PREPARATION XVI.

PICRIC ACID, C,H,N,O,=CH,(OH) (4) NO,

(a-Trinitrophenol.)

(2) NO2

(6) NO2

LITERATURE.—Woulfe (1771); Dumas (1833), Ann. Ch. Phys. 53, 178, and (1841) Ann. Ch. Phys. (3), 2, 228; Laurent (1841), Ann. Ch. Phys. (3) 3, 221; Schmidt, Glutz (1869), Ber. 2, 52.

*

Fifty grms. commercial phenol and 50 grms. conc. sulphuric acid are heated together in a porcelain basin on the water-bath until a clear solution of phenolsulphonic acid is obtained. It is diluted with double the volume of water, and slowly added, in small quantities at a time, from a tap-funnel, to 200 grms. nitric acid, sp. gr. 14, contained in a flask of about litre capacity, which is well shaken during the process. The liquid changes to a deep red colour, a considerable rise of temperature occurs, and red fumes are evolved. When the phenolsulphonic acid has been added, the flask is placed on the water-bath and heated until the red colour of the liquid changes to yellow. On cooling, picric acid separates out as a yellow crystalline mass. It is filtered (platinum cone

only) at the filter pump and washed free from the mother-liquor with water. It is then purified by recrystallisation from hot water, acidified with a few drops of sulphuric acid.

он

CH(OH) + H2SO1 = C6H5OH + H2O

Phenol

Phenolsulphonic Acid.

+3HONO2 = C6H2(OH)(NO2)3+3H2O+H2SO ̧

Picric Acid.

Properties.-Yellow prismatic crystals; m. p. 122'5°, subliming on gently heating; easily soluble in alcohol and ether; with difficulty in cold, more readily in hot water; the solution has a bitter taste. Heated gently with 2 parts of potassium cyanide in a dilute solution a brown crystalline precipitate of isopurpuric acid separates on cooling.

(Di-p-oxydiphenylphthalid.)

LITERATURE.-Baeyer (1876), Ber. 9, 1230 and (1880)

Ann. Ch. Pharm. 202, 68.

10 grms. phthalic anhydride.

Ten grms. phthalic anhydride, 20 grms. phenol, and 8 grms. conc. sulphuric acid are heated together to 115°-120° in the oil-bath for ten hours. The mass becomes semi-fluid and of a dark red colour. When the reaction is finished, the hot melt is poured into water, and boiled until the smell of phenol has disappeared, the water being renewed as it evaporates. The undissolved yellow granular precipitate is separated on cooling from the liquid by filtration, and washed with water. It is then dissolved in dilute caustic soda solution, filtered from the undissolved residue, and the filtrate acidified with acetic acid. and a few drops of hydrochloric acid. The phthaleine separates out after standing for some hours as a light yellow sandy crystalline powder. It is filtered and purified by dissolving in absolute alcohol, with the addition of animal charcoal (1 part phenolphthaleine, 6 parts alcohol, and part charcoal), and boiling the solution on the water-bath with a condenser for 1 hours. The mass is filtered hot, the charcoal washed with 2 parts boiling alcohol, and the alcoholic filtrate evaporated down to two-thirds its bulk, on the waterbath. On the addition of 8 times the quantity of cold water to the cooled solution, the latter becomes turbid. The liquid is well stirred, and after standing a few seconds, filtered through cloth from the resinous oil, which separates out. On heating the filtrate for a time on the water-bath to expel excess of alcohol,

Properties.-White, granular, crystalline powder;

m. p. 250-253°; very slightly soluble in water, readily soluble in hot alcohol; soluble in caustic alkalis with a crimson colour.

LITERATURE.-Woskresensky (1838), Ann. Ch. Pharm. 27, 268; Wöhler (1843), Ann. Ch. Pharm. 45, 354 (1850), 51, 145 (1858), 65, 349; Graebe (1868), Ann. Ch. Pharm. 146, 1; Nietzki (1882), Ann. Ch. Pharm. 215, 125 and (1886) Ber. 19, 1467.

Fifty grms. commercial aniline are dissolved in a mixture of 400 grms. conc. sulphuric acid and 1500

1 An equivalent quantity of sodium dichromate dissolved in 2 to 3 times its weight of water may be used (Nietzki).

grms. water, contained in a round-bottomed flask of about 4 litres capacity, and to the well-cooled solution of aniline sulphate 175 grms. finely powdered potassium dichromate are slowly added in small portions at a time.

It is necessary for the success of the operation that the flask be thoroughly well shaken after each fresh addition of dichromate, and that the temperature of the mixture does not rise above that of the outside atmosphere. Aniline black separates out at first, the greenish colour of which changes towards the end of the operation to a violet black. When all the dichromate has been added, the mixture is heated for a time to 35° on the water-bath, and, on cooling, extracted repeatedly with small quantities of ether. On distilling off the solvent, quinone remains in the form of yellow needle-shaped crystals, which are usually discoloured by the presence of quinhydrone. The substance is, however, sufficiently pure for most purposes, and is well adapted for the preparation of hydroquinone. By recrystallisation from ligroin the quinone is obtained well crystallised and free from quinhydrone.

The reaction consists in oxidation and elimination of the amido-group and simultaneous replacement of two hydrogen atoms in the benzene nucleus by oxygen, and cannot well be expressed in the form of equation.

Properties.-Golden yellow needle-shaped crystals; m. p. 116°; with difficulty soluble in water, readily soluble in alcohol and ether; it sublimes on heating,

E