Effect of washing on the kinetic stability of the copper(II)/APCD/IBMK system in strongly acidic media

The extraction behaviour of copper(II) with ammonium 1-pyrrolidinecarbodithioate in isobutyl methyl ketone has been investigated at various acidities of the aqueous phase. The chelate is produced even under strongly acidic conditions (0.01-6M), and if the organic phase is washed with water it remains stable for at least 1 hr. The extraction is quantitative over the entire range of acidity.     

Comparative study of IBMK and DIBK as extraction solvents in strongly acidic media: extraction behaviour and kinetic stability of Cu(PCD)(2) in these solvents

The use of di-isobutyl ketone (DIBK) and isobutyl methyl ketone (IBMK) as the solvent for extraction of copper(II) from strongly acidic media (0.01-8M hydrochloric acid) with ammonium l-pyrrolidinecarbodithioate has been studied. In contrast to IBMK, the volume of the DIBK extract remains the same, irrespective of the acidity of the aqueous phase. A certain amount of free acid is transferred into both solvents, and affects the kinetic stability of the chelate extracted; the free acid can be completely removed by washing the extract with water, and partly by filtering it through a dry filter paper. However, the chelate extracted into DIBK exhibits excellent stability without such treatment, since the amount of free acid in DIBK is much smaller than that in IBMK. When DIBK is used, the copper chelate can be quantitatively extracted as long as the extraction is done from acidic media.     

Application of APCD/DIBK extraction system in strongly acidic media: Determination of traces of copper and nickel in titanium metals by extraction-flame atomic-absorption spectrometry

Extraction of nickel in strongly acidic solution (0.01 approximately 8M hydrochloric acid) with ammonium 1-pyrrolidinecarbodithioate (APCD) into di-isobutyl ketone (DIBK) has been studied, and the APCD/DIBK system has been applied to simultaneous extraction and flame atomic-absorption spectrometric determination of trace amounts of copper and nickel in titanium metal. Nickel could be extracted with copper from strongly acidic solution such as up to 5M hydrochloric acid with APCD/DIBK system. The extraction from such a strongly acidic media made it possible to extract nickel with copper, since it did not require the addition of a large amount of the masking agent which prevents the hydrolysis of the matrix titanium and also prevents the extraction of nickel. Thus, they could be extracted directly from the titanium metal sample digested by concentrated hydrochloric acid with a small amount of tetrafluorohydroboric acid. Effect of coexistence of a large amount (at least 0.2 g) of iron on the extraction of both elements could be prevented by keeping most of the matrix titanium as Ti(III). With the method described here, mug/g levels of copper and nickel in titanium metal could be rapidly determined with good precision and accuracy.     

Extraction of copper(II) with the APCD/DIBK system from concentrated hydrochloric and nitric acid media: estimation of true limit of acidity for the extraction

The extraction of copper(II) from strongly acidic solution (0.01-8M hydrochloric and 0.01-5M nitric acid) with ammonium 1-pyrrolidinecarbodithioate in di-isobutyl ketone has been studied. Compared with the hydrochloric acid system, a considerably larger amount of the reagent is needed for complete extraction of copper chelate from nitric acid solution as the extract is more unstable in the nitric acid system. The decomposition of copper chelates extracted from nitric acid is based on the oxidation of the reagent and the chelate; the spectral change of the extract from nitric acid suggests that the copper(II) chelate is initially oxidized to copper(II) and then decomposes. The upper limit of the acidity of both acids from which the copper chelate can be quantitatively extracted strongly depends on the reagent concentration; the limit with 8 x 10(-2)M APCD (500-fold reagent: metal molar ratio) was taken as 8 and 4M for hydrochloric and nitric acid, respectively.     

The stability of polyaniline in strongly alkaline or acidic aqueous media

Polyaniline (PANI) base has been suspended in 9 M potassium hydroxide at 20 °C or 90 °C for various time intervals extending to 4 months. The fraction of acetone-soluble material increased from 1.2 wt.% to 4.5 wt.% after exposure to an alkaline medium for 60 days at 20 °C. Gel-permeation chromatography indicates that the aggregation of PANI is reduced, while the chain degradation itself is negligible. FTIR spectroscopy confirms this trend and the absence of hydrolytic changes in the PANI structure. Polyaniline retains the ability to be reprotonated with a 1 M sulfuric acid to a conducting form. No marked changes in the molecular structure have been found, even after suspension of PANI in 9 M KOH at 90 °C for 60 days.Similar immersion of PANI salt in 5 M sulfuric acid at 20 °C was responsible for changes in the protonation, and the mass increased by 11 wt.%. This was explained by the exchange of the original sulfate or chloride counter-ions for hydrogen sulfate anions or by the protonation of secondary amine sites in PANI in addition to imine ones. The changes in the molecular structure are discussed on the basis of FTIR spectra. The conductivity decreased from 1.2 S cm⁻¹ to ∼10⁻³ S cm⁻¹ but no time-dependence of conductivity was observed. There was no fraction of PANI soluble in acetone. PANI in the protonated state is thus stable also in the strongly acidic medium.The study is supplemented by the assessment of the thermal stability of PANI base, which is of importance for the processing of PANI. Loss of moisture has been observed after exposure to 250 °C for 10 h in both nitrogen atmosphere and in air. Good stability was found at 350 °C only in the nitrogen atmosphere, while a marked mass loss in weight was registered in air.     

Apparent formation constants of dithiooxamide and substituted dithiooxamide complexes of cobalt(II,III), nickel(II) and copper(II) in strongly acidic media

The apparent stability constants of the complex species formed between cobalt(II, III), nickel(II) or copper(II) and dithiooxamide or some N,N′- and tetra-substituted dithiooxamides have been determined in strongly acidic media at 25 ° C. The configuration of the complexes in solution is discussed on the basis of the electronic spectra.     

Spectrophotometric investigation of the nature and stability of silver(II) in acidic sulphate media

A spectrophotometric study of silver(II) in sulphuric acid solution indicates the formation of two sulphate complexes, in the range 4–18M H₂SO₄, with absorbance peak maxima at 361 and 260 mμ, respectively. In 15M H₂SO₄ the molar absorptivity of silver(II) is 3.11 × 10⁴ at 361 mμ. Kinetic studies of the reduction of silver(II) by the solvent suggest a rate-determining step first order in silver(II) and yield a pseudo first-order rate constant of 1.9 × 10⁻¹min⁻¹. Further studies as a function of H₂SO₄ concentration show that the specific decomposition rate of the two complexes is identical and that changes in H₂SO₄ concentration only serve to shift the concentration equilibrium between the two complexes.     

A kinetic study of the Cu(II)/Cu(I) system in Cl− media at the glassy carbon electrode

Summary Values are reported for the rate constant of the Cu(II)+e Cu(I) reaction at a glassy carbon electrode when the rotating disk technique is used. This redox system has been studied in slightly acidified 0.5M potassium chloride. The oxidation of Cu(I) in 0.5M KCl+0.1M HCl was also examined. The kinetic parameters point to a quasi-reversible process. From the limiting currents diffusion coefficients of the species in solution were evaluated.

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Kinetische Untersuchung des Systems Cu(II)/Cu(I) in Cl^–-Medium

Zusammenfassung Die rotierende Scheibenelektrode wurde angewendet für die Untersuchung der Kinetik des Vorgangs Cu(II)+e Cu(I) in 0.5M Kaliumchlorid (pH4). Auch die Oxydation von Kupfer(I) in 0,5M KCl+0,1M HCl wurde untersucht. Dabei wurde festgestellt, daß die heterogenen Durchtrittsreaktionen quasi-reversibel verlaufen. Aus den Grenzströmen wurden die Diffusionskoeffizienten der Kupferionen bestimmt.

     

The role of copper(II) ion in regulating H-bonding and coulombic interactions in copper(II)/tripod/polyphosphate systems

The tripodal ligands L, 1,3,5-tri(5-R-2,5-diazapentyl)benzene (R = Me, L1; Et, L2, n-Pr, L3; n-Bu, L4), when protonated, bind strongly and selectively with polyphosphates (Ph) such as orthophosphate (PO), pyrophosphate (PP) and tri-phosphate (tP) respectively in aqueous solution. The results are consistent with the hypothesis that the formation of hydrogen bonds as well as the coulombic interactions plays an important role in the supramolecular interactions between Ph and polyammonium receptors. Moreover, the stability constants of the ternary systems containing the Cu^II, tripod and polyphosphate were determined by the pH-metric method. Recognition of the polyphosphate anions by the protonated tripods was promoted by the introduction of Cu^II. Thus the bound metal ion can act as a messenger to regulate the H-bonding and electrostatic interactions of the counter-part of the molecular complexes. Fundamental knowledge gained from such studies may then provide valuable insights into the relationship between the structure and reactivity and how the enzymes themselves function.     

Effect of water-acetone solvent on the stability of copper(II) and nickel(II) nicotinamide complexes

Complexation of nicotinamide with Cu²⁺ and Ni²⁺ ions in a water-acetone solvent is studied. The equilibrium constants of these reactions are determined by potentiometric titration at the ionic strength 0.25 mol/l NaClO₄ and 298 K in the interval of mixed solvent compositions from 0 to 0.45 molar fraction of acetone. The Cu(II) complex with nicotinamide becomes stronger in a water-acetone mixture. The dependence of the stability constant of the Ni(II) complex with nicotinamide on the concentration of the organic component in the solution has extremum with a minimum at 0.1–0.2 molar fraction of acetone. The effect of a change in the solvate state of the reactants on the stability of the complexes is discussed.     

Effect of phenyl substituent on the dimerization of copper(II)-carboxylate in solvent extraction of copper(II) with phenylacetic acid

The effects of the phenyl substituent on the dimerization of copper(II) carboxylate in the solvent extraction of copper(II) with phenylacetic acid using benzene and 1-octanol as a solvent were investigated, at 25 degrees and at the aqueous ionic strength of 0.1M (NaClO(4)). The dimerization of copper(II) phenylacetate has been found to be written as: 2CuA(2)Cu(2)A(4) in 1-octanol, and 2CuA(2)(HA)(2)Cu(2)A(4)(HA)(2) + (HA)(2) in benzene, with the dimerization constants, log K = 2.24 and log K = 4.19, respectively. It was proved that the phenyl group inhibits the formation of the dimeric copper(II) phenylacetate, and its effect is partially shielded by a methylene substituent.     

Study of the surface mass changes during the redox transformations of copper(II) phthalocyanine-tetrasulfonic acid on gold in acidic media

Journal of Solid State Electrochemistry - An electrochemical quartz crystal nanobalance (EQCN) has been used to study the deposition (adsorption) and dissolution (desorption) during the redox...     

Unusual multi-step sequential Au(III)/Au(II) processes of gold(III) quinoxalinoporphyrins in acidic non-aqueous media

The electrochemistry of gold(III) mono- and bis-quinoxalinoporphyrins was examined in CH(2)Cl(2) or PhCN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) before and after the addition of trifluoroacetic acid to solution. The investigated porphyrins are represented as Au(PQ)PF(6) and Au(QPQ)PF(6), where P is the dianion of the 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin and Q is a quinoxaline group fused to a β,β'-pyrrolic position of the porphyrin macrocycle; in Au(QPQ)PF(6) there is a linear arrangement where the quinoxalines are fused to pyrrolic positions that are opposite each other. The porphyrin without the fused quinoxaline groups, Au(P)PF(6), was also investigated under the same solution conditions. In the absence of acid, all three gold(III) porphyrins undergo a single reversible Au(III)/Au(II) process leading to the formation of a Au(II) porphyrin which can be further reduced at more negative potentials to give stepwise the Au(II) porphyrin π-anion radical and dianion, respectively. However, in the presence of acid, the initial Au(III)/Au(II) processes of Au(PQ)PF(6) and Au(QPQ)PF(6) are followed by an internal electron transfer and protonation to regenerate new Au(III) porphyrins assigned as Au(III)(PQH)(+) and Au(III)(QPQH)(+). Both protonated gold(III) quinoxalinoporphyrins then undergo a second Au(III)/Au(II) process at more negative potentials. The electrogenerated monoprotonated monoquinoxalinoporphyrin, Au(II)(PQH), is then further reduced to its π-anion radical and dianion forms, but this is not the case for the monoprotonated bis-quinoxalinoporphyrin, Au(II)(QPQH), which accepts a second proton and is rapidly converted to Au(III)(HQPQH)(+) before undergoing a third Au(III)/Au(II) process to produce Au(II)(HQPQH) as a final product. Thus, Au(P)PF(6) undergoes one metal-centered reduction while Au(PQ)PF(6) and Au(QPQ)PF(6) exhibit two and three Au(III)/Au(II) processes, respectively. These unusual multistep sequential Au(III)/Au(II) processes were monitored by thin-layer spectroelectrochemistry and a reduction/oxidation mechanism for Au(PQ)PF(6) and Au(QPQ)PF(6) in acidic media is proposed.     

Alkylation of 4(5)-nitro-1,2,3-triazole with alcohols in strongly acidic media

Alkylation of 4(5)-nitro-1,2,3-triazole with alcohols in concentrated H₂SO₄ occurs at all three endocyclic N atoms, giving a mixture of isomeric N(1)-, N(2)-, and N(3)-alkyl-4-nitro-1,2,3-triazoles (alkyl is isopropyl, sec-butyl, and cyclohexyl). The selectivity of the alkylation depends on the alcohol used. The most selective alkylation is provided at the N(2) atom when isopropyl (81%) and sec-butyl alcohols are used (67%). With an increase in the reaction time, also in the order isopropyl-, sec-butyl-, and cyclohexyl-4-nitro-1,2,3-triazoles, the N(2)-isomers undergo isomerization into N(1)-alkyl-4-nitro-1,2,3-triazoles. In all the cases, the fraction of the N(3)-substitution products in the mixtures is 6–30%.     

Effect of a water-ethanol solvent on the stability of copper(II) complexes with L-tyrosine

Stability constants of copper(II) mono- and bis-complexes with L-tyrosine were determined by the potentiometric titration method. Gibbs energies of the transfer (Δ_tr G ⁰) of a ligand and a complex ion from water into water-ethanol solvents were calculated. Stability of the complexes [CuHTyr]⁺ and [Cu(HTyr)₂] increases as the ethanol concentration in solutions increases. Increasing stability of the complexes is promoted by weakening solvation of ligand donor groups entering into coordination.     

Thermal stability and kinetic studies of new dinuclear copper(II) complexes with octaazamacrocyclic and multidonor bidentate ligands

The thermal properties of four copper(II) complexes with N,N′,N″,N-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) and several bidentate ligands N,S (thiosemicarbazide and thiourea) or N,O donors (semicarbazide and urea), of the general formula [Cu₂(X)tpmc](ClO₄)₄, have been investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC). The thermal stability order can be recognized for the examined complexes, depending on coordinated bidentate bridging N,S or N,O ligand. Kinetic data demonstrated first-order thermal decomposition. A plausible mechanism has been proposed which explains the major products of the degradation.     

Voltammetric measurement of copper(II)/organic interactions in estuarine waters

The voltammetry of copper in organic ligand/chloride media is dominated by the formation of CuCl^?₂ species and by induced adsorption of Cu(I) in organic coatings on the electrodes. These phenomena are utilised in a novel method for evaluating Cu(II)/organic ligand interactions, based on the principle of ligand exchange. The Cu(II)/organic species competes with glycine which forms copper glycinate. These two complexes can be distinguished voltammetrically: copper glycinate gives a higher surface excess of copper at a gelatin-coated hanging mercury drop electrode, partly because of the increased production of CuCl^?₂ from copper glycinate at the electrode surface. The method proved satisfactory for pure ligand/surfactant/chloride media and for estuarine waters. It is shown that there are two type of Cu(II)-binding ligand in estuarine waters: humic material (> 10^?6 mol l^?1, assuming 1:1 site binding) with polyelectrolyte-type binding, and discrete ligands (? 10^?6 M) with stability constants around 10⁹. The extent of Cu(II) binding by the humic material decreases down the estuary because of dilution and increased salinity.