Oxidation of arylamines, arylhydroxylamines and other derivatives

Peroxyacids are the most widely used class of oxidant for aromatic amino to nitro group conversion and include peroxydisulfuric, peroxymonosulfuric, peroxyacetic, peroxytrifluo-roacetic and peroxymaleic acids. The oxidizing potential of the peroxyacid is, as a rule, proportional to the strength of the parent deoxy-acid. Dimethyldioxirane (DMDO) and ozone have also found use for amino to nitro group conversion. 

The real potential of peroxydisulfuric acid for the synthesis of highly nitrated arylenes was brought to light by research conducted at the Naval Air Warfare Center, Weapons Division, China Some of the highly nitrated polynitroarylenes syn- 

Some substrates show limited solubility in sulfuric acid solutions and this can affect the rate of oxidation. However, the main factor for slow amine oxidation is due to the high concentration of protonated amine under these highly acidic conditions. Under these conditions only weakly basic amines have a high enough concentration of unprotonated form to permit oxidation to occur. As a result, sulfuric acid solutions of peroxydisulfuric acid are only useful for the oxidation of very weakly basic amines. Peroxydisulfuric acid oxidizes trinitrotoluidines to tetranitrotoluenes (Table4.1, Entry 3) but leaves the more basic dinitrotoluidines unaffected. The opposite is true of peroxyacids like peroxytrifluoroacetic acid and so the reagents are very much complementary. 

It is unsurprising that some substrates react with peroxydisulfuric acid faster when in 100 % sulfuric acid than in oleum. A striking example of this is illustrated by the oxidation of 2,6-dinitroaniline to 1,2,3-trinitrobenzene in 56% yield when the sulfuric acid concentration is 96 % whereas in 20 % oleum this substrate is unaffeeted.  

Tahled.l Oxidation of arylamines and their derivatives with peroxydisnlfnric acid  

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