Caesium fluoride

Cubic

Cs, F

Colorless, crystalline solid

Fixed

4.12 g · cm -3

682 ° C

1251 ° C

Soluble in water ( 3670 g · l-1 at 18 ° C )

1,477

Risk

2.5 mg · m -3 ( as fluoride)

-555 KJ / mol

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Cesium fluoride ( CsF ), the cesium salt of the hydrofluoric acid. It is a colorless, hygroscopic crystalline solid which is readily soluble in polar solvents. It is used in chemistry next Tetraalkylammoniumfluoriden ( such as tetrabutylammonium fluoride TBAF) as a supplier of "naked " fluoride ions and mild base. It also has a pronounced ionic character and next to the unstable and rare Franciumfluorid is the connection between the two elements with the greatest difference in electronegativity.

Representation

Cesium can be obtained by reaction of hydrogen fluoride with cesium carbonate or cesium hydroxide and subsequent drying.

Properties

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

Only because of the relative lack of nucleophilicity of the fluoride ion cesium fluoride is used in the organic chemistry as a mild base, such as for the Knoevenagel reaction. It furthermore provides for desilylation, i.e. for the removal of silyl protecting groups, as due to the high bond energy of the Si -F bond is a strong tendency for the formation of the same is. In addition, cesium can dehydrate easily, so it can also be used for acid - and water-sensitive substrates.

Safety

The reaction with acid leads to formation of toxic hydrogen fluoride.