Coupled hydrogenation of alkenes and arenes in the presence of catalytic systems based on cobalt Bis(acetylacetonate) and tributylphosphine

The effect of the composition of the catalytic systems based on Co(acac)₂ and tertiary phosphines on the activity and efficiency of cobalt catalysts in the coupled hydrogenation of alkenes and arenes is reported. The process occurs in the presence of cobalt catalysts formed under the action of both organoaluminum compounds and tert-butoxy derivatives of complex aluminum hydrides. NMR and IR spectroscopic methods show that the interaction of the components of the catalytic systems yields mono- and/or trihydrido cobalt phosphine complexes, whose composition depends on the nature of the reducing agent and gas atmosphere. The homogeneous character of the process is hypothesized. The most probable schemes are proposed for the reaction mechanism, according to which the kinetic coupling of alkene (alkadiene) and arene hydrogenations is due to the fact that the reaction proceeds through a σ-alkyl or σ-alkenyl cobalt complex with two phosphorus-containing ligands.     

Determination of Silver‐Modified Titanium Phosphate Nanoparticles by Voltammetric and Electrocatalytic Methods

The electrochemical determination of silver‐modified titanium phosphate nanoparticles (Ag‐TiPNPs) was performed using two electrochemical features of this novel kind of nanoparticles. First, a determination using the voltammetric activity of the silver from the Ag‐TiPNPs was carried out. Secondly, the electrocatalytic effect of Ag‐TiPNPs was shown for the first time to the hydrogen evolution reaction (HER) and the determination of these nanoparticles was performed by chronoamperometry using this electrocatalysis. Moreover, it was verified that the catalytic effect was due to the electroreduced silver since the unmodified titanium phosphate nanoparticles (TiPNPs) did not exhibit this effect. Detection limits as low as 0.1 and 0.75 ng µL^?1 of Ag‐TiPNPs were obtained with the voltammetric and chronoamperometric methods, respectively. 8‐channel screen‐printed electrochemical arrays (8xSPCEs) were employed as transducers to carry out these electrochemical studies, due to its low cost and time saving.     

Rapid kinetic determination of silver (I), using in-cuvette mixing and computerized data acquisition

 The determination of silver(I) based on its catalytic effect on the oxidation of indigo carmine with hexacyanoferrate(III) is described. The reaction is monitored spectrophotometrically by means of a home-made rapid system with computer data acquisition. The decrease in absorbance of indigo carmine at 612 nm, pH 6 and at a fixed concentration of hexacyanoferrate(III) and indigo carmine is proportional to the concentration of Ag(I). The acquired data based on the initial rate and fixed time are processed. Up to 100.0 μg/ml of silver are determined. The limit of detection and average relative standard deviation are 0.13 μg/ml and 1.9%, respectively. The effect of foreign ions on the determination of silver is also discussed. The proposed method is applied to the determination of Ag(I) in expired photographic film. Received: 17 June 1996 / Revised: 26 July 1996 / Accepted: 2 August 1996     

Kinetic-spectrophotometric determination of trace amounts of silver using the oxidation of thionine with peroxodisulfate.

A simple, rapid and sensitive method has been developed for determination of traces of silver(I) (0.2 - 13 ng mL(-1)) based on its catalytic effect on the oxidation of thionine by peroxodisulfate in the presence of 1 - 10 phenanthroline as an activator. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 600 nm by the fixed time method. The detection limit is 0.098 ng mL(-1) and the relative standard deviation for 0.5, 3.0, 5.0 and 10 ng ml(-1) Ag(I) are 4.1, 1.37, 1.06 and 0.64%, respectively. The method is free from most interferences and it was applied to determination of silver in photographic solutions and well-water samples.     

Kinetic–Spectrophotometric Determination of Trace Silver(I) Using Its Catalytic Effect on the Oxidation Reaction of Fuchsin by Peroxodisulfate in the Presence of 1,10-Phenanthroline As an Activator

A kinetic spectrophotometric method for the determination of trace amounts of Ag(I) in the range of 2–20 ng mL^–1 is reported. The method is based on the catalytic effect of Ag(I) on the oxidation reaction of fuschin by potassium peroxodisulfate in the presence of 1,10-phenanthroline as an activator at pH = 5. The reaction is followed spectrophotometrically by measuring the change in absorbance (A) at 544 nm using a fixed time method (6 min). The reaction variables were optimized in order to achieve the highest sensitivity. The 3s criterion detection limit was 0.7 ng mL^–1, and the relative standard deviation for ten replicate measurements of 16 ng mL^–1 of Ag(I) was 0.95% (n = 10). The method was successfully applied to the determination of silver in expired black and white photographic films and results showed good agreements with those obtained by atomic absorption spectrometry.     

A simple thermometric technique for reaction-rate determination of inorganic species, based on the iodide-catalysed cerium(IV)-arsenic(III) reaction

A very simple reaction-rate thermometric technique is used for determination of iodide (5-20 ng ml ), based on its catalytic action on the cerium(IV)-arsenic(III) reaction, and for determination of mercury(II) (1.5-10 ng ml ) and silver(I) (2-10 ng ml ), based on their inhibitory effect on this reaction. The reaction is followed by measuring the rate of temperature increase. The method suffers from very few interferences and is applied to determination of iodide in biological and inorganic samples, and Hg(II) and Ag(I) in pharmaceutical products.     

Oxirane synthesis from diazocarbonyl compounds via NHC-Ag catalysis

A new method was developed to synthesize oxirane products from the reaction of diazocarbonyl substrates with aryl aldehydes by using Ag(I) N-heterocyclic carbene complex as the catalyst. A combination of N-heterocyclic carbene silver complex (IPrAgCl) with another silver salt (AgOTf) generated the catalytic active IPr-Ag⁺ intermediate, which then catalyzed the epoxidation reaction.     

N,N-bis-(2-benzimidazolylmethyl)L-methionine: An efficient Ag(I) extractant

A new ligand N,N-bis-(2-benzimidazolylmethyl)L-methionine has been synthesized and well characterized by different analytical techniques. The ligand has a very strong affinity for silver(I) and is used for the selective extraction of silver ions from aqueous solution into 1-butanol. The effect of concentration of Ag(I), pH, diverse ions, and temperature on the extraction is reported. The developed method has success-fully been applied to the determination of silver in different samples. Radiotracer technique, using ^110mAg(I) as a tracer, has been used for monitoring the concentration of silver ion.     

Catalytic determination of cobalt at sub-nanogram levels using the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline by manual and flow-injection methods

A catalytic photometric method was developed for the determination of sub-nanogram levels of cobalt. The method is based on the catalytic effect of cobalt(II) on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (DAOS) to form a colored dye (λ_max=525 nm) in the presence of hydrogen peroxide. In this reaction system, 1,2-dihydroxybenzene-3,5-disulfonate (Tiron) acted as an effective activator for the catalysis of cobalt(II). Variation of reaction time between 5 and 10 min allows the determination range to be extended from 0.01 to 1.0 ng ml⁻¹. The reaction system can also be successfully adapted to flow-injection analysis (FIA). The dynamic range of the proposed flow-injection method was 0.01–1.0 ng ml⁻¹ and detection limit (signal/noise, S/N=3) was 5 pg ml⁻¹ at a sampling rate of 30 h⁻¹. Manual and flow-injection methods were applied to the direct determination of cobalt in pepperbush as a standard material.     

Optimized spectrophotometric determination of trace cobalt and manganese by their catalysis of the tiron—hydrogen peroxide reaction

A kinetic—spectrophotometric method for the detemination of traces of cobalt(II) and manganese(II) based on their catalytic effect on the tiron—hydrogen peroxide indicator reaction is proposed. Optimal conditions for determination of Co(II) are deduced from response surface studies, considering the sensitivity and the blank absorbance as responses. The detection limit is 0.05 ng Co ml^?1. The Mn(II)-catalyzed reaction was optimized for 1,10-phenanthroline as the activator by the simplex method and for 2,2′-bipyridine as the activator by response surface methodology on the basis of a previously described mechanistic model of the catalytic reaction. In the presence of 2,2′-bipyridine, the detection limit is 0.2 ng Mn ml^?1. The influence of foreign metal ions on both determinations is discussed and is related in the case of the 2,2′-bipyridine—activated Mn(II)-catalyzed reaction with model generated effects of these metal ions.     

An ultrasensitive catalytic method for metal ions and cyanide-containing organic compounds

Ultrasensitive methods are described for the detection and determination of cyanide-containing organic compounds and of various metal ions. The methods are based either on the hydrolysis of the organic compounds to give cyanide ion, which then catalyzes the reduction of o-dinitrobenzene via formation of the cyanohydrin anion of p-nitrobenzaldehyde, or on the inhibition of this catalytic reaction by silver-(I), mercury(II), copper(II), cobalt(II), nickel(II), zinc(II) and cadmium(II) which form cyanide complexes. By these methods, tetracyanoethylene, p-chlorobenzylidine malononitrile, or benzoyl cyanide (0.1–10 μg/ml) may be determined with a deviation of about 2%, and Ag(i). Hg(II) (0.02–0.2 μg/ml), Cu(II) (0.003–0.030 μg/ml), Co(II) (0.06–0.40 μg/ml) and Ni(II), Zn(II) and Cd(II) (1–10 μg/ml) can be determined with a deviation of about 3%.     

Electrochemical reduction of carbon dioxide catalyzed by cofacial dinuclear metalloporphyrin

Cofacial dinuclear metalloporphyrins exhibited a catalytic activity for the electrochemical reduction of carbon dioxide. The cofacial dinuclear porphyrin was automatically generated by mixing a cationic cobalt porphyrin (CoTMPyP) and an anionic metalloporphyrin (MTPPS) in solution. The redox system of this complex was examined by electrochemical methods. According to the cyclic voltammogram, the catalytic active species was generated at −1.8V vs. Ag/Ag⁺, which was considered to be a monovalent cobalt porphyrin, Co(I)TMPyP. The catalytic activity of the dinuclear complex was two times greater than that of the mononuclear one because the anionic porphyrin acted as an electron mediator.     

Heterometallic architectures based on the combination of heteroleptic copper and cobalt complexes with silver salts

A strategy for the formation of heterometallic coordination polymers based on novel copper(II) and cobalt(III) heteroleptic complexes (acacCN)Cu(dpm) and (acacCN)Co(dpm)(2) (acacCN = 3-cyanoacetylacetonate; dpm = dipyrrin) is presented. Using dipyrrins appended with a p- or m-pyridyl group, dpm-4py and dpm-3py, four novel copper and cobalt complexes were prepared and characterized both in solution and in the solid state. These two classes of complexes show different electrochemical properties upon investigation by cyclic voltammetry in CH(2)Cl(2). While the copper complexes show only irreversible reduction processes, the voltammogram of the cobalt species reveals the presence of two quasi-reversible reductions. In the solid state, the copper(II) compounds self-assemble to form one-dimensional architectures upon coordination of the peripheral pyridyl group to the copper center, as characterized by single-crystal X-ray diffraction. Owing to the filled coordination sphere of the octahedral cobalt centers, the (acacCN)Co(dpm-py)(2) compounds crystallize as isolated molecules. Upon reaction with silver salts, these complexes form crystalline heterometallic architectures with different organization and dimensionality, depending on the nature of the metal center and the position of the nitrogen atom in the pyridyl group. The two copper complexes lead to the formation of trinuclear species, {[(acacCN)Cu(dpm-py)](2)Ag}(+), resulting from coordination of the pyridyl groups to the silver cations. However, while meta-functionalized complexes self-assemble into an extended architecture via weak interaction of the peripheral nitrile of the acacCN ligand to the Ag(+) cation, this interaction is not present in the para-functionalized analogue. In both networks based on the Ag(BF(4)) salt, coordination of the tetrafluoroborate anion to the silver center in the rather rare chelate mode is observed. Upon assembly of the cobalt metallatectons with silver salts, two-dimensional (2D) coordination polymers are obtained in crystalline form, resulting, however, from different sets of interactions. Indeed, no coordination of the peripheral nitrile of the acacCN ligand is observed in the network incorporating the m-pyridyl-appended dpm; coordination of the pyridyl groups to the silver center and d(10)-d(10) interactions lead to a 2D architecture. In the case of the para analogue, a 2D honeycomb network is observed owing to coordination of the Ag(I) ion to two pyridyl nitrogen atoms and to one peripheral nitrile group of a acacCN ligand. This latter polymer represents a geometrical hybrid of the networks reported in the literature based on homoleptic Co(dpm-4py)(3) and Cr(acacCN)(3) complexes.     

钴(Ⅱ)-过氧化氢-DCF 偶氮胂体系催化动力学光度法测定中草药中痕量钴

在邻苯二甲酸氢钾-氢氧化钠介质中,以钴(Ⅱ)催化过氧化氢氧化 DCF 偶氮胂的褪色反应为指示反应,建立了测定痕量钴(Ⅱ)的新方法。测定了反应级数和表面活化能。方法的检出限为 2.6×10-12 g/mL,线性范围为 0～23 ng/10mL。用于测定几种中草药样品中的钴,相对标准偏差为 2.8%～3.0%。     

Catalytic adsorptive stripping voltammetry versus electrothermal atomic absorption spectrometry in the determination of trace cobalt and chromium in human urine

Two methods of the determination of cobalt and chromium in human urine of non-occupationally exposed populations—highly sensitive catalytic adsorptive stripping voltammetry (CAdSV) and electrothermal atomic absorption spectrometry (ET-AAS)—are evaluated and compared. The CAdSV methods are based on adsorptive accumulation of a cobalt-nioxime (1,2-cyclohexanedione dioxime) or a chromium-DTPA (diethylenetriammine-N,N,N′,N″,N″-pentaacetic acid) complexes on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the adsorbed complex in the presence of sodium nitrite in case of cobalt or in the presence of sodium nitrate in case of chromium determination. In the CAdSV procedure UV-photolysis was used for the sample pre-treatment; the ET-AAS determination did not require any separate preliminary decomposition of the analyte urine samples. The accuracy of the procedures was checked by the analysis of commercially available quality control urine samples. The detection limits (3σ) were 0.13 μg l⁻¹ for Co and 0.18 μg l⁻¹ for Cr in ET-AAS determination and 0.007 μg l⁻¹ for Co and 0.002 μg l⁻¹ for Cr in CAdSV measurements. Precision (R.S.D.) was less than 5% for both methods. The study has shown that the CAdSV is a more reliable and sensitive technique for the determination of very low cobalt and chromium contents in urine, the detection of which is not possible when using the AAS technique.     

过硫酸钾氧化偶氮荧光桃红催化光度法测定痕量银

以过硫酸盐氧化偶氮类试剂催化动力学法测定银,多数线性范围较窄、选择性欠佳。本文建立了以偶氮荧光桃红作指示物质、α,α′-联吡啶作活化剂的催化光度法,测定痕量银检出限为1.0×10^-4μg/mL,线性范围2.0×10^-4～4.0×10^-2μg/mL,灵敏度高,选择性好。用于测定鄂铜矿中银,结果满意。采用自装的微机动力学数据处理系统,测试简便、准确。     

Giant magnetoresistance in Co–Ag granular films prepared by electrodeposition

Preparation of granular magnetic Co–Ag films produced by pulsed electrodeposition from a chloride bath containing both cobalt ions and a low concentration of silver has been investigated. Deposition of cobalt on Ag is performed by a double pulse method. Combining in situ electrochemical and microgravimetric measurements, the kinetics of silver and cobalt reduction are presented. The thickness and deposition rates are monitored using an electrochemical quartz crystal microbalance (EQCM) during the growth of each material. Magnetic measurements have shown a superparamagnetic behavior in agreement with the existence of very small cobalt particles. Giant magnetoresistance (GMR) of ∼2% at room temperature is observed for the Co₅Ag₉₅ sample.     

Ternary complexes in the spectrophotometric determination of trace amounts of silver(I) and cadmium(II)

The reaction of silver(I) and cadmium(II) with 1,10-phenanthroline (PHEN) and Eosin (2,4,5,7-tetrabromofluorescein) gives coloured association complexes. The solution spectra of the mixed-ligand complexes are characterised by high intensity (∈ ≈ 10⁴) metal-to-ligand charge-transfer bands at 540–555nm. The optimum conditions for the spectrophotometric determination of Ag(I) or Cd(II) have been established. A simple, sensitive and selective method was proposed for the determination of traces of the metal ions either in aqueous or organic media. In the presence of EDTA only aluminium and cyanide interfere.     

Liquid Phase Hydrogenolysis of Biomass‐derived Lactate to 1,2‐Propanediol over Silica Supported Cobalt Nanocatalyst

Liquid phase hydrogenolysis of ethyl lactate to 1,2‐propanediol was performed over silica supporting cobalt catalysts prepared by two different methods: precipitation‐gel (PG) technique and deposition‐precipitation (DP) procedure. The cobalt species (Co₃O₄/cobalt phyllosilicate) present in the corresponding calcined PG and DP catalysts were different as a consequence of the preparation methods, and Co OH Co olation and Si O Co oxolation molecular mechanisms were employed to elucidate the chemical phenomena during the different preparation procedures. In addition, the texture (BET), reduction behavior (TPR and in‐situ XRD), surface dispersion and state of cobalt species (XPS), and catalytic performance differ greatly between the samples. Because of small particle size, high dispersion of cobalt species and facile reducibility, the Co/SiO₂ catalyst prepared by precipitation‐gel method presented a much higher activity than the catalyst prepared by deposition‐precipitation method. Metallic cobalt is assumed to be the catalytically active site for the hydrogenolysis reaction according to the catalytic results of both cobalt samples reduced at different temperatures and the structure changes after reaction.     

Simultaneous separation and preconcentration of trace amounts of copper (II), cobalt (II) and silver (I) by modified Amberlyst®15 resin

A solid phase extraction method for simultaneous preconcentration and separation of trace amounts of copper, cobalt and silver in different samples, using a column packed with modified Amberlyst®15 resin is developed. Amberlyst®15 resin was modified with 5-(4-dimethylaminobenzylidene)rhodanine and then the modified resin was used as a support material for the solid phase extraction and preconcentration of Cu(II), Co(II) and Ag(I) ions from aqueous solution in the pH range 3.5–4.5. The adsorbed metal ions on the column were quantitatively eluted with a 7% thiourea solution prepared in 2?mol?L^?1 HNO₃, which were detected by flame atomic absorption spectrometry. The effects of analytical parameters including pH of the solution, eluent type, flow rate of samples, eluent and matrix ions were investigated for optimization of the presented procedure. The detection limits were 2.1, 0.9 and 0.9?ng?mL^?1 for Cu(II), Co(II) and Ag(I) ions, respectively based on the three times the standard deviations of the blanks. The preconcentration factor was 112.5. The calibration graphs were obtained in the ranges of 0.05 to 10.0, 0.03 to 13.0 and 0.04 to 9.0?µg?mL^?1 for Cu(II), Co(II) and Ag(I) ions concentrations, respectively. Relative standard deviations (n?=?7) for Cu(II), Co(II) and Ag(I) ions were found ±2.5 %, ±0.84% and ±3.8% respectively. The method was applied to the determination of mentioned ions in well water, waste water and lettuce sample.