Concept
In organic chemistry, ethenone is the formal name for ketene, an organic compound with formula or . It is the simplest member of the ketene class. It is an important reagent for acetylations. Ethenone is a highly reactive gas (at standard conditions) and has a sharp irritating odour. It is only reasonably stable at low temperatures (−80 °C). It must therefore always be prepared for each use and processed immediately, otherwise a dimerization to diketene occurs or it reacts to polymers that are difficult to handle. The polymer content formed during the preparation is reduced, for example, by adding sulfur dioxide to the ketene gas. Because of its cumulative double bonds, ethenone is highly reactive and reacts in an addition reaction H-acidic compounds to the corresponding acetic acid derivatives. It does for example react with water to acetic acid or with primary or secondary amines to the corresponding acetamides. In industrial chemistry, ketene is produced by the dehydration reaction of acetic acid: C2H4O2 -> C2H2O + H2O On a laboratory scale it can be produced by the thermal decomposition of Meldrum's acid at temperatures greater than 200 °C. When passed through heated pipes or electrically heated metal (like copper) wires at 500-600 °C in the presence of carbon disulfide, acetone decomposes into methane and ethenone, with 95% yield. Ethenone was discovered at the same time by Hermann Staudinger (by reaction of bromoacetyl bromide with metallic zinc) The dehydration of acetic acid was reported in 1910. The thermal decomposition of acetic anhydride was also described. Ethenone has been observed to occur in space, in comets or in gas as part of the interstellar medium. Ethenone is used to make acetic anhydride from acetic acid. Generally it is used for the acetylation of chemical compounds. Ethenone reacts with methanal in the presence of catalysts such as Lewis acids (AlCl3, ZnCl2 or BF3) to give β-propiolactone.
