Tetramethyl-1,3-cyclobutanedione [Precursor to Dimethyl Ketene]

Typical Procedure: Tetramethyl-1,3-cyclobutanedione is placed in the ketene generation apparatus, heated at 120 ℃, and sublimed, then thermally decomposed by means of the red heated Nichrome wire under the nitrogen atmosphere. Subsequently, the evolved gas is captured by means of a trap cooled in dry ice-acetone to obtain dimethylketene in about 60% yield. Dimethylketene is a yellowish liquid (bp 34 ℃) with characteristic odor, remarkable reactivity, and transforms into a solid dimer when allowed to stand at room temperature. On exposure to air it generates white solid peroxides and explodes with even the slightest stimulus. For this reason, its monomer is stored under nitrogen at -78 ℃ and it is used immediately.