Tin(IV) chloride, also known as tin tetrachloride or stannic chloride, is an inorganic compound of tin and chlorine with the formula SnCl4. It is a colorless hygroscopicliquid, which fumes on contact with air. It is used as a precursor to other tin compounds.[1] 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 115 °C (239 °F):
Sn + 2Cl 2 → SnCl 4
Structure
Anhydrous tin(IV) chloride solidifies at −33 °C to give monoclinic crystals with the P21/c space group. It is isostructural with SnBr4. The molecules adopt near-perfect tetrahedral symmetry with average Sn–Cl distances of 227.9(3) pm.[2]
Space-filling model of anhydrous SnCl4.Structure of solid SnCl4.
Reactions
Tin(IV) chloride is well known as a Lewis acid. Thus it forms hydrates. The pentahydrate SnCl4·5H2O was formerly known as butter of tin. They all consist of [SnCl4(H2O)2] molecules together with varying amounts of water of crystallization. The additional water molecules link together the molecules of [SnCl4(H2O)2] through hydrogen bonds.[3] Although the pentahydrate is the most common hydrate, lower hydrates have also been characterised.[4]
Aside from water, other Lewis bases form adducts with SnCl4. These include ammonia and organophosphines. The complex [SnCl6]2− is formed with hydrochloric acid making hexachlorostannic acid.[1]
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:[5]
These organotin halides are useful precursors to catalysts (e.g., dibutyltin dilaurate) and polymer stabilizers.[6]
Organic synthesis
SnCl4 is used in Friedel–Crafts reactions as a Lewis acid catalyst.[1] For example, the acetylation of thiophene to give 2-acetylthiophene is promoted by tin(IV) chloride.[7] Similarly, tin(IV) chloride is useful for the nitrations.[8]
^Barnes, John C.; Sampson, Hazel A.; Weakley, Timothy J. R. (1980). "Structures of di-μ-hydroxobis[aquatrichlorotin(IV)]-1,4-dioxane(1/3), di-μ-hydroxobis[aquatrichlorotin(IV)]-1,8-epoxy-p-menthane(1/4), di-m-hydroxobis[aquatribromotin(IV)]-1,8-epoxy-p-menthane(1/4), di-μ-hydroxobis[aquatrichlorotin(IV)], and cis-diaquatetrachlorotin(IV)". J. Chem. Soc., Dalton Trans. (6): 949. doi:10.1039/DT9800000949.
^G. G. Graf "Tin, Tin Alloys, and Tin Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005 Wiley-VCH, Weinheim. doi:10.1002/14356007.a27_049
^Thurston, David E.; Murty, Varanasi S.; Langley, David R.; Jones, Gary B. (1990). "O-Debenzylation of a Pyrrolo[2,1-c][1,4]benzodiazepine in the Presence of a Carbinolamine Functionality: Synthesis of DC-81". Synthesis. 1990: 81–84. doi:10.1055/s-1990-26795. S2CID98109571.
^Fries, Amos A. (2008). Chemical Warfare. Read. pp. 148–49, 407. ISBN978-1-4437-3840-8..
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