AMIDO-BENZOIC, OR BENZAMIC ACID.

607 form of a neutral oil, which is heavier than water, and emits an agreeable odour of sherry wine. Boiling water decomposes it slowly into a mixture of acetic and benzoic acids; but the solutions of the alkalies or of their carbonates quickly convert it into acetate and benzoate of the basyl. It cannot be distilled without experiencing decomposition: acetic anhydride passes over first, and if the distillation be stopped as soon as the temperature of the boiling liquid reaches 536° (280° C.), the residue in the retort solidifies on cooling into a mass of crystallized benzoic anhydride.

(1436) Benzamic Acid; Carbanilic Acid, or Amido-benzoic Acid (Є,H,NO,, or H‚¤,H,,H,N,,), as it is more appropriately termed, is not a true amidated acid (1341), but benzoic acid in which an atom of hydrogen has been displaced by an equivalent of amidogen. It is isomeric with anthranilic acid (1517) and with salicylamide, and is obtained by the action of reducing agents upon nitrobenzoic acid. If an alcoholic solution of nitrobenzoic acid be saturated with ammonia and with sulphuretted hydrogen, and then boiled, it becomes green, and a copious deposit of sulphur occurs: this operation must be repeated two or three times, in order to complete the decomposition of the nitrobenzoic acid :

Nitrobenzoic acid.

Amido-benzoic acid.

2 (HE,H,NO2,2) + 6 H2S = 2[H¤‚H ̧(H2N)→] + 4H2O+3§2. The liquid must be evaporated to the consistence of syrup, supersaturated with acetic acid, and the precipitate drained upon a porous tile. It must then be redissolved in boiling water; the solution digested with animal charcoal, filtered, and allowed to crystallize. Amido-benzoic acid crystallizes in radiated tufts of delicate needles, which are readily soluble in alcohol and in ether. It has a sweet, sourish taste, but no odour. It forms an insoluble green precipitate when mixed with salts of copper; with salts of silver it gives a white curdy precipitate, which if left in the liquid becomes crystalline.

This acid likewise possesses the property of combining with other acids. Oil of vitriol dissolves amido-benzoic acid by the aid of heat, and on cooling, it deposits brilliant crystals (2€,H,NO,, H2SO,, 2 H2O), which may be recrystallized from boiling water or from alcohol: their aqueous solution has an extremely sweet taste. A similar compound (E,H,NO,,HNO3) may be formed with nitric acid. Phosphoric, oxalic, hydrochloric, and other acids form with amido-benzoic acid similar combinations.

608

AMIDO-BENZOIC, OR BENZAMIC ACID.

The compound with hydrochloric acid forms a crystalline double salt with platinic chloride.

6' 2

10'

Amido-benzoic acid is the representative of a class of compounds which the aromatic acids furnish when their nitro-derivatives are submitted to reduction. In this manner amido-toluic (H¤ ̧н¿‚Í ̧Ñ‚Ð1⁄2), amido-cuminic (HЄ1H10,H ̧Ñ‚Ð ̧), and amidoanisic acids (HЄ,H,,H,N,,) may be procured. They all exhibit a similar tendency to combine with acids, as well as with bases; and if the silver salt of one of these acids, such as the amido-benzoate of silver, be treated with benzoyl chloride, a compound crystallizable acid is obtained, analogous to the hippuric and cuminuric (1442) which are procured by similar treatment of the compound of glycocine and zincic oxide :—

These so-called amido-acids are isologous with glycocine (1614) and its homologues, and resemble them considerably in properties.* By the action of reducing agents upon dinitro-benzoic acid, a compound (E,H.NO) analogous to the amido-benzoic acid, having

8 2

*Griess (Proceed. Roy. Soc., ix. 594, x. 309 and 591) has described a series of azotised bodies in some measure connected with the amidic bases. These new bodies are generated by the action of nitrous anhydride upon alcoholic solutions of amido-acids of the benzoic group, the change consisting in the substitution of one atom of nitrogen for three atoms of hydrogen in two molecules of the amidoacid. When, for example, amido-benzoic acid is dissolved in alcohol, an orangeyellow crystalline precipitate is obtained, constituting a dibasic acid insoluble in water, in alcohol, and in ether, but soluble in the alkalies, forming with them crystallizable salts which yield precipitates with acetate of lead and with nitrate of silver. The reaction by which it is formed may thus be represented :—

A similar substitution of one atom of nitrogen for three atoms of hydrogen was effected by Griess upon aniline and nitraniline, two molecules of each compound being linked into one molecule of the new body; for example:

4¤ ̧H,N+N ̧ ̧ = 3 H2+2€12H1N3.

If an aqueous solution of the amido-benzoic acid be decomposed by nitrous acid, nitrogen is liberated abundantly, and a new compound, the oxybenzoic acid (H,H) of Gerland is obtained. It is metameric with salicylic acid, but does not crystallize easily. It furnishes very soluble salts with the alkalies, and sparingly soluble crystalline compounds with the alkaline earths. Oxybenzoic acid is sparingly soluble in cold water and alcohol. It fuses when heated, and may be sublimed without alteration. The reaction by which it is obtained may be thus represented :

ACTION OF AMMONIA ON THE OIL OF BITTER ALMONDS. 609

2 2

the composition of diamidobenzoic acid [HЄ,H,(H,N),0,] has been obtained (Voit), but it possesses none of the characters of an acid; it combines readily with acids, the introduction of the second atom of amidogen having given it a decided basic energy.

(1437) Action of Ammonia on the Oil of Bitter Almonds.Several compounds are produced by the action of ammonia upon this essence, which are different according as the essence employed is pure, or contains hydrocyanic acid. If it be pure, hydrobenzamide and dibenzoylimide are the result of the reaction : if it be in the crude state, the hydrocyanic acid takes part in the reaction, and benzhydramide and benzoylic azotide are formed.

1. Hydrobenzamide [H1N; Fusing pt. 230° (110° C.)] is the most interesting of these compounds; it may be formed by simply agitating the oil with a solution of ammonia, and afterwards leaving it at rest for some days at the ordinary temperature but the reaction is completed in a few hours if the mixture be heated to the boiling point. In either case the mixed liquids become gradually converted into a crystalline mass of hydrobenzamide, which must be washed with ether, and crystallized from boiling alcohol:

3 ¤‚H ̧Ð + 2 H2N = €21H18N2 + 3 H2Ð.

Hydrobenzamide forms colourless octohedra with a rhombic base. It is destitute of odour, and insoluble in water, but readily soluble in ether. It melts at 230° (110° C.); and, if heated for some time to about 260°, or if boiled with a solution of potash, it is converted into the isomeric base termed amarine or benzoline (1387).

When hydrobenzamide is fused with caustic potash, several new compounds are formed, such as benzostilbine (Є31H2O2?), and benzolone (Є1HO?), whilst the nitrogen is expelled in the form of ammonia.

Hydrobenzamide, when boiled with hydrochloric acid, is decomposed; sal ammoniac is formed, and benzoyl hydride is set at liberty. A similar change is also produced by the mere boiling of its alcoholic solution, but the ammonia in that case is liberated in the uncombined form.

13

2. Dibenzoylimide (H1NO) is obtained by passing ammoniacal gas into an alcoholic solution of essential oil of bitter almonds. It is gradually separated in the form of a resinous mass which is soluble in boiling alcohol, and from which it is

610

BENZHYDRAMIDE-AZOBENZOYL-BENZOIC ALCOHOL.

deposited as a yellowish powder composed of brilliant feathery crystals (Robson) :—

22

2

3. Benzhydramide, or a Cyanazobenzoyl Hydride (EHN2O).— This body was originally stated by Laurent to be isomeric with hydrobenzamide, but when he re-examined it conjointly with Gerhardt, this statement was ascertained to be an error. If the crude essence of bitter almonds be heated to 212°, and saturated with ammonia, then dissolved in a mixture of alcohol and ether, and left to itself for three or four days, a deposit is formed which consists of two portions, viz., benzhydramide, and benzoylic azotide they may be separated by the action of boiling alcohol. Benzhydramide is soluble in boiling alcohol, from which on cooling and spontaneous evaporation it is deposited in small brilliant needles, which are freely soluble in ether; and which, when boiled with hydrochloric acid, are decomposed into hydrocyanic acid, hydrochlorate of ammonia, and benzoyl hydride.

4. The portion which is left undissolved by alcohol is the benzoylic azotide of Laurent. It is in the form of a white crystalline powder, nearly insoluble in alcohol and in ether: it fuses on the application of heat, and crystallizes on cooling.

The formation of these two compounds is explained by the following equations :

15

5. Azobenzoyl (H1N2) is a third substance which was obtained by Laurent. It is nearly insoluble in alcohol, but soluble in ether on the application of heat it fuses into a transparent mass, resembling gum in appearance.

(1438) Benzoic Alcohol (E,H,HO, Cannizzaro); Sp. gr. of liquid 1059; of vapour 384; Rel. wt. 54; Boiling pt. 400° (204° C.).— In order to obtain this compound the following process is adopted :-Oil of bitter almonds is dissolved in its own volume of alcohol, and this liquid is mixed with three or four times its bulk of an alcoholic solution of caustic potash (of sp. gr. 1'020): a considerable evolution of heat occurs, and a copious deposition

ETHERS OF THE BENZOIC SERIES.

611

of crystals of potassic benzoate takes place: when this reaction. has terminated, boiling water is added to the liquid in quantity sufficient to dissolve the benzoate. The greater part of the alcohol must then be distilled off, and more water added to dissolve the benzoate if necessary; the turbid liquid thus obtained must be agitated with ether, and the ethereal layer which separates on standing, must be drawn off and subjected to distillation. The first portions consist of ether, but subsequently pure benzoic alcohol passes over. The reaction of caustic potash upon the benzoyl hydride may be thus represented :—

5

Benzoic alcohol.

2 €,H,O + KHO = KC,H,O, + HC,H,O. Herrmann finds that benzoic alcohol may also be obtained by reducing a hot aqueous solution of benzoic acid by means of an amalgam of sodium, but the alcohol is mixed with some secondary products.

Benzoic alcohol is a colourless oily liquid, which is readily converted by nitric acid at a gentle heat into oil of bitter almonds; and is transformed by chromic acid into benzoic acid: both of these products are the results of oxidation, which may be thus represented:

It is obvious that oil of bitter almonds and benzoic acid stand in the same relation to benzoic alcohol, that aldehyd and acetic acid do to ordinary alcohol (vide Table, p. 172).

If benzoic alcohol be distilled from caustic potash, it is decomposed into potassic benzoate and the hydrocarbon known as toluol, which corresponds to olefiant gas in the alcohol series :

3 €,H,O + KHO = K€,HO, + 2 €H + 2 H,O.

8

5 2

8

:

Benzoic alcohol may be made to yield a series of ethers, among which are the following: