slowly raising the temperature of the liquid the melting-point of the substance may be readily observed. The substance is allowed to cool and is reheated. In this way the freezing and melting-points (uncorrected)1 may be repeatedly determined. The substance, if pure, melts completely and suddenly within one or two degrees; if impure the liquefaction is protracted and the melting-point usually too low. According to the temperature at which the substance melts, water, paraffin, or oil may replace the sulphuric acid in the bath used. C6H5NH2 + CH3COOH Aniline Acetic Acid = C&H NH(CH3CO) + H2O Properties.-Rhombic plates; m. p. 112°; b. p. 295°; on boiling with caustic potash or strong hydrochloric acid it is resolved into acetic acid and aniline. 1 The following expression gives the correction required by the difference of temperature of the column of mercury outside the vessel, and is added to the observed temperature. where T = N(T-t) 000154 apparent temperature in degrees t = temperature of a second thermometer, the bulb of which is placed at half the length of N above the vessel N *000154 == length of the mercury column in degrees from above the vessel to T = apparent expansion of mercury in glass. In the new apparatus of Roth (Ber. 19, 1970) this correction is obviated. LITERATURE.-Körner (1876), Chem. Soc. J. 14, 209; Witt (1875), Ber. 8, 144; Grethen (1876), Ber. 9, 775; Beilstein, Kurbatow (1879), Ann. Ch. Pharm. 197, 83. 12 grms. acetanilide. 40 fuming nitric acid, sp. gr. 1.5. Twelve grms. powdered acetanilide are added slowly and in small quantities to 40 grms. fuming nitric acid contained in a beaker cooled in water. The mixture must not be allowed to become warm, otherwise a violent reaction occurs and the nitrocompounds decompose. When the acetanilide has been added, the liquid has a deep red colour. It is now poured upon pounded ice or snow when the paraand a small quantity of ortho-compound separate out as a yellow curdy precipitate. This is rapidly filtered at the pump and washed once or twice with cold water. The filtrate, which has a red colour and contains the chief portion of the ortho-compound, is removed, the residue is again washed with water, well pressed, and dried at 100°. In order to dissolve out any ortho-nitracetanilide from the para-compound, the dried substance is powdered and washed with cold chloroform until the washings are nearly colourless. The residue on the filter has a light yellow colour, and crystallises from alcohol in almost colourless needles. The red-coloured filtrate containing the orthocompound is extracted two or three times with chloroform, which dissolves it, forming a deep red layer at the bottom of the vessel. This is carefully separated. On distilling off the chloroform on the water-bath a red oil remains, which is poured, while still warm, into a beaker. On cooling it solidifies ; more quickly if the bottom of the vessel is scratched with a glass rod. The crystals are spread upon a porous plate to drain and then dissolved in a small quantity of alcohol, in which the substance is readily soluble. To the hot alcoholic solution water is added until a cloudiness appears. On shaking, drops of red oil collect from which the liquid is filtered through a moistened filter. The clear filtrate on cooling deposits orange-coloured tabular crystals. CH5NH.C,H,O + HNO3 = CH Acetanilide NH.C,H,O+H,O NO2 Nitracetanilide. Properties.-Para-nitracetanilide colourless needles; m. p. 207°. On boiling a small quantity in a test-tube for a few minutes with an excess of concentrated hydrochloric acid, until, on diluting, no precipitate is produced, the hydrochloride of para-nitraniline is formed, and on the addition of caustic potash solution the free base is precipitated in the form of acicular clusters; m. p. 147°. Ortho-nitracetanilide orange-coloured plates; m. p. 78°. Treated with hydrochloric acid as above, it yields ortho-nitraniline, which crystallises in orange needles; m. p. 71.5°. PREPARATION VII. META-DINITROBENZENE, CH4O4N2=C6H4 (1) NO2 (3) NO2 2 LITERATURE.-Deville (1841), Ann. Ch. Phys. (3) 3, 187; Hofmann, Muspratt (1846), Ann. Ch. Pharm. 57, 214: Beilstein, Kurbatow (1875), Ann. Ch. Pharm. 176, 44; Rinne, Zincke (1874), Ber. 7, 869; Körner (1876), Chem. Soc. J. 14, 207. 50 grms. nitrobenzene. 35 fuming nitric acid, sp. gr. 1.5. 35 Fifty grms. nitrobenzene are added to a mixture of 35 grms. fuming nitric acid and 35 grms. conc. sulphuric acid contained in a flask of about half-litre capacity and well shaken after each fresh addition.* Heat is evolved, and the mass becomes somewhat deeper in colour. The rate at which the nitrobenzene is run in is regulated by the temperature of the mixture, which should be maintained at about 70°-80°. When the nitrobenzene has been thus added, the contents of the flask are boiled for a short time on the sand-bath, and are poured whilst warm into a large quantity of water. The metadinitrobenzene, mixed with small quantities of the ortho-and para-compounds, separates out as a yellow crystalline mass, which is filtered and washed with water on the filter-pump. It is then recrystallised from hot dilute alcohol. On cooling the alcoholic solution, meta-dinitrobenzene crystallises out in light yellow needles, and is free from its isomers, which remain dissolved in the mother liquor. NO2 + H2O Nitrobenzene Dinitrobenzene. Properties. Almost colourless long needles; m. p. 89.8°; b. p., 297°. PREPARATION VIII. META-NITRANILINE, CHO2N2=C6H4 (1) NH2 (3) NO2 2 LITERATURE.-Muspratt, Hofmann (1846), Ann. Ch. Pharm. 57, 217; Arppe (1855), Ann. Ch. Pharm. 96, 114; Beilstein, Kurbatow (1875), Ann. Ch. Pharm. 176, 44; Hübner, Frerichs (1877), Ber. 10, 1716. |