This compound, also known as oil of mirbane, which is prepared in large quantities, principally for the dye stuff industry, is also used in perfumery as a cheap substitute for oil of bitter almonds. The quality of the product depends on the purity of the benzene employed. In perfumery, only the socalled light nitrobenzene (sp. gr. 1,2) is used, which, if necessary, is freed from the last traces of impurities by distillation over sodium hydroxide. Nitrobenzene is a strongly refractive, faintly yellow liquid which upon standing becomes darker. Its odor resembles that of bitter almond oil. It is but sparingly soluble in water, readily soluble in alcohol, ether, benzene, etc. It is readily volatile with water vapors. In the cold it congeals and, according to Linebarger,1) melts again at +3,6°. Friswell-) records the following properties:
1) Berl. Berichte 7 (1874), 518. 2) Ibidem 1293.
3) Arch, der Pharm. 237 (1899), 111.
4) A. W. Hofmann, loc. cit 520.
Cong. p. +5°; b. p. 209° (corr., 760 mm.); d 1.5o/4o (solid) 1,3440, d 3.8o/4o (liquid) 1,2220, d 13o/4o 1,2116.
In connection with commercial preparations Schimmel & Co. observed the following constants:
Cong. p. +5,5°; m. p. +5,6°; b. p. 208 to 209° (741 mm.); d15ol,20 to 1,21; aD±0°; nD20o 1,552 to 1,553; soluble in 1 vol. of 90 p. c. alcohol.
Nitrobenzene which is to be used for perfuming soaps should stand the soap test, /. e., when boiled with 15 p. c. potassa solution, it should not color the latter. If colored yellow or brown, the presence of other nitrocompounds (nitrotoluene) is indicated. The test can be carried out in a wide test tube by heating 2 to 3 ccm. of nitrobenzene with an equal or twice its volume of potassa solution for 1 to 2 minutes. While boiling the test tube should be shaken otherwise the mixture is apt to be thrown out with explosive violence.
For its detection, nitrobenzene is reduced to aniline with tin and hydrochloric acid or with zinc and dilute sulphuric acid. The aqueous solution of aniline is identified by the violet color produced upon the careful addition of chlorinated lime solution; also by the dark green or black precipitate produced when potassium bichromate is added to the solution of aniline prepared with an excess of sulphuric acid. This precipitate is soluble in hot water or alcohol with a dark green color. The first of these two tests is the more delicate one.
1) Americ. chem. Journ. 18 (1896), 437. 2) Journ. chem. Soc. 71 (1897), 1011.
Nitrobenzene is a strong poison. Cases are known when 20, or even 7 to 8 drops have proven fatal.1) Contact of nitrobenzene with the skin can also prove dangerous.