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The oxidation of ferrocene and its derivatives (Fc) by hydrogen peroxide in an acidic medium was studied by electron spectroscopy in the visible region. The studied reaction of different Fc includes steps of their oxidation to the ferrocenium cation Fc formed in a pair with radical HO and also the earlier unknown reactions of this cation with hydrogen peroxide and with hydroxyl radical. The first reaction proceeds as a redox process leading to the reduction of the ferrocenium cation to neutral ferrocene, and the second reaction follows the mechanism of radical substitution with the consecutive formation of the hydroxy derivatives of ferrocene Fc(OH) and the corresponding ferrocenium cations with different contents of OH substituents. The necessary conditions for the second reaction to occur is an excessive concentration of hydrogen peroxide over the Fc concentration. The external manifestation of this process is a continuous shift of the absorption band of the ferrocenium cation to the long-wavelength range of the electronic spectrum, which can attain several tens of nanometers, and its broadening. The contribution of these reactions to the overall process of ferrocene oxidation can be made minimum and reduced to the ferrocenium cation formation only by decreasing the ratio of the initial concentrations C(HO)/ C(Fc). [ABSTRACT FROM AUTHOR]

Kinetic relationships of oxidation of 1,1′-diethylferrocene and decamethylferrocene with peroxides ROOR (R = H, t-CH) in organic solvents were studied and the composition of oxidation products was established. It is shown that reactivity of (CHCH)Fe is significantly lower than that of Cp*Fe [Cp* = η-C(CH)] which is seen from the ability of the first metal complex to undergo oxidation with a notable rate only in the presence of Brønsted acids, whereas the second substance is oxidized both in the presence and in the absence of these acids. Two possible mechanisms of oxidation of metal complexes in the presence of strong acids are discussed. One of them is based on the ability of ferrocene to fast and equilibrium protonation with the formation of CpFe-H structure. Another one considers the ability of metal complexes to coordinate peroxides with the formation of weakly bound charge transfer complexes of the composition CpFe·ROOR. The possibility of their formation is confirmed by the oxidation of CpFe with hydroperoxides in the absence of acids. [ABSTRACT FROM AUTHOR]

The reaction of ferrocenylacetic acid and its methyl ester with peroxides ROOR (R = H, t-Bu) in organic solvents was studied. It is shown that direct involvement of the substituent in this process leads to abnormally high reactivity of the acid toward HO and t-BuOOH as compared with both the ester and ferrocene in a model system of CpFe + PhCOOH. An unusual shift of the absorption maximum of the ferrocenyl cation formed in the reaction course to longer wavelengths reaching up to several tens of nanometers was discovered. [ABSTRACT FROM AUTHOR]

We have studied the autoxidation of ferrocenecarboxylic acid and its methyl ester in organic solvents in the presence of perchloric and trifluoroacetic acids. Based on the results of kinetic studies and data on the composition of the reaction products, we suggested the possible reaction mechanisms, including those of molecular and radical-chain macrostages of the process. The features of the solvent influence on the rate of oxidation of metallocomplexes and the reasons for its extreme dependence with increasing concentration of perchloric acid are discussed. [ABSTRACT FROM AUTHOR]

By comparison of reactivity of the ferrocene derivatives differing in the nature of the substituents the conditions were revealed of their participation as Brønstedt and Lewis acidic centers in the process of the metallocomplex molecular oxidation with oxygen in terms of manifestations of the effects of rapproachment and orientation. From this standpoint were analyzed the experimental data obtained in the oxidation of methyl ferrocenylacetate. A probable mechanism of the process is proposed that includes the molecular and radicalchain macro steps. [ABSTRACT FROM AUTHOR]

Comparative analysis of the specific features of autooxidation of ferrocenylacetic acid (FcCH2COOH) in organic solvents at 30–50°C in the absence and in the presence of trifluoroacetic acid (processes 1 and 2 respectively) was carried out. It was shown that both reactions proceed as a sequence of two macrostages, the molecular and the chain radical oxidation of the metal complex. Introduction of acid (HX) in the reaction mixture leads to a significant increase in the rate of the process, in the amount of oxygen per one mole of metal complex absorbed by the reaction mixture, and to the change in the yields of main reaction products like hydroxymethylferrocene, formylferrocene, ferrocenylpyruvic acid, and CO2. On the basis of results of the investigation performed, the kinetic and thermodynamic analysis of primary reactions of the process probable mechanisms of both macrostages in both processes were suggested. The significant effect of approach and orientation on the rate of the molecular oxidation of complex as the bifunctional reagent was noted. An assumption was made that the acid takes place in the molecular oxidation of FcCH2COOH according to two alternative mechanisms differing by the way of its coordination with O2 and the metal complex in the prereactional intermediates. The oxidative transformation of these intermediates leads to the generation of radicals of different nature, Fc+·CH2C(O)OO· and HO which initiate the chain radical oxidation of the metal complex. [ABSTRACT FROM AUTHOR]

Autooxidation of ethoxymethylferrocene at 30–50°C promoted by the participation of strong and weak carboxylic acids HX is studied. The radical chain mechanism of the process is established, its kinetics characteristics are determined as well as the composition of the products among which other derivatives of ferrocene have been found. Based on the results of the present study and the earlier obtained data on oxidation of hydroxymethylferrocene a mechanism of initiation of the chains general for both metallocomplexes is suggested. It includes the formation of the intermediate CH2OR (R = H, C2H5) and its subsequent oxidative transformations leading to the formation of the peroxide radical C5H4Fe+·C5H4-CH2O2 · and ROH. The role of the approaching and orientation effect in transformations of this intermediate is discussed as well as the mechanism of the investigated reaction in general. [ABSTRACT FROM AUTHOR]

The article discusses the effect of vortex gas flow on the physical conditions of the oxygen gas laser cutting of steel sheets. It is stated that a minimum quantity of an admixture in oxygen can deteriorate the cut quality as oxygen introduces the additional energy of chemical reactions governing the oxidation of iron. The vortex formation, as stated, under real conditions posses the property to accumulate the liquid melt of metal flowing along the wall of the laser cut.

Features of the oxidation of hydroxymethylferrocene with molecular oxygen in organic solvent in the presence of weak and strong Broensted acids were studied. The resulting data were compared with published data on ferrocene and hydroxyferrocene oxidation, which made it possible to assess the trend in the oxidation mechanism in going from ferrocene π complexes to their hydroxyferrocene and hydroxymethylferrocene analogs. A conclusion was drawn that each of the ferrocenes reacts with oxygen in quite a specific way. [ABSTRACT FROM AUTHOR]

Mechanisms of ferrocene oxidation with molecular oxygen and sulfur dioxide in acid solutions and of its direct oxidation with carboxylic acids were suggested on the basis of kinetic and thermodynamic analysis of the published data. All the mechanisms are based on a common proposition: The species reacting with an oxidant is the protonated ferrocene molecule acting as a donor of atomic hydrogen, which is favored by the low energy of the Fe-H bond. [ABSTRACT FROM AUTHOR]

The present work is devoted to the thermodynamic and kinetic analysis of literature data on the oxidation of ferrocene in the presence of Bronsted acids, since up to now the mechanism of this reaction is still not explained [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "On the Radical Chain Mechanism of Oxidation of a Series of Ferrocene Derivatives with Molecular Oxygen," by V. M. Fomin and colleagues in the 2007 issue.