Ion exchangers as catalysts. II. Catalytic decomposition of hydrogen peroxide with resin-ethylenediamine-copper(II) complex ions

Summary The slow decomposition of H₂O₂ in the presence of Dowex-50 W resin in the form of an ethylenediaminecopper(II) complex ion in water is accompanied by an induction period. The reaction is first order with respect to [H₂O₂] and the rate constant (perg of dry resin) was deduced. Autocatalytic behaviour was found for the H₂O₂ decomposition with 2% crosslinked divinylbenzene. The induction period disappeared and the reaction rate increased when the decomposition was carried out with a resin in the form of a peroxo-copper complex, which proves that the formation of an intermediate (active species) retards the reaction rate. The precursor of the active species, formed during the induction period, was not the amine-copper(II) complex ion but a product of the latter with H₂O₂. It proved impossible to carry out the decomposition in acid or buffer solutions, in which the resin is regenerated.     

Carbon‐based Nanosensors for Salicylate Determination in Pharmaceutical Preparations

Thiourea derivative‐based carbon paste electrode (TUD1‐CPE) was constructed as a potentiometric sensor for the determination of salicylate anion in pharmaceutical formulations, Aspocid® and Aspirin®. The optimized CPE contained 45.5 % graphite, 0.5 % reduced graphene oxide (rGO), 46.0 % nitrophenyl octyl ether (NPOE) plasticizer, 5.0 % TUD1 ionophore, and 3.0 % tridodecylmethyl ammonium chloride as additive. The incorporation of NPOE of high dielectric constant, and rGO in electrode caused better performance of the sensor; Nernstian response of 59.0 mV decade^?1 in the concentration range of 10^?1–10^?5 mole L^?1, a detection limit of 1×10^?5 mole L^?1 in a very short response time of 6 seconds. The prepared sensor showed high selectivity against similar anions (i. e. , benzoate, I^?, SCN^?). Selectivity was confirmed by calculating the formation constant (K_β) using sandwich membrane method, where K_β for TUD1‐salicylate is 10^0.43. Theoretical calculations at DFT‐B3LY/6‐31G** level of theory were performed to find interaction mechanism, Energies of HOMO and LUMO orbitals, non‐linear optical (NLO) properties (the electronic dipole moment (μ), first‐order hyperpolarizability (β), the hyper‐Rayleigh scattering (β_HRS) and the depolarization ratio (DR)), and other global properties; these calculations showed lower values of β and DR, higher value of β_HRS, and the shortest lengths of the four N?H bonds between TUD1 and salicylate which confirm their strong complexation and salicylate‐selectivity. Also, all the studied anion‐TUD1 exhibited relatively high NLO properties, and these results were considered as a preliminary study for investigating new types of NLO bearing materials. The sensors were applied successfully for the determination of salicylate anion in Aspocid® and Aspirin®.     

Influence of diluent on the synergic extraction of divalent cobalt by the thenoyltrifluoroacetone-tribenzylamine perchlorate system

The effect of ten pure diluents and different mixtures of nitrobenzene and toluene on the synergic extraction of Co²⁺ by the thenoyltrifluoroacetone (HTTA)-tribenzylamine (TBA) mixture is studied. The logarithm of the extraction constant of Co(TTA)₂ increases with increasing dielectric constant of the diluent, whereas the logarithm of the formation constant of the extracted adduct Co(TTA)₂TBA decreases with increasing dielectric constant of the diluent. This behaviour is explained by changes in the hydrophobic character of the extracted species. The theory of regular solutions is successfully applied to the extracted adduct. Consideration of the self-association of the amine salt is necessary in the treatment of the equilibria involved.     

Kinetic and thermodynamic studies on ligand substitution reactions and base-on/base-off equilibria of cyanoimidazolylcobamide, a vitamin B12 analog with an imidazole axial nucleoside

Ligand substitution reactions of the vitamin B12 analog cyanoimidazolylcobamide, CN(Im)Cbl, with cyanide were studied. Cyanide substitutes imidazole (Im) in the alpha-position more slowly than it substitutes dimethylbenzimidazole in cyanocobalamin (vitamin B12). The kinetics of the displacement of Im by CN- showed saturation behaviour at high cyanide concentration; the limiting rate constant was found to be 0.0264 s(-1) at 25 degrees C and is characterized by the activation parameters: DeltaH(not =) = 111 +/- 2 kJ mol(-1), DeltaS(not =) = +97 +/- 6 J K(-1) mol(-1), and DeltaV(not =) = +9.3 +/- 0.3 cm3 mol(-1). These parameters are interpreted in terms of an I(d) mechanism. The equilibrium constant for the reaction of CN(Im)Cbl with CN- was found to be 861 +/- 75 M(-1), which is significantly less than that obtained for the reaction of cyanocobalamin with CN- (viz. 10(4) M(-1)). pKbase-off for the base-on/base-off equilibrium was determined spectrophotometrically and found to be 0.99 +/- 0.05, which is about 0.9 pH units higher than that obtained previously in the case of cyanocobalamin. In addition, the kinetics of the base-on/base-off reaction was studied using a pH-jump technique and the data obtained revealed evidence for an acid catalyzed reaction path. The results obtained in this study are discussed in reference to those reported previously for cyanocobalamin.     

Selective Solid Phase Extraction and Pre-Concentration of Heavy Metals from Seawater by Physically and Chemically Immobilized 4-Amino-3-Hydroxy-2-(2-Chlorobenzene)-Azo-1-Naphthalene Sulfonic Acid Silica Gel

4-Amino-3-hydroxy-2-(2-chlorobenzene)-azo-1-naphthalene sulfonic acid (AHCANSA) was used as a chelating modifier to improve the reactivity of the silica gel surface in terms of selective binding and extraction of heavy metal ions. The surface coverage values were found to be 0.488 and 0.473mmolg^–1 for the newly modified physically adsorbed silica gel phase (I) and chemically immobilized-AHCANSA phase (II), respectively. The modified silica gel phases (I, II) were tested for stability in different acidic buffer solutions (pH 1–6) and found to be highly resistant to hydrolysis and leaching by buffer solutions above pH 2. The application of these two phases as solid extractors for a series of mono-, di-, and tri-valent metal ions from aqueous solutions was also performed with different controlling factors such as the pH value of metal ion solutions and equilibrium shaking time. The mmolg^–1 metal capacity values determined by silica gel phases (I, II) were found to confirm high affinity and selectivity characters for binding with heavy metal ions such as Cr³⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ in a range of 0.250–0.483. The tested alkali and alkaline earth metals, Na⁺, K⁺, Mg²⁺ and Ca²⁺, were found to exhibit little interaction and binding ability with the modified silica gel phases. The selectivity characters incorporated into the modified silica gel phases were further utilized and applied in solid phase extraction and pre-concentration of trace concentration levels (1.0µgmL^–1 and 2.00–2.50ngmL^–1) from real seawater samples. The percentage recovery values determined for Cr³⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were found to be in the range of 95.2–98.1±2.0–5.0%, and the pre-concentration recovery values for the same tested heavy metal ions were found to be in the range of 92.5–97.1±3.0–6.0% for the two newly modified silica gel phases with a pre-concentration factor of 500.Received December 20, 2002; accepted May 14, 2003 published online September 1, 2003     

Mixed ligand complexes of diaquo (2,2′-bipyridine)palladium(II) with cyclobutane-1,1-dicarboxylic acid and DNA constituents

Complex formation equilibria involving [Pd(bpy)(H₂O)₂]²⁺ (bpy = 2,2-bipyridine) and the cyclobutanedicarboxylate ligand (cbdca), ethylenediamine and DNA have been investigated. Mixed ligand complexes of [Pd(bpy)(cbdca)] with inosine, inosine-5-monophosphate (5-IMP), uracil, uridine and adenine have been studied. The results show ring opening of the cbdca and monodentate chelation of the DNA components. Stoichiometries and stability constants for the complexes were determined at 25 °C and at constant 0.1 M ionic strength (adjusted using NaNO₃). The coordination sites were found to be pH-dependent. The [Pd(bpy)Cl₂], [Pd(bpy)(cbdca)] and [Pd(bpy)(inosine)](NO₃) complexes were isolated.     

Enhancement of the catalytic activity of [Cu2(TS)(OH)2(OAc)] using superconductor cuprate sample

A superconducting sample (Nd_0.1Y_0.9Ba₂Cu₃O_7-δ) has been tried as a catalyst for H₂O₂ decomposition. All parameters affecting the reaction rate (concentration of H₂O₂, weight of catalyst, temperature and pH) were studied and the optimum conditions were evaluated. A mixture of the superconducting cuprate with [Cu₂(TS)(OH)(OAc)] using different percentages of the sample has been prepared and tried kinetically under the same mentioned conditions. An attempt was made to increase the activity of the complex. The data show that the cuprate sample alone was found to be almost inactive when compared with that of the mixture. The catalytic mechanism in the absence and presence of the complex was suggested.     

The chemistry of the azanonaborane cluster RNH2---B8H11NHR

The preparation and properties of the R¹R²NH---B₈H₁₁NHR cluster are described. The cluster is stable to aqueous solutions and can be made water-soluble by the introduction of a few hydrophilic groups. This makes the cluster a good candidate as the boron moiety in compounds for boron neutron capture therapy. The chemistry of the cluster preparation, the stability of the cluster, and conditions for reactions of the organic moieties are reviewed. Pyridine derivatives of the cluster show electronic interaction between the cluster and the pyridine.     

De novo enantioselective syntheses of galacto-sugars and deoxy sugars via the iterative dihydroxylation of dienoate

An efficient route to various sugar lactones has been developed. Key to the overall transformation is the sequential osmium-catalyzed dihydroxylation of 2,4-dienoates. The simplest (one-step/racemic) example of this reaction occurs when the dihydroxylation is performed with aqueous NMO in MeOH. When the first dihydroxylation is performed using the AD-mix procedure, an enantioselective variant results. When a matched AD-mix procedure is used for the second dihydroxylation, an exceedingly diastereo- and enantioselective synthesis of galacto-1,4-lactone results. [Reaction: see text]     

Reductive Elimination of Phenylsulfonyl Groups in the 3‐Position of Benzo[a]heptalene‐2,4‐diols

3‐(Phenylsulfonyl)benzo[a]heptalene‐2,4‐diols 1 can be desulfonylated with an excess of LiAlH₄/MeLi?LiBr in boiling THF in good yields (Scheme 6). When the reaction is run with LiAlH₄/MeLi, mainly the 3,3′‐disulfides 6 of the corresponding 2,4‐dihydroxybenzo[a]heptalene‐3‐thiols are formed after workup (Scheme 7). However, the best yields of desulfonylated products are obtained when the 2,4‐dimethoxy‐substituted benzo[a]heptalenes 2 are reduced with an excess of LiAlH₄/TiCl₄ at ?78→20° in THF (Scheme 10). Attempts to substitute the PhSO₂ group of 2 with freshly prepared MeONa in boiling THF led to a highly selective ether cleavage of the 4‐MeO group, rather than to desulfonylation (Scheme 13).