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1.
The reaction of peroxomonosulfate (PMS) with glycolic acid (GLYCA), an alpha hydroxy acid, in the presence of Ni(II) ions and formaldehyde was studied in the pH range 4.05–5.89 and at 31°C and 38°C. When formaldehyde and Ni(II) ions concentrations are ~5.0 × 10?4 M to 10.0 × 10?4 M, the reaction is second order in PMS concentration. The rate is catalyzed by formaldehyde, and the observed rate equation is (?d[PMS])/dt = (k′2[HCHO][Ni(II)][PMS]2)/{[H+](1+K2[GLYCA])}. The number of PMS decomposed for each mole of formaldehyde (turnover number) is 5–10, and the major reaction product is oxygen gas. The first step of the reaction mechanism is the formation of hemiacetal by the interaction of HCHO with the hydroxyl group of nickel glycolate. The peroxomonosulfate intermediate of the Ni‐hemiacetal reacts with another molecule of PMS in the rate‐limiting step to give the product. This reaction is similar to the thermal decomposition of PMS catalyzed by Ni(II) ions. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 642–649, 2009 相似文献
2.
The rates of reduction of Eu3+ and Cr3+ have been measured in mixed perchlorate + thiocyanate electrolytes at constant ionic strength, using low concentrations of thiocyanate to minimize its association with the cationic reactants. The effect of adsorbed thiocyanate anions on the reduction kinetics of Cr3+ resembled those produced by iodide and bromide on both Cr3+ and Eu3+. However, thiocyanate exhibited an unusual catalytic effect on the reduction of Eu3+ which was identified as arising from a reaction pathway involving thiocyanate-bridging between the mercury surface and the Eu3+. The diagnostic criteria used to support the proposed mechanism included analysis of the rate—potential behavior and of the effects of competitively adsorbed iodide ions upon the reduction rates. 相似文献
3.
Nandibewoor Sharanappa T. Hiremath Gouri A. Timmanagoudar Prakash L. 《Transition Metal Chemistry》2000,25(4):394-399
The oxidation of thiocyanate by periodate has been studied in alkaline media. A micro quantity of RuIII is sufficient to catalyse the reaction. The active catalytic species and oxidant in the reaction are understood to be [Ru(H2O)5OH]2+ and IO−
4. The autocatalysis exhibited by one of the products, cyanate, is attributed to adduct formation between cyanate and periodate.
A composite mechanism and rate law are proposed. The reaction constants involved in the mechanism are evaluated.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
4.
Oxidation of Antitubercular Drug Isoniazid by a Lipopathic Oxidant,Cetyltrimethylammonium Dichromate: A Mechanistic Study
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The oxidation of an antitubercular drug isoniazid by a lipopathic oxidant cetyltrimethylammonium dichromate (CTADC) in a nonpolar medium generates isonicotinic acid both in the presence and the absence of acetic acid. The conventional UV–vis spectrophotometric method is used to study the reaction kinetics. The occurrence of the Michaelis–Menten–type kinetics with respect to isoniazid confirms the binding of oxidant and substrate to form a complex before the rate‐determining step. The existence of the inverse solvent kinetic isotope effect, k(H2O)/ k(D2O) = 0.7, in an acid‐catalyzed reaction proposes a multistep reaction mechanism. A decrease in the rate constant with an increase in [CTADC] reveals the formation of reverse micellar–type aggregates of CTADC in nonpolar solvents. In the presence of different ionic and nonionic surfactants, CTADC forms mixed aggregates and controls the reaction due to the charge on the interface and also due to partition of oxidant and substrate in two different domains. High negative entropy of activation (ΔS? = –145 and –159 J K?1 mol?1 in the absence and presence of acetic acid) proposes a more ordered and highly solvated transition state than the reactants. Furthermore, the solvent polarity‐reactivity relationship reveals (i) the presence of less polar and less ionic transition state compared to the reactants during the oxidation, (ii) differential contribution from nonpolar and dipolar aprotic solvents toward the reaction process, and (iii) the existence of polarity/hydrophobic switch at log P = 0.73. A suitable mechanism has been proposed on the basis of experimental results. These results may provide insight into the mechanism of isoniazid oxidation in hydrophobic environment and may assist in understanding the drug resistance in different location. 相似文献
5.
《Analytical letters》2012,45(7):741-752
Abstract The oxidation of the 1, 2, 3, 4-thiatriazol-5-thiolate ion CS2 N? 3by, permanganate ions in an alkaline medium was investigated. The pseudo-halide undergoes a quantitative seventeen-electron change reaction yielding sulphate, nitrogen and carbon dioxide as final products. Despite the similar chemical behavior exhibited by thiocyanate and CS2N? 3 ions the experimental data strongly suggested that the oxidation reactions of the pseudo-halides dealt with in this study do not follow the same mechanism. On the basis of this reaction an oxidative analytical method was developed for the CS2N? 3. The pseudo-halide is oxidized by an excess of permanganate ions. The remaining oxidant is titrated with standardized thalium (I) or hexacyanoferrate (II) solutions. Considerable improvements over former procedures were achieved employing two polarized platinum electrodes to detect the end point, by potentiometry. The method proposed here is simple, precise, accurate, rapid and allows the determination of pseudo-halide concentrations down to 1 × 10?3 M. 相似文献
6.
Shivamurti A. Chimatadar Shankar V. Madawale Sharanappa T. Nandibewoor 《Transition Metal Chemistry》2007,32(5):634-641
A minute quantity (10−6 mol dm−3) of iodide catalysed oxidation of l-glutamic acid by CeIV has been studied in H2SO4 and SO
4
2−
media. The reaction was first order each in [CeIV] and [I−]. The order with respect to [l-glutamic acid] was less than unity (0.71). Increase in [H2SO4] decreased the reaction rate. The added HSO
4
−
and SO
4
2−
decreased the rate of reaction. The added product, succinic acid, had no effect on the reaction rate, whereas added CeIII retarded the reaction. The ionic strength and dielectric constant did not have any significant effect on the rate of reaction.
The active species of oxidant was Ce(SO4)2. A suitable mechanism was proposed. The activation parameters were determined with respect to the slow step of the mechanism.
The thermodynamic quantities were also determined and discussed. 相似文献
7.
A new simple, rapid and sensitive spectrophotometric flow injection method for the determination of trace iodide is described
based on an ion associate of iodate (IO3
–) with 2- (3,5-dibromo-2-pyridylazo)-5-diethylamino-phenol (3,5-Br2-PADAP) and thiocyanate (SCN–). In a strongly acidic medium, this unstable violet product was formed with an absorption maximum at 605 nm. Flow injection
is an ideal method to reproducibly monitor the transient signal. Various parameters were optimized using the Super Modified
Controlled Weighted Centroid Simplex Method (SMCWC). Under the optimum experimental conditions, iodide could be determined
in the range of 1.00 × 10–6 and 2.4 × 10–5 mol l–1. The correlation coefficient of the calibration curve is 0.9991. With a sampling frequency of 80 h–1, the detection limit for iodide is 5.0 × 10–7 mol l–1. The proposed method has been applied to the determination of trace iodide after oxidizing I– in table salt or laver to IO3
–. In addition, the mechanisms of the ion association reaction was studied.
Received: 15 August 1996 / Revised: 10 October 1996 / Accepted: 16 October 1996 相似文献
8.
The kinetics of oxidation of ethanolamines, monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA), by sodium N‐bromobenzenesulfonamide or bromamine‐B (BAB) in alkaline buffer medium (pH 8.7–12.2) has been studied at 40°C. The three reactions follow identical kinetics with first‐order in [oxidant] and fractional‐order each in [substrate] and [OH?]. Under comparable experimental conditions, the rate of oxidation increases in the order: DEA > TEA > MEA. The added reaction product, benzenesulfonamide, retards the reaction rate. The addition of halide ions and the variation of ionic strength of the medium have no significant effect on the rate. The dielectric effect is negative. The solvent isotope effect k′(H2O)/k′(D2O) ≈ 0.92. Activation parameters for the composite reaction and for the rate‐limiting step were computed from the Eyring plots. Michaelis‐Menten type of kinetics is observed. The formation and decomposition constants of ethanolamine‐BAB complexes are evaluated. An isokinetic relationship is observed with β = 430 K indicating that enthalpy factors control the rate. For each substrate, a mechanism consistent with the kinetic data has been proposed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 480–490, 2001 相似文献
9.
The kinetics of the bromate oxidation of tris(1,10-phenanthroline)iron(II) (Fe(phen)32+) and aquoiron(II) (Fe2+ (aq)) have been studied in aqueous sulfuric acid solutions at μ = 1.0M and with Fe(II) complexes in great excess. The rate laws for both reactions generally can be described as -d [Fe(II)]/6dt = d[Br?]/dt = k[Fe(II)] [BrO?3] for [H+]0 = 0.428–1.00M. For [BrO?3]0 = 1.00 × 10?4M. [Fe2+]0 = (0.724–1.45)x 10?2 M, and [H+]0 = 1.00M, k = 3.34 ± 0.37 M?1s?1 at 25°. For [BrO?3]0 = (1.00–1.50) × 10?4M, [Fe2+]0 = 7.24 × 10?3M ([phen]0 = 0.0353M), and [H+]0 = 1.00M, k = (4.40 ± 0.16) × 10?2 M?1s?1 at 25°. Kinetic results suggest that the BrO?3-Fe2+ reaction proceeds by an inner-sphere mechanism while the BrO?3-Fe(phen)32+ reaction by a dissociative mechanism. The implication of these results for the bromate-gallic acid and other bromate oscillators is also presented. 相似文献
10.
R. Khattak I. Imam Naqvi M. Akhyar Farrukh 《Journal of the Iranian Chemical Society》2008,5(4):631-640
Kinetics of the oxidation of tris(2,2′-bipyridine)iron(II) sulfate by ceric sulfate was spectrophotometrically studied in an aqueous sulfuric acid medium. Different methods, including isolation, integration and half-life, were employed to determine the reaction order. The redox reaction was found to be first-order with respect to the reductant, tris(2,2′-bipyridine)iron(II) sulfate, and the oxidant, ceric sulfate. Complex kinetics was observed with an increase in the initial concentration of the oxidant. The influence of the dielectric constant, [H+] and [SO4 2-] on the rate was also investigated. The increase in the dielectric constant and H+ ion concentration of the medium retard the rate, while an increase in the SO4 2- ion concentration first accelerates the rate, and then retards the reaction. The effect of each factor, i.e., the dielectric constant, H+ ions and SO4 2- ions, suggests that Ce(SO4)3 2- is the active species of cerium(IV). A rate law consistent with the observed kinetic data and the proposed mechanism is suggested to be: {fx631-1 相似文献
11.
Biswajit Pal 《国际化学动力学杂志》2014,46(1):31-40
The hexachloroiridate(IV) oxidation of α,β‐unsaturated compounds such as acrylic acid, acrylamide, and acrylonitrile (CH2=CHX; X = –COOH, –CONH2, and –CN) was carried out in NaOAc‐AcOH buffer medium. The reaction follows complex kinetics, being first order in [IrIV] and complex order in [CH2=CHX]. H+ ion has no effect on the reaction rate in the pH range 3.42–4.63. The pseudo–first‐order rate constant decreases with a decrease in the dielectric constant and with a decrease of ionic strength of the medium. The oxidation rate follows the sequence: acrylonitrile > acrylamide > acrylic acid. A mechanism is proposed involving the formation of an unstable intermediate complex between the substrate and the oxidant which is transformed to the radical cation in a slow rate‐determining step with the concomitant reduction of Ir(IV) to Ir(III). The radical cation subsequently decomposes to the aldehyde that appears as the ultimate product of the carbon–carbon double bond cleavage. The major product of oxidation was identified as HCHO by 1H NMR. Activation parameters for the slow rate‐determining step and thermodynamic parameters associated with the equilibrium step of the proposed mechanism have been evaluated. The enthalpy of activation is linearly related to the entropy of activation, and this linear relationship confirms that the oxidation of all the α,β‐unsaturated compounds follows a common mechanism. 相似文献
12.
The kinetics of oxidation of L-Alanine (Ala) by N-bromophthalimide (NBP) was studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at
308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Ala] and inverse
fractional order dependence on [H+]. The addition of reduced product of the oxidant [Phthalimide] has decreased the rate of reaction. The rate of reaction increased
with increase in inorganic salts concentration i.e., [Cl−] and [Br−], whereas a change in ionic strength of the medium and [Hg(OAc)2] had no effect on oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium.
CH3CN was identified as the main oxidation product of the reaction. The various activation parameters have been computed and
suitable mechanism consistent with the experimental findings has also been proposed. The micelle-binding constant has been
calculated.
Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 3, pp. 386–396.
The article is published in the original. 相似文献
13.
Praveen K. Tandon Alka Mehrotra Alok K. Singh Ramesh Baboo Priy B. Dwivedi 《国际化学动力学杂志》2004,36(10):545-553
RuCl3 further catalyzes the oxidation of iodide ion by K3Fe(CN)6, already catalyzed by hydrogen ions. The rate of reaction, when catalyzed only by hydrogen ions, was separated graphically from the rate when both Ru(III) and H+ ions catalyzed the reaction. Reactions studied separately in the presence as well as absence of RuCl3 under similar conditions were found to follow second‐order kinetics with respect to [I?], while the rate showed direct proportionality with respect to [Fe(CN)6]3?, [RuCl3], and [H+]. External addition of [Fe(CN)6]4? ions retards the reaction velocity, while changing the ionic strength of the medium has no effect on the rate. With the help of the intercept of the catalyst graph, the extent of the reaction that takes place without adding Ru(III) was calculated and it was in accordance with the values obtained from the reaction in which only H+ ions catalyzed the reaction. It is proposed that ruthenium forms a complex, which slowly disproportionates into the rate‐determining step. Arrhenius parameters at four different temperatures were also calculated. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 545–553, 2004 相似文献
14.
Y. Lakshman Kumar R. Venkata Nadh P. S. Radhakrishnamurti 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(3):552-559
Role of added chloride ions on the shift of reaction pathway of oxidation of aromatic ketones (acetophenone, desoxybenzoin) by dichloroisocyanuric acid (DCICA) was studied in aqueous acetic acid—perchloric acid medium. Participation of enolic and protonated forms of ketones in the rate determining steps is manifested from zero and first orders with respect to the oxidant in absence and presence of added chloride ions, respectively. Positive and negative effects of acid and dielectric constant on the reaction rate were observed. The observations deduce plausible mechanisms involving (i) rate-determining formation of enol from the conjugate acid of the ketone (SH+) in the absence of added chloride ions and (ii) rapid formation of molecular chlorine species from HOCl (hydrolytic species of DCICA) in the presence of added chloride ions, which then interacts with SH+ in a rate-determining step prior to the rapid steps of product formation. The order of Arrhenius parameters substantiate the proposed plausible mechanisms based on order of reactants both in presence and absence of added chloride ions. 相似文献
15.
Rajeshwari V. Hosahalli Anita P. Savanur Sharanappa T. Nandibewoor Shivamurti A. Chimatadar 《国际化学动力学杂志》2010,42(7):440-452
The oxidation of D ‐mannitol by cerium(IV) has been studied spectrophotometrically in aqueous sulfuric acid medium at 25°C at constant ionic strength of 1.60 mol dm?3. A microamount of ruthenium(III) (10?6 mol dm?3) is sufficient to enhance the slow reaction between D ‐mannitol and cerium(IV). The oxidation products were identified by spot test, IR and GC‐MS spectra. The stoichiometry is 1:4, i.e., [D ‐mannitol]: [Ce(IV)] = 1:4. The reaction is first order in both cerium(IV) and ruthenium(III) concentrations. The order with respect to D ‐mannitol concentration varies from first order to zero order as the D ‐mannitol concentration increases. Increase in the sulfuric acid concentration decreases the reaction rate. The added sulfate and bisulfate decreases the rate of reaction. The active species of oxidant and catalyst are Ce(SO4)2 and [Ru(H2O)6]3+, respectively. A possible mechanism is proposed. The activation parameters are determined with respect to a slow step and reaction constants involved have been determined. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 440–452, 2010 相似文献
16.
Novel, simple, rapid, highly sensitive, and direct determination of iodide and thiocyanate ions in seawater has been performed by liquid chromatography (LC) with UV detection at 220 nm. The separation was achieved on a C30 column of conventional size (150 mm × 4.6 mm i.d.) modified with poly(ethylene glycol); an aqueous solution of 300 mM sodium sulfate and 50 mM sodium chloride was used as mobile phase. Detection limits (S/N=3) obtained by injecting a 20-L sample were 0.5 and 6 ng mL–1 for iodide and thiocyanate, respectively. The method was successfully used for rapid and direct determination of iodide and thiocyanate in seawater samples, collected from the coasts of Japan, without any extra pretreatment.Dedicated to Professor K. Jinno on the occasion of his 60th birthday 相似文献
17.
The kinetics of the hexacyanoferrate (III) oxidation of dihydroxyfumaric acid to hexacyanoferrate (II) and diketosuccinic acid was looked into within the 0.04 to 5.3 M HCl acidity range under different temperatures, ionic strengths, and solvent permittivity conditions. The kinetic effect of alkali metal ions, transition metal impurities, and substrate concentrations have also been analyzed. The observed inhibition effect brought about by addition of the reaction product, hexacyanoferrate (II), is a sign of a complex mechanism. The rate constants remained essentially unchanged up to 1 M HCl, diminished between 1.0 and 3.0 M HCl, and rose above 3.0 M HCl. Depending on the medium acidity, three mechanisms can be put forward, which involve different kinetically active forms. At low acidity, the rate-determining step involves a radical cation and both the neutral and the anion substrate forms are equally reactive ( k 1 = k 2 = 2.18 +/- 0.05 M (-1) s (-1), k -1 = 0.2 +/- 0.03). When the medium acidity is boosted, the rate-determining step involves the neutral dihydroxyfumaric acid and two hexacyanoferrate (III) forms. In the intermediate region the rate constant diminished with rising [H (+)] ( k' 1 = 0.141 +/- 0.01 and k' 2 = 6.80 +/- 0.05). Specific catalytic effect by binding of alkali metal ions to oxidant has not been observed. In all instances it was assessed that the substrate decomposition is slow compared to the redox reaction. 相似文献
18.
Summary The title reaction has been followed spectrophotometrically at 325 nm (max of [Mn(CN)6]3–) under pseudo-first order conditions with cyanide in a large excess at pH=10.0, I=0.1M (NaClO4) and 25°C. The reaction follows first-order kinetics in [MnEDTA(OH)]2– and exhibits variable-order dependence in [CN–] one at high cyanide concentration, and two at low cyanide concentration. The product of above reaction has been identified as [Mn(CN)6]3–.The kinetics of the reverse reaction,i.e., the reaction of [Mn(CN)6]3- with EDTA4– have also been followed spectrophotometrically. This reactions is first-order with respect to both [Mn(CN)
6
3–
] and [EDTA4–] and exhibits an inverse first-order dependence on [CN–]. A six-step mechanism has been proposed in which the penultimate step is rate-determining. The activation parameters have been obtained and support the postulated mechanism. 相似文献
19.
Praveen K. Tandon Manisha Purwar Priy B. Dwivedi Manish Srivastava 《Transition Metal Chemistry》2008,33(6):791-795
Oxidation of benzaldehyde and p-nitro-benzaldehyde by cerium(IV) sulphate in aqueous sulphuric acid is strongly catalyzed by iridium(III) chloride. The complex
formed between cerium(IV) and the organic substrate in the first equilibrium step gives another complex in the presence of
iridium(III), which ultimately gives the corresponding aromatic acids as the product of oxidation. The order of the reaction
follows first-order kinetics at low concentrations to zero order at higher concentrations of both the oxidant and organic
substrate. The rate is directly proportional to the concentration of catalyst, but decreases sharply with increasing H+ ions and cerium(III) concentrations, while change in ionic strength of the medium or the concentration of acetic acid and
Cl− ions has no effect on the rate. 相似文献
20.
《Analytical letters》2012,45(6):695-705
Abstract Flow injection analysis (FIA) with a double injection technique was applied to catalytic determination of thiocyanate and iodide in the redox reaction between cerium (IV) and arsenic (III). Selective inactivation of the catalytic activity of thiocyanate was investigated. Amounts of only iodide and amounts of both thiocyanate and iodide were simultaneously determined by the FIA. Detection limits of the method were 0.2 ppm SCN? and 0.1 ppm I?. 相似文献