Studies on imidazole derivatives as chelating agents-V Investigations of the applicabilities of the azoimidazoles as metallochromic indicators

Applicabilities of several azoimidazoles as metallochromic indicators were investigated in the light of the general equations expressing the colour change of the visual chelatometric titrations. By using the stability constants of the nickel(II), copper(II), zinc(II) and cadmium(II) chelates, the useful pH ranges, titration errors and sharpness of colour changes were predicted theoretically and the usefulness of these reagents as indicators was established experimentally. The Cu(II)-EDTA-indicator system was also examined experimentally. The OH-containing azoimidazoles could be applied to the direct titration of copper, nickel, zinc, cadmium, lead and bismuth and to the titration of calcium and cobalt in the presence of Cu(II)-EDTA. Attempts were made to construct diagrams for the estimation of titration errors and sharpness of colour changes.     

Stability of lyophobic colloids in the presence of metal chelates and chelating agents

Summary Coagulation, electrophoresis and adsorption data of various metal chelates and chelating agents on silver halide sols, PVC latex, and montmorillonite clay have been shown. The effects are most pronounced with the silver halide sols which are believed to be due to the coordination of the chelates and chelating agents with the crystal lattice ions of the colloidal particles. The PVC latex stability in the presence of the same solute species depends strongly on the concentration of the stabilizing surface active agent (dodecyl sulfate ions).

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Zusammenfassung Koagulations-, Adsorptions- und elektrophoretische Messungen an Silberhalogeniden, Polyvinylchlorid und Montmorillonit-Solen in Anwesenheit von verschiedenen Metallchelaten und Chelatbildnern werden dargestellt. Die beobachteten Effekte sind am stärksten bei den Silberhalogeniden, was durch die Koordination der Chelatkomplexe und der Chelatmoleküle mit den Gitterionen der Kolloidteilchen erklärt wird. Die Stabilität von Polyvinylchlorid-Latex gegen die gleichen Komplexe hängt stark von der Konzentration der grenzflächenaktiven potentialbestimmenden Ionen (Dodecylsulfat-Ionen) ab.

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Part of the plenary lecture entitled Chemical Aspects of Colloid Stability delivered at the 25 th Kolloid-Tagung in Munich on October 13–15, 1971.

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Supported by the National Science Foundation Grant GP 12220.     

Determination of equilibrium constants of alkaline earth metal ion chelates with Dowex A-1 chelating resin

A complexation chemistry model is applied to chelating ion-exchange systems and a method is presented for the determination of equilibrium constants for metal ion chelates with these resins. Protonation constants for the iminodiacetic based chelating resin Dowex A-1 were determined from potentiometric pH-data. Equilibrium constants were determined for 1:1 beryllium, magnesium, calcium, strontium and barium chelates with the resin in a wide pH range by measuring the concentrations of respective metal ions in the aqueous phase with direct current plasma atomic emission spectrometry (DCP-AES). A batch technique was used for the equilibrium experiments. At pH below 7 protonated 1:1 species were also found to be formed with the resin. From the obtained equilibrium constants, theoretical distribution coefficients were calculated as function of pH for respective metal ion resin system.     

Interactions of silver halides with metal chelates and chelating agents

Summary Electrokinetic data of negatively charged silver iodide solsin statu nascendi were obtained as a function of varying concentrations of two chelate complexes, Co(phen) ₃ ³⁺ and Co(dipy) ₃ ³⁺ . The measurements were carried out with sols at two different pl values (2.72 and 3.15) and at two pH values (3.0 and 7.0). The results were interpreted in terms of the theory of the electrical double layer based on the Stern-Langmuir adsorption model.

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Zusammenfassung Die elektrokinetischen Daten für negativ geladene Silberjodid-Solein statu nascendi wurden in Abhängigkeit von verschiedenen Konzentrationen von Co(phen) ₃ ³⁺ and Co(dipy) ₃ ³⁺ Komplexen bestimmt. Die Messungen wurden mit Solen bei zwei verschiedenen pI-Werten (2.72 und 3.15) und bei pH 3.0 und 7.0 durchgeführt. Die Resultate konnten durch die Doppelschicht-Theorie, die auf der Stern-Langmuirsche Adsorption beruht, erklärt werden.

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Part I, see Ref. 3; Part 11, Ref. 5.

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With 3 figures and 2 tables     

Stability constants of some bivalent first row transition metal chelates of dicarboxylic acids containing ether linkages

The stability constants of the Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+) and Zn(2+) complexes with four acids of the type HOOCCH(2)O(CH(2)CH(2)O)(n) CH(2)COOH (n = 0-3) are reported. For n = 0 the constants are in the Irving-Williams order, but not for n = 1-3.     

Metal chelates of phosphonate-containing ligands-II: stability constants of some beta-styrylphosphonic acid metal chelates

The synthesis and properties of beta-styrylphosphonic acid (SPA) are reported. The values of the protonation constants of the ligand were determined potentiometrically at different ionic strengths and in the temperature range 0-65 degrees. The enthalpy and entropy of protonation have been calculated by using the van't Hoff isochore. The protonation process is endothermic and is stabilized by a relatively large positive entropy change. The stability constants of the complexes formed between SPA and the bivalent Mg, Ca, Ba, Co, Ni and Pd ions at 25 degrees and ionic strength of 0.12M KNO(3) were also determined. All measurements were carried out in 18% dimethylformamide-water mixture.     

Studies on chelating resins-I General equation for the calculation of the protonation constants of chelating resins

A general equation has been derived which describes the protonation equilibria of basic groups attached to an insoluble polymer matrix. The derivation is based on the application of the charge and mass-balance equations. When the relationship obtained is applied to water-soluble ligands, it reduces to the well-known Schwarzenbach equation for titration of polybasic acids.     

Determination of chelating agents and metal chelates by capillary zone electrophoresis

Aminopolycarboxylic acids such as diethylenetriaminepentaacetic acid (DTPA) are commonly used as chelating agents in many pulp and paper industries, particularly as scavengers of metal ions which catalyze the decomposition of hydrogen peroxide used as a bleaching agent. Concern for the effect of waste DTPA in the aquatic environment has led to a need for the development of methods to determine its levels in waste water. This paper describes the determination of free DTPA and several metal-DTPA complexes in water and waste water by capillary zone electrophoresis. The optimization of separation conditions included the selection of an appropriate carrier electrolyte composition (pH, organic solvents, ion-pairing reagents) and the systematic investigations of selective complexation of free DTPA as well as metal exchange reactions for metal-DTPA complexes in order to achieve selective and sensitive direct UV detection. The determination of DTPA in waste water from a paper mill was possible in the low ppm range.     

Stability constants of some metal dithizonates

The overall stability constants of electroneutral dithizonates of bismuth, cadmium, cobalt(II), copper(II), iron(II), lead(II), manganese(II), mercury(II), nickel, palladium(II), silver, tin(II) and zinc were determined by means of stoichiometric dilution in aqueous solution stabilized by hydroxylamine hydrochloride, at pH 5.50-10.02. Stability constants of complexes ML of bivalent metals were determined under similar conditions but with an excess of metal.     

Stability constants of 2-mercaptohistamine metal complexes

Summary Stability constants of 2-mercaptohistamine (2-MH) with a number of transition metal ions were determined by a potentiometric titration method and the coordination mode of (2-MH) metal complexes were thereby characterized. With Mn^II, Fe^ll, Co^II, and Ni^II, coordination occurred through both the imidazole-nitrogen and amino groups, while with Zn^II, Cd^II, Pb^II, and Hg^II, both thiolate and amino groups, contribute to the coordination. in the 2-MH copper complex, polymer formation is suggested on the basis of visible absorption and e.p.r. spectra.     

Metal chelates of phosphonate-containing ligands-V Stability of some 1-hydroxyethane-1,1-diphosphonic acid metal chelates

A detailed study of the complexes formed between 1-hydroxyethane-1,1-diphosphonic acid and twelve metal ions, including the alkaline earth and transition non-transition metal ions, is reported. The formation constants of the protonated and unprotonated complexes are measured from potentiometric data and possible structural formulae are given. The results reveal that only mononuclear (1:1) di-, mono- and unprotonated metal chelates are formed and that the general order of stability for the unprotonated complexes is Zn > Mn > Ca > Cu > Cd > Pd > Ni > Co reverse similar Sr > Mg > Ag > Ba.     

Studies on nucleation from solution of some analytically important metal chelates

The combination of precipitation from homogeneous solution and Vonnegut's droplet technique is employed in the study of nucleation from solution of bis(1,2-cyclohexanedionedioxunato)Ni(II), bis(1,2-cycloheptanedionedioximato)Ni(II), bis(1,2-cyclohexanedionedioximato)Pd(II) and bis(1,2-cycloheptanedionedioximato)-Pd(II). Values of the kinetic constant, surface energy, critical radius and the number of molecules per critical nucleus are calculated and discussed in terms of the limitations of the classical theory of nucleation when applied to crystal nucleation from aqueous solutions of electrolytes.     

The stability constants of some metal chelates of triethylenetetraminehexaacetic acid (ttha)

Stability constants for Al(III), Cd(II), Co(II), Cu(II), Fe(III), Hg(II), La(III), Nd(III), Er(III), Mg(II). Mn(II), Ni(II), Pb(II), Th(IV) and Zn(II) complexes of triethylenetetraminehexaacetic acid (TTHA) have been evaluated from data obtained by pH and pM measurements. The pM method based on measurements with the mercury electrode and the redox system Fe(III)/Fe(II) proved to be very useful when binuclear complexes are formed.     

Infrared studies of group IIB metal complexes with some imidazole derivatives

The complexes formed by zinc(II), cadmium(II) and mercury(II) halides and perchlorates with N-ethylimidazole and N-propylimidazole have been prepared and characterized by molecular conductance and i.r. spectral data down to 100 cm⁻¹. On the basis of the assignments of the metal—halogen and the metal—ligand vibrations, the stereochemistry of the compounds was inferred.     

Studies of metal chelates with the novel ligand 2,2,7-trimethyl-3,5-octanedione

The synthesis of the novel ligand 2,2,7-trimethyl-3,5-octanedione, H(tod), is described, as well as the preparation of some of the transition metal and lanthanide complexes containing the anion of this unsymmetrical beta-diketone ligand. The structure of Cu(tod)₂ has been determined by X-ray crystallography to be square-planar with the isobutyl groups cis to each other. Thermogravimetric analyses indicate that several of these metal complexes are volatile and thermally stable compounds. Metal complexes containing this ligand also show unusually high solubilities in non-polar solvents such as n-hexane. The properties of these compounds indicate that they may be useful for vapour-plating of metals, as fuel additives, and in other applications.     

Stability constants and thermodynamic functions of molybdenum and uranium chelates formed with dl-alpha-aminobutyric acid

The stability constants and thermodynamic functions involved in the formation of Mo(VI) and U(VI) chelates with dl-alpha-aminobutyric acid have been determined potentiometrically. It is observed that in the case of Mo(VI) system three chelates ML, ML(2) and ML(3) are formed stepwise, whereas in the U(VI) system only two chelates ML and ML(2) are formed before precipitation occurs, and both steps occur almost simultaneously. Results show that entropy makes a predominant contribution to the stability of both Mo(VI) and U(VI) chelates.     

Studies on the imidazole series

The reaction of 2-mercaptoimidazole and its 4(5)-aryl- and 4,5-diaryl-substituted derivatives with -halogenoketones has yielded a number of alkyl-, acyl-, and aryl-substituted imidazo[2,1-b]thiazoles.For part XLV, see [1].