Aqueous biphasic oxidation: A water-soluble Cd(II)/ 2,2′-azobispyridine-6,6′-dicarboxylic acid/phenanthroline catalyst for selective oxidation of alcohols with TBHP

The catalytic processes facilitate the efficient production of valuable chemicals from more abundant and costeffective substrates, resulting in higher yields at reasonable costs in environmentally friendly conditions. Among our efforts to develop efficient catalysts with abundant metals, a bimetallic Cd(II) complex ([Cd2(Abpy) (phen)4].2ClO4.2CH3OH) was synthesized using 2,2 '-azobispyridine-6,6 '-dicarboxylic acid (Abpy) and 1,10 '- phenantroline (phen) ligands. The structure of the complex was characterized by single-crystal X-ray diffraction. A single Abpy anion coordinated with two six-coordinated Cd(II) via bidentate bonding mode of its carboxylate oxygen and pyridine nitrogen atoms to form a ligand-bridged structure. The activity of developed catalyst was examined for various primary and secondary alcohols (benzyl alcohol, cinnamyl alcohol, cyclohexanol, cyclopentanol, 2-hexanol, 2-octanol and 1-phenylethanol) in a biphasic system of hexane-water with TBHP as oxidant (T = 80 degrees C S/C = 100, O/S = 10). The complex was found to be a very active catalyst for the oxidation of 1-phenylethanol. The effects of different solvent type, catalyst dosage, oxidant dosage, reaction temperature, and reaction time on the oxidation reaction of 1-phenylethanol were discussed. Finally, the optimized conditions were determined: 1.5 mL (H2O): 1.5 mL (hexane) mL, n(TBHP)/n(1-phenylethanol) = 10 (O/S), n(1-phenyl-ethanol)/(catalyst) =100 (S/C) 80 degrees C for 8 h. The selectivity of the Cd-catalyst was measured to be 100 % for the oxidation of 1-phenylethanol to acetophenone. The catalyst was reused by phase separation, and 1-phenyletha-nol was obtained maintained high conversion after eight recycles.