Indirect Spectrophotometric Determination of Vanadium(IV) by Flow Injection Analysis Based on the Redox Reaction with Copper(II) in the Presence of Neocuproine

Abstract

An indirect photometric method with a continuous-flow analysis is presented for the determination of trace amounts of vanadium(IV). It is based on the redox reaction of copper(II) with vanadium(1V) in the presence of neocuproine. In the presence of neocuproine, copper(I1) is reduced easily by vanadium(I V) to a copper(1)-neocuproine complex, which shows a n absorption maximum at 454 nm. By measuring t h e absorbance of the complex at this wavelength, vanadium(1V) in t h e range 2×10^?6 - 8 × mol dm^?5 mol dm^?3 can be determined at a rate of 120 samples h^?1. The fractional determination of vanadium(1V) and iron(I1) is also studied.     

Synthesis and crystal structure of a copper(II) complex of the tridentate ligand di-(2-benzimidazolylmethyl)imine

A copper complex [Cu(IDB)Cl] · 0.5[CuCl₄]?·?H₂O (1) (IDB?=?di(2-benzimidazolylmethyl)imine) was synthesized and its structure was determined by X-ray single crystal diffraction. In this complex, the central copper(II) ion is four-coordinate, IDB serves as a neutral tridentate chelating ligand for the tetragonal copper ion. The cyclic voltammogram of complex 1 in CH₃CN gave two reversible redox waves (E _1/2,1?=??0.14?V and E _1/2,2?=?0.08?V versus SCE) which correspond to the Cu(II,?II)/Cu(I,?II) and Cu(II,?II)/Cu(II,?I) redox processes, respectively.     

A novel redox system consisting of π-conjugated polymers and transition metals

Coordination of π-conjugated polymers to transition metals constructs a novel redox system due to interchangeable various oxidation states of the polymers, which permits transition metals to interact with each other through a π-conjugate chain. The redox characteristics were found to depend on the electronic interaction with metals and the doping. A combination of copper(II) or iron(III) chloride and polyanilines afforded the complex catalysts with the higher oxidation capability for dehydrogenative oxidation. A catalytic system was also realized in the transition-metal-induced oxidation reaction, in which π-conjugated polymers serve as redox-active ligands participating in the reversible redox cycle. The Wacker oxidation of terminal olefins proceeded catalytically in the presence of a catalytic amount of polyaniline or polypyrrole derivative under oxygen.     

A potentiometric study of the oxidation of cobalt(II) with gold(III) chloride in presence of 1,10 phenanthroline or 2,2'-bipyridine : A new titration of cobalt (II) and its application to nickel-base alloys

The redox reaction between cobalt(II) and gold(III) chloride in the presence of 1.10-phenanthroline or 2,2'-bipyridine was studied, and a titration of the cobalt(II) complex with a gold(III) chloride solution was developed. A 4-fold amount of 1,10-phenanthroline or 2,2'-bipyridine was necessary for rapid quantitative reaction; the permissible pH range was 1.5–5. The oxidation of the cobalt(II) complex proceeds rapidly at 40–50°C, and a direct potentiometric titration was possible. The following maximum errors were obtained: 3.3% for 0.2–1.0 mg Co, 2.0% for 1–5 mg Co, and 0.70% for 10–40 mg Co. The following ions did not interfere: Ni(II), Zn(II), Pb(II), Cd(II), Mn(II), Fe(II), Cr(III), Al(III), Th(IV), Se(IV), Ti(IV), U(VI), Mo(VI), SO^2-₄ and PO^3-₄. Even small quantities of silver(I), copper(II), palladium(II), mercury(II)and iron(III) interfered. The method was applied to the determination of high cobalt contents in high-temperature nickel-base alloys.     

Flow-injection determination of copper(II) based on its catalysis on the redox reaction of cysteine with iron(III) in the presence of 1,10-phenanthroline

A redox reaction of cysteine with iron(III) proceeds slowly in the presence of 1,10-phenanthroline (phen). However, this reaction is accelerated in the presence of copper(II) as a catalyst, producing an iron(II)-phen complex (lambda(max)=510 nm). A sensitive spectrophotometric flow-injection method is proposed for the determination of copper(II) based on its catalytic action on this redox reaction. The dynamic range was 0.1-10 ng ml(-1) of copper(II) with a relative standard deviation of 1.0% (n=10) for 1.0 ng ml(-1) of copper(II) at a sampling rate of 30 h(-1). The detection limit (S/N=3) is 0.04 ng ml(-1). The proposed method was successfully applied to the determination of copper in river water as a certified reference material.     

Formation of silver nanoparticles in the redox reaction of silver(I) nitrate with crystalline macrocyclic nickel(II) compounds

The redox reaction of crystalline macrocyclic nickel(II) carboxylates with silver(I), gold(III), and palladium(II) salts leads to the formation of nanoclusters of the corresponding metals. The reaction with silver nitrate was used to show that the size of the nanoparticles formed depends both on the chemical and crystal structure of the solid matrix and the reaction time. The results open the possibility of forming noble metal nanoparticles with desired dimensions and dispersion.     

Polystyrenes impregnated with ethers-A polymeric reagent selective for gold

A polymeric reagent selective for gold was obtained by impregnating XAD-2 polymeric absorbant with ethylene diglycol dibutyl ether, a gold-selective liquid. The reagent showed a high selectivity for gold over the platinum group metals, nickel(II) and copper(II), but the selectivity relative to iron(III) was pH-dependent.     

Oxidations by copper metalloenzymes and some biomimetic approaches

This paper illustrates the various aspects of the reactivity of the Cu(II)–Cu(I) system in biological systems, with one example of an enzymatic reaction in which Cu(II) alone is oxidizing enough to carry out the reaction (superoxide dismutase), one example in which a Cu(II)-bound peroxo intermediate is the active species (tyrosinase) and the examples of galactose oxidase and copper amine oxidases in which Cu(II) is associated with a redox active organic cofactor. In some cases, we will show some illustrations of biomimetic approaches developed in our laboratories, aimed at a better understanding of reaction mechanisms and at an original design of new catalysts with potential applications in synthetic chemistry. Some comments are given concerning the respective features of copper and iron.     

Cationic Copper(I) Complexes as Highly Efficient Catalysts for Single and Double A3‐Coupling Mannich Reactions of Terminal Alkynes: Mechanistic Insights and Comparative Studies with Analogous Gold(I) Complexes

Cationic Cu?L complexes (L=Buchwald‐type phosphane) with N co‐ligands have been characterised by structural and spectroscopic properties. These copper(I) complexes are extremely active catalysts, far more active than analogous gold(I) complexes, to promote the single and double A³ coupling of terminal alkynes, pyrrolidine and formaldehyde. The activity data show the possible ways in which the solvent can influence the catalytic performance by limiting complex solubility, by solvent decomposition or instability of the copper(I) redox state. Isolation of copper(I) complexes that are likely to be the key catalytic species has allowed light to be shed on the reaction mechanism.     

The use of nanoparticles in electroanalysis: a review

Nanoparticles can display four unique advantages over macroelectrodes when used for electroanalysis: enhancement of mass transport, catalysis, high effective surface area and control over electrode microenvironment. Therefore, much work has been carried out into their formation, characterisation and employment for the detection of many electroactive species. This paper aims to give an overview of the investigations carried out in this field. Particular attention is paid to examples of the advantages and disadvantages nanoparticles show when compared to macroelectrodes and the advantages of one nanoparticle modification over another. Most work has been carried out using gold, silver and platinum metals. However, iron, nickel and copper are also reviewed with some examples of other metals such as iridium, ruthenium, cobalt, chromium and palladium. Some bimetallic nanoparticle modifications are also mentioned because they can cause unique catalysis through the mixing of the properties of both metals.     

Galvanic replacement of semiconductor phase I CuTCNQ microrods with KAuBr4 to fabricate CuTCNQ/Au nanocomposites with photocatalytic properties

In this study, the reaction of semiconductor microrods of phase I copper 7,7,8,8-tetracyanoquinodimethane (CuTCNQ) with KAuBr(4) in acetonitrile is reported. It was found that the reaction is redox in nature and proceeds via a galvanic replacement mechanism in which the surface of CuTCNQ is replaced with metallic gold nanoparticles. Given the slight solubility of CuTCNQ in acetonitrile, two competing reactions, namely CuTCNQ dissolution and the redox reaction with KAuBr(4), were found to operate in parallel. An increase in the surface coverage of CuTCNQ microrods with gold nanoparticles occurred with an increased KAuBr(4) concentration in acetonitrile, which also inhibited CuTCNQ dissolution. The reaction progress with time was monitored using UV-visible, FT-IR, and Raman spectroscopy as well as XRD and EDX analysis, and SEM imaging. The CuTCNQ/Au nanocomposites were investigated for their photocatalytic properties, wherein the destruction of Congo red, an organic dye, by simulated solar light was found dependent on the surface coverage of gold nanoparticles on the CuTCNQ microrods. This method of decorating CuTCNQ may open the possibility of modifying this and other metal-TCNQ charge transfer complexes with a host of other metals which may have significant applications.     

Coordination-synchronized trans-cis photoisomerization of bipyridylazobenzene driven by a Cu(II)/Cu(I) redox change

The trans-cis photoisomerization behavior of azobenzene-bipyridine ligand (dmpAB) was synchronized with coordination of the bipyridine moiety to copper. The coordination reaction can be reversibly controlled with reversible redox reaction of copper, to afford [Cu(dmpAB)(2)](+) in Cu(I) state and free dmpAB in Cu(II) state. UV irradiations to Cu(I) and Cu(II) samples form trans-rich and cis-rich compositions, respectively. The results enable us to control the trans-cis isomerization reversibly through Cu(II)/Cu(I) redox and a single UV light.     

Sequential potentiometric complexometric redox determination of iron(III) and cobalt(II) with application to alloys

A simple potentiometric method is presented for successive determination of iron(III) and cobalt(II) by complexometric titration of the iron(III) with EDTA at pH 2 and 40 degrees , followed by redox titration of the cobalt(II) complex with 1,10-phenanthroline or 2,2'-bipyridyl at pH 4-5 and 40 degrees , with gold(III). There is no interference in either determination from common metal ions other than copper(II), which severely affects the cobalt determination but can be removed by electrolysis. The method has been successfully applied to determination of iron and cobalt in Kovar and Alnico magnet alloys.     

Reducing elution method for copper(II) in cation-exchange chromatography by hydroxylamine hydrocloride solution

The cation-exchange Chromatographic behaviour of copper and several other metals in hydroxylamine hydrochloride solution has been investigated. At 50 degrees copper(II) is reduced to copper(I) which is eluted quickly in a narrow band and easily separated from other metals such as zinc, nickel, cobalt and iron.     

The magic effect of endocyclic but non-sterically hindering biisoquinoline chelates: From fast-moving molecular shuttles to [3]rotaxanes

The use of 8,8′-diaryl-substituted 3,3′-biisoquinolines allows the construction of new multi-component assemblies that are inaccessible with the 2,9-diaryl-substituted 1,10-phenanthroline ligands previously developed by the Sauvage group. This is due to the sterically non-hindering nature of the new chelates, which makes three-component entanglements around octahedral metal centres such as iron(II), cobalt(II) and ruthenium(II) readily possible. Among the newly synthesized molecular assemblies are [3]rotaxanes and [3]pseudorotaxanes in which two molecular strings pass through a single macrocycle, as well as molecular shuttles that exhibit greatly improved shuttling kinetics when compared to previously investigated molecular machines that are based on copper(I)/copper(II) redox chemistry.     

Reverse flow injection analysis of complexing agents and its application to estimation of complexing capacity

A redox reaction of copper(II) with iron(II) proceeds slowly in the presence of neocuproine, although the reaction would not take place in its absence. This reaction is accelerated by the presence of complexing agents such as EDTA, DTPA, CyDTA, EDTA-OH, NTA, citrate, pyrophosphate, producing a copper(I)-neocuproine complex (lambda(max) = 454 nm). A reverse flow injection analysis (r-FIA) method is presented for the determination of trace amounts of complexing agents by measuring the increase in absorbance at 454 nm. Complexing agents at the 10(-6)M level can be determined at a rate of 120 samples/hr. By using this r-FIA system, a new procedure for the measurement of complexing capacity with metal ions such as Al(III), Cu(II), Zn(II), Cd(II) and Pb(II) has been developed. Complexing capacity for each metal ion can be measured at a rate of 120 samples/hr.     

Electron transfer function of kerateine gel and conjugated redox reaction by using the kerateine-immobilized membrane

Kerateine gel, prepared by reducing wool keratin with alkaline 2-mercaptoethanol-urea solution and by partially reoxidizing the dissolved kerateine, reduced iron(III) to iron(II). Reduction of iron(III) was enhanced by addition of copper(II). Reduction of methylene blue (MB) to leuco MB with thioglycollic acid (TGA) as a model compound of wool thiol group was investigated in the presence of copper(II) and intercuticular cementing material (δ_Cu) extracted from wool fiber. It is confirmed that copper(II) is a catalyst for the reduction of MB and the δ_Cu containing copper ion acts as a carrier for electron transfer. Some kerateine/δ_Cu-immobilized hydrophilic polyurethane membranes were prepared. A conjugated redox reaction combining the reduction of MB and the oxidation of TGA was carried out across these membranes.     

Silver-mediated intramolecular P–C coupling

Silver(I) salts mimic copper(I) but not gold(I) salts in the reaction with peri-iodo naphthyldiisopropylphosphine. The formation of the corresponding peri-cyclic phosphonium derivatives represents the first example of silver-mediated P–C coupling through a two-electron redox sequence.     

Controlled anodic generation of the catalyst in kinetic continuous flow analysis

Controlled anodic dissolution of copper in a separate generator cell yields well-defined concentrations of catalyst, depending on the voltage applied. This adjustable generation of copper catalyst makes it possible to determine iron over a wide range of concentration (10–1500 μg Fe³⁺ ml^-1) via the iron(III)—thiosulphate reaction. By the copper(II)-catalyzed hydrogen peroxide—hydroquinone reaction, EDTA can be determined as an inhibitor (0.5–5 μg ml^-1) and cadmium(II) as a reactivator (1–10 μg ml^-1). As zinc(II) forms complexes with 2,2'-bipyridine, which activates copper in this reaction, it can be determined (5–50 μg Zn²⁺ ml^-1) by measuring the decrease in activation. The electrogeneration of silver ion as a catalyst is also described. The sulphanilic acid—peroxodisulphate reaction is catalyzed by silver(I), which is again activated by 2,2'-bipyridine. Zinc(II) can be determined (0.29–2.9 mg Zn²⁺ ml^-1) by the same principle as in the copper(II)-catalyzed reaction.     

Extraction of Copper from Sulfate Solutions with Hydrazides of Versatic Higher Acids in the Presence of Accompanying Metals

Fundamental aspects of the extractive recovery of copper(II) in the presence of accompanying metals from sulfuric acid solutions with hydrazides of Versatic (GVIK 509) α-branched tertiary carboxylic acids in kerosene or its mixture with modifying agents: 2-ethylhexanol or alkylphenol. The selective extraction of copper(II) in the presence of nickel(II), cobalt(II), zinc(II), and iron(III) with hydrazides in kerosene is possible at pH 0.1–0.6. The separation coefficients of element pairs were calculated. It was found that the modifiers have no effect on the quantitative extraction of copper(II), but strongly change the extraction pattern of the metals under study. It was shown that the re-extraction of copper(II) with sulfuric acid solutions is in principle possible.