Fe_(3)O_(4) Nanoparticles: A Conveniently Reusable Catalyst for the Reduction of Nitroarenes Using Hydrazine Hydrate

摘要

Reduction of the nitro group is one of the most fundamental methods for the preparation of amines, which serve as valuable intermediates for many agrochemicals, pharmaceuticals, dyes, and pigments. Over the past several decades, much effort has been concentrated on achieving efficient and selective nitro-group reduction, and many reaction conditions have been developed for reduction of nitro compounds. The reduction of nitroarenes employing stoichio-metric reagents are often associated with unwanted side-products, such as hydroxylamine. Therefore, the catalytic hydrogenation of nitroarenes has been actively pursued using many readily available metal catalysts, such as copper, gold, iron, palladium, platinum, and rhodium immobilized on solid supports, and several hydrogen sources have been utilized, including hydrogen gas, silanes, and hydrazine derivatives. In contrast to the costly metal catalysts mentioned above, iron is one of the most economical and environmentally friendly metal catalysts. Since the traditional nitro group reduction using Fe/HCl system (Bechamp process) has been introduced, many iron-mediated catalytic systems have been developed. Homogeneous iron salts have also been used with hydrogen gas or ammonium formate for the nitro-reduction reaction. Recently, the groups of Lemaire and Beller reported the use of organosilane reagents in the presence of homogeneous iron catalysts. However, heterogeneous iron catalysts have mostly been used for nitro-group reduction; iron powders were used with various hydrogen sources, such as NH_(4)Cl, SnCl_(2), AcOH, and HCl. Hydrazine is an attractive hydrogen source because it obviates the use of autoclaves, acids, and the production of large amounts of waste. Reduction with hydrazine hydrate produces harmless by-products, such as nitrogen gas and water. Since the first report of hydrazine-mediated nitro-group reduction over 80 years ago, many heterogeneous catalytic systems that couple iron with hydrazine have been reported. Recently, we reported the use of heterobimetallic nanocrystals consisting of rhodium and Fe_(3)O_(4) as an efficient catalytic system for nitroarene reduction. However, to the best of our knowledge, there is no report of nitroarene reduction using commercially available, easily recyclable superparamagnetic Fe_(3)O_(4) nanoparticle catalysts in the presence of hydrazine hydrate.