Exchange reactions in hot atom chemistry. II. Liquid methyl iodide

1976 ◽  
Vol 29 (3) ◽  
pp. 495
Author(s):  
FCR Cattell
Keyword(s):  
Methyl Iodide ◽  
Isotope Exchange ◽  
Radioactive Iodine ◽  
Hot Spot ◽  
Iodine Concentration ◽  
Square Root ◽  
Exchange Reactions ◽  
Isotope Exchange Reaction ◽  
Organic Combination ◽  
Atom Chemistry

When dilute solutions of iodine in methyl iodide are irradiated with neutrons more than 56% of the radioactive iodine-128 appears in organic combination. This increase arises from an isotope exchange reaction with a rate independent of iodine concentration. When more concentratedsolutions are irradiated the organic radioactivity is reduced below 56% and the reduction depends on the square root of iodine concentration. Results are examined in terms of the kinetic theory of hot reactions and also a treatment for distinguishing between 'Rot' and 'hot spot diffusive'reactions.

Exchange reactions in hot atom chemistry. I. Gaseous methyl iodide

1976 ◽  
Vol 29 (3) ◽  
pp. 485
Author(s):  
FCR Cattell
Keyword(s):  
Exchange Reaction ◽  
Methyl Iodide ◽  
Significant Contribution ◽  
Radioactive Iodine ◽  
Time Dependent ◽  
Exchange Reactions ◽  
Gaseous Mixtures ◽  
Heterogeneous Exchange ◽  
Atom Chemistry

High organic retentions of iodine-128 following the 127I(n,γ)128 I reaction in gaseous mixtures of methyl iodide and iodine result from a heterogeneous exchange reaction. The time-dependent organic retention can be related quantitatively to the 'age' of the radioactive iodine atoms. There is no evidence for a significant contribution from hot atom reactions, nor from the direct homogeneous exchange of iodine atoms with methyl iodide.

Isotope exchange reactions of the hydrogen H-5 of selected pyrimidine derivatives and the preparation of tritium-labeled pyrimidines

2011 ◽  
Vol 76 (12) ◽  
pp. 1567-1577 ◽  
Author(s):  
Martin Dračínský ◽  
Petr Jansa ◽  
Tomáš Elbert
Keyword(s):  
Exchange Reaction ◽  
Isotope Exchange ◽  
Reaction Rate ◽  
Tritiated Water ◽  
Solvent Composition ◽  
Exchange Reactions ◽  
Pyrimidine Derivatives ◽  
Isotope Exchange Reaction ◽  
Nmr Techniques ◽  
Tracer Experiments

The hydrogen-to-deuterium isotope exchange reaction of hydrogen in position 5 of pyrimidine derivatives was studied using NMR techniques. The dependence of the reaction rate on the pH and on the solvent composition was explored. In tracer experiments using tritiated water, the application of this exchange reaction was tested for the preparation of pyrimidine derivatives labeled by tritium.

scholarly journals Modelling the budget of middle atmospheric water vapour isotopes

2006 ◽  
Vol 6 (8) ◽  
pp. 2073-2090 ◽  
Author(s):  
A. Zahn ◽  
P. Franz ◽  
C. Bechtel ◽  
J.-U. Grooß ◽  
T. Röckmann
Keyword(s):  
Water Vapour ◽  
Isotope Exchange ◽  
Middle Atmosphere ◽  
Isotope Ratios ◽  
Phase Changes ◽  
Rate Coefficients ◽  
Chemical Fractionation ◽  
Minor Role ◽  
Exchange Reactions ◽  
Isotope Exchange Reaction

Abstract. A one-dimensional chemistry model is applied to study the stable hydrogen (D) and stable oxygen isotope (17O, 18O) composition of water vapour in stratosphere and mesosphere. In the troposphere, this isotope composition is determined by "physical'' fractionation effects, that are phase changes (e.g. during cloud formation), diffusion processes (e.g. during evaporation from the ocean), and mixing of air masses. Due to these processes water vapour entering the stratosphere first shows isotope depletions in D/H relative to ocean water, which are ~5 times of those in 18O/16O, and secondly is mass-dependently fractionated (MDF), i.e. changes in the isotope ratio 17O/16O are ~0.52 times of those of 18O/16O. In contrast, in the stratosphere and mesosphere "chemical'' fractionation mechanisms, that are the production of HO due to the oxidation of methane, re-cycling of H2O via the HOx family, and isotope exchange reactions considerably enhance the isotope ratios in the water vapour imported from the troposphere. The model reasonably predicts overall enhancements of the stable isotope ratios in H2O by up to ~25% for D/H, ~8.5% for 17O/16O, and ~14% for 18O/16O in the mesosphere relative to the tropopause values. The 17O/16O and 18O/16O ratios in H2O are shown to be a measure of the relative fractions of HOx that receive the O atom either from the reservoirs O2 or O3. Throughout the middle atmosphere, MDF O2 is the major donator of oxygen atoms incorporated in OH and HO2 and thus in H2O. In the stratosphere the known mass-independent fractionation (MIF) signal in O3 is in a first step transferred to the NOx family and only in a second step to HOx and H2O. In contrast to CO2, O(1D) only plays a minor role in this MIF transfer. The major uncertainty in our calculation arises from poorly quantified isotope exchange reaction rate coefficients and kinetic isotope fractionation factors.

The effect of decationation of hydroxylated HNaY zeolites on their interaction with ethylene and propylene. hydrogen complexes, oligomeration and isotope exchange

1980 ◽  
Vol 45 (11) ◽  
pp. 3101-3115 ◽  
Author(s):  
Ludmila Kubelková ◽  
Jana Nováková ◽  
Zdeněk Dolejšek ◽  
Pavel Jírů
Keyword(s):  
Isotope Exchange ◽  
Decisive Role ◽  
Single Step ◽  
Hydroxyl Groups ◽  
Isotope Exchange Reaction ◽  
Factors Affecting ◽  
Step Mechanism ◽  
Formed Hydrogen ◽  
Lower Basicity ◽  
Multiple Step

The effect of decationation on the interaction of propylene and ethylene with the hydroxylated forms of HNaY zeolites has been studied. The compounds formed in the zeolite cavities were studied using their infrared spectra, the composition of the gaseous phase was followed by mass spectrometry. The results showed that among factors affecting the interaction with propylene properties of hydroxyl groups play the decisive role. With the increasing decationation of the zeolite the strength of the OH bond in the hydrogen complex of the large-cavity hydroxyls with propylene decreased and the rate of propylene oligomeration at 310 K as well as the isotope exchange rate of propylene-d6 with the zeolite hydroxyls at 570 K increased. The propylene isotope exchange reaction proceeded by the multiple-step mechanism. In the case of ethylene only the physical sorption with a non-specific character was observed at 310 K. The adsorbed amount increased with the increasing content of Na+ ions in the zeolite (with the decreasing decationation). A part of the adsorbed molecules formed hydrogen complexes with hydroxyls of large cavities. The observed lower weakening of the OH bond was in agreement with the lower basicity of ethylene if compared with propylene. The isotope exchange of ethylene-d4 with the zeolite hydroxyls proceeded by a single-step mechanism, it had an autocatalytic character and its rate was 70 times lower than that of the isotope exchange of propylene-d6 with OH.

scholarly journals Are rate and selectivity correlated in iridium-catalysed hydrogen isotope exchange reactions?

2021 ◽  
Author(s):  
Daria S. Timofeeva ◽  
David M Lindsay ◽  
W. J. Kerr ◽  
David James Nelson
Keyword(s):  
Functional Groups ◽  
Hydrogen Isotope ◽  
Isotope Exchange ◽  
Reaction Rate ◽  
Exchange Reactions ◽  
Reaction Selectivity ◽  
Hydrogen Isotope Exchange ◽  
The Relationship

Herein we examine the relationship between reaction rate and reaction selectivity in iridium-catalysed hydrogen isotope exchange (HIE) reactions directed by Lewis basic functional groups. We have recently develped a directing...

Isotope exchange reaction on Li2ZrO3

1997 ◽  
Vol 250 (1) ◽  
pp. 29-35 ◽  
Author(s):  
Atsushi Baba ◽  
Masabumi Nishikawa ◽  
Takanori Eguchi
Keyword(s):  
Exchange Reaction ◽  
Isotope Exchange ◽  
Isotope Exchange Reaction

Hydrogen isotope exchange between D2 and H2O catalyzed by platinum plate

1989 ◽  
Vol 67 (5) ◽  
pp. 857-861 ◽  
Author(s):  
Shin-Ichi Miyamoto ◽  
Tetsuo Sakka ◽  
Matae Iwasaki
Keyword(s):  
Kinetic Model ◽  
Exchange Reaction ◽  
Hydrogen Isotope ◽  
Isotope Exchange ◽  
Reaction Rate ◽  
Hydrogen Adsorption ◽  
Platinum Catalyst ◽  
Isotope Exchange Reaction ◽  
Hydrogen Isotope Exchange ◽  
Supported Platinum

The reaction rate of hydrogen isotope exchange between D2 and H2O catalyzed by platinum plate is studied. The exchange reaction is described with the kinetic model which is the modification of that for the exchange reaction catalyzed by alumina-supported platinum catalyst. For the comparison of experimental results with this model relative amount of the number of sites for hydrogen adsorption was estimated from the initial rate of hydrogen isotope exchange between H2 and D2 on the same surface. The results show that the kinetic model is applicable for the plate catalyst if the number of the sites for hydrogen absorption, which is very sensitive to the surface state of the catalyst, was estimated not from the macroscopic surface area but from our scheme. Keywords: hydrogen isotope exchange reaction, platinum plate as catalyst.

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