Synthesis, characterization and solvent extraction studies of 3,5-bis[(2-hydroxybenzylidene)- amino]-benzoic acid and its co(ii) and ni(ii) complexes

Project Abstract

<p> 3,5-Bis[(2-hydroxy-benzylidene)-amino]-benzoic acid (H2B) and its<br>cobalt(II) and nickel(II) complexes were synthesized and characterized via<br>electronic, IR, 1H NMR and 13C NMR. Job’s continuous variation method was<br>used to determine the mole ratio for both metal complexes. Solvent extraction<br>studies were carried out on H2B in 5% DMF with its cobalt(II) and nickel(II)<br>complexes using CHCl3 as organic solvent; with variable condition effects of<br>equilibrium time, buffer pH, mineral acids, salting-out agents and complexing<br>agents. IR spectral study indicates coordination through (N2O2) azomethine and<br>protonated hydroxyl groups. Job’s continuous variation method showed a metal to<br>ligand ratio, 11, for both metal complexes of H2B. Cobalt(II) complex of H2B<br>showed quantitative extraction in pH range 5 – 7, while nickel(II) complex of H2B<br>showed quantitative extraction in pH range 6 – 8. Nickel was successfully<br>separated from cobalt by four-cycle extraction at 10-3 M HNO3 aqueous mixture of<br>Ni(II) and Co(II) {10 μgcm-1 each} in 5% H2B/DMF using 0.05 M cyanide as<br>masking agent and CHCl3 as organic solvent. <br></p>

Project Overview

<p> INTRODUCTION<br>1.0 General Introduction<br>Extraction is the transfer of a solute from one phase to another. Common<br>reasons to carry out an extraction in chemistry are to isolate or concentrate the<br>desired analyte or to separate it from species that would interfere in the analysis.<br>The most common case is the extraction of an aqueous solution with an organic<br>solvent that are immiscible with and less dense than water; they form a separate<br>phase that floats on top of the aqueous phase1.<br>Solvent or liquid-liquid extraction is based on the principle that a solute can<br>distribute itself in a certain ratio between two immiscible solvents, one of which is<br>usually water and the other an organic solvent such as benzene, carbon<br>tetrachloride or chloroform. In certain cases the solute can be more or less<br>completely transferred into the organic phase. The technique can be used for<br>purposes of preparation, purification, enrichment, separation and analysis, on all<br>scales of working, from microanalysis to production processes. In chemistry,<br>solvent extraction has come to the forefront in recent years as a popular separation<br>2<br>technique because of its elegance, simplicity, speed and applicability to both tracer<br>and macro amounts of metal ions2.<br>The ability of a solute (inorganic or organic) to distribute itself between an<br>aqueous solution and an immiscible organic solvent has long been applied to<br>separation and purification of solutes either by extraction into the organic phase,<br>leaving undesirable substances in the aqueous phase; or by extraction of the<br>undesirable substances into the organic phase, leaving the desirable solute in the<br>aqueous phase.3<br>1.1 Background of Study<br>Although solvent extraction as a method of separation has long been known<br>to the chemists, only in recent years it has achieved recognition among analysts as<br>a powerful separation technique. Liquid-liquid extraction, mostly used in analysis,<br>is a technique in which a solution is brought into contact with a second solvent,<br>essentially immiscible with the first, in order to bring the transfer of one or more<br>solutes into the second solvent4. The separations that can be achieved by this<br>method are simple, convenient and rapid to perform; they are clean as much as the<br>small interfacial area certainly precludes any phenomena analogous to the<br>undesirable co-precipitation encountered in precipitation separations.<br>3<br>Solvent extraction has one of its most important applications in the<br>separation of metal cations. In this technique, the metal ion, through appropriate<br>chemistry, distributes from an aqueous phase into a water-immiscible organic<br>phase. Solvent extraction of metal ions is useful for removing them from an<br>interfering matrix, or for selectivity (with the right chemistry) separating one or a<br>group of metals from others4.<br>Solvent extraction is one of the most extensively studied and most widely<br>used techniques for the separation and pre-concentration of elements. The<br>technique has become more useful in recent years due to the development of<br>selective chelating agents for trace metal determination5<br>1.2 Scope of Work<br>The Scope of this research is limited to synthesis of the Ligand<br>Bis(salicylidene)3,5-diaminobenzoic acid, its Co(II) and Ni(II) complexes,<br>spectrophotometric characterization via UV, IR, H and NMR(1H and 13C),<br>extraction of cobalt and nickel metal ions in water using chloroform as organic<br>solvent and separation of Ni(II) from aqueous mixture of Ni(II) and Co(II).<br>4<br>1.3 Significance of Study<br>The introduction of versatile organic reagent, ‘dithizone’, dimethylglyoxime<br>about five years later and 8-hydroxylquinoline in the 1940s opened a new in liquidliquid<br>extraction studies which suffered a lull from 1900 till then.6<br>The search for new extractants for metals continues to draw attention with<br>the quest for reagents that will be discriminatory enough for particular metal ions<br>and avoid interferences at the conditions of extraction.<br>Ukoha et al7 reported the utilization of the compound Bis(4-hydroxypent-2-<br>ylidene) diaminethane as a good reagent to extract copper(II) and also separated<br>the element from a mixture of silver(I).<br>In this research, we are able to synthesize a schiff base Bis(salicylidene)3,5-<br>diaminobenzoic acid as a ligand to investigate the extraction characteristics of<br>cobalt(II) and Nickel(II) in various media. The complexes of cobalt(II) and<br>nickel(II) were characterized spectrophotometrically via UV-visible, IR, and<br>NMR(1H and 13C)<br>1.4 Aims and Objectives<br>This research is aimed at synthesizing a Schiff base ligand: 3,5-Bis-[(2-<br>hydroxy-benzylidene)-amino]-benzoic acid; its Co(II) and Ni(II) complexes;<br>characterization of the ligand and its Co(II) and Ni(II) complexes via, Uv-visible,<br>5<br>IR, 13C and 1H NMR; using the ligand to extract Co(II) and Ni(II) from aqueous<br>solutions of varying conditions. Thus, the optimum extraction condition for the<br>extraction of Co(II) and Ni(II) from aqueous solution with 3,5-[(2-hydroxybenzylidene)-<br>amino]-benzoic acid will be achieved and a favourable condition for<br>the separation of Ni(II) from Co(II) with the ligand will also be ascertained. Hence,<br>the true nature of the Co(II) and Ni(II) complexes of the ligand will be known.<br>6 <br></p>