Kinetics of reactions of 2,2′-bipyridyltetracarbonylmolybdenum(0)

Summary Kinetic results are presented for reaction of Mo(CO)₄(bipy) with cyanide in several nonaqueous solvents and in DMSO-H₂O mixtures, with methoxide, and with azide; for reaction of Mo(CO)₄(5-NO₂phen) with cyanide and with methoxide; and for reaction of Mo(CO)₄(phen) and of W(CO)₄(bipy) with cyanide. Solvent effects on the reaction of Mo(CO)₄(bipy) with cyanide are dissected into their initial state and transition state components. Here, and in the dependence of the activation volume for this and related reactions on solvent, the important role played by cyanide solvation is apparent. Preliminary investigations on reactions of compounds of this M(CO)₄(diimine) type with tertiary phosphines, diethyldithiocarbamate, and ether peroxides are described.     

Kinetics of solvolysis and cyanide attack at 2-benzoylpyridine-iminemolybdenum(0) tetracarbonyl and related compounds

Summary The kinetics of reaction of [Mo(CO)₄(bpami)], where bpami is the Schiff base derived from 2-benzoyl pyridine and ammonia, with cyanide in several solvents show parallel solvolysis and cyanide attack. Rate laws and activation parameters are consistent with an associative mechanism for the predominant pathway, cyanide attack. From kinetic and solubility measurements it is possible to analyse solvent effects on reactivity for these reactions into initial state and transition state contributions. Rate constant trends in binary mixtures of non-aqueous solvents can be understood in terms of preferential solvation of the molybdenum compound and of cyanide. Finnlly, ligand effects on reactivity have been established for a number of [Mo(CO)₄(diimine)] complexes; over a 5×10⁴ times range in rate constants for cyanide attack there is a marked correlation of reactivity with MLCT frequencies for the metal to diimine charge-transfer band.     

Determination of cyanides in electroplating solutions as Ni(CN)42– and analysis by capillary electrophoresis

A CE method was developed for the determination of total (free and weakly bound) cyanide in electroplating solutions based on the use of a cationic surfactant (TTAB) and complexation with Ni(II)-NH₃ solutions to Ni(CN)₄ ^2–. Both direct complexation and cyanide distillation combined with complexation were tested. Under optimized conditions, this method is time-saving compared to standard methods. Total cyanide determined by CE had detection limits (with respect to the initial sample concentration) of 0.5 μg/mL for direct complexation and 50 ng/mL for distillation combined with complexation. Total cyanide and cyanide not amenable by chlorination (CNAC) were determined in real samples from spent electroplating baths.     

Color Reaction Between 4-(2-Pyridylazo)Resorcinol and Mercury (II) in the Presence of Surfactant,and Improved Spectrophotometric Determinations of Mercury(II) and Cyanide Ion with its Coloring

Abstract

The reactions among 4-(2-pyridylazo)resorcinol (PAR), mercury(II) and/or cyanide ion in the presence of water soluble surfactants alone or combination were systematically investigated at about pH 9. The spectrophotometric determinations of mercury(II) and cyanide ion were investigated by using the PAR-mercury(II)-HPC complex (3:2:2 molar ratio) in the presence of N-hexadecylpyridinium chloride (HPC) alone; calibration graphs were rectilinear in the ranges of 0 – 40 μg mercury(II) and 0 –10 μg cyanide ion in a final 10 ml with the apparent molar absorptivities of 5.9 × 10⁴ for mercury(II) and 2.5 × 10⁴ 1 mol^?1 cm^?1 for cyanide ion at 590 nm. The proposed method had advantages—rapidity, simplicity without solvent extraction, and sensitivity in comparison with reported solvent extraction methods. The interference of foreign ions decreased 1/2–l//4-fold compared with that in the presence of non-ionic surfactant alone.     

Determination of cyanides in electroplating solutions as Ni(CN)42– and analysis by capillary electrophoresis

A CE method was developed for the determination of total (free and weakly bound) cyanide in electroplating solutions based on the use of a cationic surfactant (TTAB) and complexation with Ni(II)-NH₃ solutions to Ni(CN)₄ ^2–. Both direct complexation and cyanide distillation combined with complexation were tested. Under optimized conditions, this method is time-saving compared to standard methods. Total cyanide determined by CE had detection limits (with respect to the initial sample concentration) of 0.5 μg/mL for direct complexation and 50 ng/mL for distillation combined with complexation. Total cyanide and cyanide not amenable by chlorination (CNAC) were determined in real samples from spent electroplating baths. Received: 5 February 1998 / Revised: 26 July 1998 / Accepted: 1 August 1998     

Class III Delocalization in a Cyanide‐Bridged Trimetallic Mixed‐Valence Complex

The NIR and IR spectroscopic properties of the cyanide‐bridged complex, trans‐[Ru(dmap)₄{(μ‐CN)Ru(py)₄Cl}₂]³⁺ (py=pyridine, dmap=4‐dimethylaminopyridine) provide strong evidence that this trimetallic ion behaves as a Class III mixed‐valence species, the first example reported of a cyanide‐bridged system. This has been accomplished by tuning the energy of the fragments in the trimetallic complex to compensate for the intrinsic asymmetry of the cyanide bridge. Moreover, (TD)DFT calculations accurately predict the spectra of the trans‐[Ru(dmap)₄{(μ‐CN)Ru(py)₄Cl}₂]³⁺ ion and confirms its delocalized nature.     

A New Spectrophotometry Determination of Cyanide by Solvent Extraction as Tris-(1,10-Phenanthroline)-Iron (II)-Thiocymate

Abstract

By shaking aqueous cyanide solution with nitrobenzene contained sulfur, thiocyanate is formed and is extracted into the nitrobenzene as an ion pair of thiocyanate anion and tris-(1,10-phenanthroline)-iron(II) chelate cation. By measuring the color intensity of the organic phase at 516 nm, cyanide is determined spectrophotometrically. A linear calibration curve is obtained up to 4 × 10^?5M of cyanide in the aqueous phase.     

Proton‐Coupled Reduction of an Iron Cyanide Complex to Methane and Ammonia

Nitrogenase enzymes mediate the six‐electron reductive cleavage of cyanide to CH₄ and NH₃. Herein we demonstrate for the first time the liberation of CH₄ and NH₃ from a well‐defined iron cyanide coordination complex, [SiP^iPr₃]Fe(CN) (where [SiP^iPr₃] represents a tris(phosphine)silyl ligand), on exposure to proton and electron equivalents. [SiP^iPr₃]Fe(CN) additionally serves as a useful entry point to rare examples of terminally‐bound Fe(CNH) and Fe(CNH₂) species that, in accord with preliminary mechanistic studies, are plausible intermediates of the cyanide reductive protonation to generate CH₄ and NH₃. Comparative studies with a related [SiP^iPr₃]Fe(CNMe₂) complex suggests the possibility of multiple, competing mechanisms for cyanide activation and reduction.     

Addition of the cyanide ion to cyclopentadienyliron complexes of arenes containing an electron-withdrawing substituent

Reactions of cyclopentadienyliron (CpFe) complexes of arenes containing an electron-withdrawing substituent with NaCN in DMF resulted in a regiospecific addition of the cyanide ion at a position ortho to the substituent, giving rise to CpFe complexes of cyanocyclohexadienyl systems. For example, the addition of the cyanide ion to η⁶-nitrobenzene-η⁵-cyclopentadienyliron hexafluorophosphate (Ia) gave the neutral complex, 1-5-η⁵-exo-6-cyano-1-nitrocyclohexadienyl-η⁵-cyclopentadienyliron (IIa). Similar cyanide additions also took place with the CpFe complexes of benzophenone and of methyl benzoate. Reactions with η⁶-anthraquinone, xanthone, thioxanthone, or thioxanthone-10,10-dioxide-η⁵-cyclopentadienyliron hexafluorophosphate (IIIa, IIIb, IIIc or IIId, respectively) resulted in the addition of the cyanide ion solely to C(1), a position ortho to the keto substituent; for example, from IIIa, the adduct was 2,3,4,4a,9a-η⁵,-exo-1-cyano-1H-anthraquinone-η⁵-cyclopentadienyliron (IVa). With the CpFe complex of fluorenone (V), however, a 3/1 mixture of products was obtained, arising from cyanide additions to C(1) and C(4a), both positions being ortho to the keto substituent in V. A possible explanation is suggested for the failure of the cyanide ion adding to C(4a) in reactions with IIIa to IIId.     

A novel spectrophotometric method for batch and flow injection determination of cyanide in electroplating wastewater

A sensitive and highly selective spectrophotometric method is described for the determination of cyanide. It is based on a reaction of cyanide with aquacyanocobyrinic acid heptamethyl ester (ACCbs) reagent (orange color) at pH 9.5 to give dicyanocobester (DCCbs) (violet color). The increase of the absorption bands of the reaction product at 368 and 580 nm and the decrease of the reagent band at 353 nm are linearly proportional to the cyanide concentration. The method is used in static mode for determining cyanide over the concentration range 0.04-1.20 μg ml⁻¹ with a detection limit of 0.02 μg ml⁻¹ and for hydrodynamic analysis of 0.4-5.2 μg ml⁻¹ cyanide. Application for batch and flow injection monitoring of cyanide in electroplating wastewater samples gives results agree within ± 1.2% with those obtained by the standard potentiometry using the cyanide ion selective electrode. The method is practically free from interferences by PO₄³⁻, NO₃⁻, NO₂⁻, SO₄²⁻, F⁻, Cl⁻, Br⁻, I⁻, S²⁻ and SCN⁻ ions and gives results with average recoveries of 97.6-99.2%. Advantages offered by using ACCbs as a chromogen for cyanide assay are: (i) high selectivity and sensitivity of the coordination site of the reagent towards cyanide ion; (ii) fast reaction, since legation takes place at the axial position of the reagent; (iii) good solubility and stability of the reagent in aqueous solutions over a wide pH range; (iv) high stability of the reagent (ACCbs) and the colored complex product (DCCbs) and (v) possible absorbance measurements at three different wavelengths.     

Normal pulse polarographic quantification of cyanide and sulfide by the anodization of mercury

Normal pulse polarography is used to quantify cyanide and sulfide simultaneously by the anodic oxidation of mercury. The detection limit for cyanide is 18 μg l^-1 by the normal pulse polarographic technique. A supporting electrolyte system of 1 M Na₂CO₃ is optimal with regard to background interferences and sample loss. The electrode reaction for the oxidation of mercury in the presence of cyanide can be described by Hg + pCN^- α Hg(CN)_p^2-p + 2e^-, with p having values of 2, 3 and 4 depending on the surface concentration of cyanide. The feasibility of simultaneous cyanide and sulfide quantification is demonstrated with waste-water samples.     

Kinetics and mechanism of pentacyanohydroxoferrate(III) formation from the reaction of cyanide ion with [Fe2L(OH)2]2− (L=triethylenetetraaminehexaacetate)

Summary The kinetics and mechanism of the reaction between [Fe₂L(OH)₂]^2– and cyanide ion (L = TTHA, triethylenetetraaminehexaacetate) have been studied spectrophotometrically atpH=11.0±0.1,I=0.1 M(NaClO₄) and T = 25±0.1 °C. The overall reaction consists of three distinct, observable stages. The first stage involves the dissociation of the binuclear complex into a mononuclear complex [FeL(OH)]^4– which then reacts with cyanide to form [Fe(CN)₅OH]^3–. The species [Fe(CN)₅OH]^3– reacts further with an excess of cyanide and forms [Fe(CN)₆]^3– in the second stage of reaction. The last stage involves the reduction of [Fe(CN)₆]^3– formed in the second stage by the TTHA^6– released in the first stage of reaction. The formation of [Fe(CN)₅OH]^3– in the first stage is firstorder in [Fe₂L(OH)₂]^2– and third-order in cyanide over a large range of cyanide concentrations but becomes zero-order in cyanide at [CN^–] < 4×10^–2M.These observations enable us to suggest the presence of a slow step in which [Fe₂L(OH)₂]^2– dissociates into [FeL(OH)]^4– and [FeOH]²⁺ at low cyanide concentrations and a cyanide assisted rapid dissociation of [Fe₂L(OH)₂]^2– to [FeL(OH)(CN)]^5– at higher cyanide concentrations. The species [FeL(OH)(CN)]^5– reacts further with an excess of cyanide to produce [Fe(CN)₅OH]^3– finally.The reverse reaction between [Fe(CN)₅OH]^3– and TTHA^6– follows first-order dependence in each of [Fe(CN)₅OH]^3– and TTHA^6– and inverse first-order dependence on cyanide concentration. A six-step mechanism has been proposed for the first stage of reaction in which the fifth has been identified as the rate-determining step.     

Single-drop method for determination of cyanide in solution with a piezoelectric quartz crystal

The change in frequency of a horizontal quartz crystal in contact with a single drop of solution is measured. When the gold electrode of the crystal is dissolved by reaction with cyanide in alkaline solution, the further change of frequency is linearly related to cyanide concentration in the range 10^-3–10^-4 M at pH 10.4. Only silver(I) and mercury(II) interfere if EDTA is added.     

A novel spectrophotometric method for determination of cyanide using cobalt (II) phthalocyanine tetracarboxylate as a chromogen

Cobalt (II) phthalocyanine tetracarboxylate [Co (II)Pc-COOH] has been prepared and used in aqueous solutions as a novel chromogenic reagent for the spectrophotometric determination of cyanide ion. The method is based on measuring the increase in the intensity of the monomer peak in the reagent absorbance at 682 nm due to the formation of a 1 : 2 [Co (II)Pc-COOH] : [CN] complex. The complex exhibits a molar absorptivity (ε) of 7.7 × 10⁴ L mol^?1 cm^?1 and a formation constant (K_f ) of 5.4 ± 0.01 × 10⁶ at 25 ± 0.1°C. Beer's law is obeyed over the concentration range 0.15–15 µg mL^?1 (5.8 × 10^?6–5.8 × 10^?4 M) of cyanide ion, the detection limit is 20 ng mL^?1 (7.7 × 10^?7 M) the relative standard deviation is ±0.7% (n = 6) and the method accuracy is 98.6 ± 0.9%. Interference by most common ions is negligible, except that by sulphite. The proposed method is used for determining cyanide concentration in gold, silver and chromium electroplating wastewater bath solutions after a prior distillation with 1 : 1 H₂SO₄ and collection of the volatile cyanide in 1 M NaOH solution containing lead carbonate as recommended by ASTM, USEPA, ISO and APAHE separation procedures. The results agree fairly well with potentiometric data obtained using the solid state cyanide ion selective electrode.     

Quality control of analyses of mercury in hair

Summary Flow injection analysis (FIA) has been combined with a dialysis unit in order to study the effect of interferences in the determination of free cyanide in waste water. Two kinds of interferences, metals and inorganic anions, were studied. In all the cases, solutions of constant cyanide concentration containing interferences were introduced in the FIA system and free cyanide was determined after hydrogen cyanide passes the dialysis membrane.Results reveal the advantages of this methodology for Zn(II), Cu(I), Cd(II), Nr ₄ ⁺ and inorganic anions. Fe(III), Co(II), Ni(II) and carbonate show different behaviour under these conditions.

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Entfernung von Störungen bei der spektralphotometrischen Cyanidbestimmung unter Verwendung von Dialyse und Fließinjektion

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Presented at Euroanalysis VI, Paris, September 8–11, 1987     

A new generation of cyanide ion-selective membranes for flow injection application: Part III. A simple approach to the determination of toxic metal-cyanide complexes without preliminary separation

A new flow injection approach to total weak acid-dissociable (WAD) metal–cyanide complexes is proposed, which eliminates the need of a separation step (such as gas diffusion or pervaporation) prior to the detection. The cornerstone of the new methodology is based on the highly selective flow-injection potentiometric detection (FIPD) system that makes use of thin-layer electroplated silver chalcogenide ion-selective membranes of non-trivial composition and surface morphology: Ag_2 + δSe_1 − xTe_x and Ag_2 + δSe. An inherent feature of the FIP-detectors is their specific response to the sum of simple CN⁻ + Zn(CN)₄²⁻ + Cd(CN)₄²⁻. For total WAD cyanide determination, ligand exchange (LE) and a newly developed electrochemical pre-treatment procedure for release of the bound cyanide were used. The LE pre-treatment ensures complete recovery only when the sample does not contain Hg(CN)₄²⁻. This limitation is overcome by implementing electrochemical pre-treatment which liberates completely the bound WAD cyanide through cathodic reduction of the complexed metal ions. A complete recovery of toxic WAD cyanide is achieved in the concentration range from 156 μg L⁻¹ up to 13 mg L⁻¹. A three-step protocol for individual and group WAD cyanide speciation is proposed for the first time. The speciation protocol comprises three successive measurements: (i) of non-treated, (ii) LE-exchange pre-treated; (iii) electrochemically pre-treated sample. In the presence of all WAD complexes this procedure provides complete recovery of the total bound cyanide along with its quantitative differentiation into the following groups: (1) Hg(CN)₄²⁻; (2) CN⁻ + Cd(CN)₄²⁻ + Zn(CN)₄²⁻; (3) Cu(CN)₄³⁻ + Ni(CN)₄²⁻ + Ag(CN)₂⁻. The presence of a 100-fold excess in total of the following ions: CO₃²⁻, SCN⁻, NH₄⁺, SO₄²⁻ and Cl⁻ does not interferes. Thus the proposed approach offers a step ahead to meeting the ever increasing demand for cyanide-species-specific methods. The equipment simplicity makes the procedure a good candidate for implementing in portable devices for in-field cyanide monitoring.     

Voltammetric evaluation of the electrode material on the oxidation of cyanide catalyzed by copper ions

The cyanide oxidation on vitreous carbon (VC), stainless steel 304 (SS 304) and titanium (Ti) was investigated through a voltammetric study of cyanide solutions also containing copper ions. Results showed that cyanide oxidation occurs by means of a catalytic mechanism involving adsorbed species as CN^–, Cu(CN)₄^3– or Cu(CN)₄^2– depending on the electrode material. It was observed that on VC, the adsorption of Cu(CN)₄^3– controlled the oxidation rate. Instead, for SS 304 and Ti, the adsorption of CN^– controlled the global process. However, in all cases, the adsorption of Cu(CN)₄^3– on the electrode surface was required for the catalytic oxidation of CN^–. Voltammetric experiments for solutions containing cyanide oxidation products, such as cyanogen (CN)₂ and cyanate (CNO^–), confirmed that the adsorbed species mentioned above controlled the catalytic oxidation of CN^– depending on the electrode material. A voltammetric identification of the oxidation products showed that cyanogen, (CN)₂ tended to adosorb on VC, while the formation of cyanate, CNO^– predominated on SS 304.     

Synthesis and properties of sulfur cyanide trifluoride,SF3CN,sulfur dicyanide difluoride,SF2(CN)2, and sulfinyl cyanide fluoride,FS(O)CN

Sulfur cyanide trifluoride, SF₃CN, and sulfur dicyanide difluoride, SF₂(CN)₂, have been prepared by metathesis between sulfur tetrafluoride, SF₄, and trimethyl silyl cyanide, (CH₃)₃SiCN, at – 30°C. Treatment of SF₃CN with freshly sublimed selenium dioxide, SeO₂, lead to sulfinyl cyanide fluoride, FS(O)CN. IR, Raman, ¹⁹F-NMR, uv and mass spectra of the novel compounds are presented as well as some physical and chemical properties.     

Photodissociation of gaseous [C4H5N]+˙ ions

The photodissociation of [C₄H₅N]⁺˙ ions generated by ionization of pyrrole (1), allyl cyanide (2), crotonitrile (3), cyclopropyl cyanide (4) and methacrylonitrile (5) has been studied using ion beam techniques. At least four different stable ion structures have been distinguished, which is in contrast to earlier CAD studies. In addition it has been shown that [C₂H₃N]⁺˙ fragment ions formed by dissociative ionization of the same precursors have structures which are distinct from that of ionized acetonitrile.     

Simple Michael acceptor type coumarin derived turn-on fluorescence probes to detect cyanide in pure water

The present article describes design and synthesis of coumarin derived chemical reaction based chemodosimeter to recognize cyanide in aqueous medium. The Michael acceptor type coumarin derived probes 3 and 4 upon interaction with cyanide undergo Michael type nucleophilic addition reaction to form adducts in which fluorescence intensity was significantly enhanced, ‘turn-on’ by the change in intramolecular charge transfer (ICT) mechanism. The nonfluorescent color of solutions changed to a naked-eye sensitive fluorescent blue (switched-on). Job’s plot analysis revealed a 1:1 stoichiometry for the interaction between the probe and cyanide anion with a high detection limit.