ethenone

Ethenone, commonly known as ketene, is the simplest member of the ketene family, with the formula CH2=C=O. It features a cumulated C=C=O skeleton and is a highly reactive intermediate used in a range of organic transformations. In practice, ethenone is typically generated in situ from precursors because it is difficult to isolate and readily reacts with itself and with other reagents.

Preparation and handling: Ethenone is usually produced by the thermal decomposition (pyrolysis) of acetyl chloride or by dehydration of acyl chlorides, and it is then trapped in situ for immediate use. It is a colorless, volatile species at room temperature that reacts readily with water, alcohols, amines, and alkenes. Because of its high reactivity and propensity to dimerize or polymerize, it is not stored as a pure material.

Reactions and use: Hydration of ethenone affords acetic acid; reaction with alcohols yields esters, and reaction with amines gives amides. In organic synthesis, ethenone reacts with alkenes in a [2+2] cycloaddition to produce beta-lactones, providing a convenient route to four-membered ring systems. It also serves as an acetylating reagent for various derivatives, typically employed in situ due to its instability as a isolated compound.

Safety: Ethenone is a highly reactive and potentially hazardous intermediate. It should be prepared and used under stringent controls, in well-ventilated areas or closed systems, with appropriate protective equipment, and without attempting to handle it as a stable, isolated material.