Rearrangement of aromatic N-nitroamines. Part VII. The acid-catalysed transformation of N-methyl-N-nitro-9-aminoanthracene

Abstract

Treatment of N-methyl-N-nitro-9-aminoanthracene with sulphuric acid (ca. 7 ~) yielded I O-nitroanthrone (90%) together with nitrous acid (5%). The reaction which involved intramolecular shift of the nitro-group, was first order in substrate its rate was linearly correlated with the ho function ; but, unexpectedly, the reaction had a solvent isotope effect (kD1o/kHoo) of less than unity.It is proposed that rate-limiting protonation of the aromatic ring and either direct migration of the nitro-group or migration via the intermediacy of a tightly-bound ion or radical pair occurred.The present status of the ' radical-pair ' and ' cartwheel mechanisms for the nitroamine rearrangement is discussed. * D. V. Banthorpe in ' Chemistry of the Amino Group,' ed.

Products of rearrangement of m-chloro-N-nitro-N-methylaniline

“…The products of acid-catalyzed rearrangement of mchloro-IV-nitro-IV-methylaniline (5) were determined by isotope dilution analysis with the results shown in Table I. This analysis accounts for about 98% of the aromatic portion of the original nitramine and for about 85% of the nitro group.…”

“…As mentioned above, the "cartwheel" mechanism bears a superficial resemblance to the Claisen rearrangement. However, the product distribution from the nitramine (5) does not at all resemble that from rearrangement of the allyl ether (4). 10 The allyl ether provides no para-substituted isomer as does the nitramine.…”

“…On the other hand, the other two mechanisms would predict a more or less statistical distribution of products depending on the strength of binding between the ring and the dissociated nitro group. Since the product distribution in the Claisen rearrangement of allyl m-chlorophenyl ether (4) has been accurately determined,10 it was decided to investigate the products formed in acid-catalyzed reaction of m -chloro-IV-nitro-IV-methylaniline (5) and compare the results with those from the Claisen rearrangement.…”