Substitution Of Cyanide Research Articles

A Kinetic Investigation of Hg(II) Catalyzed Cyanide Substitution from [Ru(CN)6]4– by Isoniazid

A Kinetic Investigation of Hg(II) Catalyzed Cyanide Substitution from [Ru(CN)6]4– by Isoniazid

Kinetic Study of Hg(II)-Promoted Cyanide Substitution from Hexacyanoferrate(II) in an Anionic Surfactant Medium by N-R-Salt

Kinetic Study of Hg(II)-Promoted Cyanide Substitution from Hexacyanoferrate(II) in an Anionic Surfactant Medium by N-R-Salt

Kinetic study of Hg(II)‐promoted substitution of cyanide from hexacyanoferrate(II) in an anionic surfactant medium by 2,2′‐bipyridine

AbstractThe kinetic investigation of Hg(II)‐promoted reaction between [Fe(CN)6]4− and 2,2′‐bipyridine (Bipy) has been performed in anionic sodium dodecyl sulfate (SDS) micellar medium by recording the surge in absorbance at 400 nm, corresponding to ultimate reaction product [Fe(CN)4 Bipy]2− using UV–visible spectrophotometer. Pseudo‐first‐order condition has been used to examine the progress of reaction as a function of temperature, [Fe(CN)64−], ionic strength, [SDS], pH, [Hg2+], and [Bipy] by changing one parameter at a time. The results exhibit that [Hg2+], [SDS], and pH are the decisive parameter showing maximum reaction rate at 1.5 × 10−4 mol dm−3, 6.0 × 10−3 mol dm−3, and 3.8, respectively. [Fe(CN)6]4− does not show any appreciable effect on the critical micellar concentration (CMC) of SDS as the polar head of SDS and [Fe(CN)6]4− both are negatively charged. Variable order kinetics was observed for [Fe(CN)6]4− and Bipy in their examined concentration range. The reverse response observed in the reaction rate with [KNO3] shows a negative salt effect. The K+ provided by K4[Fe(CN)6] and KNO3 decreases the repulsion between the negatively charged heads of the surfactant molecules thereby decreasing the CMC of SDS. The negative value for the entropy of activation also supports the interchange dissociative (Id) mechanism recommended by us.

Benchmark Ab Initio Characterization of the Abstraction and Substitution Pathways of the Cl + CH3CN Reaction.

We investigate the reaction pathways of the Cl + CH3CN system: hydrogen abstraction, methyl substitution, hydrogen substitution, and cyanide substitution, leading to HCl + CH2CN, ClCN/CNCl + CH3, ClCH2CN + H, and CH3Cl + CN, respectively. Hydrogen abstraction is exothermic and has a low barrier, whereas the other channels are endothermic with high barriers. The latter two can proceed via a Walden inversion or front-side attack mechanism, and the front-side attack barriers are always higher. The C-side methyl substitution has a lower barrier and also a lower endothermicity than the N-side reaction. The computations utilize an accurate composite ab initio approach and the explicitly correlated CCSD(T)-F12b method. The benchmark classical and vibrationally adiabatic energies of the stationary points are determined with the most accurate CCSD(T)-F12b/aug-cc-pVQZ energies adding further contributions of the post-(T) and core correlation, scalar relativistic effects, spin–orbit coupling, and zero-point energy corrections. These contributions are found to be non-negligible to reach subchemical accuracy.

Ag(I)-Promoted Substitution of Cyanide from Hexacyanoferrate(II) with Pyrazine: A Kinetic and Mechanistic Study

Ag(I)-Promoted Substitution of Cyanide from Hexacyanoferrate(II) with Pyrazine: A Kinetic and Mechanistic Study

Study on the Cyanide Substitution Reaction of Acetone Cannolhydrin as Cyanogen Source

Study on the Cyanide Substitution Reaction of Acetone Cannolhydrin as Cyanogen Source

Quantitative Estimation of D-Penicillamine in Pure and Pharmaceutical Samples Using Inhibitory Kinetic Spectrophotometric Method

Sulfur is the key element in a large number of drugs and bioactive molecules. Organo-sulfur compounds inhibit the catalytic efficiency of Hg2+ by forming a stable complex with it. The Hg2+ catalyzed exchange rate of cyanide with pyrazine from [Ru(CN)6]4- will be reduced by the addition of the sulfur-containing drug, D-penicillamine (D-PCN). This inhibitory property of D-PCN can be employed for its micro-level kinetic determination. Optimum reaction condition viz. Temperature = 45.0 ± 0.1 o C, I = 0.1 M (KCl), [Hg+2] = 1.5 × 10-4 M, [pyrazine] = 7.5 × 10-4 M, pH = 4.0 ± 0.02, and [Ru(CN)64-] = 5.25 × 10-5 M were utilized to investigate the kinetic measurements at 370 nm (λmax of [Ru(CN)5 Pz]3- complex). To acknowledge the inhibition induced by D-PCN on Hg2+ catalyzed substitution of cyanide with pyrazine from [Ru(CN)6]4-, a modified mechanistic scheme has been proposed. D-PCN can be quantitatively determined up to 1.0 × 10-6 M level by the proposed analytical method. The methodology can be economically and effectively employed for the quantitative determination of D-PCN in different samples. This methodology can also be convincingly adopted for the quick determination of D-PCN in the pharmaceutical samples with good accuracy and reproducibility. The addition of common excipients in pharmaceuticals even up to 1000 times with [D-PCN] does not interfere significantly in the estimation of D-PCN.

Synthesis and photophysical properties of vertically π-expanded coumarins

New vertically π-expanded coumarins dyes 1-phenynyl-2H-phenaleno[1,2,3-de] chromen-2-ones and 1-cyano-2H-phenaleno[1,2,3-de]chromen-2-ones were synthesized using 1-bromo-2H-phenaleno[1,2,3-de]chromen-2-one with arylacetylene or cyano reagent via the Sonogashira reaction and cyanide substitution reaction, and obtained in high yields up to 85% from 1-bromo-2H-phenaleno [1,2,3-de]chromen-2-one. The photophysical studies revealed that 1-substituted -2H-phenaleno[1,2,3-de]chromen-2-ones have large Stokes shift (4898 cm−1) and excellent fluorescence quantum yield (Φf = 0.80) along with significant bathochromic shift. The intriguing optical properties of these vertically π-expanded coumarins are discussed on the basis of quantum chemical calculations. Furthermore, 1-cyano-2H-phenaleno[1,2,3-de]chromen-2-one exhibited good biocompatibility by onion skin staining.

Scalable synthesis of a tetrasubstituted 7-azabenzofuran as a key intermediate for a class of potent HCV NS5B inhibitors

Abstract A series of tetrasubstituted 7-azabenzofurans displays remarkable pan-genotype inhibition of HCV NS5B polymerase. One of them has been identified as a potential clinical candidate. Completely different from the original synthesis of a common and key intermediate for this class of compounds, two novel and improved synthetic approaches are developed. Almost every step of the synthesis has been optimized, including several important but not fully explored transformations, such as radical bromination with methyl pyridine and cyanide substitution with TMSCN. The 7-azabenzofuran core is prepared by an acylation-heterocyclization reaction, using acyl chloride as both the reactant and the activation reagent for the N-oxide substrate. Compared with the BMS synthesis, the overall yield has been tripled, and those harmful or cost-effective synthetic steps have been reduced. Furthermore, a transition-metal-free synthetic method for the construction of 3-cyano substituted 7-azabenzofurans is presented.

Spectrophotometric kinetic study of mercury(II)-catalyzed formation of [4-CNpyRu(CN)5]3− via ligand exchange reaction of hexacyanoruthenate(II) with 4-cyanopyridine: a mechanistic approach

The kinetics of the formation of yellow-colored complex [4-CNpy Ru(CN)5]3− via cyanide substitution from the coordination sphere of [Ru(CN)6]4− using Hg(II) as catalyst by nitrogen heterocyclic ligand 4-cyanopyridine (4-CNpy) has been studied spectrophotometrically in an aqueous medium by monitoring the increment in absorbance at 400 nm, the λmax of yellow-colored product [4-CNpy Ru(CN)5]3−. The reaction rate followed first-order kinetics in [4-CNpy] and was independent to [Ru(CN)64−]. The complex behavior in the reaction rate was observed with increasing [Hg2+]. Negative salt effect upon variation in ionic strength was noticed in the progressive course of the reaction. A suitable mechanistic scheme compatible with the experimental results has been suggested which is supported by activation parameters.

Treatment of Cyanide-Free Wastewater from Brass Electrodeposition with EDTA by Electrodialysis: Evaluation of Underlimiting and Overlimiting Operations.

Growing environmental concerns have led to the development of cleaner processes, such as the substitution of cyanide in electroplating industries and changes in the treatment of wastewaters. Hence, we evaluated the treatment of cyanide-free wastewater from the brass electroplating industry with EDTA as a complexing agent by electrodialysis, aimed at recovering water and concentrated solutions for reuse. The electrodialysis tests were performed in underlimiting and overlimiting conditions. The results suggested that intense water dissociation occurred at the cathodic side of the commercial anion-exchange membrane (HDX) during the overlimiting test. Consequently, the pH reduction at this membrane may have led to the reaction of protons with complexes of EDTA-metals and insoluble species. This allowed the migration of free Cu2+ and Zn2+ to the cation-exchange membrane as a result of the intense electric field and electroconvection. These overlimiting phenomena accounted for the improvement of the percent extraction and percent concentration, since in the electrodialysis stack employed herein, the concentrate compartments of cationic and anionic species were connected to the same reservoir. Chronopotentiometric studies showed that electroconvective vortices minimized fouling/scaling at both membranes. The electrodialysis in the overlimiting condition seemed to be more advantageous due to water dissociation and electroconvection.

Free-Cyanide Synthesis and Characterization of Cu–Zn Alloy by an Electrodeposition-Annealing Route

Substitution of cyanide in electroplating is a current challenge. We present an alternative method aiming to reduce the toxicity and the cost of electroplating of Cu–Zn alloy (usually prepared from cyanide baths) while maintaining the decorative qualities and anticorrosive properties of the coating. For this purpose, Cu–Zn alloys were obtained in two steps from non-cyanide electrolytes. First, a copper layer electrodeposited onto a nickel under-layer, followed by a thin layer of zinc from three different simple non-cyanide zinc baths. The Zn/Cu/Ni sandwich system was then subjected to heat treatment at a temperature of 400°C, to ensure the diffusion of zinc into the copper layer to give the desired Cu–Zn alloy structure. The synthesized films were characterized by using X-ray diffraction XRD, scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS). XRD demonstrated that the electrodeposited films are crystalline and present the Cu0.7Zn0.3 phase with preferential (111) orientation. An analysis of XRD patterns revealed that after heat treatment, the Cu–Zn alloys were composed of a predominating α-phase structure. The morphology and composition of the coatings depends on the zinc plating bath type. After annealing, well defined pseudospherical Cu–Zn grains were formed covering the entire substrate surface. The EDS analysis indicated the formation of Cu0.7Zn0.3 brass alloys. The results showed the feasibility of this low-cost new route for the preparation of good quality Cu–Zn alloys from cyanide-free electrolytes.

A study of the metallic silver dissolution with the MEA-NH3-Cu system

Leaching of silver from minerals has been studied for decades. Recently, research has been focused on the substitution of cyanide (because of its high toxicity) from hydrometallurgical operations. In this sense, the development of alternative-green leaching solutions for the recovery of metallic silver from minerals and urban mines is necessary. In this research, a thermodynamic-kinetic study of the alternative system “monoethanolamine (MEA)-ammonium sulfate-cupric sulfate” was performed for the dissolution of metallic silver, varying the pH and the cupric ion concentration at room temperature. Furthermore, this research aims to evaluate the silver dissolution behavior at a pH lower than 10.2, elucidating the rate determining step of the silver dissolution process at these conditions of pH and cupric ion concentration. Thermodynamic results confirm that the MEA and NH3 can complex silver generating the species: Ag(MEA)2 +, AgMEA-, Ag(NH3)2 +, AgNH3 + respectively. It was evaluated the effect of varying the pH (8.8, 9.9 and 9) and the cupric sulfate concentration (0.1, 0.15 and, 0.2 M at pH 9) on the kinetics of silver dissolution. The results revealed, the possibility to leach a 39% of silver using a leaching solution containing: 0.15 M cupric sulfate, 0.05 M MEA and 0.4 M ammonium sulfate at pH 9. The kinetic analysis showed that the silver dissolution is controlled by the diffusion of fluid species through a porous layer composed of copper oxides, which was ratified by SEM and EDS analysis. Finally the present paper, open the possibility to optimize the molar ratio MEA:NH3 to maximize the silver dissolution kinetics. Keywords: Leaching, metallic silver, MEA, ammonium.

Chronopotentiometry of an anion-exchange membrane for treating a synthesized free-cyanide effluent from brass electrodeposition with EDTA as chelating agent

Abstract The promising substitution of cyanide by EDTA as chelating agent in brass electrodeposition has been evaluated by many researchers in the last few years. This is very interesting for treating the effluent generated, since the presence of EDTA facilitates the recovery of the metals using electrodialysis, for example. Hence, using chronopotentiometry, our aim was to investigate the transport properties of the chelates involved in the potential treatment by electrodialysis of the effluent generated in the free-cyanide brass electrodeposition. We assessed the limiting current density, ohmic resistance, plateau length, concentration polarization and the undesirable precipitate formation in function of the solution pH, Cu2+/Zn2+ proportion and EDTA/Cu2+ molar ratio using the anionic HDX200 membrane. The pH solution showed a strong relation with all the properties and under higher pH, precipitate formation by the curves behavior was verified. Besides, the precipitate formation was also observed for the lower proportion of Cu2+, while no unexpected behavior was verified for Cu2+ concentrations ≥ Zn2+. Finally, the EDTA concentration altered only the limiting current density, since similar typical chronopotentiograms and current-voltage curves were obtained. It was found that the better conditions of the effluent to be treated may be pH 9/10, Cu2+ proportion = 50% and EDTA/Cu2+ = 2.5.

Inhibitory kinetic spectrophotometric method for the quantitative estimation of d-penicillamine at micro levels

Biologically active thiol, d-penicillamine (d-PA), based on the hard soft acid base (HSAB) principle, binds strongly with Hg(II) ions leading to the inhibition of the rate of Hg(II) catalyzed substitution of cyanide in hexacyanoruthenate(II) i.e. [Ru(CN)6]4− by nitroso-R-salt (NRS). This formed the basis for the development of a novel kinetic spectrophotometric method for the quantitative determination of d-PA at micro levels. The reaction was followed spectrophotometrically at 525nm (λmax of [Ru(CN)5NRS]3− complex) under optimized reaction conditions at 8.75×10−5M [Ru(CN)64−], 3.50×10−4M [NRS], pH7.00±0.02, ionic strength (μ) 0.1M (KCl) and temperature 45.0±0.1°C. The modified mechanistic scheme is proposed to understand the inhibition caused by d-PA on Hg(II) catalyzed substitution of cyanide by NRS in [Ru(CN)6]4−. The detection limit of the proposed method was found to be 2.5×10−7M. The method has successfully been applied for the determination of d-PA in real samples with quantitative results.

Catalytic ligand exchange reaction between hexacyanoferrate(II) and 4-cyanopyridine applied to trace kinetic analysis of palladium(II)

The present paper describes a novel and fairly inexpensive catalytic kinetic method for the determination of Pd2+ in the concentration range 17.71–177.14ppb (ngmL−1). The method is based on the catalytic effect of Pd2+ on the substitution of cyanide by 4-cyanopyridine (4-CNpy) in hexacyanoferrate(II) in acidic media. The reaction was followed by measuring an increase in the initial rate of the indicator reaction with respect to the product, [Fe(CN)5(4-CNpy)]3−, formation at 477nm. The effects of various parameters, such as pH and ionic strength of the reaction medium, concentration of the reactants and temperature, on the rate of the indicator reaction were studied to optimize the reaction conditions to achieve the highest sensitivity and to get lowest limit of detection of [Pd2+]. The fixed time procedure, as a measure of the initial rate, was followed to obtain a linear regression equation relating the absorbance and [Pd2+] in the range 17.71–177.14ppb i.e. 1×10−7 to 1×10−6molL−1. The effects of the presence of various cations commonly associated with Pd2+ and some anions have also been investigated and discussed. The detection limit of the method was calculated to be 9ppb. The maximum average error of the proposed method was quite low. The method was successfully applied for the determination of Pd2+ in synthetic and environmental water samples. The proposed method is selective, accurate and inexpensive compared to many other methods available in literature for Pd2+ determination.

Impact of sulfur heteroatoms on the activity of quaternary ammonium salts as phase transfer catalysts for nucleophilic displacement reactions

The application of a new class of alkylammonium salts as phase-transfer catalysts was investigated. These salts are tetra(4-thiaalkyl) ammonium bromides, and the key questions of the study focus on how the incorporation of a sulfur atom in the alkyl chains affects the efficacy of the salts as phase-transfer catalysts. Employing the nucleophilic substitution of cyanide for bromide on 1-bromopentane as a model reaction, reaction rate constants and activation energies are evaluated. The kinetic parameters obtained using the tetrathiaalkylammonium salts are compared to those obtained using their tetraalkylammonium analogs. The general trend is that the presence of sulfur in the alkyl chains reduces the reaction rates and increases activation energies. This trend is analyzed both in terms of computational modeling and experimental distribution coefficients to determine the cause of the slower reaction rates. Thiaquats are shown to distribute more into the aqueous phase than traditional quat salts of similar chain length, resulting in lower organic phase concentrations. Quantum calculations indicate stronger ion pairing for the thiaquats, increasing activation energies and slowing reaction rates. Thus, differences in rate enhancements are attributable both to phase distribution and ion pairing effects.

Efficient synthesis of prasugrel, a novel P2Y12 receptor inhibitor

An efficient synthesis of prasugrel, a novel P2Y12 receptor inhibitor, is described. The cyclopropyl-phenylethanone intermediate was prepared by cyanide substitution, bromination, N-substitution, and the Grignard reaction. After acid hydrolyzation of the methyl ether and subsequent acetylation, the title product was obtained with a total yield of 21% after 10 linear steps from simple and commercially available raw materials.

A kinetic method for the determination of organosulfur compounds by inhibition: determination of cysteine, 2,3-dimercaptopropanol and thioglycolic acid

A kinetic method for the determination of organosulfur compounds by UV spectrophotometry is described. Organosulfur compounds have been shown to inhibit the Hg(II)-catalyzed substitution of cyanide in hexacyanoferrate(II) by 2-methylpyrazine (2-Mepz). The inhibitory effect is proportional to the concentration of inhibitor and can be used as the basis for the determination of trace amounts of organosulfur compounds such as cysteine, 2,3-dimercaptopropanol (DMP) and thioglycolic acid (TGA). Both the influence of the reaction variables and interference of a variety of ions have been studied. A mechanism for the inhibition process is proposed. The determination range depends on the amount of Hg(II) added and stability of the Hg(II)–ligand complex. Kinetic parameters were determined from Lineweaver–Burk plots, obtained in the absence and presence of the inhibitor. Excellent linearity is observed for all analytes over their respective concentration ranges with correlation coefficient >0.9. The condition calibration curves were linear in the range of 5 × 10−6–15 × 10−6 M for cysteine, 1 × 10−7–7 × 10−7 M for DMP and 1 × 10−6–10 × 10−6 M for TGA. The detection limits were 1.18 × 10−7 M for cysteine, 4.16 × 10−8 M for DMP and 1.30 × 10−7 M for TGA. The effects of amino acids that can interfere in the determination of cysteine were studied.

Determination of trace amounts of mercury(II) in water samples using a novel kinetic catalytic ligand substitution reaction of hexacyanoruthenate(II)

A simple, sensitive, selective and rapid kinetic catalytic method has been developed for the determination of Hg(II) ions at micro-level. This method is based on the catalytic effect of Hg(II) ion on the rate of substitution of cyanide in hexacyanoruthenate(II) with nitroso-R-salt (NRS) in aqueous medium and provides good accuracy and precision. The concentration of Hg(II) catalyst varied from 4.0 to 10.0 × 10 −6 M and the progress of reaction was followed spectrophotometrically at 525 nm ( λ max of purple-red complex [Ru(CN) 5NRS] 3−, ɛ = 3.1 × 10 3 M −1 s −1) under the optimized reaction conditions; 8.75 × 10 −5 M [Ru(CN) 6 4−], 3.50 × 10 −4 M [nitroso-R-salt], pH 7.00 ± 0.02, ionic strength, I = 0.1 M (KCl), temp 45.0 ± 0.1 °C. The linear calibration curves, i.e. calibration equations between the absorbance at fixed times ( t = 15, 20 and 25 min) versus concentration of Hg(II) ions were established under the optimized experimental conditions. The detection limit was found to be 1.0 × 10 −7 M of Hg(II). The effect of various foreign ions on the proposed method has also been studied and discussed. The method has been applied to the determination of mercury(II) in aqueous solutions.