Deuterium oxide, conductivity

Besides its use as a mechanistic probe, deuteriation of anions under kinetically controlled conditions is a potentially promising way to access deuteriated molecules in a regio- and stereo- controlled manner, in opposition to the thermodynamic equilibration in the presence of an excess of deuterium donor. Thus, treatment of the lithium anion of 2-methyltetralone (p E = 7.31, pfsfEa = 10.8, pKkr = 18.1 in water)335, by one equivalent of a solution of deuterium chloride in deuterium oxide, generates the intermediate O-deuteriated enol whose reaction with water or with an excess of deuterium chloride in deuterium oxide conducts to, respectively, the tetralone or the deuteriated tetralone (Scheme 69)336. 

The estimation of flow functions from an actual experiment is reported next. A multi-rate primary drainage experiment was conducted on a Texas Cream limestone sample. Hexadecane was used as the oleic phase and deuterium oxide (D20) was used as the aqueous phase. Protons are imaged, so only the oil phase is observed. The pressure drop data, production data and saturation data are shown in Figures 4.1.11-... 

The stereochemistry of dienes has been found to have a pronounced effect in the concerted cyclo-additions with benzyne 64>65h A concerted disrotatory cyclo-addition of tetrafluorobenzyne, leading for example with trans- (3-methylstyrene to (63, R = Me), is likely and in accord with the conservation of orbital symmetry 68>. However while the electro-cyclic rearrangement of (63, R = H) to (65, R = H) is not allowed, base catalysed prototropic rearrangement is possible. A carbanion (64, R = H) cannot have more than a transient existence in the reaction of tetrafluorobenzyne with styrene because no deuterium incorporation in (65) was detected when either the reaction mixture was quenched with deuterium oxide or when the reaction was conducted in the presence of a ten molar excess of deuteriopentafluorobenzene. 

D-glucose and D-fructose in acidified deuterium oxide, and acid conversion of D-[2- H]glucose were conducted, in order to determine the importance of 39 as an intermediate from the proportion of deuterium incorporated at C-3 of 5-(hydroxymethyl)-2-furaldehyde. However, the 2-furaldehyde formed in the reactions contained no deuterium. Thus, an essentially irreversible sequence that involves hexose, 36, 38, 40, and 11 best explains the acid-catalyzed, dehydration reaction. 

Replacement of water in gelatin by deuterium oxide, which replaces the )N-H group by >N-D decreases the conductivity by a factor of l/j/2. While this does suggest that the amide protons are involved in conduction, the method of replacing the hydrogen atom does not rule out the possibility that conduction takes place through the water contained in the material (20, 138). 

Sprinson and coworkers [30] conducted the methylmalonyl-CoA mutase reaction in deuterium oxide using a crude mitochondrial preparation. The presence of methylmalonyl-CoA epimerase insured that (1) all substrate molecules incorporated one atom of deuterium into position 2, and (2) in the course of the reaction the (2R)-epimer of methylmalonyl-CoA was continuously supplied by epimerization of the (25)-epimer, which was in turn generated by the enzymic carboxylation of propionyl-CoA. Alkaline hydrolysis of the product and subsequent purification furnished succinic acid which was mainly monodeuterated (70% 2H,-, 15% 2H2-labelled and 13% unlabelled species). A positive ORD curve revealed its (5) configuration indicating stereochemical retention for the AdoCbl-dependent rearrangement (Fig. 22). No plausible explanation could be offered for the formation of doubly deuterated and unlabelled species. Essentially the same results were later obtained with a highly purified mutase preparation from Propionibacterium sher-manii (J. Retey, unpublished). 

The direct coupling of liquid chromatography with proton NMR has been attempted numerous times. Early experiments of coupled HPLC- H-NMR were conducted in a stop-flow mode or with very low flow rates [193-195]. This was necessary to accumulate a sufficient number of spectra per sample volume in order to improve the signal-to-noise ratio. Other problems associated with the implementation of on-line HPLC-NMR have included the need for deuterated solvents. However, with the exception of deuterium oxide, the use of deuterated eluents is too expensive for routine analysis. Therefore, proton-containing solvents, such as acetonitrile or methanol, must be used. To get rid of the solvent signals in the spectra, the proton NMR signals of the solvents have to be suppressed. 

The analysis of a technical poly(ethylene oxide) with respect to chemical composition and degree of polymerization has been performed by Pasch and Hiller [210]. This investigation was conducted under conditions which are common for HPLC separations, i.e. sufficiently high flow rate, moderate sample com-centration, and on-flow detection. Using an octadecyl-modified silica gel as the stationary phase and an eluent of acetonitrile/deuterium oxide 50 50 (v/v), the sample was separated into different functionality fractions (see Fig. 38). The major fraction of the sample eluting between 14 and 25 min exhibited a partial oligomer separation. 

Deuterated compounds may be needed for mechanistic or physical studies and a very high purity (i.e., preferably at least 97% of the product should consist of the compound having the D-atom on the desired place) is often necessary. A general method consists in treating the alkali-metal derivative with deuterium oxide or deuteriomethanol or -ethanol. The presence of undeuterated compound may be due to incomplete metallation, therefore this reaction is carried out with an excess of the basic reagent. This involves, however, some risk of introduction of more than one D-atom, especially when the quench operation is not conducted in the proper way ... 

The Wacker reaction has found most use for the oxidation of terminal alkenes to give methyl ketones. It is believed to take place by an initial trans hydroxypallada-tion of the alkene to form an unstable complex that undergoes rapid p-elimination to the enol 112 (5.112). Hydropalladation then reductive elimination completes the overall process that involves transfer of hydride ion from one carbon to the other, via the palladium atom. The hydride migration is required to explain the observation that when the reaction is conducted in deuterium oxide, no deuterium is incorporated in the aldehyde produced. 

Boden has investigated the mechanism of Pb oxidation and the role of water through isotope-exchange experiments [21]. He has used deuterium oxide instead of water. In the presence of D2O, the rate constant of the reaction of Pb oxidation diminishes almost twice. This indicates that water takes part in the reactions of lead oxidation. The bond D—O is stronger than the bond H—O. Isotope-exchange experiments have been conducted with H2O and H20 isotopes. It has been established that almost 50% of PbO obtained as a result of Pb oxidation contains O isotope. On grounds of these results, the following mechanism of Pb oxidation with involvement of H2O has been proposed ... 

This treatise is an exhaustive compilation of physical data on heavy water (deuterium oxide). Some of the more relevant properties that are covered include densities, critical constants, vapor pressures, enthalpies of transition, viscosity, and thermal conductivity, equation of state, and tables of thermodynamic properties as functions of temperature and pressure. 

The calcium-catalyzed epimerization is clearly different from the LdB-AvE transformation. It does not proceed through the enediol when it is conducted in deuterium oxide, there is no incorporation of deuterium and, if C-1 is substituted by the substituent shifts to become C-2. The mechanism is therefore the same as in the Bilik and in the nickel-amine catalyzed epimerization, a carbon-carbon migration. This mechanism is explained [52] by the formation of a complex between calcium cations and the anionic form of the sugar this holds the sugar in a conformation suitable for the migration of the bond from C-2 to C-3, just as molybdic acid and nickel-amine do. To convert most of the sugar to this complex, an amount of calcium hydroxide equivalent to the sugar is required, or even more this is where the reaction conditions differ from those of the LdB-AvE reaction. 

Formulations for general and sdentiflc use have also been adopted for other properties of water. The most industrially important of these are probably the viscosity and the thermal conductivity, although some other properties such as the static dielectric constant and the refractive index are important in research. There are also lAPWS formulations for some properties of heavy water (deuterium oxide, D2O). 

Isotope concentration While deuterium model reactions are often conducted with pure deuterium oxide as the isotope source, tritium oxide is rarely used at anything close to nuclidic purity (note that tritiated water at 50 Ci/mL, the highest specific activity normally available commercially, has a tritium/hydrogen ratio of only about 1.6/98.4). Therefore, the concentration of tritium in HHO is usually much lower than that of deuterium in HjO, and this difference will be important if the source concentration is a factor in the rate equation. Analogously, model exchange reactions with deuterium gas are often done at one atmosphere of pressure, whereas in most cases tritium gas is used at lower pressures. This can result in substantially slower tritium exchange rates. 

Voltz and Weller 14S) measured the activity of chromic oxide for hydro-gen-deuterium exchange at —78° and —195°, after pretreatment at 5(X)° in an atmosphere of oxygen or hydrogen. They found the catalytic activity of the reduced state to be higher than that of the oxidized state, although the latter had a higher concentration of defects (positive holes) responsible for electrical conductivity. The relation between catalytic activity and conductivity is thus opposite to that for zinc oxide, although in both cases the activity appears to increase with the electron concentration. The interpretation advanced earlier for zinc oxide has also been extended to chromic oxide (Baker and Jenkins, 14S). 

That products of intermediate oxidation level can be detected in the photocatalytic reactions of hydrocarbons and fossil fuels is also consistent with a surface bound radical intermediate . Photocatalytic isotope exchange between cyclopentane and deuterium on bifunctional platinum/titanium dioxide catalysts indicates the importance of weakly adsorbed pentane at oxide sites. The platinum serves to attract free electrons, decreasing the efficiency of electron-hole recombination, and to regenerate the surface oxide after exchange. Much better control of the exchange is afforded with photoelectrochemical than thermal catalysis > ) As before, hydrocarbon oxidations can also be conducted at the gas-solid interface... 

Additional experiments conducted by Cope and co workere93l> , "> oo the ctV and fams-iaomers of cydodeoene oxide yielded similar results. Detailed mechanistic aspects of these traosannul r epoxide iBotnemations have recently been further clarified by Cope and on workers8 8 848 by deuterium labeling. 

A subsequent study ° from the Arnold group showed an intriguing stereoelectronic effect in oxidative benzylic carbon-hydrogen bond cleavage reactions of substrates 8 and 9 (Scheme 3.7). In this study, electron transfer reactions were conducted in the presence of a nonnucleophilic base. Radical cation formation also weakens benzylic carbon-hydrogen bonds, thereby enhancing their acidity. Deprotonation of benzylic hydrogens yields benzylic radicals that can be reduced by the radical anion of dicyanobenzene to form benzylic anions that will be protonated by solvent. This sequence of oxidation, deprotonation, reduction, and protonation provides a sequence by which epimerization can be effected at the benzylic center. In this study, tram isomer 10 showed no propensity to isomerize to cis isomer 11 (equation 1 in Scheme 3.7), but 11 readily converted to 10 (equation 2 in Scheme 3.7). The reactions were repeated in deuterated solvents to assure that these observations resulted from kinetic rather than thermodynamic factors. Trans isomer 9 showed no incorporation of deuterium (equation 3 in Scheme 3.7) whereas cis isomer 11 showed complete deuterium incorporation. The authors attributed this difference in reactivity to... 

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