352

ACETONE AND ITS DERIVATIVES.

valeric, œnanthylic and caprylic aldehyds, were formed: calcic formiate when distilled, yielding hydrogen instead of methyl (ЄHg), as in Williamson's experiment :

The following results obtained by Stædeler from acetone (Ann. de Chimie, III. xlii. 226) have tended to confirm these views. Chlorine forms with acetone various substitution-products, the most remarkable of which is one in which five atoms of hydrogen are displaced by five of chlorine: a compound, Є,HCI,, analogous to chloral is thus formed; it has a sp. gr. of from 16 to 17, it is not solidified by a cold of -4° (-20° C.), and it boils at about 374° (190 C.). This body has the property of combining with four atoms of water, with which it forms a soluble crystallizable substance analogous to hydrate of chloral.

Acetone when saturated with gaseous ammonia yields a liquid which reduces the salts of silver, in a manner similar to the corresponding mixture with aldehyd. If this acetonic solution of ammonia be left to itself for some time, it is spontaneously transformed into a new base, acetonine or acetonia (Є,H1N2); and the same change is effected more rapidly by exposing the mixture for some hours in a sealed tube to a heat of 212°. The decomposition by which it is formed is similar to that by which benzoline is produced from the oil of bitter almonds (1387) :—

18

Acetonia is a colourless alkaline liquid, of a peculiar urinous odour and a burning taste. It is readily soluble in water, alcohol, and ether. Hydrochlorate of acetonia forms with platinic chloride an orange-yellow crystalline double salt [2 (Є,H1N,HCl), PtCl]. The acid oxalate (E,H12H ̧¤ ̧Ð ̧‚н2) is soluble in alcohol, and crystallizes readily from this solution.

9 181 2 2

9 18

Acetone may also be made to furnish an acid homologous with the lactic. This compound, termed acetonic acid (HЄ,H,g) may be obtained by heating a mixture of acetone and hydrocyanic acid with hydrochloric acid, when the following reaction

Acetonic acid crystallizes in prisms; it has a sour taste, and is freely soluble in water, in alcohol, and in ether. It forms crystallizable salts: zincic acetonate (Zn2¤ ̧Н‚¤ ̧,2H2) is very sparingly soluble. The barium salt is soluble in alcohol.

Ꮎ

The attempt to procure a base homologous with glycocine and alanine, by the action of hydrocyanic acid upon acetone, was unsuccessful.

It is probable that each of the other ketones would yield compounds analogous to those which Stædeler has procured from acetone. Each of the ketones is metameric with a corresponding term in the series of true aldehyds; for example :

Ꮎ =

=

=

Propionic aldehyd.
Valeric aldehyd.
Enanthylic aldehyd.

By careful oxidation, Stædeler succeeded in converting acetone into propionic acid.

The formation of ketones has also been observed in the case of several monobasic acids which do not belong to the series of the fatty acids. Benzoic acid, for example, is decomposed in the following manner

The products of the distillation of the calcium salts of the dibasic acids, such as the suberic acid, do not fall strictly into the class of ketones. The substance termed suberone, for instance, consists of H1, instead Є,H,,.

8 14

12

It will be useful here, before passing to the consideration of the special series of acids produced by the oxidation of the aldehyds, to consider briefly the general properties of the organic acids, as a class, and some of the more important groups of derivatives from them.

§ II. GENERAL REMARKS ON THE ORGANIC ACIDS.

(1260) THE ORGANIC ACIDS constitute an extremely numerous and important class of compounds; but many of them are so intimately related to a large number of other well-defined natural groups, that it would be far from advantageous to detach each acid from the group to which it properly belongs, for the sake of describing it with other bodies to which, often, it may bear little resemblance save in the circumstance that, like them, it possesses

354

MONOBASIC AND POLYBASIC ACIDS.

the power of forming salts with bases. Accordingly, some of these bodies have already been described in the previous sections, where they seemed to be naturally connected with the compounds under examination; and although it will be convenient to associate together certain of the acids in the present chapter, the consideration of others will be postponed until the substances to which they are most nearly allied pass under review.

At present no organic alkali is known into the composition of which nitrogen does not enter; so that if it be ascertained that nitrogen is absent from any particular compound, it may at once be concluded that the body in question cannot belong to the class of organic bases; but there is no elementary substance with the presence of which the acid character can be thus specifically connected and no general law of composition has hitherto been arrived at, by which it is rendered possible from a knowledge of the empirical formula of a substance to predict that it will or will not possess the properties of an acid.

:

(1261) Monobasic and Polybasic Acids.-The organic acids may be subdivided into monobasic, dibasic, tribasic, or polybasic, according as they contain one, two, three or more atoms of hydrogen, susceptible of displacement (554). The important group derived from the monobasic alcohols by oxidation, furnishes a good illustration of the monobasic acids; whilst some of the more important and widely diffused vegetable acids, such as the citric, the tartaric, and the malic, afford examples of the polybasic class, and have been traced to the polybasic alcohols.

The following table may serve to illustrate the connexion of several of the most interesting groups of acids, and of their relation to the alcohol groups: :

Tetratomia. H-10, HH, } 0.

Н

}

Ꮎ

H

Many attempts have been made, without success, to account for the polybasic or monobasic character of the acids from their composition. Kekulé has offered the following ingenious sug

gestions upon this subject. According to this chemist,-1. Bodies, whether monatomic or polyatomic, which are formed upon the type

H

of water-i.e. which are of the form x →, which contain only

H

carbon and hydrogen in the radicle that displaces the typical hydrogen in the molecule, belong to the class of alcohols; as for example :

2. Those bodies which, in addition to carbon, or to carbon and hydrogen, contain an atom of oxygen in the displacing radicle, constitute well defined monobasic* acids; for example:

They allow one atom only of the typical hydrogen in the molecule to be displaced readily by a metal.

3. Those compounds which contain 2 atoms of oxygen in the displacing radicle, constitute dibasic acids, whether they contain 2, 3, or 4 atoms of oxygen external to the radicle; as for example :

The basicity of the acid, therefore, upon this view, depends, not upon the molecular type of the compound, for in the case of the three acids last cited the first is diatomic, the second triatomic, and the third tetratomic,-but on the amount of oxygen in the radicle.

(1262) Simple, and Compound or Colligated Acids.-The organic acids may further be regarded as belonging to one or other of the following classes:

a. Hydrated oxides of organic radicles, and acids derived from them by substitution.

b. Compound or colligated acids.

(a) Hydrated Oxides of Organic Radicles.-Examples of this

*It is obvious that this statement is not universally true. Carbonic acid, ᏟᎾ which in combination with potassium may be represented as K12, is manifestly dibasic, though it ought to be monobasic by the foregoing rule.