Lanthanum(III) Chloride1

LaCl3.7H2O
(anhydrous)

[10099-58-8]  · Cl3La  · Lanthanum(III) Chloride  · (MW 245.26) (heptahydrate)

[17272-45-6]  · Cl3H14LaO7  · Lanthanum(III) Chloride  · (MW 371.40)

(mild Lewis acid for acetalization;2 selective reducing agent in association with NaBH43 or LiAlH4;4 preparation of organolanthanum reagents;5 catalyst for various acid mediated reactions6 -8)

Physical Data: triclinic crystals; mp (hydrate) 91 °C (dec); mp (anhyd) 852 °C; bp 1750 °C; density (anhyd) 3.8 g cm-3.

Solubility: 3.89 g L-1 in H2O; sol methanol, ethanol; anhydrous form sol pyridine.

Form Supplied in: white crystals, deliquescent.

Preparative Methods: anhydrous lanthanum chloride is obtained from the hydrate by refluxing in thionyl chloride, or by heating to 400 °C in a HCl stream (see also Cerium(III) Chloride). The reagent can also be prepared by treatment of a lanthanum benzoate suspension with dry ethereal HCl solution.9

Handling, Storage, and Precautions: anhydrous LaCl3 should be freshly prepared and used without delay. Oral toxicity: LD50 4.2 g kg-1 in rats.

Acetalization and Thioacetalization.

LaCl3 has been used in the preparation of acetals (eqs 1 and 2), though it is less efficient than Erbium(III) Chloride or ytterbium(III) chloride.2,10

The anhydrous form of LaCl3 permits the convenient production of thioacetals (eqs 3 and 4).11 Hindered (camphor) and aromatic (benzophenone) ketones react in low yield. Lanthanum trichloride is much less efficient than Samarium(III) Chloride for acetal cleavage.12

Regioselective Reduction of a,b-Unsaturated Carbonyl Compounds.

In the presence of Sodium Borohydride, a,b-unsaturated ketones are reduced to allylic alcohols in high yield (eq 5).3 In THF, Lithium Aluminum Hydride shows the same selectivity with both ketones and aldehydes (eq 6).4

Organolanthanum Reagents.

Upon treatment with 1 equiv of n-Butyllithium, anhydrous LaCl3 yields a reagent of reduced basicity and good nucleophilicity, similar to the analogous cerium reagent (eq 7).5 With Methyllithium, the reagent exhibits a good selectivity for additions to aldehydes in the presence of a ketone (eq 8). Lanthanum gives the highest selectivity of all the lanthanides tested.13

Catalytic Properties in Various Reactions.

The Diels-Alder cycloaddition of acrolein with n-butyl vinyl ether is catalyzed by lanthanum chloride.6 Cross-aldol reactions can be effected with ketene trimethylsilyl acetals and aldehydes. For instance, the trimethylsilyl ether of methyl 2-methylpropionate couples with benzaldehyde in the presence of catalytic amounts of LaCl3; a mixture of the protected and unprotected hydroxy esters is obtained (eq 9).7

A mixture of LaCl3 and Tin(II) Chloride condenses a-bromo ketones with aldehydes to form aldol products (eq 10). Although cerium chloride is preferred for most cases, lanthanum chloride offers a combination of the highest yield and satisfactory selectivity.8 With a,a-dibromo ketones, the same reagent mixture leads to oxyallyl cations which add to furan under mild conditions (see Cerium(III) Chloride).14


1. (a) Molander, G. A. CRV 1992, 92, 29. (b) Kagan, H. B.; Namy, J. L. T 1986, 42, 6573.
2. Luche, J. L.; Gemal, A. L. CC 1978, 976.
3. Gemal, A. L.; Luche, J. L. JACS 1981, 103, 5454.
4. Fukuzawa, S.; Fujinami, T.; Yamaguchi, S.; Sakai, S. JCS(P1) 1986, 1929.
5. Imamoto, T.; Kusumoto, T.; Tawarayama, Y.; Sugiura, Y.; Mita, T.; Hatanaka, Y.; Yokoyama, M. JOC 1984, 49, 3904.
6. Liao, S.; Yu, S.; Chen, Z.; Yu, D.; Shi, L.; Yang, R.; Shen, Q. J. Mol. Catal. 1992, 72, 209.
7. Vougioukas, A. E.; Kagan, H. B.; TL 1987, 28, 5513.
8. Fukuzawa, S.; Tsuruta, T.; Fujinami, T.; Sakai, S. JCS(P1) 1987, 1473.
9. Trombe, F.; Loriers, J.; Gaume-Mahn, F.; Henry La Blanchetais, C. Nouveau Traité de Chimie Minérale; Pascal, P., Ed.; Masson: Paris, 1959.
10. McMurry, J. E.; Bosch, G. K. JOC 1987, 52, 4885.
11. Garlaschelli, L.; Vidari, G. TL 1990, 31, 5815.
12. Ukaji, Y.; Koumoto, N.; Fujisawa, T. CL 1989, 1623.
13. Kauffmann, T.; Pahde, C.; Tannert, A.; Wingbermühle, D. TL 1985, 26, 4063.
14. Fukuzawa, S.; Fukushima, M.; Fujinami, T.; Sakai, S. BCJ 1989, 62, 2348.

Jean-Louis Luche

Université Paul Sabatier, Toulouse, France



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