Reductive Oligomerization of Nitroaniline Catalyzed by Fe3O4 Spheres Decorated with Group 11 Metal Nanoparticles

The present work demonstrates a simple and sustainable method for forming azo oligomers from low-value compounds such as nitroaniline. The reductive oligomerization of 4-nitroaniline was achieved via azo bonding using nanometric Fe3O4 spheres doped with metallic nanoparticles (Cu NPs, Ag NPs, and Au NPs), which were characterized by different analytical methods. The magnetic saturation (Ms) of the samples showed that they are magnetically recoverable from aqueous environments. The effective reduction of nitroaniline followed pseudo-first-order kinetics, reaching a maximum conversion of about 97%. Fe3O4-Au is the best catalyst, its a reaction rate (kFe(3)O(4)-Au = 0.416 mM L-1 min(-1)) is about 20 times higher than that of bare Fe3O4 (kFe(3)O(4) = 0.018 mM L-1 min(-1)). The formation of the two main products was determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS), evidencing the effective oligomerization of NA through N = N azo linkage. It is consistent with the total carbon balance and the structural analysis by density functional theory (DFT)-based total energy. The first product, a six-unit azo oligomer, was formed at the beginning of the reaction through a shorter, two-unit molecule. The nitroaniline reduction is controllable and thermodynamically viable, as shown in the computational studies.

Automated summary

This study presents a simple and sustainable method for forming azo oligomers from low-value compounds such as nitroaniline. Nanometric Fe3O4 spheres doped with metallic nanoparticles were used as catalysts for the reductive oligomerization of 4-nitroaniline. The study found that Fe3O4-Au showed the highest catalytic activity among the different catalysts tested.