Methods of Preparation of Haloalkanes

Haloalkanes can be built up from several different starting materials, and the route chosen usually depends on which alkyl halide is needed and how pure it must be. Three broad strategies are used in the laboratory:

• Starting from alcohols — the –OH group of an alcohol is swapped for a halogen using a halogen acid, a phosphorus halide, or thionyl chloride.
• Starting from hydrocarbons — an alkane is halogenated directly by a free-radical pathway, or an alkene is made to add on a hydrogen halide or a halogen molecule across its double bond.
• By halogen exchange — a halogen already present in one alkyl halide is swapped for a different halogen, which is especially useful for reaching alkyl iodides and alkyl fluorides that are otherwise hard to prepare directly. …