الفهرس 
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Abstract
The aim of this study is to prepare and investigate the structure of the new Schiff-base chemically anchoring on natural polymer (chitosan; reapting units of glucosamine) which synthesize from the condensation of chitosan with 2,4-dihydroxybenzaldehyde (2CS-H2dhba) and number of its transition metal complexes with Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ru(III), Rh(III), Pd(II) and Au(III). Physico-chemical measurements of the isolated Schiff-base and complexes included IR, solid 13C NMR, electronic and ESR spectra, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), elemental analysis, magnetic, thermal (TG) and pH-metric measurements. All the results confirm that the ligand in this study has one Schiff-base unit per two units of chitosan, i.e, (2CS-H2dhba). pH-metric measurements determine of the de-protonation constants (pKa1*, pKa2 *) of 2CS-H2dhba and formation constant of the complexes confirming that 2CS-H2dhba coordinate via a zomethine and oxygen atom from hydroxyl group 2(OH) behaves as a monoprotic species. The use of some of these complexes ; Fe(III), Co(II), Ni(II), Cu(II), Pd(II), Ru(III) and Rh(III) as catalytic oxidants for epoxidation of alkenes (n-hexene and cyclohexene) in presence of H2O2 as co-oxidant in heterogeneous system. These complexes show high yield, selectivity and turn over numbers. Also, all the reported complexes were easily separated from the epoxidation reaction mixture and recovered up to 10 times. Also, 2CS-H2dhba have been used as a good sorbent for the separation of the heavy toxic Pb(II) ions from aqueous media by the adsorption on its surface as well as successfully recovered from different natural water samples.Also, 2CS-H2dhba was found to be recovered for consecutive uses after desorption of Pb(II) ions, i.e, 2CS-H2dhba exhibits good reusability.