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{{chembox |
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{{Chembox |
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| verifiedrevid = 396305984 |
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| Verifiedfields = changed |
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| Name = Caesium fluoride |
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| Watchedfields = changed |
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| ImageFile = Caesium fluoride.jpg |
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| verifiedrevid = 444641443 |
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| ImageName = Caesium fluoride |
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| ImageFile1 = Caesium-fluoride-3D-ionic.png |
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| Name = Caesium fluoride |
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| ImageName1 = Caesium fluoride |
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| ImageFile = Caesium fluoride.jpg |
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| IUPACName = Caesium fluoride |
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| ImageName = Caesium fluoride |
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| OtherNames = Cesium fluoride |
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| ImageFile1 = Caesium-fluoride-3D-ionic.png |
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| ImageName1 = Caesium fluoride |
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| Section1 = {{Chembox Identifiers |
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| IUPACName = Caesium fluoride |
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| OtherNames = Cesium fluoride |
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| Section1 = {{Chembox Identifiers |
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| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |
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| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |
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| ChemSpiderID = 24179 |
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| ChemSpiderID = 24179 |
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| CASNo_Ref = {{cascite|correct|CAS}} |
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| CASNo_Ref = {{cascite|correct|CAS}} |
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| RTECS = FK9650000 |
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| RTECS = FK9650000 |
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| PubChem = 25953 |
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| EC_number = 236-487-3 |
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| UNII = T76A371HJR |
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}} |
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}} |
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| Section2 = {{Chembox Properties |
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| Section2 = {{Chembox Properties |
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| Formula = CsF |
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| Formula = CsF |
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| MolarMass = 151.90 g/mol |
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| MolarMass = 151.903 g/mol<ref name=crc/> |
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| Appearance = white crystalline solid |
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| Appearance = white crystalline solid |
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| Density = 4.115 g/cm<sup>3</sup> |
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| Density = 4.64 g/cm<sup>3</sup><ref name=crc/> |
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| Solubility = 367 g/100 ml (18 °C) |
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| Solubility = 573.0 g/100 mL (25 °C)<ref name=crc>{{RubberBible92nd|page=4.57}}</ref> |
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| SolubleOther = Insoluble in ], ], ] and ]<br>191 g/100 mL in ]. |
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| MeltingPt = 682 °C (955 K) |
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| MeltingPtC = 703 |
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| BoilingPt = 1251 °C (1524 K) |
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| MeltingPt_ref = <ref name=crc/> |
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| pKb = |
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| BoilingPtC = 1251 |
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| BoilingPt_notes = (2,284 °F; 1,524 K) |
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| pKb = −744 kJ/mol |
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| RefractIndex = 1.477 |
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| MagSus = -44.5·10<sup>−6</sup> cm<sup>3</sup>/mol<ref>{{RubberBible92nd|page=4.132}}</ref> |
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| Section3 = {{Chembox Structure |
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| Section3 = {{Chembox Structure |
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| Coordination = ] |
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| Coordination = ] |
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| CrystalStruct = ], ] |
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| CrystalStruct = ], ] |
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| SpaceGroup = Fm{{overline|3}}m, No. 225<ref name=str>{{cite journal|doi=10.1103/PhysRev.21.143|title=Precision Measurements of Crystals of the Alkali Halides|journal=Physical Review|volume=21|issue=2|pages=143–161|year=1923|last1=Davey|first1=Wheeler P.|bibcode=1923PhRv...21..143D}}</ref> |
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| SpaceGroup = Fm<u style="text-decoration:overline">3</u>m, No. 225 |
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| LattConst_a = 0.6008 nm<ref name=str/> |
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| UnitCellFormulas = 4 |
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| UnitCellVolume = 0.2169 nm<sup>3</sup><ref name=str/> |
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| Dipole = 7.9 ] |
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| Dipole = 7.9 ] |
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| Section7 = {{Chembox Hazards |
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| Section4 = {{Chembox Thermochemistry |
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| DeltaHf = -553.5 kJ/mol<ref name=b92t>{{RubberBible92nd|page=5.10}}</ref> |
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| ExternalMSDS = |
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| Entropy = 92.8 J/mol·K<ref name=b92t/> |
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| EUIndex = Not listed |
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| DeltaGf = -525.5 kJ/mol<ref name=b92t/> |
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| RPhrases = |
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| HeatCapacity = 51.1 J/mol·K<ref name=b92t/> |
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| SPhrases = |
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}} |
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| Section7 = {{Chembox Hazards |
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| MainHazards = toxic |
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| GHSPictograms = {{GHS05}}{{GHS06}}{{GHS08}} |
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| GHSSignalWord = Danger |
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| HPhrases = {{H-phrases|301|311|315|318|331|361f}} |
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| PPhrases = {{P-phrases|201|202|260|261|264|270|271|280|281|301+310|301+330+331|302+352|303+361+353|304+340|305+351+338|308+313|310|311|312|321|322|330|332+313|361|362|363|403+233|405|501}} |
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| NFPA-H = 3 |
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| NFPA-F = 0 |
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| NFPA-R = 0 |
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| ExternalSDS = |
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| FlashPt = Non-flammable |
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| FlashPt = Non-flammable |
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}} |
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| Section8 = {{Chembox Related |
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| Section8 = {{Chembox Related |
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| OtherAnions = ]<br/>]<br/>] |
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| OtherAnions = ]<br/>]<br/>]<br/>Caesium astatide |
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| OtherCations = ]<br/>]<br/>]<br/>] |
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| OtherCations = ]<br/>]<br/>]<br/>]<br/>Francium fluoride |
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'''Caesium fluoride''' ('''cesium fluoride''' in North America), is an ] usually encountered as a hygroscopic white solid. It is more soluble and more readily ] than ] or ]. 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 '']''.<ref name="Friestad">{{cite book|author=Friestad, G. K.; Branchaud, B. P.|title=Handbook of Reagents for Organic Synthesis: Acidic and Basic Reagents|editor=Reich, H. J.; Rigby, J. H.|publisher=Wiley|location=New York|year=1999|pages=99–103}}</ref> Like all soluble fluorides, it is mildly ]. A notable fact about this compound is that it is the most ionic compound. Caesium has the lowest ] and fluorine has the highest electronegativity. |
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'''Caesium fluoride''' ('''cesium fluoride''' in ]) is an ] with the formula CsF. A ] white salt, caesium fluoride is used in the ] as a source of the fluoride anion.<ref>{{cite book |doi=10.1002/047084289X.rc050.pub2 |chapter=Cesium Fluoride |title=Encyclopedia of Reagents for Organic Synthesis |date=2007 |last1=Friestad |first1=Gregory K. |last2=Branchaud |first2=Bruce P. |last3=Navarrini |first3=Walter |last4=Sansotera |first4=Maurizio |isbn=978-0-471-93623-7 }}</ref> The compound is noteworthy from the pedagogical perspective as ] also has the highest ] of all commonly available elements and ] has the highest electronegativity. |
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==Synthesis and properties== |
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==Synthesis and properties== |
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]s.<ref name=chains>{{cite journal|doi=10.1038/ncomms8943|pmid=26228378|pmc=4532884|title=Single-atom electron energy loss spectroscopy of light elements|journal=Nature Communications|volume=6|pages=7943|year=2015|last1=Senga|first1=Ryosuke|last2=Suenaga|first2=Kazu|bibcode=2015NatCo...6.7943S}} (Supplementary information)</ref>]] |
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Caesium fluoride is prepared by the action of ] on ] or ], followed by removal of water. |
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Caesium fluoride can be prepared by the reaction of ] (CsOH) with ] (HF) and the resulting salt can then be purified by recrystallization. The reaction is shown below: |
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:CsOH + HF → CsF + H<sub>2</sub>O |
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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, for example:<ref name="greenwood">Greenwood, N.N.; Earnshaw, A. ''Chemistry of the Elements'', Pergamon Press, Oxford, UK, 1984.</ref> |
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Using the same reaction, another way to create caesium fluoride is to treat ] (Cs<sub>2</sub>CO<sub>3</sub>) with hydrofluoric acid and again, the resulting salt can then be purified by recrystallization. The reaction is shown below: |
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:2 CsF + CaCl<sub>2</sub> → 2 CsCl + CaF<sub>2</sub> |
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:Cs<sub>2</sub>CO<sub>3</sub> + 2 HF → 2 CsF + H<sub>2</sub>O + CO<sub>2</sub> |
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CsF is more soluble than ] or ] in organic solvents. It is available in its anhydrous form, and if water has been absorbed, it is easy to dry by heating at 100 °C for two hours '']''.<ref name="Friestad">{{cite book|author1=Friestad, G. K. |author2=Branchaud, B. P. |title=Handbook of Reagents for Organic Synthesis: Acidic and Basic Reagents|editor1=Reich, H. J. |editor2=Rigby, J. H. |publisher=Wiley|location=New York|year=1999|pages=99–103|isbn=978-0-471-97925-8}}</ref> CsF reaches a ] of 1 ] at 825 °C, 10 kPa at 999 °C, and 100 kPa at 1249 °C.<ref>{{cite book | editor = Lide, D. R. | title = CRC Handbook of Chemistry and Physics | edition = 86th | location = Boca Raton (FL) | publisher = CRC Press | year = 2005 | isbn = 0-8493-0486-5 |page=6.63|chapter=Vapor Pressure|chapter-url=http://www.physics.nyu.edu/kentlab/How_to/ChemicalInfo/VaporPressure/morepressure.pdf}}</ref> |
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==Crystal structure== |
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Caesium fluoride has the halite structure, which means that the Cs<sup>+</sup> and F<sup>−</sup> pack in a ] array as do Na<sup>+</sup> and Cl<sup>−</sup> in sodium chloride. Caesium cations are larger than fluoride anions, whereas in the lithium, sodium, potassium, and rubidium halides, the cations are smaller than the anion. <ref name="greenwood"/><ref name="CRC">''Handbook of Chemistry and Physics'', 71st edition, CRC Press, Ann Arbor, Michigan, 1990.</ref> |
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==Applications== |
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==Structure== |
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Caesium fluoride has the ] structure, which means that the Cs<sup>+</sup> and F<sup>−</sup> pack in a ] array as do Na<sup>+</sup> and Cl<sup>−</sup> in sodium chloride.<ref name=str/> Unlike sodium chloride, caesium fluoride's anion is smaller than its cation, so it is the anion size that sterically inhibits larger coordination numbers than six under normally encountered conditions. A larger halide ion would allow for the eight-coordination seen in other caesium halide crystals. |
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===In organic synthesis=== |
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Being highly dissociated it is a more reactive source of fluoride than related salts. CsF is less ] alternative to ] (TBAF) and ] (TASF) when anhydrous "naked" ] ] is needed. |
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==Applications in organic synthesis== |
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====As a base==== |
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Being highly dissociated, CsF is a more reactive source of fluoride than related alkali metal salts. CsF is an alternative to ] (TBAF) and ] (TASF). |
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As with other soluble fluorides, CsF is moderately basic, because ] is a weak acid. The low ] of fluoride means it can be a useful base in organic chemistry.<ref name="greenwood"/>Caesium fluoride is a useful base in ], due the fact that fluoride ] is a relatively poor ]. CsF gives higher yields in ] reactions than ] or ].<ref name="Fiorenza">{{cite journal|year=1985|journal=Tetrahedron Letters|volume=26|page=787|doi=10.1016/S0040-4039(00)89137-6|title=Fluoride ion induced reactions of organosilanes: the preparation of mono and dicarbonyl compounds from β-ketosilanes|author1=Fiorenza, M|author2=Mordini, A|author3=Papaleo, S|author4=Pastorelli, S|author5=Ricci, A}}</ref> |
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====Formation of C-F bonds==== |
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===As a base=== |
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As with other soluble fluorides, CsF is moderately basic, because ] is a ]. The low ] of ] means it can be a useful base in ].<ref name="greenwood">{{Greenwood&Earnshaw1st|pages=82–83}}</ref> CsF gives higher yields in ] reactions than ] or ].<ref name="Fiorenza">{{cite journal|year=1985|journal=Tetrahedron Letters|volume=26|pages=787–788|doi=10.1016/S0040-4039(00)89137-6|title=Fluoride ion induced reactions of organosilanes: the preparation of mono and dicarbonyl compounds from β-ketosilanes|author1=Fiorenza, M|author2=Mordini, A|author3=Papaleo, S|author4=Pastorelli, S|author5=Ricci, A|issue=6}}</ref> |
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Caesium fluoride is also a popular source of fluoride in ]. For example, CsF reacts with ] to form a caesium perfluoroalkoxide salt, which is stable up to 60 °C, unlike the corresponding ] or ] salt. It will convert ] ]s to ] fluorides (]).<ref>{{cite journal|author=F. W. Evans, M. H. Litt, A. M. Weidler-Kubanek, F. P. Avonda|title=Reactions Catalyzed by Potassium Fluoride. 111. The Knoevenagel Reaction|year=1968|journal=Journal of Organic Chemistry|volume=33|pages=1837–1839|doi=10.1021/jo01269a028}}</ref> |
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====Deprotection agent==== |
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===Formation of Cs-F bonds=== |
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Caesium fluoride serves as a source of fluoride in ]. Similarly to ] fluoride, CsF reacts with ] to form a stable perfluoroalkoxide salt.<ref>{{cite journal|author1=Evans, F. W. |author2=Litt, M. H. |author3=Weidler-Kubanek, A. M. |author4=Avonda, F. P. |title=Formation of adducts between fluorinated ketones and metal fluorides|year=1968|journal=Journal of Organic Chemistry|volume=33|pages=1837–1839|doi=10.1021/jo01269a028|issue=5}}</ref> It will convert ] ]s to ] fluorides (]), although potassium fluoride is more commonly used. |
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Due to the strength of the ]–] bond, fluoride ion is useful for ] reactions (removal of Si groups) in ]; caesium fluoride is an excellent source of anhydrous fluoride for such reactions. Removal of silicon groups (]) is a major application for CsF in the laboratory, as its ] nature allows clean formation of ]-sensitive intermediates. Solutions of caesium fluoride in ] or ] attack a wide variety of ] compounds to produce an organosilicon fluoride and a ], which can then react with ]s,<ref name="CRC"/> for example:<ref name="Fiorenza"/> |
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===Deprotection agent=== |
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Due to the strength of the ]–] bond, fluoride is useful for ] reactions, i.e., cleavage of Si-O bonds in ].<ref>{{OrgSynth |author=Smith, Adam P. |author2=Lamba, Jaydeep J. S. |author3=Fraser, Cassandra L. |name-list-style=amp |title=Efficient Synthesis of Halomethyl-2,2'-bipyridines: 4,4'-Bis(chloromethyl)-2,2'-bipyridine|volume=78|page=82 |year=2002|collvol= 10|collvolpages=107 |prep=v78p0082}}</ref> CsF is commonly used for such reactions. Solutions of caesium fluoride in ] or ] attack a wide variety of ] compounds to produce an organosilicon fluoride and a ], which can then react with ]s, for example:<ref name="Fiorenza"/> |
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Desilylation is also useful for the removal of ] ]s.<ref>Adam P. Smith, Jaydeep J. S. Lamba, and Cassandra L. Fraser “Efficient Synthesis of Halomethyl-2,2'-bipyridines: 4,4'-Bis(chloromethyl)-2,2'-bipyridine” Organic Syntheses, Vol. 78, p. 82 (2002); Collected Volume 10, p.107 (2004).</ref> |
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===Other uses=== |
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Single crystals of the salt are transparent into the deep ]. For this reason it is sometimes used as the windows of cells used for ]. |
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==Precautions== |
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==Precautions== |
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Like other soluble fluorides, CsF is moderately toxic.<ref name="msds-csf">. ''.'' MSDS Date: April 27, 1993. Retrieved on September 7, 2007.</ref> Contact with ] should be avoided, as this forms highly toxic/corrosive ]. Caesium ] (Cs<sup>+</sup>), or caesium chloride, is generally not considered toxic.<ref name="msds-cscl">"." ''.'' MSDS Date: January 16, 2006. Retrieved on September 7, 2007.</ref> |
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Like other soluble fluorides, CsF is moderately toxic.<ref name="msds-csf">{{cite web |url=http://www.hazard.com/msds/f2/bms/bmsqc.html |title=MSDS Listing for cesium fluoride |date=April 27, 1993 |website=hazard.com |access-date=September 7, 2007 |url-status=usurped |archive-url=https://web.archive.org/web/20120209103840/http://www.hazard.com/msds/f2/bms/bmsqc.html |archive-date=2012-02-09 }}</ref> Contact with ] should be avoided, as this forms highly toxic/corrosive ]. The caesium ] (Cs<sup>+</sup>) and ] are generally not considered toxic.<ref name="msds-cscl">{{cite web |url=http://hazard.com/msds/mf/baker/baker/files/c1903.htm |title=MSDS Listing for cesium chloride |date=January 16, 2006 |website=hazard.com |publisher=JT Baker |access-date=September 7, 2007 |url-status=usurped |archive-url=https://web.archive.org/web/20120313200630/http://hazard.com/msds/mf/baker/baker/files/c1903.htm |archive-date=2012-03-13 }}</ref> |
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==References== |
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==References== |
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{{reflist}} |
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==External links== |
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{{Authority control}} |
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{{Caesium compounds}} |
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{{Fluorides}} |
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{{Caesium compounds}} |
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