New Experimental and Mechanistic Investigation on the KSCN‐H2O2‐NaOH‐Cu(II)‐Catalyzed Oscillating System (Orbàn–Epstein Reaction): Inhibitory Effects by Diphenols

The KSCN‐H₂O₂‐NaOH‐Cu(II)‐catalyzed system is one of the few reactions in which chemical oscillations can be observed in batch conditions. In the present paper, this oscillating reaction was revisited in a wide range of initial concentrations of all components in batch. A mixture with a long lasting oscillation time (1 h 34 min) and a great number of oscillations (24) was found and used to investigate the effect of temperature. An Arrhenius‐type temperature dependence was observed from which an apparent “average activation energy” E_av = 76 ± 5 kJ for the overall oscillatory reaction was observed. A mechanistic study based on a modified model analyzed by the stoichiometric network analysis approach gave a satisfactory agreement between calculated and experimental oscillating behaviors and temperature dependence. The addition of the three diphenols (catechol, resorcinol, and hydroquinone) causes perturbations similar to those observed in the Briggs‐Rauscher oscillating system, i.e., an inhibition of the oscillatory regime. These inhibitory effects were described in detail, and a reasonable qualitative interpretation is given.     

Studies of oscillating chemical in the H<Subscript>2</Subscript>O<Subscript>2</Subscript>–KSCN–CuSO<Subscript>4</Subscript>–NaOH system using a conductometry method

This paper reports a new methodological approach for investigating oscillating chemical reactions using simple and fast analytical information by measuring the conductivity of the solution. Although this technique is very common, and one of the simplest methods among the analytical techniques, however no work has been reported so far using this method for studying an oscillating system. For measuring conductivity, we use the oscillating system of H₂O₂–KSCN–CuSO₄–NaOH. Results indicate that the conductivity of the system fluctuates during the oscillating reaction. The oscillating conduction of this system was studied by changing the concentration of species involved in the oscillating reaction. Results indicate that the oscillating behaviour is varied by changing the concentration of the species.     

Cu(II) catalyzed reaction between phenyl hydrazine and toluidine blue—dual role of acid

The detailed kinetics of Cu(II) catalyzed reduction of toluidine blue (TB⁺) by phenyl hydrazine (Pz) in aqueous solution is studied. Toluidine white (TBH) and the diazonium ions are the main products of the reaction. The diazonium ion further decomposes to phenol (PhOH) and nitrogen. At low concentrations of acid, H⁺ ion autocatalyzes the uncatalyzed reaction and hampers the Cu(II) catalyzed reaction. At high concentrations, H⁺ hinders both the uncatalyzed and Cu(II) catalyzed reactions. Cu(II) catalyzed had stoichiometry similar to the uncatalyzed reaction, Pz+2 TB⁺+H₂O=PhOH+2 TBH+2 H⁺+N₂. Cu(II) catalyzed reaction occurs possibly through ternary complex formation between the unprotonated toluidine blue and phenyl hydrazine and catalyst. The rate coefficient for the Cu(II) catalyzed reaction is 2.1×10⁴ M⁻² s⁻¹. A detailed 13‐step mechanistic scheme for the Cu(II) catalyzed reaction is proposed, which is supported by simulations. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 271–276, 1999     

Luminol/H2O2/KSCN/CuSO4 Oscillating Chemiluminescence System in the Presence of Complexing Agents

The oscillating system luminol/H₂O₂/KSCN/CuSO₄ with (2‐hydroxyethyl)trimethylammoniumhydroxide (2‐HETMAOH) was investigated by using luminometry technique. Temperature and solvent effects on the behavior of the oscillating system were studied. The influences of complexing agents such as ethylenediaminetetraacetic acid (EDTA) and methionine were also investigated for this system. All experiments were performed by using the luminometer technique in a batch reactor.     

Silicon Nitride Capacitive Chemical Sensor for Phosphate Ion Detection Based on Copper Phthalocyanine – Acrylate‐polymer

In this work, we report the development of a highly sensitive capacitance chemical sensor based on a copper C,C,C,C‐ tetra‐carboxylic phthalocyanine‐acrylate polymer adduct (Cu(II)TCPc‐PAA) for phosphate ions detection. A capacitance silicon nitride substrate based Al−Cu/Si‐p/SiO₂/Si₃N₄ structure was used as transducer. These materials have provided good stability of electrochemical measurements. The functionalized silicon‐based transducers with a Cu(II)Pc‐PAA membrane were characterized by using Mott‐Schottky technique measurements at different frequency ranges and for different phosphate concentrations. The morphological surface of the Cu(II)Pc‐PAA modified silicon‐nitride based transducer was characterized by contact angle measurements and atomic force microscopy. The pH effect was also investigated by the Mott‐Schottcky technique for different Tris‐HCl buffer solutions. The sensitivity of silicon nitride was studied at different pH of Tris‐HCl buffer solutions. This pH test has provided a sensitivity value of 51 mV/decade. The developed chemical sensor showed a good performance for phosphate ions detection within the range of 10⁻¹⁰ to 10⁻⁵ M with a Nernstian sensitivity of 27.7 mV/decade. The limit of detection of phosphate ions was determined at 1 nM. This chemical sensor was highly specific for phosphate ions when compared to other interfering ions as chloride, sulfate, carbonate and perchlorate. The present capacitive chemical sensor is thus very promising for sensitive and rapid detection of phosphate in environmental applications.     

Crystal Structures,Magnetic Properties and Catecholase‐Like Activities of μ‐Alkoxo‐μ‐Carboxylato Double Bridged Dinuclear and Tetranuclear Copper(II) Complexes

One μ‐alkoxo‐μ‐carboxylato bridged dinuclear copper(II) complex, [Cu₂(L¹)(μ‐C₆H₅CO₂)] ( 1 )(H₃L¹ = 1,3‐bis(salicylideneamino)‐2‐propanol)), and two μ‐alkoxo‐μ‐dicarboxylato doubly‐bridged tetranuclear copper(II) complexes, [Cu₄(L¹)₂(μ‐C₈H₁₀O₄)(DMF)₂]·H₂O ( 2 ) and [Cu₄(L²)₂(μ‐C₅H₆O₄]·2H₂O·2CH₃CN ( 3 ) (H₃L² = 1,3‐bis(5‐bromo‐salicylideneamino)‐2‐propanol)) have been prepared and characterized. The single crystal X‐ray analysis shows that the structure of complex 1 is dimeric with two adjacent copper(II) atoms bridged by μ‐alkoxo‐μ‐carboxylato ligands where the Cu···Cu distances and Cu‐O(alkoxo)‐Cu angles are 3.5 11 Å and 132.8°, respectively. Complexes 2 and 3 consist of a μ‐alkoxo‐μ‐dicarboxylato doubly‐bridged tetranuclear Cu(II) complex with mean Cu‐Cu distances and Cu‐O‐Cu angles of 3.092 Å and 104.2° for 2 and 3.486 Å and 129.9° for 3 , respectively. Magnetic measurements reveal that 1 is strong antiferromagnetically coupled with 2J =‐210 cm^?1 while 2 and 3 exhibit ferromagnetic coupling with 2J = 126 cm^?1 and 82 cm^?1 (averaged), respectively. The 2J values of 1–3 are correlated to dihedral angles and the Cu‐O‐Cu angles. Dependence of the pH at 25 °C on the reaction rate of oxidation of 3,5‐di‐tert‐butylcatechol (3,5‐DTBC) to the corresponding quinone (3,5‐DTBQ) catalyzed by 1–3 was studied. Complexes 1–3 exhibit catecholase‐like active at above pH 8 and 25 °C for oxidation of 3,5‐di‐tert‐butylcatechol.     

A new hybrid organic–inorganic chain: [(phen)Cu–μ‐(κ2O:O′‐VP2O10H3)2–Cu(phen)]n

The structure of the title compound, poly[(dihydrogenphosphato‐κO)(μ₃‐hydrogenphosphato)di‐μ‐oxido‐(1,10‐phenanthroline)copper(II)vanadium(V)], [CuV(HPO₄)(H₂PO₄)O₂(C₁₂H₈N₂)]_n, is defined by [(phen)Cu–μ‐(κ²O:O′‐VP₂O₁₀H₃)₂–Cu(phen)] units (phen is 1,10‐phenanthroline), which are connected to neighbouring units through vanadyl bridges. Neighbouring chains have no covalent bonds between them, although they interdigitate through the phen groups viaπ–π interactions.     

5‐n‐Butylpyridine‐2‐carboxylate–copper(II) and –iron(III) complexes

In trans‐bis(5‐n‐butyl­pyridine‐2‐carboxyl­ato‐κ²N,O)­bis­(methanol‐κO)copper(II), [Cu(C₁₀H₁₂NO₂)₂(CH₄O)₂], the Cu atom lies on a centre of symmetry and has a distorted octahedral coordination. The Cu—O(methanol) bond length in the axial direction is 2.596 (3) Å, which is much longer than the Cu—­O(carboxylate) and Cu—N distances in the equatorial plane [1.952 (2) and 1.977 (2) Å, respectively]. In mer‐tris(5‐n‐bu­tyl­pyridine‐2‐carboxyl­ato‐κ²N,O)­iron(III), [Fe(C₁₀H₁₂NO₂)₃], the Fe atom also has a distorted octahedral geometry, with Fe—O and Fe—N bond‐length ranges of 1.949 (4)–1.970 (4) and 2.116 (5)–2.161 (5) Å, respectively. Both crystals are stabilized by stacking interactions of the 5‐n‐butyl­pyridine‐2‐carboxyl­ate ligand, although hydrogen bonds also contribute to the stabilization of the copper(II) complex.     

Pedagogic Interest of the H2O2, Cu2+, SCN-, OH- Oscillating Reaction

Chemical reactivity is generally taught by considering the chemical properties of the reacting entities (acid-base, oxidation-reduction, complexation, and precipitation) and the values of the corresponding equilibrium thermodynamic constants (K_a, E⁰ K_d, K_s). This approach, however, is not well-suited to the dynamic chemical systems that are often encountered in industrial and environmental chemistry where nonequilibrium conditions prevail. In this respect, oscillating reactions are a good illustration of the limits of equilibrium thermodynamics and show the need for a complementary dynamic nonequilibrium study. We describe here an oscillating reaction that is easy to carry out in an inorganic chemistry practical class as it uses common reactants (H₂O₂, KSCN, CuSO₄, NaOH). This example should enable students to obtain a more realistic grasp of chemical reactivity based on a comprehension of coupled reaction processes, similar to those encountered in population dynamics or in enzymatic regulation.     

Highly Efficient One‐Pot Three Component Synthesis of 2H‐Indazoles by Consecutive Condensation,C–N and N–N Bond Formations Using Cu/Aminoclay/Reduced Graphene Oxide Nanohybrid

A simple and straightforward one‐pot three‐component synthesis of 2H‐indazoles through copper‐catalyzed consecutive condensation, C–N and N–N bond formations of easily accessible starting materials under ligand‐free conditions is described. In this protocol, treatment of substituted 2‐bromobenzaldehydes, structurally diverse amines, and [bmim]N₃ in the presence of Cu/aminoclay/reduced graphene oxide nanohybrid (Cu/AC/r‐GO nanohybrid) as an efficient heterogeneous catalyst affords the corresponding 2H‐indazoles in good to excellent yields. The influence of effective parameters on the efficient progress of the reaction was studied. The Cu/AC/r‐GO nanohybrid is a stable and inexpensive catalyst that could be simply prepared, recovered, and reused for several reaction runs with no significant decrease in its reactivity.     

Oxidative polymerization of 2,6‐dimethylphenol to form poly(2,6‐dimethyl‐1,4‐phenylene oxide) in water through one water‐soluble copper(II) complex of a zwitterionic calix[4]arene

In the presence of excess NaOH, reaction of Cu(OAc)₂·H₂O with equimolar ammonium calix[4]arene [H₄L]I₄ ( 1 , H₄L = [5,11,17,23‐tetrakis(trimethylammonium)‐25,26,27,28‐tetrahydroxycalix[4]arene]) resulted in the formation of a mononuclear cationic Cu(II) complex [Cu(II)L(H₂O)]I₂ ( 2 ) in 43% yield. Complex 2 was characterized by elemental analysis, infrared (IR), and single crystal X‐ray diffraction. The Cu(II) atom in 2 is coordinated by four oxygen atoms of one L^4? ligand and one O atom from one water molecule, forming a square pyramidal geometry. Complex 2 exhibited high catalytic activity in the oxidative polymerization of 2,6‐dimethylphenol using O₂ as oxidizing agent in water under mild conditions. The selective polymerization produced poly(2,6‐dimethyl‐1,4‐phenylene oxide) in high yields with almost no diphenoquinone. The influence of the polymerization temperature, the time interval, the molar ratio of 2,6‐dimethylphenol/ 2 , the concentrations of sodium hydroxide, and sodium n‐dodecyl sulfate were examined. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A heterotrimetallic Cu–Co–Zn complex with the 2,2′‐iminodiethanol ligand

The crystal structure of the title compound, triacetato‐1κO;3κ⁴O,O′‐(2,2′‐imino­diethanol)‐1κ³O,N,O′‐bis­(μ‐2,2′‐iminodi­ethanol­ato)‐1κ²O:2κ⁶O,N,O′:3κ²O′‐cobalt(III)copper(II)zinc(II), [CoCuZn(C₄H₉NO₂)₂(C₂H₃O₂)₃(C₄H₁₁NO₂)], shows a mol­ecule with a triangular three‐metal core. The metal sites were refined with full occupancies, but the possibility that the Zn and Cu positions are actually mixed Cu/Zn sites cannot be excluded. The inter­metallic Cu⋯Co and Co⋯Zn distances are 2.924 (3) and 2.906 (3) Å, respectively. The neutral mol­ecules are held together by N—H⋯O hydrogen bonds involving amine groups from the 2,2′‐iminodiethanol ligands and acetate groups to build two‐dimensional layers.     

CuII‐Catalyzed Oxidative Formation of 5‐Alkynyltriazoles

In an alcoholic solvent under the catalysis of Cu(OAc)₂?H₂O, organic azide and terminal alkyne could oxidatively couple to afford 5‐alkynyl‐1,2,3‐triazole (alkynyltriazole) at room temperature under an atmosphere of O₂ in a few hours. The involvement of 1,5‐diazabicyclo[4.3.0]non‐5‐ene (DBN) is essential, without which the redox neutral coupling instead proceeds to produce 5‐H‐1,2,3‐triazole (protiotriazole) as the major product. Therefore, DBN switches the redox neutral coupling between terminal alkyne and organic azide, the copper‐catalyzed “click” reaction to afford protiotriazole, to an oxidation reaction that results in alkynyltriazole. The organic base DBN is effective in accelerating the copper(II)‐catalyzed oxidation of terminal alkyne or copper(I) acetylide, which is intercepted by an organic azide to produce alkynyltriazole. The proposed mechanistic model suggests that the selectivity between alkynyl‐ and protiotriazole, and other acetylide or triazolide oxidation products is determined by the competition between copper(I)‐catalyzed redox neutral cycloaddition and copper(II)/O₂‐mediated acetylide oxidation after the formation of copper(I) acetylide.     

3‐(4‐Cyano­phenyl)­pentane‐2,4‐dione and its copper(II) complex

The β‐diketone 3‐(4‐cyano­phenyl)­pentane‐2,4‐dione crystallizes as the enol tautomer 4‐(2‐hydroxy‐4‐oxopent‐2‐en‐3‐yl)­benzo­nitrile, C₁₂H₁₁NO₂, (I), with an intramolecular O—H⋯O hydrogen bond [O⋯O = 2.456 (2) Å]. Reaction of (I) with copper acetate monohydrate in the presence of triethyl­amine leads to the formation of the copper(II) complexbis­[3‐(4‐cyano­phenyl)­pentane‐2,4‐dionato‐κ²O,O]copper(II), [Cu(C₁₂H₁₀NO₂)₂], (II). In the structure of (II), the Cu atom is coordinated by four β‐diketonate O atoms in a slightly distorted square‐planar geometry, with Cu—O distances in the range 1.8946 (11)–1.9092 (11) Å. The nitrile moieties in (II) make it a candidate for reaction with other metal ions to produce supramolecular structures.     

The Model of “Minimal Oscillator” Derived from the Kinetic Mechanism of the H2O2–NaSCN–NaOH–CuSO4 Dynamical System

Dissipative chemical reactions, which involve oscillatory variations of the concentrations of the intermediates in time, are usually characterized with complicated kinetic mechanisms. However, the essential source of the oscillations can often be reduced to only a few reaction steps providing the alternative domination of the positive and negative feedback loops. In an extreme case such a reduction leads to the so–called “minimal oscillator,” the concept used in the past for the well‐known Belousov‐Zhabotinsky (BZ) reaction. In the present work, we construct such a minimal system for the (discovered by M. Orbán) H₂O₂–NaSCN–NaOH–CuSO₄ homogeneous oscillator, in which instabilities originate from kinetic mechanism substantially different from that proposed for the BZ system. The methodology involves intuitive analysis of the reaction mechanism, supported by numerical calculations and spectrophotometric measurements. We show how the actual, only three‐variable model evolves from our previously elaborated: nine‐ and five–variable mechanisms and prove that its further reduction to two–variable one is not possible. Thus the present work is a final step in our searches for the “minimal Orbán oscillator”.     

Active role of hydrogen bond and ambient water in Meyer–Schuster rearrangements in high‐temperature water

Meyer–Schuster rearrangements of 2‐phenyl‐3‐butyn‐2‐ol with H₃O⁺ and (H₂O)₆ model in high‐temperature water (HTW) have been investigated by the use of density functional theory calculations. In the substrate 2‐phenyl‐3‐butyn‐2‐ol catalyzed by H₃O⁺ and (H₂O)₆, the Meyer–Schuster rearrangements were predicted by the frontier molecular orbital theory. The results show that the rearrangement does not involve the carbonium ion intermediates, but the first transition state is carboniumion like. Dehydration and hydration may occur via the intermolecular proton relay along the hydrogen‐bond chains and the second step of reaction path is a total acid–base catalytic process. Based on the results, a model considered both HTW ambient and water molecules are proposed to represent mechanisms of other reactions in HTW. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Synthesis,structure and photocatalytic degradation of organic dyes of a copper(II) metal–organic framework (Cu–MOF) with a 4‐coordinated three‐dimensional CdSO4 topology

Metal–organic frameworks (MOFs) have attracted much interest in the fields of gas separation and storage, catalysis synthesis, nonlinear optics, sensors, luminescence, magnetism, photocatalysis gradation and crystal engineering because of their diverse properties and intriguing topologies. A Cu–MOF, namely poly[[(μ₂‐succinato‐κ²O:O′){μ₂‐tris[4‐(1,2,4‐triazol‐1‐yl)phenyl]amine‐κ²N:N′}copper(II)] dihydrate], {[Cu(C₄H₄O₄)(C₂₄H₁₈N₁₀)]·2H₂O}_n or {[Cu(suc)(ttpa)]·2H₂O}_n, (I), was synthesized by the hydrothermal method using tris[4‐(1,2,4‐triazol‐1‐yl)phenyl]amine (ttpa) and succinate (suc^2?), and characterized by IR, powder X‐ray diffraction (PXRD), luminescence, optical band gap and valence band X‐ray photoelectron spectroscopy (VB XPS). Cu–MOF (I) shows a twofold interpenetrating 4‐coordinated three‐dimensional CdSO₄ topology with point symbol {6⁵·8}. It presents good photocatalytic degradation of methylene blue (MB) and rhodamine B (RhB) under visible‐light irradiation. A photocatalytic mechanism was proposed and confirmed.     

A bis(amine–carboxylate) copper(II) coordination compound forms a two‐dimensional metal–organic framework when crystallized from water and methanol

When {2,2′‐[(2‐methyl‐2‐nitropropane‐1,3‐diyl)diimino]diacetato}copper(II), [Cu(C₈H₁₃N₃O₆)], (I), was crystallized from a binary mixture of methanol and water, a monoclinic two‐dimensional water‐ and methanol‐solvated metal–organic framework (MOF) structure, distinctly different from the known orthorhombic one‐dimensional coordination polymer of (I), was isolated, namely catena‐poly[[copper(II)‐μ₃‐2,2′‐[(2‐methyl‐2‐nitropropane‐1,3‐diyl)diimino]diacetato] methanol 0.45‐solvate 0.55‐hydrate], {[Cu(C₈H₁₃N₃O₆)]·0.45CH₃OH·0.55H₂O}_n, (II). The monoclinic structure of (II) comprises centrosymmetric dimers stabilized by a dative covalent Cu₂O₂ core and intramolecular N—H...O hydrogen bonds. Each dimer is linked to four neighbouring dimers via symmetry‐related (opposing) pairs of bridging carboxylate O atoms to generate a `diamondoid' net or two‐dimensional coordination network. Tight voids of 166 ų are located between these two‐dimensional MOF sheets and contain a mixture of water and methanol with fractional occupancies of 0.55 and 0.45, respectively. The two‐dimensional MOF sheets have nanometre‐scale spacings (11.2 Å) in the crystal structure. Hydrogen‐bonding between the methanol/water hydroxy groups and a Cu‐bound bridging carboxylate O atom apparently negates thermal desolvation of the structure below 358 K in an uncrushed crystal of (II).     

Heterogeneous kinetic studies of the hydrogen peroxide decomposition with some transition metal‐heterocyclic complexes

The heterocyclic compounds piperidine (Pip), piperazine (Pz), morpholine (Morph), and N‐methyl piperazine (N‐MPz) were used as ligands to form transition metal complexes with Ni(II), Cu(II), and Co(II) ions. These complexes were supported on Dowex‐50W resin so as to form new potential active catalysts for H₂O₂ decomposition in an aqueous medium. In all cases the reaction showed a first‐order kinetics with respect to H₂O₂ concentration, except with Co(II) complexes, the reaction showed a second‐order kinetics with 2% divinyl benzene (DVB) (50–100 mesh and 200–400 mesh). The rate constant k (per gram dry resin) was evaluated with a resin of cross‐linkage 2 and 8% DVB (50–100 mesh) and 2% DVB (200–400 mesh) over temperature range 25–40°C. With a given resin cross‐linkage, the rate constant has the following order: Ni(II) complexes < Co(II) complexes < Cu(II) complexes. With Pz ligand, k increased in the following sequence: Ni(II) complexes < Cu(II) complexes < Co(II) complexes. The reaction mechanisms of the first‐ and second‐order kinetics were discussed and the activation parameters were deduced. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 617–624, 2001     

Spatiotemporal Heterogeneity of Reactions in Solution Observed with High‐Speed Single‐Nanorod Rotational Sensing

A high‐speed darkfield microscope has been developed to monitor the rapid rotation of single gold nanorods (AuNRs) and used to study the spatiotemporal heterogeneity of chemical reactions in free solution. A wide range of viscosities from 237 cP to 0.8 cP could be detected conveniently. We studied H₂O₂ decomposition reactions that were catalyzed by AuNRs coated with Pt nanodots (AuNR@PtNDs) and observed two different rotational states. The two states and their transitions are related to the production and the amalgamation of O₂ nanobubbles on the nanorod surface depending on H₂O₂ concentration. In addition, the local fluidic environment of pure water was found to be non‐uniform in time and space. This technique could be applied to study other chemical and biochemical reactions in solution.