Alkylaation

Alkylation is a chemical reaction in which an alkyl group (a saturated carbon chain) is transferred to another molecule. The process alters the substrate’s reactivity and properties and is widely used in organic synthesis, petrochemistry, and biology. Mechanistically, alkylation is usually classified as electrophilic or nucleophilic.

Electrophilic alkylation involves an electron-rich substrate, typically an aromatic ring, reacting with an electrophilic alkylating agent in the presence of a Lewis acid. Friedel–Crafts alkylation is a classic example, using alkyl halides or olefins to form alkyl-substituted arenes. The reaction can suffer from polyalkylation and rearrangements, and selectivity is influenced by substituents and reaction conditions.

Nucleophilic alkylation proceeds when a nucleophile displaces a leaving group on an alkyl donor, commonly an alkyl halide or sulfate. Classic examples include the Williamson ether synthesis (alkoxide attacking a primary alkyl halide to give an ether) and the formation of tertiary amines or thioethers by alkylating nitrogen or sulfur nucleophiles.

Industrial relevance includes gasoline fuel production: alkylation units combine isobutane with light olefins to produce high-octane alkylate using sulfuric or hydrofluoric acid catalysts; newer catalysts aim to improve safety and environmental performance.

In biology and medicine, alkylation also describes the transfer of alkyl groups to nucleic acids or proteins by alkylating agents. Some agents are used in chemotherapy, while others are toxic or carcinogenic.

Overall, alkylation is a versatile tool across synthesis, industry, and biology, with selectivity governed by mechanism, catalysts, and reaction conditions.