Green nitration of aromatics: Efficiency and selectivity with FeCl3-H2SiO3 catalysts and nitrogen dioxide

para -Nitroaromatic compounds are extensively utilized in the chemical and pharmaceutical sectors, functioning as essential synthetic intermediates for the production of dyes, pharmaceuticals, and pesticides, as well as integral structural components in drug molecules. Conventional aromatic nitration predominantly employs the nitro‑sulfuric acid method, which is associated with several limitations, including harsh reaction conditions, safety and environmental issues, and low para -selectivity. In response to these challenges, this thesis explores the use of nitrogen dioxide as an environmentally friendly nitrating agent in conjunction with a supported Lewis acid serving as a solid acid catalyst to facilitate nitration reactions of various simple aromatic compounds under mild conditions. Remarkably, the nitration of toluene achieved a conversion rate of 87.5%, with a para -selectivity of 59.2%. Additionally, this research examined the nitration of other simple aromatic compounds, such as fluorobenzene, chlorobenzene, bromobenzene, iodobenzene, and anisole, resulting in improved conversion rates and increased selectivity for ortho products in all instances. The physical and chemical properties of FeCl 3 -H 2 SiO 3 silicates at varying loadings were characterized through techniques such as X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG/DTG), pyridine-adsorbed FT-IR (Py-FT-IR), ammonia temperature programmed desorption (NH 3 -TPD), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope energy dispersive spectrometer (SEM-EDS). Repeatability tests were conducted to ensure the reliability of the results. The repeatability tests demonstrated exceptional stability of the catalyst, and subsequent post-use characterization provided further insights into the fundamental mechanisms contributing to this stability. Density Functional Theory (DFT) calculations were conducted to examine the adsorption and desorption processes of various reactants and products on different catalysts, as well as to explore the reaction transition states. These theoretical analyses offered an explanation for the superior performance of this catalyst.