Alkyliodide

Alkyliodide is a term used to describe alkyl iodides, a class of organoiodine compounds with the general formula R–I, where R is an alkyl group. They include simple species such as methyl iodide (CH3I) and longer-chain examples such as ethyl iodide and tert-butyl iodide. Alkyliodides are typically colorless liquids or solids at room temperature, with physical properties that depend on the length and branching of the alkyl group. The carbon–iodine bond is relatively weak and highly polarizable, which makes these compounds reactive toward nucleophiles and suitable substrates for various organic transformations.

Reactivity in alkyliodides is governed by the substituent on the carbon bearing iodine. Primary alkyl iodides predominantly undergo bimolecular nucleophilic substitution (SN2) with strong nucleophiles. Secondary alkyl iodides can react by either SN2 or, less commonly, SN1 pathways depending on the reaction conditions and the nucleophile. Tertiary alkyl iodides readily form carbocations and participate in SN1 reactions, though competing elimination can occur with certain bases. The high reactivity of the C–I bond also enables radical processes and the generation of organometallics such as Grignard reagents from alkyl iodides.

Preparation methods include conversion of alcohols to alkyl iodides using reagents such as phosphorus triiodide or hydroiodic acid, and halide exchange (Finkelstein reaction) from alkyl chlorides or bromides with sodium iodide in suitable solvents. Methyl iodide is often prepared by iodination of methanol or via dedicated iodination routes.

Safety and handling: alkyl iodides are generally toxic and can be volatile; methyl iodide is recognized as a potential carcinogen. Proper ventilation, protective equipment, and careful handling are essential. See also alkyl halides and iodoalkanes.