Tin(IV) chloride, also known as tin tetrachloride or stannic chloride, is an inorganic compound of tin and chlorine with the formula . It is a colorless hygroscopic liquid, which fumes on contact with air. It is used as a precursor to other tin compounds. It was first discovered by Andreas Libavius (1550–1616) and was known as spiritus fumans libavii.
Preparation It is prepared from reaction of chlorine gas with tin at :
Structure
Anhydrous tin(IV) chloride solidifies at to give monoclinic crystals with the P2/c space group. It is isostructural with . The molecules adopt near-perfect tetrahedral symmetry with average Sn–Cl distances of .
Reactions Tin(IV) chloride is well known as a Lewis acid. Thus it forms hydrates. The pentahydrate was formerly known as butter of tin. These hydrates consist of cis-[] molecules together with varying amounts of water of crystallization. The additional water molecules link together the molecules of [] through hydrogen bonds. A pentahydrate has also been crystallized. In cis-, the Sn-Cl bonds are . Although the pentahydrate is the most common hydrate, lower hydrates have also been characterised.
Aside from water, other Lewis bases form adducts with . These include ammonia and organophosphines.
The ammonium salt of is formed from ammonium chloride. It is called "pink salt":
The analogous reaction with hydrochloric acid gives "hexachlorostannic acid".
Reaction of the tetrachloride with hydrogen fluoride gives tin tetrafluoride:
Tin(IV) chloride undergoes redistribution with tin(IV) bromide as assessed by NMR and Raman spectroscopy. Equilibrium is achieved in seconds at room temperature. By contrast, halide exchange for related germanium and especially silicon halides is slower.
Applications Precursor to organotin compounds Anhydrous tin(IV) chloride is a major precursor in organotin chemistry. Upon treatment with Grignard reagents, tin(IV) chloride gives tetraalkyltin compounds:
Anhydrous tin(IV) chloride reacts with tetraorganotin compounds in redistribution reactions:
These organotin halides are useful precursors to catalysts (e.g., dibutyltin dilaurate) and polymer stabilizers.
Organic synthesis SnCl4 is used in Friedel–Crafts reactions as a Lewis acid catalyst. For example, the acetylation of thiophene to give 2-acetylthiophene is promoted by tin(IV) chloride. Similarly, tin(IV) chloride is useful for nitrations.
Safety Stannic chloride was used as a chemical weapon in World War I, as it formed an irritating (but non-deadly) dense smoke on contact with air. It was supplanted by a mixture of silicon tetrachloride and titanium tetrachloride near the end of the war due to shortages of tin..
References
External links
International Chemical Safety Card 0953