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Caesium fluoride

2007 Schools Wikipedia Selection. Related subjects: Chemical compounds

                               Caesium fluoride
                               Caesium fluoride
                                    General
        Systematic name                                      Caesium fluoride
            Other names                                       Cesium fluoride
      Molecular formula                                                   CsF
             Molar mass                                         151.904 g/mol
             Appearance                               white crystalline solid
             CAS number                                          [13400-13-0]
                                  Properties
      Density and phase                                    4.115 g/cm³, solid
    Solubility in water                                  367 g/100 ml (18 °C)
            In methanol                                               soluble
   In dioxane, pyridine                                             insoluble
          Melting point                                        682 °C (955 K)
          Boiling point                                      1251 °C (1524 K)
       Basicity (pK[b])                                                     ?
                                   Structure
           Coordination
               geometry                                                     ?
      Crystal structure                                                 cubic
          Dipole moment                                                 7.9 D
                                    Hazards
                   MSDS                                         External MSDS
           Main hazards                             toxic, forms HF with acid
               NFPA 704 image:nfpa_h3.png image:nfpa_f0.png image:nfpa_r0.png
                                                                    estimated
          R/S statement                                       R: 23/24/25, 34
                                                         S: 26, 36/37, 39, 45
           RTECS number                                             FK9650000
                            Supplementary data page
          Structure and
             properties                                         n, ε[r], etc.
     Thermodynamic data                                       Phase behaviour
                                                           Solid, liquid, gas
          Spectral data                                       UV, IR, NMR, MS
                               Related compounds
           Other anions                         caesium chloride
                                                              caesium bromide
                                                               caesium iodide
          Other cations                         sodium fluoride
                                                           potassium fluoride
                                                            rubidium fluoride
      Related compounds                                        tetra-n-butyl-
                                                            ammonium fluoride
               Except where noted otherwise, data are given for
                       materials in their standard state (at 25°C, 100 kPa)
                                           Infobox disclaimer and references

   Caesium fluoride (cesium fluoride in North America), is an ionic
   compound usually found as a hygroscopic white solid. It is more soluble
   and more readily dissociated than sodium fluoride or potassium
   fluoride. CsF is commercially available – on a lab scale it costs
   around $50 per 100g ( Synquest), cheaper than RbF. It is available in
   anhydrous form, and if water has been absorbed it is easy to dry by
   heating at 100 ° C for two hours in vacuo^. It is therefore a useful,
   less hygroscopic alternative to tetra-n-butylammonium fluoride (TBAF)
   and TAS-fluoride (TASF) when anhydrous "naked" fluoride ion is needed.
   Like all soluble fluorides, it is mildly basic. Contact with acid
   should be avoided, as this forms highly toxic/corrosive hydrofluoric
   acid.

Chemical Properties

   Caesium fluoride reacts usually as a source of fluoride ion, F^-. It
   therefore undergoes all of the usual reactions associated with soluble
   fluorides such as potassium fluoride, for example:

   2 CsF ( aq) + CaCl[2] ( aq) → 2 CsCl ( aq) + CaF[2] ( s)

   Being highly dissociated it is quite reactive as a fluoride source
   under anhydrous conditions too, and it will react with
   electron-deficient aryl chlorides to form aryl fluorides ( halex
   reaction). Due to the strength of the Si-F bond, fluoride ion is useful
   for desilylation reactions (removal of Si groups) in organic chemistry;
   caesium fluoride is an excellent source of anhydrous fluoride for such
   reactions (see uses below). As with other soluble fluorides, CsF is
   moderately basic, due to the fact that HF is a weak acid. The low
   nucleophilicity of fluoride means it can be a useful base in organic
   chemistry (see uses below).

Preparation

   Caesium fluoride may be prepared by the action of hydrofluoric acid on
   caesium hydroxide or caesium carbonate, followed by removal of water.

Uses

   Caesium fluoride is a useful base in organic chemistry, due the fact
   that fluoride ion is largely unreactive as a nucleophile. It is
   reported that CsF gives higher yields in Knoevenagel condensation
   reactions than KF or NaF^.

   Removal of silicon groups (desilylation) is a major application for CsF
   in the laboratory, as its anhydrous nature allows clean formation of
   water-sensitive intermediates. Caesium fluoride in THF or DMF can
   attack a wide variety of organosilicon compounds to produce an
   organosilicon fluoride and a carbanion, which can then react with
   electrophiles^, for example^:

   Desilylation is also useful for the removal of silyl protecting groups.

   Caesium fluoride is also a popular source of fluoride in organofluorine
   chemistry. For example, CsF reacts with hexafluoroacetone to form a
   caesium perfluoroalkoxide salt which is stable up to 60 ° C, unlike the
   corresponding sodium or potassium salt^.

   Single crystals of the salt are transparent into the deep infrared. For
   this reason it is often used as the windows of cells used for infrared
   spectroscopy.

Precautions

   Like soluble fluorides, CsF is moderately toxic, see Elf Atochem MSDS
   sheet. Contact with acid should be avoided, as this forms highly
   toxic/corrosive hydrofluoric acid. Caesium ion (Cs^+) per se (for
   example as CsCl) is not generally considered toxic.
   Retrieved from " http://en.wikipedia.org/wiki/Caesium_fluoride"
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   with only minor checks and changes (see www.wikipedia.org for details
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