[AndersHoveland]

The traditional route to making SiCl4 and SiI4 is to burn elemental silicon with the halogen. While this route is very direct, it requires very high temperatures. It can also be difficult to obtain the silicon to begin with since silica can only be reduced with carbon in an electric furnace.

Here is an interesting new alternative:

Dissolving CaCl2 into molten zinc chloride (which melts at only 292 °C ), then bubbling in SiF4 (made by reacting silica with hydrofluoric acid). Anhydrous aluminum trichloride has an even lower melting point, 192.4 °C (this surprising number is not an error!)

(2)CaCl2 + SiF4 --> (2)CaF2 + SiCl4

The silicon tetrachloride could then be combined with sodium iodide and used just like anhydrous HI for most reaction purposes.

ZnCl2 can be made by passing dry chlorine gas into ethyl ether with a piece of metallic zinc. The ZnCl2 that forms actually dissolves in the ether. It might work for aluminum also. "Solutions of Aluminum Chloride in Ethers", Gordon G. Evans, Thomas R. P. Gibb Jr., J. Kevin Kennedy, Frank P. Del Greco
J. Am. Chem. Soc., 1954, 76 (19), pp 4861–4862


Aluminum triiodide melts at 189.4 °C, so if this was used as the solvent, silicon tetraiodide could be obtained.

(2)CaI2 + SiF4 --> (2)CaF2 + SiI4

The formation of calcium fluoride is driven by the fact that it is so insoluble, having such a high crystal lattice energy. Otherwise, of course, the reaction would be just the opposite.

Silicon tetraiodide could be dissolved in chloroform, then reacted with a limited quantity of water to form anhydrous hydrogen iodide.

SiI4 + (2)H2O --> SiO2 + (4)HI

It is interesting to note that SiF4 has much less of a tendancy to hydrolyse in water than the other silicon-halogen compounds.

(3)SiF4 + (4)H2O <==> (2)H2SiF6 + Si(OH)4

Indeed, although it is a very well known reaction, it is otherwise quite exceptional that hydrofluoric acid can react with silica. Silicon tetrafluoride is a gas.

SiO2 + (4)HF --> SiF4 + (2)H2O


Does this idea seem like it would be feasible? Do you think it would be practical?

[jimdbell1]

I am very interested in this proposed reaction, because I will need to make SiF4 into SiCl4 in an industrial setting, although in a batch-size process.  (liters).   I am intererested in knowing if this process has ever been tested.

[AWK]

I am very interested in this proposed reaction, because I will need to make SiF4 into SiCl4 in an industrial setting, although in a batch-size process.  (liters).   I am intererested in knowing if this process has ever been tested.

This conversion is known for nearly 70 years.
https://doi.org/10.1021/ja01127a043