Facile Synthesis of Anhydrous Rare-Earth Trichlorides from their Oxides in Chloridoaluminate Ionic Liquids

Wide applications of anhydrous rare-earth (RE) trichlorides RECl3 in organometallic chemistry, for the synthesis of optical and magnetic materials, and as catalysts require a facile approach for their synthesis. The known methods use or produce toxic substances, are complicated and have limited reliability and upscaling. It has been shown that task-specific ionic liquids (ILs) can dissolve many metal oxides without special reaction conditions at moderate temperature, making the metals accessible to downstream chemistry. Using imidazolium chloridoaluminate ILs, pure crystalline anhydrous RECl3 (RE=La-Nd, Sm-Dy) can be synthesized in one step from RE oxides in high yield. The Lewis acidic IL acts as solvent and reaction partner. The by-product [Al4O2Cl10]2-, which was detected spectroscopically, remains in solution. The reacted IL can be removed quantitatively by washing. ILs with various imidazolium cations and AlCl3 content and the effect of temperature and reaction time were tested. Anhydrous rare-earth trichlorides RECl3 with high purity and yield are obtained by reacting rare-earth oxides RE2O3 with aluminum chloride AlCl3 containing ionic liquids at 175 degrees C. The easy-to-perform process provides a reliable and scalable alternative to the production of these difficult-to-access anhydrous chlorides. In contrast to previous approaches, neither high temperatures nor highly toxic substances are required.image