Alcohol can be converted to haloalkanes. Direct reaction with a hydrohalic acid rarely gives a pure product, instead generating ethers.  However, some exceptions are known: ionic liquids suppress the formation or promote the cleavage of ethers, hydrochloric acid converts tertiary alcohols to choloroalkanes, and primary and secondary alcohols convert similarly in the presence of a Lewis acid activator, such as zinc chloride. The latter is exploited in the Lucas test.
In the laboratory, more active deoxygenating and halogenating agents combine with base to effect the conversion.  In the "Darzens halogenation", thionyl chloride  () with pyridine converts less reactive alcohols to chlorides. Both phosphorus pentachloride () and phosphorus trichloride () function similarly, and alcohols convert to bromoalkanes under hydrobromic acid or phosphorus tribromide (PBr). The heavier halogens do not require preformed reagents: A catalytic amount of  may be used for the transformation using phosphorus and bromine;  is formed in situ.  Iodoalkanes may similarly be prepared using red phosphorus and iodine (equivalent to phosphorus triiodide). 
One family of named reactions relies on the deoxygenating effect of triphenylphosphine.  In the Appel reaction, the reagent is tetrahalomethane and triphenylphosphine; the co-products are haloform and triphenylphosphine oxide.  In the Mitsunobu reaction, the reagents are any nucleophile, triphenylphosphine, and a diazodicarboxylate; the coproducts are triphenyl&shy;phosphine oxide and a hydrazodiamide.