Cerium(III) chloride

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Cerium(III) chloride
Cerium(III) chloride
UCl3 without caption.png Cerium bromide (space filling) 2.png
Identifiers
CAS number 7790-86-5 YesY
18618-55-8 (heptahydrate)
PubChem 24636
ChemSpider 23038 YesY
UNII TH8E3IE00V N
ChEBI CHEBI:35458 YesY
Jmol-3D images Image 1
Properties
Molecular formula CeCl3
Molar mass 246.48 g/mol (anhydrous)
372.58 g/mol (heptahydrate)
Appearance fine white powder
Density 3.97 g/cm3
Melting point 817 °C (anhydrous)
90 °C (heptahydrate, decomp)
Boiling point 1727 °C
Solubility in water 100 g/100 ml
Solubility soluble in alcohol
Structure
Crystal structure hexagonal (UCl3 type), hP8
Space group P63/m, No. 176
Coordination
geometry
Tricapped trigonal prismatic
(nine-coordinate)
Hazards
EU classification Not listed
Flash point Non-flammable
Related compounds
Other anions Cerium(III) oxide
Cerium(III) fluoride
Cerium(III) bromide
Cerium(III) iodide
Other cations Lanthanum(III) chloride
Praseodymium(III) chloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

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,[1] though the heptahydrate CeCl3·7 H2O is known. It is highly soluble in water, and (when anhydrous) it is soluble in ethanol and acetone.[2]

Preparation of anhydrous CeCl3[edit]

Simple rapid heating of the hydrate alone may cause small amounts of hydrolysis.[3] A useful form of anhydrous CeCl3 can be prepared if care is taken to heat the heptahydrate gradually to 140 °C (284 °F) over many hours under vacuum.[2][4][5] 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 (752 °F) with 4–6 equivalents of ammonium chloride under high vacuum,[3][6][7][8] or by heating with an excess of thionyl chloride for three hours.[3][9] The anhydrous halide may alternatively be prepared from cerium metal and hydrogen chloride.[10][11] It is usually purified by high temperature sublimation under high vacuum.

Uses[edit]

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.[12]

Luche reduction[13] 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

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:[4]

CeCl3 directed alkylation reaction

It is reported that organolithiums work more effectively in this reaction than do Grignard reagents.[4]

References[edit]

  1. ^ 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.
  2. ^ a b Paquette, L. A. (1999). Coates, R. M.; Denmark, S. E. (eds.), ed. Handbook of Reagents for Organic Synthesis: Reagents, Auxiliaries and Catalysts for C-C Bond Formation. New York: Wiley. ISBN 0-471-97924-4. 
  3. ^ a b c Edelmann, F. T.; Poremba, P. (1997). Herrmann, W. A. (ed.), ed. Synthetic Methods of Organometallic and Inorganic Chemistry VI. Stuttgart: Georg Thieme Verlag. ISBN 3-13-103021-6. 
  4. ^ a b c Johnson, C. R.; Tait, B. D. (1987). "A cerium(III) modification of the Peterson reaction: methylenation of readily enolizable carbonyl compounds". Journal of Organic Chemistry 52 (2): 281–283. doi:10.1021/jo00378a024. ISSN 0022-3263. 
  5. ^ Dimitrov, Vladimir; Kostova, Kalina; Genov, Miroslav (1996). "Anhydrous cerium(III) chloride — Effect of the drying process on activity and efficiency". Tetrahedron Letters 37 (37): 6787–6790. doi:10.1016/S0040-4039(96)01479-7. 
  6. ^ Taylor, M. D.; Carter, P. C. (1962). "Preparation of anhydrous lanthanide halides, especially iodides". Journal of Inorganic and Nuclear Chemistry 24 (4): 387–391. doi:10.1016/0022-1902(62)80034-7. 
  7. ^ Kutscher, J.; Schneider, A. (1971). "Notiz zur Präparation von wasserfreien Lanthaniden-Haloge-niden, Insbesondere von Jodiden". Inorg. Nucl. Chem. Lett. 7 (9): 815. doi:10.1016/0020-1650(71)80253-2. 
  8. ^ Greenwood, N. N.; Earnshaw, A. (1984). Chemistry of the Elements. New York: Pergamon Press. ISBN 0-08-022056-8. 
  9. ^ Freeman, J. H.; Smith, M. L. (1958). "The preparation of anhydrous inorganic chlorides by dehydration with thionyl chloride". Journal of Inorganic and Nuclear Chemistry 7 (3): 224–227. doi:10.1016/0022-1902(58)80073-1. 
  10. ^ Druding, L. F.; Corbett, J. D. (1961). Journal of the American Chemical Society 83 (11): 2462–2467. doi:10.1021/ja01472a010. ISSN 0002-7863. 
  11. ^ Corbett, J. D. (1973). Rev. Chim. Minerale 10: 239. 
  12. ^ Mine, Norioki; Fujiwara, Yuzo; Taniguchi, Hiroshi (1986). "Trichlorolanthanoid (LnCl3)-catalyzed Friedel-Crafts alkylation reactions". Chemistry Letters 15 (3): 357–360. doi:10.1246/cl.1986.357. 
  13. ^ Luche, Jean-Louis; Rodriguez-Hahn, Lydia; Crabbé, Pierre (1978). "Reduction of natural enones in the presence of cerium trichloride". Journal of the Chemical Society, Chemical Communications (14): 601–602. doi:10.1039/C39780000601. 

Further reading[edit]

  • CRC Handbook of Chemistry and Physics (58th edition), CRC Press, West Palm Beach, Florida, 1977.
  • Anwander, R. (1999). Kobayashi, S. (ed.), ed. Lanthanides: Chemistry and Use in Organic Synthesis. Berlin: Springer-Verlag. pp. 10–12.