Benzidine from nitrobenzene

Bis-(4-dimethylaminobenzylidene)benzidine [6001-51-0] Crystallise the benzidine from nitrobenzene. [Beilstein 14 H 35.]... 

Haussermann 2 reduced nitrobenzene and nitrotoluenes both in alkaline and acid solution, the former with iron, the latter with platinum, electrodes. By reduction in alkaline solution, he obtained as principal product hydrazobenzene and hydrazo-toluene respectively in sulphuric-acid solution he got from nitrobenzene, as chief products, benzidine sulphate and azoxy-benzene, besides an easily changeable body which was not further determined. o-Nitrotoluene3 under like conditions gave o-tolui-dine sulphate besides small quantities of o-toluidine p-nitro-toluene yielded principally p-toluidine. 

Benzidine rearrangement of hydrazobenzene is used to obtain 4,4 -diphenyldi-amines from nitrobenzenes. This reaction occurs intra-molecularly, by way of a p-quinonoid intermediate. 

The use of the compound benzidine in the preparation of what were later known as azo dyes had been observed by Caro and Griess during their collaboration in Manchester in the mid 1860s, and was included in a patent application of 1866. Benzidine was made from nitrobenzene, and contained two free amino groups. Caro s dye known as Palatine orange, and discovered in 1869, was also based on... 

The procedure for isolating and purifying the aniline formed in this experiment represents an excellent example of how the physical and chemical properties of a component in a mixture of organic substances can be exploited to isolate it without using chromatographic techniques. For example, after completing the procedure for the chemical reduction of nitrobenzene, it is necessary to remove aniline from its principal impurities, which are unchanged nitrobenzene and two by-products, benzidine (12), and 4-aminophenol (13). 

Steam distillation (Secs. 2.16 and 4.5) is a good technique for separating volatile organic compounds from nonvolatile organic and inorganic substances. However, the reaction mixture is acidic, and it must be made basic prior to performing the steam distillation so aniline is present as the free base, and the 4-aminophenol is converted to its water-soluble sodium phenoxide salt. The aniline and nitrobenzene are then removed from the reaction mixture by steam distillation. The nonvolatile salt of 4-aminophenol and the nonvolatile benzidine remain in the aqueous phase. 

From the many possibilities of polarographic determination of organic compounds for the sake of brevity the following few substances may be enumerated acetaldehyde (and aliphatic and aromatic aldehydes,) acetophenone, acridine-compounds, aromatic amines, aniline, benzidines, benzal-dehyde, benzene and its homologues (after nitration) chlorphenols, nitrobenzene and nitro compounds in general, phenols (after nitration,) phthalic acid, polychlorinated biphenyls, methacrylates, naphthylamines, etc. 

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