Tin_tetrachloride

Tin(IV) chloride

Tin(IV) chloride

Chemical compound

Tin(IV) chloride, also known as tin tetrachloride or stannic chloride, is an inorganic compound with the formula SnCl4. It is a colorless hygroscopic liquid, 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.

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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]

SnCl4 + 4 RMgCl → SnR4 + 4 MgCl2

Anhydrous tin(IV) chloride reacts with tetraorganotin compounds in redistribution reactions:

SnCl4 + SnR4 → 2 SnCl2R2

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]

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.[9]

References

  1. [1]
    Egon Wiberg, Nils Wiberg, Arnold Frederick Holleman (2001). Inorganic Chemistry. Elsevier. ISBN 0-12-352651-5.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. [2]
    Reuter, Hans; Pawlak, Rüdiger (April 2000). "Die Molekül- und Kristallstruktur von Zinn(IV)-chlorid". Zeitschrift für anorganische und allgemeine Chemie (in German). 626 (4): 925–929. doi:10.1002/(SICI)1521-3749(200004)626:4<925::AID-ZAAC925>3.0.CO;2-R.
  3. [3]
    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.
  4. [4]
    Genge, Anthony R. J.; Levason, William; Patel, Rina; et al. (2004). "Hydrates of tin tetrachloride". Acta Crystallographica Section C. 60 (4): i47–i49. doi:10.1107/S0108270104005633. PMID 15071197.
  5. [5]
    Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  6. [6]
    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
  7. [7]
    John R. Johnson, G. E. May (1938). "2-Acetothienone". Organic Syntheses. 18: 1. doi:10.15227/orgsyn.018.0001.
  8. [8]
    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. S2CID 98109571.
  9. [9]
    Fries, Amos A. (2008). Chemical Warfare. Read. pp. 148–49, 407. ISBN 978-1-4437-3840-8..
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