GLYCOLS).
(2) Addition Products.—Such products are formed less readily by ketones than by aldehydes. Water and the alcohols do not combine with ketones, but the latter and the mercaptans form addition compounds, the mercaptols, such as (CH3)2C(SC2H5)2 from acetone and ethyl mercaptan. This mercaptol on oxidation furnishes the drug sulphonal. Grignard reagents (q.v.) add on to ketones, and the products when decomposed by water give rise to tertiary alcohols. Hydrogen cyanide and ketones give rise to nitriles hydrolysable to hydroxycarboxylic acids, and ketones con taining the group unite with sodium hydrogen sulphite yielding bisulphite compounds from which the ketone can be regenerated by aqueous sodium carbonate.
(3) Condensation Products.—Ketones condense with hydrox ylamine, giving ketoximes although not always so readily as aldehydes give aldoximes. With a mixed ketone, R.CO.R', two oximes, R.CR':NOH, are obtained, the isomerism of which is usually explained by assuming a different spatial arrangement of the groups R, R' and OH about the doubly-linked residue :C:N. (Hantzsch and Werner, 189o). In studying the stereoisomeric oximes (see STEREOCHEMISTRY), considerable use has been made of a characteristic chemical change undergone by ketoximes, known as the Beckmann rearrangement (i886), which results in each of these isomeric oximes, R.CR':NOH, changing into the corresponding amide, R.CO.NHR' or R'CO.NHR (see OximEs). This change is effected by phosphorus pentachloride, benzene sulphonyl chloride or warm concentrated sulphuric acid. Ketones condense with phenyihydrazine and other hydrazines to yield char acteristic hydrazones which are useful for the purposes of isola tion and identification.
Diacetyl, the simplest member of the I :2 or a-diketones, is a yellowish-green liquid boiling at 88° C and of specific gravity 0.9734 at 22° C. It is found in the aqueous distillates of many essential oils, for example, bay, cedarwood, iris and sandalwood oils, to which it communicates its colour and quinone-like odour. Diacetyl polymerizes to a trimeric form, and with warm alkali it condenses to form para-xyloquinone. Diacetyl is made from methyl ethyl ketone by treatment of this ketone with amyl nitrite and subsequent hydrolysis of the result ing diacetyl-monoxime with dilute sulphuric acid. Diacetyldi
oxime or dimethylglyoxime is prepared by acting on methyl ethyl ketone successively with amyl nitrite in presence of hydrogen chloride and with hydroxylamine chloride. The dioxime separates from alcohol in colourless crystals melting with partial sublimation at 245-246° C; it is insoluble in water, but dissolves readily in alcohol or ether.
Acetylacetone, the simplest member of the i :3- or /3-diketones, is a colourless pungent liquid boiling at 139° C. It is soluble in eight parts of water and miscible in all proportions with alcohol, ether or chloroform. It is regarded as an equilibrium mixture of two isomeric forms, and : CH.CO-CH3, the latter predominating. Acetylacetone is prepared by adding successively ethyl acetate and acetone to sodium wire under dry ether. The mixture is left for some hours in a freezing mixture and then acidified, the (3-diketone being isolated in the form of its copper derivative. The metallic derivatives of acetyl acetone have remarkable properties ; they are usually insoluble in water but soluble in organic media, they are generally non ionized, and are sometimes volatile without decomposition. The condensation products of acetylacetone with the chlorides of non metals are also of interest (cf. Beilstein's Handbuch der Orga nischen Chemie, 4th ed., 1918, vol. 1, pp. Acetonylacetone, the lowest member of the 1 :4- or 'y-diketone class, is a colourless liquid, boiling at 194° C and solidifying to leaflets which melt at —9° C. It is miscible in all proportions with water, alcohol or ether. In its preparation, 2 mols. of ethyl sodioacetoacetate are condensed together by means of iodine and the resulting diethyl diacetylsuccinate is hydrolysed with warm dilute caustic soda. Acetonylacetone is chiefly of interest when it reacts in its dienolic form, :CH with fuming hydrochloric acid, zinc chloride or acetic anhydride to yield dimethylfuran (see FURFURAL), with phosphorus pen tasulphide to give dimethylthiophen, and with ammonia to fur nish dimethylpyrrole. These reactions afford general methods for passing from open-chain to cyclic organic compounds.
For a comprehensive essay on ketones see T. E. Thorpe, Dictionary of Applied Chemistry (1922, vol. iii.). (G. T. M.)