Hydrocarbon-oxygen complex

Effective fluorescence quenching of polycyclic hydrocarbons by oxygen was observed by Terenin,45,46 who proposed a quenching mechanism according to which the overall result was the production of an electronically excited hydrocarbon-oxygen complex. 

We propose that the first step in the formation of quinones, as shown in Scheme 3 for BP, involves an electron transfer from the hydrocarbon to the activated cytochrome P-450-iron-oxygen complex. The generate nucleophilic oxygen atom of this complex would react at C-6 of BP in which the positive charge is appreciably localized. The 6-oxy-BP radical formed would then dissociate to leave the iron of cytochrome P-450 in the normal ferric state. Autoxidation of the 6-oxy-BP radical in which the spin density is localized mainly on the oxygen, C-l, C-3 and C-12 (19,20) would produce the three BP diones. 

The primary product from Fischer-Tropsch synthesis is a complex multiphase mixture of hydrocarbons, oxygenates, and water. The composition of this mixture is dependent on the Fischer-Tropsch technology and considerable variation in carbon number distribution, as well as the relative abundance of different compound classes is possible. The primary Fischer-Tropsch product has to be refined to produce final products, and in this respect, it is comparable to crude oil. The primary product from Fischer-Tropsch synthesis can therefore be seen as a synthetic crude oil (syncrude). There are nevertheless significant differences between crude oil and Fischer-Tropsch syncrude, thus requiring a different refining approach.1... 

The low-temperature oxidation represents a complex system and can be better interpreted when the elementary reactions are firmly established. We arc inclined to assign formaldehyde only a minor role in the low-temperature regime. Further experimental work is required to clarify the interactions between formaldehyde and peroxides, the radical-induced formaldehyde oxidation, and the effect of formaldehyde addition in the low-temperature hydrocarbon-oxygen systems. It has been established that mercury vapor is effective for the destruction of peroxides. Mercury vapor addition to systems in the cool-flame zone would perhaps be of value in assessing not only the role of peroxides, but also that of formaldehyde in this interesting region. 

A number of transition metals are now known147-156 to form stable dioxygen complexes, and many of these reactions are reversible. In the case of cobalt, numerous complexes have been shown to combine oxygen reversibly.157 158 Since cobalt compounds are also the most common catalysts for autoxidations, cobalt-oxygen complexes have often been implicated in chain initiation of liquid phase autoxidations. However, there is no unequivocal evidence for chain initiation of autoxidations via an oxygen activation mechanism. Theories are based on kinetic evidence alone, and many authors have failed to appreciate that conventional procedures for purifying substrate do not remove the last traces of alkyl hydroperoxides from many hydrocarbons. It is usually these trace amounts of alkyl hydroperoxide that are responsible for chain initiation during catalytic reaction with metal complexes. 

We ve also got the ana is on the substance that was in one of the krife marks on Sa% Palmer s vertebra, I told Mackenzie. I read fromny own copy of the report. It s a hydrocarbon FaE complex, but around eighty per cent carbon, ten per cent hydrogen, wEh smaE amounts of si4)hur, oxygen, nEro n and a few trace metals. ... 

It is noteworthy that the enzyme docs not activate the hydrocarbon, but rather generates a very active oxygen complex [3] a coordinated hydroxyl radical would be the reactive species and its selectivity w ould be the result of the precise proteinic environment of the catalytic center. 

The behaviour of these samples measured by IGC shows a reduction of the adsorption capacity for both linear and cyclic hydrocarbons (Table 5). Moreover, Vs for the hydrocarbon 2,2 DMB on the oxidized carbons is quite close to the gas hold up time, similar to that on the original samples, and the separation ratio for the couple benzene/cyclohexane is similar in both cases. These results show that the oxygen surface complexes fixed on the surface produce constrictions at the entrance of the pores, but do not result in the production of carbon materials with improved molecular sieve properties. One reason for this could be that the size of the oxygen complexes is not large enough. Therefore, if the size of the chemical complexes is increased the molecular sieve character for the couple benzene/cyclohexane would be expected to be developed. For this purpose, the S900 carbon was treated to introduce sulphur complexes on the surface [30]. Also a commercial acti-... 

TT-cation radical complexes.In the reactions, oxoiron(IV) porphyrin rr-cation radicals of electron-rich porphyrins reacted fast with ROOH (i.e., catalase and peroxidase type of chemistry one-electron oxidation of ROOH) (Scheme 2, pathway A). On the other hand, oxoiron(IV) porphyrin rr-cation radicals of electron-deficient porphyrins reacted fast with olefins to yield epoxide products (i.e., cytochrome P450 type of chemistry oxygen atom transfer) (Scheme 2, pathway B). These results demonstrated that electron-deficient iron porphyrin complexes are better catalysts in hydrocarbon oxygenations by hydroperoxides, since these complexes can avoid the facile decomposition of oxoiron intermediates by ROOH (Scheme 2, pathway A). Indeed, highly electron-deficient iron(III) porphyrin complexes efficiently catalyze alkane hydroxylations by H2O2 in aprotic solvents. 

This paper will describe our use of polynuclear manganese complexes of the type believed to be present at the active site of the oxygen evolving complex (OEC) of photosystem II (PSII) as catalysts for hydrocarbon oxygenation. 

Nickel complexes act as catalysts for the oxidation of ditertiary diphosphines. Palladium(o) complexes catalyse the autoxidation of hydrocarbons. The reactivity is sensitive to the nature of the arylphosphine ligands. The mechanism involves intermediate formation of a palladium-molecular oxygen complex. ... 

Essential oils are complex mixtures, constituted by terpenoid hydrocarbons, oxygenated terpenes and sesquiterpenes. They originate from the plant secondary metabohsm and are responsible for their characteristic aroma. 

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