Mechanism of oxygen-18 exchange between water and the vanadium(V) oxyanion: V/sub 10/O/sub 28//sup 6 -/
The rate of isotopic oxygen exchange between water and the discrete polyanion V/sub 10/O/sub 28//sup 6 -/ has a half-life of approximately 15 h at 25/sup 0/C, 0.01 M, with all oxygens being equivalent. At constant pH the overall rate of exchange is first order in (V/sub 10/O/sub 28//sup 6 -/)/sub T/ with a small ionic strength dependence. The rate of exchange is nearly constant in the pH range 4.0 to 6.3, increases dramatically with increasing hydrogen ion concentration below pH approximately 4.0, and decreases above pH approximately 6.3, reaching essentially zero at pH greater than 10.0. This behavior is discussed in terms of the protonated species present in the pH range (2.5 to 10.0). Comparison of the kinetics of depolymerization and exchange of the ion in slightly basic media suggests a ''common intermediate'' mechanism involving the one-ended dissociation of a V/sub 4/ group leading to dissociation and/or exchange. This mechanism provides for the exchange equivalency of all oxygens and is consistent with the activation parameters: ..delta..V/sup 2 +/ = -5.0 +- 2 cm/sup 3//mol, ..delta..H/sup 2 +/ = 21 +- 0.5 kcal/mol, ..delta..S/sup 2 +/ = -7 +- 0.5 cal/(mol K). A definitive /sup 49/VO/sub 4//sup 3 -/ transfer experiment during exchange and dissociation is in agreement with this mechanism.
- Research Organization:
- Univ. of Missouri, Columbia
- OSTI ID:
- 6856000
- Journal Information:
- Inorg. Chem.; (United States), Vol. 17:5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
OXYGEN 18
ISOTOPIC EXCHANGE
ANIONS
AQUEOUS SOLUTIONS
CHEMICAL REACTION KINETICS
DECOMPOSITION
EXCITED STATES
LABELLING
MEDIUM TEMPERATURE
PH VALUE
SAMPLE PREPARATION
TEMPERATURE DEPENDENCE
VANADIUM OXIDES
WATER
CHALCOGENIDES
CHARGED PARTICLES
CHEMICAL REACTIONS
DISPERSIONS
ENERGY LEVELS
EVEN-EVEN NUCLEI
HYDROGEN COMPOUNDS
IONS
ISOTOPES
KINETICS
LIGHT NUCLEI
MIXTURES
NUCLEI
OXIDES
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
REACTION KINETICS
SOLUTIONS
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS
400201* - Chemical & Physicochemical Properties
400203 - Isotope Exchange & Isotope Separation- (-1987)