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1.
The kinetics of oxidation of ethanol by cerium(IV) in presence of ruthenium(III) (in the order of 10?7 mol dm?3) in aqueous sulfuric acid media have been followed at different temperatures (25–40°C). The rate of disappearance of cerium(IV) in the title reaction increases sharply with increasing [C2H5OH] to a value independent of [C2H5OH] over a large range (0.2–1.0 mol dm?3) in which the rate law conforms to: where [Ru]T gives the total ruthenium (III) concentration. The values of 10?3kc and 10?3kd are 3.6 ± 0.1 dm3 mol?1 s?1 and 3.9 ± 0.2 s?1, respectively, at 40°C, I = 3.0 mol dm?3. The proposed mechanism involves the formation of ruthenium(III)? substrate complex which undergoes oxidation at the rate determining step by cerium(IV) to form ruthenium(IV)? substrate complex followed by the rapid red-ox decomposition giving rise to the catalyst and ethoxide radical which is oxidized by cerium(IV) rapidly. The mechanism is consistent with the existence of the complexes RuIII · (C2H5OH) and RuIII · (C2H5O?) and both are kinetically active. The overall bisulphate dependence conforms to: kobsd = A[Ru]T/{1 + C[HSO4?]} where A = 2.2 × 104 dm3 mol?1 s?1, C = 1.3 at 40°C, [H+] = 0.5 mol dm?3, and I = 3.0 mol dm?3. The observations are consistent with the Ce(SO4)2 as the kinetically active species. © 1995 John Wiley & Sons, Inc. 相似文献
2.
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
3.
The kinetics of the oxidation of oxalic acid by cerium(IV) in sulfuric acid medium has been studied voltammetrically. The specific reaction rate is 132±4.0 M–1s–1 at 25.0 °C. The energy of activation is 62.6±3.0 kJ mol–1. The entropy of activation is –2.7 J mol–1K–1. The specific reaction rate is influenced by complexation and also by ionic strength (). The most likely mechanism has been suggested.
(IV) . 132±4,0 M–1c–1 25,0 °C. 62,6±3,0 ·M–1. –2,7 ·K–1M–1. , (). .相似文献
4.
The kinetics and mechanism of IrIII-catalysed oxidation of dioxane by CeIV in both aqueous H2SO4 and HClO4 media have been studied at different temperatures under the conditions: [dioxane]T [CeIV]T [Ir]T (ca. 10–6–10–8moldm–3). In aqueous HClO4 media a slow uncatalysed path exists alongside the catalysed path, while in aqueous H2SO4 media the catalysed path is the only kinetically detectable path. In both media, the overall process shows a first-order dependence on [CeIV]T; the catalytic path is first order in [Ir]T and exhibits a non-linear dependence on [dioxane]T. The catalysed path probably involves a pre-equilibrium interaction between the catalyst and substrate leading to an outer-sphere complex followed by the electron transfer in the rate-determining step involving CeIV and an outer-sphere complex formed in pre-equilibrium steps. The catalytic path presumably involves the IrIII/IrIV cycle. In HClO4 media the catalytic efficiency is greater than in H2SO4 media. Activation parameters for different paths have been determined in order to rationalise the mechanistic steps. 相似文献
5.
Yongjun Ma 《Analytica chimica acta》2003,489(2):173-181
The chemiluminescence (CL) of the rhodamine B (RhB)-cerium(IV) system was investigated by flow-injection. Rhodamine B was suggested to be a suitable chemiluminescent reagent in acidic conditions. When the concentration of rhodamine B was 100 mg l−1 and cerium sulfate was 1.6 mmol l−1 in sulfuric acid, the chemiluminescent intensity was found to be highest by using 0.3 mol l−1 sulfuric acid as a carrier solution. The particular chemiluminescent system could tolerate such distinct acidic environments that it was utilized for detecting many compounds that are stable in acidic solutions. Furthermore, by virtue of IR, UV-Vis and luminescence spectroscopic measurements, the chemiluminescent behavior of rhodamine B was studied and a possible mechanism for this chemiluminescent reaction was proposed. The emitter was affirmed to be a radical species due to one of the oxidation products of RhB; the chemiluminescent emissive wavelength was about 425 nm. 相似文献
6.
7.
Under the experimental conditions [DMSO]T [CeIV]T [Os]T the kinetics of oxidation of dimethylsulfoxide (DMSO) to dimethylsulfone (DMSO2) have been followed at different temperatures (40–55°C) in 1.0 mol dm–3 sulfuric acid media. The rate of disappearance of [CeIV] shows a first-order dependence on both [Os]T and [DMSO]T and zeroth-order kinetics with respect to [CeIV]. The suggested mechanism involves oxidation of DMSO by OsVIII in a rate-determining step through an outer-sphere mechanism, followed by rapid regeneration of OsVIII by CeIV from OsVI. The rate law conforms to: –d[CeIV]/dt=k0=k[Os]T[DMSO]T. The values of k and the activation parameters are: 102k=(4.9 ± 0.10) mol–1 dm3 s–1 at 40°C, [H2SO4] =1.0 mol dm–3;H=58±3kJmol–1, S= –88 ±5JK–1mol–1. 相似文献
8.
A new chemiluminescence (CL) method is proposed for the determination of chlorpromazine hydrochloride, a drug often used to treat the psychiatric patients suffering from clinical depression. The method is based on the reaction between studied drug and Ce(IV) in a nitric acid medium and measurement of the CL intensity produced by rhodamine 6G used as a sensitizer. In the optimum conditions, CL intensities are proportional to concentrations of the studied drug over the range 0-1x10(-5) g ml(-1) with a detection limit of 6.5x10(-9) g ml(-1). The relative standard deviation (R.S.D.) is 4.1% for 1.5x10(-6) g ml(-1) chlorpromazine hydrochloride (n=11). The method has been applied to the determination of studied drug in tablets and biological fluids with satisfactory results. 相似文献
9.
The kinetics of oxidation of tartaric acid by Ce(IV) in the absence and presence of acrylamide has been investigated spectrophotometrically in aqueous H2SO4–HClO4 media at a constant ionic strength 2.0M and 25°C. Oxidation of tartaric acid in both cases was first order with respect to Ce(IV). Kinetic data showed that the reaction involves the formation of an unstable complex and an intermediate free radical. The activation parameters were calculated to be E
a
=91.3±0.4 kJ-mol–1, S=20.2±1.0 J-mol–1-K–1, H=88.8±0.4 kJ-mol–1. A polymerization mechanism is discussed. 相似文献
10.
11.
The kinetics and mechanism of Ag(I)-catalyzed oxidation of l-alanine by cerium (IV) in sulfuric acid media have been investigated by titrimetric technique of redox in the temperature range of 298–313 K. It is found that the reaction is of first order with respect to Ce(IV) and l-alanine, and it is of a positive fractional order with respect to Ag(I). It is found that the pseudo first order ([l-alanine] ? [Ce(IV)] ? [Ag(I)]) rate constant k′ increases with the increase of[H+]. The major oxidation product of alanine has been identified as acetaldehyde by an 1H NMR and IR spectroscopy. Under the experimental conditions, the kinetically active species has been found to be Ce4+. Under nitrogen atmosphere, the reaction system can initiate the polymerization of acrylonitrile, indicating generation of free radicals. On the basis of the experimental results, a suitable mechanism has been proposed. The rate constants of the rate-determining step together with the activation parameters were evaluated. 相似文献
12.
13.
The kinetics and mechanism of cerium(IV) oxidation of hexitols, i.e. D ‐sorbitol and D ‐mannitol, in aqueous sulfuric acid media have been studied in the presence and absence of surfactants. Under the kinetic conditions, [S]T ? [Ce(IV)]T, where [S]T is the total substrate (D ‐sorbitol or D ‐mannitol) concentration, the overall process shows a first‐order dependence on [Ce(IV)]T and [S]T. The process is acid catalyzed and inhibited by [HSO]. From the [HSO] dependence, it has been noted that the both Ce(SO4)2+ and Ce(SO4)2 have been found kinetically active. The different rate constants in the presence and absence of surfactants have been estimated with the activation parameters. N‐cetylpyridinium chloride has been found to retard the oxidation process of hexitols, whereas sodium dodecyl sulfate has been found to accelerate the rate process. All these findings including the micellar effects have been interpreted in terms of the proposed reaction mechanism and partitioning behavior of the kinetically active different species of Ce(IV) between the aqueous and pseudomicellar phase. © 2008 Wiley Periodicals, Inc. 40: 445–453, 2008 相似文献
14.
Kinetics of the oxidation of D ‐fructose by cerium(IV) has been investigated both in the absence and presence of surfactants (cetyltrimethylammonium bromide, CTAB, and sodium dodecyl sulfate, SDS) in sulfuric acid medium. The reaction exhibits first‐order kinetics each in [cerium(IV)] and [D ‐fructose] and inverse first order in [H2SO4]. The Arrhenius equation is found to be valid for the reaction between 30–50°C. A detailed mechanism with the associated reaction kinetics is presented and discussed. While SDS has no effect, CTAB increases the reaction rate with the same kinetic behavior in its presence. The catalytic role of CTAB micelles is discussed in terms of the pseudophase model proposed by Menger and Portnoy. The association constant Ks that equals to 286 mol?1 dm3 is found for the association of cerium(IV) with the positive head group of CTAB micelles. The effect of inorganic electrolytes (Na2SO4, NaNO3, NaCl) has also been studied and discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 18–25, 2006 相似文献
15.
For the first time sequential injection analysis (SIA) technique has been employed for titrimetry. A new SI titrimetric spectrophotometric method for the assay of vitamin C in drug formulations was explored. The method is based on the oxidation reaction of vitamin C with cerium(IV) in sulfuric acid media using a spectrophotometer as a detector with the wavelength monitored at 410 nm. A 2(3) factorial design chemometric approach was employed to study the interaction effect of the chemical and system variables, mainly cerium(IV), sulfuric acid concentrations and the flow rate. The results of the chemometric optimization revealed that the optimum operating conditions for the SI titrimetric analysis of vitamin C were 7.0 x 10(-3) M cerium(IV), 0.455 M sulfuric acid and 28.9 microL s-1 flow rate. A linear calibration plot for the determination of vitamin C was obtained in the concentration range between 30 to 200 ppm. The method was applied to the determination of vitamin C in pharmaceutical preparations and no excipient was found to pose any interference, thus rendering the method suitable for the determination of the drug in pharmaceutical preparations. The SIA method is found to be accurate when the results were statistically compared with the results obtained by the BP standard method. The SIA method is superior when compared to the conventional titration method, the BP standard method and previous methods with respect to precision and automation in solution handling. 相似文献
16.
The oxidation of methylene blue (MB+) by cerium(IV) was studied in 0.1–5 M H2SO4. The reaction proceeds via MB radical (MB2+•) formed by one electron transfer to the oxidant. The radical is observed spectrophotometrically by a very intense absorbance
at λmax = 526 nm and by the e.p.r signal at g = 2.000. The kinetics of the fast radical formation are two orders of magnitude slower than its decomposition, which were
examined using a stopped-flow method at 298 K under pseudo-first order conditions. The rate laws for the both steps were determined
and a likely mechanism reported. 相似文献
17.
18.
Yongjun Ma 《Analytica chimica acta》2004,501(1):25-30
A novel flow-injection chemiluminescence method for the determination of DNA at ultra-trace level has been established. In 0.8 M sulfuric acid media, the chemiluminescence of the rhodamine B-cerium (IV) or Ce(IV) system is enhanced by DNA, activated previously by imidazole-HCl buffer solution (pH 7.0). The enhanced intensity of chemiluminescence is in proportion to log DNA concentration 1.0×10−8 to 0.1 μg ml−1 for herring sperm DNA and 2.0×10−6 to 0.2 μg ml−1 for calf thymus DNA with 3σ detection limits of 8.3×10−9 μg ml−1 for herring sperm DNA and 3.5×10−7 μg ml−1 for calf thymus DNA, respectively. The relative standard deviation for 1.0×10−4 μg ml−1 herring sperm DNA was 0.99% and 2.0×10−3 μg ml−1 for calf thymus DNA was 1.1% (n=11). Using the optimized system, DNA contents in six synthetic samples has been determined with recoveries of 99.5-109.0%. The possible mechanism has also been studied in this paper. 相似文献
19.
The kinetics of the reaction have been investigated in H2SO4 medium under different conditions. The observed bimolecular rate constant kobs, has been found to depend on [H+]?0.55 and to increase with the initial concentration ratio of the reactants R0 = [H2O2]0/[U (IV)]0 above 0.49. The activation energy of the overall reaction has been determined as 13.79 and 14.3 kcal/mol at R0 = 1 and 0.35, respectively. Consistent with experimental data, a detailed reaction mechanism has been proposed where the hydrolytic reaction (4) followed by the rate-controlling reaction (10) and subsequent fast reactions of U (V) and OH radicals are involved: A kinetic expression has been derived from which a graphical evaluation of (kK4)?1 and k?1 has been made at R0 = 1 as (12.30 ± 0.09) × 10?3 M min, (6.23 ± 2.19) × 10?4 M min; and at R0 = 0.35 as (12.63 ± 2.13) × 10?3 M min, (8.32 ± 6.62) × 10?4 M min, respectively. Indications of some participation of a chain reactionat R0 = 1 have been obtained without affecting thesecond-order kinetics as observed. 相似文献