Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/580

Rh 568 CHEMISTRY [OEGANIC. Of the aldehydes of the aromatic series mention may be made of benzoic aldehyde, which can be obtained from bitter-almond oil; cumic aldehyde, existing in oil of cumin; salicylic aldehyde, which exists in the flowers of &quot; meadow sweet;&quot; and cinnamic aldehyde, the chief constituent of the oils of cassia and cinnamon. The aromatic aldehydes, by the action of ammonia, are converted into hydramides of the general formula (C n H 2n _ T CH) 3 &quot;N 2 VII. KETONflS. These compounds are derived from secondary alcohols, in the same manner that aldehydes are derived from primary alcohols : (C B H 2B+1 ) 2 CH.OH _ H 2 = (C n H 2n+1 ) 2 CO. Secondary alcohol. Ketone. The ketones may thus be regarded as compounds of C n H 2n+1, &c., radicles with CO, or as aldehydes in which the H of the COH group is replaced by such radicles. The compounds of this family bear considerable resem blance to the aldehydes, but are distinguished by their behaviour on oxidation, for whereas the aldehydes are readily converted into acids containing the same number of carbon atoms, the ketones are converted (with some difficulty) into a mixture of two acids of the C n H 2n+ r COOH series, each containing a smaller number of carbon atoms. The law of the oxidation of ketones appears to be that the less complex of the two hydrocarbon radicles remains attached to the CO ; thus Methyl-pentyl ketone. 3O = CH 3 .COOH Acetic acid. C 4 H 9 .COOH Valeric acid. Ketones are converted by the action of nascent hydiogen into secondary alcohols (see p. 563). The ketones are liable to isomeric modification depending on the isomerism of their contained hydrocarbon radicles. {CH j| (methyl propyl ketone) is iso- {CT~T CH(CH ) ( metli yl-P seuclo P ro Pyl ketone). Furthermore, there can be metamerism among ketones owing to the presence of different radicles in the molecule, and every ketone is metameric with an aldehyde of the same series. Thus, the following are metameric : Methyl-butyl ketone. Ethyl-propyl ketone. . Hexyl aldehyde Ketoues corresponding to the general formulae CO(C n H 2n + 1 ) 2 ,Co{^J^S and CO(C B H 2n _ r ) 2 are known, and are formed by various methods, of which the following are the most important : 1. By the oxidation of secondary alcohols (see beginning of section). 2. By the action of sodium organo-metallic bodies on CO : 2Na(C n H 2n + j) + CO = CO(C n H 2n + z ) 2 + Na 2. 3. By the action of zinc organo-metallic compounds on acid chlorides (chlorides of acid radicles) : ZnCl 2. 4. By the dry distillation of the Ca and Ba salts of monobasic acids of the series C n H 2B+1 .C0 2 H , C n H 2n _ r .C0 2 H, &amp;lt;fcc., Ca&quot;0 2 (C n H 2n + 1 .CO) 2 = CO(C B H 2n+1 ) 2 + CaC0 3 Ba&quot;0 2 (C B H 2n _ 7 .CO) 2 = CO(C n H 2n _ 7 ) 2 + BaCO 3. By employing a mixture of the salts of acids belonging to two different series, or of two different acids belonging to the same series, ketones containing two different radicles are obtained. The ketones of the series CO(C n H 2n+1 ) 2 and CO { S n S 2n+1 ( ^nii 2r) _&amp;gt;r are, with few exceptions, mobile or oily colourless liquids, possessed of most characteristic and penetrating odours ; those of the series CO(C n H 2n _ 7 ) 2 are crystalline solids. Ketones containing methyl form with acid sulphites white crystalline compounds, from which the ketone is obtained unaltered on distillation with an alkali. The best known ketone of the series CO(C n H 2B + 1 ) 2 is dimethyl- ketone or acetone, CO(CH 3 ) 2, a limpid, inflammable liquid, boiling at 55 5 C., and readily miscible with water. In addition to the general modes of formation previously given, this ketone can be obtained by the destructive dis tillation of citric acid, and also by distilling certain carbohydrates with quicklime. Heated with ammonia, acetone forms acetonine, a basic substance, of the formula (C 3 H 6 )&quot; 3 N 2. Of the aromatic ketones methyl-phenyl ketone or acetop/ienone is interesting as furnishing, by the action of fuming nitric acid, a nitro-derivative, ( CTT CO &amp;lt; n TT /xrn &amp;gt; which, when heated with soda-lime and I ^e^l-N U 2^ zinc dust, yields indigotin or indigo-blue I C H (NO ) _ 9 H O O U Indigotin. VIII. ORGANIC ACIDS. The relationship of the organic acids to the hydro carbons and to the alcohols has been previously pointed out (pp. 553 and 567). A further development of this relationship, as bearing on the formation of acids from polyhydric alcohols, is shown in the following examples : CH .OH CO.OH CH 2 .OH CH 2 .OH Ethene glycol. CO.OH Glycollic acid. CO.OH Oxalic acid In the formation of acids from alcohols, therefore (disre garding the intermediate formation of aldehydes), one atom of oxygen is substituted for H 2 in the group CH 2 OH, thus converting this group into carboxyl, COOH. 1 It has been before mentioned that CH 2 OH is derived from methyl by the substitution of HO for H, so that carboxyl may be regarded as a methyl derivative, and a similar view may be extended to cyanogen CN, where N &quot; may be regarded as replacing H 3 . This connection between CN and COOH is shown by the various reactions in which the one radicle is converted into the other, but more particularly, so far as the compounds now under consideration are con cerned, by the synthesis of organic acids from the corre sponding nitriles (p. 555). A few comparative formuke will serve to illustrate still further this important relation ship : CH CH, CH 3 CO.OH Acetic acid. CH 3 CH 2 .OH CH 2 .CN CH 2 .COOP CH 2 (
 * H.OH

CH.CN CH.COOH CH 3 Propane. CH 2 .OH Propenyl alcohol, or glycerin. CH 2 .CN Propenyl tricyanide. CH 2 .COOH Trlcarbullylic acid. 1 &quot; Organic hydroxides are converted iuto acids, not only by trans formation of the group CH 2 OH into COOH, but also when negative elements or radicles accumulate near an alcoholic hydroxyl.&quot; Watts s Dictionary of Chemistry, second supplement.