Cerium(III) Chloride
Properties
| State | Solid (anhydrous is hygroscopic; commonly heptahydrate) |
| Color | Colorless to pale yellow |
| Solubility | Very soluble in water (1000 g/L as heptahydrate); soluble in alcohols |
| Melting Point | 817 °C (anhydrous); heptahydrate loses water starting at 90 °C |
| Boiling Point | 1727 °C (anhydrous) |
About Cerium(III) Chloride
Cerium(III) chloride is one of those reagents that sat quietly on the lanthanide shelf for decades until Jean-Louis Luche showed in 1978 that adding CeCl3·7H2O to a sodium borohydride reduction in methanol changes the product distribution entirely. The ordinary problem with NaBH4 on an α,β-unsaturated ketone is that it gives a mixture of 1,2-reduction (carbonyl to allylic alcohol) and 1,4-conjugate reduction (saturating the C=C), and you usually want only the 1,2 product. Add a stoichiometric amount of CeCl3·7H2O — about 1 to 1.1 equivalents — and the Lewis-acidic Ce(III) coordinates to the carbonyl oxygen, raising the LUMO of the C=O to favor direct hydride attack at the carbonyl carbon while suppressing the conjugate addition pathway. The result is highly chemoselective 1,2-reduction of enones to allylic alcohols, often above 95:5 selectivity. The Luche reduction is now in every undergraduate organic textbook and is the default move in total synthesis when an enone needs to be reduced cleanly without touching the alkene. Beyond Luche, CeCl3 is a mild Lewis-acid catalyst for Mukaiyama aldol reactions, Friedel–Crafts acylations of activated arenes, and acetal formation under conditions that more aggressive Lewis acids like AlCl3 or BF3·OEt2 would damage. Structurally, the anhydrous compound is built on the UCl3-type hexagonal motif with Ce³⁺ in 9-coordinate tricapped trigonal-prismatic geometry — a coordination number that is characteristic of the early lanthanides and reflects the large ionic radius (1.196 Å for 9-coordinate Ce³⁺). The commercially common heptahydrate, CeCl3·7H2O, is what shows up in catalog jars; it loses water in stages on heating and converts cleanly to anhydrous CeCl3 only under thionyl chloride or vacuum/HCl conditions.
Where you'll encounter it
If you have ever weighed out a half-equivalent of cerium chloride heptahydrate and added it to a chilled methanolic NaBH4 reduction of an enone, you have run a Luche reduction — and the gentle effervescence of evolved H2 is the same in every lab. CeCl3·7H2O sits in the rare-earth section of every well-stocked synthesis lab, and 25 grams (roughly 0.067 mol) costs about the same as a comparable mass of common organocerium reagents. In materials chemistry, CeCl3 is the chloride precursor for YAG:Ce yellow phosphor synthesis — the workhorse phosphor that converts the 450 nm blue light of an InGaN LED chip into the broadband yellow centered at 550 nm that mixes back to white in mainstream LED lamps. In glass polishing, the related CeO2 is the abrasive of choice for optical surfaces, and CeCl3 is one of its synthesis precursors.
Common Uses
- Luche reduction (CeCl3·7H2O / NaBH4 in MeOH) for chemoselective 1,2-reduction of α,β-unsaturated ketones
- Mild Lewis-acid catalyst in Mukaiyama aldol reactions and Friedel–Crafts acylations of activated arenes
- Precursor to organocerium reagents (RCeCl2) for nucleophilic addition to ketones without enolization
- Chloride source in the synthesis of YAG:Ce yellow phosphor for white LED lighting
- Starting material for cerium metal production by electrolysis of molten CeCl3/KCl mixtures
Safety Information
GHS: H315 (skin irritation Cat. 2), H319 (eye irritation Cat. 2A), H335 (single-exposure respiratory irritation Cat. 3). Moderate dermal and ocular irritant; the heptahydrate is hygroscopic and the anhydrous form releases HCl on contact with moisture, which is the more reactive hazard. No specific OSHA PEL for CeCl3 — handle as a soluble lanthanide salt with standard nuisance-dust controls. Cerium has very low systemic toxicity (LD50 oral rat for CeCl3·7H2O is about 2,100 mg/kg), but inhalation of cerium dust over the long term has been associated with rare-earth pneumoconiosis in metal-grinding workers. Standard PPE: nitrile gloves, lab coat, splash goggles. Store the anhydrous form in a sealed container under inert atmosphere to prevent uptake of atmospheric water.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.