Two classes may be distinguished: the aldo-ketenes, including ketene itself, together with its monoalkyl derivatives and carbon suboxide, and the keto-ketenes which comprise the dialkyl ketenes.
The ketoketenes are coloured compounds, which undergo autoxidation readily, form ketene bases on the addition of pyridine and quinoline, and yield addition compounds with substances containing the C:N and C:0 groupings.
Ketene, CH, :CO, was discovered by N.
Dimethyli ketene, (CH3)2C :CO, obtained by the action of zinc on a-brom-isobutyryl bromide, is a yellowish coloured liquid.
Diethyl ketene, (C2H5)2C :CO, is formed on heating diethylmalonic anhydride (Staudinger, ibid.).