Arylhydroxylamines

Addition of arylhydroxylamines to electrophilic allenes such as methyl propadienoate or l-methancsulfonyl-l,2-propadiene is another route to 0-vinyl derivatives[2]. The addition step is carried out by forming the salt of the hydroxylamine using NaH and the addition is catalysed with LiO CCFj. The intermediate adducts are cyclized by warming in formic acid. Yields are typically 80% or better. 

The reactions of arenediazonium ions with 7V-alkyl- or 7V-arylhydroxylamines were investigated by Bamberger (1920b, and earlier papers). Mitsuhashi et al. (1965) showed that the l,3-diaryl-3-hydroxytriazenes are tautomeric with 1,3-diaryltriazene-3-oxides (Scheme 6-16). Oxidation of 1,3-diaryltriazenes with peroxybenzoic acid in ether yields the same product as that from diazonium salts and TV-arylhydroxyl-amine. The infrared spectrum of the product obtained by coupling diazotized relabeled aniline with A/-phenylhydroxylamine indicates that the diaryltriazene-oxide is the preponderant tautomer. 

Aromatic compounds that do not contain meta-directing groups can be converted to diarylamines by treatment with aryl azides in the presence of phenol at — 60°C ArH -f- Ar N3 —> ArNHAr. Diarylamines are also obtained by the reaction of N-arylhydroxylamines with aromatic compounds (benzene, toluene, anisole) in the presence of F3CCOOH ArH -f Ar NHOH ArNHAr. ... 

The same group showed (Baumeister et al., 1997) that addition of vanadyl compounds as cocatalysts solved a recurring problem in hydrogenations the build-up of arylhydroxylamine intermediates, which can lead to runaway reaction conditions. Vanadyl complexes catalyse the disproportionation of aiylhydroxylamines and, hence, prevent their build-up during... 

The reaction of IV-alkyl- and iV-arylhydroxylamines with ethyl cyanoformate (193) leads to carbethoxyamino nitrones (194) (Scheme 2.68), which appear to be excellent starting materials for the synthesis of various nitrogen-bearing... 

Ammonium hydrogen sulphide is also a very suitable reagent for the reduction of nitrocompounds to arylhydroxylamines it is used in alcoholic solution in the cold.1... 

The arylhydroxylamines are weak bases which dissolve in dilute acids to form salts. The instability of phenylhydroxylamine has three causes the effect of atmospheric oxygen, of alkalis, and of acids. On exposure to air the compound, especially if impure, is oxidised to nitrosobenzene, which can be detected in decomposing phenylhydroxylamine by its pungent odour. As is often the case, the velocity of this process, which is known as autoxidation, is increased by alkalis it is accompanied by the production of hydrogen peroxide according to the equation ... 

The change which arylhydroxylamines undergo by the action of mineral acids, especially when warm, is worthy of special note. If the position para to the NHOH-group is free, a rearrangement takes place to the isomeric p-aminophenol, e.g. in the case of phenylhydroxylamine according to the equation ... 

Acylhydrazines R1 CONF1NF1R2 (R1 = Ph or PhCH2 R2 = Bu, PhCH2 or Ph) are produced by the action of hydroxamic acids R ONHOH on the primary amines R2NH2 in the presence of tosyl chloride or 2-chloro-l-methylpyridinium chloride94. O-(Diphenylphosphinoyl)-A-arylhydroxylamines 77 (R = NO2, Ac, Tos or CN) react with A-methylaniline to afford the hydrazine derivatives 7895. 

Scheme 4. The compounds and intermediates on the rear plane of the bicubic system (farthest from the reader) are protonated on the pyridine nitrogen atom those on the front plane (nearest the reader) are not. Laviron s work has shown that the reduction of 14 and its corresponding N-oxide34, and indeed probably most aryl nitro compounds, proceeds by an ECEC sequence leading to the neutral N,N-dihydroxy [ArN(OH)2] intermediate at all proton concentrations from Ho = —6 to pH 9.6. This substance then loses water to form the nitroso compound, which then undergoes a second sequence leading to the arylhydroxylamine.

The alkene (5 mmol) in PhMe (8 ml) is stirred with the W-acyl arylhydroxylamine (0.52 mmol) and the chiral catalyst (0.05 mmol) in aqueous NaOH (33%, l ml) at room temperature for 2.5 h. A further amount (0.05 mmol) of catalyst is added and the mixture stirred for an additional 2 h. The solvent and excess alkene are removed under vacuum and the residue is taken up in Et20 (15 ml). The extract is washed with H20 (3 x 20 ml), dried (Na2S04), and evaporated to yield the aziridine. ( Higher ee is achieved using 9% aqueous NaOH.)... 

Ahmad, F., and Hughes J. B., 2002, Reactivity of partially reduced arylhydroxylamine and nitrosoarene metahohtes of 2,4,6-trinitrotoluene (TNT) toward biomass and humic acids, Environ. Sci. Technol. 36 4370-4381. 

The oxidation of arylhydroxylamines and their O-alkylated derivatives to the corresponding nitro compounds can be achieved with both ozone and nitric acid. This strategy is a useful alternative to the oxidation of arylamines. 

Polynitroarylenes containing a variety of leaving groups are very susceptible to nucleophilic displacement (Section 4.8), and so, treatment of such substrates with hydroxylamine or an alkoxyamine usually generates the corresponding arylhydroxylamine or its O-alkyl derivative. 

Nielsen and co-workers studied the oxidation of arylhydroxylamines and their O-methyl derivatives with ozone in inert solvents at subambient temperature. 1,2,3,5-Tetranitrobenzene (54) is formed in quantitative yield from the oxidation of both N-hydroxy-2,4,6-trinitroaniline... 

Both fuming (90 %+) and concentrated (70 %) nitric acids have been used for the oxidation of arylhydroxylamines to the corresponding nitro compounds. Reactions are conducted at elevated temperatures where the oxidizing potential of nitric acid is at its highest. Yields are generally poor to moderate. 

Electrolytic reduction of an emulsion of the nitro compound in 1 M zinc chloride solution at high current density is another proposed method for conversion to the amine. Finely divided zinc is produced and this reduces the nitrocompound. Zinc ions also function as Lewis acid in the reduction of arylhydroxylamines [44]. 

Conversion of substituted nitrobenzenes to the arylhydroxylamine is easily achieved by reduction in neutral or slightly acid solution. In the first classical experiments, Haber [35] used a platinum cathode and ammonia ammonium chloride buffer and die process was improved by Brand [57] using either a nickel or silvered copper cathode in an acetate buffer. The hydroxylamine can also be obtained from reduction in dilute sulphuric acid provided tire temperature is kept below 15° C to suppress furtlier reduction [58]. This electrochemical route to arylhydroxylamines due to Brand is superior to the chemical reduction using zinc dust and ammonium chloride solution. The latter process is known to give variable yields depending on... 

Many organic chemicals are analyzed by RPC. These include various arylhydroxylamines as the N-hydroxyurea derivative with methyl isocyanate (614) alkyl- and alkoxy-disubstituted azoxybenzenes (6t5), n-alkyl-4-nitrophenylcarbonate esters ranging in length from methyl to octyl (616), 4-nitrophenol in the presence of 4-nitrophenyl phosphate (617), ben-zilic acid, and benactyzine-HCI using ion-pair chromatography (618), as well as aniline and its various metabolites (619), stereoisomers of 4,4 -dihydroxyhydrobenzoin (620), and aldehydes and ketones as the 2,4-dinitrophenylhydrazones (621). The technique has also been used to analyze propellants and hydrazine and 1,1-dimethylhydrazine were quantitita-vely determined (622, 623). 

Argenlalion chromalography, 261 Aromatic acids in human urine, 285 Aromatic hydrocarbons, 69 Arylhydroxylamines, 298 Ascorbic acid, 296 Aspirin, 282 Asymmetric diens, 290 Asymmetrical peaks, 58, 82, 160 AIT, stability constants of metal complexes. 278 Atrazine, 292 Atropine, 297 Axial diffusion mobile phase. 8 stationary phase, 8,9 Aza-arenes, 293 Azoxybenzenes, 298... 

Nucleophilic substitution of halogen atom in aromatic and heteroaromatic halides with a hydroxyamino group proceeds only in substrates that are activated by a strong electron-withdrawing substituent in the benzene ring (e.g. 27, equation 17). Despite this limitation this reaction is useful for synthesis of arylhydroxylamines and usually provides good yields of products. Along with activated aryl halides and sulfonates, activated methyl aryl ethers such as 28 can be used (equation 18). 

An alternative approach to 0-arylation involves converting the OH function of hydrox-ylamine to a leaving group, followed by nucleophilic substitution with phenolate ions. Reaction of hydroxylaminesulfonic acid as well as 0-sulfonylhydroxylamines (e.g. 37, equation 26) with phenolates produces 0-arylhydroxylamines of type 38. 

O-Alkyl- and O-arylhydroxylamines and their A-substituted derivatives have been the most extensively used reagents for amination of C-nucleophiles (Table 1). O-Methyl hydroxylamine la is the most extensively used O-organylhydroxylamine-type reagent. 

The A-acyl-O-arylhydroxylamine 166 rearranges in the presence of trifluoroacetic acid to 168 by a [3,3]-sigmatropic shift. An isourea intermediate 167 was proposed to explain the observed transformation (equation 49). 

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