Silico-ethane, Si₂H₆

Silico-ethane, Si₂H₆, was discovered by Moissan and Smiles among the products of the action of hydrochloric acid on magnesium silicide, formed by heating magnesium and silicon together in the proportion 2Mg:Si. The gas obtained consists of a mixture of hydrogen, silicane, and silico-ethane. The two latter gases were separated from the hydrogen by solidification in tubes surrounded by liquid air; the silicane was removed from the tubes by fractional vaporisation, leaving the silico-ethane behind.

Silico-ethane may also be prepared from lithium silicide, which has the corresponding composition, Si₂Li₆, by decomposing it with concentrated hydrochloric acid.

Silico-ethane is a mobile, colourless liquid, heavier than, and sparingly soluble in, water. It boils at 52° C. or, according to Lebeau, at -7° C., and after solidification by means of liquid air, melts at - 138° C. Its vapour may be heated to 100° C. without decomposition, at which temperature the density is found to be 2.37 (air = 1), whilst silico-ethane requires 2.41. It is decomposed into its elements at 240° C., and electric sparks decompose it, separating amorphous silicon.

Silico-ethane takes fire spontaneously and even explosively in the air, burning to silica and water; drying with sulphuric acid increases the vigour of the reaction; it precipitates the metals from aqueous solutions of mercuric chloride, auric chloride, and silver nitrate; potassium dichromate and permanganate solutions, as well as bromine water, oxidise it to silicic acid. Carbon tetrachloride and sulphur hexafluoride react explosively with silico-ethane, with formation of the halogen hydracids and separation of the solid elements. Silico-ethane reacts with caustic potash solution similarly to silicane; in this way one molecule produces seven molecules of hydrogen:

Si₂H₆ + 2H₂O + 4KOH = 2K₂SiO₃ + 7H₂,

and the volume of hydrogen evolved serves to estimate the substance.

It appears from these reactions that silico-ethane resembles silicane in chemical properties, and differs entirely from ethane. There is no reason to suppose it differs from this hydrocarbon in constitution, but there are two reasons why it has different properties. For not only does it easily lose hydrogen, a property it shares with silicane, but the two silicon atoms permit of oxygen intervening between them in the process of oxidation.