Reduction of Nitroarenes into Aryl Amines and N-Aryl hydroxylamines via Activation of NaBH4 and Ammonia-Borane Complexes by Ag/TiO2 Catalyst

• Main Authors: Dimitrios Andreou, Domna Iordanidou, Ioannis Tamiolakis, Gerasimos S. Armatas, Ioannis N. Lykakis
• Format: Article
• Language: English
• Published: MDPI AG 2016-03-01
• Series: Nanomaterials
• Subjects: silver nanoparticles; nitroarenes; aryl amines; N-aryl hydroxylamines; titania; heterogeneous catalysis; selective reduction
• Online Access: http://www.mdpi.com/2079-4991/6/3/54

In this study, we report the fabrication of mesoporous assemblies of silver and TiO2 nanoparticles (Ag/MTA) and demonstrate their catalytic efficiency for the selective reduction of nitroarenes. The Ag/TiO2 assemblies, which show large surface areas (119–128 m2·g−1) and narrow-sized mesopores (ca. 7.1–7.4 nm), perform as highly active catalysts for the reduction of nitroarenes, giving the corresponding aryl amines and N-aryl hydroxylamines with NaBH4 and ammonia-borane (NH3BH3), respectively, in moderate to high yields, even in large scale reactions (up to 5 mmol). Kinetic studies indicate that nitroarenes substituted with electron-withdrawing groups reduced faster than those with electron-donating groups. The measured positive ρ values from the formal Hammett-type kinetic analysis of X-substituted nitroarenes are consistent with the proposed mechanism that include the formation of possible [Ag]-H hybrid species, which are responsible for the reduction process. Because of the high observed chemo selectivities and the clean reaction processes, the present catalytic systems, i.e., Ag/MTA-NaBH4 and Ag/MTA-NH3BH3, show promise for the efficient synthesis of aryl amines and N-aryl hydroxylamines at industrial levels.