Ketyl

[1] Ketyls can be formed as radical anions by one-electron reduction of carbonyls with alkali metals.

Sodium and potassium metal reduce benzophenone in THF solution to the soluble ketyl radical.

The ketyl radicals derived from the reaction of sodium and benzophenone is a common laboratory desiccant.

The method for drying is still popular in many laboratories due to its ability to produce such pure solvent quickly.

[3] When excess alkali metal is present, benzophenone ketyl may be reduced to the ketone dianion, resulting in a color transformation from deep blue to purple:[4]: 899–900

Before: Toluene is refluxed with sodium-benzophenone to dry and deoxygenate it.
After: The deep blue coloration of the benzophenone ketyl radical shows that the toluene to be distilled is dry and oxygen-free.