A. P. Bezruchenko

Functionalisation of methane under dioxygen and carbon monoxide catalyzed by rhodium complexes Oxidation and oxidative carbonylation

Abstract This work is aimed at the development of catalytic metal complex systems for the functionalisation of methane. Methane, dioxygen, and carbon monoxide react in the presence of RhCl3-NaCl-KI system as a catalyst to form methanol, formic and acetic acids. The system activity changes on varying reaction media and increases at turning from water to aqueous organic acids, trifluoroacetic acid being the most efficient. The yield of reaction products strongly depends on mole fraction of water in the solution, carbon monoxide pressure and concentration of iodine ions. With the increase of chloride ions concentration, the yield of acetic acid passes through the maximum, the yields of methanol, formic acid and methyl trifluoroacetate decrease. The substitution of CF3COOH–H2O for CF3COOD–D2O results in a kinetic isotope effect in kH/kD∼1.7–2.0 for all the products formed. Hypoiodic acid and (or) hydrogen peroxide seem to be intermediate oxidants in the course of the reaction. Possible reaction mechanisms are considered.

Isotope effects in the oxidative functionalization of methane in the presence of rhodium-containing homogeneous catalytic systems

The combined oxidation of carbon monoxide, CH4, and CD4 by molecular oxygen (16O2 and 18O2) in aqueous solutions of trifluoroacetic acid labeled with 18O in the presence of rhodium and copper compounds and potassium iodide has been studied. The distribution of 18O in isotopically substituted products suggests that oxygen entered into the methane molecule from an active oxidizing agent. This oxidizing agent was produced from molecular oxygen under the action of reagents and catalytic system components. The kinetic isotope effect observed for methane (kH/kD=3.9−4.3) suggests a nonradical character of the step at which the oxygen atom passes from an active oxidizing agent to the methane molecule or its fragments—transition-state components of the corresponding step.

Oxidative carbonylation of methane in the presence of Rh complexes in aqueous acetic acid

Abstract The formation of acetic acid by the oxidative carbonylation of methane in the presence of a RhCl 3 –DCl–KI catalytic system is strongly accelerated when an aqueous medium is substituted by an aqueous–acetic one.

Catalytic carbonylation of ethylene in the presence of the Pd(acac)2-m-Ph2PC6H4SO3Na(H)-AcOH system

Catalytic systems based on phosphine complexes of palladium have been developed for synthesizing propionic acid (monocarbonylation) and alternating (1∶1) ethylene-carbon monoxide copolymers,i.e., polyketones (polycarbonylation).m-(Diphenylphosphino)benzenesulfonic acid or its sodium salt were used as ligands. Monocarbonylation proceeds at atmospheric pressure in dioxane or acetic acid solvents. Under high pressure, the reaction pathway can change from monocarbonylation, which occurs in the presense of the sodium salt of the ligand, to polycarbonylation when the sodium ion at the sulfo group is completely replaced by a proton. This change in reaction selectivity is observed when the process is performed in acetic acid. When the ligand is present both in the acid and the neutral form, products of di- and oligocarbonylation are formed along with propionic acid and the polyketone. These products were characterized by1H and13C NMR spectra as alternating keto acids C2H5(COCH2CH2)nCOOH, wheren=1÷3. Kinetic equations were derived for the selective synthesis of propionic acid and polyketones.

Homogeneous Rhodium–Copper–Halide Catalytic Systems for the Oxidation and Oxidative Carbonylation of Methane

Homogeneous catalytic systems for the oxidation and oxidative carbonylation of methane in aqueous trifluoroacetic acid solutions were developed. The system included rhodium compounds and copper compounds as cocatalysts. Methanol, methyl trifluoroacetate, formic acid, and acetic acid were the reaction products. The process was accompanied by the intense oxidation of CO to CO2. Regularities of the process were studied, optimum process parameters were determined, and conditions at which methyl trifluoroacetate was formed with ∼90% selectivity were found. Kinetic isotope effects with respect to the solvent were determined. For the formation of organic products, kH/kD was ∼1, whereas it was ∼1.6 for the oxidation of CO. Studies were also performed with the use of compounds containing the 18O isotope. Conceivable mechanistic models of this process are discussed.

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.

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 oxidation of hydrocarbons of natural and oil gas

Alkane oxidation by O2 and CO in the presence of Rh-, Pd-, and Pt-containing catalytic systems leads to the product of C-H bond oxidation and the products of C-C bond oxidative destruction. A deuterated methyl group in acetic acid is observed in the oxidation of n-propane in a deuterium-donor medium. The possible mechanisms of alkane C2-C4 conversion are proposed.

The Oxidation of Carbon Monoxide as an Integrated Part of the Coupled Alkane Oxidation Process: Gas-Phase Oxidation over Supported Metal-Complex Catalysts

Heterogeneous rhodium–copper chloride catalysts for gas-phase oxidation processes were prepared via the cold impregnation of γ-Al2O3 with aqueous RhCl3 and CuCl2 solutions. Heptafluorobutyric or pentafluorobenzoic acids were additionally deposited onto these catalysts to simulate the action of homogeneous rhodium–copper chloride catalytic systems in the coupled alkane–carbon monoxide oxidation reaction. The catalysts were studied in the reactions of carbon monoxide oxidation and coupled propane–CO oxidation with dioxygen by diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) and electron paramagnetic resonance (EPR). The obtained data indicate the probable transfer of electrons between rhodium and copper compounds.