E. G. Chepaikin

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.

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.

Hydromenthoxycarbonylation of isobutylene in the presence of Tetrakis(triphenylphosphine)palladium-based catalyst systems

The catalytic activity of the Pd(PPh3)4-TsOH and Pd(PPh3)4-PPh3-TsOH systems in the reaction of isobutylene hydromenthoxycarbonylation with carbon monoxide and l-menthol has been examined. It has been found that the reaction proceeds regioselectively yielding the linear product l-menthyl isovalerate. Optimal conditions have been found for running the process. The spatial structure of l-menthyl isovalerate synthesized via the isobutylene hydromenthoxycarbonylation reaction has been established by 1H and 13C NMR techniques.

Hydroalkoxycarbonylation of isobutylene with polyhydric alcohols in the presence of catalytic systems based on palladium compounds and tertiary phosphines

The reaction of isobutylene hydroalkoxycarbonylation at low carbon monoxide pressures (≤2.0 MPa) with ethylene glycol and glycerol in the presence of catalytic systems based on Pd and mono- and bidentate organic phosphines has been studied. The effect of different conditions of the reaction in the presence of the Pd(Acac)2-PPh3-TsOH catalyst system on the ratio of the products, mono- and diglycolides (mono-, di-and triglycerides) of isovaleric acid has been investigated. The relative catalytic activity of a number of binary and ternary systems based on synthesized Pd(Acac)2, Pd(PPh3)4, and PdCl2(PPH3)2 complexes has been determined.

Hydroalkoxycarbonylation of olefins in the presence of palladium phosphine complexes: High activity and regioselectivity

Several types of catalyst systems were examined in the olefin hydroalkoxycarbonylation reaction. The systems contained Pd(PPh3)4, PdCl2(PPh3)2, or some other palladium compounds as a principal component. The second component (promoter) was p-toluenesulfonic acid or diphenyl(m-sulfophenyl)phosphine, which combines both the ligand and promoter functions. An important feature of these systems is their high activity in the hydroalkoxycarbonylation of ethylene and a high regioselectivity (83–100%) in the hydroalkoxycarbonylation of α-olefins with respect to linear products. Thus, it was unnecessary to introduce additional stabilizing ligands to augment the catalyst and promoter. The esters obtained can find application in the pharmaceutical industry and perfumery, as well as in other industries.