Heterogeneous exchange reactions

Slow heterogeneous exchange reactions between gaseous oxygen or oxidized products with catalyst oxides were observed but they were not quick to exert any serious effect on the evaluation of the participation of lattice oxide ion in the oxidation of propylene. 160 atom from the bulk of the catalyst was... 

After separation of compounds (1) and (2), their activity is measured and the mass m can be calculated from eq. (17.20). Homogeneous as well as heterogeneous exchange reactions may be apphed in analytical chemistry. An example is the determination of small amounts of Bi Bi is selectively extracted by diethyldithio-carbamate in chloroform, a known amount of Bil labelled with " Bi is added, after about 30 s Bil4 is extracted into water, and the activities in both phases are measured. In the case of heterogeneous exchange reactions, separation of the components is simple. 

In most cases, curves of the kind shown in Fig. 18.5 are measured. By evaluation of these curves, the kinetics of heterogeneous exchange reactions, the surface area involved in the exchange or the kinetics of diffusion or recrystallization can be determined. 

To make use of an isotopic fractionation for an enrichment of isotopes, a different isotopic distribution has to be carried out in two phases which can be easily separated. On the one hand, polyethers are soluble in various solvents On the other hand, these compounds can also be fixed as anchor groups at organic or inorganic matrices Therefore, as a heterogeneous exchange reaction for metal ions, liquid/liquid as well as liquid/solid systems can be used in connexion with polyethers. 

The exchange rate varies depending on not only the concentration of reactants, but also the characteristics of the solvent. Heterogeneous exchange reactions between iodide, elemental iodine, and other iodine species with radioactive iodine atoms adsorbed on platinum surfaces have also been reported (Toth, 1972). This is of interest, and probably very useful in preparing labeled compounds by this heterogeneous exchange reaction ... 

In this review paper we will be primarily concerned with the exchange between hydrogen and deuterium in aromatic compounds. Completely deuterated aromatics are available commercially. These are usually prepared by repeated treatment of the aromatic compound with DaO at about 350° in an autoclave in the presence of a platinum catalyst (Pt02 reduced with D2) h Such heterogeneous exchange reactions are not included in this review. 

This i>aper describes two broad types of intercalation conpomds which are based on graphite on the one hand and sheet aluminosilicate (clay) hosts on the other. Taken together these provide a rich veiriety of examples of heterogeneously catalysed reactions. Appropriately cation exchanged clays, for example, act as efficient catalysts for a number of commercially important proton catalysed reactions (10-13) (see Table I). Graphite intercalates, whilst also capable of... 

Ion-exchange processes are strictly heterogeneous reactions that involve two phases. They, however, mostly comply with homogeneous, second-order reaction kinetics. An exchange reaction represented by... 

The electronic theory furnishes, as we have already seen, a general recipe for the consideration of heterogeneous photocatalytic reactions. This recipe was obtained in Section I of the present article. In Sections III, IV, and V it was applied to the reactions of hydrogen-deuterium exchange, oxidation of CO, and synthesis of hydrogen peroxide, respectively. These are the most thoroughly studied photocatalytic reactions. 

The first reaction yields a mixture of all deuterobenzenes, the second one, the deuteration reaction, a mixture of deuterocyclohexanes, mainly C6H6D6 up to C6Di2. The rates of these reactions can be measured with fair accuracy, and additional information can be derived from the isotopic distributions of the reaction products. Schrage and Burwell 36) already demonstrated the usefulness of exchange reactions for studying the heterogeneity of catalyst surfaces. 

In the simplest case, it can be assumed that the water exchange reaction with a complexing site of a heterogeneous ligand will be governed by the Eigen-Wilkens mechanism as for complexes with simple ligands. In this case, equations (26) and (29) can be combined to yield ... 

Astatobenzene has also been prepared by heterogeneous halogen-exchange reaction between At adsorbed on solid sodium iodide, and bromobenzene at its boiling point 84). A further development in this technique has been to allow the reaction of bromobenzene in sealed ampuls at 250°C with At adsorbed on sodiiun hydroxide this resulted in high yields of about 70% 141,142). 

Specific astatohalobenzenes can be conveniently prepared by using heterogeneous halogen-exchange reactions, starting from the corresponding bromohalobenzene isomer, under the same conditions used for... 

That is, the 0/ 0 ratio in a sample is compared with a standard, and the difference is expressed as per mil (per thousand). The standard for oxygen isotopes is standard mean ocean water (SMOW). The exchange reaction of 0 and O between two minerals is a heterogeneous reaction and may be written as, e.g.. 

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