Boehmite nanoparticles are not air or moisture sensitive; therefore, they were prepared in water at room temperature using inexpensive materials, without inert atmosphere, by a very simple and inexpensive procedure. When the surface of boehmite nanoparticles was modified by N,N,N′,N′-tetraethyldiethylenetriamine (TEDETA), tribromide ions became immobilized on modified boehmite nanoparticles (Br₃-TEDETA@Boehmite). These materials were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller, X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy techniques. Finally, the catalytic activity of Br₃-TEDETA@Boehmite was examined in the selective oxidation of sulfides to sulfoxides. Besides, the catalytic activity of Br₃-TEDETA@Boehmite was extended to the synthesis of organic heterocyclic compounds, such as 2,3-dihydroquinazolin-4(1H)-one and polyhydroquinoline derivatives. This catalyst was reused several times without significant loss of its catalytic efficiency.