Oxygen selective transfer

Ruthenium(in) catalyses the oxidative decarboxylation of n-butyric acid and isobutyric acid by ceric sulfate in aqueous acid. A mechanism for the Ru(III)-catalysed oxidation of o-hydroxybenzoic acid by an acidic solution of bromamine-B (PhS02-NNaBr, BAB) has been proposed based on a kinetic smdy. An ionic mechanism is suggested for the ruthenium(III) analogue of the Udenfriend-type system Ru(III)-EDTA-ascorbate-02, for the selective oxygen-atom transfer to saturated and unsaturated hydrocarbons. The kinetics of the oxidation of p-XC6H4CHPhOH(X =... 

VII. OXYGEN ATOM TRANSFER FROM SELECTED HYDROPEROXIDES 67... 

Dimesityldioxirane, a crystalline derivative, has been isolated by Sander and colleagues and subjected to X-ray analysis. The microwave and X-ray data both suggest that dioxiranes have an atypically long 0—0 bond in excess of 1.5 A. Those factors that determine the stability of dioxiranes are not yet completely understood but what is known today will be addressed in this review. A series of achiral, and more recently chiral oxygen atom transfer reagents, have been adapted to very selective applications in the preparation of complex epoxides and related products of oxidation. A detailed history and survey of the rather remarkable evolution of dioxirane chemistry and their numerous synthetic applications is presented in Chapter 14 of this volume by Adam and Cong-Gui Zhao. Our objective in this part of the review is to first provide a detailed theoretical description of the electronic nature of dioxiranes and then to describe the nuances of the mechanism of oxygen atom transfer to a variety of nucleophilic substrates. 

We point out that the mechanism sketched in path A of Scheme 11 is in agreement with the kinetic and spectroscopic data collected from several research groups. On the other hand, a series of contradictions was encountered in fitting the experimental data into the mechanism proposed in path B. Furthermore, several other papers have appeared in the last decade, based on both experimental results and theoretical calculations, supporting an epoxidation mechanism involving a direct oxygen atom transfer to olefins. For selected examples, see References 34, 145-155. 

Deeper oxidation products like furan and, particularly, maleic acid anhydride, can be produced by catalysts that have a stronger oxidative power than the above type-(a) catalysts, but, at the same time, have retained the capacity to transfer oxygen selectively to the organic molecule (a capacity which is absent in the type-(b) catalysts). Besides, a more acidic character of the catalyst surface is probably required to produce an acidic product like maleic anhydride effectively. The most interesting catalysts of this group are V2Os-based catalysts and certain molybdates and Mo03-based catalysts. 

There is keen interest in developing nitrogen-carbon bond-forming reactions akin to oxygen atom transfer and selective oxidations in organic chemistry. 

The oxygen anions created are selectively transferred through the oxygen-permeable membrane to the anode, where they experience a similar half-cell reaction with a gaseous fuel, either H2, syngas (CO + Hj), or a hydrocarbon, to produce H20 and C02. For example, if the fuel is CH4, the oxidation reaction in the anode is given by... 

Dioxirane (RR C02) compounds are relatively new in the arsenal of the synthetic chemist, however since the isolation of dimethyldioxirane by Murray and Jeyaraman in 1985,146 it has become a very important oxidant for preparative oxygen transfer chemistry.147 The dioxiranes are ideal oxidants in that they are efficient in their oxygen atom transfer, exhibit high chemio- and regio-selectivities, act catalytically, are mild towards the substrate and oxidized product, and perform under strictly neutral conditions. The compounds are prepared from peroxymonosulfate and ketones under neutral to mildly alkaline conditions (Figure 2.46). 

Ion-molecular reactions are used to resolve isobaric interferences, as discussed, in ICP-MS with a collision/reaction cell or by utilizing ion traps. The mass spectra of Sr, Y and Zr (Fig. 6.10a) without O2 admitted into the collision cell and (Fig. 6.10b) with 10 Pa Oj are different. By introducing oxygen, selective formation of YO and ZrO, but not SrO, is observed. This behaviour of different oxide formation is relevant for an interference free determination of Sr. Ultrahigh mass resolving power ICP mass spectrometry (at m/Am 260 000) selectively removes unwanted ions prior to transfer to the FTICR analyzer cell by gas-phase chemical reactions, e.g., for separation of Ca from " Ar+ obtained with a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer equipped with a 3 tesla superconducting magnet. ... 

However, it is noteworthy that oxygen atom transfer to the magnesium alkyl derivative does not occur rapidly at room temperature. This is presumably one of the factors that is responsible for the observation that the reactions of [Tp ]MgR with O2 are selective in the formation of alkylperoxo complexes, rather than the alkoxo derivatives. It is likely that this is a consequence of the sterically encumbered nature of the magnesium centers in these complexes. 

These studies have demonstrated that the homogeneously catalyzed oxychlorination of ethylene to 1,2-dichloroethane is feasible under relatively mild operating conditions without the need for catalyst circulation and that selectivities better than 96% can be achieved in sustained operations. A rational basis for reactor design has been devised, taking into account such factors as ethylene- and oxygen-mass transfer rates, chemical kinetics, water vapor pressure over the catalyst, selectivity relation-... 

The choice of solvent for solution degradations of PS with 254 nm radiation is somewhat limited. For the present purpose, DMM was selected because It lacked a strong oxygen charge-transfer absorption band such as that observed In aerated tetrahydrofuran or dloxane. In DMM, 0° for PS-7 were similar to those observed In tetrahydrofuran or methylene chloride. 

J. P. Collman, J. 1. Brauman, B. Mcunicr, T. Hayashi, T. Kodadek, S. A. Raybuck, Epoxidation of olefins by cytochrome P-450 model compounds Kinetics and stereochemistry of oxygen atom transfer and origin of shape selectivity, J. Am. Chem. Soc. 107 (1985) 2000. 

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