New methodology for the selective transformation of saturated hydrocarbons into ketones/alcohols and alkenes is described. A crucial aspect of this new process is that no reaction solvent is required since the Fe(III) and Cu(II) complexes used are completely soluble in the hydrocarbon substrates. Thus, the large quantity of pyridine, acetic acid or acetonitrile required in previous systems is no longer a prerequisite.

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New methodology for the oxidation of alcohols to ketones in good yield utilizing catalytic amounts of FeIII salts and TBHP as the oxidant is highlighted. Competition between alcohol and hydrocarbon oxidation has been clearly demonstrated. The "normal" Gif-type solvent system (pyridine / acetic acid) can be replaced by the alcohol itself.

GoAggIV chemistry (Fe (III) species, tert-butyl hydroperoxide in a mixture of pyridine and acetic acid) in the presence of LiCl can transform saturated hydrocarbons efficiently into the corresponding alkyl chlorides. The transformation into monosubstituted alkyl derivatives by “ionic trapping” reagents arising from the interception of the first intermediate of the system supports the presence of a high valent VFe-C species. Mechanistic studies suggest a possible pathway operating via an Fe-centered ligand coupling. In addition, the production of alkyl chlorides and alkyl bromides could also be achieved employing this system in the presence of halogenating reagents such as CCl4 and BrCCl3.

Cycloalkanes are transformed into the corresponding cycloalkenes by treatment with tert-butyl hydroperoxide (TBHP) in pyridine/acetic acid solution in the presence of Cu(OAc)2.H2O. When iron salts used instead of copper salts, the major reaction product is the corresponding ketone. Differences between the iron-catalyzed and the copper-catalyzed reactions support a metal-dependent reaction pathway.

The usual formation of ketone and alcohol under GoAggII conditions [FeCl3·6H2O (cat.), H2O2 in pyridine-acetic acid] can be totally replaced by the formation of the corresponding mono-alkyl substituted derivatives by addition of PPh3 and alkali metal salts.

Cycloalkanes are transformed into monosubstituted cycloalkyl derivatives (chloride, azide, cyanide, thiocyanate, dicycloalkyl disulfide, or nitroalkane

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.

The selective functionalisation of saturated hydrocarbons catalyzed by copper or iron salts are compared. In addition to further studies on the homogeneous oxidation by Cu(II)-H2O2 is pyridine-acetic acid (GoChAgg system), we introduce a heterogeneous GifIII-analog based on Cu0 and dioxygen in pyridine-acetic acid. Both Cu-based systems display Gif-type reactivity. The intermediacy of alkyl hydroperoxides in the Cu(II)-catalyzed reaction has been proven spectroscopically (following the reaction on [1-13C]-cyclohexane by 13C-N.M.R. spectroscopy) and chemically (quenching the reaction with triphenylphosphine to reduce the hydroperoxide to alcohol). The same holds for Cu0/O2 system, as shown by the effect of triphenylphosphine added to the reaction mixture. Thus, both reactions follow the pathway alkane → alkyl hydroperoxide → alcohol or ketone. Experiments running the GoChAgg reaction (H2O2-based) under an 18O2-atmosphere showed the incorporation of 18O2 into the hydroperoxide and the alcohol (which derives itself from the alkyl hydroperoxide). The relative reactivity of this Cu(II) system was studied for a series of cycloalkanes. The participation of another reaction intermediate (A) has also been demonstrated. However, some important differences are presented, that show that the chemical properties of the Cu-A and the Fe-A intermediates are different. Thus, Gif-type reactivity is metal-dependent and involves two chemically different non-radical species.

The Fe(III)-catalyzed ketonization of saturated hydrocarbons by tert-butyl hydroperoxide (TBHP) in pyridine-acetic acid or acetonitrile solution follows the reaction pathway alkane → alkyl hydroperoxide → ketone or alcohol. Dioxygen (O2) is the precursor of the oxygen atoms in the alkyl hydroperoxide, the alcohol, and the ketone.

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.

Chemical and C-13 and H-2 NMR spectroscopic evidence is presented, proving that secondary alkyl hydroperoxides are reaction intermediates in the oxidation of saturated hydrocarbons under GoAgg(II) conditions (ferric chloride, hydrogen peroxide in pyridine-acetic acid solution). Isolation of cyclohexyl hydroperoxide from a GoAgg(III) oxidation of cyclohexane (GoAgg(II) + picolinic acid as catalyst) and the effect of reducing agents (such as thiophenol, benzeneselenol, diphenyl disulfide, and diphenyl diselenide) on the Gif(IV) oxidation of cyclohexane (ferrous chloride, zinc powder, oxygen gas, in pyridine-acetic acid solution) permit a generalization of the alkyl hydroperoxide intermediacy to the whole family of Gif systems. All those reducing agents lower the ketone/alcohol ratio, with either a decrease in the total amount of hydrocarbon activation or formation of phenylseleno derivatives. Triphenylphosphine (up to 3.5 mmol) shows the same effect on the ketone/alcohol ratio, but the total amount of activation remains approximately constant and no byproduct is formed. The mechanism of formation of the alkyl hydroperoxide intermediate has been studied using O-18(2). The results indicate that the oxygen atoms in the alkyl hydroperoxide do not arise directly from hydrogen peroxide but from O2, formed in situ by the well-known iron(III)-catalyzed decomposition of hydrogen peroxide. The mechanism of formation of alcohols under these conditions has been addressed as well. The results from experiments in the presence of (H2O)-O-18, combined with those from the above-mentioned experiments under an O-18(2) atmosphere, proved that the oxygen atom in the alcohol does not arise from a hydroxy species but from reduction of the intermediate alkyl hydroperoxide. The participation of another reaction intermediate (prior to the alkyl hydroperoxide) has been secured. If O2 is eliminated from the reaction mixture (running the reaction at reduced pressure) this first intermediate A can be trapped with Tempo. However, when the reaction was carried out at reduced pressure and in the absence of Tempo, no traces of alkylpyridine coupled products were detected. These alkylpyridines have been demonstrated to be formed when carbon radicals are generated under the same reaction conditions by photolysis of the corresponding N-hydroxypyridine-2-thione derivative of an alkyl carboxylic acid. This paradox can only be explained if intermediate A is not a carbon-centered radical. In a competitive experiment a ratio cyclopentyl-Tempo adduct/cyclohexyl-Tempo adduct of 0.66 was obtained. This figure differs from the values reported for typical carbon-radical competitive experiments, where cyclopentane is more reactive than cyclohexane. This further supports the nonradical nature of reaction intermediate A. Finally, studies with trimethyl phosphite, which affords with cyclohexane cyclohexyl dimethyl phosphate, show that cyclohexyl peroxyl radical is not an intermediate in the formation of the hydroperoxide as it would be if the cyclohexyl radical was reacting with oxygen.

The nature of the Fe(III) species present in solution before the addition of hydrogen peroxide in the oxidation reaction of saturated hydrocarbons by hydrogen peroxide in pyridine-acetic acid solution in the presence of picolinic acid (GoAgg(III) system) has been investigated. A single-iron core structure for the Fe(III)-catalyst in the presence of picolinic acid is deduced. A new single-iron complex 2 [(Picolinate)2FeCl2]-[Py2H]+ has been isolated from the reaction mixture and characterized by X-ray crystallography and solid state magnetic moment measurements. The cell parameters for this complex are: monoclinic, C2/c (No. 15), a = 22.437 (7) angstrom, b = 17.577 (5) angstrom, c = 15.841 (6) angstrom, beta = 133.50 (2)-degrees, V = 4531 (3) angstrom3, D(x) = 1.554 gcm-3, mu = 0.938 mm-1, Z = 8, F(000) = 2168e-. These results indicate that the GoAgg(III) system is a model that mimics single-iron non-heme enzymatic oxidations. Upon addition of hydrogen peroxide to a solution of complex 2 in pyridine-acetic acid a purple complex is formed instantly. The formation and decay of this complex could be correlated with the oxidation of the hydrocarbon at two different temperatures. The influences of different reaction variables (picolinic acid/iron ratio, pH, solvent) on the formation of this complex have been investigated. A eta2-peroxo bridge is proposed for the structure of this purple complex. The possibility of hydroxyl radicals participating in the hydrocarbon activation process has been studied. Hydroxyl radicals were generated by photolysis of N-hydroxy-2-thiopyridone 3 in pyridine-acetic acid solution, and the products derived from pyridine oxidation analyzed. 2-Hydroxypyridine 4 and 4-hydroxypyridine 5 were found as the only oxidized pyridine species, together with 2,2'-bipyridine 6, 4,4'-bipyridine 7 and 2,4'-bipyridine 8. When the pyridine oxidation products from a GoAgg(II) and a GoAgg(III) reaction were examined, both in the presence or absence of hydrocarbon, the major product found was 3-hydroxypyridine 9. Bipyridines and pyridine N-oxide 10 were found as minor reaction products. The possibility of having a pyridine-free solvent matrix was examined. We found that pyridine can be completely replaced with tert-butanol, retaining the typical Gif selectivity and with a small reduction of the total hydrocarbon activation; only the ketone/alcohol ratio decreases slightly. The mixture pyridine-acetic acid affords the righ pH value to favor the formation of ketone over the alcohol. These results are in agreement with a mechanism involving a common reaction intermediate for the ketone and the alcohol (the alkyl hydroperoxide) which fragments to ketone through an, acid-bass catalyzed process.

Treatment of alkanes under GifIV conditions [FedCl2.4H2O (cat.), Zn0, and O2 in pyridine-acetic acid] in the presence of trimethylphosphite afforded alkyl dimethyl phosphates; 13C-NMR experiments showed that the phosphates are formed from the reaction between the intermediate alkyl hydroperoxide and trimethyl phosphite in the presence of an iron catalyst.