Oxidation of arylamines, arylhydroxylamines and other derivatives 155Dimethyldioxirane is a powerful oxidant prepared as a solution in acetone from the dis-
tillation of a buffered solution of oxone (2KHSO 5 .KHSO 4 .K 2 SO 4 ) in acetone.^174 Murray
and co-workers^175 ,^176 used dimethyldioxirane for the synthesis of numerous aromatic nitro
compounds. This reagent efficiently converts isomeric nitroanilines and phenylenediamines
to the corresponding dinitrobenzenes.^175 In the case ofp-phenylenediamine the hydrochlo-
ride salt was used in the oxidation, demonstrating the high potential of dimethyldioxirane
as an oxidant. Dimethyldioxirane has also been used to convert 3,5-dinitroaniline (30) to
1,3,5-trinitrobenzene (2) in excellent yield.^175 Despite the clear potential of dimethyldioxi-
rane as an oxidant for amino to nitro group conversion it has not found wide use. Some
moderately basic arylamines are converted to nitro compounds on direct treatment with
oxone.^177
4.7.1.8 Other oxidants
The oxidation of arylamines with ozone is generally not a feasible route to the corresponding
nitro compound.^178 First absorbing the arylamine onto silica gel and then passing a stream of
ozone over the surface has achieved some success.^179 m-Chloroperoxybenzoic acid (m-CPBA)
in 1,2-dichloroethane at reflux has found limited use.^180 Other more obscure reagents have been
described.^159 ,^181 ,^182
Some reagents are milder and less powerful oxidants and have been used to oxidize ary-
lamines to the corresponding nitroso compounds. These include 30 % hydrogen peroxide in
acetic acid,^169 ,^170 aqueous solutions of potassium permanganate,^183 and alkaline hypochlor-
ite^184 amongst others. The hypochlorite oxidation of arylamines containingo-nitro substituents
is reported to yield benzofuroxans.^185 For a discussion of the synthesis of aromatic nitroso com-
pounds the readers are directed to a review by Boyer.^186
Reagents effecting nitroso to nitro group conversion include: nitric acid,^187 acidic dich-
romate,^188 hydrogen peroxide,^189 permanganate,^190 chromium trioxide,^191 hypochlorite,^191
ozone,^192 and all other reagents previously discussed in this section for amino to nitro group
conversion.^186
4.7.2 Oxidation of arylhydroxylamines and their derivatives
The oxidation of arylhydroxylamines and theirO-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 itsO-alkyl derivative.
4.7.2.1 Ozone
Nielsen and co-workers^39 studied the oxidation of arylhydroxylamines and theirO-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 bothN-hydroxy-2,4,6-trinitroaniline