Aniline, formation identification

In the known absence of bromoform, iodoform, chloral, and other halogenated methanes, the formation of phenyhsonitrile with aniline provides a simple and faidy sensitive but nonspecific test for the presence of chloroform, the carbylamine test. Phenyhsonitrile formation is the identification test given in the British Pharmacopoeia. A small quantity of resorcinol and caustic soda solution (10% concentration) added to chloroform results in the appearance of a yellowish red color, fluorescing yeUow-green. When 0.5 mL of a 5% thymol solution is boiled with a drop of chloroform and a small quantity of potassium hydroxide solution, a yellow color with a reddish sheen develops the addition of sulfuric acid causes a change to brilliant violet, which, diluted with water, finally changes to blue (33). 

Primary aromatic amines (e.g., aniline) and secondary aliphatic-aromatic amines (e. g., 7V-methylaniline) usually form triazenes in coupling reactions with benzenedi-azonium salts. If the nucleophilicity of the aryl residue is increased by addition of substituents or fused rings, as in 3-methylaniline and 1- and 2-naphthylamine, aminoazo formation takes place (C-coupling). However, the possibility has also been noted that in aminoazo formation the initial attack of the diazonium ion may still be at the amine N-atom, but the aN-complex might rearrange too rapidly to allow its identification (Beranek and Vecera, 1970). 

The general pattern of anodic behavior of para-substituted anilines (68) was established in aqueous acidic media by Bacon and Adams17,106. The postulated one-electron oxidation of the substrate to the radical cation 681 is followed by rapid head-to-tail coupling of 681 with the substrate 68 giving protonated 4 -substituted 4-aminodiphenylamine in the oxidized form (69) as the final main product. The product 69 shows reversible redox peaks at more cathodic potentials, supporting its identification beside the spectral and chemical analysis. The product formation is preceded by elimination of one para-substituent and, if it leaves as an anion (e.g. halide, methoxide or ethoxide ion), then the overall electrochemical process (equation 1) corresponds to a one-electron (two electrons per two reactant molecules) process. However, if it leaves as a neutral group (e.g. CO2 in the oxidation of p-aminobenzoic acid), a dimer is formed in the reduced form and the overall reaction is a two-electron process. 

Magnetic resonance should prove a useful tool in facilitating identification of coordination sites in complexes. For example , in the aniline-iodine complex, a large selective downfield shift is observed for the N-H protons on complex formation. Such a large deshielding of these protons can only indicate that charge is indeed transferred from nitrogen and that this is the site of coordination with iodine. 

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