Oxidation intermediates identity

Organic molecules, oxidation, chemical identity of adsorbed intermediates, 38 21 Organic reactions, catalyzed by crystalline aluminosilicates, 18 305-365 see also Aluminosilicates Organic substates... 

Comparison of the Reductive and Oxidative Pentose Phosphate Pathways The reductive pentose phosphate pathway generates a number of intermediates identical to those of the oxidative pentose phosphate pathway (Chapter 14). What role does each pathway play in cells where it is active ... 

As a further possibility the ac electrolysis may lead to other products than those of the photolysis. In this case an excited state mechanism is, of course, excluded. Although there is a certain similarity between the electronic structure of an excited state and the reduced or oxidized form of a molecule, they are not identical. Consequently, it is not surprising when photolysis and electrolysis do not yield the same product. Another reason for such an observation may be the different lifetimes. An excited state can be extremely short-lived. Non-reactive deactivation could then compete successfully with a photoreaction. The compound is not light-sensitive. On the contrary, the reduced and oxidized intermediates generated by ac electrolysis should have comparably long life times which may permit a reaction. The ac electrolysis of Ni(II)(BABA)(MNT) (BABA = biacetyl-bis(anil) and MNT - = disulfidomaleonitrile) is an example of this reaction type (63). 

Method I. Addition of RH to H2 + O2 mixtures at about 750 K This approach has been remarkably successful over the last 30 years with a wide variety of organic compounds. It is, however, limited in its use to pressures between 200-600 Torr and temperatures between 720-800 K. Use of small amounts of the additive (RH) and an aged boric-acid-coated Pyrex vessel permits an investigation of the oxidation of alkanes, alkenes, aromatics and related oxygenated compounds in the total absence of surface effects in a constant and controllable radical environment determined almost entirely by the H2 + O2 mixture. Many different RH compounds may then be oxidized under identical conditions. This is in marked contrast to the direct oxidation method where the radical environment is controlled by the oxidant and changes constantly as the intermediates are formed and then oxidized. Two types of experiment are carried out ... 

Preparation of the 2-chloro-3-methoxy-4-nitropyridine A -oxide intermediate in the synthesis was considerably improved by the methylation of commercially available 2-chloro-3-pyridinol using dimethylsulfate and tet-rabutylammonium bromide as the catalyst under phase-transfer conditions (370), instead of diazomethane (Scheme 48). In the synthesis of orellanines elaborated by Tiecco et al. (299,301,309), shown in Scheme 49, the commercially available 3-hydroxypyridine was the starting material. The structures of the synthetic compounds were proved to be identical to those... 

Another approach to determining if the iron-cyclam-catalyzed reactions of H2O2, PhIO, and MCPBA occur via a common intermediate is to study intramolecular and intermolecular competitive olefin epoxidations, with the assumption that all three oxidants should give similar reactivity patterns if the active oxygenating intermediates generated from these oxidants are identical. If different active oxidants are generated, then different reactivity patterns would be expected. From the relative reactivity studies... 

The mechanism of sealing has been shown to involve an initial dissolution and reprecipitation of hydrated aluminium oxide on the pore walls, pseudo-boehmite gel formation within the pores, and conversion of this to crystalline boehmite at the film surface. The presence of an intermediate layer close to the film surface, in which the identity of the original pores has been lost, has also been recognised . 

As a rule, the anabolic pathway by which a substance is made is not the reverse of the catabolic pathway by which the same substance is degraded. The two paths must differ in some respects for both to be energetically favorable. Thus, the y3-oxidation pathway for converting fatty acids into acetyl CoA and the biosynthesis of fatty acids from acetyl CoA are related but are not exact opposites. Differences include the identity of the acvl-group carrier, the stereochemistry of the / -hydroxyacyl reaction intermediate, and the identity of the redox coenzyme. FAD is used to introduce a double bond in jS-oxidalion, while NADPH is used to reduce the double bond in fatty-acid biosynthesis. 

It is probable that during hydrosilylations these Ni(II) complexes are reduced to 7r-olefin Ni(0) species which then undergo an oxidative addition in an identical manner to that already discussed for the chloroplatinic acid case. There is current interest in such oxidations (83), and the platinum analog (Ph3P)2Pt(olefin) has been shown in one case (olefin = C2H4) to be an excellent hydrosilylation catalyst (240). In this system, intermediate low oxidation state Pt species have been isolated their nature is dependent on the electronegativity of the other groups attached to silicon. 

Although Ce(IV) oxidation of carboxylic acids is slow and incomplete under similar reaction conditions , the rate is greatly enhanced on addition of perchloric acid. No kinetics were obtained but product analysis of the oxidations of -butyric, isobutyric, pivalic and acetic acids indicates an identical oxidative decarboxylation to take place. Photochemical decomposition of Ce(IV) carbo-xylates is highly efficient unity) and Cu(ll) diverts the course of reaction in the same way as in the thermal oxidation by Co(IIl). Direct spectroscopic evidence for the intermediate formation of alkyl radicals was obtained by Greatorex and Kemp ° who photoirradiated several Ce(IV) carboxylates in a degassed perchloric acid glass at 77 °K in the cavity of an electron spin resonance spectro-... 

The chemical and physical properties of the polymers obtained by these alternate methods are identical, except insofar as they are affected by differences in molecular weight. In order to avoid the confusion which would result if classification of the products were to be based on the method of synthesis actually employed in each case, it has been proposed that the substance be referred to as a condensation polymer in such instances, irrespective of whether a condensation or an addition polymerization process was used in its preparation. The cyclic compound is after all a condensation product of one or more bifunctional compounds, and in this sense the linear polymer obtained from the cyclic intermediate can be regarded as the polymeric derivative of the bifunctional monomer(s). Furthermore, each of the polymers listed in Table III may be degraded to bifunctional monomers differing in composition from the structural unit, although such degradation of polyethylene oxide and the polythioether may be difficult. Apart from the demands of any particular definition, it is clearly desirable to include all of these substances among the condensation... 

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