Tin(IV) chloride

Tin(IV) chloride, also known as stannic chloride, is a compound of tin and chlorine with the formula SnCl₄. Despite what the name implies, it is not an ionic salt that contains Sn⁴⁺ ions, but a covalent compound containing covalent Sn-Cl bonds. Because of this, it has a much lower melting point than typical metal chlorides, and is a colorless liquid at room temperature when anhydrous.

Properties

Chemical

Anhydrous tin(IV) chloride fumes in humid air forming a white smoke of tin(IV) oxide and hydrogen chloride.

SnCl₄ + 2H₂O —> SnO₂ + 4HCl

When the anhydrous species is added to liquid water, it reacts exothermically and forms white crystals of the pentahydrate. Anhydrous tin(IV) chloride is a lewis acid, and is a very useful precursor to organotin compounds.

Physical

In the anhydrous state, tin(IV) chloride is a colorless liquid that fumes in contact with humid air. It has a melting point of -34.07°C and a boiling point of 114.15°C. The pentahydrate is a white, crystalline solid. Similarly to aluminum chloride, the anhydrous version isn't obtainable by heating the hydrate, as it decomposes, releasing hydrogen chloride and leaving tin(IV) oxide behind.

Availability

Tin(IV) chloride can only be purchased form chemical suppliers, as it doesn't currently have any uses other than as a chemical reagent.

Preparation

Tin(IV) chloride can be prepared in a home lab setting in a few different ways.

Reaction of tin and chlorine

Tin will react with dry chlorine gas to produce anhydrous tin(IV) chloride. The reaction is very exothermic. Chlorine gas is led from a chlorine generator through a drying tube filled with calcium chloride, or a gas washing bottle containing concentated sulfuric acid. It is then passed over the tin metal. It will react readily with chunks of tin, although higher surface area tin powder would react faster. A flask containing sodium hydroxide is used to absorb excess chlorine gas that doesn't react with the tin. It is recommended that an empty trap vessel is placed between the reaction chamber and the sodium hydroxide to prevent suckback into the reaction vessel.

Pyrolysis of potassium hexachlorostannate

Potassium hexachlorostannate (K₂SnCl₆), which can be prepared by dissolving tin in aqua regia and adding potassium chloride to the heated solution. Cooling this solution causes rapid crystallization of the K₂SnCl₆. Strongly heating this salt causes it to decompose into tin(IV) chloride and potassium chloride.

K₂SnCl₆ —> 2KCl + SnCl₄

The tin(IV) chloride boils off and can be condensed.

Oxidation of tin(II) chloride

Hydrated tin(IV) chloride can be prepared by oxidizing tin(II) chloride in solution using potassium nitrate. This is not a practical procedure for obtaining the anhydrous compound, only the pentahydrate.

Projects

• Make organotin compounds

Handling

Safety

Anhydrous tin(IV) chloride produces very irritating fumes in air, and should be used in a fume hood or at least a very well ventilated area. These precautions do not apply to the pentahydrate.

Storage

Anhydrous tin(IV) chloride should be stored in an air tight container to prevent it from reacting with moisture in the air. The pentahydrate can be stored as a general compound.

References

Relevant Sciencemadness threads

Small scale preparation of Stannic Chloride (SnCl4) (Describes both procedures for producing anhydrous tin(IV) chloride, with pictures)