T. Mlodnicka

Metal-dependent reactivity of some metalloporphyrins in oxidation with dioxygen

Abstract p-Tetratolylporphyrins with different metal centres such as Cr3+, Mn3+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+ have been used as catalysts for epoxidation of propylene in the presence of propionaldehyde and dioxygen. It has been found that the induction time as well as the distribution of the main reaction products, i.e. peroxy acid, epoxide and carbon dioxide, vary with the metalloporphyrin applied. These differences in the catalytic behaviour shed light on the character of the active forms of the catalysts and on the mechanism of the investigated reaction.

Reactivity of polyhalogenated and zeolite-encapsulated metalloporphyrins in oxidation with dioxygen

Catalytic activity of some halogenated and perhalogenated metalloporphyrins in the reaction of cyclohexane oxidation with dioxygen in the presence of aldehyde have been investigated. Also, the effects derived from encapsulation of some metalloporphyrins in zeolite micropores and their influence on the reaction course have been examined. Both, the changes in the structure and the encapsulation have been found to exert significant effect on the catalyst stability, activity and selectivity. From the changes in the distribution of the main reaction products some important conclusions concerning the reaction mechanism are drawn.

Metalloporphyrins as catalysts in autoxidation processes: a review

Abstract Metalloporphyrins, because of their ability to enter into reactions involving valence change and/or ligand oxidation-reduction mechanisms, are suitable catalysts for a variety of redox processes. Autoxidation reactions catalyzed by metalloporphyrins are reviewed, and their oxygen-activating performance as well as the reactivity of the oxygen adducts towards aldehydes and hydrocarbons are discussed. The role of porphyrin π cation radicals in these processes is emphasized. The importance of such factors as presence of substituents in the porphyrin macrocycle, type of solvent and nature of the axial ligand for the initiation step and the selectivity of autoxidation reactions is discussed.

Oxidation of hydrocarbons with dioxygen

Abstract Activation of molecular oxygen by binding to an appropriate transition-metal centre at the surface of a solid and in a complex, as well as the properties of the active, oxygen-containing species, are compared. At oxide surfaces metal—oxo groups show strongly nucleophilic properties, whereas in porphyrin complexes their character may be modified from nucleophilic to electrophilic by introduction of appropriate substituents and axial ligands. The activities of some metalloporphyrin catalysts in the liquid-phase epoxidation and hydroxylation of hydrocarbons are given. The influence of such factors as type of metal centre and character of the peripheral substituents and axial ligands on the electrophilic and nucleophilic behaviour of the metal—oxo species is shown and discussed.

Oxidation of cyclohexane with H2O2 and chloro-tetratolylporphyrinatochromium(III) as catalyst

Abstract The reaction of cyclohexane oxidation with hydrogen peroxide and chloro-tetratolylporphyrinatochromium(III) as a catalyst has been investigated. The influence of various nitrogen bases on the yields of the main reaction products, i.e. cyclohexanol and cyclohexanone, has been studied. A correlation between the pKa value of some of the bases investigated and the total yield of products has been found. On the basis of the results obtained, a mechanism is discussed for the reaction.

Reactivity-structure correlations in oxidation with metalloporphyrins

Abstract Metalloporphyrins of the first transition series have been studied as catalysts in the oxidation of propene by dioxygen in ethyl acetate in the presence of propionaldehyde. With Mn III TTP and Fe III TTP of low redox potential, the reaction starts with generation of acyl radicals by transfer of electrons to metal orbitals, followed by formation of peroxy acid. In the case of Co II TTP, acyl radicals are generated through abstraction of hydrogen by the readily formed Co II TTP-O 2 complex. Co-porphyrin binds peroxy acid in two types of complexes: through oxygen of the carbonyl group with the peroxy oxygen atoms sticking out, or through peroxy oxygen with double-bonded oxygen of the carbonyl group exposed. Quantum chemical calculations revealed that only the terminal oxygen of the exposed peroxy group in the first type of complexes acquires electrophilic properties and can perform the addition of oxygen atom to the olefinic double bond. Such a complex of Mn III -porphyrin is unstable and decomposes to form manganese oxo species which are responsible for epoxidation. Mn III -porphyrin also shows high activity in the homolytic decomposition of peroxy acid with evolution of CO 2 . In the case of Cr(III), Ni(II), Cu(II) and Zn(II) porphyrins, the reduction potential is too high to allow electron transfer from aldehyde to the metal centre, rendering the first step of the reaction difficult.

Cobalt tetra(p-tolyl)prorphyrin as catalyst in oxidation of propionaldehyde

Abstract The effect of solvent in the homogeneous oxidation of propionaldehyde has been investigated. It was observed that the induction period of the reaction depends on the donor number of the solvent. Changes in the structure of the catalyst during the course of the reaction as revealed spectrophotometrically are discussed, the species which appear are identified and a mechanism for their transformation is proposed.

Spectrophotometric studies of the homogeneous oxidation of acrolein with CO(II) complexes as catalysts

Abstract Spectrophotometric investigations have been carried out for the systems CoCl2.6H2O—acrolein—molecular oxygen and CoCl2.6H2O—peroxyacetic acid in acetone solutions. It is postulated that the bands appearing in the initial stage of the reaction correspond to the active intermediates formed in consecutive steps. Their half-lives have been determined, the rate equation for their formation in the presence of HCl has been derived and their nature discussed.

Liquid phase oxidation of acrolein catalyzed by Co and Mo complexes

Liquid phase catalytic oxidation of acrolein in the presence of Co(III) and Mo(VI) complexes was investigated. The addition of a Mo(VI) complex was found to accelerate the reaction at higher, and retard it at lower, Co(III) concentrations.AbstractБыло исследовано жидкофазное каталитическое окисление акролеина в присутствии комплексов Co(III) и Mo(VI). Добавление комплекса Mo(VI) ускоряет реакцию при высоких концентрациях Co(III) и уменьшает при низких концентрациях Co(III).

Kinetics and mechanism of the co-oxidation of propylene and benzaldehyde in the presence of some cobalt complexes

Abstract Cobalt(II)(p-CH3TPP), Co(NAP)2 and Co(OAc)2·4H2O differ in their catalytic properties and for this reason the acceleration of various steps in the title reaction were studied. It has been found that induction periods as well as variations in the distribution of the principal products, i.e. propylene oxide, CO2 and peracid, depend markedly on the applied catalyst. A reaction scheme is proposed and the active form of the catalyst suggested. The observed dependence of the induction period on the concentration of catalyst and benzaldehyde as well as on the oxygen pressure allows the determination of the exponents in the rate equation for the induction period.