Reduction of Nitroarenes into Aryl Amines and N-Aryl hydroxylamines via Activation of NaBH₄ and Ammonia-Borane Complexes by Ag/TiO₂ Catalyst.
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 andN-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 ofX-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 andN-aryl hydroxylamines at industrial levels.
Department of Chemistry, Aristotle University of Thessaloniki, University Campus, Thessaloniki 54124, Greece. dandreou@chem.auth.gr.
Dimitrios
D
Andreou
Department of Chemistry, Aristotle University of Thessaloniki, University Campus, Thessaloniki 54124, Greece. diordani@chem.auth.gr.
Domna
D
Iordanidou
Department of Materials Science and Technology, University of Crete, Vassilika Vouton, Heraklion 71003, Greece. gtam@materials.uoc.gr.
Ioannis
I
Tamiolakis
Department of Materials Science and Technology, University of Crete, Vassilika Vouton, Heraklion 71003, Greece. garmatas@materials.uoc.gr.
Gerasimos S
GS
Armatas
Department of Chemistry, Aristotle University of Thessaloniki, University Campus, Thessaloniki 54124, Greece. lykakis@chem.auth.gr.
Ioannis N
IN
Lykakis
N-aryl hydroxylamines; aryl amines; heterogeneous catalysis; nitroarenes; selective reduction; silver nanoparticles; titania