Formula SnCl4 Melting point -33 °C Density 2.23 g/cm³ | Molar mass 260.5 g/mol Boiling point 114.2 °C Pubchem 24287 | |
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Appearance colorless to slightly yellow fuming liquid | ||
Tin(IV) chloride, also known as tin tetrachloride or stannic chloride is a inorganic compound with the formula SnCl4. At room temperature it is a colourless liquid, which fumes on contact with air, giving a stinging odor. It is used as precursor to other tin compounds. It was first discovered by Andreas Libavius (1550–1616) and was known as spiritus fumans libavii.
Contents
Preparation
It is prepared from reaction of chlorine gas with elemental tin at 115 °C (239 °F).
Sn + 2 Cl2 → SnCl4Structure
Anhydrous tin(IV) chloride solidifies at −33 °C to give monoclinic crystals with the P21/c space group; making it isostructural to solidified SnBr4. Within this the molecules adopt near perfect tetrahedral symmetry with average Sn–Cl distances of 227.9(3) pm.
Several forms of hydrated tin tetrachloride are known. They all consist of [SnCl4(H2O)2] molecules together with varying amouts of water of crystallization. The additional water molecules link together the molecules of [SnCl4(H2O)2] through hydrogen bonds. Although the pentahydrate is most common of the hydrates, lower hydrates have also been characterised.
Reactions
Anhydrous tin(IV) chloride is a Lewis acid. It forms adducts with ammonia, organophosphines, and other Lewis bases. When mixed with a small amount of water a semi-solid crystalline mass of the pentahydrate, SnCl4·5H2O is formed. This solid was formerly known as butter of tin. With hydrochloric acid the complex [SnCl6]2− is formed making the so-called hexachlorostannic acid.
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:
SnCl4 + 4 RMgCl → SnR4 + 4 MgCl2Anhydrous tin(IV) chloride reacts with tetraorganotin compounds in redistribution reactions:
SnCl4 + SnR4 → 2 SnCl2R2These organotin halides are more useful than the tetraorganotin derivatives.
Applications in high organic synthesis
Although a specialized application, SnCl4 is used in Friedel-Crafts reactions as a Lewis acidic catalyst for alkylation and cyclisation. Stannic chloride is used in chemical reactions with fuming (90%) nitric acid for the selective nitration of activated aromatic rings in the presence of inactivated ones.
Uses
The main application of SnCl4 is as a precursor to organotin compounds, which are used as catalysts and polymer stabilizers. It can be used in a sol-gel process to prepare SnO2 coatings (for example for toughening glass); nanocrystals of SnO2 can be produced by refinements of this method.
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 substituted for by a mixture of silicon tetrachloride and titanium tetrachloride near the end of the War due to shortages of tin.