Gif Systems Research Articles

Advances and perspectives in catalysts for liquid-phase oxidation of cyclohexane

The latest progress and developments in catalysts for the oxidation of cyclohexane are reviewed. Catalytic systems for the oxidation of cyclohexane including metal supported, metal oxides, molecular sieves, metal substituted polyoxometalates, photocatalysts, organocatalysts, Gif systems, metal-organic catalysts and metalloporphyrins are discussed with a particular emphasis on metalloporphyrin catalytic systems. The advantages and disadvantages of these methods are summarized and analyzed. Finally, the development trends in the oxidation technology of cyclohexane are examined.

The gif paradox.

This Account summarizes research work on the structural aspects and functional features encountered in all major branches of the Gif family of hydrocarbon-oxidizing reagents. Despite assertions by the inventor of Gif chemistry, D. H. R. Barton, to the effect that nonradical pathways could better explain the behavior of Gif systems, detailed experimental investigations provide compelling evidence to support the preponderance of oxygen- and carbon-centered radical chemistry.

Radical and non-radical chemistry of the Fenton-like systems in the presence of organic substrates

The review deals with the chemistry concerning the processes of mild and selective oxidation of alkanes and cycloalkanes by using synthetic iron complexes as catalytic systems. These cover a number of coordinated species of iron ions including the so-called Gif systems up to the polydentated Que’s models, aimed to mimic or emulate the non-haem enzymatic oxidation of alkanes. Special attention is paid to the mechanisms proposed by the various Authors and to the arguments set out for and against the free-radical interpretation to account for the activation of the CH bonds. The schemes of the free-radical chemistry of Fenton reagents in the presence of organic substrates are quoted as a reference basis for the discussion.

The selective functionalization of saturated hydrocarbons: Recent developments in Gif chemistry

Abstract

The carboxylation of saturated hydrocarbons by Gif systems. (Fe III trispicolinate/P(OMe) 3/CO/H 2O 2 in pyridine-acetic acid).

Saturated hydrocarbons are transformed into the corresponding homologous carboxylic acids by treatment with Fe(Pa) 3/P(OMe) 3/CO/H 2O 2 in pyridine-acetic acid. Optimisation of the reaction conditions and mechanistics studies are reported.

Models for non-heme oxidation enzymes

Abstract

The FeII-FeIV and FeIII-FeV manifolds in an expanded world of Gif chemistry

The Gif systems for the selective functionalization of saturated hydrocarbons based on the reactions of Superoxide with FeII and of hydrogen peroxide with FeIII are described. Both systems are relatively efficient, but not nearly so efficient as the electrochemical system developed in collaboration with Prof. G. Balavoine and Dr. Aurore Gref (Universite de Paris-Sud-Orsay, France). All of the systems afford mainly ketones. This is an unusual selectivity, which implies a non-radical mechanism. It has been proven for the FeIII-H2O2 system that the activation of the FeIII is independent of the formation of ketone, which involves a hydroperoxide (derived from oxygen) as an intermediate. This intermediate controls the formation of ketone and of secondary alcohol. The addition of a number of trapping reagents such as BrCCl3 diverts the reaction from oxygenation to bromide formation. Although BrCCl3 is indeed a good trap for carbon radicals, the pattern of selectivity across a range of saturated hydrocarbons is completely different for Gif chemistry when compared with normal radical bromination. The chemistry is explained in terms of an FeV oxenoid species that inserts itself into secondary C-H bonds (a compromise between bond strength and steric hindrance). This gives an FeV intermediateA with an iron-carbon bond, which is probably rapidly reduced to the FeIII state by hydrogen peroxide. Then oxygen is inserted into the FeIII-C bond. Hydrolysis affords the isolateable intermediate hydroperoxide (intermediateB). A system based ontert-butyl hydroperoxide (TBHP) is described. This is similar to the above Gif systems, but the kinetic isotope effect is very different and the selectivity for adamantane substitution is different. However, FeIII is activated by TBHP to an FeV oxenoid which, after reaction with a hydrocarbon, reacts with oxygen to give a hydroperoxide. So the pattern of intermediatesA andB is maintained with TBHP. Radical chemistry is involved in some of the reactions that involve ionic coupling to saturated hydrocarbons. The importance of the FeII-FeIV manifold in providing a mechanism that permits the selective functionalization of saturated hydrocarbons by ionic trapping with chloride, azide, and other anions is made manifest. Comparison is made with the FeIII-FeV manifold where ionic trapping is never seen. Traditional Fenton chemistry (hydroxyl radical formation) is not operative here, but the trapping does involve the formation of carbon radicals. These react very efficiently with anions bonded to FeIII.

Investigation of the nature of the active oxygen intermediate at graphite-supported SmCl3 and FeCl3 working as a cathode for the partial oxidation of alkanes and aromatics

The nature of the active oxygen species on SmCl3-supported and FeCl3-supported graphite cathodes (Sm/Gr and Fe/Gr) and the reaction mechanism of the oxidation of cyclohexane initiated by these active oxygens have been studied. The active oxygen species on Sm/Gr and Fe/Gr exhibited a similar regioselectivity to that of HO˙ for the oxidation of alkanes (hexane, adamantane, cyclohexane) rather than those of the metal–prophyrin or the Gif(IV) systems. The active oxygen on Sm/Gr exhibited lower electrophilicity for the oxidation of alkanes than that on Fe/Gr. The product selectivities in the oxidation of toluene over Fe/Gr were those expected from Fenton chemistry. However, the selectivities over Sm/Gr could not be explained in terms of Fenton chemistry. The product yield of Fe/Gr decreased appreciably upon addition of CCl4 and (CH3)2S as radical scavengers; however, that for Sm/Gr was affected only slightly. These results suggest that the active oxygen on Sm/Gr is not of radical character in contrast with that on Fe/Gr. The kinetic isotope effect in the oxidation of cyclohexane over Sm/Gr (1.7) was larger than that over Fe/Gr (1.3) and that for HO˙(1.3). This result suggests that the active oxygen species on Fe/Gr is HO˙. On the other hand, the active oxygen species on Sm/Gr was suggested to be Sm(3–δ)(O2H)δ+ from the results of cyclic voltammetry experiments. It was suggested that the cyclohexyl radical was the common reaction intermediate for formation of cyclohexanol (CyOH) and of cyclohexanone (CyO) in the oxidation of cyclohexane on Sm/Gr. Because cyclohexyl chloride (CyCl) was produced by addition of CCl4 and the CyOH : CyO ratio did not change during oxidation with or without addition of CCl4, the cyclohexyl radical was suggested to be the reaction intermediate for CyO formation but not for CyOH formation over Fe/Gr. The oxygen isotope experiments for the reaction over Sm/Gr indicated that 93% of the oxygen in the products came from the gaseous oxygen and 7% from electrolyte solutions. In the case of Fe/Gr, all of the oxygen in the products came from the gas phase. Reasonable reaction mechanisms on the basis of the results described above have been proposed for the oxidation of cyclohexane on Sm/Gr and Fe/Gr.

ChemInform Abstract: The Carboxylation of Saturated Hydrocarbons by Gif Systems (Fe0/CO/O2 and Cu0/CO/O2 in Pyridine‐Acetic Acid).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Car☐ylation of saturated hydrocarbons by gif systems (Fe 0/CO/O 2, and CU 0/CO/O 2 in pyridine-acetic acid)

Saturated hydrocarbons are transformed into the corresponding homologous car☐ylic acid by treatment with Fe 0/CO/O 2 or Cu 0/CO/O 2 in pyridine/acetic acid. Mechanistic studies support a reaction pathway involving the insertion of CO into a carbon-iron or carbon-copper bond.

Mechanism of the selective functionalization of saturated hydrocarbons by Gif systems: relationship with methane monooxygenase.

Two intermediates, A and B, have been identified in the selective oxidation of saturated hydrocarbons to ketones by Gif-type systems. Intermediate A has been characterized as an Fev species with a secondary iron sigma-bond to carbon; it is captured by four different reagents or transformed into the second intermediate, B, which hydrolyzes to form a secondary alcohol. A mu-oxo Fe2III dimer is proposed as a basis for Gif-type reactivity. If the first iron is involved in the synthesis of intermediate A, the second is used to oxidize intermediate B intramolecularly to a ketal, which on hydrolysis yields a ketone. The enzyme methane monooxygenase shows a remarkable similarity to Gif-type systems in its selective hydrocarbon oxidation, particularly in the case of adamantane.

Functionalisation of saturated hydrocarbons. part x.1 a comparative study of chemical and electrochemical processes (gif and gif-orsay systems) in pyridine in acetone and in pyridine-co-solvent mixtures

Six saturated hydrocarbons (cyclohexane, 3-ethylpentane, methylcyclopentane, cis - and trans -decalin and adamantane) were oxidised by the Gif IV system (iron catalyst, oxygen, zinc, carboxylic acid) and its electrochemical equivalent (Gif-Orsay system). Results obtained using various solvents (pyridine, acetone, pyridine-acetone mixtures) were similar for both systems. Total or partial replacement of pyridine with acetone affects the selectivity for secondary positions and lowers the ketone/secondary alcohol ratio. The formation of the same ratio of cis - and trans -decal-9-ol from both cis - and trans -decalin clearly demonstrates that tertiary alcohols result from a mechanism essentially radical in nature.