ChemInform Abstract: Rapid Synthesis of Alkylaminophenols via the Petasis Borono—Mannich Reaction Using Protonated Trititanate Nanotubes as Robust Solid—Acid Catalysts.

Abstract

An effective and rapid synthesis of alkylaminophenols using the one-pot three-component Petasis borono–Mannich (PBM) reaction was carried out using protonated trititanate (H2Ti3O7) nanotubes as a heterogeneous solid–acid catalyst. Complimentary to earlier reports, Ti–O based materials with various morphologies, such as fine particles, nanospheres, nanorods, and tubes were explored for their catalytic activity in the PBM reaction. The XRD pattern revealed the layered trititanate structure of nanotubes and nanorods; anatase and biphasic anatase–rutile structures for fine particles and nanospheres, respectively. Surface area analysis and NH3-TPD adsorption results confirmed the larger surface area and high concentration of Bronsted and Lewis acid sites present in H2Ti3O7 nanotubes. The catalytic efficiency for the PBM reaction is observed in the following order: H2Ti3O7 nanotubes > H2Ti3O7 nanorods > TiO2 nanospheres > TiO2 fine particles. The remarkable catalytic performance of H2Ti3O7 nanotubes was ascribed to a sufficient amount of hydroxy groups and high concentration of Bronsted and Lewis acid sites on the tubular surface, which are essential for adsorption and catalytic reactions. The recyclability of H2Ti3O7 catalyst is another emphasis for the proposed methodology. For the first time, we reported novel alkylaminophenols bearing 2-(pyrimidin-2-yl)-2,5-diazabicyclo[2.2.1]-heptane.