Preparation of SnCl4 Without Using Elemental Chlorine

(Cross posted from my blog)

SnCl₄ (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 SnCl₄ can also be prepared by pyrolysis of potassium hexachlorostannate (K₂SnCl₆. 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) K₂SnCl₆. Moisture would cause hydrolysis of the SnCl₄.

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:

K₂SnCl₆(s) → 2 KCl(s) + SnCl₄(g)

Results:

Minutes after switching on the heat, thick fumes of SnCl₄ 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 SnCl₄ (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 SnCl₄ 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 SnCl₄ 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]

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?

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?

Quote: Originally posted by Töilet Plünger

If you add in potassium chloride will the solid hexachlorostannate form?

If this is true, would this be a double salt? I've been confused about them for a while....

Quote: Originally posted by The Volatile Chemist

If this is true, would this be a double salt? I've been confused about them for a while....

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 H₂SnCl₆ (which can be isolated fairly easily).

Evidence that it is a complex is as follows. SnCl₄ fumes in air and in plain water immediately hydrolyses more or less fully. But not when there are plenty Cl^- in excess, then the complex anion is formed. There's much more evidence besides that (crystal structure, for instance).

The anion is the SnCl₆^- ion, from which plenty of salts exist: NH4, Na, K, Rb, Cs, among others.

It is quite similar to KSbCl₆, KAlCl₄, (NH₄₂SiF₆ etc, all of which are true complexes (to varying degrees).


[Edited on 24-3-2014 by blogfast25]