Oxidation of aromatic amines

Obsolete uses of urea peroxohydrate, as a convenient source of aqueous hydrogen peroxide, include the chemical deburring of metals, as a topical disinfectant and mouth wash, and as a hairdresser s bleach. In the 1990s the compound has been studied as a laboratory oxidant in organic chemistry (99,100). It effects epoxidation, the Baeyer-Villiger reaction, oxidation of aromatic amines to nitro compounds, and the conversion of sodium and nitrogen compounds to S—O and N—O compounds. 

Nitroso compounds are formed selectively via the oxidation of a primary aromatic amine with Caro s acid [7722-86-3] (H2SO ) or Oxone (Du Pont trademark) monopersulfate compound (2KHSO KHSO K SO aniline black [13007-86-8] is obtained if the oxidation is carried out with salts of persulfiiric acid (31). Oxidation of aromatic amines to nitro compounds can be carried out with peroxytrifluoroacetic acid (32). Hydrogen peroxide with acetonitrile converts aniline in a methanol solution to azoxybenzene [495-48-7] (33), perborate in glacial acetic acid yields azobenzene [103-33-3] (34). 

Azo Coupling. The coupling reaction between an aromatic diazo compound and a coupling component is the single most important synthetic route to azo dyes. Of the total dyes manufactured, about 60% are produced by this reaction. Other methods iaclude oxidative coupling, reaction of aryUiydraziae with quiaones, and oxidation of aromatic amines. These methods, however, have limited iadustrial appHcations. 

Oxidation of Aromatic Amines. The technically important dye Direct Yellow 28 (23) [10114-47-3] (Cl 19555) for cotton usage is manufactured by oxidation of dehydrothio- i ra-toluidinesulfonic acid sodium salt with sodium hypochlorite ia aqueous alkaline solutioa. 

INDICATIVE OXIDATION OF AROMATIC AMINES IN PLATINUM METALS CATALIMETRY... 

Iodosobenzene diacetate is used as a reagent for the preparation of glycol diacetates from olefins,9 for the oxidation of aromatic amines to corresponding azo compounds,10 for the ring acetylation of N-arylacetamides,11 for oxidation of some phenols to phenyl ethers,12 and as a coupling agent in the preparation of iodonium salts.13 Its hydrolysis to iodosobenzene constitutes the best synthesis of that compound.14... 

The effect of pH on the periodate oxidation of seven anilines has been investigated. " The kinetics of periodate oxidation of aromatic amines have been studied. " - " Periodate oxidation of oxalic acid is catalysed by Mn(II). " The reaction of ethane-1,2-diol with periodate has been investigated under a variety of conditions and the results compared with those of earlier work and analogous studies on pinacol. " The 104 ion is the primary reactant, with H5IO6 as a secondary reactant the reverse is true for pinacol. The complex observed in previous work is shown not to be an intermediate, but rather to deactivate the reactants. 

General Procedure for Oxidation of Aromatic Amines with Active Manganese... 

Among the oxidative procedures for preparing azo compounds are oxidation of aromatic amines with activated manganese dioxide oxidation of fluorinated aromatic amines with sodium hypochlorite oxidation of aromatic amines with peracids in the presence of cupric ions oxidation of hindered aliphatic amines with iodine pentafluoride oxidation of both aromatic and aliphatic hydrazine derivatives with a variety of reagents such as hydrogen peroxide, halogens or hypochlorites, mercuric oxide, A-bromosuccinimide, nitric acid, and oxides of nitrogen. 

The oxidation of aromatic amines with peracids had been the subject of some dispute. It has now been demonstrated that simple oxidation of aromatic amines with peracids produces azoxy compounds without the intermediate formation of azo compounds [71]. To be sure, small amounts of azo compounds were isolated from the reaction mixture, but this was considered a side reaction. 

The oxidation of aromatic amines generally produces highly colored, tarry product mixtures. However, some aromatic amines have been successfully converted into azoxy compounds by peracetic acid oxidations. In regard to the factors influencing the reaction, several observations may be pertinent. 

The reduction of nitro groups may also be catalyzed by microsomal reductases and gut bacterial enzymes. The reduction passes through several stages to yield the fully reduced primary amine, as illustrated for nitrobenzene (Fig. 4.39). The intermediates are nitrosobenzene and phenylhydroxylamine, which are also reduced in the microsomal system. These intermediates, which may also be produced by the oxidation of aromatic amines (Fig. 4.21), are involved in the toxicity of nitrobenzene to red blood cells after oral administration to rats. The importance of the gut bacterial reductases in this process is illustrated by the drastic reduction in nitrobenzene toxicity in animals devoid of gut bacteria, or when nitrobenzene is given by the intraperitoneal route. 

In plasma, ca 90 vvl or copper is in the ineialloprotein ceruloplasmin. also known as ay-globulin, mol wi 151.000. which contains 8 atoms of copper per molecule. Ceruloplasmin has been identified as a ferroxi dasctll which catalyses Ihc oxidation of aromatic amines and of Pc to Fe . The ferric ion is then incorporated inlo iranslcrrin which is necessary lor the transport ol iron to tissues involved in Ihe synthesis or iron-containing compounds, e.g.. hemoglobin. Lowered levels of ceruloplasmin interfere with hemoglobin synthesis. 

Selective oxidation of aromatic amines to nitroso-derivatives with hydrogen peroxide and a catalyst is also studied [68, 69], In kinetic systems with transition metal complexes substrate oxidation is accompanied by H202 dissociation to H20 and 02. Therefore, in this case, the occurrence of chemical induction would be expected. 

Karasyova El, Naumchik IV, Metelitza DI (2003) Activation of peroxidase-catalyzed oxidation of aromatic amines with 2-aminothiazole and melamine. Biochemistry 68 54—62... 

In contrast to aliphatic amines, the anodic oxidation of aromatic amines shows a rather complex reaction pattern. Although extensive studies on the electrochemical reaction mechanism have been carried out, there are very few examples for the application of the anodic oxidation of aromatic amines to organic synthesis. 

Oxidation of aromatic amines Boyland-Sims reaction)... 

Anodic oxidation of aromatic amines has been well studied [1-3, 68, 72, 73]. These reactions are rather complex and are substantially affected by the reaction condition. 

Sayari et al. [172,174] found that like their Ti containing analogs, V-HMS and V-MCM-41 are efficient catalysts for the hydroxylation of bulky aromatic molecules such as naphthol and 2,6 DTBP. Gontier et al. [186,237] found that V-HMS has no activity in the oxidation of aromatic amines in the presence of H2O2. However, it oxidizes aniline selectively into nitrobenzene when TBHP and acetonitrile are used as oxidant and solvent, respectively. Notice that Ti-HMS is active even in the presence of H2O2 and gives a different product distribution, particularly azoxybenzene [237], Das et al. [193] also reported that Sn-MCM-41 is effective in the liquid phase hydroxylation of phenol and naphthol. 

Azobenzenes may be prepared by oxidation of hydrazobenzenes this may be made in an undivided cell by reduction of the nitro compound with constant current [178]. Additionally, azobenzenes may be obtained in low to fair yield by anodic oxidation of aromatic amines at a rotating platinum screen cylinder anode in aqueous DMF [179]. 

The indulines are formed in a great number of reactions. Nearly all azo-, azoxy-, and amidoazo-compounds, if heated ivith salts of aniline or other aromatic amines, produce indulines, and the dyestuffs formed on oxidation of aromatic amines under certain conditions belong in all probability to this class. It is difficult to say with certainty to what extent the products of different reactions are identical with one another. 

The phenoloxidase enzymes (peroxidases, tyrosinases, and laccases) are known to occur extracellularly in soils (16,17), and have been considered to play a role in catalyzing the coupling of aromatic amines to humic substances (3). Peroxidases have been studied most extensively. They use hydrogen peroxide to promote the one electron oxidation of aromatic amines and of phenolic moieties within humic substances to form free radicals. (12,18). 

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