An alkyl halide is an organic compound consisting of an alkyl group bonded to a halogen atom; polyhalogen derivatives of alkanes are similar. They are prepared by direct halogenation of alkanes (except for the iodides), addition of hydrogen halides to alkenes, or halogenation of alcohols by hydrogen halides, phosphorus (III) halides, etc. Alkyl halides are used as solvents and as intermediates in chemical manufacture. The halogen atom is readily replaced by other nucleophiles such as hydroxide or cyanide. Elimination of hydrogen halides (base-catalyzed) yields alkenes.