Oxide exchange

In pyridazin-3(2//)-one only the hydrogen at position 6 is replaced at 180 °C, while in 3-hydroxypyridazine 1-oxide the deuterium exchange takes place first at position 6 and then at position 4 at 140 °C. 5-Hydroxy- and 5-methoxy-pyridazine 1-oxide exchange only the hydrogen at position 6 at 150 °C. 

The distribution of the major elements (Ca, Mg, Na, K,. ..) in soils is well known to be governed by ion-exchange processes (1). The behaviour of transition elements such as Co, Ni, Cd, Cu, etc. in natural systems (soils, sediments) often results from a combination of different effects such as precipitation, sorption in oxides, exchange in clay minerals and complexation with organic... 

The toxicities of nine alkyl aromatics (4) are appreciably less than those of the polycyclic aromatics. No signihcant retardation is observed in benzene-deuterium oxide exchange reactions at 30° even when the poisons are present in benzene in concentrations of 3.6 mole %. The high temperature exchange rate (Table II) of sterieally unhindered ring positions in the alkylbenzenes indicates that adsorption strength... 

Molybdenum(VI) and tungsten(VI) are stable oxidation states and only mild oxidants. Exchange with H2O obeys the rate law ... 

Treatment of pyridine with NaOD/D20 at elevated temperatures results in eventual replacement of all hydrogen atoms by deuterium. This process presumably involves deprotonation followed by rapid deuteration of the intermediate negatively charged species (cf. equation 21) in a sequential manner. Azine N- oxides are deuterated in a similar way, positions adjacent to the N- oxide exchanging particularly rapidly. Controlled deprotonation of ring carbon atoms a and y to the heteroatom can be accomplished by the use of strong, non-nucleophilic bases and the intermediate carbanions may be trapped by electrophiles (equation 27). The yields in these reactions are in most cases only moderate, however. As expected, deprotonation occurs more easily if the heteroatom is positively charged. 

The usefulness of infrared spectroscopy of proteins and membranes is increased when spectra of dry films are compared with those taken in deuterium oxide. Exchange of protons for deuterons can affect both the amide I and amide II bands. For randomly coiled proteins in D20 the amide I band is shifted down by about 10 cm."1 but for many proteins D20 does not affect the frequency of the carbonyl stretch of either the ft structure or the a-helix. In addition, upon complete exchange the amide... 

Diphenyl-telluretin, (C6H5)2Te(OH).CH2.COOH.—The preceding bromide, when treated with moist silver oxide, exchanges its bromine for the hydroxyl group. The product sinters at 100° C., melts at 117° to 118° C., dissolves readily in warm chloroform, but is insoluble in benzene, toluene, ligroin or ether. It forms salts with acids. 

Sorption on oxides and hydrous oxides has been extensively studied both experimentally and theoretically. In order to define an ideal oxide or hydrous oxide exchanger, we will rely on experiments with well-defined sorbents such as chromatographic alumina (1-4). Briefly, the adsorption characteristics of oxides and hydrous oxides are (1) At high pH, they act as cation exchangers but with less sensitivity to the total salt concentration than clay minerals. This behavior is illustrated in Figure 2, where sorption of strontium on alumina is shown. 

In semiconducting oxides such as iron-doped SrTi03 (e.g., SrTio.8Feo.2O3) the conductivity depends thermodynamically on the oxygen partial pressure. In the thermodynamic equilibrium a metal oxide exchanges lattice oxygen Oq with the ambient gas phase. 

Difluoramine-Deuterium Oxide Exchange. Table I summarizes the results of this investigation. The exchange is first order with respect to HNF2 and zero order with respect to water. The mechanism proposed for this exchange is ... 

The results in Table XII show that self-activated platinum oxide exchanges in both a and /3 positions of thiophene, whereas self-activated ruthenium oxide catalyzes deuteration almost exclusively in the a. position. A similar type of selectivity has been observed for the exchange of thiophene on the disulfides of tungsten (both a and /3 deuteration) and molybdenum (predominantly a) using evaporated metal films.116... 

Figure 3 Uptake of K+ and Cl by hydrous bismuth oxide. Exchanger, 0.25 g total volume, 12.5 cm ionic strength, 0.1 M (HCl + KCl) or (KOH + KCl), temp. 30°C. (From M. Abe and T. Ito, Nippon Kagaku Zasshi, 85 817 (1965). With permission.)...

Hydrous oxides Exchange cations References (type of isotherm )... 

Fig. 19, Possible processes occurring on the surface of metals or metal oxides in the reduction of nitric oxide with synthesis gas, where (a) denotes products readily desorbed and observed as products, (b) denotes species believed to occur in oxide-exchange reactions, and (c) denotes intermediates observed by infrared spectroscopy.

Bell et al. (13), using similar conditions, prepared l-(4- H)ascorbic acid via tritium oxide exchange. 

The method of deuterium exchange as followed by NMR-analysis has also greatly facilitated the structural assignments for aporphines. A phenol when placed in hot alkaline deuterium oxide exchanges only its ortho and hr " gens for deuterinin. Examination of the NMR-... 

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