The rearrangement of aromatic nitro compounds. Part 3. The mechanism of rearrangement of nitrated hydrocarbons in trifluoromethanesulphonic acid
Abstract
1,3-Dialkyl-2-nitrobenzenes (C6H3R2NO2; R = Me, Et, and Pri) rearrange in trifluoromethane-sulphonic acid to the corresponding 4-nitro derivatives; with R = Et, this reaction is accompanied by dehydration to 7-ethyl-3-methylanthranil. The reaction rate increases markedly with the size of the alkyl group; with R = Me, the reaction was studied at 110 °C but, with R = Pri, temperatures of 36–54 °C were used. The studies with R = Me show the reaction to be first-order with the rate coefficients (k1) increasing rapidly with the acidity of the solution [d(log k1)/d(–H0)]= 1.45, decreasing with acidity to 0.49. Double-labelling experiments with 2H and 15N show the reaction to be intramolecular. 1,2,4-Trimethyl-3-nitrobenzene also rearranges under these conditions to give mainly the 5-nitro isomer. The above results are discussed in terms of a direct 1,3-shift of the nitro group.