BROMOBARBITURIC, BARBITURIC ACID.

817

or prisms, which are soluble in water, and very soluble in absolute alcohol and in ether. If the aqueous solution is boiled, it is quickly decomposed into hydrobromic acid and alloxan, but it may be crystallized easily from nitric acid, which does not decompose it. Dibromobarbituric acid is readily soluble in alkalies, and furnishes compounds which are easily decomposed by heat, with loss of part of their bromine. It appears to be a dibrominated acid, which, by means of reducing agents, may be converted into its corresponding simple acid, the barbituric of Baeyer (H,C,H,N,O).

2 2

If a solution of dibromobarbituric acid be digested upon metallic zinc, it loses half its bromine and furnishes bromobarbituric acid :

By sulphuretted hydrogen it is reduced to dialuric acid in the presence of water :

If a small proportion of hydriodic acid be employed, hydurilic acid is the result:

4 6

2 € HẸN,Br Og +6 HI = ЄHN +4 HBr + 3 I1⁄2 ;

2 2 3

and if heated with hydriodic acid in excess, the reduction proceeds a step further :—

:

2

(1633) Barbituric Acid (H,,H,N1⁄2Ð ̧, 2 H2→) crystallizes in beautiful prisms, or sometimes in plates, or needles, which are sparingly soluble in cold water, but readily soluble in hot water. Fuming nitric acid converts it into dilituric acid, potassic nitrite into potassic violurate, and bromine into dibromobarbituric acid.

2 3 2

If boiled with caustic potash, ammonia is expelled, and potassic malonate (K,Є,H,,) is formed, from which Baeyer concludes that barbituric acid is malonyl urea ЄH2(¤ ̧H2O)′′N,→, or urca in which 2 atoms of hydrogen have been displaced by the dyad radicle malonyl (Є ̧H ̧Ð1⁄2)”.

3

If heated to 302° (150° C.) in glycerin, barbituric acid loses the elements of water, and the residues of two molecules of the acid coalesce and form a new compound, dibarbituric acid;

=

2 €1H ̧Ñ‚Ð ̧ - H ̧→ н ̧¤ ̧н ̧Ñ‚Ð. The decomposition is always

2 3

2 8

818

REVIEW OF THE DERIVATIVES OF BARBITURIC ACID.

attended with the formation of some secondary products, including ammonium.

(1634) If a hot saturated solution of dibromobarbituric acid be treated with bromine in excess, carbonic anhydride is expelled, and long colourless prismatic needles of tribromacetyl urea are obtained :

:-

This substance is sparingly soluble in cold water, but readily soluble in hot alcohol, from which it crystallizes in brilliant tufts of needles on cooling. If heated to 298° (148° C.), it melts without decomposition to a colourless liquid, which solidifies to a crystalline mass on cooling. When its solution is boiled it is decomposed, bromoform (EHBr,) being produced, while pungent vapours which attack the eyes are evolved. The powdered tribromacetyl exerts a very irritating effect upon the mucous membranes of the eyes and nose.

2

Acetyl urea [ЄH ̧(Є,H,O)NO] or acetureide has been already mentioned (1605).

(1635) Review of the derivatives of Barbituric Acid.-From the details above given it will be easy to trace the connexion between several of the foregoing compounds. Barbituric acid may itself be derived from malonic acid and urea, being malonyl urea. If one of the atoms of hydrogen in the acid be displaced by bromine, we have bromobarbituric acid; if a second atom of hydrogen be displaced, we arrive at dibromobarbituric acid. If two atoms of hydroxyl be introduced in the place of the two of bromine, the formula indicates the composition of alloxanic acid. Violuric acid is barbituric acid in which an atom of hydrogen has been displaced by nitrosyl (NO); dilituric acid the sam compound in which (NO) nitroxyl has taken the place of one atom of hydrogen, and dialuric acid is the compound in which an atom of hydroxyl (HO) has taken the place of the same atom of hydrogen; whilst in uramil an atom of amidogen may be regarded as having taken the place of the atom of hydrogen, as is represented in the following table:

2

(1636) Uramil, or Dialuramide (H2N‚¤ ̧Н ̧Ñ‚Ð ̧).—This compound may be obtained by decomposing ammonium thionurate (1637) by boiling it for a few minutes with an acid :—

Ammonium thionurate.

Uramil.

5

(H ̧N),¤ ̧H ̧Ñ‚Ð ̧,§03 + 2 HCl + H20=2 H ̧NCl + H ̧§Ð ̧ +¤ ̧Н ̧Ñ303. It may also be procured by mixing boiling solutions of alloxantin and muriate of ammonia freed from air (1627); as well as by the reducing action of sulphuretted hydrogen upon violuric acid (1630), or that of hydriodic upon dilituric acid (1631). Uramil crystallizes in penniform groups of brilliant hard needles, which are insoluble in cold water, and sparingly soluble even in boiling water. When exposed to an atmosphere containing traces of ammonia it acquires a rose tint. Uramil is freely soluble in dilute alkaline solutions at ordinary temperatures, and is deposited from them unaltered on adding an acid. But if its solution in ammonia be boiled, it absorbs oxygen, gradually acquiring a rich purple colour, and on cooling deposits crystals of murexid. If uramil be boiled for some time with mercuric oxide or oxide of silver, a similar change occurs; the metallic oxide is reduced, and if the liquid be filtered while hot, beautiful crystals of pure murexid are deposited :

An excess of the metallic oxide must be carefully avoided, otherwise the purple colour disappears, and ammonium alloxanate is formed in the liquid. A solution of uramil in caustic potash evolves ammonia when heated; at ordinary temperatures it slowly absorbs oxygen from the air, acquiring a fine purple colour, and depositing crystals of potassic purpurate; the liquid becomes neutral, and contains potassic alloxanate and mesoxalate.

(1637) Thionuric Acid (H,,H,N ̧ ̧,SO3).—If an aqueous solution of alloxan be added to a solution of ammonium sulphite containing a considerable quantity of free ammonia, and the mixture be boiled for a few minutes, the ammonia and sulphurous acid unite with the elements of alloxan; hence the name, which indicates its connexion with Oriov, sulphur, and uric acid. As the liquid, cools, a beautiful salt, termed ammonium thionurate, is deposited :

820

MUREXID, OR PURPURATE OF AMMONIUM.

Its

By adding a solution of acetate of lead to the solution of this salt, an insoluble gelatinous thionurate of lead is procured, which on standing becomes converted into concentric groups of delicate needles. This precipitate, on being decomposed by sulphuretted hydrogen, gives pure thionuric acid, which may be obtained by evaporation at a gentle heat, crystallized in slender needles. aqueous solution may be preserved unchanged at ordinary temperatures, but it undergoes decomposition when boiled; sulphuric acid being formed, whilst silky crystals of uramil are deposited. The thionurate of ammonium gives a pale yellowish-brown precipitate with salts of copper. It gives no precipitate in acid solutions with salts of barium, but a white one in neutral solutions when mixed with nitrate of silver the metal is gradually reduced, and forms a mirror-like coating on the sides of the vessel which contains it.

6

:

(1638) Murexid, or Purpurate of Ammonium (E.H ̧Ñ‚Ð ̧).— This beautiful compound derives its name from murer, the shellfish from which the celebrated Tyrian purple was obtained. There are several modes of preparing it. The decomposition of uramil by ammonia under the influence of oxygen, and by the action of mercuric oxide, has been already mentioned (1636). Another advantageous method of preparing murexid consists in adding alloxan to an ammoniacal solution of uramil:

Murexid may also be obtained by adding a solution of carbonate of ammonium, drop by drop, to a boiling solution of alloxan, until the liquid has a slightly ammoniacal odour; the solution then acquires a beautiful purple tint, becomes turbid, and on cooling deposits 4-sided prismatic crystals of murexid. Murexid may

also be prepared on a small scale by dissolving 4 grains of alloxantin with 7 of hydrated alloxan, in half an ounce of boiling water, and mixing the solution whilst hot with 80 grains of a cold saturated solution of carbonate of ammonium; brisk effervescence ensues, and a splendid purple liquid is produced, which on cooling deposits magnificent green crystals of murexid, with a golden lustre. These crystals, when heated to 212°, lose water to the extent of 3 or 4 per cent. The brilliant colour of the compound is speedily destroyed by sulphuretted hydrogen, as well as by free ammonia. Murexid is but sparingly soluble in cold water, to which, however, it communicates its intense purple colour; hot water takes it up more freely.

TEST FOR URIC ACID-PSEUDO-URIC ACID.

821

When the solution of murexid is mixed with one of a salt of lead, of barium, or of silver, it yields a purple precipitate. Corrosive sublimate slowly but completely decolorizes a solution of murexid, giving a beautiful purple precipitate. A solution of acetate of zinc yields a golden-yellow precipitate in a solution of murexid, forming a brilliant iridescent film in which green and yellow tints predominate. Dilute acids decompose the crystals of murexid, and cause the separation of scales of a sparingly soluble yellowish substance, termed murexan, which, in all probability, is an impure form of uramil; the solution contains a mixture of alloxan and alloxantin.

The colouring principle of murexid has lately been applied successfully to the dyeing of silks and cotton, and less perfectly to wool. Silk may be dyed by simple immersion in a concentrated solution of corrosive sublimate mixed with murexid. Cotton goods are mordanted with lead. Nitrate of lead is thickened and mixed with a proportion of murexid sufficient to give the desired shade: it is then printed, the cloth dried and immersed in a bath containing I part of corrosive sublimate, 1 of sodic acetate, and 100 of water (Lauth). Dyeing on wool with murexid may be effected. if the fabric be first mordanted with pink salt,' the double chloride of tin and ammonium (2 H,NCI,SnCl).

Test for Uric Acid.-Advantage is taken of the formation of murexid, in order to detect very minute quantities of uric acid by the action of nitric acid. In applying this test, the substance supposed to contain uric acid is heated on a slip of glass with a drop of nitric acid, and evaporated cautiously to dryness. If uric acid be present, the residue has a red colour, which is converted by exposure to the vapour of ammonia into a fine crimson; further, the addition of a drop of a solution of potash developes a splendid purple colour, which disappears on the application of heat, with extrication of ammonia.

(1639) Pseudo-Uric Acid (H¤ ̧н ̧Ñ‚Ð ̧). — If uramil be boiled with a concentrated solution of potassic cyanate until it no longer becomes red on exposure to the air, a solution is obtained which deposits a yellow crystalline powder on cooling (Baeyer), consisting of potassic pseudo-urate :—

Uramil. Potassic cyanate. Potassic pseudo-urate.

H2N2+ KENO =

5 3 3

5 4 4'

If this salt be dissolved in excess of potash and decomposed by hydrochloric acid, a white crystalline deposit of pseudo-uric acid, H.NO, is obtained. Sodic pseudo-urate is rather soluble in