- Square-wave Amperometric Monitoring of Reaction Rates
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The application of square-wave amperometry, an analytical technique involving the use of two indicator electrodes polarized by a square wave, in the determination of reaction rates is described.Kinetic measurements have been made on the bromination of anisole in aqueous solution.Square-wave amperometry in conjunction with a stopped-flow apparatus equipped with Pt electrodes in the observation tube was used to monitor the disappearance of bromine in dilute solutions.Reaction rates with half-lives down to ca. 5 ms can be measured using relatively high-frequency square waves (ca. 800-1000 Hz).The results are in good agreement with values measured spectrophotometrically at higher bromine concentrations.The rate of dissociation of Ag(1+) from its macrobicyclic cryptand 211 complex was also measured, using a pair of silver indicator electrodes.Free Ag(1+) may be monitored selectively in the presence of its cryptate complex by using a low-amplitude square wave (+/- 150 mV).The advantages and limitations of the amperometric technique for kinetic measurements are discussed.
- Cox, Brian G.,Jedral, Wojciech
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- Features of electrolysis of nitric acid solutions of silver: I. Behavior of Ag(II) in HNO3 solutions
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The current efficiency of Ag(II) formation in the course of electrochemical oxidative dissolution of PuO2 was determined. It approaches 72% at the anodic potentials from 1.9 to 2.1 V (vs. SHE) and the anodic current densities of 0.006-0.013 A cm-2. The behavior of Ag(II) in 4 M HNO3 at 8, 25, and 40°C was studied. The reaction of Ag(II) with water can be described by the equation d[Ag(II)]/dt = kapp[Ag(II)] n, where n ~ 2 at 8-25°C and 2-1.5 at 39-41°C. The apparent rate constants of the reaction are 1.5 and 3.8 1 mol-1 min-1 at 8.5°C and 25°C, respectively. At 39-41°C, the reaction order with respect to Ag(II) ranges from 2 to 1.5, and the rate constant is about 1.2 11/2 mol-1/2 min-1.
- Rance,Nikitina,Korolev,Kirshin,Listopadov,Egorova
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- Dual mechanism of oxidation of dl-methionine by diperiodatoargentate(III) in aqueous alkaline medium (stopped flow technique)
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The kinetics of oxidation of dl-methionine by diperiodatoargentate(III) (DPA) has been studied spectrophotometrically in a wide range, 0.01-1.0 mol dm-3, of alkali at constant ionic strength of 0.50 mol dm-3. In a lower range, 0.01-0
- Thabaj,Chimatadar,Nandibewoor
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- Complex Formation followed by Internal Electron Transfer: the Reaction of silver(III) with Ascorbic Acid
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silver(III) 3+ 1 has been found to oxidize ascorbic acid (H2asc) in acidic aqueous solution via an inner-sphere mechanism to give dehydroascorbic acid, silver(I) and free ethylenebis(biguanide).The 1:1 adduct formed as an intermediate between 1 and ascorbic acid decomposes after a non-separable two-electron-transfer reaction.The decomposition of the three complexes actually formed, co-ordinating different numbers of protons, occurs through two parallel pathways: one via decomposition of the unprotonated adduct III(H2L)(H2asc)>, another via the deprotonated adduct III(H2L)(Hasc)>, while the protonated adduct III(H3L)(H2asc)> appears to be rather stable.The equilibrium constant for the adduct formation has been found to be 4.08 +/- 0.45 dm3 mol-1, whereas the acid and base constants of this complex are 0.41 mol dm-3 and 2.86 dm3 mol-1, respectively.The two rate constants for the decomposition are 25 +/- 3 and 220 +/- 25 s-1 for III(H2L)(H2asc)> and III(H2L)(Hasc)>, respectively.The possibility of an outer-sphere mechanism is discussed.
- Dasgupta, Subrata,Herlinger, Erwin,Linert, Wolfgang
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- Kinetics of the reaction of silver(II) with dithionate
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The reaction 2Ag(II) + S2O62- + 2H2O = 2Ag+ + 2HSO4- + 2H+ proceeds by a mechanism in which the oxidizing agent, silver(II), participates in the rate-determining step. This is unlike previously known reactions of dithionate with certain strong oxidizing agents, for which disproportionation or hydrolysis of dithionate has been rate determining. The dominant term in the rate law is -d[Ag(II)]/dt = k[H+][Ag(II)][S2O62-], with k = 5.5 × 10-2 M-2 sec-1 at I = 3.5 M and 25.0°.
- Veith, Gilman,Guthals, Elise,Viste, Arlen
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- Kinetics of dissolution of silver nanoparticles inside triton N-42 reversed micelles
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Our spectrophotometric study of the kinetics of dissolution of silver nanoparticles by nitric acid inside inverted micelles of Triton N-42 (a nonionic surfactant) verified the universal character of the mechanism for this type of process, which includes t
- Tatarchuk,Bulavchenko,Druzhinina
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- Kinetics of Oxidation of Azide by [Ethylenebis(biguanide)]silver(III) in Aqueous Acidic Media
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In aqueous acidic media sodium azide and the orange-yellow title complex react quantitatively generating N2 gas along with a colourless solution of Ag+ ion and the ligand, ethylenebis(biguanide). The parent complex, [Ag(H2L)]3+, and one of its conjugate bases, [Ag(HL)]2+, participate in the reaction with N 3- as the kinetically reactive reductant. Ag+ has no catalytic effect. At 25.0 °C, I = 1.0 M (NaNO3), rate constants for the reactions [Ag(H2L)]3+ + N 3- and that for [Ag(HL)]2+ + N3 - are (12.3±0.5) and (3.8±0.6) M-1· S-1, respectively. The high rate constants along with the very low equilibrium constant (10-15 M-1) calculated for the first reaction strongly suggest inner-sphere redox mechanism. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Bandyopadhyay, Prabir,Dhar, Basab Bijayi,Bhattacharyya, Jhimli,Mukhopadhyay, Subrata
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- Gas-phase studies of group-11 cation (Cu+, Ag+, and Au+) reactions with 2-propanol in a supersonic beam-expansion source
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The gas-phase reactions of group-11 ions (Cu+,Ag+, and Au+) with 2-propanol were investigated using laser vaporization combined with supersonic beam expansion in a time-of-flight mass spectrometer. A number of reaction pathways, including assoication, dehydrogenation, and dehydration, were observed. Among these metal ions, Au+ is highly reactive toward 2-propanol. The experimental results are parallel to studies by Wilkins et al. using an FT-ICR mass spectrometer (J. Am. Chem. Soc., 107, 7316 (1985)). The geometries and binding energies of all complexes M+-L, where M+ = Cu+, Ag+, and Au+, L = 2-propanol, acetone, propene, and H2O, were estimated using Moller-Plesset perturbation (MP2) and density functional theory (BLYP). The bond strengths of the complex ions involving gold revealed the strongest bonding, due to a relativistic effect. The energetic relationship between the reactants and the products facilitated an interpretation of the observed exit channels. Because of the supersonic beam source employed, larger clusters containing metal ions were generated as well. Because the cluster sizes with solvent molecules were ≥ 2, the reactivities were apparently limited to Cu+ and Ag+ clusters, while the reactive nature changed in Au+ along with the formation of acetone, lacking in the bare Au+ reactions. For larger clusters, calculations on Ag+ - (2-propanol)2 and Ag+ - (2-propanol)(acetone) complexes using BLYP were performed to obtain their energetics.
- Huang,Su,Yeh
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- Kinetics of oxidation of glyoxylic acid by [ethylenebis(biguanide)] silver(III) in aqueous media
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The complex cation, [ethylenebis(biguanide)]silver(III), [Ag(H 2L)]3+, and its conjugate bases, [Ag(HL)]2+ and [AgL]+ oxidise glyoxylic acid, CHOCO2H quantitatively to formic acid and carbon dioxide, themselves being reduced to Ag+. Free ethylenebis(biguanide) was recovered in near-quantitative yield. In the investigated pH range (1.00-7.00), the reaction is first order in both [complex] and total glyoxylate, [HGX]T. The reaction proceeds through four parallel paths: [Ag(H2L)]3+ - HGX (k1), [Ag(H2L)]3+ - GX- (k2), [Ag(HL)]2+ - GX- (k3), and [AgL]+ - GX- (k4). The respective rate constants (in 10 4 M-1s-1) are, respectively, 7.34, 112, 40.7 and 19.2 at 25.0°C and I = 1.0 M (NaNO3). Formation of adducts by the reducing species with the metal complex via hydrogen-bonding or electrostriction may be proposed for the low-energy pathway for electron-transfer. A substantial rate retardation in presence of the radical scavenger acrylonitrile suggests successive one-electron changes, Ag III → AgII → AgI.
- Das, Amit,Mukhopadhyay, Subrata
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- Luminescent coordination polymers with extended Au(I)-Ag(I) interactions supported by a pyridyl-substituted NHC ligand
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Reaction of [Ag(CH3impy)2]PF6, 1, with Au(tht)Cl produces the monometallic Au(I)-species [Au(CH3impy) 2]PF6, 2. Treatment of 2 with excess AgBF4 in acetonitrile, benzonitrile or benzylnitrile produces the polymeric species {[AuAg(CH3impy)2(L)](BF4)2} n, (L = CH3CN,3; L = C6H5CN, 4; L = C6H5CH2CN, 5) where the Au(I) centers remain bound to two carbene moieties while the Ag(I) centers are coordinated to two alternating pyridyl groups and a solvent molecule (L). Reaction of 2 with AgNO3 in acetonitrile produces the zig-zag mixed-metal polymer {[AuAg(CH3impy)2(NO3)]NO3} n, 6, that contains a coordinated nitrate ion in place of the coordinated solvent species. All of these polymeric materials are dynamic in solution and dissociate into their respective monometallic components. Compounds 2-6 are intensely luminescent in the solid-state and in frozen solution. All of these complexes were characterized by 1H, 13C NMR, electronic absorption and emission spectroscopy and elemental analysis.
- Catalano, Vincent J.,Etogo, Anthony O.
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- Kinetics of Formation and Dissociation of the Cryptates Ag(2,2,2)+ and K(2,2,2)+ in Acetonitrile+Water Mixtures at 25 deg C
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The dissociation rates of Ag(2,2,2)+ and K(2,2,2)+ in acetonitrile (AN)+ water system show a quite different dependence upon solvent mole fraction.The dissociation rate constant, kd, of Ag(2,2,2)+ is almost indepependent of solvent composition and the rapid decrease of the stability constant, Ks, near xAN = 0 is determined completely by the variation in the formation rate constant, kf.The constant value for kd for Ag(2,2,2)+ in the mixtures indicates that in the transition state the silver ion is strongly bonded to the (2,2,2) nitrogen atoms in a manner typical of the partially covalent interaction of monovalent d10 ions with nitrogen donors (e.g., in nitrilic solvents).This result, and the very similar variation of the Gibbs free energies of the transition state and stable cryptate complex with solvent composition, suggests that the transition state is very close to that of the products.The result is striking because for alkali-metal cryptates, particularly in nonaqueous solvents, a very similar solvent dependence is found for the reactants and transition state.The interaction between K+ and (2,2,2) is also found to be very different in this binary solvent system from that of Ag(2,2,2)+.Both kd andKf contribute similarly to the increase of the stability constant of K(2,2,2)+ with increasing mole fraction of acetonitrile, and comparisons of the Gibbs free energies of reactants, transition state, and product do not indicate any simple correlations between the solvation behavior of the three over the whole range of solvent composition.
- Cox, B. G.,Guminski, C.,Firman, P.,Schneider, H.
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- Formation of small negative and positive cluster ions of gold, silver, and copper by direct laser vaporization
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Direct laser vaporization techniques have been employed to produce small cluster cations and anions of gold, silver, and copper in a Fourier transform ion cylotron resonance mass spectrometer using pure metal samples.Aunp (p = +1 and -1, n = 1-6), Agn+ (n = 1-3 ), Ag-, Cun+ (n = 1-3), and Cun- (n = 1-2) were observed, using two different experimental configurations.In one configuration ions were produced by Nd:YAG laser irradiation directed collinear with the magnetic field in the FTICR mass spectrometer while in the second laser light directed perpendicularly to the magnetic field was used.Relative kinetic energies of the aggregates, the relative intensities of positive vs negative ions, and the nature of the neutrals in the plasma formed by direct laser vaporization are discussed.
- Moini, Mehdi,Eyler, John R.
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- The kinetics and mechanism of the oxidation of water by silver(II) in concentrated nitric acid solution
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The kinetics of the oxidation of water by silver(II) in 2.00-6.18 M HNO3 has been studied between 298.15 and 308.15°K under a variety of conditions. Studies at [Ag(II)] > 1 × 10-4 M show that the reaction is second order in [Ag(II)] and the observed rate law is -d[Ag(II)]/dt = ka[Ag(II)]2 / kb + kd[Ag(I)][H+]2 = kII[Ag(II)]2 At 6.13-6.17 M HNO3 and 104[AgO]0 = 8.33-8.50 M, kII = 1.78 M-1 sec-1 at 298.15°K. The enthalpy of activation for kII under these concentration conditions is 23.0 ± 0.4 kcal/mole. The proposed mechanism (reactions 1-5) conforms to the observed rate law. The notation [Ag(II)] has been used in place of [AgNO3+] for simplicity. Studies at [Ag(II)] -4 M show that there is a first-order reaction with the rate law -d[Ag(II)]/dt = {ke + kf[Ag(I)] / (kr + ks[Ag(I)])(km + kn[H+]2)} [Ag(II)] = kI[Ag(II)] At the same temperature and concentration conditions kII was reported kI = (2.38 ± 0.10) × 10-4 sec-1. The enthalpy of activation, ΔHI?, for kI is 22.3 ± 0.9 kcal/mole. The mechanism proposed (reactions 8-15) involves a free-radical reaction.
- Po, Henry N.,Swinehart, James H.,Allen, Thomas L.
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- DEVICES FOR TREATMENT OF SKIN DISORDERS
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The present invention discloses a layer of fabrics having antibacterial/microbe-resistant properties that are designed for contacting with the human skin. The fabric layer can be disposed, directly or indirectly, onto a pillowcase, pillow, comforter, comforter cover, head support, bed cloth, sleeping bag, mattress, cushion, blanket, and garment.
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- Os(VIII)/Ru(III) catalysed oxidation of aspirin drug by a new oxidant, diperiodatoargentate(III) in aqueous alkaline medium: A comparative kinetic study
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The kinetics of Os(VIII) and Ru(III) catalysed oxidation of anti-pyretic drug, aspirin by diperiodatoargentate(III) (DPA) in alkaline medium at 298 K and a constant ionic strength of 0.10 mol dm-3 was studied spectrophotometrically. The oxidation products in both the cases are 1,4-benzoquinone2-carboxylate ion and Ag(I). The stoichiometry is the same in both the catalysed reactions i.e., [aspirin]:[DPA] = 1:2. The reaction is of first order in Os(VIII)/Ru(III) and [DPA] and has less than unit order in both [ASP] and [alkali]. The oxidation reaction in alkaline medium has been shown to proceed via a Os(VIII)/Ru(III)-aspirin complex, which further reacts with one molecule of DPA in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR, NMR and GC-MS. The reaction constants involved in the different steps of the mechanism are calculated. The catalytic constant (Kc) 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.
- Hiremath, Chanabasayya V.,Kiran,Nandibewoor, Sharanappa T.
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p. 163 - 174
(2008/10/09)
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- Formation of coordination polymeric structures on the basis of 4,4'-dipyridylethylene and Ag(+) in solutions
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The formation of coordination polymeric chain structures in which silverions alternate with dipyridylethylene (DPyEt) ligands was studied. In a homogeneous ethanol solution, complex formation of DPyEt with silver ca tions takes place. The outcome of this reaction depends on the ligand/cation molar ratio, the initial ligand concentration, and the counter-ion type. Conditions were identified under which the coordination polymer isformed as a microdispersed solid precipitating from the solution. The p recipitates formed in the DpyEt-AgNO3 and DpyEt-AgClO4 systems were investigated by various experimental techniques. The counter-ion was found to be incorporated in the polymer and to influence the structure of the precipitate particles.
- Razumov, V. F.,Brichkin, S. B.,Pilugina, O. M.,Karpova, T. P.,Vatsadze, S. Z.,et al.
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p. 476 - 480
(2008/10/08)
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- Study of reactions of silver and sulfur clusters
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The reactions between silver and sulfur clusters are studied with a laser double ablation reactor. The main reaction products are [AgS4]+, [AgS8]+, [AgS12]+, and [AgS16]+, which have different compositions from those of Ag/S clusters produced from Ag/S mixed sample by laser ablation. The photolysis of the products with a 193 nm excimer laser indicates that [AgS12]+ and [AgS16]+ have a photodissociation efficiency much higher than that of [AgS4]+ and [AgS8]+. The structure of the products and the mechanism of the reactions to form products [AgS12]+ and [AgS16]+ are discussed.
- Liu, Peng,Han, Chunying,Gao, Zhen,Kong, Fanao,Zhu, Qihe
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p. 3337 - 3339
(2007/10/03)
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- Kinetics and mechanism of oxidation of pyrimidine nucleobases by diperiodato- Argentate(III) in aqueous alkaline medium
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The kinetics of oxidation of pyrimidine nucleobases, viz., uracil, thymine, 5-bromouracil, 6-methyluracil and cytosine by diperiodatoargentate(III) (DPA) in aqueous alkaline medium have been studied. The reaction is first order both with respect to [DPA] and [pyrimidine base]. The oxidation rate increases with increase in [OH-] and decreases with increase in added [periodate]. The reaction rate is not affected by varying the ionic strength. The stoichiometry of the reactions is 1:1 and the product of oxidation under kinetic conditions has been found to be the corresponding 5, 6-dihydroxy-5, 6-dihydropyrimidine. The reactions have been studied in the temperature range 278-303 K and the activation parameters calculated. It is assumed that the metal entity, i.e., Ag(III) is initially involved in η2-binding to the C(5)-C(6) double bond of the pyrimidine in a slow step. The Ag(III)-pyrimidine complex thus formed dissociates in a subsequent fast step to give the products. The order of reactivity of the pyrimidines has been found to be: cytosine>uracil>5-bromouracil~6-methyluracil>thymine and the reasons for the observed order discussed.
- Krishna, Kondamudi Venkata,Jaya Prakash Rao
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p. 1106 - 1110
(2007/10/03)
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- Spectrophotometric studies of [bis(pyrazine)silver(II)-peroxodisulphate] and kinetics and mechanism of oxidation of water by it in aqueous perchloric acid
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Pyrazine stabilises silver(II) through formation of complex, bis(pyrazine)silver(II)-peroxodisulphate in 4.0 M perchloric acid which has been studied spectrophotometrically at λmax 460 and 619 nm and the molar absorpuvities are found to be 2100 and 2242M-1 cm-1 respectively. Ag(pyz)22+ gradually oxidises water. The effect of [H+], [pyrazine], [AgII] and temperature on the rate constants have been determined. A mechanism has been proposed for the reduction of Ag(pyz)22+ to Ag+.
- Shukla,Indrayan
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- Kinetics and mechanism of oxidation of iodide by diperiodatoargentate(III)
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The kinetics of oxidation of iodide by diperiodatoargentate(III) has been investigated in alkaline medium. The reaction is found to be first order in oxidant, inverse first order in alkali and fractional order in periodate. The order in substrate is nearly one at low concentrations and increases beyond unity at its higher concentrations. The rate of the reaction is found to be unaffected by added excess of iodine or by the ionic strength of the medium. The activation parameters for the overall reaction have been obtained and a mechanism involving an intermediate between iodide and a protonated and undissociated diperiodatoargentate(III) species has been proposed.
- Sridevi,Mohammed Yusuff
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p. 894 - 896
(2007/10/03)
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- Kinetics of silver(I)-catalyzed oxidation of formic acid by the (ethylenebis(biguanidine))silver(III) cation in acid perchlorate media
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In the presence of added Ag+, the title reaction follows the rate law -d[complex]/dr = k° = Kk1[Ag+]2[HCO2H]/([H+] + K[HCO2H]), where k° is the observed zero-order rate constant for a large excess of Ag+, H+, and HCO2H over the complex. 103k1 was found to be 1.0 ± 0.1 M-1 min-1 at 30°C and I = 1.0 M. Corresponding ΔH? and ΔS? values are 13 ± 1 kcal/mol and -37 ± 3 eu, respectively. Under these conditions, K, the formation constant of Ag(HCO2) from HCO2H and Ag+, was found from kinetic results to be 0.1 ± 0.01. The acid dissociation constants (pK1 and pK2) of the complex cation under similar conditions in a 50% (v/v) aqueous-DMF medium are 3.8 ± 0.2 and 6.8 ± 0.3. There is evidence for the Ag+ ion acting here as the actual oxidant for HCO2H with use of the complex as an oxidant regenerating Ag+ from Ag0 formed as an intermediate. Under the experimental conditions where Ag(II) is detectable in concentrations less than about 10-6 M, the whole reaction course is EPR silent. This has been discussed in terms of possible reaction schemes.
- Banerjee, Rupendranath,Das, Kaushik,Das, Amitava,Dasgupta, Subrata
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p. 585 - 588
(2008/10/08)
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- Chemical and Electrochemical Oxidation of Solutions of Silver Nitrate in Acetonitrile
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In anhydrous acetonitrile the unstable, brown species Ag(NO3)42-, I, can be produced either by the electrolysis of silver nitrate or by the equilibrium reaction N2O5 + Ag+ + 3NO3- ->/-3.The ESR spectrum of I at 77 K is that of a Ag(II) ion in a field with pronounced axial distortion.Its resonance Raman spectrum indicates square-planar coordination of the metal ion by unidentate nitrate ligands.The complex decomposes to form cyanomethyl nitrate and nitric acid by the rate law -d/dt = k/->.In the presence of p-xylene a major organic product is p-methylbenzyl nitrate.Equilibrium and electrochemical studies lead to estimated ΔG0298 values for the free radical and ionic dissociation pathways of N2O5 in acetonitrile solution of +38 and -26 kJ, respectively.
- Tracy, Mark L.,Nash, Charles P.
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p. 1239 - 1242
(2007/10/02)
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- The kinetics of the silver(II)-thallium(I) reaction in nitric acid
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Kinetic data for the Ag(II)-Tl(I) reaction in 6.18 F HNO3 at 26.2° are interpreted in terms of the mechanism (Chemical Equation Presented) Values for combinations of rate constants found from a least-square treatment of the data are k1 = 0.403, k2/(k1k3) = 2.03 × 10-2, and k2k4/(k1k3k5) = 1.41 × 10-6 where time is in seconds, concentrations are in moles/liter, and rate is expressed as disappearance of Ag(II). These values are consistent with equilibrium and rate constants for related reactions. Unlike other reactions with Ag(II), the oxidation of Tl(I) is independent of HNO3 concentration over the range 4.66 to 8.82 F.
- Dundon, Robert W.,Gryder, John W.
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p. 986 - 989
(2008/10/08)
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