462

QUINONE-HYDROQUINONE,

long needles; to this substance the name of quinone has been given :

It may also be obtained from the aqueous extract of coffee by treating it in a similar manner. Hofmann has also obtained quinone by treating ẞ phenylene diamine [(E,,H,N) the base obtained by reducing ẞ nitraniline with acetic acid and iron] with sulphuric acid and black oxide of manganese. Quinone fuses at 212°. It is sparingly soluble in water, but is dissolved more freely by alcohol and by ether.

Hydroquinone (H.).-When quinone is treated with reducing agents, such as sulphurous acid or stannous chloride, it is first converted into a green compound, but it ultimately furnishes a colourless body, termed hydroquinone. This substance, mixed with benzoic acid, is the principal product of the dry distillation of quinic acid :

But the simplest plan of preparing it consists in suspending quinone in water and transmitting sulphurous acid gas until the quinone is dissolved; by evaporating this solution, crystals of hydroquinone are obtained, whilst the liquid contains sulphuric acid. Hydroquinone forms six-sided colourless prisms, which are very soluble in water, alcohol, and ether. It is without odour, and has a sweetish taste; it fuses readily, and may be sublimed in brilliant plates, resembling those of benzoic acid.

4 2)

The action of oxidizing agents upon hydroquinone is remarkable. When its solution is mixed with a solution of ferric chloride, the liquid immediately assumes a deep blackish-red colour, and in a few moments it becomes filled with magnificent green acicular crystals, which have a metallic lustre. These crystals consist of a combination of quinone with hydroquinone, which has been called green hydroquinone (Eн ̧Ð ̧‚¤ ̧н ̧Ð ̧). Chlorine, nitric acid, nitrate of silver, and potassic chromate, when mixed with a solution of hydroquinone, also occasion the formation of the same compound: the same substance is likewise formed by mixing a solution of quinone with one of hydroquinone. This beautiful compound fuses on the application of a gentle heat; it is partially decomposed by a further elevation of temperature, and emits vapour of quinone. It is freely soluble in

PERCHLOROQUINONE-SORBIC ACID.

463

boiling water, and sparingly so in cold water; the solution has a styptic taste. Alcohol and ether dissolve it readily, and form yellow solutions.

Both quinone and hydroquinone yield several substitution compounds with chlorine, and with sulphur.

Perchloroquinone, or chloranile (ECI).Of the chlorinated derivatives of quinone, the substance which has been designated chloranile is the most interesting, since through this body the relation of quinone to the phenic, salicylic, and indigo groups of compounds is indicated. Perchloroquinone may be produced by the action of a mixture of potassic chlorate and hydrochloric acid upon quinone, and upon a variety of other substances; viz., on aniline, on carbolic and carbazotic acid of the phenyl series, on salicin, salicyl hydride, and salicylic acid, of the salicyl group, and on isatin, and its chlorinated derivatives in the indigo group. The easiest method of obtaining it consists in preparing a warm dilute solution of salicin acidulated with hydrochloric acid, and adding powdered potassic chlorate in small quantities at a time. A brisk reaction occurs on each addition of the chlorate, and a heavy orange-coloured oil is formed, which solidifies on cooling. This solid mass is perchloroquinone; it may be purified by crystallization from boiling alcohol. Perchloroquinone forms pale yellow flakes of pearly and metallic lustre. It may be sublimed unaltered by the application of a gentle heat. It is insoluble in cold water, and is but sparingly soluble in cold alcohol. Ether dissolves it rather more freely. A warm dilute solution of potash dissolves perchloroquinone readily, giving a purple liquid, which on cooling deposits scales of potassic dichloroquinonate (K,€ Cl_Ꮎ H Ꮎ) .

7

8 & 9. Sorbic and Parasorbic Acids.

(1338) Hofmann has pointed out the existence of an acid derived from the berries of the service-tree, Sorbus aucuparia (Q. J. Chem. Soc. xii. 43), which he has termed sorbic acid (HЄ,H,O), and which is one of a group intermediate between the fatty and the aromatic acids. If we compare together the terms of the fatty and aromatic series which contain an equal number of atoms of hydrogen, the new acid will contain a number of atoms of carbon intermediate between them; e.g., the three corresponding acids in each group are:

464

PARASORBIC AND SORBIC ACIDS.

2n-1

The general formula of the group of fatty acids being HЄ,H2 Ꮎ, that of the sorbic group is HE,H2-5, that of the benzoic group is HЄH2-9. We may confidently anticipate the discovery of aldehyds, alcohols, and other acids of this family from the labours of future inquirers.

n

Parasorbic Acid (H,H). Sp. gr. of liquid 10681; Boiling pt. 430° (221° C.)-If the juice of the unripe berries of the mountain-ash be partially neutralized with lime and submitted to distillation, an acid liquid passes over: after saturating this with sodic carbonate, concentrating the solution by evaporation and decomposing it by the addition of sulphuric acid somewhat diluted, a brownish oil rises to the surface of the liquid: it may be purified by solution in ether, and redistillation after the ether has been allowed to evaporate.

This oil has a peculiar, powerful, somewhat pungent aromatic odour: when pure, it is colourless, is somewhat soluble in water, and abundantly so in alcohol and ether. It possesses the properties of an acid, which Hofmann calls parasorbic; it is readily soluble in solutions of the alkalies and alkaline earths.

On gently treating this oil with solid caustic potash, a transformation of the acid occurs analogous to that of oleic acid by the agency of peroxide of nitrogen. A new isomeric acid is formed termed sorbic acid. When the potassium salt is decomposed by hydrochloric acid, this compound is set at liberty, furnishing an oil which rapidly solidifies into a hard crystalline substance. A similar transformation of parasorbic acid occurs when the oil is boiled for a short time with concentrated hydrochloric acid. Oil of vitriol dissolves parasorbic acid, and on dilution, the substance which is separated gradually becomes crystallized as sorbic acid.

Sorbic Acid [(HEн,,); Fusing pt. 274° (134°5 C.)] as thus obtained is nearly insoluble in cold water, but moderately soluble in boiling water. Ether and alcohol both dissolve it very readily. It may be obtained crystallized in magnificent white needles by dissolving it in a mixture of 1 volume of alcohol and 2 volumes of water by the aid of heat, and allowing the solution to cool. On the application of heat the acid fuses, and at a higher temperature may be distilled unaltered.

The sorbates of potassium and sodium are very soluble, and crystallize with difficulty. Sorbate of ammonium is also very soluble, but crystallizes in slender needles. The salts of calcium and barium are less soluble, and crystallize in anhydrous silvery scales on adding alcohol to their boiling aqueous solutions.

CHAPTER VI.

AMIDES, AND ORGANIC BASES.

§ I. AMIDES AND THEIR VARIETIES.

(1339) Amides.-It has been already stated (371), that under certain circumstances a portion of the hydrogen of ammonia may be displaced by potassium, and a compound may be formed consisting of KH,N, which has been termed amide of potassium. When ammonium oxalate is submitted to distillation, a white sublimate is obtained (610, note), in which the elements of oxalate of ammonium, minus 2 atoms of water, are present; to this sublimate, Dumas, by whom it was discovered, gave the name of oxamide. The following equation represents the relation which exists between oxamide and ammonium oxalate :

(H ̧N)‚¤‚Ð ̧ — 2 H‚Ð = (H‚N)‚¤‚Ð ̧.

Ꮋ Ꮎ

2

Now it is found that other salts of ammonium, when submitted to dry distillation, or otherwise deprived of water, yield compounds analogous to oxamide. When one molecule of an ammonium salt of a monobasic acid loses one atom of water, or when I molecule of a neutral ammonium salt of a dibasic acid loses 2 atoms of water, the resulting compound is called an amide; the amides obtained from the dibasic acids being further distinguished as diamides. It has been proposed to account for the formation of these compounds by the hypothesis, that they contain a certain hydride of nitrogen, which has not hitherto been procured in a separate form, but to which the composition H,N, and the name of amidogen (371) has been assigned.

(1340) Nitriles.-But the amides themselves also admit of being deprived of water: and when an atom of the amide of a monobasic acid has thus been made to lose an additional atom of water, it yields a compound belonging to a class known under the generic term of nitriles. Acetamide, less one atom of water, yields aceto-nitrile :

and, in like manner, oxamide gives oxalo-nitrile :

It is worthy of remark, that oxalonitrile has the same composition as cyanogen, and is not only metameric, but also identical with it; so that cyanogen admits of being regarded as the nitrile of oxalic acid; and thus a certain analogy may be traced between cyanogen and the products obtained by the dehydration of the ammonium salts; the nitriles of the fatty acids of the type HЄH2-12, being in fact identical with the hydrocyanic ethers (1149). These nitriles, when fused with potassium, yield potassic cyanide, and disengage hydrogen mixed with gaseous hydrocarbons. The nitriles, when treated with an alkali, do not reproduce hydrocyanic acid, and their corresponding alcohol; but they recombine with the elements of water, and form ammonia, and a salt of the original acid from which the nitrile was obtained. For instance, benzonitrile when boiled with a solution of potash, yields potassic benzoate and ammonia :

C,HẸN + KHO + HẠO = KC,H,O + HẠN.

5 2

The nitriles may be obtained from the corresponding ammoniacal salts, or from their amides, by the action of an excess of phosphoric anhydride, or of phosphoric pentachloride :—in this way ammonium benzoate may be converted into benzonitrile, since the latter contains the elements of ammonium benzoate deprived of 2 atoms of water; the hydrogen being supplied from the elements of the ammonium, whilst the oxygen is derived from those of the acid :

PC1, + €,H,,H,N = 2 HCl + POCI ̧ + €,H ̧N.

None of the nitriles hitherto procured contain oxygen, since all the salts which at present are known to yield them are formed either from monobasic acids of the form (HE,H,,), or from dibasic acids of the form (H,H‚¤).

The relations subsisting between ammonium benzoate, benzamide, and benzonitrile, will exhibit the nature of the connexion between the ammonium salt, the amide, and the nitrile of a monobasic acid :

: