Aniline black, production

By continued action of aniline on aniline black, products resembling the indulines are formed. One of these has heen isolated, and is a blue dyestuff of the formula, C3eH2 N5 or [18]... 

Minor uses of vanadium chemicals are preparation of vanadium metal from refined pentoxide or vanadium tetrachloride Hquid-phase organic oxidation reactions, eg, production of aniline black dyes for textile use and printing inks color modifiers in mercury-vapor lamps vanadyl fatty acids as driers in paints and varnish and ammonium or sodium vanadates as corrosion inhibitors in flue-gas scmbbers. 

Aniline black was first prepared in the last century [164] when it was found that anodic oxidation of aniline at a Pt electrode in aqueous H2S04 gave a dark green powdery product. Aniline blacks have subsequently produced under a variety of conditions via both chemical and electrochemical routes with a low level of interest... 

This process is used principally in Europe. It was first developed in 1854 for the production of aniline. Nitrobenzene was reduced to aniline using metallic iron, hence the process was termed the aniline or nitrobenzene process. Iron oxides were formed as unusable, grey/black products. Around 1925, Laux found that addition of iron chloride modified the process so that iron oxides suitable for use as pigments could be produced. With this additive alone, magnetite with a high tinting strength results, i. e. 

Potassium chlorate is employed for various purposes as an oxidizer, examples being the manufacture of dyes such as aniline-black, and the production of safety matches and fireworks. 

The coal tar dye industry received its first stimulus when the manufacture of aniline was started — first in England — and aniline has remained one of its most important products. A considerable amount of aniline is still used today in the production of aniline black on the fiber. Large quantities are ako used in the preparation of dyes of various classes, either direcdy or after conversion into numerous other intermediates. Aniline is also an im rtant starting material in the preparation of pharmaceutical products. Apparently, the largest consumer of aniline derivatives in modem times, however, is the rubber industry, which uses huge quantities of diphenylguanidine, thiocarbanilide, and other sulfur containing aniline derivatives as vulcanization accelerators. 

Synthesis is performed in 0.1-1 m H2SO4 at the anode, mostly potentiodynami-cally (cf. [348]) or chemically with persulfates. The material has known as aniline black for more than a century, and it is an intermediate for the synthesis of quinone. Benzidine, a carcinogen, may be a side-product, but it was possible to minimize this... 

When Perkin poured an alcohol on the black product, it turned a mauve color. He found a way to extract the purple substance from the black product and determined that his newly discovered substance was perfect for dyeing clothes. He named his accidental discovery aniline purple, but the fashionable people of Paris soon renamed it mauve. 

Some conclusions as to the constitution of aniline black are obtained from its decomposition on oxidation and reduction. The production of quinone in the former, and of paraphenylamine, c., in the latter, render it apparent that the nitrogen atom of one benzene residue enters the chain of another benzene residue in the para position to the nitrogen atom, Goppelsroeder s formula [15], in which the benzene chains are represented as linked in a circle of imido-groups, corresponds to this view to a certain extent. This entirely symmetrical formula, however, does not account for the tinctorial character of the compound in a satisfactory manner and from the formation of a stable leuco-compound it may be deduced that in all probability at least two nitrogen atoms of the molecule are linked together. 

Besides the compound described in detail, aniline black generally contains others. One of these is the product of a less energetic oxidation, and is distinguished from the former compound by the brighter green colour of its salts and a brighter violet... 

On further oxidation, especially with chlorinating agents, aniline black yields a darker product which is no longer turned green with acids. 

When coal is distilled many products are formed. Among these is aniline, one of the greatest dyestuff intermediates. This compound is the basis of many dyes such as aniline black, Rosaniline, and nearly every color of the rainbow. 

Aromatic amines, which are far less basic than the aliphatic forms, tend to react by substitution on the ring rather than by N-chlorination the amino group is a powerful electron donor (cf. Chapter 1). Thus, aniline gives rise to /7-chloroaniline as the principal product of reaction with HOCl (Barnhart and Campbell, 1972 Hwang et al., 1990). However, benzidine (43) reacts rapidly with HOCl to form a deeply colored polymer without ring chlorine substitution. It was suggested that an oxidized polymer similar to the common dye, aniline black (44) had been produced (Jenkins et al., 1978). 

PANI is one of the earliest known synthetic polymers, which can date back to 1835 as aniline black for any products produced by the oxidation of aniline. The interest toward PANI increased significantly over the past decades due to its low cost, easy preparation, high conductivity, mechanical flexibility, environmentally stability, and unusually doping/dedoping chemistry. Besides, PANI also has three distinct oxidation states with different colors, naming leucoemeraldine, emeraldine, and pernigraniline. 

Another heterochain polymer which has received a lot of attention recently is polyaniline. This material is produced by chemical or electrochemical oxidation of aniline, and it seems likely that it is very similar to, if not always identical with, aniline black , an ill-defined material of some antiquity. The propensity of hetero-substituted aromatics to undergo coupling via intermediate radical cations is well established and, since a monosubstituted benzene is effectively a trifunctional monomer in this context, it seems likely that this product is a network or highly branched material, which would account for its unattractive handling properties. 

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