Osmium(VIII) catalyzed oxidation of a sulfur containing amino acid—a kinetics and mechanistic approach

The kinetics of osmium (VIII) catalyzed oxidation of DL-methionine by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm^?3 was studied spectrophoto-metrically. The reaction between hexacyanoferrate(III) and DL-methionine in alkaline medium exhibits 2:1 stoichiometry (2HCF:DL-methionine). The reaction is of first order each in [HCF] and [Os(VIII)], less than unit order in [alkali] and zero order for [DL-methionine]. The decrease in dielectric constant of the medium increases the rate of the reaction. The added products have no effect on the rate of reaction. The main products were identified by spot test. A free radical mechanism has been proposed. In a prior equilibrium step Os(VIII) binds to OH^? species to form a hydroxide species and reacts with [Fe(CN)₆]^3? in slow step to form an intermediate species(C₁). This reacts with a molecule of DL-methionine in a fast step to give the sulfur radical cation of methionine and yields the sulfoxide product by reacting with another molecule of [Fe(CN)₆]^3?. The rate constant of the slow step of the mechanism is calculated. The activation parameters with respect to slow step of the mechanism are evaluated and discussed.     

Osmium(VIII)/Ruthenium(III) Catalysed Oxidation of l-lysine by Diperiodatocuprate(III) in Aqueous Alkaline Medium: A Comparative Mechanistic Approach by Stopped Flow Technique

Abstract The kinetics of osmium(VIII) and ruthenium(III) catalysed oxidation of l-lysine (l-lys) by diperiodatocuprate(III) (DPC) in alkaline medium at a constant ionic strength of 0.15 mol dm⁻³ was studied spectrophotometrically. The reaction between l-lys and DPC in alkaline medium exhibits 1:2 stoichiometry in both catalysed reaction (l-lys: DPC). The reaction is first order in [DPC] and has less than unit order both in [l-lys] and [alkali]. Increase in periodate concentration decreases the rate. Intervention of free radicals was observed in the reaction. The main products were identified by spot test, IR and GC-MS studies. Probable mechanisms are proposed and discussed. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The active species of catalyst and oxidant have been identified. Graphical Abstract The kinetic and mechanistic investigations of the reaction between DPC and l-lysine has been studied in presence of microamounts of ruthenium(III) and osmium(VIII) in alkaline medium. The monoperiodatoargentate(III), [Ru(H₂O)₅OH]²⁺ and [OsO₄(OH)₂]²⁻ are considered as the active species of oxidant, DPC, ruthenium(III) and osmium(VIII) respectively.      

Mechanistic Aspects of Os(VIII)/Ru(III) Catalysed Oxidation of L-phenylalanine by Ag(III) Periodate Complex in Aqueous Alkaline Medium

The kinetics of oxidation of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalysed oxidation of L-phenylalanine (L-Pal) by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at 27 °C and a constant ionic strength of 0.25 mol dm^?3 was studied spectrophotometrically. The involvement of free radicals was observed in the reactions. The reaction between DPA and L-Pal in alkaline medium exhibits stoichiometry as [L-Pal]:[DPA] = 1:1. The reaction is of first order in [Os(VIII)], [Ru(III)] and [DPA] and has negative fractional order in [IO₄ ^?]. It has less than unit order in [L-Pal] and [OH^?]. However, the order in [L-Pal] and [OH^?] changes from first order to zero order as their concentrations increase. The main oxidation products were identified by spot test and spectral studies. The probable mechanisms were proposed and discussed. The catalytic constant (K _c) was also calculated for Os(VIII) and Ru(III) catalysis at different temperatures. The activation parameters with respect to slow step of the mechanisms were computed and discussed and thermodynamic quantities were also calculated. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The active species of catalyst and oxidant have been identified.     

Homonuclear tris-dithiocarbamato ruthenium(III) complexes as single-molecule precursors for the synthesis of ruthenium(III) sulfide nanoparticles

Tris(N-phenyldithiocarbamato) ruthenium(III) complexes, [Ru(L¹)₃] (1); tris(N-(4-methylphenyl)dithiocarbamato)) ruthenium(III), [Ru(L²)₃] (2); and tris(N-(4-methoxyphenyl)dithiocarbamato)) ruthenium(III), [Ru(L³)₃] (3) were synthesized and characterized by elemental analysis, thermogravimetric analysis, FTIR, UV–VIS and NMR spectroscopy. TGA analyses show major degradation of all complexes in the range 120–350°C, leading to the formation of residual weight corresponding to ruthenium (III) sulfides. The ¹H-NMR spectra of the ligands and complexes are in agreement with the proposed structures. FTIR studies confirmed that the ligands coordinate the Ru³⁺ ion in a bidentate chelating mode. The complexes were thermolysed at 180°C to prepare hexadecylamine-capped Ru₂S₃ nanoparticles. Powder X-ray diffraction patterns revealed the formation of hexagonal-phase Ru₂S₃ nanoparticles with average crystallite sizes ranging from 8.3 to 9.5?nm. TEM images showed the crystalline clusters with shapes ranging from square to hexagonal, while SEM images elucidated that the particles were agglomerated. Energy-dispersive X-ray spectra confirmed the presents of Ru₂S₃ nanoparticles.     

Kinetics of graft copolymerization of poly(hexanedioic acid ethylene glycol) and methyl acrylate initiated by potassium diperiodatocuprate(III)

A redox system, potassium diperiodatocuprate(III) [DPC]/poly(hexanedioic acid ethylene glycol) (PEA) system, was employed to initiate graft copolymers of methyl acrylate (MA) and PEA in alkaline medium. The results indicate that the equation of the polymerization rate (R_p) is as follows: R_p = k [MA]^1.62[Cu(III)]^0.69, and that the overall activation energy of graft polymerization is 42.5 kJ/mol. The total conversion at different conditions (concentration of reactants, temperature, concentration of the DPC, and reaction time) was also investigated. The infrared spectra proved that the graft copolymers were synthesized successfully. Some basic properties of the graft copolymer were studied by instrumental analyses, including thermogravimetry and scanning electron microscope. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2376–2381, 2007     

Investigation of electron-transfer reaction between alkaline hexacyanoferrate(III) and ranitidine hydrochloride – a histamine H2 receptor antagonist,in the presence of homogenous ruthenium(III) catalyst

The ruthenium(III)-catalyzed electron-transfer reaction between hexacyanoferrate(III) and ranitidine hydrochloride is studied in alkaline medium at 25°C and at an ionic strength of 1.10?mol/dm³. The reaction stoichiometry is established and is found to be 1:4, that is, for the oxidation of one mole of ranitidine, four moles of hexacyanoferrate(III) are consumed. The reaction products were characterized by spectral studies such as IR, GC-MS, ¹H-NMR and ¹³C-NMR. The reaction rate shows a less than unit order in substrate and alkali and a first-order dependence in oxidant, [Fe(CN)₆]^3? and the catalyst, ruthenium(III) concentrations. The active species of ruthenium(III), [Ru(H₂O)₅OH]²⁺, forms an intermediate complex with the substrate. The attack of complex by hexacyanoferrate(III) in the rate determining step produces a radical cation, which is further oxidized in the subsequent step to form the oxidation product. The effect of the reaction environment on the rate constant upon adding varying concentrations of KNO₃ and t-butanol was studied. The initially added products did not have any significant effect on the reaction rate. A plausible mechanism is proposed based on the experimental results. The effect of varying temperature on the reaction rate was also studied. The activation parameters for the slow step and the thermodynamic quantities for the equilibrium steps were evaluated.

The mechanism of title reaction has been studied and one mole of ranitidine consumes four moles of [Fe(CN)₆]^3?, as shown in the following equation:     

Kinetic,Mechanistic and Spectral Investigation of Ruthenium(III) Catalysed Oxidation of Atenolol by Alkaline Diperiodatonickelate(IV) (Stopped Flow Technique)

The kinetics of ruthenium(III) catalysed oxidation of atenolol by diperiodatonickelate(IV) (DPN) in alkaline medium at a constant ionic strength of 1.0 mol dm^–3 has been studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 1:1 stoichiometry (DPN:atenolol). The reaction shows first order dependence on [DPN] and [Ruthenium(III)] and apparent less than unit order dependence each in atenolol and alkali concentrations. Addition of periodate has no effect on the rate of reaction. Effect of added products, ionic strength and dielectric constant of the reaction medium have been investigated. The main products were identified by IR, NMR, fluorimetry and mass spectral studies. The results suggest the formation of a complex between the atenolol and ruthenium(III) species which reacts with one mole of diperiodatonickelate(IV) species in a rate determining step, resulting in the formation of a free radical, which in a subsequent fast step yields the products. The reaction constants involved in the mechanism were evaluated. The activation parameters were computed with respect to the slow step of the mechanism and discussed.     

Ru(III)/Os(VIII) Catalysed Oxidation of Gabapentin (Neurotin) Drug by Diperiodatoargentate(III) in Aqueous Alkaline Medium (Stopped Flow Technique): A Comparative Study

The kinetics of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalysed oxidation of neuroleptic drug, gabapentin (GBP) by diperiodatoargentate(III) (DPA) in alkaline medium at 27 °C and a constant ionic strength of 0.60 mol dm^?3 was studied spectrophotometrically. The oxidation products in both the cases are 1-(hydroxymethyl) cyclohexane acetic acid and Ag(I). The stoichiometry is the same in both the catalysed reactions i.e. [gabapentin]:[DPA] = 1:1. The reaction is of first order in Os(VIII)/Ru(III) and [DPA] and has less than unit order in both [GBP] and [alkali]. The oxidation reaction in alkaline medium has been shown to proceed via a Os(VIII)/Ru(III)-gabapentin complex, which further reacts with one mole of monoperiodatoargentate(III) (MPA) species in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectroscopic studies. The reaction constants involved in the different steps of the mechanism are calculated. The catalytic constant (K _c) was also calculated for both catalysed reactions at different temperatures. From the plots of log K _c versus 1/T, values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII)>Ru(III). The probable active species of catalyst and oxidant have been identified.     

Photopolymerization of Methyl Methacrylate Sensitized by Tris(2,2′-bipyridine)iron(III)

The photopolymerization of methyl methacrylate (MMA) sensitized by tris(2,2′-bipyridine)iron(III ) complex, [Fe(bpy)₃]³⁺, was studied at 35°C in the presence of an electron donor, triethylamine (TEA) with UV radiation of wavelength 254nm. The initial rate of polymerization, R_p, shows a linear dependence on [MMA] with an exponential value of 1·18±0·04. R_p varies linearly with the square root of the photosensitizer concentration up to 2·00×10^-4moll^-1, and above this concentration, R_p decreases with the increase of photosensitizer concentration. The rate of polymerization is not affected by the concentration of the co-initiator, [TEA]. A suitable mechanism for the reaction is proposed to explain the kinetics of the reaction. © 1997 SCI.     

Synthesis and characterization of copper(I) complexes from triphenylphosphine and isatin Schiff bases of semi- and thiosemicarbazide

The reaction of isatin-3-thiosemicarbazone (ITC, 1) or isatin-3-semicarbazone (ISC, 2) with nitrato bis(triphenylphosphine)copper(I) gave the four coordinate copper(I) complexes [Cu(PPh₃)₂(ITC)]NO₃ (3) and [Cu(PPh₃)₂(ISC)]NO₃ (4). The synthesized complexes were characterized by FT-IR, UV–VIS, Raman and elemental analysis. The crystal structure of 3 was investigated by single crystal X-ray diffraction. The ITC coordinates to the copper(I) ion in a bidentate fashion via the N(imine) and S atoms which along with two triphenylphosphine ligands form a tetracoordinate complex. The complex has a distorted tetrahedral coordination environment. Crystal data at 150.0 K: space group P2₁/c with a=12.5777(4), b=15.2062(5), c=21.9057(7) Å, β=95.628(3)^o, Z=4, R ₁=0.049.

     

NMR STUDY OF LANTHANIDE(III) NITRATE-CMPO EXTRACTION SYSTEM (II)MOLECULAR MOVEMENT OF CMPO AND La(III)(NO3) 3-CMPO COMPLEX AND LIGAND-EXCHANGE REACTION FOR Eu(III)-CMPO AND Gd(III)-CMPO SYSTEMS

ABSTRACT

NMR( Nuclear Magnetic Resonance ) measurements were car ried out to study the molecular movement of CMPO and La(III)(NO₃) _3? CMPO complex and the ligand-exchange reaction for Eu(III) and Gd(III)-CMPO systems. From the ¹³C relaxation time measurement of La(NO₃) ₃ 3CMPO it was found that the T₁ value for the isobutyl CH and CH₂ carbons and the carbonyl carbon became considerably shorter on complexation, indicating that the carbonyl group participates in the bonding between CMPO and La³⁺ ion as well as the phosphoryl group. The numbers of CMPO molecules coordinated to Eu³⁺ and Gd³⁺ ions in CDCl₃ solution were estimated to be 3 and 2, respectively, in the presence of excess CMPO. The activation parameters for the ligand-exchange reaction were evaluated to be ΔH^* = 37.8±1.9[kJ/mol],ΔS^* = -59.9±6.5[J/molk? K] and ΔH^* = 41.3±1.6[kJ/mol], ΔS^* = -44.1±5.3[J/mol-K] for Eu(III)-CMPO and Gd(III)-CMPO systems, respectively. The independence of the exchange rate constants on the concentration of CMPO indicates that these ligand-exchange reactions seem to proceed through either a dissociative ( D ) mechanism or an interchange dissociative ( Id ) mechanism characterized by a stability constant of outer-sphere complex( KQ ) ≥ 100.     

Kinetics of Solvent Extraction of Iron(III) from Sulfate Medium by Purified Cyanex 272 using a Lewis Cell

Abstract

The kinetics of the forward and backward extraction of the title process have been investigated using a Lewis cell operated at 3 Hz and flux or (F) – method of data treatment. The dependences of (F) in the forward extraction on [Fe³⁺], [H₂A₂]_(o), pH, and [HSO₄ ^?] are 1, 0.5, 1, and ?1, respectively. The value of the forward extraction rate constant (k _f ) has been estimated to be 10^?7.37 kmol^3/2 m^?7/2 s^?1. The analysis of the experimentally found flux equation gives the following simple equation: F _f =10^0.13 [FeHSO₄ ²⁺] [A^?], on considering the monomeric model of BTMPPA and the stability constants of Fe(III)‐HSO₄ ^? complexes. This indicates the following elementary reaction occurring in the aqueous film of the interface as rate determining: [FeHSO₄]²⁺+A^?→[FeHSO₄.A]⁺. The very high activation energy of 91 kJ mol^?1 supports this chemical reaction step as rate-determining. The negative value of the entropy change of activation (?94 J mol^?1 K^?1) indicates that the slow chemical reaction step occurs via the S_N2 mechanism.

The backward extraction rate can be expressed by the equation: F _b =10^?5.13 [[FeHSO₄A₂]]_(o) [H⁺] [H₂A₂]_(o) ^?0.5. An analysis of this equation leads to the following chemical reaction step as rate-determining: [FeHSO₄A₂]_(int)→[FeHSO₄A]+A_(i) ^?. However, the activation energy of 24 kJ mol^?1 suggests that the backward extraction process is intermediate controlled with greater contribution of the diffusion of one or the other species as a slow process. The equilibrium constant obtained from the rate study matches well with that obtained from the equilibrium study.     

Graft copolymerization of methyl acrylate onto poly(vinyl alcohol) initiated by potassium diperiodatoargentate(III)

The graft copolymerization of methyl acrylate onto poly(vinyl alcohol) (PVA) using potassium diperiodatoargentate(III) [Ag(III)]–PVA redox system as initiator was studied in an alkaline medium. Some structural features and properties of the graft copolymer were confirmed by Fourier‐transfer infrared spectroscopy, scanning electron microscope, X‐ray diffraction and thermogravimetric analysis. The grafting parameters were determined as a function of concentrations of monomer, initiator, macromolecular backbone (X?_n = 1750, M? = 80 000 g mol^?1), reaction temperature and reaction time. A mechanism based on two single‐electron transfer steps is proposed to explain the formation of radicals and the initiation profile. Other acrylate monomers, such as methyl methacrylate, ethyl acrylate and n‐butyl acrylate, were also used to produce graft copolymerizations. It has been confirmed that grafting occurred to some degree. Thermogravimetric analysis was performed in a study of the moisture resistance of the graft copolymer. Copyright © 2004 Society of Chemical Industry     

Studies on extraction and permeation of lanthanum(III) and cerium(III) using cyphos IL 104 as extractant and ion carrier

ABSTRACT

This work shows application of Cyphos IL 104 (trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate) as the extractant and the ion carrier of Ce(III) and La(III) from aqueous solutions through polymer inclusion membranes (PIM). These membranes were used for separation of Ce(III) from solution containing La(III), Cu(II), Co(II) and Ni(II). The best results of the separation process were obtained for PIM containing: 20.0 wt.% CTA, 55.0 wt.% NPOE and 25.0 wt.% Cyphos IL 104 at pH 3.8 into 1 M H₂SO₄. The separation coefficients were found in order of S _Ce/La < S _Ce/Cu < S _Ce/Co < S _Ce/Ni.     

Separation of scandium(III) from lanthanides(III) with room temperature ionic liquid based extraction containing Cyanex 925

The separation of Sc(III) from Y(III), La(III) and Yb(III) in [C₈mim][PF₆] containing Cyanex 925 has been investigated, and is reported in this paper. A cation exchange mechanism of Sc(III) in [C₈mim][PF₆] and Cyanex 925 is proposed by study of the influence of anionic and cationic species on the extraction. The coefficient of the equilibrium equation of Sc(III) was confirmed by slope analysis of log D_Sc vs log [Cyanex 925], and the loading capacity also confirmed the stoichiometry of Cyanex 925 to Sc(III) was close to 3:1. Infrared data for Cyanex 925 saturated with Sc(III) in [C₈mim][PF₆] indicated strong interaction between P?O of Cyanex 925 and Sc(III). In addition, the relationship between log D_Sc and temperature showed that temperature had little influence on the extraction process, and the resulting thermodynamic parameters indicated that an exothermic process was involved. Copyright © 2007 Society of Chemical Industry     

Extraction of Lanthanides(III) and Am(III) by Mixtures of Malonamide and Dialkylphosphoric Acid

Abstract

N,N′‐dimethyl‐N,N′‐dioctylhexylethoxymalonamide, DMDOHEMA, and di‐n‐hexylphosphoric acid, HDHP, are the extractants of reference for the French DIAMEX–SANEX process for the separation of trivalent actinide ions from the lanthanide ions. In this work, the extraction of Eu³⁺ and Am³⁺ by the two extractants, alone or in mixtures, has been investigated under a variety of experimental conditions. The two cations are extracted by HDHP as the M(DHP · HDHP)₃ complexes with an Eu/Am separation factor of ～10. With DMDOHEMA, Eu³⁺ and Am³⁺ are extracted as the M(NO₃)₃(DMDOHEMA)₂ disolvate species with an Am/Eu separation factor of ～2. The metal distribution ratios measured with a mixture of the two reagents indicated that almost all lanthanides are extracted equally well. The extraction of Eu³⁺ and Am³⁺ by HDHP‐DMDOHEMA mixtures exhibits a change of extraction mechanism and a reversal of selectivity taking place at ～1 M HNO₃ in the aqueous phase. Below this aqueous acidity, HDHP dominates the metal extraction by the mixture, whereas DMDOHEMA is the predominant extractant at higher aqueous acidities. Some measurements indicated apparent modest antagonism between the two extractants in the extraction of Eu³⁺ and synergism in the extraction of Am³⁺. These data were interpreted as resulting from the formation in the organic phase of mixed HDHP‐DMDOHEMA species containing two HDHP and five DMDOHEMA molecules.     

A Novel Oxidation of Valine by N-Bromophthalimide in the Presence of Ruthenium(III) Chloride as a Homogeneous Catalyst

Kinetics of Ruthenium(III) [Ru(III)] chloride catalyzed oxidation of valine (Val) has been studied by N-bromophthalimide (NBP) in the acidic medium at 35 °C. The reaction rate follows first-order and zero-order dependence with respect to [NBP] and [Val]. First-order kinetics was observed for Ru(III) chloride at low range of concentrations and tending towards zero-order at higher concentrations. A negative effect was observed for [H⁺] and [phthalimide], while a positive effect was observed for [Cl^?] on the reaction rate. Hg(OAc)₂, ionic strength (I), and dielectric constant (D) of the medium did not change significantly the reaction rate. The rate constants as a function of temperature (298–318 K) were used to calculate activation parameters of the oxidation of Val by NBP. A plausible mechanism was proposed to explain the results of kinetic studies, reaction stoichiometry and product analysis.     

Multivariate Optimization and Adsorption Characterization of As(III) by Using Fraxinus Tree Leaves

This study introduces Fraxinus tree leaves as a new, efficient biosorbent of As(III). A suitable response surface was achieved by running a central composite design. Simultaneous optimization of both responses (R% and q) was carried out and 67% of the goal of desirability function was attained. The results obtained for simultaneous optimization are R = 70% and q = 80.6 mg g^?1 with 67% desirability in m = 600 mg L^?1 where s = 0.10 g and pH = 3.9. Langmuir and Freundlich isotherms model were applied in explaining the sorbent–sorbate equilibrium study, and maximum capacity uptake equals 99.97 mg g^?1 and K_L = 0.05 L mg^?1 has been obtained. Fourier Transfer Infra-Red (FT-IR) and kinetic results were considered to examine the functional groups involved and the adsorption mechanism.     

Electric dichroism studies of the bonding of Co(III) chelate with synthetic polyelectrolytes

The interactions of bis-2-(2-pyridylazo)-1-naphthol Co(III), [Co(III) (αPAN)₂⁺], with five kinds of synthetic polyelectrolytes have been studied by spectrophotometric and transient electric dichroism measurements. The polyelectrolytes were: poly(styrene sulphonic acid) (PSS); poly(acrylic acid) (PAA); poly(l-glutamic acid) (PLG); $\text{poly}\text{(N}{}^{\mathrm{<mtext>e</mtext>}}\text{,N}{}^{\mathrm{<mtext>e</mtext>}}\text{-}\text{dicarboxylmethyl-}\text{l}\text{-lysine}$ (PDCML); and poly(l-lysine) (PLL). The equilibrium constant of the reaction:

with P = polyelectrolyte residue was determined spectrophotometrically: K₁ is > 10⁷ M^?1 (PSS); (1.4 ± 0.2) × 10⁴ M^?1 (PAA); (4.0 ± 0.4) × 10³ M^?1 (PLG); (1.4 ± 0.2) × 10⁶ M^?1 (PDCML); and < 10² M^?1 (PLL) at pH 6–8. From transient electric dichroism, the angle (ψ) between the αPAN plane and the polymer axis was determined to be 65° (PSS); 52° (PAA); 55° (PLG); and 52° (PDCML). The large K₁ and ψ values for PSS are ascribed to the hydrophobic interaction between the aromatic αPAN ring and the styrene sulphonate residues of PSS. Using stopped-flow electric dichroism measurements, rapid transfer of a bound Co(III) chelate from the PDCML to PSS chains was shown to occur.