New dendrimers containing ruthenium nanoparticles as catalysts for hydrogenation of citral to 3,7-dimethyloctanol

Abstract

Two silica-supported dendrimers containing ruthenium nanoparticles (S-D/RuNPs) have been synthesized through the divergent method and characterized by the attenuated total reflectance-infrared (ATR-IR), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), and inductively coupled plasma (ICP) techniques. To prepare S-D/RuNPs, a first-generation dendrimer was synthesized from hexakis(bromomethyl)benzene (hex) core and vanillin branches. In the next step, second-generation dendrimers, hexpyD and hexbzaD, were synthesized by the reaction of the first-generation dendrimer with ortho-aminopyridine (py) and para-aminobenzoic acid (bza), respectively. The second-generation dendrimers, hexpyD and hexbzaD, were then reacted with ruthenium(III) chloride to form the hexanuclear Ru(III) complexes which were immobilized on a silica support and reduced by NaBH4 in 2-methoxyethanol as the solvent. The mean size of the ruthenium nanoparticles encapsulated within the dendrimers was found to be 2 and 6 nm in hexpyD and hexbzaD, respectively. In addition, the catalytic activity of the synthesized nanoparticles were investigated on the hydrogenation of citral (3,7-dimethyl-2,6-octadienal) to 3,7-dimethyloctanol. The effect of S-D/RuNPs catalysts on the hydrogenation reaction was monitored by gas chromatography-mass spectrometry (GC/MS). The results revealed that the increase of the reaction temperature and reaction time leads to a higher reaction yield at a constant pressure.