Voltammetric, Potentiometric and Spectrophotometric Studies of Some Hydrazones and Their Metal Complexes in Ethanolic-Aqueous Buffered Solutions (original) (raw)
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Diprotonated hydrazones and oximes as reactive intermediates in electrochemical reductions
Tetrahedron Letters, 2004
The shape of plots of limiting currents of some hydrazones and oximes as a function of pH, the slopes of E 1=2 -pH plots (particularly for benzaldehyde N,N,N-trimethylhydrazonium ion) and the presence of separate two or three waves in reductions of some oximes bearing electron withdrawing groups represent a proof of formation of diprotonated forms of hydrazones and oximes as reaction intermediates. They are formed at the surface of the electrode in an equilibrium preceding the uptake of the first electron.
Review: Voltammetric properties and applications of hydrazones and azo moieties
Polyhedron, 2019
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Organometallics, 2003
A series of new monocationic organo-iron(II) benzaldehyde-hydrazone complexes of general formula [CpFe(η 6 -o-RC 6 H 4 -NHNdCH-C 6 H 4 -p-R′)] + PF 6 -(Cp ) η 5 -C 5 H 5 ; R,R′ ) H, H 5; H, Me 6; H, MeO 7; H, NMe 2 8; Me, Me 9; Me, MeO 10; Me, NMe 2 11; MeO, Me 12; MeO, MeO 13; MeO, NMe 2 14; Cl, Me 15; Cl, MeO 16; Cl, NMe 2 17) have been synthesized. These mononuclear hydrazones were stereoselectively obtained as their trans-isomers about the NdC double bond, by reaction of the corresponding organometallic hydrazine precursors [CpFe(η 6 -o-RC 6 H 4 -NHNH 2 )] + PF 6 -(R ) H, 1; Me, 2; MeO, 3; Cl, 4) with p-substituted benzaldehydes p-R′C 6 H 4 CHO (R′ ) H, Me, MeO, NMe 2 ) in refluxing ethanol. The N-methyl derivatives formulated as [CpFe{η 6 -C 6 H 5 -N(Me)NdCH-C 6 H 4 -p-R′}] + PF 6 -(R′ ) Me, 18;
2014
The CV and DPV behaviour is investigated for two hydrazine derivatives, 2,2-diphenyl-1-(2,4-dinitrophenyl)hydrazine (A), and 2,2-diphenyl-1-(3,5-dinitropyridin-2-yl)hydrazine (B) which differ structurally by the presence of a nitrogen atom (in the pyridinyl moiety of B) instead of a carbon atom (in the phenyl moiety of A) in an aromatic ring. The studies take advantage of the presence of an acidic hydrogen atom which can be removed by the methoxide ion base. So that each compound is studied in the absence and in the presence of this hydrogen abstractor. In each case a mechanism of the electrode reaction is proposed. The structure of each compound allows the electronic conjugation (electron withdrawing and electron donating effects being present in different degrees) which leads to similar and/or different CV and DPV behaviour. The anodic and cathodic peak potentials, the half-wave potentials, the shape factor and the peak separation are found and used to explain electrochemical mech...
ChemInform, 2015
This is the first comprehensive review of the biological activity of hydrazone-transition metal complexes. Hydrazone complexes gained much attention because of their antifugial, antibacterial anticonvulsant, and analgesic, antiinflammatory, antimalarial, antimicrobial, antituberculosis, anticancer, and antiviral activities. Additionally, some of the hydrazone complexes were used in treatment of iron overload diseases. One application, which reflects the importance of hydrazone complexes, is their use in detection and determination of metals and some organic constituents in pharmaceutical formulations. This review will provide an overview of the biological, analytical and catalytic applications of this category of complexes.
RAD Proceedings, 2017
UV spectroscopic methods were used in order to determine dissociation constants of some aromatic hydrazones. The acid-base properties of investigated hydrazones were followed in sodium hydroxide media at constant ionic strength of 0.5 mol/dm 3 adjusted with sodium perchlorate. Absorption band with the maximum of 330 nm was noticed in neutral media. A batochromic shift of this band was observed in basic media, probably due to the dissociation process. The dissociation process took place in one step for four investigated hydrazones and in two steps for the hydrazone with a phenol group in its molecule. The absorbance data from the UV spectra were used for the calculation of dissociation constants. The obtained pKHA values were between 2.11 and 2.62 which suggested that the influence of the substituents is not significant. At the same time, pKHA values were determined graphically from the intercept of the dependence of logI on pH. There are no important differences between calculated and graphically determined dissociation constant values.
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).
Electroreduction of Some Substituted Hydrazones on Platinum Electrode in Dimethylformamide
2009
The electrochemical behaviors of 4-(1-phenyl-1-methylcyclobutane-3-yl)-2-(2-hydroxybenzylidenehydrazino)thiazole (I), 4-(1-p-xylene-1-methylcyclobutane-3-yl)-2-(2- hydroxybenzylidenehydrazino)thiazole (II), 4-(1-mesytylene-1-methylcyclobutane-3-yl)-2-(2- hydroxybenzylidenehydrazino)thiazole (III), 4-(1-phenyl-1-methylcyclobutane-3-yl)-2-(2-hydroxy-5-bromobenzylidenehydrazino)thiazole (IV), 4-(1-phenyl-1-1-methylcyclobutane-3-yl)-2-(2-hydroxy-3-metoxybenzylidenehydrazino)thiazole (V), 4-(1-phenyl-1-methylcyclobutane-3-yl)-2-(2,4-dihydroxybenzylidenehydrazino)thiazole (VI) were investigated by cyclic voltammetry (CV), controlled potential electrolysis, and chronoamperometry (CA) techniques in the presence of 0.10 M tetrabutylammonium tetrafluoroborate (TBATFB) in dimethylformamide (DMF) at platinum electrode. Hydrazones display two cathodic peaks at about ―1.60 V and ―2.20 V. Diffusion coefficients and the number of electrons transferred were calculated by using an ultramicro electrod...
RAD Conference Proceedings
UV spectroscopic methods were used in order to determine dissociation constants of some aromatic hydrazones. The acid-base properties of investigated hydrazones were followed in sodium hydroxide media at constant ionic strength of 0.5 mol/dm 3 adjusted with sodium perchlorate. Absorption band with the maximum of 330 nm was noticed in neutral media. A batochromic shift of this band was observed in basic media, probably due to the dissociation process. The dissociation process took place in one step for four investigated hydrazones and in two steps for the hydrazone with a phenol group in its molecule. The absorbance data from the UV spectra were used for the calculation of dissociation constants. The obtained pKHA values were between 2.11 and 2.62 which suggested that the influence of the substituents is not significant. At the same time, pKHA values were determined graphically from the intercept of the dependence of logI on pH. There are no important differences between calculated and graphically determined dissociation constant values.
DETERMINATION OF THE DISSOCIATION CONSTANTS OF SOME p-SUBSTITUTED AROMATIC HYDRAZONES
Contributions, Sec. Math. Tech. Sci., MANU, 2011
The acid-base behavior of five p-substituted aromatic hydrazones has been studied, using UV spectrophoto-metric method. The influence of the acidity of the medium on the absorption spectra is followed in aqueous sodium hydroxide solutions in pH region from 7 to 14. The measurements are performed at room temperature, and at ionic strength of 0.1, 0.25 and 0.5 mol dm-3. A batochromic shift of the absorption band that appears in neutral media is observed, when pH is up to 7. It suggests that the dissociation process of the amide and hydroxyl group takes place. Deprotonation enthalpies and total energy values are calculated by using the semiempirical methods AM1 and PM3. Using the changes in the UV spectra with pH of the solution, the determination of dissociation constants, pK BH , at three different ionic strengths, as well as, the thermodynamic dissociation constants at zero ionic strength, is performed. In order to obtain more precise results, the calculations are made from the absorbance values at four selected wavelengths. Furthermore, the pK BH values were determined graphically from the intercept of the dependence of logI on pH. The results showed that the numerically calculated pK BH values are identical to those graphically obtained.