Cerium(III) chloride

Cerium(III) chloride (CeCl₃), also known as cerous chloride or cerium trichloride, is a compound of cerium and chlorine. It is a white hygroscopic salt; it rapidly absorbs water to form hydrates, which may be of variable composition.The hexa- and heptahydrate CeCl₃·7H₂O are known.<ref>Template:Cite journal</ref> All forms are highly soluble in water, and the anhydrous derivative is soluble in ethanol and acetone.<ref name="Paquette1999">Template:Cite book</ref><ref>Template:Cite journal</ref>

Preparation of anhydrous CeCl₃

Simple rapid heating of the hydrate alone may cause small amounts of hydrolysis.<ref name="EdelmannPoremba1997">Template:Cite book</ref>

A useful form of anhydrous CeCl₃ can be prepared if care is taken to heat the heptahydrate gradually to Template:Convert over many hours under vacuum.<ref name="Paquette1999" /><ref name="JohnsonTait1987">Template:Cite journal</ref><ref name="Dimitrov1996">Template:Cite journal</ref> This may or may not contain a little CeOCl from hydrolysis, but it is suitable for use with organolithium and Grignard reagents. Pure anhydrous CeCl₃ can be made by dehydration of the hydrate either by slowly heating to Template:Convert with 4–6 equivalents of ammonium chloride under high vacuum,<ref name="EdelmannPoremba1997" /><ref name="Taylor1962">Template:Cite journal</ref><ref name="KutscherSchneider1971">Template:Cite journal</ref><ref name="Greenwood1984">Template:Cite book</ref> or by heating with an excess of thionyl chloride for three hours.<ref name="EdelmannPoremba1997" /><ref name="Freeman1958">Template:Cite journal</ref> The anhydrous halide may alternatively be prepared from cerium metal and hydrogen chloride.<ref name="Druding1961">Template:Cite journal</ref><ref name="Corbett1973">Template:Cite journal</ref> It is usually purified by high temperature sublimation under high vacuum. Soxhlet extraction of Template:Chem2 with thf gives Template:Chem2.<ref>Template:Cite journal</ref>

Uses

Cerium(III) chloride can be used as a starting point for the preparation of other cerium salts, such as the Lewis acid cerium(III) trifluoromethanesulfonate.<ref>Template:Cite journal</ref>

Organic synthesis

Cerium(III) chloride is a reagent in several procedures used in organic synthesis.<ref>Template:Cite book</ref> Luche reduction<ref name="Luche1978">Template:Cite journal</ref> of alpha, beta-unsaturated carbonyl compounds has become a popular method in organic synthesis, where CeCl₃·7H₂O is used in conjunction with sodium borohydride. For example, carvone gives only the allylic alcohol 1 and none of the saturated alcohol 2. Without CeCl₃, a mixture of 1 and 2 is formed.

Luche reduction

It can also deprotect MEM group to alcohol in the presence of other acetal protecting groups (e.g. THP.)

Another important use in organic synthesis is for alkylation of ketones, which would otherwise form enolates if simple organolithium reagents were to be used. For example, compound 3 would be expected to simply form an enolate without CeCl₃ being present, but in the presence of CeCl₃ smooth alkylation occurs: <ref name="JohnsonTait1987" />

CeCl3 directed alkylation reaction

It is reported that organolithium reagents work more effectively in this reaction than do Grignard reagents.<ref name="JohnsonTait1987" />

Further reading

• CRC Handbook of Chemistry and Physics (58th edition), CRC Press, West Palm Beach, Florida, 1977.
• Template:Cite book