Oxygen exchange reactions

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). 

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 ... 

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... 

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...

Other anomeric-oxygen exchange reactions have been recently investigated quite extensively. Closely related to the Koenigs-Knorr method is the introduction offluorine as the leaving group (Scheme 1, path B) (6,9-13). Because of the difference in halophilicity of this element as compared with bromine and chlorine, additional promoter systems besides silver salts were found useful as activators for glycosylation reactions (14-16). However,... 

Fig. 9. Rate coefficients for reactions of protonated ethyl acetate. The open circles represent data for hydrolysis. Closed circles are for the oxygen-exchange reaction of the carbonyl- 80 labelled...

A. Activation through anomeric oxygen-exchange reactions 285... 

Glycosyl Oonors via Anomeric Oxygen Exchange Reaction... 

A. Activation Through Anomeric Oxygen-Exchange Reactions... 

The sulfidation mechanism was investigated by temperature-programmed sulfidation, as the oxidic catalyst was heated in a flow of H2S and ff2, and the consumption of IH S and ff2 and the evolution of H20 were measured continuously (13). ft was found that IH S is taken up and H20 given off, even at room temperature, indicating a sulfur-oxygen exchange reaction. This conclusion was confirmed by quick extended X-ray absorption fine structure (QEXAFS) studies (Fig. f, phase 2), which also demonstrated... 

At 800°C with excess carbon, Kshift is approximately 1.0. Invariably the oxygen exchange reactions never reached equilibrium. The apparent or pseudo values for K8hift were generally less than 0.2. Ergun and Menster found similar low values when steam conversion was low. 

Ill) microfacets ( 3.9). Small ensembles of three-coordinated atoms with a p3Tamidal structure resembling a reconstructed (111) polar surface can in principle form and have been indeed been proposed as the centers where oxygen exchange reactions occur. 

Infrared spectroscopic studies (185-188) indicate that nitric oxide is adsorbed onto metal surfaces, not only as the familiar nitrosyl ligand but also as [N202] (hyponitrite) units. On metal oxide surfaces, chelating nitrite has also been detected, and such species are believed to be intermediates in oxygen-exchange reactions between N 0 and bulk oxide in NiO or Fo203. The rate of this process is measurable under conditions (e.g., room temperature) in which gas-phase dissociation is minimal. Spectroscopic studies also suggest that nitric oxide reacts... 

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