Cerium(III) chloride (CeCl₃), also known as cerous chloride or cerium trichloride, is a compound of cerium and chlorine. It is a white hygroscopic solid; It rapidly absorbs water on exposure to moist air to form a hydrate which appears to be of variable composition^[2], though the heptahydrate CeCl₃.7 H₂O is known. It is highly soluble in water_(molecule), and (when anhydrous) it is soluble in ethanol and acetone^[4].

Preparation of anhydrous CeCl₃

Simple rapid heating of the hydrate alone may cause small amounts of hydrolysis ^[1]. 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^[4],[5],[9]. 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^[1],[6],[12], or by heating with an excess of thionyl chloride for three hours^[1],[7]. The anhydrous halide may alternatively be prepared from cerium metal and hydrogen chloride ^[8]. It is usually purified by high temperature sublimation under high vacuum.

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 , used for Friedel-Crafts acylations. It is also used itself as a Lewis acid, for example as a catalyst in Friedel-Crafts alkylation reactions.^[10]

[['Luche reduction]]^[11] of alpha, beta-unsaturated carbonyl compounds has become a popular method in organic synthesis, where CeCl₃.6H₂O 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.

Another important use in organic synthesis is for alkylation of ketones which would otherwise form enolates if simple organolithiums or Grignard 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^[5]:

It is reported^[5] that organolithiums work more effectively in this reaction than do Grignard reagents.

Suppliers

Aldrich: http://www.sigmaaldrich.com

Lancaster: http://www.structuresearch.com:8080/catalog/displayproduct.jsp?prodid=10864

Strem: http://www.strem.com/code/index.ghc

Alfa: http://www.alfa.com/alf/index.htm

GFS: http://www.gfschemicals.com/productcatalog/Rare_Earth_Compounds.asp

In the US, several of these suppliers also distribute through

Fisher: https://www1.fishersci.com/index.jsp

or VWR: http://www.vwr.com/index.htm

References

1. F. T. Edelmann, P. Poremba, in: Synthetic Methods of Organometallic and Inorganic Chemistry, (W. A. Herrmann, ed.), Vol. 6, Georg Thieme Verlag, Stuttgart, 1997.
2. Several major manufacturers such as Alfa and Strem list their products simply as a "hydrate" with "xH₂O" in the formula, but Aldrich sells a heptahydrate.
3. CRC Handbook of Chemistry and Physics (58th edition), CRC Press, West Palm Beach, Florida, 1977.
4. L. A. Paquette, in: Handbook of Reagents for Organic Synthesis: Reagents, Auxiliaries and Catalysts for C-C Bond Formation, (R. M. Coates, S. E. Denmark, eds.), Wiley, New York, 1999.
5. C. R. Johnson, B. D. Tait, J. Org. Chem. 52, 281-283 (1987).
6. M. D. Taylor, P. C. Carter, J. Inorg. Nucl. Chem. 24, 387 (1962); J. Kutscher, A. Schneider, Inorg. Nucl. Chem. Lett. 7, 815 (1971).
7. J. H. Freeman, M. L. Smith, J. Inorg. Nucl. Chem. 7, 224 (1958).
8. L. F. Druding, J. D. Corbett, J. Am. Chem. Soc. 83, 2462 (1961); J. D. Corbett, Rev. Chim. Minerale 10, 239 (1973).
9. V. Dimitrov, K. Kostova, M. Genov, Tetrahedron Letters, 37, 6787 (1996).
10. N. Mine et al., Chem. Lett., 357-360 (1986).
11. J-L. Luche, L. Rodriguez-Hahn, P. Crabbe, J. Chem. Soc. Chem. Commun., 601-602 (1978).
12. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, 1984.
13. R. Anwander, in Lanthanides: Chemistry and Use in Organic Synthesis, (S. Kobayashi, ed.), Springer-Verlag, Berlin, 1999, p10-12.