DIKETONES  .—The diketones contain two carbonyl

groups, and are distinguished as a or 1.2 diketones, (3 or 1.3 diketones, 7 or 1.4 diketones, &c., according as they contain the groupings -CO . CO-, -CO . CH2•CO-,-CO•CH2•CH2•CO-, &c . The a-diketones may be prepared by boiling the product of the action of alkaline bisulphites on isonitrosoketones with 15 % sulphuric acid (H. v . Pechmann, Ber.,1887, 20, p . 3112 ; 1889, 22, p . 2115), CH3.CO.0 :(N•OH)•CH3 CH3.CO.0 :(NHSO3) •CH3 ->CH3-CO--CO.CH3; or by the action of isoamyl nitrite on the isonitrosoketones (O . Manasse, Ber., 1888, 21, P-2177), C2H6•CO•C :(NOH)•CH3-+nC6HONO= C2H6•CO•CO•CH3+C5HnOH+N20 . They condense with orthodiamines to form quinoxalines (O . Hinsberg, Ann., 1887,237, p . 327), and with ammonia and aldehydes to form imidazoles . Diacetyl, CH3•CO•CO•CH3, is a yellowish green liquid,which boils at 87-88°C., and possesses a pungent smell .

It combines with

sodium bisulphite and with hydrocyanic acid . Dilute alkalis convert it into paraxyloquinone . The -diketones form characteristic copper salts, and in alcoholic solution they combine with semicarbazide to form products which on boiling with ammoniacal silver nitrate solution give pyrazoles (T . Posner, Ber., 1901, 34, p . 3975); with hydroxylamine they form isoxazoles, and with phenylhydrazine pyrazoles . Acetyl acetone, CH3•CO•CH2•CO•CH3, may be prepared by the action of aluminium chloride on acetyl chloride, or by condensing ethyl acetate with acetone in the presence of sodium (L . Claisen) . It is a liquid of boiling point 136° C . It condenses readily with aniline to give ay-dimethyl quinoline . The 7-diketones are characterized by the readiness with which they yield furfurane, pyrrol and thiophene derivatives, the furfurane derivatives being formed by heating the ketones with a de-4 hydrating agent, the thiophenes by heating with phosphorus pentasulphide, and the pyrrols by the action of alcoholic ammonia or amines . Acetonylacetone,CH3•CO•CH2•CH2•CO•CH3,aliquid boiling at 194° C., may be obtained by condensing sodium aceto-acetate with mono-chloracetone (C . Paal, Ber., 1885, 18, p .

59), CH 3000H2C1+Na•CH •COCH3(COOR) - > CH3CO•CH2•CH •COCH3(COOR) — CH3CO•CH2•CH2•000H3; or by the

hydrolysis of diaceto-succinic ester, prepared by the action of iodine on sodium aceto-acetate (L . Knorr, Ber., 1889, 22, pp . 169, 2100) . 1.5 diketones have been prepared by L . Claisen by condensing ethoxymethylene aceto-acetic esters and similar compounds with 0-ketonic esters and with 1.3 diketones . The ethoxymethylene aceto-acetic esters are prepared by condensing aceto-acetic ester with ortho-formic ester in the presence of acetic anhydride (German patents 77354, 79087, '79863) . The 1.5 diketones of this type, when heated with aqueous ammonia, form pyridine derivatives . Those in which the keto groups are in combination with phenyl residues give pyridine derivatives on treatment with hydroxylamine, thus benzamarone, C6H5CH[CH(C6H5)•C0•C6H5], gives pentaphenylpyridine, NC5(CBH5)5 . On the general reactions of the 1.5 diketones, see E . Knoevenagel (Ann., 1894, 281, p . 25 et seq.) and H . Stobbe (Ber., 1902, 35, p .

1445) . Many cyclic ketones are known, and in most respects they resemble the

ordinary aliphatic ketones (see POLYMETHYLENES; TERPENES) .