Reactions between vanadium ions

4 Reactions between vanadium ions A detailed study of the reaction 

During this study, an intermediate absorbing at 425 m/i was detected and shown in a further study to be a dimer (VOV ), with nearly two-thirds of the V(IV)-V(II) reaction proceeding via this species in an inner-sphere step, the remainder reacting via an outer-sphere pathway. The mechanism proposed for the reaction was 

From spectrophotometric measurements (at 425 mfi) on the appearance and disappearance of dimer, values for the rate coefficients ki and k were found to be (at 0 °C and ionic strength 1.0 M) 6.7x10 and 3.3x10 l.mole . sec , respectively. Under the same conditions k, was calculated to be 3.9x10 1. mole . sec.  

Both sulphate and chloride ions were found to accelerate the reaction under constant ionic strength conditions and, although medium effects may operate, pathways involving chloride and sulphate ions are possible. For the sulphate ion addition Newton and Baker conclude that the step 

Daugherty and Newton have examined the reaction between VO2 and and have found their results to be consistent with a rate law 

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Preliminary results of the reaction between vanadium(iii)-tetrasulpho-phthalocyanine complex with oxygen have been reported these data were compared with those obtained for the corresponding reaction of the hexa-aquo complex ion. The oxidation of methyl ethyl ketone by oxygen in the presence of Mn"-phenanthroline complexes has been studied Mn " complexes were detected as intermediates in the reaction and the enolic form of the ketone hydroperoxide decomposed in a free-radical mechanism. In the oxidation of 1,3,5-trimethylcyclohexane, transition-metal [Cu", Co", Ni", and Fe"] laurates act as catalysts and whereas in the absence of these complexes there is pronounced hydroperoxide formation, this falls to a low stationary concentration in the presence of these species, the assumption being made that a metal-hydroperoxide complex is the initiator in the radical reaction. In the case of nickel, the presence of such hydroperoxides is considered to stabilise the Ni"02 complex. Ruthenium(i) chloride complexes in dimethylacetamide are active hydrogenation catalysts for olefinic substrates but in the presence of oxygen, the metal ion is oxidised to ruthenium(m), the reaction proceeding stoicheiometrically. Rhodium(i) carbonyl halides have also been shown to catalyse the oxidation of carbon monoxide to carbon dioxide under acidic conditions ... 

Rate law flooding. The second-order rate constant for the reaction between the hydrated ions of vanadium(3+) and chromium(2+) depends on [H+ ]. From the data given, which refer to T = 25.0 °C and a constant ionic strength of 0.500 M, formulate a two-parameter equation that describes the functional dependence. Evaluate the two constants. Compare your result to the one derived in to Problem 1 -2. 

Luther and Rutter have observed the induced oxidation of iodide during the reactions between chromic acid and vanadium(IV), vanadium(ri[), and vana-dium(II) ions. In all the three systems ci = 2, therefore it is probable that the coupling intermediates are chromium(V) species, these being, especially the two latter systems, too complicated for a detailed kinetic treatment to be given. 

Nitrogenase (ferredoxin) [EC 1.18.6.1] catalyzes the reaction of three reduced ferredoxin molecules with protons, N2, and n ATP molecules to produce three oxidized ferredoxin molecules, two ammonia molecules, n ADP molecules, and n orthophosphate molecules where n is between 12 and 18. This iron-sulfur system also uses either molybdenum or vanadium ions. (2) Nitrogenase (flavodoxin) [EC 1.19.6.1] catalyzes the reaction of six reduced flavodoxin molecules with protons, N2, and n ATP molecules to produce six oxidized flavodoxin molecules, two ammonia molecules, n ADP molecules, and n orthophosphate molecules. This system uses iron-sulfur and molybdenum ions. 

Rapid reaction between gases and ions requires that the vanadium ion salt be molten (Folkmann et al., 1991 Hatem et al., 2002). Melting at moderate temperatures (-650 K) is obtained by combining high melting point ... 

Also, coordination compounds and metal carbonyls are able to undergo a PET, resulting in initiating radicals [63]. Recently investigated examples are iron chloride based ammonium salts [149], vanadium(V) organo-metallic complexes [150], and metal sulfoxide complexes [151]. However, the polymerization efficiency of some systems is only low due to redox reactions between the central metal ion and the growing polymer radical, and the low quantum yields of PET. 

Ally alcohol oxidation into acrolein on the rhombic phase of molybdenum oxide modified with vanadium oxide has been studied by the kinetic molhod ami Ijy ESR of ions in situ. II was shown, that active sites for this reaction are V ions situated in the bulk of the catalyst, or near its surface, but not at the surface. Fast diffusion of e.lectrons and a more slower diffusion of oxygen ions between the surface and the bulk occur during the reaction. 

FOLLOW-UP PROBLEM 21.3 A voltaic cell based on the reaction between aqueous Brj and vanadium(III) ions has Eceii = 1-39 V ... 

The synthesis of V2 02,45(alkylamine) nanotubes, by a sol-gel reaction using vanadium oxide triisopropoxide in the presence of hexadecyl amine template and hydrothermal treatment was descrihed [6, 31]. These nanotuhes consist of concentric shells with alternating V202.45(alkylamine) layers. Most of them are obtained as scrolls. Further studies [61] showed that the nanotuhe material could he used as a li insertion electrode. To obtain the electrode material, the nanotubes were refluxed, first, for 24 hours in ethanolic solution of NaCl, in order to remove the hexadecylamine template. Sodium ions were intercalated between... 

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