Difference between revisions of "Caesium fluoride"
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| MeltingPt = 682 °C (955 K) | | MeltingPt = 682 °C (955 K) | ||
| BoilingPt = 1251 °C (1524 K) | | BoilingPt = 1251 °C (1524 K) | ||
| − | | | + | | Dipole = 7.9 D (gas) |
}} | }} | ||
| Section3 = {{Chembox Structure | | Section3 = {{Chembox Structure | ||
| − | | Coordination = | + | | Coordination = Octahedral (Cs<sup>+</sup>)<br/>Octahedral (F<sup>−</sup>) |
| − | | CrystalStruct = [[ | + | | CrystalStruct = [[Sodium chloride structure|NaCl]], [[Pearson symbol|cF8]] |
| − | | | + | | SpaceGroup = Fm<u style="text-decoration:overline">3</u>m, No. 225 |
}} | }} | ||
| Section7 = {{Chembox Hazards | | Section7 = {{Chembox Hazards | ||
| ExternalMSDS = [http://www.sciencelab.com/xMSDS-Cesium_fluoride-9923357 External MSDS] | | ExternalMSDS = [http://www.sciencelab.com/xMSDS-Cesium_fluoride-9923357 External MSDS] | ||
| − | | EUIndex = | + | | EUIndex = not listed |
| − | + | | FlashPt = non-flammable | |
| − | |||
| − | | FlashPt = | ||
}} | }} | ||
| Section8 = {{Chembox Related | | Section8 = {{Chembox Related | ||
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}} | }} | ||
| − | '''Caesium fluoride''' | + | '''Caesium fluoride''' is an ionic compound usually found as a hygroscopic white solid. It is more soluble and more readily [[Dissociation (chemistry)|dissociated]] than [[sodium fluoride]] or [[potassium fluoride]]. 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''.<ref name="Friestad">{{last1 = Friestad | first1 = G. K. | last2 = Branchaud | first2 = B. P. | title = Handbook of Reagents for Organic Synthesis: Acidic and Basic Reagents | editor1-last = Reich | editor1-first = H. J. | editor2-last = Rigby | editor2-first = J. H. | publisher = Wiley | location = New York | year = 1999 | pages = 99–103}}.</ref> It is therefore a useful, less [[hygroscopic]] alternative to [[tetrabutylammonium fluoride]] (TBAF) and [[TASF reagent|TAS-fluoride]] (TASF) when anhydrous "naked" [[fluoride]] [[ion]] is needed. Like all soluble fluorides, it is mildly [[base (chemistry)|basic]]. Contact with [[acid]] should be avoided, as this forms highly toxic/corrosive [[hydrofluoric acid]]. |
==Chemical properties== | ==Chemical properties== | ||
| − | Caesium fluoride reacts usually as a source of fluoride ion, F<sup>-</sup>. It therefore undergoes all of the usual reactions associated with soluble fluorides such as potassium fluoride, for example:<ref name="greenwood">Greenwood | + | Caesium fluoride reacts usually as a source of fluoride ion, F<sup>-</sup>. It therefore undergoes all of the usual reactions associated with soluble fluorides such as potassium fluoride, for example:<ref name="greenwood">{{Greenwood&Earnshaw1st}}.</ref> |
| + | :2CsF + CaCl<sub>2</sub> → 2CsCl + CaF<sub>2</sub> | ||
| − | + | Being highly dissociated, it is quite reactive as a fluoride source under anhydrous conditions too, and it will react with [[electron-deficient]] [[aryl chloride]]s to form [[aromatic|aryl]] fluorides ([[halex reaction]]). Due to the strength of the silicon–fluorine 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 (''vide infra''). As with other soluble fluorides, CsF is moderately basic, because hydrofluoric acid is a weak acid. The low [[nucleophile|nucleophilicity]] of fluoride means it can be a useful base in organic chemistry.<ref name="greenwood"/> | |
| − | |||
| − | Being highly dissociated it is quite reactive as a fluoride source under anhydrous conditions too, and it will react with [[electron-deficient]] [[aryl chloride]]s to form [[aromatic|aryl]] fluorides ([[halex reaction]]). Due to the strength of the | ||
==Crystal structure== | ==Crystal structure== | ||
| − | Caesium fluoride has the inverse halite structure, because caesium ions are larger than fluoride ions; in the lithium, sodium, potassium, and rubidium halides, the cation is smaller than the anion. The caesium ions form a [[cubic closest packed]] array with fluoride ions in the octahedral holes.<ref name="greenwood"/><ref name="CRC"> | + | Caesium fluoride has the inverse halite structure, because caesium ions are larger than fluoride ions; in the lithium, sodium, potassium, and rubidium halides, the cation is smaller than the anion. The caesium ions form a [[cubic closest packed]] array with fluoride ions in the octahedral holes.<ref name="greenwood"/><ref name="CRC">{{RubberBible71st}}.</ref> |
==Preparation== | ==Preparation== | ||
| Line 58: | Line 55: | ||
==Uses== | ==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 [[potassium fluoride|KF]] or [[sodium fluoride|NaF]].<ref name="Fiorenza">Fiorenza | + | 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 [[potassium fluoride|KF]] or [[sodium fluoride|NaF]].<ref name="Fiorenza">{{citation | last1 = Fiorenza | first1 = Mariella | last2 = Mordini | first2 = Alessandro | last3 = Papaleo | first3 = Sandro | last4 = Pastorelli | first4 = Stefania | last5 = Ricci | first5 = Alfredo | title = Fluoride ion induced reactions of organosilanes: the preparation of mono and dicarbonyl compounds from β-ketosilanes | journal = Tetrahedron Lett. | year = 1985 | volume = 26 | pages = 787–88 | doi = 10.1016/S0040-4039(00)89137-6}}.</ref> |
| − | Removal of silicon groups (desilylation) is a major application for CsF in the laboratory, as its [[anhydrous]] nature allows clean formation of [[ | + | 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 [[Dimethylformamide|DMF]] can attack a wide variety of [[organosilicon]] compounds to produce an organosilicon fluoride and a [[carbanion]], which can then react with [[electrophile]]s,<ref name="CRC"/> for example:<ref name="Fiorenza"/> |
[[Image:CsF desilylation.png|350px]] | [[Image:CsF desilylation.png|350px]] | ||
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Desilylation is also useful for the removal of [[silyl]] [[protecting group]]s. | Desilylation is also useful for the removal of [[silyl]] [[protecting group]]s. | ||
| − | 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.<ref name="">F. W. Evans | + | 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.<ref name="">{{citation | first1 = F. W. | last1 = Evans | first2 = M. H. | last2 = Litt | first3 = A. M. | last3 = Weidler-Kubanek | first4 = F. P. | last4 = Avonda | title = Formation of adducts between fluorinated ketones and metal fluorides | journal = J. Org. Chem. | year = 1968 | volume = 33 | pages = 1837–39 | doi = 10.1021/jo01269a028}}.</ref> |
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]]. | 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== | ==Precautions== | ||
| − | Like other soluble fluorides, CsF is moderately toxic.<ref name="msds-csf"> | + | Like other soluble fluorides, CsF is moderately toxic.<ref name="msds-csf">{{citation | url = http://www.hazard.com/msds/f2/bms/bmsqc.html | webpage = MSDS Listing for cesium fluoride | website = hazard.com | date = 1993-04-27 | accessdate = 2007-09-07}}.</ref> Contact with [[acid]] should be avoided, as this forms highly toxic/corrosive [[hydrofluoric acid]]. Cesium [[ion]] (Cs<sup>+</sup>), or Cesium chloride, is generally not considered toxic.<ref name="msds-cscl">{{citation | url = http://www.jtbaker.com/msds/englishhtml/c1903.htm | webpage = MSDS Listing for cesium chloride | webpage = jtbaker.com | date = 2009-01-16 | accessdate = 2007-09-07}}.</ref> |
==References== | ==References== | ||
| − | {{reflist | + | {{reflist}} |
==External links== | ==External links== | ||
| − | * | + | *{{NPI|id=44|name=Fluoride compounds}} |
[[Category:Caesium compounds]] | [[Category:Caesium compounds]] | ||
Revision as of 21:55, 24 August 2009
| Caesium fluoride | |
|---|---|
| |
| |
| IUPAC name | Caesium fluoride |
| Other names | Cesium fluoride |
| Identifiers | |
| CAS number | [] |
| RTECS | FK9650000 |
| Properties | |
| Chemical formula | CsF |
| Molar mass | 151.90 g/mol |
| Appearance | white crystalline solid |
| Density | 4.115 g/cm3 |
| Melting point |
682 °C (955 K) |
| Boiling point |
1251 °C (1524 K) |
| Solubility in water | 367 g/100 ml (18 °C) |
| Dipole moment | 7.9 D (gas) |
| Structure | |
| Crystal structure | NaCl, cF8 |
| Space group | Fm3m, No. 225 |
| Coordination geometry | Octahedral (Cs+) Octahedral (F−) |
| Hazards | |
| Material safety data sheet (MSDS) | External MSDS |
| EU index number | not listed |
| Flash point | non-flammable |
| Related compounds | |
| Other anions | Caesium chloride Caesium bromide Caesium iodide |
| Other cations | Lithium fluoride Sodium fluoride Potassium fluoride Rubidium fluoride |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
Caesium fluoride 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. 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.[1] It is therefore a useful, less hygroscopic alternative to tetrabutylammonium 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.
Contents
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]
- 2CsF + CaCl2 → 2CsCl + CaF2
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 silicon–fluorine 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 (vide infra). As with other soluble fluorides, CsF is moderately basic, because hydrofluoric acid is a weak acid. The low nucleophilicity of fluoride means it can be a useful base in organic chemistry.[2]
Crystal structure
Caesium fluoride has the inverse halite structure, because caesium ions are larger than fluoride ions; in the lithium, sodium, potassium, and rubidium halides, the cation is smaller than the anion. The caesium ions form a cubic closest packed array with fluoride ions in the octahedral holes.[2][3]
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.[4]
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,[3] for example:[4]
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.[5]
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 other soluble fluorides, CsF is moderately toxic.[6] Contact with acid should be avoided, as this forms highly toxic/corrosive hydrofluoric acid. Cesium ion (Cs+), or Cesium chloride, is generally not considered toxic.[7]
References
- ↑ Template:Last1 = Friestad.
- ↑ 2.0 2.1 2.2 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984. ISBN 0-08-022057-6.
- ↑ 3.0 3.1 CRC Handbook of Chemistry and Physics, 71st ed.; CRC Press: Ann Arbor, MI, 1990.
- ↑ 4.0 4.1 Fiorenza, Mariella; Mordini, Alessandro; Papaleo, Sandro; Pastorelli, Stefania; Ricci, Alfredo Fluoride ion induced reactions of organosilanes: the preparation of mono and dicarbonyl compounds from β-ketosilanes. Tetrahedron Lett. 1985, 26, 787–88. DOI: 10.1016/S0040-4039(00)89137-6.
- ↑ Evans, F. W.; Litt, M. H.; Weidler-Kubanek, A. M.; Avonda, F. P. Formation of adducts between fluorinated ketones and metal fluorides. J. Org. Chem. 1968, 33, 1837–39. DOI: 10.1021/jo01269a028.
- ↑ MSDS Listing for cesium fluoride, <http://www.hazard.com/msds/f2/bms/bmsqc.html> (accessed 7 September 2007), hazard.com; .
- ↑ jtbaker.com, <http://www.jtbaker.com/msds/englishhtml/c1903.htm> (accessed 7 September 2007).
External links
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