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61.
Summary The kinetics and mechanism of exchange of HPDTA in [Fe2HPDTA(OH)2] with cyanide ion (HPDTA=2-hydroxytrimethylenediaminetetraacetic acid) was investigated spectrophotometrically by monitoring the peak at 395 nm (
max of [Fe(CN)5OH]3– at pH=11.0±0.02,I=0.25m (NaClO4) at ±0.1°C).Three distinct observable stages were identified; the first is the formation of [Fe(CN)5OH]3–, the second the formation of [Fe(CN)6]3– from it and the third the reduction of [Fe(CN)6]3– to [Fe(CN)6]4– by HPDTA4– released in the first stage.The first stage follows first-order kinetics in [Fe2HPDTA(OH)2] and second-order in [CN–] over a wide range of [CN–], but becomes zero order at [CN–]<5×10–2
m. We suggest a cyanide-independent dissociation of [Fe2HPDTA)(OH)2] into [FeHPDTA(OH)] and [Fe(OH)]2+ at low cyanide concentrations and a cyanide-assisted rapid dissociation of [Fe2HPDTA(OH)2] to [FeHPDTA(OH)(CN)]3– and [Fe(OH)]2+ at higher cyanide concentrations. The excess of cyanide reacts further with [FeHPDTA(OH)(CN)]3– finally to form [Fe(CN)5OH]3–.The reverse reaction between [Fe(CN)5OH]3– and HPDTA4– is first-order in [Fe(CN)5OH]3– and HPDTA4–, and exhibits inverse first-order dependence on cyanide concentration.A six-step mechanism is proposed for the first stage of reaction, with the fifth step as rate determining. 相似文献
62.
Summary Kinetics and mechanism of formation of a 113 mixed cyano-complex from [FeIII (Par)2]– (where Par represents 4-(2-pyridylazo)resorcional) and cyanide ion has been studied spectrophotometrically at 720 nm [max=Fe(III)(Par)
2
–
], pH=10.0±0.02, temp=25±0.1°C and 1=0.1 M (NaClO4). The order with respect to cyanidevaries from one to two at high and low cyanide concentrations respectively. The rate constants for respective reactions are k1=10.8±0.6×10–2 M–1 s–1, k2=7.7±0.5 M–2 s–1. The reverse reaction does not occur at a measurable rate even in presence of large excess of par. These observations suggest that FeIII (Par)
2
–
forms a mixed complex, [FePar(CN)3]2-, in presence of an excess of cyanide ions. A three-step mechanism consistent with these results is proposed. The activation parameters for the reaction have been derived and used to support the proposed mechanism. The effect of ionic strength lends further support to the mechanism. 相似文献
63.
Prem Paul Singh Keith G. McCurdy Earl M. Woolley Loren G. Hepler 《Journal of solution chemistry》1977,6(5):327-330
We have used a Picker flow calorimeter for measurements leading to apparent molal heat capacities of dilute aqueous solutions of HClO4 and NaClO4 at 298°K. Results have been used to derive
c
°
=–27.1J-°K
–1-mole
–1 for HClO4 (aq.),
c
°
=15.2J-°K
–1-mole
–1 for NaClO4 (aq.), and C
p=–213.8J-°K–1-mole–1 for ionization of water. 相似文献
64.
Molar excess volume V
E
and enthalpy H
E
data have been measured at 25°C for pyridine A saturated with anhydrous cupric chloride (S) [A(S)]+ B [where B is aniline or o-toluidine (OT) or formamide (FD) or N, N-dimethylformamide (NND)] mixtures on the assumption that while the standard state of B is that of pure components B, the standard state of A(S) is that of A saturated with the salt S. The excess volume or enthalpy data for an equimolar mixture at a given temperature have been utilized to evaluate the interactional parameter X12 of the Sanchez and Lacombe theory of fluid mixtures at that temperature, and the same has been combined with V
E
(x
A
) data for a good prediction not only of the coresponding H
E
(x
A
) data for the mixture but also the extent of unlike interactions between the A(S) and B components of these A(S)+B mixtures. 相似文献
65.
Prem C. Srivastava Furn F. Knapp Carol D. Pruitt 《Journal of heterocyclic chemistry》1988,25(2):667-669
The synthesis of a 1,4-disubstituted dihydropyridine, 1-(E-1[125I]iodo-1-penten-5-yl)-4-(β-N-acetylaminoethyl)-1,4-dihydropyridine ([125I] 10 ), is described. Acetylation of 4-(β-aminoethylpyridine) with acetic anhydride followed by condensation with E-1-borono-5-iodo-1-pentene ( 7 ) gave 1-(E-1-borono-1-penten-5-yl)-4-(β-N-acetylaminoethyl)pyridinium iodide ( 8 ). Chloramine-T and sodium iodide iodination of 8 gave the corresponding E-1-iodo compound 9 which was reduced with sodium borohydride to furnish 1-(E-1-iodo-1-penten-5-yl)-4-(β-N-acetylaminoethyl)-1,4-dihydropyridine ( 10 ). The corresponding radioiodinated compound was prepared similarly using Na[125I]. The tissue distribution studies in rats indicate that [125I] 10 crosses the blood brain barrier (0.49% dose/g in the brain) but gradually washes out from the brain. 相似文献
66.
The nitrogen analog of the pinacol rearrangement has been utilized for the preparation of a 4-phenylisoquinoline 9 from the intermediate amino alcohol 8. 相似文献
67.
N-alkyiation of primary amines has been carried out with alkylbromide using commercial Me2SO and K2CO3 as a base. This process offers a method of selection for obtaining either mono or dialkyl amines. 相似文献
68.
Sharma S Kumar A Chand P Sharma BK Sarkar S 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(3):556-564
3,4,5-Trimetoxytetraphenylporphyrinoxovanadium (IV) complex (3,4,5-TMVOTPP) was synthesized by a new one pot synthetic method. The complex was studied in the form of single crystal, powder (polycrystalline state), solution and frozen solution (glassy state) by electron paramagnetic resonance (EPR) between room temperature (RT) and liquid nitrogen temperature (LNT). Interestingly a well-resolved octet in the EPR spectrum at RT is observed in the pure paramagnetic state of the crystal. This observation is attributed to a greatly reduced dipolar interaction between paramagnetic vanadyl ions due to the large size of the molecule and the resultant stacking in the crystalline state. The line width of the EPR signals in single crystal at RT is approximately 3.3 mT which is more than the usual line width in diluted paramagnets ( approximately 1.5 mT) and is attributed to some kind of broadening effect akin to slow motion broadening. The line width in solvents is more than the crystal value but decreases appreciably at low temperatures. The decrease in line width at low temperature is attributed to the increase in spin-lattice-relaxation time and quenching of RT broadening motion. Only one octet is observed in the crystal EPR spectra which suggests only one formula unit per unit cell or a parallel/antiparallel ordering of V=O vectors in case the formula units per unit cell are more than one. This result needs verification by a detailed X-ray investigation. The crystalline field symmetry around the V(4+) metal ion is revealed to be axial by the observed angular dependence of the EPR spectrum and the powder EPR spectrum. No super hyperfine splitting of the hyperfine lines of the vanadyl ion is observed in solid state or diluted glass up to liquid nitrogen temperature. This suggests an expected weak in-plane pi-bonding with ligands. The spin Hamiltonian parameters for vanadyl ion in crystal, powder, diluted solutions and frozen glasses are evaluated and discussed. 相似文献
69.
The migration and diffusion modulated excitation energy transfer has been studied in a new dye pair 7-diethylamino-4-methylcoumarin (donor) to 3,3'-dimethyloxacarbocyanine iodide (acceptor) by steady-state and picosecond time-resolved spectroscopy. To reduce the artifact of self-absorption, at high donor concentrations, the time-resolved studies have been carried out in thin films of polyvinyl alcohol (solid matrix) and in methanol (liquid phase) at front-face geometry of excitation. The Forster-type (nonradiative) energy transfer [Discuss. Faraday Soc. 27, 7 (1959)] takes place directly from donor to acceptor in case of solid matrix, while Yokota-Tanimoto model [J. Phys. Soc. Jpn. 22, 779 (1967)] for diffusion has been found to be operating in the liquid phase. It has been found here that the high interaction strength between donor and acceptor molecules as compared to that among donors masks the effect of energy migration and diffusion at high donor concentrations. The rate and efficiency of energy transfer increase with increasing the acceptor concentration. This has been confirmed by the study of acceptor kinetics. 相似文献
70.
We study the purity of correlated photon pairs generated in a dispersion-shifted fiber at various temperatures. The ratio of coincidence to accidental-coincidence counts greater than 100 can be obtained as the fiber is cooled to liquid-nitrogen temperature (77 K). We then generate polarization-entangled photon pairs by using a compact counterpropagating scheme. Two-photon interference with visibility >98% and Bell's inequality violation by >8 standard deviations of measurement uncertainty are observed at 77 K, without subtracting the accidental-coincidence counts due to background Raman photons. 相似文献