Selective reductions of nitroarenes to anilines using metallic zinc in near-critical water

A new procedure for the preparation of anilines (2) in good yield by reduction of the corresponding nitroarenes (1) using Zn in H2O at 250–300 °C is described. The procedure is powerful enough to reduce sterically hindered 2-nitro-m-xylene (1c) and is chemoselective for the NO2 groups in 1-chloro-2-nitrobenzene (1d) and 1-nitro-3-vinylbenzene (1h). The process involves the reduction of H2O by Zn to generate H2 followed by hydrogenation of the NO2 group catalysed by residual traces of Zn.