排序方式: 共有105条查询结果,搜索用时 31 毫秒
41.
Jyothi C. Abbar Shekappa D. Lamani Sharanappa T. Nandibewoor 《Journal of solution chemistry》2011,40(3):502-520
The oxidation of amitriptyline by potassium permanganate has been investigated spectrophotometrically in the presence of ruthenium(III)
as catalyst in aqueous acidic medium at a constant ionic strength of 0.20 mol⋅dm−3. The stoichiometry was found to be 1:1 in terms of the mole ratio of amitriptyline and permanganate ions consumed. The order
of the reaction with respect to manganese(VII) and ruthenium(III) concentration was unity while the order with respect to
amitriptyline was less than unity over the concentration range studied. The rate increased with an increase in acid concentration.
The reaction rates revealed that the Ru(III) catalyzed reaction was about eight-fold faster than the uncatalyzed reaction.
The oxidation products were identified by spectral analysis. A tentative mechanism consistent with the kinetics has been proposed.
The reaction constants involved in the different steps of the reaction mechanism were calculated. Kinetic experiments suggest
that HMnO4 is the reactive permanganate species and [Ru(H2O)6]3+ is the reactive Ru(III) species. 相似文献
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Hochreuther S Nandibewoor ST Puchta R van Eldik R 《Dalton transactions (Cambridge, England : 2003)》2012,41(2):512-522
The diaqua complex [Pt(2-methylthiomethylpyridine)(OH(2))(2)](2+), Pt(mtp), was synthesized and investigated thermodynamically as well as kinetically. Spectrophotometric acid-base titrations were performed to determine the pK(a) values of the two coordinated water ligands. A low pK(a1) value of 3.15 was observed for the water molecule trans to the pyridine donor, whereas a pK(a2) value of 6.84 was found for the water molecule trans to the labilising sulphur donor. The substitution of coordinated water by a series of sterically hindered S-containing nucleophiles, viz. thiourea (tu), N,N'-dimethylthiourea (dmtu) and N,N,N',N'-tetramethylthiourea (tmtu), was studied under pseudo first-order conditions as a function of nucleophile concentration, pH (2, 4.75, 7.4), temperature and pressure, using stopped-flow techniques and UV-vis spectroscopy. In general the first substitution reaction takes place trans to the sulphur donor. At pH 2 the nucleophiles react in the order tu (634 ± 10) > dmtu (507 ± 5) ? tmtu (165 ± 3 M(-1) s(-1) at 25 °C), which is caused by steric hindrance. The second observed reaction involves two steps, viz. the displacement of the second water ligand and dechelation of the pyridine ring with the third-order rate constants 73.3 ± 0.8 (tu), 22.1 ± 0.1 (dmtu) and 6.8 ± 0.2 M(-2) s(-1) (tmtu) at 25 °C. At pH 4.75 the reactions are in general slower due to the presence of aqua-hydroxo species. The same order in reactivity was found, viz. tu (106 ± 1) > dmtu (72 ± 1) ? tmtu (14.1 ± 0.5 M(-1) s(-1) at 25 °C). No evidence for ring-dechelation could be observed under these conditions. At pH 7.4 the inert dihydroxo species is predominantly present in solution and consequently no substitution reaction was observed. Quantum chemical calculations were performed to support the interpretation and discussion of the experimental results. 相似文献
44.
Nagaraj P. Shetti Rajesh N. Hegde Sharanappa. T. Nandibewoor 《Central European Journal of Chemistry》2009,7(4):929-937
Oxidation of an amino acid, L-tyrosine (L-Tyr) by diperiodatocuprate(III) (DPC) in alkaline medium at a constant ionic strength
of 0.1 mol dm−3 was studied spectrophotometrically at different temperatures (288.1–313.1 K). The reaction between DPC and L-Tyr in alkaline
medium exhibits 1:4 stoichiometry (L-Tyr:DPC). Intervention of free radicals was observed in the reaction. Based on the observed
orders and experimental evidence, a mechanism involving monoperiodatocuprate(III) (MPC) as the reactive oxidant species has
been proposed. A suitable mechanism is proposed through the formation of a complex and free radical intermediate. The products
were identified by spot test and characterized by spectral studies. The reaction constants involved in the different steps
of the mechanism were calculated. The activation parameters with respect to slow step of the mechanism were computed and are
discussed. The thermodynamic quantities were determined for different equilibrium steps. Isokinetic temperature was also calculated
and found to be 252.3 K.
相似文献
45.
Veeresh Seregar T. M. Veeresh Sharanappa T. Nandibewoor 《Transition Metal Chemistry》2009,34(6):647-654
The kinetics of Ru(III)-catalyzed oxidation of l-alanine (Ala) by diperiodatoargentate(III) (DPA) in alkaline medium at 25 °C and a constant ionic strength of 0.90 mol dm−3 was studied spectrophotometrically. The products are acetaldehyde, Ag(I), ammonia and bicarbonate. The [Ala] to [DPA] stoichiometry
is 1:1. The reaction is first order in both [Ru(III)] and [DPA] and has less than unit order in both [Ala] and [alkali]. Addition
of periodate has a retarding effect on the reaction. The effects of added products, ionic strength and dielectric constant
of the reaction medium have been investigated. The reaction proceeds via a Ru(III)–Ala complex, which further reacts with
one molecule of monoperiodatoargentate(III) in the rate-determining step. The reaction constants were calculated at different
temperatures and the activation parameters have been evaluated. 相似文献
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48.
Chimatadar Shivamurti A. Koujalagi Sangappa B. Nandibewoor Sharanappa T. 《Transition Metal Chemistry》2002,27(7):704-711
Quinolinium dichromate (QDC) oxidation of TlI in aqueous AcOH containing large concentrations of HCl is considerably accelerated both by H+ and Cl– ions as well as by increasing the AcOH concentration in the medium; oxidation is made possible by altering the redox potentials. The reaction is first order in oxidant and in reductant but apparently less than unit order in [Cl–] and nearly second order in [H+]. The active species of QDC and TlI are ClCrO3
– and TlCl2
– respectively. A possible mechanism is proposed and verified, and the reaction constants involved have been evaluated. 相似文献
49.
Rahamatalla M. Mulla Gurubasavaraj C. Hiremath Sharanappa T. Nandibewoor 《Monatshefte für Chemie / Chemical Monthly》2004,135(12):1489-1502
Summary. The kinetics of ruthenium(III) catalysed oxidation of sulfanilic acid (p-aminobenzenesulfonic acid) by hexacyanoferrate(III) in alkaline medium at a constant ionic strength of 2.5mol·dm–3 has been studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 2:8 stoichiometry (SNA:HCF(III)). The reaction showed first order kinetics in [hexacyanoferrate(III)] and [ruthenium(III)] and apparent less than unit order in both sulfanilic acid and alkali concentrations. The reaction rate increases with increasing ionic strength but the relative permittivity (T) of the medium has a negligible effect on the rate of the reaction. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the formation of a complex between sulfanilic acid and hydroxylated species of ruthenium(III) has been proposed. The active species of HCF(III) and ruthenium(III) are understood as [Fe(CN)63–] and [Ru(H2O)5OH]2+, respectively. The main products were identified by IR, NMR, and mass spectral studies. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated. 相似文献
50.
Pandurang D. Pol Ramdurg T. Mahesh Sharanappa T. Nandibewoor 《Reaction Kinetics and Catalysis Letters》2004,81(1):113-119
The kinetics of chromium(III) catalyzed oxidation of 1,10-phenanthroline by permanganate in alkaline medium at a constant ionic strength has been studied spectrophotometrically. The reaction between permanganate and 1,10-phenanthroline in alkaline medium exhibits 4:1 stoichiometry (KMnO4:1,10-phenanthroline). The reaction shows first order dependence on [permanganate] and [chromium(III)] and less than unit order dependence in 1,10-phenanthroline, zero order in alkali concentrations. The results suggest the formation of a complex between the 1,10-phenanthroline and the chromium(III) which reacts further with one mole of permanganate species in the rate-determining step, resulting in the formation of a free radical, which again reacts with three moles of permangante species in a subsequent fast step to yield the products. The reaction constants involved in the mechanism were evaluated. The activation parameters were computed with respect to the slow step of the mechanism.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献