The rearrangement of aromatic nitro compounds. Part 2. The rearrangement of substituted nitrophenols in trifluoromethanesulphonic acid

Abstract

o-Nitrophenols with an additional substituent (Y = NO₂, Cl, or Me) in the 3-position rearrange in trifluoromethanesulphonic acid at 100 °C to give mainly the product with the nitro group in the opposite ortho position; no more than 1–4% of other products are formed. The reactions give first-order kinetics, are acid-catalysed and (at least when Y = NO₂) are intramolecular. The rate of rearrangement varies with the 3-substituent in the order Me > Cl > NO₂. The results are discussed in terms of a rate-determining migration of the nitro group in the Wheland intermediate formed by protonation at the 2-position. A much slower rearrangement occurs with 3,4-dinitrophenol under the same conditions to give a small yield of 2,5-dinitrophenol accompanied by decomposition of the substrate.