12dicarbonyls

1,2-dicarbonyls, sometimes written as 12-dicarbonyls, are a class of organic compounds featuring two carbonyl groups on adjacent carbon atoms. They may be aldehydes, ketones, or a mixture of both. The simplest member is glyoxal (ethanedial, OHC-CHO). Other well-known examples include diacetyl (2,3-butanedione) and methylglyoxal (2-oxopropanal). The proximity of two carbonyls on neighboring carbons increases electrophilicity and facilitates enolization, influencing their reactivity toward nucleophiles such as amines, hydrazines, and thiols to form imines, hydrazones, or related adducts. They also participate in aldol condensations and, for aldehyde-containing members lacking alpha-hydrogens, Cannizzaro reactions.

Applications and occurrence: in organic synthesis as versatile building blocks; diacetyl is used as a flavoring agent and fragrance, imparting buttery notes; methylglyoxal is a metabolic and environmental intermediate. In biology, reactive 1,2-dicarbonyls contribute to dicarbonyl stress by modifying proteins and nucleic acids, forming advanced glycation end products.

Synthesis and handling: glyoxal is produced industrially by oxidation of ethylene glycol; many other 1,2-dicarbonyls are prepared by oxidation of vicinal diols or related precursors. They are typically moisture- and air-sensitive and can be lachrymatory or irritant; proper handling and safety measures are required.