Speciation of phytate ion in aqueous solution. Alkali metal complex formation in different ionic media

The acid–base properties of phytic acid [myo-inositol 1,2,3,4,5,6-hexakis(dihydrogen phosphate)] (H₁₂Phy; Phy^12–=phytate anion) were studied in aqueous solution by potentiometric measurements ([H⁺]-glass electrode) in lithium and potassium chloride aqueous media at different ionic strengths (0<I mol L^–13) and at t=25 °C. The protonation of phytate proved strongly dependent on both ionic medium and ionic strength. The protonation constants obtained in alkali metal chlorides are considerably lower than the corresponding ones obtained in a previous paper in tetraethylammonium iodide (Et₄NI; e.g., at I=0.5 mol L^–1, logK₃^H=11.7, 8.0, 9.1, and 9.1 in Et₄NI, LiCl, NaCl and KCl, respectively; the protonation constants in Et₄NI and NaCl were already reported), owing to the strong interactions occurring between the phytate and alkaline cations present in the background salt. We explained this in terms of complex formation between phytate and alkali metal ions. Experimental evidence allows us to consider the formation of 13 mixed proton–metal–ligand complexes, M_jH_iPhy^{(12–i–j)–}, (M⁺=Li⁺, Na⁺, K⁺), with j7 and i6, in the range 2.5pH10 (some measurements, at low ionic strength, were extended to pH=11). In particular, all the species formed are negatively charged: i+j–12=–5, –6. Very high formation percentages of M⁺–phytate species are observed in all the pH ranges investigated. The stability of alkali metal complexes follows the trend Li⁺Na⁺K⁺. Some measurements were also performed at constant ionic strength (I=0.5 mol L^–1), using different mixtures of Et₄NI and alkali metal chlorides, in order to confirm the formation of hypothesized and calculated metal–proton–ligand complex species and to obtain conditional protonation constants in these multi-component ionic media.Presented at SIMEC–02, Santiago de Compostela, 2–6 June 2002     

The hydrolysis and fluoride complexation behavior of Fe(III) at 25°C and 0.68 molal ionic strength

Fe(III) hydrolysis and fluoride complexation behavior was examined in 0.68 molal sodium perchlorate at 25°C. Our assessment of the complexation of Fe(III) by fluoride ions produced the following results: log_F1 = 5.15₅, log_F2 = 9.10₇, log_F3 = 11.96, log_F4 = 13.7₅, where log_Fn = 5.15₅=[FeF _n ^(3-n)+ ][Fe³⁺]^–1[F^–]^–n. The stepwise fluoride complexation constants,FK _n+1, obtained in our work (where log_F K _n+1 =log_Fn) indicate that K _n+1/K _n =0.072±0.01. Formation constants for equilibria, Fe³⁺+nH₂OFe(OH) _n ^(3–n)+ +nH⁺, expressed in the form _n ^* [Fe(OH) _n ^(3-n)+ ][H⁺]ⁿ ,[Fe ³⁺]^-1, were estimated as ₁ ^* = –2.754, and ₂ ^* –7. Our study indicates that the results of previous hydrolysis investigations include very large overestimates of Fe(OH) ₂ ⁺ formation constants.     

Thermodynamics of Protonated Amine–Hexacyanoferrate(II) Complex Formation in Aqueous Solution

Thermodynamic parameters, G°, H° and TS° are reported for the formation of proton amine–hexacyanoferrate(II) complexes, in aqueous solution, at 25°C. H° were determined by the temperature dependence of formation constants and/ or by direct calorimetry in aqueous solution, at T = 25°C. Enthalpy changes for the reaction H_iAⁱ⁺ + H_j Fe(CN) ₆ ^j-4 = AFe (CN)₆H _i+j ^i+j-4 (where A = methylamine, ethylenediamine, and tetraethylenepentamine) are quite low and the main contribution to the stability of these complexes arises from the entropic term, as expected for electrostatic interactions. When j = 0, the formation entropy is linearly dependent on i according to the simple equation TS° = 13.4 i kJ-mol^–1.     

On the discriminating and stability increasing properties of alizarin maroon in mixed-ligand complexes of yttrium(III)

The stability constants of the yttrium(III) mixed ligand complexes (1:1:1) containing alizarin maroon (azm) and as a second ligand salicylic acid (sa), 5-sulphosalicylic acid (ssa), 5-nitrosalicylic acid (nsa), 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen) have been determined potentiometrically in 20% (v/v) ethanol-water medium (I=100 mmol dm^–3 NaClO₄, 25±0.1 °C). The complexation equilibria of the different biligand systems were demonstrated. All of these mixed-ligand complexes are considerably more stable than expected from purely statistical reasons. The results obtained were discussed in relation to the nature of the secondary ligands involved. For the equilibrium, Y(azm)₂ + Y(L)₂ 2 Y(azm)(L), the following constants, logX, were determined: Y(azm)(sa) 3.11 (0.46); Y(azm)(ssa) 2.76 (0.33); Y(azm)(nsa) 3.02 (0.48); Y(azm)(bipy) 3.96 (0.99); Yazm(phen) 4.33 (1.07). The constants given in parentheses correspond to logK _Y=[logK _Y(azm)(L) ^Y(azm) - log K _Y(L) ^Y ].

---

Die stabilitätserhöhenden Eigenschaften von Alizarin-Maron in Yttrium(III)-Komplexen mit gemischten Liganden

Zusammenfassung Es wurden die Stabilitätskonstanten der 1:1:1-Yttrium(III)-Komplexe mit Alizari-Maron (azm) und mit einer Reihe weiterer Zweitliganden [Salizylsäure (sa), 5-Sulfosalizylsäure (ssa), 5-Nitrosalizylsäure (nsa), 2,2-bipyridyl (bipy) und 1,10-Phenanthrolin (phen)] potentiometrisch in 20% (v/v) Ethanol-Wasser (I=100 mmol dm^–3 NaClO₄,t=25±0.1 °C) bestimmt. Es werden die Komplexierungsgleichgewichte der verschiedenen Zweiligandensysteme angeführt. Alle gemischtligandigen Komplexe zeigten eine deutlich höhere Stabilinisse werden in Relation zur chemischen Natur der Sekundärliganden gesetzt. Für das Gleichgewicht Y(azm)₂ + Y(L)₂ 2 Y(azm)(L) wurden folgende Konstanten logX ermittelt: Y(azm)(sa) 3.11 (0.46); Y(azm)(ssa) 2.76 (0.33); Y(azm)(nsa) 3.02 (0.48); Y(azm)(bipy) 3.96 (0.99); Y(azm)(phen) 4.33 (1.07). Die Werte in Klammern entsprechen logK _Y=[logK _Y(L) ^Y –logK _Y(L) ^Y ].

     

Zur Reaktion von Germaniums?ure mit ?thylendiamintetraessigs?ure

Zusammenfassung Germaniumsäure reagiert mit den Formen H₄Y und H₃Y- der Äthylendiamintetraessigsäure unter Bildung von 11-Komplexverbindungen mit den folgenden Stabilitätskonstanten: K _H4Y=6.27·10⁴ bzw. K _H4Y=5.99·10⁴ und K _H3Y=3,78·10⁴ bzw. K _H3Y=2,35·10⁴ (25°C; Ionenstarke 0,1 m), je nachdem, mit welchen Werten für die Dissoziationskonstanten der ÄDTE gerechnet wird.

---

Summary Germanic acid reacts with the species H₄Y and H₃Y- of EDTA forming 11 complex compounds. The following stability constants have been obtained: K _H4Y=6.27x10⁴ resp. K _H4Y=5.99x10⁴ and K _HaY=3.78x10⁴ resp. K _H2Y=2.35x10⁴ (25°C; ionic strength 0.1 m), depending on the values inserted for the dissociation constants of the EDTA.

---

---

Herrn Prof. Dr. M. von Stackelberg zum 70. Geburtstag gewidmet.

---

Herrn Prof. Dr. H. Nowotny danke ich für wertvolle Diskussionen. Bei der Ausführung der Experimente haben mich in dankenswerter Weise vor allem Herr A. Grumer, ferner Frl. L. Docekal, Frl. E. Hofmeister und Herr P. Angelbeger unterstützt.     

Bis-substituted benzo-15-crown-5 ethers as ion carriers in potassium ion-selective electrodes

Lipophilic bis-substituted ester and ether derivatives of benzo-15-crown-5 have been synthesised. The correlation between the structure and potentiometric ion-selectivity has been studied in PVC membrane ion-selective electrodes. An ion-selective potassium sensitive electrode based on 4,5-bis (biphenyloxymethyl)benzo-15-crown-5 exhibited the best electrode properties. The detection limit was loga _K = -5.4; logK _K,Na ^ppot = -3.5. The effect of the lipophilicity of neutral carriers upon electrode performance has been also discussed.     

Thermodynamics of the dissociations of glycine in 50 mass % aqueous monoglyme from 5 to 55°C

Electromotive-force measurements on cells without liquid junction have been used to determine the pK ₁ and pK ₂ values of glycine in 50 mass % aqueous monoglyme at 11 temperatures from 5 to 55°C. The change in the first dissociation constant is given as a function of the thermodynamic temperatureT by the equation pK ₁=–2058.6/T+15.421–0.019169T, whereas that for the second dissociation constant is given by the equation pK ₂=1200.5/T+6.7211–0.0042897T. At 25°C, the pK ₁ is 2.806 in the mixed solvent, as compared with 2.350 in water; hence, protonated glycine becomes a weaker acid in the mixed solvent. The pK ₂ is 9.453 in the mixed solvent, whereas that in water is 9.780, suggesting that the second dissociation process becomes stronger in terms of acidity. The thermodynamic quantities G ^o, H ^o, S ^o, and C _p ^o have been calculated, and the results have been discussed with respect to preferential solvation and also compared with similar data for the same two processes in 50 mass % methanol.     

Hydrolysis of (CH3)3Sn+ in Various Salt Media

The hydrolysis of trimethyltin(IV) has been studied by potentiometry (H⁺ -glass electrode) and calorimetry in various salt media (NaNO₃, NaCl, KCl, Na₂SO₄, and NaNO₃—NaCl mixtures). The effect of ionic strength on the hydrolysis constants is accounted for by a simple Debye–Hückel type equation and by Pitzer equations. The results allow us to obtain H for hydrolysis and the temperature dependence of the Pitzer parameters. The resulting coefficients can be used to examine the speciation of (CH₃)₃Sn⁺ in multicomponent electrolyte solutions, such as natural waters, over a wide range of temperature and ionic strength.     

Evaluation of a direct1H NMR method for determining logK and ΔH values for crown ether -alkylammonium cation complexation

A direct¹H NMR method for determining logK and H values for crown ether-ammonium cation complexation using milligrams of sample was tested and evaluated for accuracy and precision by comparing the results with those obtained using a titration calorimetric method. LogK values for the interactions of a non-chiral crown ether, diketopyridino-18-crown-6 (K₂P18C6), with -phenylethylammonium (PhEt⁺) perchlorate in 50%–50% and 90%–10% (v/v) mixtures of deuterated methanol (CD₃OD) and deuterated chloroform (CDCl₃) at four temperatures and, with -(1-naphthyl)ethylammonium (NapEt⁺) perchlorate in 50%CD₃OD-50%CDCl₃ (v/v) at 25°C were determined by a direct¹H NMR method. Values of H for the interactions of K₂P18C6 with PhEt⁺ in the two solvents were calculated from the temperature dependence of logK. LogK values for the interactions of a chiral crown ether, dimethyldiketopyridino-18-crown-6 (M₂K₂P18C6), with (R) and (S) enantiomers of NapEt⁺ in pure CD₃OD at 25.0°C were also determined by the NMR method. The results were compared with those determined by a calorimetric method at 25.0°C in 50%-50% and 90%–10% (v/v) mixtures of plain methanol and chloroform, in 100% plain methanol, and in a 50%-50% mixture of partially deuterated methanol (with deuterium substitution on the methanol OH group, CH₃OD) and deuterated chloroform. The log K values determined by both methods were found to be in good agreement, but the standard deviations associated with the NMR logK values were two to three times greater. The agreement of the H values determined by the two methods was poor, differing by approximately 10 kJ/mol with the NMR method giving more negative values. The standard deviations associated with the NMR H values were approximately ten times greater than those for the calorimetric values. Ion-pairing was observed for the interaction of perchlorate ion with both free and bound PhEt⁺ in 50%methanol-50%chloroform mixture. It is concluded that the NMR procedure is satisfactory for the determination of logK, but not H values.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Stereochemical nonrigidity of (O—Ge)-chelate bis[(2-oxo-1-hexahydroazepinyl)methyl]dichlorogermane: substantiation of the dissociative mechanism of chelating ligand exchange

Stereochemical nonrigidity of the hexacoordinated (O—Ge)-chelate bis(2-oxo-1-hexahydroazepinylmethyl)dichlorogermane in CDCl₃ was studied by dynamic NMR. The activation parameters of the intramolecular rearrangement at the coordination center are G ^# ₂₉₈ = 12.3±0.2 kcal mol^–1, H ^# = 16.9±0.2 kcal mol^–1, and S ^# = 15.3±0.7 cal mol^–1 K^–1. The dissociative mechanism of ligand exchange involving the cleavage of the OGe coordination bond is discussed based on the positive entropy of activation.     

Application of the Specific Ion Interaction Theory → the Solubility Product and First Hydrolysis Constant of Europium

The specific ion interaction theory (SIT) was applied to the first hydrolysis constants of Eu(III) and solubility product of Eu(OH)₃ in aqueous 2, 3 and 4 mol⋅dm⁻³ NaClO₄ at 303.0 K, under CO₂-free conditions. Diagrams of pEu_aq versus pC_H were constructed from solubilities obtained by a radiometric method, the solubility product log₁₀ K_{sp, Eu(OH)3}^I {Eu(OH)_3(s) Eu_aq³⁺+ 3OH_aq⁻ } values were calculated from these diagrams and the results obtained are log₁₀ K_sp,Eu(OH)3^I = − 22.65 ± 0.29, −23.32 ± 0.33 and −23.70 ± 0.35 for ionic strengths of 2, 3 and 4 mol⋅dm⁻³ NaClO₄, respectively. First hydrolysis constants {Eu_aq³⁺+H₂O Eu(OH)_(aq)²⁺+H⁺ } were also determined in these media by pH titration and the values found are log₁₀β_Eu,H^I = − 8.19 ± 0.15, −7.90 ± 0.7 and −7.61 ± 0.01 for ionic strengths of 2, 3, and 4 mol⋅dm⁻³ NaClO₄, respectively. Total solubilities were estimated taking into account the formation of both Eu³⁺ and Eu(OH)²⁺ (7.7 < pC_H < 9) and the values found are: 1.4 × 10⁻⁶ mol⋅dm⁻³, 1.2 × 10⁻⁶ mol⋅dm⁻³ and 1.3 × 10⁻⁶ mol⋅dm⁻³, for ionic strengths of 2, 3 and 4 mol⋅dm⁻³ NaClO₄, respectively. The limiting values at zero ionic strength were extrapolated by means of the SIT from the experimental results of the present research together with some other published values. The results obtained are log₁₀ K_{sp, Eu(OH)3}^o = − 23.94 ± 0.51 (1.96 SD) and log₁₀β_Eu,H⁰ = − 7.49 ± 0.15 (1.96 SD).     

Potentiometrische Untersuchung der Komplexbildung von β-Resorcylsäure mit Be+2-Ionen

Stability constants of Be complexes of -resorcylic acid (H₃ A) have been determined potentiometrically at 30°C, maintaining ionic strength at 0.1M with KNO₃. The logK ₁ and logK ₂ values for 1:1 and 1:2 complexes are found to be 18.15 and 14.95 resp.

---

---

Mit 3 Abbildungen     

Spectrophotometric determination of lanthanides using 4-(2-Pyridylazo) resorcinol

Summary The formation of red colour produced by the interaction of 4-(2-pyridylazo) resorcinol (PAR) and rare earths has been studied to determine the composition, stability and other characteristics of the chelates formed. The _max of all the chelates was found to be 515 nm atph 6.2 whereas the _max of the PAR reagent at this p_H is 410 nm. The composition of the chelates was found to be 12 (metalPAR) and has been established by two different methods. The stability constant values have been calculated by three different methods. The values of logK, lies in the range of 9.2–10.4 for different rare earth chelates. The chelates are stable over a wide range of p_H. A tentative suggestion has also been made for the position of the chelate ring.

---

Zusammenfassung Die rote Farbreaktion von 4-(2-Pyridylazo)-resorcin (PAR) mit Seltenen Erden wurde untersucht, um die Zusammensetzung, die Stabilität und andere Merkmale der dabei entstehenden Chelate zu bestimmen. Beiph 6,2 wurde das Absorptionsmaximum aller Chelate bei 515 nm, das Absorptionsmaximum von PAR bei 410 nm gefunden. Die Zusammensetzung entspricht dem Verhältnis Metall: PAR=12; sie wurde nach zwei verschiedenen Methoden ermittelt. Die Komplexkonstante wurde auf drei verschiedenen Wegen bestimmt. logK liegt bei den verschiedenen Seltenen Erdmetall-Chelaten zwischen 9,2 und 10,4. Die Chelate sind in einem weitenph-Bereich beständig. Die Lage des Chelatrings wurde erörtert.

     

Coordination Properties of Sterically Stressed Zincporphyrins

Spectrophotometric titration and computer simulation were used to study how the nature of porphyrin and extra ligand affect the formation of extra complexes of zincporphyrins in o-xylene. The compounds under study were zincporphyrins (ZnP) with different substituents and phenyl radicals in meso-positions (zinc-5,15-(p-butyloxyphenyl)-2,8,12,18-tetramethyl-3,7,13,17-tetraethylporphyrin (ZnP¹), zinc-5,15-(p-butyloxyphenyl)-2,8,12,18-tetramethyl-3,7,13,17-tetrabutylporphyrin (ZnP²), zinctetraphenylporphine (ZnP³), and zinc complexes with overlapped porphyrin (ZnP⁴). N-Methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole, and dimethylformamide were used as extra ligands (L). The strength of Zn–L bonding was found to decrease in extra complexes (L)ZnP in the series of ZnP as follows: ZnP⁴> ZnP¹> ZnP²> ZnP³. It was established that the stability constant (logK _st) for sterically nonstressed complexes (L)ZnP⁴linearly increases with growth in the extra ligand basicity (log ) and is proportional to the shift of the main absorption bands () in the electronic spectra of extra complexes of zinctetraphenylporphine. For spatially distorted (L)ZnP¹, (L)ZnP², and (L)ZnP³, the values of logK _stand log , as well as logK _stand , change symbatically. The geometric structure and energy characteristics of pentacoordinated zincporphyrins were calculated by quantum-chemical methods. Correlations were established between the calculated values of the energy of the interaction of the central metal atom with the extra ligand molecule and the stability of the extra complexes of zincporphyrins.     

The Molecular Structure and NMR Properties of P-Phosphinoylmethyl Aminophosphonium Salts

The molecular structures of two aminophosphonium salts (bromide and tetrafluoroborate) have been determined by X-ray analysis. They have similar conformations and hydrogen bond (HB) networks: the N–H acid proton is bonded to the anion and, in the case of the fluoroborate, to the oxygen atom of the phosphine oxide, forming a pseudo six-membered ring closed by a weak N–HO intramolecular hydrogen bond (IMHB). These compounds have been studied by multinuclear NMR in solution, including the ¹⁵N-labeled derivatives, to determine a complete set of coupling constants. A coupling of 1.5 Hz between the ¹⁵N and the ³¹P nuclei, separated by three bonds, was observed experimentally for the bromide in CDCl₃ solution, which appears to be a classical ³ J _N-P across the covalent bonds and not a ^3h J _N-P across the IMHB.     

Stability of bivalent metal complex with L-hydroxyproline

Potentiometric titration of L-hydroxyproline with NaOH solution at 30° ±0.1°C in a medium of constant ionic strenth, =0.1M (KNO₃) gave the stepwise formation constants of the complexes formed between Mn(II), Co(II) and Zn(II) ions. The values were logK ₁=3.45; logK ₁=4.58, logK ₂=4.03; logK ₁=5.08, logK ₂=4.66; for Mn(II), Co(II) and Zn(II) complexes. The order of stability constant is in accordance with theIrving-Williams series.

---

Die Stabilität bivalenter metall-komplexe mit L-hydroxyprolin

Zusammenfassung Potentiometrische Titration von L-Hydroxyprolin in NaOH-Lösung bei 30±0,1°C und einer konstanten Ionenstärke von =0,1M-KNO₃ ergab stufenweise die Bildungskonstanten der entsprechenden Komplexe mit Mn(II), Co(II) und Zn(II). Die Werte sind logK ₁=3,45; logK ₁=4,58, logK ₂=4,03; logK ₁=5,08, logK ₂=4,66; für Mn(II); Co(II); Zn(II). Die Reihenfolge der Stabilität der Komplexe ist im Einklang mit derIrving-Williams-Reihung.

     

Freezing points and enthalpies of dilution of aqueous formic,acetic, propionic,and butyric acids. Free energies and enthalpies of solute—Solute interactions

Freezing-point depressions and enthalpies of dilution for aqueous solutions of the straight chain, aliphatic carboxylic acids, C₁ through C₄, have been measured. These data, together with the corresponding apparent molal heat capacities, have been used to calculate the pairwise free energy and enthalpy of interaction of undissociated acid molecules at 298.15⁰K. As expected, the effect of dimer and triplet interaction increases with chain length, reflecting the hydrophobic nature of the hydrocarbon portion of the molecules. The group-interaction additivity principle of Savage and Wood applied to these results gives an excellent correlation and yields values of the group interaction parameters,G _i,j andH _i,j for the CH₂ and COOH groups. These parameters confirm previous results for the interaction of polar and hydrophobic groups in water. The primary data have been fitted to the activity expansion equations of Wood, Lilley, and Thompson to yield values of dimer and trimer sociation constants and their temperature derivatives. This procedure allows for the simultaneous treatment of the dissociation effects of these acids as weak electrolytes together with their tendency to form associated clusters.     

Determination of enthalpies of formation of organic free radicals based on bond dissociation energies. 4. Alkyl-substituted derivatives of phenyl and benzyl

The enthalpies of formation (H _f°) of 16 alkyl-substituted phenyl and benzyl radicals (R^·) were determined for the first time by the published values of energies of R—X bond dissociation. For the initial molecules of RX, alkyl-substituted benzenes, the additive-group procedure was developed for the calculation of H _f°. In the framework of the additive-group model for considered R^·, we studied the structure-property interrelation, analyzed the obtained H _f°(R^·) values, and confirmed their reliability. The influence of nonvalent interactions on H _f°(R^·) was systematized and detailed. The parameters, from which it is possible to calculate H _f° of the 51 radicals, were proposed.     

Transition metal complexes of N,N-dimethylthreonine: Stability and UV/Vis spectra

Summary Acidity (dehydronation) constants of N,N-dimethylthreonine (DMT) and stability constants of its complexes with Cu⁺², Ni⁺², and Co⁺² were determined in aqueous solution by means of potentiometric titration. UV/Vis spectra were also taken during the titration. It is suggested thatDMT acts as a bidentate ligand toward copper(II) by engaging either (a) amino and carboxyl groups (in [Cu(DMT)] and [Cu(DMT)₂]), or, (b) upon dehydronation, amino and hydroxyl groups (in [Cu(DMT)H_–1], [Cu(DMT)₂H_–1], and [Cu(DMT)₂H_–2]). It is suggested that the coordination in threoninato andallo-threoninato complexes is similar to that described under (a).Based upon Master of Science thesis submitted to the University of Zagreb, Croatia byB. Blagovi     

Reaktion von Phlorein mit Kupfer(II)-ionen und deren elektrophile Substitution mit Konkurrenzkationen

Zusammenfassung Die vorliegende Arbeit behandelt die Reaktion von Phlorein mit Kupfer(II). In äquimolaren Lösungen kommt es im p_H-Bereich 4,5 bis 8,2 zur Bildung eines Komplexes im Verhältnis der Komponenten 11. Die scheinbare Stabilitätskonstante entspricht beipH4,18 dem Wert logK _1,1= =5,1±0,1 und bei p_H 5,88 dem Wert log K_1,1=5,4±0,1. Bei einem mehr als zehnfachen Überschuß von Cu²⁺-Ionen ist es besonders in alkalischem Medium möglich, eine Komplexbildung mit erhöhter Anzahl koordinierter Metallionen anzunehmen.Mit Hilfe elektrophiler Substitution des Kupfers durch andere Kationen wurde Phlorein als analytisches Reagens für eine Reihe zwei- und einwertiger Kationen charakterisiert.

---

Reaction of phlorein with copper(II) Ions and their electrophilic substitution with competing cations

Summary The present study deals with the reaction of phlorein with copper(II). In equimolar solutions and in the p_H range 4.5 to 8.2, there results a complex in which the components are in the ratio 11. The apparent stability constant at p_H 4.18 corresponds to the value log K_1,1=5.1±0.1 and at p_H 5.88 the value is log K_1,1=5.4±0.1. In the presence of a more than 10-fold excess of Cu²⁺ ions it is possible, especially in alkaline medium, to assume a complex formation with an increased number of coordinated metal ions.With the aid of electrophilic substitution of the copper by other cations, phlorein was characterized as an analytical reagent for a number of di- and monovalent cations.

---

Symbolverzeichnis M Verdrängungskation - X Bezeichnung von Phlorein - [ ] Gleichgewichtskonzentrationen - analytische Gesamtkonzentrationen - g Anzahl koordinierter Metallionen - n Bjerrumsche komplexbildende Funktion - k _g stufenweise Stabilitätskonstante einesg-Komplexes - K _g totale Stabilitätskonstante einesg-Komplexes - K Gleichgewichtskonstante der Verdrängungsreaktion - Kd Dissoziationskonstante eines Cu²⁺-Komplexes - Proportionalitätskonstante der Ilkovi-Gleichung - Id polarographischer Grenzstromwert - E Potentialwert eines polarographischen Grenzstromes - R Variationsspannweite - (%) Variationskoeffizient in Prozent - (%) Relativfehler in Prozent - A C _X/C _Cu - B C _Cu/C _X