Ketones

Ketones, in chemistry, organic compounds of the type R·CO·R′, where R, R′ = alkyl or aryl groups. If the groups R and R′ are identical, the ketone is called a simple ketone, if unlike, a mixed ketone. They may be prepared by the oxidation of secondary alcohols; by the addition of the elements of water to hydrocarbons of the acetylene type RC CH; by oxidation of primary alcohols of the type RR′CH·CH2OH:RR′·CH·CH2OH -> R·CO·R′ \+ H2O + H2CO2; by distillation of the calcium salts of the fatty acids, CnH2nO2; by heating the sodium salts of these acids CnH2nO2 with the corresponding acid anhydride to 190° C. (W. H. Perkin, Jour. Chem. Soc., 1886, 49, p. 322); by the action of anhydrous ferric chloride on acid chlorides (J. Hamonet, Bull. de la soc. chim., 1888, 50, p. 357),

2C2H5COCl | -> C2H5·CO·CH(CH3)·COCl  
---|---  
  | -> C2H5·CO·CH(CH3)·CO2H  
  | -> C2H5·CO·CH2·CH3;  
  
and by the action of zinc alkyls on acid chlorides (M. Freund, Ann., 1861, 118, p. 1), 2CH3COCl + ZnC(H3)2 = ZnCl2 \+ 2CH3·CO·CH3. In the last reaction complex addition products are formed, and must be quickly decomposed by water, otherwise tertiary alcohols are produced (A. M. Butlerow, Jahresb., 1864, p. 496; Ann. 1867, 144, p. 1). They may also be prepared by the decomposition of ketone chlorides with water; by the oxidation of the tertiary hydroxyacids; by the hydrolysis of the ketonic acids or their esters with dilute alkalis or baryta water (see Aceto-acetic Ester); by the hydrolysis of alkyl derivatives of acetone dicarboxylic acid, HO2C·CH2·CO·CHR·CO2H; and by the action of the Grignard reagent on nitriles (E. Blaise, Comptes rendus, 1901, 132, p. 38),

R·CN + R′MgI -> RR′C:N·MgI -> R·CO·R′ \+ NH3 \+ MgI·OH.

The ketones are of neutral reaction, the lower members of the series being colourless, volatile, pleasant-smelling liquids. They do not reduce silver solutions, and are not so readily oxidized as the aldehydes. On oxidation, the molecule is split at the carbonyl group and a mixture of acids is obtained. Sodium amalgam reduces them to secondary alcohols; phosphorus pentachloride replaces the carbonyl oxygen by chlorine, forming the ketone chlorides. Only those ketones which contain a methyl group are capable of forming crystalline addition compounds with the alkaline bisulphites (F. Grimm, Ann., 1871, 157, p. 262). They combine with hydrocyanic acid to form nitriles, which on hydrolysis furnish hydroxyacids,

(CH2)2CO -> (CH3)2C·OH·CN -> (CH3)2·C·OH·CO2H;

with phenylhydrazine they yield hydrazones; with hydrazine they yield in addition ketazines RR′·C:N·N:C·RR′ (T. Curtius), and with hydroxylamine ketoximes. The latter readily undergo the “Beckmann” transformation on treatment with acid chlorides, yielding substituted acid amides.

RR′·C:NOH -> RC(NR′)·OH -> R·CO·NHR′

(see Oximes, also A. Hantzsch, Ber., 1891, 24, p. 13). The ketones react with mercaptan to form mercaptols (E. Baumann, Ber., 1885, 18, p. 883), and with concentrated nitric acid they yield dinitroparaffins (G. Chancel, Bull. de la soc. chim., 1879, 31, p. 503). With nitrous acid (obtained from amyl nitrite and gaseous hydrochloric acid, the ketone being dissolved in acetic acid) they form isonitrosoketones, R·CO·CH:NOH (L. Claisen, Ber., 1887, 20, pp. 656, 2194). With ammonia they yield complex condensation products; acetone forming di- and tri-acetonamines (W. Heintz, Ann. 1875, 178, p. 305; 1877, 189, p. 214). They also condense with aldehydes, under the influence of alkalis or sodium ethylate (L. Claisen, Ann., 1883, 218, pp. 121, 129, 145; 1884, 223, p. 137; S. Kostanecki and G. Rossbach, Ber., 1896, 29, pp. 1488, 1495, 1893, &c.). On treatment with the Grignard reagent, in absolute ether solution, they yield addition products which are decomposed by water with production of tertiary alcohols (V. Grignard, Comptes rendus, 1900, 130, P. 1322 et seq.),

RR′CO -> RR′·C(OMgI)·R″ -> RR′R″·C(OH) + MgI·OH.

Ketones do not polymerize in the same way as aldehydes, but under the influence of acids and bases yield condensation products; thus acetone gives mesityl oxide, phorone and mesitylene (see below).

For dimethyl ketone or acetone, see Acetone. Diethyl ketone, (C2H5)2·CO, is a pleasant-smelling liquid boiling at 102.7° C. With concentrated nitric acid it forms dinitroethane, and it is oxidized by chromic acid to acetic and propionic acids. Methylnonylketone, CH3·CO·C9H19, is the chief constituent of oil of rue, which also contains methylheptylketone, CH3·CO·C7H15, a liquid of boiling-point 85-90° C. (7 mm.), which yields normal caprylic acid on oxidation with hypobromites.

Mesityl oxide, (CH3)2C:CH·CO·CH3, is an aromatic smelling liquid of boiling point 129.5-130° C. It is insoluble in water, but readily dissolves in alcohol. On heating with dilute sulphuric acid it yields acetone, but with the concentrated acid it gives mesitylene, C9H12. Potassium permanganate oxidizes it to acetic acid and hydroxyisobutyric acid (A. Pinner, Ber., 1882, 15, p. 591). It forms hydroxyhydrocollidine when heated with acetamide and anhydrous zinc chloride (F. Canzoneri and G. Spica, Gazz. chim. Ital., 1884, 14, p. 349). Phorone, (CH3)2C:CH·CO·CH:C(CH3)2, forms yellow crystals which melt at 28° C. and boil at 197.2° C. When heated with phosphorus pentoxide it yields acetone, water and some pseudo-cumene. Dilute nitric acid oxidizes it to acetic and oxalic acids, while potassium permanganate oxidizes it to acetone, carbon dioxide and oxalic acid.

Diketones.—The diketones contain two carbonyl groups, and are distinguished as α or 1.2 diketones, β or 1.3 diketones, γ or 1.4 diketones, &c., according as they contain the groupings -CO·CO-, -CO·CH2·CO-, -CO·CH2·CH2·CO-, &c.

The α-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·C:(N·OH)·CH3 -> CH3·CO·C:(NHSO3)·CH3 -> CH3·CO·CO·CH3; or by the action of isoamyl nitrite on the isonitrosoketones (O. Manasse, Ber., 1888, 21, p. 2177), C2H5·CO·C = (NOH)·CH3 \+ 11C5HONO = C2H5·CO·CO·CH3 \+ C5H11OH + N2O. 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 β-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 αγ-dimethyl quinoline.

The γ-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 dehydrating agent, the thiophenes by heating with phosphorus pentasulphide, and the pyrrols by the action of alcoholic ammonia or amines. Acetonyl acetone, CH3·CO·CH2·CH2·CO·CH3, a liquid boiling at 194° C., may be obtained by condensing sodium aceto-acetate with mono-chloracetone (C. Paal, Ber., 1885, 18, p. 59),

CH3COCH2Cl + Na·CH·COCH3(COOR)  
---  
-> CH3CO·CH2·CH·COCH3(COOR)  
-> CH3CO·CH2·CH2·COCH3;  
  
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 β-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)·CO·C6H5], gives pentaphenylpyridine, NC5(C6H5)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).