Nitramine rearrangement, aromatic nitration

Depending on the amine substrate and the nitrating conditions used, it is not uncommon for an intermediate nitramine to undergo direct rearrangement to the ring-nitrated product without prior isolation, in which case, the formation of the nitramine as an intermediate can only be postulated. Due to the high o-selectivity often observed with this type of reaction the o/p-ratio can be very different to that where the aromatic ring is directly nitrated. 

Aromatic nitramines undergo a rearrangement in which the nitro group migrates to the benzene ring. Such a rearrangement is believed to occur in the synthesis of tetryl, which is made by the nitration and nitrolysis... 

The reaction of many aromatic amines with nitric acid in concentrated sulphuric acid is well known to give C-nitro products but whether this is a direct C-substitution or an N-substitution followed by rearrangement is usually unknown. The currently accepted view (1) appears to be that nitramine intermediates are seldom involved this conclusion is based on the marked difference in the product compositions obtained in the nitration of aniline and the rearrangement of phenylnitramine when both reactions are carried out in 85% sulphuric acid (2). 

---