Aromatic amines oxidation

Owiag to the lower basicity of the parent amines, aromatic amine oxides cannot be formed directiy by hydrogen peroxide oxidation. These compounds may be obtained by oxidation of the corresponding amine with a peracid perbenzoic, monoperphthaUc, and monopermaleic acids have been employed. 

Radical Scavengers Hydrogen-donating antioxidants (AH), such as hindered phenols and secondary aromatic amines, inhibit oxidation by competing with the organic substrate (RH) for peroxy radicals. This shortens the kinetic chain length of the propagation reactions. 

Low concentiations of alkylated paiaphenylenediamines such as -di-ti t-butyl-j )-phenylenediamine [69796 7-OJ are added to gasoline to inhibit oxidation (see Amines, AROMATic-PHENYLENEDiAMiNEs). 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

Nonvolatile compounds cannot be analysed unless pyrolysis or derivatisation converts them to a condition amenable to GC. Derivatisation GC (or LC) has been used for several components such as erucamide (imidi-sation for volatility), fatty amines (aromatic amidation for UV detectability), and polyethylene oxides (esterification for both volatility and detectability) [178]. The surface concentration of erucamide on extruded LLDPE films was determined quantitatively by surface washings with ether, followed by evaporation, dissolution... 

The synergistic action of a phenol and aromatic amine mixture on hydrocarbon oxidation was found by Karpukhina et al. [16]. A synergistic effect of binary mixtures of some phenols and aromatic amines in oxidizing hydrocarbon is related to the interaction of inhibitors and their radicals [16-26]. In the case of a combined addition of phenyl-A-2-naphthylamine and 2,6-bis(l,l-dimethylethyl)phenol to oxidizing ethylbenzene (v, = const, 343 K), the consumption of amine begins only after the phenol has been exhausted [16], in spite of the fact that peroxyl radicals interact with amine more rapidly than with phenol (7c7 (amine) = 1.3 x 105 and /c7 (phenol) = 1.3 x 104 L mol 1 s respectively 333 K). This phenomenon can be explained in terms of the fast equilibrium reaction [27-30] ... 

Interesting examples of the addition of N-nucleophiles to nitrile oxides are syntheses of chelated Z-amidoxime, N-[2-(dimethylaminomethyl)phenyl]mesitylene-carboamidoxime (118), and pyranosyl amidoximes (119) from the respective nitrile oxides and amines. Aromatic aldoximes undergo unusual reactions with chloramine-T (4 equiv, in refluxing MeOH). N-(p-toly 1 )-N-(p-tosy 1 )benzamides are formed via addition of 2 equiv of chloramine-T to the intermediate nitrile oxide followed by elimination of sulfur dioxide (120). 

Oxidation of heterocyclic aromatic amines, N-oxide reduction... 

Dinitrobenzenesulfenyl chloride is a versatile analytical reagent for the characterization of a wide variety of organic compounds, including alcohols, mercaptans, ketones, olefins, amines, aromatic compounds, olefin oxides, and hydroxysteroids. Review articles summarize these applications.9 10... 

Aromatic amines are oxidized by Oxone in acetone to produce the corresponding nitro arenes in good to high yield (50-100%) [12]. The reaction is thought to proceed via the initial formation of dimethyldioxirane. Electron excessive heteroarenes, which are normally very susceptible to oxidation are untouched by the reaction. 

Behaviour with halogenated solvents, bases, oxidizing adds, amines, aromatic oxygenated solvents can be limited... 

Finally, a very simple way to deoxygenate aliphatic or aromatic amine A-oxides involved the sameNiCl2-2H20/LiyDTBB (10%) combination, so, for instance, compounds 546-550 are examples of this reaction in 66-80% yield °. 

Interestingly, persulfate reacts differently with aliphatic and aromatic amines. Aliphatic primary amines are dehydrogenated to imines and further converted to aldehydes when reacted with peroxy disulfate , whereas aromatic primary amines are oxidized to nitroso compounds using potassium persulfate in the presence of H2SO4 (equation 14) °. 

Krohn and coworkers reported that aliphatic and aromatic primary amines are oxidized to the corresponding nitro compounds by reaction with a combination of Zr(OBu-t)4 and The oxidation of a variety of aliphatic primary amines with different... 

The beneficial effects of amine A-oxide promoters are well documented in the example given in Equation (1). While the aromatized product 12 instead of the PKR product was obtained from the reaction of diethylacetylene 10 and compound 11 under thermal conditions, the desired PKR product 13 was formed only by the aid of amine A-oxide. 

Aromatic amines are known as to be efficient inhibitors of hydrocarbon and polymer oxidation (see Chapters 15 and 19). Aliphatic amines are oxidized by dioxygen via the chain mechanism under mild conditions [1,2]. Peroxyl and hydroperoxyl radicals participate as chain propagating species in the chain oxidation of amines. The weakest C—H bonds in aliphatic amines are adjacent to the amine group. The bond dissociation energy (BDE) of C—H and N—H bonds of amines are collected in Table 9.1. One can see that the BDE of the N—H bond of the NH2 group is higher than the BDE of the a-C—H bond in the amine molecule. For example, DN = 418.4 kJ mol 1 and DC H = 400 kJmol-1 in methaneamine. However, the BDE of N—H bond of dialkylamine is lower than that of the C—H bond of... 

Whenever only primary amines need to be derivatized, fluorescamine often constitutes the reagent of choice. Fluorescamine, although nonfluorescent itself, can react with primary amines forming highly fluorescent pyrrolinones (139-144). Aliphatic primary amines favor derivatization reaction at pH 8-9, whereas primary aromatic amines exhibit optimal reactivity at pH 3-4. Secondary amines are also fully reactive with fluorescamine but their products do not fluoresce. However, secondary amines can be detected with fluorescamine if they are converted to primary amines by oxidation with N-chlorosuccinimide prior to their fluorescamine derivatization (145, 146). Alcohols can also interact with fluorescamine but this reaction is reversible as a result, alcohols just slow down the reaction rate of fluorescamine with primary amines. On the other hand, tertiary amines and guanidines are not reactive at all with fluorescamine. 

The Photochemical Reactions of Azoxy Compounds, Nitrones, and Aromatic Amines N-Oxides G. G. Spence, E. C. Taylor and O. Buchardt, Chem. Rev., 1970, 70, 231-265. 

The coordination chemistry of aromatic amine vV-oxides and dioxides has been the subject of numerous studies in recent years.281-283... 

The basicity of the aromatic amine iV-oxide can be substantially varied by the introduction of substituents on the aromatic ring. IR spectra of free N-oxides display a prominent band between 1200 and 1300 cm-1, attributable to the nitrogen-oxygen stretching frequency v(NO). The more activating the substituent, the lower the energy of the absorption. Upon coordination, v(NO) is decreased by up to 60 cm-1. IR data for pyrazole and pyridine derivatives are given in Table 42.281-286... 

However, the production of the />-phenylenediamine [106-50-3] intermediate is more complex, because it involves the diazotization and coupling of aniline [65-53-3]. Aniline reacts with nitrogen oxides, produced via the oxidation of ammonia, to form 1,3-diphenyltriazene [136-35-6] in the process used by Du Pont (208,209) (see Amines, aromatic-aniline and its derivatives). In the Akzo process a metal nitrite salt and acid in water is used (210). The triazene rearranges in the presence of acid and an excess of aniline to form predominately the p-aminoazobenzene [60-09-3] and a small amount of the ortho isomer, 0-aminoazobenzene [2835-58-7]. The mixture of isomers is catalytically reduced to the respective diamines, and they are then separated from the aniline, which is recycled (208,209). The 0-phenylenedi amine [95-54-5] is used in the manufacture of herbicides (see Amines, aromatic-phenylenediamines). 

Like phenols, aromatic amines are oxidized at a graphite electrode over a wide range of oxidation potentials. Some compounds (phenylenediamines, benzidines, and aminophenols) are ideal candidates due to their very low oxidation potentials numerous applications have been developed. 

---