Ba/ZrO2 nanoparticles as efficient heterogeneous base catalyst for the synthesis of β-nitro alcohols and 2-amino 2-chromenes

Zirconia nanoparticles were synthesized by precipitation, urea hydrolysis, amorphous citrate and combustion synthesis methods. The zirconia surface was subsequently modified by grafting Ba2+ species. The Ba2+ modified zirconia (Ba/ZrO2) materials were characterized using XRD, Fourier analysis, UV-vis-DRS, FESEM and HRTEM techniques. XRD study indicated selective stabilization of the tetragonal phase of zirconia in the presence of Ba2+ species. Fourier line profile analysis of the XRD peaks revealed that the average crystallite size of the zirconia nanoparticles is in the range of 5-15 nm. The surface area, basicity and barium content of the material depend strongly on the method of synthesis. The Ba/ZrO2 catalyst prepared by urea hydrolysis method exhibited higher surface area and barium content compared to other samples. The catalytic activity of the Ba/ZrO2 catalyst was evaluated for synthesis of beta-nitro alcohols and 2-amino 2-chromenes. The beta-nitro alcohols were synthesized by condensation of aryl aldehydes and nitromethane. Similarly, the 2-amino 2-chromenes were synthesized by condensation of arylaldehydes, alpha-naphthol and malononitrile. The Ba/ZrO2 catalyst was found to be highly efficient for synthesis of both classes of compounds providing excellent yield and purity of the products.