Displacement reactions involving a halogen atom

Alkyl fluorides may be prepared in moderate yield by interaction of an alkyl bromide with anhydrous potassium fluoride in the presence of dry ethylene glycol as a solvent for the inorganic fluoride (e.g. Expt 5.61). A little alkene accompanies the alkyl fluoride produced and is readily removed by treatment with KBr/Br2 solution. 

The most widely used example of halogen exchange is provided by the preparation of alkyl iodides from chlorides or bromides using sodium iodide in a 

These halogen displacement reactions may be carried out under PTC conditions, and have been reviewed.91 

CAUTION Alkyl fluorides are said to be highly toxic. Great care should be taken not to inhale the vapours conduct the entire operation in an efficient fume cupboard. 

(1) Any fractionating column of moderate efficiency is satisfactory, e.g. a Dufton column (20 cm long containing a spiral 10 cm in length, 2 cm in diameter with 8 turns of the helix) or a Vigreux column (20-25 cm long). 

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