Isotope exchange reactions deuterium

Curulli, A. and Slcitcr, G., Electrophilic heteroaromatic substitutions. VIII. Studies on the mechanism of the a-side-chain aminomethy-lation and hydrogen/deuterium isotope exchange reactions of a-methylpyrroles, J. Org. Chem... 50, 4925, 1985. 

Gupta NM, Mishra K, Belapurkar AD, et al Deuterium isotope exchange reaction between hydrogen and water over polyester-supported platinum catalysts, J Catal 121 (2) 386-395, 1990. 

Isotopic Exchange Reactions. Exchange reactions between the isotopes of hydrogen are well known and well substantiated. The equihbrium constants for exchange between the various hydrogen molecular species have been documented (18). Kinetics of the radiation-induced exchange reactions of hydrogen, deuterium, and tritium have been critically and authoritatively reviewed (31). The reaction T2 + H2 — 2HT equiUbrates at room temperature even without a catalyst (30). 

The kinetics of deuterium isotope exchange between diphenyl phosphine and t-butylthiol have been studied by H n.m.r. spectroscopy.274 A negative temperature coefficient was observed for the reaction of a perf1uoroalky1 phosphite with a fluorinated aldehyde.275 The kinetics for the reaction of alcohols with phosphoryl trichloride bore strong similarities to those of carboxylic acid derivatives.276 An interesting report desribed the solvolysis of ary 1 hydroxymethyl-phosphonates. It was shown that a phosphoryl group does not prevent carbocation formation on an immediately adjacent carbon atom.277... 

Deuterium labelling can, in principle, provide mechanistic information on hydro-formylation reactions, but complications may arise if scrambling of the D-label bet veen a metal hydride and D2 is fast. The isotopic exchange reaction shown in Eq. (9) was probed by rapid scan HP IR spectroscopy (1.3 scans s" ) where 21 is the bidentate pyrrolyl-based phosphorus amidite ligand illustrated [8]. 

The observed overabundance of deuterated species in molecular clouds and outer disks compared to the measured interstellar D/H ratio of 10 5 is well established. A classical isotopic deuterium fractionation is possible at low temperatures of 10-20 K owing to disbalance between forward and reversed reaction efficiencies H+ + HD 5 H2D+ + H2 + 232K (e.g. Millar et al. 1989 Gerlich et al. 2002). The temperature dependency in an isotope exchange reaction is a consequence of the zero-point vibrational energy difference for the isotopically substituted molecules (Bigeleisen Mayer 1947 Urey 1947). This leads to an elevated ratio ol H2t)+/H compared to HD/H2, which is quickly transferred into other molecules by ion-molecule reactions (see e.g. Roberts Millar 2000 Roberts et al. 2003). For example, the dominant reaction pathway to produce DCO+ is via ion-molecule reactions of CO with H2D+. In disks it results in a DCO+ to HCO+ ratio that increases with radius owing to the outward decrease of temperature (Aikawa Herbst 2001 Willacy 2007 Qi et al. 2008). 

Isotopic Exchange Reactions of Difluoramine with Deuterium Oxide and Trifluoroacetic Acid... 

By contrast with the radiation-induced procedures, isotope exchange reactions catalyzed by Group VIII transition metals are applicable to both deuterium and tritium labeling of heterocyclic compounds. Because of recent mechanistic developments in this field, it is possible to predict with some degree of certainty the reactivity of a molecule for deuteration and also for moderate levels of tritiation. If compensation for additional radiation-induced interactions is made, then the theory also satisfactorily explains high specific activity tritiations. 

The mechanism of transfer hydrogenation is complicated because of the need to activate the reagents in the correct order. Since several of the more successfiil transfer-hydrogenation catalysts are monohydride complexes, deuterium-labeling experiments to ascertain the source and destination of the transferred hydrogen are subject to some uncertainty. This complication arises from the simultaneous isotope exchange reactions that occur. 

With the development of liquid scintillation counters which permit tracer levels of tritium to be measured accurately, isotope exchange reactions are now usually carried out with tritium rather than deuterium. Frequently, however, it is useful to compare rates of exchange for all three isotopes and deuterium exchange may be followed using, for example, mass spectrometry [22]. An example of the application of isotope exchange to proton transfer from carbon is shown in eqns. (8) and (9) for the hydroxide ion catalysed exchange of phenylacetylene in aqueous solution [23], viz. 

Of the remaining studies of the overall reaction between deuterium and oxygen, the measurements of the first explosion limit by Kurzius and Boudart [58], and their deduction of an expression for in the temperature range 800—1000 K, have already been discussed in Sect. 3.6.4. A shock tube study of the development of the ignition, as well as of deuterium dissociation in the presence of argon and the isotopic exchange reactions (xxiv) and (xxv)... 

The deuterium isotope effect in the photo-induced chlorine atom exchange reaction with HCl has been investigated by Klein et over the range 30-150 °C by using the competition for chlorine atoms between D2 and DCl (or HCl). The exchange reactions were labeled with radioactive C1. Known mixtures of Cl2, D2, and DCl (or HCl) were irradiated followed by measurement of the residual D2 as well as the activity of the DCl. From this data the rate of the isotope exchange reaction could be determined with respect to the rate of chlorination of deuterium. The results are listed in Table 12 for the reactions... 

Problem Determine the equilibrium constant of the homogeneous gaseous isotopic exchange reaction between hydrogen and deuterium iodide, via.,... 

Another application of pulse chromatographic methods is in studies of the kinetics of isotope-exchange reactions [75]. A deuterium-labelled compound was formed as a pulse of a volatile compound (reagent) passed through a column packed with Gas-Chrom A with 10% of Carbowax 6000 and 10% of KO H applied on its surface. The isotope exchange rate is a characteristic of the nature of the substance under investigation and is of... 

The isotopic exchange reaction between deuterium and (+)3-methyl-hexane on nickel and palladium catalysts at temperatures above 100° leads to racemization of the optically active hydrocarbon. In exchange between deuterium and cycloalkanes at temperatures between —50° and about 75°, a discontinuity separates the concentrations of C H D and. In cyclopentane at about 50°, for example, exchange... 

The isotopic exchange reaction of MeOH, containing a Pt -Sn chloride complex, with D2 in the temperature range 0— 20 °C and up to 100 Torr is first-order in deuterium. The rate exhibits a maximum at a Sn/Pt ratio of 5.5, lending support to the idea that the active catalyst is Pt (SnCl3). ii The catalytic efficiencies of 80X4 (X = Cl or Br) and PhSnClg in the racemization of a-methylbenzyl chloride in ether have been studied. For all catalysts, the reaction is first-order in alkyl halide, but a mixture of first- and second-order... 

The third important concept introduced by Taylor was the use of model reactions, "yard sticks" to determine the mode of activation of molecules by surfaces. For hydrogen activation, Taylor(15) proposed the conversion of ortho to para hydrogen as a measure of the catalytic activity of a surface. This turned out to be more complicated than was first realized. A physical magnetic effect was also operative as was shown among others by Diamond and Taylor(27) for the case of rare earths and by Turkevich and Selwood.(25) Later Laroche and Turkevlch(29) used magnetic resonance to quantify the catalytic effect of charcoal and to differentiate it from dissociative process. The discovery of deuterium opened up the use of isotope exchange reactions as delicate "model reactions" for elucidation of the activation of molecules. Immediately after H. Urey announced the discovery of heavy water in 1932, Taylor(30) realized its potential as a tool in catalytic research and engaged in a massive production in Princeton of heavy water. 

A last case of sonication-sensitive catalytic reactions is the hydrogen-deuterium isotope exchange observed in carbohydrates in the presence of nickel or a nickel-aluminum alloy. A good selectivity is observed, probably due to the lower temperature allowed by sonication. However, a more complex origin can be responsible for these effects, since the sonicated alloy exhibits new features such as distinct catalytic centers, and elemental redistribution within the catalyst bulk, along with more classical consequences (surface cleaning, absence of surface area... 

Since 1952, most of the tritium measured in the atmosphere originates from thermonuclear explosions. Like hydrogen, deuterium and tritium also exhibit molecular isomerism. Because of the important differences between the relative atomic masses of the three isotopes, their physical properties (e.g., density, enthalpy of vaporization) differ greatly. This allows an easier isotopic separation than for any other element. Several separation processes are used for the enrichment and separation of hydrogen isotopes. Most of these processes use isotopic exchange reactions (e.g., H D-H O or NH3-HD) and to a lesser extent fractional distillation and water electrolysis (e.g., Norway, Canada). 

Established from the study of many isotope exchange reactions, this rule can fail for larger species ). This is a statement that the fractionation of deuterium in interstellar molecules via Reaction (2) is thermodynamically allowed. Since exoergic ion-molecule reactions proceed generally with high reaction efficiency, reaction (2) should incorporate deuterium efficiently into interstellar molecules. 

The most important reactions which extract deuterium from HD involve ion-neutral isotope exchange reactions ... 

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