Titration of cyanide and hexacyanoferrate(II) with silver nitrate-I Calculation of titration curves for potentiometric and conductometric titration

Stepwise potentiometric titration of cyanide and hexacyanoferrate(II) with silver nitrate is possible in the absence of potassium ions. At an initial concentration below 5.00 x 10(-4)M, cyanide can be titrated with silver nitrate (Ag:CN = 1:2) and the end-point indicated by precipitation of silver hexacyanoferrate(II); hexacyanoferrate(II) can be titrated with silver nitrate (Ag: Fe(CN)(6) = 4:1) and the end-point indicated by precipitation of silver dicyanoargentate. The hexacyanoferrate(II) reacts with silver to form two poorly soluble salts, Ag(4)Fe(CN)(6), KAg(3)Fe(CN)(6). The formation of these salts has been confirmed by conductometric titration of hexacyanoferrate(II) with silver nitrate in solutions containing varying concentrations of potassium nitrate.     

Cobalt(II)-8-mercaptoquinolines complexing in cobalt(II) hexacyanoferrate(II) gelatin-immobilized matrix materials

Complexing processes between Co^II and 8-mercaptoquinoline, or its various alkyl- and aryl-substituted derivatives, in contact with Co₂[Fe(CN)₆]-gelatin-immobilized matrix materials, with aqueous solutions of corresponding ligands, have been studied. When R² = Me or Ph, formation of Co^II chelates having a 1:2 metal ion/singly deprotonated ligand is observed, whereas when R² = H, formation of Co^III chelates having metal ion/singly deprotonated ligand 1:3 ratios occur.     

The silver(I)‐catalyzed exchange of coordinated cyanide in hexacyanoferrate(II) by phenylhydrazine in aqueous medium

The [Ag]⁺‐catalyzed exchange of coordinated cyanide in [Fe(CN)₆]^4? by phenylhydrazine (PhNHNH₂) has been studied spectrophotometrically at 488 nm by monitoring increase in the absorbance for the formation of cherry red colored complex [Fe(CN)₅PhNHNH₂]^3?. The other reaction conditions were pH 2.80±,0.02, temperature = 30.0 ± 0.1^°C, and ionic strength (I) = 0.02 M (KNO₃). The reaction was followed as a function of pH, ionic strength, temperature, [Fe(CN)^4?₆], [PhNHNH₂], [Ag⁺] by varying one variable at a time. The initial rates were evaluated for each variation using the plane mirror method. The initial rates evaluated as a function of [Fe(CN)^4?₆] clearly indicate that the initial rate increases with the increase in [Fe(CN)^4?₆] and finally reaches to a limiting value when [Fe(CN)^4?₆]/[AgNO₃] ? 1000. It indicates the formation of a strong adduct between [Fe(CN)₆]^4? and AgNO₃ prior to the abstraction of CN^?. The variation in initial rates with [PhNHNH₂] also showed limiting values at [Fe(CN)^4?₆]/[PhNHNH₂] ? 8.30. The complex behavior due to pH and [Ag⁺] variations on the rate has been explained in detail. The composition of the final reaction product [Fe(CN)₅PhNHNH₂] formed during the course of reaction has been found to be 1:1 using the mole ratio method. The evaluated values of activation parameters for the catalyzed reaction are E_a = 53.85 kJ mol^?1, Δ H^≠, = 51.33 kJ mol^?1, and Δ S^≠ = ?134.63 J K^?1 mol^?1, which suggest an interchange dissociative mechanism. A most plausible mechanistic scheme has been proposed based on the experimental observations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 447–456, 2007     

Kinetics and mechanism of mercury(II)-catalysed replacement of cyanide in hexacyanoferrate(II) by p-nitrosodiphenylamine

The mercury(II)-catalysed replacement of cyanide in hexacyanoferrate(II) by p-nitrosodiphenylamine (p-NDA) in aqueous solution has been investigated spectrophotometrically by measuring the change in absorbance of the green complex ion, [Fe(CN)(5).p-NDA](3-), at 640 nm. Activation parameters of the catalysed and uncatalysed reactions have been calculated. The effects of the dielectric constant and water content of the medium on reaction rates are used to explain the formation of a polar activated complex and suggest an I(d) mechanism for the catalysed reaction. The varying catalytic activity of Hg(II) as a function of concentration has been discussed.     

Determination of hexacyanoferrate(II) with electrolytically generated octacyanomolybdate(V)

The determination of hexacyanoferrate(II) with electrolytically generated octacyanomolybdate(V) at a platinum anode over a wide pH range is described. From 1 to 20 muequiv are determined with a relative standard deviation of 0.3%.     

Cobalt(III)-8-mercaptoquinoline complexing in cobalt(III)hexacyanoferrate(II) gelatin-immobilized matrix systems

Novel complexing processes in binary systems containing Co^III and 8-mercaptoquinoline or its derivatives (5-Cl-, 5-Br-, 5-Me-, 5-Ph- and 5-SMe- 8-mercaptoquinoline), with a cobalt(III)hexacyanoferrate(II) gelatin-immobilized matrix in contact with an aqueous solution of the corresponding ligand, have been observed. Under the specific conditions described, three water-insoluble coordination compounds are formed in each of the systems indicated, whereas upon complexing in solution or the solid phase the formation of only one complex is observed.     

Determination of radiocesium in environmental water samples using copper ferro(II)cyanide and sodium tetraphenylborate

Summary A procedure for the radiochemical separation and radiochemical purification of radiocesium (¹³⁴Cs and ¹³⁷Cs) in bulk environmental water samples is proposed. Radiocesium was removed from the water by cation-exchange with copper ferro(II)cyanide and was purified by precipitation with sodium tetraphenylborate. The influence of the concentration of potassium in the water sample on the chemical yield was investigated. The validation of the proposed method was carried out by analyzing reference materials. The application of the method was demonstrated with the determination of the concentration of radiocesium in water samples from rivers around NPP “Kozloduy”, Bulgaria, Danube and Ogosta.     

Kinetics and mechanism of exchange of cyanide in hexacyanoferrate(II) by N-methylpyrazinium ion in the presence of mercury(II) as a catalyst

The kinetics of the mercury(II) catalysed ligand exchange of the hexacyanoferrate(II) complex with the N-methylpyrazinium ion (Mpz⁺) in a potassium hydrogen phthalate buffer medium has been investigated at 25.0 ± 0.1 °C, pH = 5.0 ± 0.02 and ionic strength, I = 0.1 M (KNO₃). The reaction was followed spectrophotometrically in the aqueous medium by measuring the increase in absorbance of the intense blue complex [Fe(CN)₅Mpz]^2– at its _max 655 nm. The effect of pH, and the concentrations of [Fe(CN)₆ ^4–] and Mpz⁺ on the reaction rate have been studied and analysed. The varying catalytic activity of mercury(II) as a function of concentration has also been explained. The kinetic data suggest that substitution follows an interchange dissociative (I _d) mechanism and occurs via formation of a solvent-bound intermediate. The effects of the dielectric constant of the medium on the reaction rates have been used to visualize the formation of a polar activated complex and an interchange dissociative mechanism for the reaction. A mechanism has been proposed in order to interpret the kinetic data. Kinetic evidence is reported for the displacement of CN^– by Mpz⁺ in [Fe(CN)₆ ^4–]. Activation parameters for the catalysed and uncatalysed reaction have been evaluated, and lend further support to the proposed mechanism.     

Determination of Pb(II), Cu(II) and Fe(III) with capillary electrophoresis using ethylenediaminetetraacetic acid as a complexing agent and vancomycin as a complex selector.

The simultaneous determination of metal ions using ethylenediaminetetraacetic acid (EDTA) as a complexing agent and vancomycin as a complex selector was successfully studied by capillary electrophoresis with the U-shaped cell. The partial filling method (counter current mode) was used in order to gain selectivity of the separation, and also to increase the detection sensitivity. The effect of the vancomycin concentration on the separation behavior of free EDTA and metal products, and the effect of the EDTA concentration on the stability of metal-EDTA products were considered. Under the optimal condition, the reproducibilities (RSD) of the migration time and the peak area were less than 3.39% and 9.61%, respectively. With the high sensitivity of the method, Pb(II), Cu(II) and Fe(III) in tap water were successfully determined, and the recoveries were 99 - 105%. The concentrations of these metal ions found in tap water did not exceed the maximum allowed concentrations regulated by the U.S. Environmental Protection Agency.     

Thermal decomposition of hydrotalcite with hexacyanoferrate(II) and hexacyanoferrate(III) anions in the interlayer

The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. The thermal decomposition of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer has been studied using controlled rate thermal analysis technology. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 10.9 and 11.1 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. Calculations show dehydration with a total loss of 7 moles of water proving the formula of hexacyanoferrate(II) intercalated hydrotalcite is Mg₆Al₂(OH)₁₆[Fe(CN)₆]_0.5·7H₂O and 9.0 moles for the hexacyanoferrate(III) intercalated hydrotalcite with the formula of Mg₆Al₂(OH)₁₆[Fe(CN)₆]_0.66·9H₂O. CRTA technology indicates the partial collapse of the dehydrated mineral. Dehydroxylation combined with CN unit loss occurs in two isothermal stages at 377 and 390°C for the hexacyanoferrate(III) and in a single isothermal process at 374°C for the hexacyanoferrate(III) hydrotalcite.     

Sodium silver tricobalt bis(diphosphate) and sodium silver copper(II) diphosphate

The crystal structures of two new diphosphates, sodium silver tricobalt bis(diphosphate), (Na_1.42Ag_0.58)Co₃(P₂O₇)₂, and sodium silver copper(II) diphosphate, (Na_1.12Ag_0.88)CuP₂O₇, provide examples of the effect of mixing Na and Ag in the same site of known host phosphate compounds. The small differences in ionic radii of the two monocations do not lead to significant differences in the structural details. In the latter compound, the Cu atom lies on an inversion center.     

Determination of low levels of cyanide with a silver/silver sulphide wire electrode

A silver/silver sulphide electrode is prepred quickly by holding a cleaned silver wire in vapours from molten sulphur. In 1000–10 mg l^?1 cyanide solutions, the electrode exhibits a linear E/log C_CN function which becomes slightly sinusoidal for 10–0.1 mg l^–1 cyanide. The average slope is slightl super-Nerstian (10 mV/decade concentration). The applicability of the electrode is demonstrated for the determinations of microgram quantities of water-soluble cyanide from the Prussian blue pigments which are constituents of externally applied cosmetics. The home-made electrode provides results agreing with those obtained with commercially available electrodes.     

Determination of chloride by displacement of hydrogen cyanide from mercury(II) cyanide

A method, based on the passivity of mercury(II) cyanide in dilute sulphuric acid and its reaction with hydrochloric acid to produce hydrogen cyanide, has been developed for the determination of small amounts of chloride. Hydrogen cyanide, distilled from a mercury(II) cyanide-halide-dilute sulphuric acid system is found by iodometric measurement to be directly proportional to the amount of chloride or bromide and of hydrogen ion in acids such as sulphuric acid. A linear correlation also holds for iodide but the stoichiometry is different, the titration values being about three times larger than expected. By conversion of the cyanide into a dye by means of the pyridine-pyrazolone reagent, 0.014-0.43 mug ml chloride concentrations have been determined. The method is also applicable to bromide and sulphuric acid in small amounts but not to fluoride and iodide. Results are reproducible to within +/-2%.     

Regioselective 1,4-conjugate hydrocyanation of dienones using potassium hexacyanoferrate(II) as an eco-friendly cyanide source

A highly regioselective 1,4-conjugate hydrocyanation of dienones using potassium hexacyanoferrate(II) as an original eco-friendly cyanide source, benzoyl chloride as a promoter and potassium carbonate as a catalyst is described. This protocol has advantages of non-toxic cyanating agent, high regioselectivity, high yield, and simple work-up procedure.     

Thermal decomposition of hydrotalcitewith hexacyanoferrate(II) and hexacyanoferrate(III) anions in the interlayer

The thermal decompositions of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer have been studied using thermogravimetry combined with mass spectrometry. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 11.1 and 10.9 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. XRD was also used to determine the products of the thermal decomposition. For the hydrotalcite decomposition the products were MgO, Fe₂O₃ and a spinel MgAl₂O₄. Dehydration and dehydroxylation take place in three steps each and the loss of cyanide ions in two steps.     

Decomposition of hexacyanoferrate(II) in analysis

Summary On the base of the catalytic effect of Ag⁺ upon the decomposition of [Fe(CN)₆]^4–, a very sensitive spot test for the detection of silver has been developed. The sensitivity of the test for the pure system is 0,00075 g/ drop at the concentration limit 146.400.000. Hg, Au and Pd react analogously. Chlorides and bromides even in high concentrations do not impair the detection of silver. In presence of iodides the sensitivity of the test is slightly reduced.

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Zusammenfassung Es wurde eine sehr empfindliche Tüpfelprobe zum Nachweis von Silber entwickelt. Sie beruht auf der katalytischen Zersetzung des [Fe(CN)₆]^4–-Komplexes durch Silberionen. In reinen Lösungen können noch 0,00075 g Silber in einem Tropfen nachgewiesen werden (Grenzkonzentration: 146400000). Hg, Au und Pd reagieren ähnlich wie Ag. Chlorid und Bromid stören auch in großen Mengen nicht. Jodid setzt die Empfindlichkeit des Nachweises etwas herab.

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Part V.: Acta Pharm. Jug., 10, 37 (1960).     

Titration of mercury (ii) with sodium tetraphenylboron

A direct visual titration of mercury (II) with sodium tetraphenylboron (“Kalignost”) is described Phenylmercurie salts are formed and the end-point is indicated by a turbidity of insoluble diphenylmercury.     

Loss of water and hydrogen cyanide from aquopentamminecobalt(III) hexacyanoferrate(III)

Previous studies on the non-isothermal decomposition of [Co(NH₃)₅H₂O] [Fe(CN)₆] showed that H₂O and three molecules of HCN are lost simultaneously but the results of the isothermal studies reported here show that these processes can be partially separated. It was found that the first reaction involves the loss of H₂O and two molecules of HCN and the second reaction results in the loss of an additional molecule of HCN. Kinetic studies have been performed and kinetic parameters are reported here and possible mechanisms are discussed.     

The reaction of pentaborane(9) with sodium cyanide and sodium cyanotrihydroborate

The reaction of pentaborane(9) with NaCN occurs in a 1:1 molar ratio at temperatures between ? 30° and + 10°C to yield the complex Na[B₅H₉CN], which can be isolated in the form of a dioxanate. When excess pentaborane(9) is used the reaction is relatively clean and yields predominantly the [B₉H₁₄]^? ion. With NaBH ₃CN no intermediates of the type Na[B₅H₉CN] are detected, and the major product is the [B₉H₁₄]^? ion, but no hydrogen is evolved in the reaction. Structures for the intermediate anions are suggested. No monocarbon carbaboranes were detected in any of the reactions.