Syntheses And Properties Of 8-Hydroxyquinoline Derivatives And Their Metal Complexes

Chemical properties of quinoline and its derivatives are of interest due to their biological activity, coordination capacity and their use as metal extracting agents. In view of novel structural features and biological activity the quinolinol Schiff bases have also attracted attention. In recent years, there has been of great interest in the synthesis and characterization of transition metal complexes containing Schiff bases as ligands. Besides ,some carbonyl complexes of quinoline has played an important role in some fields. Schiff-base complexes incorporating one or two similar or different metal ions have received much attention . Quinolinol complexes showed a positive result in antibacterial activity studies. In view of growing interest in oxygenation and carbonylation with quinoline complexes, we describe in this paper the synthesis and characterization of stable quinolinol complexes . All of the Schiff bases and their complexes were characterized by EA, IR, UV, 1H NMR, 13C NMR. The antibacterial activities of the Schiff bases, and complexes were also studied.1. Formylation of 8-hydroxyquinoline on 2-, 5-, 7-positions was studied.(1) 5-Formyl-8-hydroxyquinoline and 7-formyl-8-hydroxyquinoline were prepared by the reaction of Reimer-Tiemann. The reaction conditions were optimized by considering the reaction's mechanism.(2) 8-Hydroxyquinoline-2-carboxaldehyde was synthesized by two syntheticroutes. First, 2-methyl-8-hydroxyquinoline reacted with acetic anhydride to produce 2-methyI-8-acetyloxyquinoline, followed by oxidation with selenium dioxide and removal of acetyl protecting group to obtain 2-formyl-8-hydroxyquinoline. Second, the hydroxy group was protected by benzyl group and then the methyl was oxidated by selenium dioxide. Removal of benzyl group gave 2-formyl-8- hydroxyquinoline. Route A:2. Five Schiff base type derivatives of 8-hydroxyquinoline (L1 ,L2 ,L3 ,L4 and L5 were synthesized by the reaction of 2-formyl-8-hydroxyquinoline with aniline derivatives. The data of their elemental analyses, IR, UV, and NMR spectra are consistent with the proposed structures. The synthetic route is shown as follows.3. Thirty-eight complexes of the Schiff base type derivatives of 8-hydroxyquinoline with transition metal ions were prepared and characterized on the basis of elemental analyses, IR, UV-Visible, NMR spectroscopy and conductance measurements. The results indicate that all of the complexes are 1:1 (ligand:metal ion) type complex and the oxygen and nitrogen atoms in the ligands coordinate to the metal ion.4. The antibacterial activity of these Schiff base type derivatives of 8-hydroxyquinoline ligands and their transition metal complexes were determined . The study results show that most of the compounds have antibacterial activities, and some compounds have excellent antibacterial activities.