Lithium Sand

Lithium sand is often used as a high surface area reducing agent or in the preparation of organo-lithium species.

Note: All manipulations with elemental lithium must be performed under an atmosphere of dry argon. Lithium sand is highly pyrophoric – ensure that appropriate fire and safety precautions are in place!

Step 1: Dry the Paraffin oil by stirring over finely ground CaH₂ overnight under an atmosphere of argon. You will need around 100 mL of oil for every 10 g of lithium.

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Drying the Paraffin oil over calcium hydride.

Step 2: Filter the suspension through a glass frit to remove the Ca(OH)₂ and excess CaH₂. See Filtration through Celite for more detailed information. a) Cycle a large glass fritted filter stick and round-bottomed Schlenk flask onto the line. Flame dry the apparatus to ensure that it is free of residual moisture. Once cooled to room temperature, backfill with argon and connect to the Schlenk flask containing the paraffin oil/CaH₂ slurry. b) Carefully rotate the apparatus 180° to pour the slurry onto the glass frit. c) Pull a static vacuum on the receiving flask to initiate the filtration. d) Repeat until all of the paraffin oil has been filtered. Replace the filter frit with a greased glass stopper under a flow of Argon, and then quench the residual solids in the filter frit with toluene/IPA (see Schlenk Line Safety for more information on quenching pyrophoric material).

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Removing the calcium hydroxide and excess calcium hydride by filtration through a frit.

Step 3: Cut up lithium rods into 1 inch lengths and add to the paraffin oil under a flow of argon. Remove excess oxide or nitride coating from the lithium prior to use to prevent contamination of the final lithium sand. Lower the Schlenk flask into an appropriate heating mantle or aluminium heating block (the temperatures required to melt the lithium are too high to use an oil bath). Begin heating the oil with magnetic stirring (∼ 200+ °C).

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Melting lithium rods.

Step 4: Once all of the lithium is molten, replace the glass stopper with an overhead homogeniser or Herschberg stirrer and begin dispersing the molten metal.

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Dispersing the molten lithium.

Step 5: Once all of the molten lithium metal has been evenly dispersed (it should look frothy, almost like a cappuccino), remove the overhead homogeniser or stirrer, replacing it with a greased glass stopper, and lower the heating mantle/block. Allow to cool fully to room temperature without stirring. If the lithium begins to coalesce, it may be necessary to repeat Step 4.

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Dispersed lithium sand floating on the oil.

Step 6: Filter the slurry through a glass frit to isolate the lithium sand (see Step 2 for more details).

 

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Filtering the lithium sand and oil through a frit.

Step 7: Once all of the Paraffin oil has been removed, replace the top transfer Schlenk flask with a rubber septum and wash the lithium sand with three portions of dry hexane (see Cannula Transfer for more information), repeating the filtering steps outlined above to remove the hexane each time.

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Washing the lithium sand with dry hexane.

Step 8: Replace the rubber septum with a greased Schlenk cap, and then transfer the filter frit onto a clean Schlenk flask that has previously been cycled onto the Schlenk line under a flow of argon. Dry the lithium sand thoroughly under vacuum. Pulling a vacuum from the bottom of the filter frit prevents the risk of fine lithium powder being sucked into the line.

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Drying the lithium sand under vacuum.

Step 9: Isolate the lithium sand in an argon glovebox. Quench all glassware used for the preparation of lithium sand with toluene/IPA (see Schlenk Line Safety).

 

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Isolated lithium sand.