Aromatisation

Aromatisation, or aromatisation in British spelling, is the chemical process by which a non-aromatic compound or ring system becomes aromatic. This typically involves the formation of one or more conjugated, planar rings that satisfy Hückel's rule for aromaticity, usually with 4n + 2 π electrons. The term covers various pathways that convert aliphatic or partially unsaturated structures into stable aromatic systems.

Common mechanisms include dehydrogenation of cycloalkadienes to benzene, oxidative cyclization and rearrangement, and dehydrogenative cyclization that build polycyclic aromatic hydrocarbons. In practice, aromatisation can proceed via metal-catalyzed dehydrogenation, acid- or base-catalyzed steps, or oxidation using reagents such as oxygen, DDQ, or other oxidants. In biological systems, aromatisation occurs during the biosynthesis of aromatic compounds, where enzymes catalyze oxidation, cyclization, and rearrangement steps to generate phenylpropanoid, polyketide, and other aromatic structures.

Applications and significance span organic synthesis, materials science, and industrial chemistry. Aromatised rings are foundational in the production of dyes, pharmaceuticals, polymers, and agrochemicals. In petroleum refining, catalytic reforming or aromatisation converts low-octane hydrocarbons into aromatics, improving fuel quality. Aromatisation is often thermodynamically favorable due to the stability of aromatic systems, but some processes require substantial energy input and can yield undesired byproducts or environmental concerns, particularly with polycyclic aromatic compounds.

See also: aromatization, aromaticity, catalytic reforming.