Oxidation of aniline

Oxidation of anilines with alkaline potassium persulfate (K2S2O8) followed by hydrolysis to give ortho-hydroxyl anilines is known as the Boyland-Sims oxidation.  

Hypervalent iodine(V) reagents, such as IBX (2-iodoxybenzoic acid) and DMP, have found widespread synthetic application as stoichiometric oxidants for the facile and selective oxidation of primary alcohols and secondary alcohols to the respective carbonyl compounds and for other important oxidative transformations 

NH2 ArNH2 (2 equiv), 2-IC6H4CO2H (0.15 equiv) AcOOH, CH2CI2. rt, 20-24 h 

Ar = 3-CIC6H4,4-CIC6H4,3-BrC6H4,4-BrCeH4, 4-FC6H4,4-MeOC6H4 

Page and coworkers have demonstrated that primary and secondary alcohols can be oxidized to the respective aldehydes and ketones under reflux conditions in acetonitrile or dichloroethane in the presence of a catalytic amount of 2-iodobenzoic acid and using tetraphenylphosphonium monoperoxysulfate, Ph4P+HS05 , 

2-IC6H4CO2H (10 mol%), Ph4P+HS05- (3 equiv) CICH2CH2CI or MeCN, 80 °C, 3-12 h 

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Benzoquinone ( quinone ) is obtained as the end product of the oxidation of aniline by acid dichromate solution. Industrially, the crude product is reduced with sulphur dioxide to hydroquinone, and the latter is oxidised either with dichromate mixture or in very dilute sulphuric acid solution with sodium chlorate in the presence of a little vanadium pentoxide as catalyst. For the preparation in the laboratory, it is best to oxidise the inexpensive hydroquinone with chromic acid or with sodium chlorate in the presence of vanadium pent-oxide. Naphthalene may be converted into 1 4-naphthoquinone by oxidation with chromic acid. 

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

Oxidation. Aromatic amines can undergo a variety of oxidation reactions, depending on the oxidizing agent and the reaction conditions. For example, oxidation of aniline can lead to formation of phenyUiydroxylamine, nitrosobenzene, nitrobenzene, azobenzene, azoxybenzene or -benzoquinone. Oxidation was of great importance in the early stages of the development of aniline and the manufacture of synthetic dyes, such as aniline black and Perkin s mauve. 

Oxidation of aniline with a mixture of manganese dioxide and sulfuric acid has been used commercially for production of -benzoquinone [106-51-4] (35). 

The oxidizing properties of MnOy are utilized in the oxidation of aniline for the preparation of hydroquinone which is important as a photographic developer and also in the production of dyes and paints. 

Many anodic oxidations involve an ECE pathway. For example, the neurotransmitter epinephrine can be oxidized to its quinone, which proceeds via cyclization to leukoadrenochrome. The latter can rapidly undergo electron transfer to form adrenochrome (5). The electrochemical oxidation of aniline is another classical example of an ECE pathway (6). The cation radical thus formed rapidly undergoes a dimerization reaction to yield an easily oxidized p-aminodiphenylamine product. Another example (of industrial relevance) is the reductive coupling of activated olefins to yield a radical anion, which reacts with the parent olefin to give a reducible dimer (7). If the chemical step is very fast (in comparison to the electron-transfer process), the system will behave as an EE mechanism (of two successive charge-transfer steps). Table 2-1 summarizes common electrochemical mechanisms involving coupled chemical reactions. Powerful cyclic voltammetric computational simulators, exploring the behavior of virtually any user-specific mechanism, have... 

The existence of materials now included among the conducting polymers has long been known. The first electrochemical syntheses and their characterization as insoluble systems took place well over a century ago. In 1862 Letheby reported the anodic oxidation of aniline in a solution of diluted sulphuric acid, and that the blue-black, shiny powder deposited on a platinum electrode was insoluble in HjO, alcohol, and other organic solvents. Further experiments, including analytical studies, led Goppelsroeder to postulate in 1876 that oligomers were formed by the oxidation of aniline. 

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... 

Marinescu L, Molbach M, Rousseau C, Bols M (2005) Supramolecular oxidation of anilines using hydrogen peroxide as stoichiometric oxidant. J Am Chem Soc 127(50) 17578-17579... 

The oxidation of aniline by Caro s acid to nitrosobenzene, which proceeds in a quite different way, may be recalled here (p. 179). 

Quinone may be prepared by the oxidation of aniline with dichromate or manganese dioxide and sulfuric acid.1 This is a more feasible commercial method than the one given. However, the oxidation of hydroquinone is more rapid and convenient and, hence is more desirable for use in the laboratory. Various materials have been oxidized by chemical means to give quinone they are quinic acid,2 hydroquinone,3 benzidine,4 -phenylene-diamine,5 sulfanilic acid,6 / -phenolsulfonic acid,7 arbutin,8 aniline black,9 and the leaves of various plants.10 Quinone is also formed by several other methods by the fermentation of fresh grass 11 by the action of iodine on the lead salt of hydroquin-... 

Bulky quaternary ammonium salts promote the ruthenium-catalysed oxidation of anilines by hydrogen peroxide to nitrobenzenes [25]. In the absence of the ammonium salt, the major product is the azoxybenzene, whereas lower molecular weight tetra-alkylammonium salts produce a mixture of products. 

PANI is usually produced by the anodic oxidation of aniline in acidic aqueous solution [5, 139], but can also be produced by chemical oxidation [138b, 140]. Hence, it is not surprising that the oxidation of PANI is pH-dependent and that, therefore, in addition to electron-transfer processes, proton-transfer reactions occur during charging. Although it is usually assumed that PANI has a chain structure (emeraldine) with head-tail connections... 

Polyaniline can also be prepared electrochemically, e.g. by oxidation of aniline in acid media (MacDiarmid and Maxfield, 1987). An interesting aspect of this polymer is that by doping, the oxidation state of the polyaniline may be continuously varied from the totally reduced insulator, leucoemeraldine (oxidation state y = 1) ... 

Dichloronitrobenzene has been prepared by deamination of 3,5-dichloro-4-nitroaniline and of 2,4-dichloro-3-nitroaniline. This procedure is an example of the rather general oxidation of anilines to nitrobenzenes with peroxytrifluoroacetic acid. Use of this reagent is frequently the method of choice for carrying out this transformation, and it is particularly suitable for oxidation of negatively substituted aromatic amines. Conversely, those aromatic amines, such as />-anisidine and j8-naphthylamine, whose aromatic nuclei are unusually sensitive to electrophilic attack give intractable mixtures with this reagent. This is not... 

Laha, S. and Luthy, R.G. Oxidation of aniline and other primary aromatic amines by manganese dioxide. Environ. Sci. TechnoL, 24(3) 363-373, 1990. 

Pillai, P., Helling, C.S., and Dragun, J. Soil-catalyzed oxidation of aniline, Chemosphere, 11(3) 299-317, 1982. 

Oxidation of anilines to phenols using alkaline persulfate. 

The synthesis of polyaniline and copolymers of aniline with o-nitroaniline is aimed at obtaining an electroactive material. This material can be used, for example, as an electrode in conjunction with the magnesium electrode to construct chemical power sources. The polymers were prepared by oxidation of aniline or its mixture with nitroaniline ammonium persulfate in aqueous hydrochloric... 

One-electron oxidation of aniline derivatives gives a radical-cation in which the unpaired electron is distributed over both the nitrogen atom and the aromatic system. The further reactions of these intermediates more resemble those of aromatic compounds than of aliphatic amines. Some of the radical-cations are very stable in solution Wurster s blue, prepared by oxidation of tetramethyl-1,4-pheny ene-diamine [152], and Wurster s red from N,N-dimethyI-l,4-phenylenediamine [153] have been known since 1879. They were recognised as radical-cations by Mi-chaelis [154]. 

Aniline itself undergoes intramolecular coupling and further oxidation to give aniline black. Poly(aniline) can be deposited as a thin coherent film on the anode by continuously cycling the potential between -0.2 and 0.8 V vs. see [165], Oxidation of aniline using manganese(ll) - roanganese(IIl) as mediator in dilute sulphuric... 

Another facet of the reactivity of aminoxyl radicals has been brought to attention by recent studies of the oxidation of substrates endowed with low redox potential. Some aminoxyl radicals, depending on the reduction potential value of the couple >N—O / >N—O, can behave as moderate one-electron abstractor towards substrates endowed with appropriate oxidation potential. This rather unprecedented reactivity feature, outlined in Scheme 10, has been substantiated by the oxidation of aniline or phenol derivatives, whose redox potential is conveniently located in the 0.4-1.0 V/NHE range ". 

SCHEME 151. Metal-catalyzed oxidation of anilines by TBHP... 

Monopersulfuric acid (monoperoxysulfuric acid, H2SO5, Caro s acid) was first detected during electrolysis of sulfuric acid . Later, in 1898, Caro found the oxidation of aniline to nitrobenzene with ammonium peroxydisulfate Ic in H2SO4. Later, the oxidizing species was found to be 112805. ... 

Polyaniline is a repeating unit of benzene rings each joined by an N—H group (13, Fig. 13.7). This polymer and its derivatives are of interest because they are electrically conductive when doped with oxidants. This material is prepared by oxidation of aniline electrochemically, ° enzymaticaUy, or with simple chemical reagents. Polyaniline can be formally regarded as a polymer of... 

The oxidation of aniline by Cu+2 (60), which was claimed to proceed completely analogous to Reaction 5, is an example of Cu(II) as the oxidant. 

As is well known, the oxidation of aniline with various oxidizing agents leads to a variety of products, usually highly colored polymeric materials. However, the reaction with Caro s acid (permonosulfuric acid, H2SOs) with aniline produces nitrosoaniline rapidly [76]. With this reagent, many aromatic amines have been oxidized to the corresponding nitroso compounds, e.g., the three nitronitrosobenzenes were prepared from the corresponding nitroani-lines [77, 78]. The reaction is normally carried out in an aqueous medium. In... 

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