Oxygen exchange

Previous studies of the exchange of labelled carbon dioxide between the [Co(NH3)5(C03)]+ cation and carbonate are to a certain extent inconsistent. By studying the kinetics of exchange between water and dissolved carbonate (COg -HCO 3) on the one hand, and between water and [Co(NH3)6-(COa)]+ on the other, it has now been shown that the earlier proposal that it is the hydration of carbon dioxide which is the rate-determining step in the [Co(NH3)6(C08)]+-carbonate exchange reaction is correct.  

There has been considerable activity over the past few years in the area of oxygen exchange between chromium(m)-oxalate complexes and water. Now a consistent pattern appears to be emerging, as is shown by the discussion of recent work on oxygpn exchange with the [Cr(ox)(OH2)4]+ cation. In this, as in other chromium(m)- and platinum(n)-oxalate complexes, all the oxalate 

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The operation of the nitronium ion in these media was later proved conclusively. "- The rates of nitration of 2-phenylethanesulphonate anion ([Aromatic] < c. 0-5 mol l i), toluene-(U-sulphonate anion, p-nitrophenol, A(-methyl-2,4-dinitroaniline and A(-methyl-iV,2,4-trinitro-aniline in aqueous solutions of nitric acid depend on the first power of the concentration of the aromatic. The dependence on acidity of the rate of 0-exchange between nitric acid and water was measured, " and formal first-order rate constants for oxygen exchange were defined by dividing the rates of exchange by the concentration of water. Comparison of these constants with the corresponding results for the reactions of the aromatic compounds yielded the scale of relative reactivities sho-wn in table 2.1. 

Thioacetyl derivatives (155) are obtained by direct heterocyclization reactions (365. 378, 563) and by a sulfur-oxygen exchange" reaction involving thioacetic acid and A-2-oxazoline-5-one (154) or A-2-thiazoline-5-one (156) (Scheme 81) (365, 378, 379). Ra-Ni reduction of 155 affords the 5-unsubstituted thiazole (379). 

Another example is the absence of oxygen exchange with solvent in the hydrolysis of gluconolactone. Simple acyclic esters usually undergo isotopic exchange at a rate that is conqietitive with hydrolysis. This occurs through the tetrahedral addition intermediate. 

M s , in agreement with independent measurements of the rate of hydration. Thus, it appears that the oxygen exchange rate can be completely accounted for by the hydration reaction. 

Bromyl fluoride is also produced by fluorine-oxygen exchange between BrPs and oxoiodine compounds (p. 881), e.g. ... 

Shimomura, O., and Johnson, F. FI. (1975a). Influence of buffer system and pH on the amount of oxygen exchanged between solvent F420 and the C02 produced in the aerobic oxidation of Cypridina luciferin catalyzed by Cypridina luciferase. Anal. Biochem. 64 601-605. 

The chemical properties of oxide surfaces have been studied by several methods, including oxygen exchange. This method has been used to investigate the mechanisms of heterogeneous reactions for which oxides are active catalysts [36]. The dimerization step does not necessarily precede desorption and Malinin and Tolmachev [634], in one of the few reviews of decomposition kinetics of solid metal oxides, use this criterion to distinguish two alternative reaction mechanisms, examples being... 

Highest rates of biochemical oxidation are found in shallow, surface active reaches where attached microbiota and interfacial oxygen exchange are at their maxima. 

Oxygen-exchange reactions of square-pyramidal metal(V) complexes have been reported [14]. In monooxotechnetium(V) and monooxorhenium(V) complexes with N,iV -bis(mercaptoaeetyl)butane-l,4-diamine(DBDS), the exchange of oxygen between the complexes and water in DMSO medium ... 

Oxygen exchange was also found in the case of Tc(VII) and Re(VII) complexes. For the permetallate, [MVII04], the rate law of oxygen exchange can be expressed as... 

Mbars, W. H., and H. Sobotka Heavy Oxygen Exchange of Proteins and... 

Esterification and Oxygen Exchange of Carboxylic Acids. J. Amer. chem. Soc. 61, 2584 (1939). 

Kinetic studies on racemization, oxygen exchange reaction using H2lsO, and theoretical studies clarified the mechanism for racemization of optically active chalcogenic acids.34,37 The mechanism of racemization of tellurinic acids is different from that of the corresponding seleninic acids. In fact, the mechanism for racemization of optically active tellurinic acids was found to involve an... 

These observations illustrate that there are two transformations open to metallocarboxylic acid intermediates reversible loss of OH" accompanied by oxygen exchange, and metal-hydride formation with expulsion of C02. Our entry into this area of chemistry was in 1975 when extensive studies of oxygen lability in metal carbonyl cations were initiated (10). These... 

We have exploited this base catalysis of the oxygen exchange process to effect oxygen lability in the less electrophilic carbonyl sites of neutral metal carbonyl species. Because [MCOOH] intermediates are readily decarboxylated in the presence of excess hydroxide ion, in order to observe oxygen exchange processes in neutral metal carbonyl complexes it was convenient to carry out these reactions in a biphasic system employing phase transfer catalysis () (16, 17. 18). Under conditions (eq. 7) the... 

Figures 6 and 7 also point out the two principal techniques we have employed in monitoring these oxygen exchange reactions, namely, frequency shifts in the...

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