172

ISOLOGOUS GROUPS-POLYBASIC ALCOHOLS.

scarcely be doubted that other homologous series of each of these varieties of alcohol will be found.

The following table will serve to elucidate the general relations of these groups to each other; and it will also indicate the analogy of the compounds which they form with corresponding compounds in the comprehensive family to which ethylic alcohol belongs::

(1123) Polyad Alcohols.—In addition to the various alcohols of which we have spoken, and which are all monobasic, and formed

H

upon the type HS

O, we meet with others of more complicated

Hs)

some higher multiples of H2O. Chevreul, when he published his masterly researches upon the fatty bodies, pointed out the analogy between the fixed oils and fats, and the compound ethers; when under the influence of bases the fats undergo saponification, they are decomposed with the assimilation of the elements of water into a fatty acid, and into glycerin, a body which in this respect presents an analogy with alcohol: but he did not see the precise difference between the fats and fixed oils and the compound ethers; and the completeness of the parallel has only recently been established, and the distinction between the two pointed out. Berthelot, by synthetic experiments (1240) has shown that the neutral fats are derived from three atoms of a monobasic acid, and one atom of glycerin; glycerin being in fact a triad alcohol, and presenting a constitution which has its representative among the acids, in the tribasic phosphoric acid.

Stearin (Є,H,,3 Є18H352), for instance, consists of

And if glycerin be a triad alcohol, the composition of glycerin and that of stearin may be represented as follows, on the type of 3 molecules of water :—

Intermediate between this triad alcohol, glycerin, which is the only one of this series at present known, is a series of dyad or diatomic alcohols, the glycols, the existence of which was inferred by Wurtz, and which by synthetic operations he succeeded in discovering. They are purely artificial bodies obtained from the hydrocarbons of the olefiant gas series (1213).

The glycols yield compound ethers which are derived from two atoms of a monobasic acid and one of the glycol, so that they may be represented as formed on the type of two molecules of water

174

POLYATOMIC ALCOHOLS.

3

In the case of glycerin the triad radicle (H.)"" which it contains impresses its character upon the compound; whilst in the glycols the dyad hydrocarbon (EH)" or one of its homologues imparts a dibasic constitution to the body.

The active study of the compounds of which glycerin and glycol are the representatives, is daily bringing to light a multitude of new bodies, and rapidly extending our views upon the constitution of many organic bodies of very complicated composition.

PREPARATION OF THE ALCOHOLS.

175

For example, it appears to be very probable that mannite and the sugars are polyatomic alcohols, mannite, and possibly glucose, being hexatomic (1244):—

Each polyatomic alcohol has its hydrocarbon radicle, its corresponding ethers, its aldehyds, and its acids; and all these heterologous derivatives from the alcohol are themselves, like it, polyatomic. A general idea of the very numerous bodies which are correlated by this view may be formed from an examination of the preceding table.

Although many of these polyatomic alcohols are artificial bodies, yet the study of this class of compounds presents high attractions to the chemist, as it is amongst these substances that many of the most interesting and extensively diffused natural compounds occur, as, for instance, the sugars, the different forms of mannite, glycerin, and all its compounds in the natural fats and fixed oils.

(A.) MONATOMIC OR MONAD ALCOHOLS.

(1124) General Methods of Preparation.-1. The monatomic alcohols homologous with ordinary alcohols are usually formed by a process of fermentation from sugar, as occurs with ethylic, tritylic, tetrylic, amylic, and hexylic alcohol. 2. Some, however, are procured by destructive distillation, as in the preparation of wood spirit. 3. Others are obtained by treating certain fatty bodies with caustic potash, as in the process of obtaining octylic, laurylic, cetylic, cerylic, and melissylic alcohols. 4. Certain of the alcohols may also be formed synthetically by dissolving the dyad hydrocarbons, such as ethylene and tritylene, in oil of vitriol, diluting the liquid and then distilling. For example :—

Ethylene, Sulph. acid.

Alcohol.

Sulph. acid.

€H + H,SO + H,O = C,H,O + H,SO;

5. They may also be obtained by causing a hydrocarbon of the ethylene series (1209), to combine with a hydracid, and then decomposing the compound so obtained by long continued exposure to the action of caustic potash. Berthelot has in this way

176

FORMATION OF THE ALCOHOLS.

obtained tritylic, amylic, octylic, and cetylic alcohols, by the reaction shown in the equations which follow* :

A more perfect reaction may be effected by subjecting the chloride to potassic or argentic acetate, and then distilling with caustic potash the acetic ether so obtained; for example :

6. Another method practised by Wurtz consists in treating the aldehyds with nascent hydrogen, by acting upon them in the presence of water with an amalgam of sodium; direct union between two atoms (one molecule) of hydrogen and one molecule of aldehyd then occurs; as for instance :

Aldehyd.

Alcohol.

7. It is usually stated that it is possible to decompose one of the alcoholic derivatives of ammonia (1373) by nitrous acid. If ammonia be gently warmed with nitrous acid, two atoms of water are liberated and two of nitrogen—

(H) H2N+HNO2=2H2O+N2 ;

and it seems reasonable to expect that if instead of ammonia an atom of an alcohol base in which one of the atoms of hydrogen in the molecule of ammonia is displaced by an alcohol radicle, such as ethyl, the atom of hydrogen in one of the two atoms of water formed in the reaction will be displaced by ethyl, and consequently an atom of alcohol will be formed in its place: e.g.—

(¤ ̧H¿)H‚N + HNO2 = H ̧Ð + (€2H ̧)H‡ + N.

Ng

* Wurtz has shown that the higher terms of the alcohols obtained by these methods are not identical with the alcohols obtained by fermentation, but only isomeric with them (1201).