Anhydrous Cerium(III) chloride + LiBr solution in THF

 

LiBr 24.5g (282 mmol) was dried in a 0.5L RB flask on highvac (0.2 Torr) at 150C for 12h (overnight), then cooled under Ar to RT and anh THF 0.4L was added via cannula. The the mixture was stirred under Ar until complete dissolution (20 min).

Meanwhile, powdered CeCl3.7H2O 47.5g (Aldrich; 127.5 mmol) was combined with re-distilled thionyl chloride 175mL (2.4 mol) in a 0.5L flask equipped with an efficient reflux condenser topped with a gas outlet tube (vented into a large Erlenmeyer flask filled with soda lime pellets). The mixture was placed on a 70C bath and stirred vigorously for 2 hours; at the end  of this period the gas evolution and SOCl2 reflux nearly ceased. The bath temperature was then raised to 110C and the slurry was refluxed for 12 hours (overnight). The condenser was replaced with a short-path distillation head and the unreacted thionyl chloride was recovered by distillation from a 110C bath. The solid residue remaining in the distillation flask was  briefly dried by using a teflon pump at 10 Torr at 110C/15 min and then flushed with Ar. The bath temperature was raised to 200C and a stream of dry Ar was passed into the flask through the septa for 1 hour at 200C. The solid was further dried on highvac (0.2Torr) at 200C for 12 hours. The obtained anhydrous CeCl3 (a fine white heavy powder) was cooled to 0C under Ar, the anh LiBr THF solution was added via cannula with stirring, the cooling bath was removed and the mixture volume in the flask was adjusted with additional anh THF to about 0.5L total volume. The mixture was then stirred at RT to a complete dissolution (6-12 hours), then used as such.

This procedure yields 0.5L of aprox 0.25M CeCl3.2LiBr in THF as a yellow cloudy solution. The trace amount of a very fine insoluble material present in the mixture can be removed by sedimentation but for most applications this seems unnecessary.

Note 1: The used SOCl2 was re-distilled before use because a new bottle of Aldrich’s “Low Fe 99.5% SOCl2″ came brightly colored. (Don’t listen to Aldrich tech support folks telling you that pure SOCl2 is canary-yellow according to ther specification). The used THF was a common Aldrich BHT-stabilised anhydrous Sure-Seal grade.

Note 2: LiBr and CeCl3.7H2O are hygroscopic and must be stored in a tight bottle. (CeCl3.7H2O powders up very nicely with a mortar and pestle but a soggy material is difficult to use in this procedure). Care was taken to avoid contaminating the flask joints when loading up the solids as this could cause the joints to seize or leak.