Catalytic oxidation of acrolein to acrylic acid over a molybdenum-vanadium catalyst

By the method of gas chromatography it has been found that the adsorption of acrolein takes place without dissociation whereas acrylic acid is adsorbed dissociatively. The adsorption of water vapor proceeds also dissociatively and results in increasing the number of the Brönsted acid centers. The presence of water vapor has a positive effect on the desorption rate of acrylic acid and a negative effect on the reoxidation rate of the catalyst.

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Inhibition of acrylic acid polymerization by phenothiazine and p-methoxyphenol. II. Catalytic inhibition by phenothiazine

Inhibition of acrylic acid by p-methoxyphenol fits a conventional stoichiometric mechanism but phenothiazine inhibits acrylic acid via a completely different, catalytic cycle which does not depend on the presence of oxygen. We propose that this mechanism may involve a pair of single electron transfer reactions between free radicals, phenothiazine N-radicalcation, and phenothiazine itself, the latter being cyclically regenerated. Arrhenius equations were derived for the rates of disappearance of inhibitor and oxygen in acrylic acid stabilized with phenothiazine and with p-methoxyphenol and also with phenothiazine in the absence of oxygen. The practical implication of high oxygen to p-methoxyphenol consumption ratios is quite important: if commercial acrylic acid (usually stabilized with p-methoxyphenol) is inadvertently heated during storage, the limiting substance determining the onset of polymerization will be the dissolved oxygen and not p-methoxyphenol unless oxygen (air) is being supplied to and dissolved in the liquid at a rate sufficient to overcome the rate of its consumption.     

Liquid phase oxidation of acrolein to acrylic acid

The active catalytic system containing Co(acac)₃ and acetaldehyde in dioxane for the homogeneous oxidation of acrolein to acrylic acid at 40°C and 1–9 atm has been studied.

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Co(acac)₃ 40°C 1–9 .

     

Complex iron ions as catalysts for the autooscillating oxidation of malonic acid and its analogs with bromate

Conclusions The complex ions of iron with,-dipyridyl and 1,10-phenanthroline can serve as catalysts for the autooscillating oxidation of malonic acid and its analogs with bromate. It is postulated that ions of variable valency with a single electron transition and a standard redox potential in the region 0.9–1.6 V can act as catalysts for this autooscillating reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2618–2619, November, 1969.     

Kinetics and mechanism of the oxidation of acrylic acid and methyl methacrylate

The kinetics of the initiated oxidation of acrylic acid and methyl methacrylate in the liquid phase were studied volumetrically by measuring oxygen uptake during the reaction. Both processes proceed via the chain mechanism with quadratic-law chain termination. The oxidation rate is described by the equation w = k ₂/(2k ₆)^1/2[monomer]w _i ^1/2 , where w _i is the initiation rate and k ₂ and k ₆ are the rate constants of chain propagation and termination. The parameter k ₂/(2k ₆)^1/2 is 7.58 × 10^?4 (l mol^?1 s^?1)^1/2 for acrylic acid oxidation and 2.09 × 10^?3 (l mol^?1 s^?1)^1/2 for the oxidation of methyl methacrylate (T = 333 K). For the oxidation of acrylic acid, k ₂ = 2.84 l mol^?1 s^?1 (T = 333 K) and the activation energy is E ₂ = 54.5 kJ/mol; for methyl methacrylate oxidation, k ₂ = 2.96 l mol^?1 s^?1 (T = 333 K) and E ₂ = 54.4 kJ/mol. The enthalpies of the reactions of RO ₂ ^? with acrylic acid and methyl methacrylate were calculated, and their activation energies were determined by the intersecting parabolas method. The contribution from the polar interaction to the activation energy was determined by comparing experimental and calculated E ₂ values: ΔE _μ = 5.7 kJ/mol for the reaction of RO ₂ ^? with acrylic acid and ΔE _μ = 0.9 kJ/mol for the reaction of RO ₂ ^? with methyl methacrylate. Experiments on the spontaneous oxidation of acrylic acid provided an estimate of the rate of chain initiation via the reaction of oxygen with the monomer: w _i,0 = (3.51 ± 0.85) × 10^?11 mol l^?1 s^?1 (T = 333 K).     

Catalytic oxidation of thiocyanates in an acid medium

Fundamental aspects of the oxidative destruction of thiocyanates by hydrogen peroxide in an acid medium in the presence of a catalyst, iron(III) ions, was studied. The effect of copper(II) ions on the mechanism and kinetics of SCN-oxidation in the presence of thiosulfates was considered.     

Mechanism of hydroquinone-inhibited oxidation of acrylic acid and methyl methacrylate

The kinetics of hydroquinone-inhibited oxidation of acrylic acid and methyl methacrylate was studied volumetrically by measuring the oxygen uptake in the presence of an initiator (azobisisobutyronitrile) at T = 333 K and P _{O 2} = 1 and 0.21 atm. The oxidation of acrylic acid inhibited by 4-methoxyphenol was studied under the same conditions for comparison. The rate constants of the reactions of the peroxyl radicals of acrylic acid (∼CH₂CH(COOH)O₂^·) and methyl methacrylate (∼CH₂CMe(COOMe)O₂^·) with hydroquinone (HOC₆H₄OH) (1.20 × 10⁵ and 7.16 × 10⁴ l mol⁻¹ s⁻¹, respectively) and of the reaction of peroxyl radicals of acrylic acid with 4-methoxyphenol (p-CH₃OC₆H₄OH) (3.25 × 10⁴ l mol⁻¹ s⁻¹) were measured. The stoichiometric inhibition factors f were determined. The reaction between the semiquinone radical and oxygen, O₂ + HOC₆H₄O^·, plays an important role, decreasing the factor f and the efficiency of the inhibition effect of hydroquinone. The rate constants of this reaction were calculated from kinetic data: k = 5.72 × 10² (in acrylic acid) and 4.60 × 10² l mol⁻¹ s⁻¹ (in methyl methacrylate).     

Catalytic inhibition of olefin oxidation with Mn and Cu compounds

Russian Chemical Bulletin - The rate constants and kinetic coefficients of inhibition (fkin) for olefins oxidized with the transition metal compounds (Mn) were measured by highly sensitive...     

On the oxidation of malonic acid by ceric ions

The oxidation of malonic acid by ceric ions has been investigated in sulfuric acid solution under a variety of conditions. The initial rate at low ceric ion concentrations is first order in each of the two reactants and has an activation energy of 11.6 kcal/mol; the instantaneous rate constant increases somewhat with time during a single run. At higher concentrations of ceric ion, semilogarithmic plots are sigmoid with a reduced rate constant at long times. The rate decreases slightly with increasing sulfuric acid concentration. Rates of carbon dioxide evolution may be much less than rates of ceric ion reduction because of supersaturation effects. The observations can be explained if dissolved oxygen reacts with organic radicals to catalyze the rate of initial attack on malonic acid, but oxygen must also be consumed irreversibly during these reactions. Computations with plausible rate constants have simulated the experimental observations. These oxygen effects can rationalize peculiar almost discontinuous changes in rate when bromomalonic acid is oxidized by ceric ion. These effects may also explain the previously puzzling observation that some Belousov–Zhabotinsky solutions are oscillatory in bulk but become quiescent but excitable when spread in a thin film in contact with air.     

Kinetics of the oxidation of acrylic acid by ce(IV) in acid perchlorate solution

The kinetics of oxidation of acrylic acid by Ce(IV)-perchlorate in perchloric acid were studied by following the rate of dissappearance of Ce(IV). The reaction order was zero with respect of Ce(IV) and unity with the acrylic acid. The addition of [H⁺] shows a proton catalysis and no salt effect is observed. Spectrophotometric studies do not reveal the formation of intermediate complex and thus a mechanism postulating the hydrolysis of the acid is suggested which undergoes first oxidation by the reactive species of Ce(IV). Thermodynamic parameters have also been calculated.     

Size effects in the catalysis of atmospheric oxidation of SO2 by iron ions

The oxidation of SO₂ catalyzed by iron ions in cloud drops of various sizes is analyzed in terms of the reduced model of atmospheric processes. It is demonstrated for the first time that iron ions exert a catalytic effect only in the smallest (<5 μm) and the largest (>100 μm) drops. This behavior of iron ions is due to the variation of the concentration ratio between the active form Fe(III) and the inactive form Fe(II) in the drops. SO₂ oxidation in drops of intermediate sizes is slower, because most of the iron in these drops is in the Fe(II) state.     

Catalytic oxidation of methanol on high-dispersity iron oxide in micro- and mesoporous molecular sieves

The catalytic properties of high-dispersity iron oxide deposited on micro-and mesoporous molecular sieves were studied. The deposition was performed by the in situ thermooxidative degradation of various precursors. The atomic catalytic activity of the catalysts in the oxidation of methanol was found to depend on both iron concentration and the accessibility of iron oxide particles.     

Catalytic oxidation of toluene by ozone in the acetic acid-sulfuric acid system

Oxidation of toluene by ozone was studied in the system constituted by acetic and sulfuric acids in the presence of manganese(II) acetate and sodium bromide. The effect of sulfuric acid and the catalyst on the yield of benzoic acid and on the oxidation rate was considered. The optimal ozonization conditions were determined. A scheme of redox catalysis that accounts for experimental data was suggested.     

Electrochemical copolymerization of N-vinylazoles with acrylic acid at iron and copper electrodes

Possibility of electrochemical synthesis of polymeric coatings based on copolymers of 1-vinyl-1,2,4-triazole and 1-vinylimidazole with acrylic acid at iron and copper electrodes with aryldiazonium salt as initiator has been demonstrated. Dielectric properties of the so prepared polymeric coatings have been studied. Degradation of 1-vinylimidazole copolymers with acrylic acid has been slower than that of other acrylic acid copolymers.     

Corrosion inhibition of iron in hydrochloric acid using pyrazole

The corrosion and corrosion inhibition of iron in HCl solutions in the absence and presence of pyrazole (PA) were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Changes in impedance parameters (R_ct and C_dl) were indicative of the adsorption of PA on the iron surface. The adsorption of PA is found to obey Langmuir adsorption isotherm. The study suggests that this compound is an anodic inhibitor.     

Thermodynamic functions of the mixing of acrylic acid solutions in hexane,benzene, and acetonitrile

The saturated vapor pressure over solutions of acrylic acid in hexane, benzene, and acetonitrile was measured tensimetrically over a temperature range of 295 to 355 K. The composition of the equilibrium phases, the activity coefficients of the components, and the thermodynamic functions of mixing (H ^E , G ^E , and S ^E ) of the solutions under study were calculated using the data on temperature dependence. A connection was established between the heat and Gibbs energy of mixing and the physical properties of the solvents.     

Importance of nanostructured vanadia for selective oxidation of propane to acrylic acid

Highly dispersed nanostructured vanadia supported on mesoporous silica SBA-15, prepared by controlled grafting/ion-exchange, has been found to exhibit high selectivities in propane partial oxidation to acrylic acid demonstrating its unique potential for mixed metal oxide catalyst development.