Heterogeneous isotope exchange

Astatobenzoic acid isomers have also been prepared by heterogeneous isotopic exchange by using the corresponding iodobenzoic acid. Halogen exchange has been effected under molten conditions, or with the substrate dissolved in a molten inert high-dielectric solvent, such as acetamide yields of 60-70% have been obtained (35). 

Fig. 4. Synthesis of 6- At-MNDP by in vacuo thermal heterogeneous isotopic exchange ( At"/I) (32).

The equations of heterogeneous isotope exchange are simpler than ion-exchange equations because the two ions are chemically the same. In the treatment by the law of mass action, it means that the equilibrium constant is equal to 1. The selectivity coefficients at X = 0 and X = 1 can be determined by measuring heterogeneous isotope exchange in which the concentration of the radioactive isotopes is very low and approaches zero (carrier-free radioactive isotope). 

In the case of heterogeneous isotopic exchange, the ratio of K/K2= 1. From Equation 1.95 we can conclude that... 

Nagy, N. M., J. Konya, and T. Budai. 1998. Mn2+/54Mn2+ Heterogeneous isotope exchange reaction on montmorillonite in the presence of complex-forming agents. Coll. Surf. 138 81-89. 

Equations 2.25-2.34 represent the reactions between solid and liquid (Boxes 3 and 4). Among them, Equations 2.25-2.28 represent the dynamic heterogeneous exchange of ions between montmorillonite and solution if the ions are labeled by radioactive isotopes, they also include heterogeneous isotope exchange ... 

Figure 18.5. Determination of surface area by heterogeneous isotope exchange activity in solution as a function of time.

An interesting example is the heterogeneous isotope exchange between CO2 in the gas phase and solid BaCOs ... 

The determination of the surface area of ionic crystals by heterogeneous isotope exchange was first shown by Paneth. It is based on the even distribution of labelled ions between the surface and a solution to which these ions have been added ... 

The heterogeneous isotopic exchange reaction in an extraction system is analogous to Eq. (18). If one assumes that the crown ether or cryptand complex of the metal ion only exists in the organic phase, then the isotopic exchange reaction, for example between and Ca, can be described as ... 

The method of heterogeneous isotopic exchange was used to determine the self-diffusion coefficient of oxygen in Pr70j2 (iota phase) as a function of temperature and pressure. The results indicated that there are two types of hyperstoichiometric material depending on the degree of oxygen excess. When the compound is close to stoichiometry, the diffusion coefficient can be written... 

Heterogeneous isotopic exchange using deuterated (D2, D2O, CH3OD, CF3COOD, and so forth) and tritiated (HTO) substances, combined with mass spectrometry, IR spectroscopy and NMR spectroscopy Adsorption and wetting ... 

The determination of equilibrium constants for heterogeneous isotope-exchange reactions involving isotope-exchange between pure phases and solution phases yields partition-function ratios for the isotopic, solution-phase species. In favorable cases a comparison of calculated values for the solute partition-function ratio with the experimental value allows one to distinguish between possible solute models. 

In heterogeneous isotope exchange, the aqueous solution containing an unknown amount of the elements to be determined is mixed with a solution of a known amount of a suitable complex of the same element in an organic diluent that does not contain an excess of the free complexing agent. One of the chemical forms of the element is labeled. This technique has been used to assay traces of silver in water by shaking the aqueous solution with a solution of labeled (with ° Ag) silver dithizonate in carbon tetrachloride. 

Using the heterogeneous isotope exchange technique, a study was made of the diffusion of 22]sfa in type-A synthetic zeolite at 21C. The exchange rate did not fit the classical function for the time-independence of an ideal diffusion process. For the initial exchange, the diffiisivity at 21C was about 3 x lO cm /s. Over the range of 0 to 30C, the diffusivity was described by ... 

Ph.D. thesis Surface Investigations Using the BET-Method and Heterogeneous Isotope Exchange on Barium Sulfate , Ph.D. Mit Auszeichnung ... 

Studies of selfdiffusion of oxygen in Nd203, Sm203 and Er203 have been undertaken employing heterogeneous isotope exchange (Stone et al., 1968). They... 

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