Cerium(III) chloride

Preparation of anhydrous CeCl₃

Simple rapid heating of the hydrate alone may cause small amounts of hydrolysis.

A useful form of anhydrous CeCl3 can be prepared if care is taken to heat the heptahydrate gradually to 140 °C over many hours under vacuum. 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 400 °C with 4–6 equivalents of ammonium chloride under high vacuum, or by heating with an excess of thionyl chloride for three hours. The anhydrous halide may alternatively be prepared from cerium metal and hydrogen chloride. It is usually purified by high temperature sublimation under high vacuum. Soxhlet extraction of with thf gives .

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.

Organic synthesis

Cerium(III) chloride is a reagent in several procedures used in organic synthesis. Luche reduction 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.

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:

It is reported that organolithium reagents work more effectively in this reaction than do Grignard reagents.

References

References

1. (2013). "The observation of scintillation in a hydrated inorganic compound: CeCl3·6H2O". Applied Physics Letters.
2. Paquette, L. A.. (1999). "Handbook of Reagents for Organic Synthesis: Reagents, Auxiliaries and Catalysts for C-C Bond Formation". Wiley.
3. (2008). "Single-crystal CeCl3(CH3OH)4: A new metal-organic cerium chloride methanol adduct for scintillator applications". Applied Physics Letters.
4. Edelmann, F. T.. (1997). "Synthetic Methods of Organometallic and Inorganic Chemistry". Georg Thieme Verlag.
5. Johnson, C. R.. (1987). "A cerium(III) modification of the Peterson reaction: methylenation of readily enolizable carbonyl compounds". Journal of Organic Chemistry.
6. Dimitrov, Vladimir. (1996). "Anhydrous cerium(III) chloride — Effect of the drying process on activity and efficiency". Tetrahedron Letters.
7. Taylor, M. D.. (1962). "Preparation of anhydrous lanthanide halides, especially iodides". Journal of Inorganic and Nuclear Chemistry.
8. Kutscher, J.. (1971). "Notiz zur Präparation von wasserfreien Lanthaniden-Haloge-niden, Insbesondere von Jodiden". Inorg. Nucl. Chem. Lett..
9. Greenwood, N. N.. (1984). "Chemistry of the Elements". Pergamon Press.
10. Freeman, J. H.. (1958). "The preparation of anhydrous inorganic chlorides by dehydration with thionyl chloride". Journal of Inorganic and Nuclear Chemistry.
11. Druding, L. F.. (1961). "Lower Oxidation States of the Lanthanides. Neodymium(II) Chloride and Iodide". Journal of the American Chemical Society.
12. Corbett, J. D.. (1973). "Reduced Halides of the Rare Earth Elements". Rev. Chim. Minérale.
13. (2022). "Cerium Fluorenyl Complexes Including CC Coupling Reactions". Organometallics.
14. Mine, Norioki. (1986). "Trichlorolanthanoid (LnCl₃)-catalyzed Friedel-Crafts alkylation reactions". Chemistry Letters.
15. (2021). "Encyclopedia of Reagents for Organic Synthesis".
16. Luche, Jean-Louis. (1978). "Reduction of natural enones in the presence of cerium trichloride". Journal of the Chemical Society, Chemical Communications.