discharge on a mixture of hydrogen and silicon tetrachloride. Si₅Cl₁₂ is an extremely viscous liquid boiling at 190° C./15 mm. Si₆Cl₁₄ is a white solid which melts with decomposition at 170° C. and sublimes in a vacuum at 200° C.

The conditions of formation of the higher chlorides of silicon have recently been investigated by Martin, who has prepared hexachloro-silico-ethane and octachlorosilicopropane in quantity, as well as smaller amounts of the higher chlorides, together with silicon tetrachloride, by the action of chlorine on 50 per cent, ferro-silicon at temperatures not exceeding 310° C. Martin affirms that the higher chlorides are first formed by the chlorination of chains of silicon atoms, which probably exist in ferrosilicon as well as in the free solid element, and that these chains, by further chlorination, yield simpler products, and finally silicon tetrachloride, according to the scheme:



The alternative view, of Gattermann and Weinlig, that silicon tetrachloride is first formed and then combines with silicon to form higher chlorides, is controverted on the ground that the production of hexachlorosilico-ethane from silicon tetrachloride and silicon is an endothermic reaction unlikely to take place at so low a temperature as 300° C., that the yield of hexachlorosilico-ethane reaches its maximum at a still lower temperature, viz. 180°-200° C., and that when silicon tetrachloride is distilled over silicon or ferro-silicon between 200° C. and 340° C. the formation of hexachlorosilico-ethane is not observed, but that, on the other hand, hexachlorosilico-ethane unites with chlorine at 300° C., producing silicon tetrachloride. From hexachloro-silico-ethane Martin has prepared the following ethoxy-derivatives:

Substance.	Boiling-point under 34 mm.	Density	Refractive Index D line.
Si2Cl6	60.5° C.	1.5624 at 15° C.	1.4748 at 18° C.
Si2Cl5OEt	84° C.	1.388 at 20° C.	1.4568 at 14.5° C.
Si2Cl4(OEt)2	104° C.	1.270 at 20° C.	1.4432 at 14.5° C.
Si2Cl3(OEt)3	122° C.	1.163 at 20° C.	1.4333 at 14.5° C.
Si2Cl2(OEt)4	-	-	-
Si2Cl(OEt)5	138° C.	1.092 at 17° C.	1.4205 at 14.5° C.
Si2(OEt)6	141° C.	0.9718 at 17° C.	1.4134 at 14.5° C.

These compounds react with alkalis with the evolution of hydrogen and

the interpolation of an oxygen atom between two silicon atoms, thus: