Efficiency of Ag(0)@chitosan gel beads in catalytic reduction of nitroaromatic compounds by sodium borohydride.

Metal-catalysed reduction of nitroaromatic compounds to aniline derivatives is a useful and important synthetic route in many applications. Metallic silver particles have gained much recent interest as efficient catalysts in catalytic reduction of nitroaromatic compounds by sodium borohydride. In the study metallic Ag particles were stabilized on glutaraldehyde cross-linked chitosan gel beads in water by a simple and green thermal treatment. Ag(0)@chitosan gel beads exhibited an excellent catalytic activity in hydrogenation of 4-nitrophenol, 2-nitroaniline, 4-nitro-o-phenylenediamine and 2,4-dinitrophenol when NaBH4 was used as the hydrogen source. The catalytic activity tests were repeated by varying the catalyst dose, NaBH4 concentration, the amount of nitroaromatic compounds and temperature. The reduction reactions were greatly affected by the temperature of reaction medium and the concentration of NaBH4. At elevated temperatures, for example at 43 °C, some reduction reactions went to completion in just 8 s. The study revealed that Ag(0)@chitosan gel beads can be used in catalytic reduction of nitroaromatic compounds to anilines by NaBH4. This catalytic system can be tested an alternative to the catalytic systems requiring use of expensive transition metals such as palladium and platinum.