Silico-iodoform, SiHI₃

Silico-iodoform was prepared by Buff and Wohler by the action of hydrogen iodide gas on heated silicon, and the method was improved upon by Friedel, who mixed hydrogen with the hydrogen iodide. Ruff has found that when silicochloroform reacts with ammonia at -15° C. siliconitrogen hydride, SiHN, is formed; and when this is suspended in carbon disulphide and treated with hydrogen iodide at low temperature, silico-iodoform is produced according to the reaction:

SiHN + 4HI = SiHI₃ + NH₄I.

The ammonium iodide is filtered off and the silico-iodoform freed from the solvent, carbon disulphide, and from silicon tetra-iodide by distillation. An even better result is obtained by employing aniline instead of ammonia. Silicon hydrotrianilide is formed, which reacts with hydrogen iodide thus:

SiH(NHC₆H₅)₃ + 6HI = SiHI₃ + 3C₆H₅NH₂.HI.

Silico-iodoform is a colourless liquid having a density of 3.286 at 23° C. or 3.314 at 20° C. and 3.362 at 0° C., which solidifies at +8° C. and distils under reduced pressure as follows:

Pressure mm.	Temperature ° C.
14	106
22	111
67	132
122	155

At about 150° C. it begins to decompose, but on further heating some of it can be distilled, and condensed at about 220° C. under atmospheric pressure. Silico-iodoform vapour burns in the air, and the liquid is decomposed by water like the chlorine compound, yielding silicoformic anhydride and hydriodic acid.