Browsing by Author "Ogutu, Hezron Felix Odhiambo"
Now showing 1 - 1 of 1
Results Per Page
Sort Options
- ItemSynthesis of 5- and 6-donor schiff base ligands for the selective extraction and transport of selected base metals ions(Stellenbosch : Stellenbosch University, 2018-12) Ogutu, Hezron Felix Odhiambo; Luckay, Robert C.; Malgas-Enus, Rehana; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Schiff base ligands have various advantageous properties that can be employed for use in solvent extraction processes. They are relatively cheap to synthesize, stable, robust and can be modified to accommodate multiple donor groups. Schiff base ligands were therefore synthesized through a Schiff base condensation method using five aldehydes; salicylaldehyde, para-methoxy salicylaldehyde; para-tertbutyl salicylaldehyde, para-nonyl salicylaldehyde and 2-hydroxynaphthylaldehyde with N-(2-aminoethyl)ethane-1,2-diamine, N-(3-aminopropyl)propane-1,3-diamine, N,N-bis(2-aminoethyl)ethane-1,2-diamine to make five pentadentate ligands with ethylalkyl spacers (class A ligands L1-L5). Five pentadentate ligands with propylalkyl spacer groups (class B ligands L6-L10) and five heptadentate tripodal with ethyl alkyl spacers (class C ligands L11-L15) with N-donor groups. 2-(2-Aminoethoxy) ethylamine and 2,2'-[ethane-1,2-diylbis(oxy)]diethanamine was then used to synthesise the pentadentate (class D ligands L16-L20) and hexadentate O-donor ligands (class E ligands L21-L25). All these ligands were obtained in good yield and were fully characterized by FTIR, 1H NMR, and 13C {H}NMR, ESI-MS, and CHN analysis. The IR and NMR studies of the imine peak of the synthesized products show different shifts due to the different substituents. The analysis of the ligands on the IR showed a red shift for methoxy, tertbutyl and nonyl substituents in comparison to the unsubstituted salicylaldehyde. The naphthylaldehyde showed a blue shift in comparison to the unsubstituted salicylaldehyde. The analysis through the 1H and 13C {H} NMR of the imine peak also showed the same trend with the chemical shift indicating an upfield shift of the imine peak and downfield shift due to the naphthylaldehyde. The addition of the alkyl group in the spacer and the change of the different donor group from the N-donor to the O- donor group did not show a significant shift of the imine peaks. The results obtained for the class B ligands with the naphthylaldehyde showed that the ligand exists in two tautomeric forms; the quaternary imine and the hydroxyl form. A study of the 1H NMR of class D ligands shows that these ligands undergo molecular dynamism caused by the symmetry and flexibility of these molecules. One of the class E ligands, ligand, L22 containing the methoxy substituent was observed to undergo photochromic colour change that was attributed to tautomerism which is unusual behavior for Schiff base ligands. The colour change was studied using confocal microscopy showing fluorescence emission of the ligand in solid state with a wide band gap of between 611 nm - 407 nm. Three of the class D ligands were studied using single crystal X-ray diffraction (SXRD). The ligand L18 with the naphthylaldehyde was obtained showing the tautomeric form of the ligand with the proton shift of the OH proton to the imine N-atom with the phenolic oxygen stabilized by the aromatic system. The Schiff base ligand complexes were synthesized and fully characterized using ATIR, UV-Vis and ESI-MS analysis. Five crystal structures of L1-Cu, L1Co, L4-Cu, L17-Cu, L18-Cu, L19-CuPb were also obtained and analyzed using the SXRD. The complexes synthesized from the class A ligands L1-Co was obtained showing an octahedral coordinate complex around the Co metal, while the L1-Cu, L4-Cu, were obtained showing a metal induced hydrolyzed square planar geometry. The L17-Cu, L18-Cu complexes synthesized from class D ligands with the methoxy, and naphthyl groups respectively were observed to form metallocycles with Cu-metal. The geometry of the Cu-centre was observed to be four coordinate, forming a distorted square-planar geometry. L19-CuPb with the tertbutyl substituent was observed to form a bi-metallic Cu-Pb complex with four Cu-metallocyles coordinated to one Pb-metal in octahedral geometry. All the ligands were subjected to solvent extraction studies. The results obtained showed that all the class A and class C ligands, except the nonyl based substituent, showed a high degree of bleeding into the aqueous phase. The ligands with the nonyl-containing substituents for class A and class C were observed to selectively extract 83% and 86% of Cu2+. The ligands that showed high degree of bleeding to the aqueous phase were subsequently used for synergistic solvent extraction studies using three different synergists. Synergist A (palmitic acid) was observed to synergistically promote selectivity of Pb2+, synergist B (dodecylsulfonate) synergistically promoted selectivity of Cu2+ and Pb2+ while synergist C (dodecylbenzylsulfonate) was observed to extract both Cu2+ and Pb2+ slightly since it showedlow selectivity. The ligands that did not show bleeding into the aqueous phase (class B, D and E ligands) were observed to be very selective towards Cu2+ in accordance with the nature of stability of their complexes as shown by the Irving Williams series. The class D and E ligands containing the O-donor group showed excellent extraction and selectivity of Cu2+. The highest extraction was observed for the non-substituted salicylaldehyde based ligand at 87% and 95% for the naphthylaldehyde based ligand for class D and class E ligands respectively. For all the O-donor based ligands, the % extraction of a secondary metal was less than 10% indicating exceptional selectivity of Cu2+. These results were very good and showed that despite the increased organic nature of the alkyl chain substituent, the non-substituted ligand showed the highest extraction of Cu2+. This high selectivity and extraction were correlated to the crystal structure obtained. This correlation showed that the nature of coordination of the ligand to the metal ion has a profound effect on the % extraction of the ligand in solvent extraction.