Polarographic behaviour of salicylaldehyde-2-pyridylhydrazone and its copper(II) complex (original) (raw)
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Microchemical Journal, 1991
Differential pulse polarography has been investigated for the simultaneous determination of copper and cobalt in the presence of phenyl-2-picolylketone-2-pyridylhydrazone, PPKPyH, as a complexing agent at pH 4.2; I.l. = 0.1. Well-defined diffusion-controlled waves were obtained for both systems. Reversible and irreversible waves were observed for copper and cobalt systems, respectively. A method is proposed for the simultaneous determination of these metals when they are present together in pure solution as the difference in their E1/2 values is sufficient for this purpose. The method has also been applied to the simultaneous determination of these metal ions in some synthetic samples.
Journal of the Serbian Chemical Society, 2003
The synthesis and characterization of benzene- and p-toluenesulphonylhydrazones derived from salicylaldehyde and 2-hydroxy-1-naphthaldehyde and their Cu(II) complexes are reported. The compounds were characterized on the basis of elemental analyses, electronic and IR spectra, magnetic moments, and conductance measurements. The electrochemical behavior of the Cu(II) complexes was investigated in DMSO by cyclic voltammetry (CV), rotating disc electrode (RDE) and coulometry. The oxidative polymerization of the copper complexes on a glassy carbon electrode was carried out in DMSO.
Monatshefte für Chemie - Chemical Monthly, 2006
The electrochemical behavior of some hydrazones derived from 6-chloro-2-hydrazinopyridine in the Britton-Robinson universal buffer of pH 2-11 containing 35% ethanol was investigated at the mercury electrode using dc-polarography, controlled-potential coulometry, and cyclic voltammetry techniques. The examined hydrazones were reduced in solutions of pH< 9 in a single 4-electron diffusion-controlled irreversible step corresponding to both the saturation of -N¼C< double bond and cleavage of the -HN-NH-single bond of the hydrazone molecule via the consumption of two electrons for each center. Whereas the starting compound, 6-chloro-2-hydrazinopyridine, was reduced in a single 2-electron diffusion-controlled irreversible step corresponding to cleavage of its -NH-NH 2 single bond. The mechanistic pathway of the electrode reaction of the studied compounds was elucidated and discussed. The pK a values of the examined hydrazones and the stoichiometry of their complexes in solution with some transition metal ions were determined spectrophotometrically. The dissociation constants and the thermodynamic parameters of the investigated hydrazones, and the stability constants of their metal complexes in solution were determined potentiometrically.
Russian Journal of General Chemistry, 2007
Acid-base properties of hydrazones derived from 8-hydrazinoquinoline and substituted salicylaldehydes were studied. Under the experimental conditions, only the first step of ionization of the hydrazones is realized. The ionization constants were calculated quantum-chemically. Copper(II) complexes of these hydrazones, (HL)Cu(X)(CH3OH)n, were isolated (HL− is the monodeprotonated form of hydrazones, and X− is the acid residue). According to the data of elemental analysis, IR spectroscopy, conductometry, and magnetochemistry, the majority of the complexes have a binuclear structure. The copper(II) ions in the dimeric complex show antiferromagnetic exchange coupling. The ionization constants of the hydrazones and the exchange parameters strongly depend on the substituent in the salicylaldehyde moiety.
Linear free energy relations. III. Electrochemical characterization of salicylaldehyde anils
The Journal of Organic Chemistry, 1975
The polarographic half-wave potential in a series of 14 salicylaldehyde anils is a linear function of ux-(except for the m-and p-NO2 compounds in which the nitro group is electroactive); analyses of potential as a function of the currents indicate a one-electron process. The half-wave oxidation potential is directly proportional to ux+ (except for m-and p-NMe2 compounds in which the dimethylamino group is electroactive). Cyclic voltammetry reveals that the reduction process is irreversible. Oxidative cyclic voltammetry demonstrates that with the exception of the nitro and dimethylamino compounds the initial irreversible one-electron oxidation product undergoes chemical transformation to a tertiary product that forms a reversible one-electron couple; the average of the peak potentials, Le., the half-wave potential, of the couple is directly proportional to the normal Hammett substituent constant, u. In addition to the anils, the half-wave reduction and oxidation potentials of the isoelectronic series stilbene, benzaldehyde anil, and azobenzene were linearly correlated to the calculated energies of the lowest unoccupied and highest occupied molecular orbitals, respectively. The effects of anil substituent and intramolecular hydrogen bonding are rationalized on this basis.
International Journal of Electrochemical Science
In this work, the electrochemical behavior of 4-(2-pyridylazo)resorcinol (PAR) azo dye was studied in Britton-Robinson (BR) buffer (pH 2.0-12.0) media by employing square wave voltammetry (SWV), differential pulse polarography (DPP), direct current polarography (DCP) and cyclic voltammetry (CV) techniques. From the polarographic and voltammetric results, the electrochemical reaction mechanism of the azo dye has been proposed. At the same time, the electrochemical behavior of the copper(II) complex with PAR was investigated by using SWV in 0.1 M KNO3 supporting electrolyte. SWV behavior of Cu(II)-PAR complex at different metal and ligand concentrations have been determined in KNO3 supporting electrolyte media. The metal:ligand molar ratio and stability constant of the Cu(II)-PAR complex were determined to be 1:2 and 5.42x10 10 , respectively.
Influence of the HEPES Buffer on Electrochemical Reaction of the Copper(II)-Salicylaldoxime Complex
Electroanalysis, 1998
The effect of the 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) on the redox process of copper(II)-salicylaldoxime complex [Cu(II)-SA] was studied. The measurements were performed on a hanging mercury drop electrode (HMDE) using various electrochemical techniques. The presence of the HEPES buffer (pH 8.0) doubled the reduction current of the Cu(II)-SA complex, whereas the reduction potential shifted to more positive values (about 50 mV). The results obtained indicate that the presence of the HEPES buffer facilitates the electron transfer between the mercury electrode and the adsorbed Cu(II)-SA complex during the reduction process. The experiments carried out using chronocoulometry with a double step potential revealed that the surface coverage of the Cu(II)-SA complex remained unchanged (in the range between 9 and 10.5 × 10 ¹11 mol cm ¹2 ), regardless of the presence of the HEPES buffer. Square-wave voltammetric measurements also indicate that the redox process of the Cu(II)-SA complex is electrochemically reversible with the reactant adsorption, in spite of the presence of the HEPES buffer.
The Voltammetric Characteristics and Mechanism of Electrooxidation of Hydrazine
Vol. 84 a partial decomposition of Schiff base. Possibly a higher activation energy is required to convert compound I to II than that for the Schiff base formation in the absence of metal, since the former requires splitting a nickel-oxygen bond that does not occur in the latter case. Reaction between Copper(II), Salicylaldehyde and Glycine.-The reactions between glycine and salicylaldehyde with copper(II) ion proved to be not so favorable for quantitative studies as those with nickel. Fig. 8-A, B, C and D are the spectra of copper ion and the copper complexes of salicyl-aldehyde, glycine and salicylaldehyde-glycine, respectively. The lower three curves of Fig. 9 represent the changes in optical density with time for the addition of salicylaldehyde to copper-glycine. As in the nickel system, there is a transition from the glycine complex spectrum to the Schiff base complex spectrum. The upper curve of Fig. 9 represents the optical density changes for the addition of copper(II) to salicylaldehyde-glycine. The initial optical density in this case, again as in the nickel system, is not that of the glycine complex but fairly close to the absorption of the Schiff base complex. Again the attainment of equilibrium is much faster when the Schiff base components are mixed initially than when the metal is permitted first to react with one of them. In fact, the initial optical density is equivalent to that obtained after more than 1.5 hr. when salicylaldehyde is added to copper-glycine. The behavior of copper differs from that of nickel in two respects: (1) copper increases the amount of Schiff base present at equilibrium, and (2) all of the reactions are very much slower than those with nickel, as a comparison of Figs. 2 and 4 with Fig. 9 will demonstrate. Conclusions These experiments demonstrate that the nature of the participation of metal ions in Schiff base formation is determined by the order in which the reactants are mixed; equilibrium is achieved most rapidly when the metal ion is added last. It is noteworthy that the thermodynamic stabilization of the product of a reaction by a metal ion can be accompanied by a retardation of the reaction with the metal. The instantaneous production of the spectrum characteristic of nickel Schiff base complexes upon the addition of nickel to the Schiff base components indicates that the Schiff base is formed in solution without the aid of metal. The addition of either copper or nickel ions to the premixed organic re-agents results in the immediate formation of Schiff base complex in concentrations not very different from those at equilibrium; further progress toward equilibrium produces somewhat more Schiff base with copper and less with nickel. The prior formation of a metal complex with gly-cine results in drastic retardation of Schiff base formation both with nickel and with copper. It is concluded that, even when the metal thermo-dynamically favors Schiff base formation, as is the case with copper, the metal tends to prevent rapid attainment of equilibrium. Ikawa and Snell21 and Christensen and Riggs'9 have found that salicylaldehyde does not participate in transamination and the other vitamin Be-catalyzed reactions. Salicylaldehyde is therefore not analogous to pyridoxal in the molecular rearrangements that follow Schiff base formation, since these rearrangements require either the pyridoxal nitrogen or another electron-attracting group.9·19 However, all of the ligands that bind metal in the pyridoxal-amino acid Schiff bases are also present when salicylaldehyde is substituted for pyridoxal. The conclusions drawn from the salicylaldehyde system are therefore also applicable to pyridoxal Schiff base formation. Since this reaction is retarded by metal ions, it would appear that the effect of metal ions on the vitamin Be-catalyzed reactions occurs after, and not before, Schiff base formation. Acknowledgments.-The authors wish to thank the Research Corporation for its generous financial support of a portion of this project. They are grateful to Mrs. Mary Ann Stevan and Miss Bar-bara Randall for technical assistance and to Drs. Jack Dunitz and Bernard Witkop for helpful discussion. (21) M. Ikawa and E. E. Snell, J. Am. Chem. Soc., 76, 653 (1954).