Organo-modified Fe-montmorillonite as a solid acid catalyst for reduction of nitroarenes and Biginelli reactions

Abstract In order to develop a new class of solid acid catalysts, interlayer ferric ions of Fe(III)-montmorillonite (Mt) was reduced to Fe2+ and coordinated with o-phenanthroline (L) during the solid-state reaction at >150 °C. Such a reduction is ascribed to the partial aggregation of Fe3+–O-Fe3+ followed by self-reduction to Fe2+ with the elimination of oxide ion. In-situ complexation to form ferroin, [FeL3]2+ at the interlayer is evident from TG/DTA, DR UV–Vis spectra, XRD, FT-IR, photoluminescence spectra and SQUID magnetometer. Basal spacing (d001) of Fe(III)-Mt-L was 18 A for the products heated from 200 to 350 °C. The decomposition of this interlayer complex occurred around 450 °C. Fe(III)-Mt-L@200 °C showed characteristic absorption for [FeL3]2+ around 510 nm. Lewis and Bronsted acid sites are confirmed from the FTIR spectra of pyridine adsorbed samples. The catalytic behavior of Fe(III)-Mt-L@300 °C was observed during the reduction of 4-nitrophenol to 4-aminophenol and also in the Biginelli reactions.