156 Synthetic Routes to AromaticC-Nitro Compounds
Table 4.3 Oxidation of arylhydroxylamines with ozone (ref. 39)
NHOMeNO 2NHOHNO 2NO 2NHOMe
NO 2Br
NO 2NHOHNO 2O 2 N NO 2O 2 NO 2 NO 2 NNO 2NO 2NO 2NO 2NO 2NO 2NO 2Br
NO 2NO 2NO 2O 2 N NO 2O 2 NO 2 NO 2 NEntry Substrate Conditions Product Yield (%)1001001002341 (80) 100(81)(82)(83)(54)(2)(54)(84)O 3 , CH 2 Cl 2 , -10 °C,
15 minsO 3 , CH 2 Cl 2 , -35 °C,
25 minsO 3 , CH 2 Cl 2 , -10 °C,
75 minsO 3 , EtOAc, 25 °C,
120 mins(80) andN-methoxy-2,4,6-trinitroaniline (82) with ozone (Table 4.3, Entries 1 and 3). Both
ethyl acetate and carbon tetrachloride have been used as solvents for the oxidation ofN-
methoxy-3-bromo-2,4,6-trinitroaniline (83) to 1-bromo-2,3,4,6-tetranitrobenzene (84) (Ta-
ble 4.3, Entry 4). Yields for these reactions are usually very high and reactions are ex-
tremely rapid even at the subambient temperatures used. The method fails to efficiently oxidize
substrates containing two or more hydroxyamino or methoxyamino groups on the same aro-
matic ring.
4.7.2.2 Nitric acid
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^193 synthesized both 1,2,4- and 1,2,3-trinitrobenzenes by treatingN-hydroxy-2,4-
dinitroaniline andN-hydroxy-2,6-dinitroaniline, respectively, with fuming nitric acid. The
method is very convenient for the synthesis of such substrates because the starting mate-
rials are readily obtainable from the reaction of hydroxylamine with the appropriate dini-
trochlorobenzene isomer. Borsche^193 ,^194 also synthesized 1,2,3,5-tetranitrobenzene (60 %)