Oxidation of arylhydroxylamines and their derivatives

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. 

Borsche synthesized both 1,2,4- and 1,2,3-trinitrobenzenes by treating Af-hydroxy-2,4-dinitroaniline and Al-hydroxy-2,6-dinitroaniline, respectively, with fuming nitric acid. The method is very convenient for the synthesis of such substrates because the starting materials are readily obtainable from the reaction of hydroxylamine with the appropriate dini-trochlorobenzene isomer. Borsche also synthesized 1,2,3,5-tetranitrobenzene (60%) 

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