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1.
Kinetics and mechanism of bromide ions oxidation by cerium(IV) in sulphuric acid solutions revisited
Anna Katafias 《Transition Metal Chemistry》2006,31(7):907-911
Kinetics of Br− anion oxidation by cerium(IV) species in aqueous H2SO4 solutions have been reexamined. The rate of reaction was determined spectrophotometrically based on a factor analysis of
the absorbance – time data collected in the wavelength range 318–390 nm – the region characteristic for the cerium(IV) sulphato
complexes. The data fit very well to a pseudo-first order dependence under a large molar excess of the reductant. The rate
law of the form –d[CeIV]/dt = k[CeIV][Br–]2 has been obtained at constant H2SO4 concentration and ionic strength I = 2 m. The pseudo-first order rate constant decreases with an [H2SO4] increase from 0.1 to ca. 0.4 m range, then increases for higher [H2SO4]. The apparent activation parameters have been calculated from the third order rate constants k for different [H2SO4]. 相似文献
2.
Kiran A. Thabaj Shivamurti A. Chimatadar Sharanappa T. Nandibewoor 《Transition Metal Chemistry》2006,31(2):186-193
The kinetics of oxidation of PdII by CeIV have been studied spectrophotometrically in HClO4 media at 40 °C. The reaction is first order each in [CeIV] and [PdII] at constant [H+]. Increasing [H+] accelerates the reaction rate with fractional order in [H+]. The initially added products, palladium(IV) and cerium(III) do not have any significant effect on the reaction rate. At
constant acidity, increasing the added chloride concentration enhances the rate of reaction. H3Ce(SO4)4− and PdCl42− are the active species of oxidant and reductant respectively. The possible mechanisms are proposed and the reaction constants
involved have been determined. 相似文献
3.
Ponnusamy Sami Kandasamy Venkateshwari Natarajan Mariselvi Arunachalam Sarathi Kasi Rajasekaran 《Transition Metal Chemistry》2009,34(7):733-737
The rates of the electron transfer reaction of l-cysteine and thioglycolic acid with the polyoxometalate, [PVVW11O40]4−, have been measured spectrophotometrically in aqueous acid medium. The polyoxometalate oxidizes cysteine to cystine and thioglycolic
acid to dithioglycolic acid and gets reduced to heteropoly blue, [PVIVW11O40]5−. The order of the reaction with respect to oxidant is one, whereas the reaction shows second order dependence on the substrates.
The rate–pH profile shows that both the unionized and ionized thiol groups of the substrates are active species involved in
electron transfer. A suitable mechanism has been proposed for the title reaction based on the results of kinetic studies. 相似文献
4.
Aqueous solution of water soluble colloidal MnO2 was prepared by Perez-Benito method. Kinetics of l-methionine oxidation by colloidal MnO2 in perchloric acid (0.93 × 10−4 to 3.72 × 10−4 mol dm−3) has been studied spectrophotometrically. The reaction follows first-order kinetics with respect to [H+]. The first-order kinetics with respect to l-methionine at low concentration shifts to zero order at higher concentration. The effects of [Mn(II)] and [F−] on the reaction rate were also determined. Manganese (II) has sigmoidal effect on the rate reaction and act as auto catalyst.
The exact dependence on [Mn(II)] cannot be explained due to its oxidation by colloidal MnO2. Methionine sulfoxide was formed as the oxidation product of l-methionine. Ammonia and carbon dioxide have not been identified as the reaction products. The mechanism with the observed
kinetics has been proposed and discussed. 相似文献
5.
Yongqing Zhai Hongmei Liu Baosheng Liu Yukai Liu Jia Xiao Weisong Bai 《Transition Metal Chemistry》2007,32(5):570-575
The kinetics and mechanism of ruthenium(III) catalyzed oxidation of tetrahydrofurfuryl alcohol (THFA) by cerium(IV) in sulfuric
acid media have been investigated spectrophotometrically in the temperature range 298–313 K. It is found that the reaction
is first-order with respect to CeIV, and exhibits a positive fractional order with respect to THFA and RuIII. The pseudo first-order ([THFA]≫[CeIV]≫[RuIII]) rate constant k
obs decreases with the increase of [HSO
4
−
]. Under the protection of nitrogen, the reaction system can initiate polymerization of acrylonitrile, indicating the generation
of free radicals. On the basis of the experimental results, a reasonable mechanism has been proposed and the rate equations
derived from the mechanism can explain all the experimental results. From the dependence of k
obs on the concentration of HSO
4
−
,
has been found as the kinetically active species. Furthermore, the rate constants of the rate determining step together with
the activation parameters were evaluated. 相似文献
6.
Ponnusamy Sami Natarajan Mariselvi Kandasamy Venkateshwari Murugesan Vairalakshmi Arunachalam Sarathi Kasi Rajasekaran 《Transition Metal Chemistry》2010,35(5):563-570
The kinetics of reduction of heteropoly 11-tungstovanadophosphate, [PVVW11O40]4−, (HPA1) and heteropoly 10-tungstodivanadophosphate, [PVVVVW10O40]5−, (HPA2) by thiourea has been investigated in HClO4/phthalate/acetate buffer solutions spectrophotometrically at 25 °C in aqueous medium. The stoichiometry of the reaction is
1:1 in both cases. The HPAs are converted into the corresponding one-electron reduced heteropoly blues, namely, [PVIVW11O40]5− and [PVIVVVW10O40]6−, and thiourea is oxidised to formamidine disulphide. The reaction shows first-order dependence in both [HPA] and [thiourea]
at constant pH. The rate–pH profile shows the participation of both the neutral and deprotonated forms of thiourea in the
reaction. The reaction proceeds through an outer sphere electron transfer mechanism in which activation-controlled electron
transfer is the rate-determining step. Self-exchange rate constants for the couples [PVVW11O40]4−/[PVIVW11O40]5−, [PVVVVW10O40]5−/[PVIVVVW10O40]6− and H2NCSNH2/H2NCS·+NH2 have been evaluated by Marcus theory. 相似文献
7.
Rupendranath Banerjee Anamika Bhattacharya Amiya Kumar Chakraburtty 《Transition Metal Chemistry》1989,14(1):55-57
Summary In the title reaction each mole of N1-phenylbiguanidine, R–HNC(=X)NHC(=NH)NH2 (R=Ph, X=NH), consumes 4 moles of CeIV and produces guanylurea (R=H, X=O), 1,4-benzoquinone and ammonia. On the other hand, the reaction of N1-phenylbiguanidine (pbg) with [MnO4]– proceeds with variable stoicheiometry which depends on reaction conditions. In the case of [MnO4]– no benzoquinone is detected among the reaction products; instead, carbon dioxide, guanylurea, and ammonia were identified. Pbg itself in acid solution slowly hydrolyses to aniline which rapidly reacts with CeIV and [MnO4]–. The kinetics for the reactions of pbg with the oxidants is consistent with the rate law –d[oxidant]/dt=k[pbg].The k values and the corresponding activation enthalpies and entropies for the reaction of bpg with CeIV, [MnO4]–, and CrVI lie within a narrow range. These results are interpreted in terms of rate-determining hydrolysis of pbg in all the three cases. 相似文献
8.
Joanna Wiśniewska 《Transition Metal Chemistry》2007,32(6):811-815
The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en)2(H2O)2]3+ in CF3SO3H solution ([CoIII] = (2–6) × 10−3
m, [ptz] = 2.5 × 10−4
m, [H+] = 0.02 − 0.05 m, I = 0.1 m (H+, K+, CF3SO
3
−
), T = 288–308 K) and [Co(edta)]− in aqueous HCl ([CoIII] = (1 − 4) × 10−3
m, [ptz] = 1 × 10−4
m, [H+] = 0.1 − 0.5 m, I = 1.0 m (H+, Na+, Cl−), T = 313 − 333 K) were studied under the condition of excess CoIII using u.v.–vis. spectroscopy. The reactions produce a CoII species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k
obs) on [CoIII] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en)2(H2O)2]3+ ion was found to be independent of [H+]. In the case of the [Co(edta)]− ion, the k
obs dependence on [H+] was linear and the increasing [H+] accelerates the rate of the outer-sphere electron-transfer reaction. The activation parameters were calculated as follows:
ΔH
≠ = 105 ± 4 kJ mol−1, ΔS
≠ = 93 ± 11 J K−1mol−1 for [Co(en)2(H2O)2]3+; ΔH
≠ = 67 ± 9 kJ mol−1, ΔS
≠ = − 54 ± 28 J K−1mol−1 for [Co(edta)]−. 相似文献
9.
Summary Manganese(III) acetate was prepared by the electrolytic oxidation of Mn(OAc)2 in aqueous AcOH. The electro-generated manganese(III) species was characterised by spectroscopic and redox potential studies.
The kinetics of oxidation of pyridoxine (PRX) by manganese(III) in aqueous AcOH were investigated and is first order with
respect to [MnIII]. The effects of varying [MnIII], [PRX], added manganese(II), pH and added anions such as AcO−, F−, Cl− and ClO
inf4
sup−
and SO
inf4
sup2−
were studied. The rate decreased slowly with increasing [H+] up to 0.2 mol dm−3 and increased steeply thereafter. The orders in [PRX] and [MnII] were unity and inverse fractional, respectively, in both low and high [H+] ranges. The dependence of reaction rate on temperature was studied and activation parameters were computed from Arrhenius
and Eyring plots. A mechanism consistent with the observed results is proposed and discussed. 相似文献
10.
Balesh A. Deganatti Nagaraj P. Shetti Sharanappa T. Nandibewoor 《Transition Metal Chemistry》2009,34(2):143-152
The oxidation of l-valine (l-val) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 3.0 × 10−3 mol dm−3 was studied spectrophotometrically at 298 K and follows the rate law;
where K
4, K
5 and K
6 are the equilibrium constants for the different steps involved in the mechanism, k is the rate constant for the slow step of the reaction. The appearance of [l-val] term in both numerator and denominator explains the observed less than unit order in [l-val]. Similarly the appearances of [H3IO6
2−] and [OH−] in the denominator obey the experimental negative less than unit order in [H3IO6
2−] and [OH−], respectively. The oxidation reaction in alkaline medium proceeds via a DPC-l-valine complex, which decomposes slowly 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. 相似文献
11.
The synthesised complex cis-[Cr(C2O4)(AaraNH2)(OH2)(OSO2)]− anion with SO
3
2−
as a ligand in the inner coordination sphere, where AaraNH2 denotes methyl 3-amino-2,3-dideoxy-α-d-arabino-hexopyranoside, was hydrolysed in the presence of acid at H+ concentrations from 0.01 to 2.7 m (HClO4). The reaction kinetics was studied with the stopped-flow spectrophotometric (u.v.–vis.) technique at temperatures of 5,
10, 15, 18 and 20 °C. This hydrolysis turned out to be a single-step process. Determined for this reaction were the rate constant
k
1 for the removal of SO2 from the coordination sphere of the cis-[Cr(C2O4)(AaraNH2)(OH2)(OSO2)]− ion and the constant pK
1 of the protonation of this species in the reaction preceding the hydrolysis. The final product of this reaction – a new complex
of CrIII, cis-[Cr(C2O4)(AaraNH2)(OH2)2]+, was obtained. A mechanism for the acid hydrolysis reaction is put forward based on the analysis of the rate constants obtained. 相似文献
12.
Sanjay D. Kadam Amit R. Supale Gavisiddappa S. Gokavi 《Transition Metal Chemistry》2008,33(8):989-994
Oxidation of benzoic acid hydrazide by bromate in the presence of octamolybdomanganate(II), [MnIIMo8O27]4−, was studied in hydrochloric acid medium. The mechanism of the reaction involves oxidation of the catalyst to [MnIVMo8O27]2− by bromate which then forms a complex with the unoxidized catalyst. Both the complex and [MnIVMo8O27]2− react with the substrate in rate-determining steps to generate an intermediate acyl diimide, RCONNH. The reaction of water
with the diimide then leads to the formation of benzoic acid and nitrogen as products through an NH–NH intermediate. There
was no formation of free radical, indicating the involvement of only two-electron transfer steps in the mechanism. The order
of more than unity in catalyst concentration is due to the formation of complex between the catalyst and the oxidized form
of the catalyst. A rate law explaining all the kinetic results has been derived and verified. The effects of ionic strength
and solvent polarity have also been studied, and the thermodynamic parameters were determined. A less solvated transition
state as a result of interaction between the complex and oxidized form of the catalyst satisfactorily explains all the effects
observed.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
Summary The kinetics of oxidation of aldoses, namely xylose, arabinose, galactose and glucose, by CeIV have been studied in HClO4 + H2SO4 medium and in the presence of PdII. The reactions exhibit a first order rate dependence with respect to oxidant. The rate is inversely dependent on the [HSO
inf4
sup–
][H+] ratio. The order of reaction with respect to aldose decreases at higher [aldose]. Due to the formation of a complex between CeIV and PdII, a retarding effect of [PdII] on the rate of disappearance of [CeIV] has been observed. A mechanism consistent with the observed kinetic data is proposed. 相似文献
14.
Rudragouda K. Patil Shivamurti A. Chimatadar Sharanappa T. Nandibewoor 《Transition Metal Chemistry》2008,33(5):625-633
The oxidation of antimony(III) by cerium(IV) has been studied spectrometrically (stopped flow technique) in aqueous sulphuric
acid medium. A minute amount of manganese(II) (10−5 mol dm−3) is sufficient to enhance the slow reaction between antimony(III) and cerium(IV). The stoichiometry is 1:2, i.e. one mole
of antimony(III) requires two moles of cerium(IV). The reaction is first order in both cerium(IV) and manganese(II) concentrations.
The order with respect to antimony(III) concentration is less than unity (ca 0.3). Increase in sulphuric acid concentration
decreases the reaction rate. The added sulphate and bisulphate decreases the rate of reaction. The added products cerium(III)
and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant, substrate and catalyst
are Ce(SO4)2, [Sb(OH)(HSO4)]+ and [Mn(H2O)4]2+, respectively. The activation parameters were determined with respect to the slow step. Possible mechanisms are proposed
and reaction constants involved have been determined. 相似文献
15.
R. Thangamuthu S. M. Senthilkumar K. Chandrasekara Pillai 《Journal of Solid State Electrochemistry》2007,11(1):126-133
Poly(4-vinylpyridine) (PVP)-based anion exchange polymers are not studied as much as cation exchange polymers Nafion and Eastman
Kodak AQ for electroanalytical applications. Similarly, octacyanomolybdate [Mo(CN)8
4−] has not been studied much as a redox mediator. This communication presents results from examinations of the behaviour of
Mo(CN)8
4−-doped PVP ionomer film electrode to highlight the opportunities for realization of the application of this composite electrode
for l-ascorbic acid (AH2) estimation via electrocatalytic mediation in acidic medium. The modified electrodes were characterized by cyclic voltammetry
and rotating disc electrode voltammetry. PVP coatings possess strong anion-binding capacity for Mo(CN)8
4− mediator with an extraction coefficient of 990, and electrostatically cross-linked PVP films offer insignificant resistance
to permeation of AH2, facilitating a cross-exchange reaction between the substrate and the mediator in the entire film volume. They show effective
electrocatalytic oxidation of AH2, with the oxidation potential of AH2 decreased by ∼200 mV in overpotential compared to that at bare electrode. Mo(CN)8
4−/PVP composite electrode does not respond to the more common interferents of l-ascorbic acid estimation even at high positive potentials. These and several other attractive potentialities of the modified
electrode are demonstrated by direct determination of AH2 in a commercial vitamin C tablet without any special treatment, with the value closely agreeing (±0.75%) with the reference
method. 相似文献
16.
Dillip Kumar Baral Sudhanshu Sekhar Rout Jashoda Behera Sudam Chandra Si Prakash Mohanty 《Transition Metal Chemistry》2011,36(2):231-236
The kinetics and mechanism of the substitution reaction between [Cr(H2O)6]3+ and l-Dopa in aqueous medium has been studied over the range 1.8 ≤ pH ≤ 2.6, 1.68 × 10−2 mol dm−3 ≤ [Dopa] ≤ 5.04 × 10−2 mol dm−3, I = 0.1 mol dm−3 (KNO3) at 50 °C. The reaction takes place via an outer sphere association between Cr3+ and l-Dopa followed by chelation. The product was characterized by physicochemical and infrared spectroscopic methods. The antiparkinsonian
activity of the product was found to be higher than that of l-Dopa. 相似文献
17.
The kinetics of oxidation of uric acid by thallium(III) has been studied in acetate buffers; the oxidation products are alloxan
and urea. Deprotonated uric acid, UaH−, and T1(OAc)3 are the reacting species. A probable reaction mechanism has been proposed conforming with rate law (1)-d[T1III]/dt=(k′1K′1+k′2K′2K1/[H+]) [T1III][UaH2]/1+K4[OAc−] A comparative analysis with other soft acids HgII and PbIV has been attempted. 相似文献
18.
Suresh M. Tuwar Vidyavati A. Morab Sharanappa T. Nandibewoor Javali R. Raju 《Transition Metal Chemistry》1991,16(4):430-434
Summary Catalysis of the CeIV-allyl alcohol (AA) reaction in acid solution depends both on the of rate enhancement and product distribution on the catalyst used: OsVIII results mainly in acrolein, whereas PdII gives acrylic acid. The rate laws in the two cases also differ:viz., Equations 1 and 2K1 is the equilibrium constant of formation of the OsVIII-allyl alcohol complex and k1 is the rate constant of its oxidation by CeIV; K2 is the equilibrium constant for the formation of the CeIV-PdII-allyl alcohol complex and k2 is its rate constant of decomposition. Rate = K1k1[CeIV][AA][OsVIII]/(1+K1[AA]) (1) Rate = K1k1[CeIV][PdII]/(1+K2[CeIV]) (2)While OsVIII is effective in H2SO4 solution, aqueous HClO4 is needed for PdII. Both reactions proceed through formation of catalyst-allyl alcohol complexes with participation of free radicals. The details of these observations are discussed. 相似文献
19.
Chimatadar Shivamurti A. Koujalagi Sangappa B. Nandibewoor Sharanappa T. 《Transition Metal Chemistry》2001,26(1-2):241-245
The oxidation of HgI by CeIV has been studied in aqueous H2SO4. A minute amount (10–6 mol dm–3) of OsVIII is sufficient to catalyse the reaction. The active catalyst, substrate and oxidant species are H2OsO5, [Hg2(SO4)HSO4]– and H3Ce(SO4)–
4, respectively. Possible mechanisms are proposed and the reaction constants involved have been determined. 相似文献
20.
The oxidation of [CrIII(HNTA)(Hist)(H2O)]− and [CrIII(HNTA)(Asp)(H2O)]− (NTA = nitrilotriacetate, Hist = l-histidinate and Asp = dl-aspartate) by periodate in aqueous medium has been studied spectrophotometrically between 15.0 and 35.0 °C under pseudo-first-order
conditions, [IO4
−] ≫ [complex]. The rate increases over the pH range 3.40–4.45 in both cases, but the two complexes give different rate laws.
It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO4
− to chromium(III). A common mechanism for the oxidation of some chromium(III) complexes by periodate is proposed, and this
is supported by an excellent isokinetic relationship between ΔH* and ΔS* values for these reactions. 相似文献