Aniline [62-53-3] M 93.1, f -6.0o, b 68.3/10mm, 184.4o/760mm, d 4 20 1.0220, n D 20 1 . 5 8 5 , n D 25 1.5832, pK25 4.60. Aniline is hygroscopic.
It can be dried with KOH or CaH2, and distilled under reduced pressure. Treatment with stannous chloride removes sulfur-containing impurities,
reducing the tendency to become coloured by aerial oxidation. It can be crystallised from Et2O at low temperatures. More extensive purifications
involve preparation of derivatives, such as the double salt of aniline hydrochloride and cuprous chloride or zinc chloride, or N-acetylaniline (m
114o) which can be recrystallised from water. Redistilled aniline is dropped slowly into a strong aqueous solution of recrystallised oxalic acid.
Aniline oxalate (m 174-175o) is filtered off, washed several times with water and recrystallised three times from 95% EtOH. Treatment with saturated
Na2CO3 solution regenerated aniline which was distilled from the solution, dried and redistilled under reduced pressure [Knowles Ind Eng Chem 12 881
1920]. After refluxing with 10% acetone for 10hours, aniline is acidified with HCl (Congo Red as indicator) and extracted with Et2O until
colourless. The hydrochloride is purified by repeated crystallisation before aniline is liberated by addition of alkali, then dried with solid KOH,
and distilled. The product is sulfur-free and remains colourless in air [Hantzsch & Freese Chem Ber 27 2529, 2966 1894]. Non-basic materials,
including nitro compounds, are removed from aniline in 40% H2SO4 by passing steam through the solution for 1hour. Pellets of KOH are then added to
liberate the aniline which is steam distilled, dried with KOH, distilled twice from zinc dust at 20mm, dried with freshly prepared BaO, and finally
distilled from BaO in an all-glass apparatus [Few & Smith J Chem Soc 753 1949]. Aniline is absorbed through skin and is TOXIC. [Beilstein 12 IV
223.]
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