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Ketenes

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in chemistry, a group of organic compounds which may be considered as internal anhydrides of acetic acid and its substitution derivatives. 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 aldo-ketenes are colourless compounds which are not capable of autoxidation, are polymerized by pyridine or quinoline, and are inert towards compounds containing the groupings C :N and C :O. 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. The ketenes are usually obtained by the action of zinc on ethereal or ethyl acetate solutions of halogen substituted acid chlorides or bromides. They are characterized by their additive reactions: combining with water to form acids, with alcohols to form esters, and with primary amines to form amides.

Ketene, CH, :CO, was discovered by N. T. M. Wilsmore (Jour. Chem. Soc., 1907, vol. 91, p. 1938) among the gaseous products formed when a platinum wire is electrically heated under the surface of acetic anhydride. It is also obtained by the action of zinc on bromacetyl bromide (H. Staudinger, Ber. 1908, 41, P594): At ordinary temperatures it is a gas, but it may be condensed to a liquid and finally solidified, the solid melting at -151 ° C. It is characterized by its penetrating smell. On standing for some time a brown-coloured liquid is obtained, from which a colourless liquid boiling at 126-127° C., has been isolated (Wilsmore, ibid., 1908, 93, p. 94 6). Although originally described as acetylketen, it has proved to be a cyclic compound (Ber., 1909, 4 2, p. 4908). It is soluble in water, the solution showing an acid reaction, owing to the formation of aceto-acetic acid, and with alkalis it yields acetates. It differs from the simple ketenes in that it is apparently unacted upon by phenols and alcohols. Dimethyli ketene, (CH3)2C :CO, obtained by the action of zinc on a-brom-isobutyryl bromide, is a yellowish coloured liquid. At ordinary temperatures it rapidly polymerizes (probably to a tetramethylcylobutanedione). It boils at 34° C. (750 (Staudinger, Ber. 1905, 38, p. 1 735; 1908, 41, p. 2208). Oxygen rapidly converts it into a white explosive solid. Diethyl ketene, (C2H5)2C :CO, is formed on heating diethylmalonic anhydride (Staudinger, ibid.). Diphenyl ketene, (C6H5)2C :CO, obtained by the action of zinc on diphenyl-chloracetyl chloride, is an orangered liquid which boils at 146° C. (12 mm.). It does not polymerize. Magnesium phenyl bromide gives triphenyl vinyl alcohol.