492

NATURE OF THE ORGANIC BASES.

when uncombined with acid, are sufficiently soluble in ether to admit of extraction by the foregoing method.

process.

Many of the organic bases are also dissolved by chloroform, which may often be advantageously substituted for ether in Stas's The liquid is filtered if necessary, and agitated with about one-thirtieth of its bulk of chloroform; the chloroform speedily separates in the form of a heavy oily layer, which can be decanted; it will be found to contain nearly the whole of the base, which may afterwards be purified by the usual methods. The following bases are especially soluble in chloroform-viz., veratria, quinia, brucia, narcotine, atropia, and strychnia; cinchonia is but sparingly soluble, and morphia still less so.

(1358) Nature of the Organic Bases.-The composition of the vegetable alkalies is remarkable; all of them contain nitrogen, and in the greater number each atom of base includes one atom of nitrogen. Berzelius regarded ammonia as the compound which confers upon them their basic character: and he considered them to be compounds of ammonia with a variety of neutral principles, which in most cases are not susceptible of isolation; the union of the neutral principle or colligate with the ammonia being of the same intimate nature as that of alcohol with sulphuric acid in the ethylsulphuric acid, where neither of the constituents exhibits its ordinary characters. Thus quinia (C20H12NO2, 3 HO; halving the formula now adopted) was represented by Berzelius as (CH,O,,H,NO) 2 HO, or as a compound of the colligate, CH,O2, with oxide of ammonium and water of crystallization. This mode of viewing the composition of certain vegetable bases acquired some support from the discovery that, by the direct union of ammonia with a limited class of neutral substances, such as oil of mustard, and oil of bitter almonds, a number of basic compounds may be obtained, which present a striking analogy both in composition and properties to many of the organic bases produced by living plants; but this theory of Berzelius is now generally abandoned.

9

A different view was proposed several years ago by Liebig, who, finding that these bases gave no evidence of the presence of ammonia ready formed within them, suggested that they might be compounds containing H,N, or amidogen; and that they might be derivatives from ammonia, in which an atom of hydrogen had been displaced by an equivalent organic group: he even predicted that if it should be found possible to displace this atom of hydrogen by ethyl, or by some electro-positive hydrocarben, a powerful volatile base would probably be obtained. This sagacious

CONSTITUTION OF THE ORGANIC BASES.

493

conjecture has since been fully verified by the discoveries of Wurtz and Hofmann, who have succeeded in obtaining the very compounds anticipated by Liebig; and Hofmann, as we have already seen, has extended the process of substitution much further. Liebig's view, with the extension and modifications required by the progress of discovery in this direction, admits in many instances of being happily applied to the natural vegetable bases, since these bodies themselves can be subjected to operations analogous to those which are applied in the formation of the alcohol bases; and portions of the hydrogen which they contain may thus be displaced by basic hydrocarbons: for instance, conylia [(EH)"H,N] may be converted into ethyl-conylia [(¤ ̧H1) ́¤ ̧H ̧‚ N] by displacing an atom of hydrogen by an equivalent of ethyl. The number of exchangeable atoms of hydrogen in the different bases depends upon the molecular constitution of the particular base under experiment (1373, 1374).

8

2

But the hydrocarbons either originally existing in the base or subsequently introduced into it, may also experience a change in their components by a species of secondary substitution by chlorine or bromine, whilst the general basic properties of the compound remain unchanged. Aniline (ЄH,,H,N), for example, may be represented as ammonia in which one atom of its hydrogen is displaced by EH, (phenyl); but aniline may lose a part of its hydrogen, and receive chlorine in its place, without having its basic character destroyed, becoming chioraniline (H ̧Cl,H,N) : and even NO, may be substituted for a portion of the hydrogen in aniline, while the new body (nitraniline, ЄH,NO,,H,N) still retains its power of forming salts with acids. Nitraniline affords

an instance of the artificial formation of a monobasic alkaloid containing two atoms of nitrogen; and examples of the occurrence of bases which contain more than one atom of nitrogen without any corresponding increase in basic power are not wanting among the products of organic nature. The relations of aniline to chloraniline and nitraniline may be represented in the following manner :

Hofmann, in the course of his researches upon aniline, dis

494

ANALOGY OF ORGANIC BASES WITH AMMONIA.

covered another method of combination which is worthy of remark, since it explains a second mode in which an additional atom of nitrogen may be introduced into the alkaloid without increasing its basic power:-cyanogen unites directly with aniline, forming a body, the composition of which is represented by Є,H,N, but which is evidently not aniline hydrocyanate, for this would be represented by the formula H,N,HEN, or (Є,H,N); nor is it a substitution-product formed by the displacement of 1 atom of hydrogen by an equivalent of cyanogen; but a new body, cyaniline, which possesses basic properties, and enters into combination with acids in the proportion of one equivalent of acid to each atom of aniline which the new base contains.*

6 5

8

It is evident that changes such as these affect that portion only of the compound which, like ЄH, in aniline, has been introduced into the ammonia by substitution; the compound retaining the basic power which it originally derived from the ammonia, upon the type of which it has been constructed. When this type

For

is destroyed, the basic power of the compound disappears. example, just as an atom of ammonium oxalate by the abstraction of the elements of two atoms of water, loses its saline character, and becomes converted into an indifferent insoluble body, oxamide, and this by the further abstraction of two more atoms of water furnishes cyanogen (1339); so the atom of aniline oxalate, by losing two atoms of water, becomes oxanilide; and by abstraction of two more atoms of water becomes oxanilo-nitrile, or phenylocyanogen, which still retains an atom of nitrogen intimately combined both with carbon and hydrogen, but which has lost its relationship or homology with ammonia, and with it has also lost its basic character. Thus:

(1359) Analogy of Organic Bases with Ammonia.-The remarkable parallelism in properties of the salts of the organic bases with those of ammonia, will be rendered still more evident by the following additional particulars :

Many of these bases may be obtained, like ammonia, in the

*Bases will be described hereafter, which, like guanidine and methyluramine (1610), appear to be formed upon the polyatomic type, and are derived from 2 or 3 atoms of ammonia united into one group.

GENERAL PROPERTIES OF ORGANIC BASES.

24

49

24

495

anhydrous state: such, for instance, are cinchonia €20H2N2O, and strychnia H22N22; and the same is the case almost [22] 21 without exception with the aniline class. These anhydrous bases combine directly like ammonia with hydrochloric acid, and the corresponding halogen acids, and do not require any addition of the elements of water; cinchonia hydrochlorate, for example, consists of (H2N1⁄2Ð, 2 HCl); and, as is the case also with ammonia, whenever these bases unite with the oxyacids the basic hydrogen of the normal acid unites with the organic alkali, and no separation of water occurs. Cinchonia sulphate, for instance, which contains (20H2N ̧‡‚Í‚§Ð ̧‚ 4 H), loses its 4 atoms of water of crystallization by heat, but the hydrogen of the acid cannot be expelled in the form of water without decomposing the salt. The double salts which the organic bases form, also closely resemble the corresponding compounds of ammonia :-for example, with platinic chloride they yield yellow crystalline double chlorides of sparing solubility. These compounds are of considerable importance to the chemist, since they furnish him with very accurate means of determining the combining number of the organic base. Trichloride of gold likewise forms with them similar compounds, which Hofmann has proposed to employ for the same purpose. Most of the organic bases also furnish nearly insoluble white precipitates when their solutions are mixed with one of corrosive sublimate, or with a solution of mercuric iodide in potassic iodide. They yield extremely insoluble compounds with sodic phosphomolybdate; and a solution of ferric sulphate, when mixed with one of quinia sulphate, yields by spontaneous evaporation crystals having the octohedral form of alum (Will). Octohedral crystals are also obtained when a solution of sulphate of conylia, which is an analogue of ammonia, is mixed with one of aluminic sulphate, and left to spontaneous evaporation.

In addition to these compounds there are some others peculiar to this class of bodies. Solutions of salts of the vegetable bases for the most part, when mixed with potassic diniodide (KI), yield precipitates insoluble in water, but soluble in boiling alcohol, from which they crystallize on cooling. It has been proposed to use these compounds in determining the bases quantitatively for the purposes of analysis. With this object the precipitate formed by the diniodide is placed in very dilute sulphuric acid, and treated with fragments of zinc; zincic iodide and hydriodate of the base are dissolved; and on the addition of ammonia in excess, the organic alkali is precipitated, whilst the zinc is retained in solution. In some cases it is found preferable

496

ARTIFICIAL FORMATION OF ORGANIC BASES.

to throw down both the zincic oxide and the alkali by means of ammonium carbonate; the precipitate after washing with water is treated with boiling alcohol, which dissolves out the alkali, leaving the zincic oxide; and on evaporating the alcoholic solution, the alkali is obtained in a state of purity.

Nearly all the organic bases form insoluble curdy precipitates with gallotannic acid; indeed, this acid is one of the most complete precipitants of the vegetable alkalies. These gallotannates, when heated, melt to a resinous mass, and are soluble to some extent in boiling water: they are also dissolved freely by boiling alcohol.

The action of tartaric acid upon the vegetable bases is analogous to that which it exerts on many of the inorganic bases; for instance, the tartrates of iron, copper, and some other metals, are not precipitated by the addition of the alkalies to their aqueous solutions; but tartrate of lead is decomposed with separation of the metallic oxide. So it is with many of the organic bases; the tartrates of brucia, quinia, and morphia, are not precipitated by an excess of caustic potash or soda; by converting these organic bases into tartrates, and adding an excess of an alkaline solution, they may be separated from strychnia, cinchonia, and narcotine, the tartrates of which are decomposed in the usual way on the addition of potash or of ammonia.

The greater number of the vegetable bases, when in solution, produce the phenomenon of left-handed rotation on a ray of polarized light. The artificial bases in general do not possess the power of affecting a polarized ray (Laurent). The left-handed rotation exerted by narcotine becomes right-handed when this base is combined with acids; and, generally speaking, the effect of the addition of an acid to a base is to reduce its power of rotation, though with quinia the rotatory power is exalted by the addition of an acid.

Artificial Formation of Organic Bases.

(1360) It has already been stated that many organic bases may be prepared by artificial means. All attempts at obtaining those which occur naturally in plants have, however, hitherto been unsuccessful. The following are the principal processes resorted to for the purpose of preparing organic bases artificially :—

1. By destructive distillation of organic bodies containing nitrogen.

2. By distillation of the organic alkalies with caustic potash (Gerhardt).