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61.
62.
Kinetics of oxidation of cinnamaldehyde (Cinn) by chloramine-T (CAT) has been studied in solutions containing HCl and H2SO4 at 313 K. The respective experimental rate laws obtained in HCl and H2SO4 media are as follows: and Here the value of x varies from 0.9 to zero while the values of y and z are 0.83 and 0.72, respectively. Effects, on the reaction rate, of ionic strength, reaction product (p-toluenesulfonamide), dielectric constant of the solvent medium, and the anions, Cl− and SO42−, have been investigated. Activation parameters have been computed, based on the rate constants determined at different temperatures. Mechanisms proposed and the rate laws derived are consistent with the observed kinetic data represented by the experimental rate laws. 相似文献
63.
Kinetics of oxidation of thiocarbohydrazide (TCH) in the free state and as its metal complex, and as a hydrazone by chloramine-T
(CAT) in aqueous HClO4 medium, and by dichloramine-T (DCT) in 1:1 (v/v) water-methanol medium in the presence of HClO4 have been studied. Rates of oxidation of TCH in the free state and in metal complex by CAT were determined. The rate law
for the oxidation of TCH at high [H+ ] and for complex oxidations were identical to that for CAT oxidations. The conversion of TCH into its hydrazone changed
the order in [H+] from a positive to a negative value, probably signalling the change of reaction site. The rate law for oxidation under these
conditions was determined. Addition of the reduced product of the oxidants had no effect on the rate of oxidations. Variation
in ionic strength of the medium had little positive effect, while decrease in dielectric constant of the medium decreased
the rate in both the oxidations. Oxidation processes generally follow a Michaelis-Menten type of mechanism. Constants of the
rate limiting steps have been calculated at different temperatures and these constants have been used to calculate the activation
parameters from the Arrhenius plots. The proposed mechanisms are supported by investigations with HOC1 under identical reaction
conditions. Metal complexation of the substrate decreased the reactivity, while conversion of TCH into its hydrazone changed
the rate dependence on [H+]. 相似文献
64.
Manikyanahally N. Kumara Dase Gowda Channe Gowda Kanchugarakoppal S. Rangappa 《Reaction Kinetics and Catalysis Letters》2001,72(2):331-342
Synthesis and characterization of the dipeptides(DP) namely Glycyl-Proline (Gly-Pro), Alanyl-Proline (Ala-Pro) and Valyl-Proline (Val-Pro), were made. Kinetics of oxidation of these DP by Mn(III) have been studied in the presence of sulfate ions in acidic medium at 26C. The reaction was followed spectrophotometrically at max = 500 nm. A first order dependence of rate on both Mn(III) and DP was observed. The rate is independent of the concentration of reduction product, Mn(II) and hydrogen ions. Effects of varying dielectric constant of the medium and addition of anions such as sulfate, chloride and perchlorate were studied. Activation parameters have been evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of DP with Mn(III) in the rate limiting step is suggested. 相似文献
65.
Netkal M. Made Gowda V.M.Sadagopa Ramanujam Norman M. Trieff G.John Stanton Dandinasivara S. Mahadevappa 《Microchemical Journal》1981,26(1):95-104
A new oxidimetric reagent, dichloramine-N (N,N′-dichloro-p-nitrobenzenesulfonamide; DCN) has been synthesized and its structure elucidated from the spectral data and elemental analyses. The ultraviolet, infrared, nuclear magnetic resonance, and mass spectral data have been presented. Analytical applications of DCN as a potential redox titrant in the determination of diverse reductants such as ascorbic acid, methionine, sulfite, arsenite, glutathione, and indigocarmine have been described. 相似文献
66.
V.M. Sadagopa Ramanujam Netkal M.Made Gowda Norman M. Trieff Marvin S. Legator 《Microchemical Journal》1980,25(3):295-300
A simple ultraviolet spectrophotometric method for the assay of microgram amounts (0.1–25 μg/ml) of 16 different p-aminobenzenesulfonamides (sulfonamides) in 0.1 N sodium hydroxide has been developed. The method is simple, accurate, and highly sensitive within the limits of the experimental conditions described and can be used in pharmacies for the assay of sulfonamides in tablets and in pharmaceutical industries for quality control or environmental monitoring as well. The present method is more rapid than any analytical assay reported for these compounds thus far. The values of λmax and ?max for these sulfonamides have also been presented. 相似文献
67.
Two simple, rapid and sensitive spectrophotometric methods for the determination of catecholamine derivatives (pyrocatechol, dopamine, levodopa and methyldopa) are developed. The first method involves the oxidation of o-dihydroxybenzene derivatives by N-bromosuccinimide followed by oxidative coupling with isoniazid leading to the formation of a red-coloured products of maximum absorbance (lambda(max)=480-490 nm). The second method is based on the formation of green to blue complex (lambda(max)=635-660 nm) between o- dihydroxybenzene derivatives and sodium nitroprusside in the presence of hydroxylamine hydrochloride. All measurements of the two procedures are carried out in an alkaline medium at room temperature. The two methods are successfully applied for the determination of dopamine hydrochloride, levodopa and methyldopa in injections and tablets of pharmaceutical preparation. The common excipients used as additives in pharmaceuticals do not interfere in the proposed methods. The reliability of these methods are established by parallel determination with the reported and official methods. 相似文献
68.
Summary A vanadametric method has been developed which has definite advantages over iodimetric assay and bromimetric assay for the estimation of isonicotinic acid hydrazide in tablets. The excepients such as lactose, glucose and starch do not interfere in the estimation of the hydrazide with vanadate. Unlike iodimetric and bromimetric assays, the vanadametric assay is rapid.See also Z. analyt. Chem. 160, 117 (1958). 相似文献
69.
Dandinasivara S. Mahadevappa K.S. Rangappa B.T. Gowda Netkal M. Made Gowda 《Microchemical Journal》1982,27(1):77-86
Simple, rapid, and reproducible methods for the determination of thiocyanate and cyanide ions in metal salts and complexes with bromamine-B (BAB) and dichloramine-B (DCB) have been developed. The oxidation involves eight and two electron changes, respectively, with NCS? and CN? ions in 0.05–0.20 N NaOH medium in the case of BAB and in partially aqueous medium with DCB. The proposed methods could be employed for computing the number of thiocyanate and cyanide ligands present in the respective metal complexes. 相似文献
70.
M.A. Mastro S. Maximenko M. Gowda B.S. Simpkins P.E. Pehrsson J.P. Long A.J. Makinen J.A. Freitas Jr. J.K. Hite C.R. Eddy Jr. J. Kim 《Journal of Crystal Growth》2009,311(10):2982-2986
Photo- and cathodo-luminescence measurements of a variable-diameter ensemble of GaN nanowires revealed a diameter-dependent, spectral emission distribution between 350 nm and 850 nm. Spectral analysis indicated that wires with a diameter less than 400 nm were dominated by a yellow luminescence with a weaker near UV/violet emission also present. Examination of this ensemble showed that there was a general trend in the ratio of near-UV-to-yellow emission intensities with increasing nanowire diameter. Additionally, a broad green emission appears in the nanowires with a diameter above approximately 200 nm. A calculation based on the nanoheteroepitaxy model indicates that this diameter represents a transitional thickness where strain is relieved by defect formation mechanisms with a characteristic green emission. 相似文献