Cesium fluoride

Crystal structure
__ Cs +      __ F -
Crystal system	cubic
Space group	Fm 3 m (No. 225)
Coordination numbers	Cs [6], F [6]
General
Surname	Cesium fluoride
Ratio formula	CsF
Brief description	colorless, crystalline solid
External identifiers / databases
CAS number 13400-13-0 EC number 236-487-3 ECHA InfoCard 100.033.156 PubChem 25953 Wikidata Q50694
properties
Molar mass	151.90 g mol −1
Physical state	firmly
density	4.12 g cm −3
Melting point	682 ° C
boiling point	1251 ° C
solubility	soluble in water (3670 g l −1 at 18 ° C)
Refractive index	1.477
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 301-311-314-331 P: 261-280-301 + 310-305 + 351 + 338-310
MAK	2.5 mg m −3 (as fluoride)
Thermodynamic properties
ΔH f 0	−555 kJ / mol
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Cesium fluoride ( CsF ) is the cesium salt of hydrofluoric acid . It is a colorless, hygroscopic , crystalline solid that dissolves well in polar solvents. In addition to tetraalkylammonium fluorides (such as tetrabutylammonium fluoride TBAF), it is used in chemistry as a supplier of “naked” fluoride ions and mild bases . In addition, it has a strongly pronounced ionic character and, in addition to the unstable and rare francium fluoride, is the combination of the two elements with the greatest possible difference in electronegativities .

presentation

Cesium fluoride can be obtained by reacting hydrogen fluoride with cesium carbonate or cesium hydroxide and then drying.

${\displaystyle {\ce {Cs2CO3 + 2HF -> 2CsF + CO2 ^ + H2O}}}$

${\displaystyle {\ce {CsOH + HF -> CsF + H2O}}}$

properties

Watch glass bowl with a cesium fluoride sample

Because of its good solubility and easy availability, cesium fluoride can be used as a fluoride ion donor . It is more soluble than its relatives with the smaller alkali metals sodium and potassium .

Because of the only slightly pronounced nucleophilicity of the fluoride ions, cesium fluoride is used as a mild base in organic chemistry , e.g. B. in the Knoevenagel reaction . It is also used for desilylation, i.e. H. for the removal of silyl - protective groups , since due to the high bond energy of Si-F bond is a strong tendency to form consists Selbiger. In addition, cesium fluoride can be dehydrated without any problems, so that it can also be used on acid and water-sensitive substrates.

safety instructions

The reaction with acids leads to the formation of toxic hydrogen fluoride .

Individual evidence

1. ↑ ^{a b c d e f} data sheet cesium fluoride at AlfaAesar, accessed on February 3, 2010 ( PDF )(JavaScript required) . .
2. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Index of Refraction of Inorganic Crystals, pp. 10-246.
3. ↑ ^{a b} data sheet cesium fluoride from Sigma-Aldrich , accessed on March 15, 2011 ( PDF ).
4. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 1170.

literature

• GK Friestad, BP Branchaud, in: Handbook of Reagents for Organic Synthesis: Acidic and Basic Reagents , (HJ Reich, JH Rigby, eds.), Pp. 99-103, Wiley, New York, 1999.
• L. Rand, JV Swisher, CJ Cronin, Journal of Organic Chemistry , 27 , p. 3505 (1962).
• M. Fiorenza, A. Mordini, S. Papaleo, S. Pastorelli, A. Ricci, Tetrahedron Letters , 26 , p. 787 (1985).
• Evans FW, Litt MH, Weidler-Kubanek AM, Avonda FP, Journal of Organic Chemistry , 33 , pp. 1837-1839 (1968).