N. I. Moiseeva

Direct catalytic oxidation of lower alkanes in ionic liquid media

Immobilization of rhodium (palladium)-copper-chloride catalytic systems in ionic liquids as high-boiling-point solvents affects the distribution of propane oxidation products: the acetone yield increases and the yield of alcohols decreases. Propane is oxidized to acetone, bypassing the isopropanol formation step. Methane is oxidized under more severe conditions than propane, giving methyl trifluoroacetate as the main product. Mechanisms of action of the catalytic systems based on rhodium and palladium are close to each other and likely include oxo or peroxo complexes as intermediates.

Homogeneous catalytic oxidation of light alkanes: C-C bond cleavage under mild conditions

The combined oxidation of CO and C2–C4 alkanes (associated petroleum gas and natural gas components) under the action of oxygen in trifluoroacetic acid solutions in the presence of rhodium and copper chlorides was accompanied by the oxidative degradation of C-C bonds in a hydrocarbon chain with the formation of carbonyl compounds, alcohols, and esters. For butane and isobutane, the reaction path with C-C bond cleavage was predominant. The buildup curves of isobutane oxidation products (both with the retention and with the degradation of the chain) were S-shaped and characterized by the same induction period; they did not pass through a maximum. A reaction scheme was proposed to reflect the main special features of the mechanism of transformations occurring in the O2/Rh/Cu/Cl− oxidation system.

Mechanism and energetics of 1,2-addition of dioxygen 1O2(1Δg) to ethylene

The optimal geometry and energy parameters for five electronic states of the {1O2 (1Δg) + C2H4} system that characterize the elementary reactions of two-step 1,2-addition giving the dioxetane molecule were calculated using various quantum chemical methods (RHF, B3LYP, MPn, n = 2–4, QCISD, and CCSD) and basis sets (from 6-31+G(d,p) to 6-311+G(3df,2p) and pVTZ). The first step of the reaction was found to pass through the ethylene perepoxide intermediate. Considering experimental and published calculated data, the dependence of the results on the calculation procedure was exampled. The higher-level methods (QCISD, CCSD, CASSCF) and the standard methods (DFT, MPn) were found to reliably lead to virtually the same description of the energetics of this two-step reaction corresponding to experimental estimates.

Aquaperoxovanadium(V) complexes: Quantum-chemical study

The addition of a water molecule to mono-, di-, and triperoxovanadium(V) complexes has been studied at the density functional theory (B3LYP/6-31G**) and Møller-Plesset perturbation theory (MP2/6-31G**) levels. It has been demonstrated that the H2O…V donor-acceptor interaction cannot compete with hydrogen bonds and becomes weaker with an increase in the number of peroxo groups in the complex. In the most stable isomers of aquaperoxo complexes, water is mainly held by intermediate hydrogen bonds. The energy of addition of a water molecule to peroxovanadate is lower than or close to the heat of evaporation of water; i.e., the formation of stable aquaperoxovanadium complexes in aqueous solutions is improbable. This conclusion is consistent with the mass spectra of aqueous solutions of peroxovanadates, which show that the concentration of water-free peroxo complexes considerably exceeds the concentration of complexes with a coordinated water molecule. The coordination of the water molecule through the V…OH2 donor-acceptor interaction is prevented by the cis effect of the peroxo group, which has the HOMO orbital of symmetry suitable for interaction with the LUMO orbital of the VO group.

Oxidative functionalization of methane in the presence of a homogeneous rhodium-copper-chloride catalytic system: Transformation of acetic and propionic acids as solvent components

The oxidative functionalization of methane (O2, CO, 95°C, RhIII/CuI, II/Cl− catalytic system) was studied in an aqueous acetic or propionic acid medium. It was shown that oxidative decarbonylation of carboxylic acids takes place along with methanol and methyl carboxylate formation.

Oxidative decarbonylation of acetic and propionic acids: Unexpected H/D exchange of propionic acid with a solvent

A problem facing chemists engaged in study of bio� mass treatment—how to eliminate a carboxyl group from lipid fatty acids—can be solved by means of acid decarbonylation and subsequent alcohol dehydration (1). In the present work, we demonstrated for the first time that rhodiumcatalyzed joint oxidation of car� boxylic acids and CO under mild conditions 1 leads to the oxidative decarbonylation of acetic and propionic acids to methanol (methyl acetate) and ethanol (ethyl propionate), respectively. We also observed an unusual substitution of deuterium for a hydrogen atom in the alkyl radical of the molecules of the products of oxida� tive decarbonylation of propionic acid. The oxidation of СН4 in the Rh III /Cu I,II /Cl - sys� tem in a CF 3 COOH solution leads to the formation of methanol (or trifluoromethyl acetate) and formic acid (2, 3). The change of the solvent for aqueous acetic acid (both with and without adding sulfuric acid

Catalytic peroxide oxidation: The structure of key intermediates in the VV/H2O2 system according to quantum chemical data

The inner-sphere isomerization of the peroxo complexes of vanadium(V) with the general formula [VO6]− was studied using approximations based on the density functional theory (B3LYP/6-31G**) and the Møller-Plesset perturbation theory (MP2/6-31G**). It was found that the complex [V(=O)(ηO2)(O3)]− containing the O3 group as a bidentate ligand was the most stable isomer. The transition state region of a rear-rangement of the triperoxo complex [V(ηO2)3]− into [V(=O)(ηO2)(O3)]− was localized. It was found that the activation barrier (∼30 kcal/mol) was mainly due to O-O bond cleavage in the peroxo ligand. According to calculations, the reaction proceeds through two intermediate complexes whose structure can be interpreted as that containing coordinated singlet dioxygen (especially in the limiting case) because of noticeably shortened O-O bonds in the ηO2 ligand. The calculated reaction scheme of the conversion of [V(ηO2)3]− into [V(=O)(ηO2)(O3)]− is qualitatively consistent with the previously found kinetics of the formation of ozone and the oxidation of alkanes, olefins, arenes, and singlet dioxygen traps.

Quantum-chemical simulation of the elementary step of the oxidation reactions of styrene and its derivatives involving 1О2 (1Δg)

The results of simulation of the oxidation reaction of styrene and its methyl (two isomers) and phenyl derivatives with molecular oxygen in the excited singlet state (1Δg) have enabled the conclusion that the reaction can proceed through several mechanisms. For styrene and its phenyl derivative, three reaction channels are possible, and for the methyl derivative, there are four possible channels. For the first two substrates, the major channel is 1,2-addition to form dioxetane; for the methyl derivatives, an extra channel to give a hydroperoxide species is possible in addition to the above channel. The multichannel reaction character revealed by calculations makes it possible to qualitatively understand the reason behind the moderate selectivity (no more than 70%) of such reactions in the case of styrene and its derivatives.

Quantum-chemical simulation of unit process for the oxidation reactions of ethylene and its derivatives invoving 1O2 (1Δg)

The results of simulation of oxidation reactions of ethylene derivatives with different substituents (F atoms, CH3O and CH3 groups) and butadiene molecule with participation of 1O2 (1Δg) have shown the possibility to realize different routes for the majority of the considered reactions. The largest product variety is obtained for butadiene and CH3 derivatives of ethylene. For butadiene, along with 1,2-cycloaddition reactions resulting in four-membered dioxetane (which is realized in all cases), the possibility to form six-membered cyclic epidioxides (1,4-addition) and diepoxide products with two three-membered rings (epoxidation) has been found. The formation of hydroperoxide forms along with 1,2-addition reactions is also possible for all CH3 derivatives of ethylene. Formation conditions and relative stability of the noted products have been analyzed for each case and certain features of the revealed reaction pathways with the transfer of two oxygen atoms have been discussed.

Mechanism of oxygen transfer from the vanadium(V) complexes with ligands O22− and O32−

The oxygen transfer from the vanadium(V) complexes containing peroxo, oxo, and ozonide ligands to electron-donating substrates (ethylene and vinyl methyl ether) was studied in the framework of the DFT with the M06 hybrid functional. The O atom of the ozonide fragment in the O3VO(η-O2)− complex is transferred to the electron-donating substrates with lower energy expenses than the O atom of the peroxo group of the isomeric triperoxo complex, in spite of the fact that the presence of the peroxo group in the ozonide complexes stabilizes it favoring the formation of the V-Oc bond according to the data of topological analysis of the electron density in terms of the theory of atoms in molecules (AIM). The calculation results are in agreement with the experimental kinetic data indicating somewhat lower reactivity of triperoxovanadate compared to the isomeric oxygenyl complexes.