Deuterium/hydroxyl exchange

Studies in deuterated water have shown that the hydroxyl proton does not end up in the ethanal formed. The decomposition of the 2-hydroxyethyl is not a simple P-elimination to palladium hydride and vinyl alcohol, which then isomerises to ethanal. Instead, the four protons stemming from ethene are all present in the initial ethanal product [6] (measured at 5 °C in order to suppress deuterium/hydrogen exchange in the product) and most authors have therefore accepted an intramolecular hydride shift as the key-step of the mechanism (see Figure 15.2). There remains some doubt as to how the hydride shift takes place. 

It is probable, then, that the activated complex for exchange of deuterium with water contains deuterium, hydroxyl ion, and possibly water molecules. Wirtz and Bonhoeffer had suggested the following two-step mechanism ... 

Because of the weakness of the Bronsted acidity of the surface hydroxyl groups, one can suppose that the synchronous mechanism is relatively efficient for these substitution reactions. The simplest reaction of this type is H/D isotopic heteroexchange with D-containing molecules. The heteroexchange with water is known to proceed rapidly at a temperature as low as 20°C. With molecular deuterium, such exchange occurs at 350-400°C with an activation energy of 15-20 kcal/mol (55). 

By combining deuterium and exchange, it was demonstrated that the deformation 6(MOH) mode of H-bonded hydroxyls on oxides is located at 1100 cm for AI2O3, 953 cm for Zr02, and around... 

Deuterium does not give a signal under the conditions of H NMR spectroscopy Thus replacement of a hydroxyl proton by deuterium leads to the disappearance of the OH peak of the alcohol Protons bonded to nitrogen and sulfur also undergo exchange with... 

Beyer synthesis, 2, 474 electrolytic oxidation, 2, 325 7r-electron density calculations, 2, 316 1-electron reduction, 2, 282, 283 electrophilic halogenation, 2, 49 electrophilic substitution, 2, 49 Emmert reaction, 2, 276 food preservative, 1,411 free radical acylation, 2, 298 free radical alkylation, 2, 45, 295 free radical amidation, 2, 299 free radical arylation, 2, 295 Friedel-Crafts reactions, 2, 208 Friedlander synthesis, 2, 70, 443 fluorination, 2, 199 halogenation, 2, 40 hydrogenation, 2, 45, 284-285, 327 hydrogen-deuterium exchange, 2, 196, 286 hydroxylation, 2, 325 iodination, 2, 202, 320 ionization constants, 2, 172 IR spectra, 2, 18 lithiation, 2, 267... 

The efficiency of reduction of benzophenone derivatives is greatly diminished when an ortho alkyl substituent is present because a new photoreaction, intramolecular hydrogen-atom abstraction, then becomes the dominant process. The abstraction takes place from the benzylic position on the adjacent alkyl chain, giving an unstable enol that can revert to the original benzophenone without photoreduction. This process is known as photoenolization Photoenolization can be detected, even though no net transformation of the reactant occurs, by photolysis in deuterated hydroxylic solvents. The proton of the enolic hydroxyl is rapidly exchanged with solvent, so deuterium is introduced at the benzylic position. Deuterium is also introduced if the enol is protonated at the benzylic carbon by solvent ... 

The compounds were also run with D20 leaking into the ion source from a stainless steel reservoir. The resulting mass spectra show partial exchange of the hydroxyl protons with deuterium. From the shifts of the peaks in the mass spectra of the deuterated analogs, the number of exchangeable hydrogens retained in each fragment can be determined. 

The alcohol hydroxyl hydrogen typically produced a broad H NMR signal of variable chemical shift which can be eliminated by exchange with deuterium from D20. 

The essential features of the above picture are shown schematically in Fig. 6. Hydrogen or deuterium adsorbs and desorbs rapidly on these sites (half-time less than 1 min) hence, the slower H2-D2 equilibration (half-time about 8 min) appears to be determined by the site-to-site migration required for exchange. Poisoning experiments show that water also prefers these sites in agreement with the limited IR data, Fig. 6 shows the adsorbed water yields surface hydroxyls (10). 

Direct labelling with deuterium is another approach, and three promising methods have been reported. One, described by Koch and Stuart and coworkers,41 is based on the specific exchange of hydrogen attached to hydroxylated carbon atoms by deuterium atoms that occurs on treatment with Raney nickel-D20. Although no exchange was observed with soluble starch or glycogen, the H-2, H-3, and H-6 atoms of... 

FIGURE 32. H NMR spectrum of filipin III, 3 mM in DMSO-dg, recorded at 400 MHz and 25 °C. The expanded region contains nine hydroxylic proton resonances that fully exchange with deuterium oxide and correspond to the nine hydroxyl groups of filipin III. No apodization functions were applied prior to the Fourier transformation. Reproduced by permission of John Wiley Sons from Reference 50... 

Deuterium exchange with DjO was used by Shuravlev and Kiselev (199) in the determination of surface hydroxyl groups of silica gel. Adsorption isotherms of HgO and DjO were determined gravi-metrically they agreed with each other within the limits of experimental error. 

Goshe M.B., Anderson V.E. Hydroxyl radical-induced hydrogen/ deuterium exchange in amino acid carbon-... 

Liu et al. [43] have demonstrated the use of online hydrogen/deuterium exchange, LC-MS and LC-MS-MS for successfully distinguishing between S-oxidation and hydroxylation in metabolite identification for compound I. 

The surface of silica is highly reactive and hydroxyl groups exchange hydrogen for deuterium with D20 [14—16] but not with D2. They can be replaced by Cl from Cl2 or CC14 [16] and they react with silanes and aluminium chloride [15,19], Surface alcoholates are formed when silica is contacted with primary or secondary alcohols [20] either by the reaction with hydroxyl groups... 

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