blogfast25
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Preparation of SnCl4 Without Using Elemental Chlorine
(Cross posted from my blog)
SnCl<sub>4</sub> (tin tetrachloride, tin IV chloride) can be prepared by direct union of chlorine with tin or with anhydrous tin II
chloride. The use of toxic chlorine gas at high temperature makes this a potentially hazardous enterprise. But SnCl<sub>4</sub> can also
be prepared by pyrolysis of potassium hexachlorostannate (K<sub>2</sub>SnCl<sub>6</sub> . This post presents a second preparation using this method.
Apparatus:
Left: 150 x 24 mm rimmed boiling tube, loaded with 15.0 g thoroughly dried (about 2 h at 200 C) K<sub>2</sub>SnCl<sub>6</sub>.
Moisture would cause hydrolysis of the SnCl<sub>4</sub>.
Middle: bent connecting glass tube, one hole rubber stopper at each end.
Right: 20 mm active length Liebig condenser, air cooled with a small compressor, 100 ml Erlenmeyer suspended in iced water acting as recipient.
During the run, a propane Bunsen burner on max air supply was used to heat the boiling tube and its content.
Reaction:
K<sub>2</sub>SnCl<sub>6</sub>(s) → 2 KCl(s) + SnCl<sub>4</sub>(g)
Results:
Minutes after switching on the heat, thick fumes of SnCl<sub>4</sub> started coming over. These condensed into a clear liquid at the end
of the connecting tube, BEFORE entering the intended condenser. This is due to the high boiling point of SnCl<sub>4</sub> (114.2 Celsius)
and indicates that an even simpler apparatus would work, by replacing the Liebig condenser with a longish piece of borosilicate glass tubing.
Droplets came over initially at a rate of about 1 per 2 seconds but gradually this rate slowed down. The content of the boiling tube glowed a dull red
heat by then.
Over the course of about 45 minutes about 7.7 g (3.5 ml) of SnCl<sub>4</sub> was fumed off and condensed, representing an Actual Yield of
about 81 %.
Here’s the finished product in a suitable vial:
The boiling tube with K2SnCl6 had been weighed prior to heating, as well as at the end of the experiment (after cooling). The weight loss was about
7.9 g, in good agreement with the actual product yield.
Just how much this compound fumes in air became apparent when transferring the product from Erlenmeyer to vial, as well as on disassembly of the
apparatus: thick, somewhat choking fumes evolved on both occasions.
On disassembly it also became clear the hot SnCl<sub>4</sub> fumes had attacked the rubber stopper, albeit mostly superficially. Using
ground glass joints would be preferable, to avoid product contamination.
[Edited on 22-3-2014 by blogfast25]
[Edited on 22-3-2014 by blogfast25]
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Töilet Plünger
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Cool prep!
I've seen a few of your threads on the preparation of stannic chloride. At my school we have several containers of the compound. They're liquid, but
have a solid ball in the middle. What causes this.
In Britain is it customary to place a space between the number and the percent sign? Here in the US we don't.
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blogfast25
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TP:
I've never seen SnCl4 before this prep so I've no idea what the ball is all about.
Not sure about the percentage sign: maybe it's just me?
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Töilet Plünger
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I believe the ball is caused by a solid hydrate forming. Weird that two volatile liquids can form a solid. I'll try to confirm this if I can access
the stannic chloride.
If you add in potassium chloride will the solid hexachlorostannate form?
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blogfast25
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Quote: Originally posted by Töilet Plünger  | I believe the ball is caused by a solid hydrate forming. Weird that two volatile liquids can form a solid. I'll try to confirm this if I can access
the stannic chloride.
If you add in potassium chloride will the solid hexachlorostannate form? |
Yes, a hydrate of SnCl4 exists. I guess if over time the compound absorbs water, such a ball can form.
K2SnCl6 can be obtained by adding the SnCl4 to a strongly acidified (HCl) solution of KCl. Reduce in volume by simmering till first crystals appear,
then cool and chill. The salt forms nice crystals. But I prepare it differently...
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The Volatile Chemist
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If this is true, would this be a double salt? I've been confused about them for a while.... 
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gdflp
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No it is not a double salt, note the naming conventions. If it was a double salt it would the names of both cations, and would be stannic potassium
chloride. This is a compound where potassium is the cation(K+ and the anion is hexachlorostannate(SnCl62-).
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blogfast25
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In 'Ye Olde Textbookes' you might still find this described as a double salt but it really is a complex salt, derived from the strong acid
H<sub>2</sub>SnCl<sub>6</sub> (which can be isolated fairly easily).
Evidence that it is a complex is as follows. SnCl<sub>4</sub> fumes in air and in plain water immediately hydrolyses more or less fully.
But not when there are plenty Cl<sup>-</sup> in excess, then the complex anion is formed. There's much more evidence besides that (crystal
structure, for instance).
The anion is the SnCl<sub>6</sub><sup>-</sup> ion, from which plenty of salts exist: NH4, Na, K, Rb, Cs, among others.
It is quite similar to KSbCl<sub>6</sub>, KAlCl<sub>4</sub>, (NH<sub>4</sub><sub>2</sub>SiF<sub>6</sub> etc, all of which are true complexes (to varying degrees).
[Edited on 24-3-2014 by blogfast25]
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