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812

PARABANIC AND OXALURIC ACIDS-ALLOXANTIN.

€2+HNO2+H2O. This is to be dried on a tile, redissolved in water, and recrystallized, when it forms thin, colourless, six-sided prisms: it is a powerful acid, very permanent in its uncombined condition, and very soluble in water. It may be viewed as oxalyl urea ЄH2(¤ ̧Ð ̧)"N,O. At a heat of 212° it acquires a reddish tint at a higher temperature it undergoes partial sublimation, but a portion of it is decomposed, and furnishes hydrocyanic acid. Parabanic acid forms salts which are exceedingly unstable; parabanate of silver being the only salt which is permanent. All the other parabanates during evaporation combine with the elements of one atom of water, and become converted into oxalurates: ammonium parabanate, for instance, when boiled furnishes brilliant crystals of ammonium oxalurate ::

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(1626) Oxaluric Acid (H¤ ̧H ̧Ñ2).—This acid, so named because it breaks up easily into oxalic acid and urea, is best obtained from ammonium oxalurate: a hot saturated solution of this salt when mixed with dilute sulphuric acid, and cooled rapidly, yields pure oxaluric acid as a sparingly soluble heavy white powder. By long boiling with water this acid is decomposed into oxalic acid and urea oxalate :

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Oxalurate of silver is a white salt, soluble in hot water, from which it crystallizes in beautiful silky needles as the solution cools. (1627) Alloxantin (ЄH ̧Ñ‚Ð,, 3 H2O).—This compound may be regarded as a combination of dialuric acid with alloxan, since it may be formed by mixing solutions of these two bodies in equivalent proportions:

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the crystals of alloxantin are slowly deposited from the mixture. Alloxantin may also be obtained by the action of deoxidizing agents upon alloxan. If alloxan be dissolved in water, and a current of sulphuretted hydrogen be transmitted, the liquid in a short time becomes turbid, from the separation of sulphur, and crystals of alloxantin are gradually deposited. The acid motherliquor which remains after the preparation of alloxan by nitric acid is well adapted for furnishing alloxantin; it should be neutralized with chalk, and submitted to the action of a current of

ALLOXANTIN-DIALURIC ACID.

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sulphuretted hydrogen gas. Many other processes may, however, be adopted for preparing alloxantin; for example, if stannous chloride be mixed with a solution of alloxan, crystals of alloxantin are deposited. Also, if a solution of alloxan be acidulated with hydrochloric acid, and a bar of zinc be introduced, hydrogen is evolved, and crystalline crusts of alloxantin are slowly produced.

Alloxantin forms small white, hard, brilliant, prismatic crystals, which become pink by exposure to an atmosphere containing ammonia. It is very sparingly dissolved by cold water, but more freely by boiling water; its solution reddens litmus. Crystallized alloxantin may be heated to 212° without losing weight, but at a higher temperature it gives off 154 per cent. of water. Baryta water, when added to its solution, gives a characteristic violet precipitate, which becomes white if boiled in the liquid. A solution of alloxantin reduces the salts of silver, and is converted into alloxan; thus affording an instance of the facility with which oxidizing agents reconvert it into alloxan. Hlasiwetz found that when alloxantin is heated under pressure with water to 360° or 370° (about 180° or 185° C.), it is slowly decomposed, evolving gas in large quantity, whilst ammonium oxalate is formed, probably owing to the following reaction:

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If a boiling solution of alloxantin be mixed with a solution of ammonia hydrochlorate, also at a boiling temperature, and the mixture be allowed to cool in a well-corked vessel, crystals of uramil (dialuramide) are deposited, whilst the liquid retains alloxan and free hydrochloric acid in solution :—

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When alloxantin is boiled with hydrochloric acid it is gradually decomposed, alloxan and parabanic acid are formed, accompanied by two compounds, termed by Schlieper allituric acid (CHN) and dilituric acid (E,H ̧Ñ‚Ð ̧‚ 3 H ̧‡). 31 3 53 H2O).

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(1628) Dialuric Acid (HII,N2O).—If a stream of sulphuretted hydrogen be transmitted in excess through a hot solution of alloxan or of alloxantin, sulphur is deposited, and the liquid becomes strongly acid, owing to the formation of dialuric acid. If this acid liquid be neutralized with ammonia, ammonium dialurate is deposited in silky needles (HN,,H,N). The

814

DIALURIC AND HYDURILIC ACIDS.

same salt may be obtained by reducing alloxan by means of zinc and hydrochloric acid, and adding a sufficient excess of ammonia to redissolve the oxide of zinc, which is at first precipitated by the ammonia.

If ammonium dialurate be added to hot hydrochloric acid, so long as it is dissolved, and the liquid be allowed to cool, long needles of dialuric acid are deposited. They become red by exposure to the air, and are gradually converted into alloxantin. Dialuric acid forms a sparingly soluble salt with potassium, which may be obtained by adding a solution of potassic cyanide to one of alloxan: the brown-yellow precipitate thus obtained must be dissolved in a weak potash ley, and neutralized by acetic acid, when it falls as a white precipitate. In this case, however, half the alloxan passes into the form of oxaluramide (H2N,E,H,N2O) mixed with potassic oxalurate.

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If a magma of alloxantin and water be treated with amalgam of sodium, sodic dialurate is formed; H10N410+ Na=2 Na€,H ̧Ñ‚Ð ̧+2 H ̧Ð ; and from a hot solution of this salt the acid crystallizes on adding hydrochloric acid in excess. A still better process, according to Baeyer, consists in reducing alloxan by means of excess of stannous chloride in a larger excess of hydrochloric acid. The ammonium dialurate is white at the moment of its formation, but as it dries it becomes of a splendid pink or blood-red colour. This salt is freely soluble in boiling water. It occasions a white precipitate with the salts of barium, and a yellow one with salts of lead. Nitrate of silver is reduced by it to the metallic state. (1629) Hydurilic Acid (H,E,H,NO, 2H,O).-If 9 parts of dry dialuric acid be mixed with 5 of concentrated glycerin, and heated gradually, by means of an oil bath, to 284° (140° C.) in a capacious flask, a brisk and steady disengagement of carbonic anhydride takes place; the contents of the flask gradually become solid, and the disengagement of gas ceases; during the operation the temperature may be gradually raised to 320° (160° C.): the mass is then allowed to cool, and the glycerin containing formic acid is to be washed out with cold water, when a yellowish-white granular mass of acid ammonium hydurilate is left. The glycerin merely acts as a vehicle, whilst the following reaction occurs:—

Dialuric acid.

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If this acid ammonium salt be neutralized with ammonia and mixed with cupric sulphate, the liquid becomes of a dark green colour, and gradually deposits from a hot solution black, anhydrous, or, from a cold solution, red hydrated crystals of normal

VIOLURIC AND DILITURIC ACIDS.

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cupric hydurilate. From this salt hydrochloric acid sets free white crystalline hydurilic acid, which is sparingly soluble, and crystallizes from a hot solution in small four-sided prisms. It is best recognized by the beautiful green colour produced on mixing solutions of the acid or its salts with ferric chloride. The colour passes into red when heated, whilst hydurilic acid is decomposed. If treated with fuming nitric acid, hydurilic acid is converted into alloxan, but if the acid be used in a less concentrated form, three nitro-substitution products are formed in succession, viz. :— Violuric (nitrosobarbituric) acid Violantin

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Dilituric acid is not further decomposed by the nitric acid.

(1630) Violuric Acid crystallizes from hot water in brilliant transparent rhombic octohedra. Its salts are very beautiful, and brilliant in colour: potassic violurate crystallizes in blue prisms, giving a violet solution, which becomes red when potash is added in excess; the magnesic salt yields purple-red crystals; the calcic salt is brick red. Baric violurate crystallizes in brilliant square tables with truncated angles: it is of a beautiful red colour, and nearly insoluble in cold water. An aqueous solution of violuric acid is decomposed if boiled; and from its behaviour when heated with soda-lime there is no doubt that it is a nitrosyl (NO) substitution-compound: reducing agents like sulphuretted hydrogen and hydriodic acid convert it into uramil, changing the nitric oxide group into amidogen, e.g. :—

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If boiled with ammonium sulphite, violuric acid becomes converted into ammonium thionurate :

Violuric acid. Ammon, sulphite. Ammonium thionur. Ammon, sulphate.
¤ ̧H ̧(NO)N ̧Ð ̧ + 2 (H ̧N),§0 ̧ = (H ̧N),¤ ̧H ̧Ñ‚§Ð ̧ + (H1N)2S04.

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(1631) Dilituric Acid (H,EN,5, 3 H,O) is the final result of the action of nitric acid of moderate strength upon hydurilic acid. It crystallizes in colourless square prisms and plates which effloresce in the air, and are soluble freely in hot water, less soluble in cold water, furnishing an intensely yellow solution. When heated it is decomposed, emitting nitrous fumes. The acid appears to be tribasic (Baeyer), but it most usually forms salts containing 1 atom of a metallic monad, like the potassiodihydric salt (KH,EN,O;). These acid salts are very stable: they do not give up their basyl when treated with a dilute

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VIOLANTIN-DIBROMOBARBITURIC ACID.

mineral acid, and they usually have a yellow colour. The hydrodipotassic salt (HK,,N,,) is anhydrous, and explodes feebly when heated, or when moistened with oil of vitriol. Many other diliturates, such as the ferric, cupric, and argentic salts, explode when heated. The soluble diliturates yield white precipitates with salts of ammonium, white needle-shaped crystals with solution of ferrous sulphate, and a lemon-yellow precipitate with silver acetate, consisting of Age,Ñ ̧Ð ̧·

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Dilituric acid is a compound of nitroxyl (NO) or nitrobarbituric acid; it may be reduced to uramil by the action of hydriodic acid, but not by sulphuretted hydrogen :—

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When a mixture of strong solutions of violuric and dilituric acids is made, a compound of the two bodies, violantin, crystallizes out. It bears a relation to violuric and dilituric acids somewhat similar to that which exists between alloxantin, and the dialuric acid and alloxan ::

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Violantin is an unstable compound, and separates into its constituents when it is attempted to purify it by recrystallization.

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(1632) Dibromobarbituric Acid.-This arbitrary name was given by Baeyer to a substance at first called by him bromalloxan (¤ ̧Н‚Bг ̧Ñ‚Ð ̧). It is best prepared by triturating hydurilic with nitric acid into a paste, and adding bromine gradually, so long as it enters into combination. If the mixture is then heated, the crystals which had formed become dissolved, with evolution of nitrous fumes; and dibromobarbituric acid crystallizes as it cools in colourless brilliant plates. In this operation the hydurilic passes first into violuric or dilituric acid, and then the bromine displaces the nitrosyl or nitroxyl, together with part of the hydrogen, as shown by the following equations :

Violuric acid.

Dibromobarbituric.

¤ ̧H ̧(N→)N ̧Ð ̧+ 2 Br2+H2 = €,H,N,Br ̧ ̧ + 2HBr + HNO2.

Dilituric.

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2 2 2 3 Dibromobarbituric.

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¤ ̧H ̧(NO)N ̧Ð ̧+2 Br2+ H ̧→ = € ̧H2N ̧Br ̧ ̧ + 2 HBr+HNƏ ̧.
Dibromobarbituric acid crystallizes in colourless brilliant plates

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