Trimethylsilyl Trifluoromethanesulfonate (TMSOTf)
19 September 2003 (online)
The title compound is a colourless, mobile liquid, which dissolves in aliphatic or aromatic hydrocarbons and haloalkanes without any reaction.  Due to the presence of the electron-withdrawing trifluoromethanesulfonyl moiety the silicon atom is extremely electron deficient. Subsequently the silicon atom reacts with heteroatoms, especially oxygen to form onium ions. In contrast to more conventional Lewis acids such as AlCl3 and TiCl4, TMSOTf tends to bind to a single hetero functional group. TMSOTf is 6.7 × 108 times more reactive than TMSCl, and this is manifested in an extreme sensitivity towards moisture which must be excluded from all reactions.  The ability of TMSOTf to form supercationic species with organic substrates results in it’s utilization in a wide range of synthetic applications. 
TMSOTf,  is prepared by the gradual addition of chlorotrimethylsilane to trifluoromethanesulfonic acid with stirring and protection from moisture. The mixture is heated until hydrogen chloride evolution ceases and then the product is isolated by fractional distillation. TMSOTf is also commercially available.
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