Catalytic Air Oxidation Research Articles

The removal of cyanides from water by catalytic air oxidation in a fixed bed reactor

The removal of cyanides from water by catalytic air oxidation was studied. Experiments were separately performed in a fixed bed reactor with co- and counter-current flow. Effects of concentration, flow type, liquid and gas flow rates on oxidation yield were investigated. It was consequently observed that the yield was increased with decreasing gas flow rate. The yields attained at countercurrent conditions were higher than those of cocurrent ones. The yield was not significantly affected by the change in concentration and liquid flow rate. The reaction was found to be of zero-order with respect to cyanide in water. Although this study was carried out at a continuously operating system, a yield of 99% was achieved at low gas flow rates and countercurrent conditions.

Aldehydic lipid peroxidation products derived from linoleic acid

Lipid peroxidation (LPO) processes observed in diseases connected with inflammation involve mainly linoleic acid. Its primary LPO products, 9-hydroperoxy-10,12-octadecadienoic acid (9-HPODE) and 13-hydroperoxy-9,11-octadecadienoic acid (13-HPODE), decompose in multistep degradation reactions. These reactions were investigated in model studies: decomposition of either 9-HPODE or 13-HPODE by Fe 2+ catalyzed air oxidation generates (with the exception of corresponding hydroxy and oxo derivatives) identical products in often nearly equal amounts, pointing to a common intermediate. Pairs of carbonyl compounds were recognized by reacting the oxidation mixtures with pentafluorobenzylhydroxylamine. Even if a pure lipid hydroperoxide is subjected to decomposition a great variety of products is generated, since primary products suffer further transformations. Therefore pure primarily decomposition products of HPODEs were exposed to stirring in air with or without addition of iron ions. Thus we observed that primary products containing the structural element R-CH=CH-CH=CH-CH=O add water and then they are cleaved by retroaldol reactions. 2,4-Decadienal is degraded in the absence of iron ions to 2-butenal, hexanal and 5-oxodecanal. Small amounts of buten-1,4-dial were also detected. Addition of m-chloroperbenzoic acid transforms 2,4-decadienal to 4-hydroxy-2-nonenal. 4,5-Epoxy-2-decenal, synthetically available by treatment of 2,4-decadienal with dimethyldioxirane, is hydrolyzed to 4,5-dihydroxy-2-decenal.

Synthesis of 2,5-Diformylfuran and Furan-2,5-Dicarboxylic Acid by Catalytic Air-Oxidation of 5-Hydroxymethylfurfural. Unexpectedly Selective Aerobic Oxidation of Benzyl Alcohol to Benzaldehyde with Metal/Bromide Catalysts

The alcohol group of hydroxymethylfurfural (compound 1, HMF) is preferentially oxidized by dioxygen and metal/bromide catalysts [Co/Mn/Br, Co/Mn/Zr/Br; Co/Mn=Br/(Co+Mn) = 1.0 mol/mol] to form the dialdehyde, 2,5-diformylfuran (compound 2, DFF) in 57% isolated yield. HMF can be also oxidized, via a network of identified intermediates, to the highly insoluble 2,5-furandicarboxylic acid (compound 5, FDA) in 60% yield. For comparison, benzyl alcohol gives benzaldehyde in 80% using the same catalyst system. Over-oxidation (to CO2) of HMF is much higher than that of the benzyl alcohol but can be greatly reduced by increasing catalyst concentration.

Synthesis of 2,5-Diformylfuran and Furan-2,5-Dicarboxylic Acid by Catalytic Air-Oxidation of 5-Hydroxymethylfurfural. Unexpectedly Selective Aerobic Oxidation of Benzyl Alcohol to Benzaldehyde with Metal/Bromide Catalysts

The alcohol group of hydroxymethylfurfural (compound 1, HMF) is preferentially oxidized by dioxygen and metal/bromide catalysts [Co/Mn/Br, Co/Mn/Zr/Br; Co/Mn=Br/(Co+Mn) = 1.0 mol/mol] to form the dialdehyde, 2,5-diformylfuran (compound 2, DFF) in 57% isolated yield. HMF can be also oxidized, via a network of identified intermediates, to the highly insoluble 2,5-furandicarboxylic acid (compound 5, FDA) in 60% yield. For comparison, benzyl alcohol gives benzaldehyde in 80% using the same catalyst system. Over-oxidation (to CO2) of HMF is much higher than that of the benzyl alcohol but can be greatly reduced by increasing catalyst concentration.

Dioxomolybdenum(VI) and Dioxotungsten(VI) Structure with Mono(Dithiolato) Coordination: Crystal Structures, Properties and Reactivity of [{MVIO2(dithiolato)}2(μ-O)]2− (M = Mo and W) Complexes

Abstract Novel mono(dithiolato) molybdenum(VI) and tungsten(VI) complexes were isolated through the searching for potential active species in the catalytic air oxidation of benzoin by [MoVO(SR)4]− complexes. Among these, (NEt4)2[{MoVIO2(3-triphenylsilyl-1,2-benzenedithiolato)}2(μ-O)]·2DMF (1), (PPh4)2[{WVIO2(1,2-benzenedithiolato)}2(μ-O)] (3), and (NEt4)2[{WVIO2(2,3-naphthalenedithiolato)}2(μ-O)] (5) were structurally characterized by X-ray crystallography. The electrochemical, electronic, as well as Raman/IR spectral properties of the tungsten complexes, 3 and 5, have been investigated and compared with the corresponding bis(dithiolato) complexes, e.g. [WVIO2(dithiolato)2]2−. The μ-oxo-binuclear species, [{MoVIO2(SR)2}2(μ-O)]2−, is proposed as a possible active species for the catalytic air oxidation of benzoin by the Mo(V) thiolato complexes.

Catalytic air oxidation of cyclooctene using cis-[MoO 2(SAL-SH)(DMF)] (SAL-SH=salcylidene salicyloyl hydrazinato-) and its zeolite-Y encapsulated composite

Oxidation of cyclooctene to cyclooctene epoxide using cis-MoO 2(SAL-SH)(DMF) and its zeolite-Y encapsulated composite as catalysts is reported. The percent conversion into epoxide was 68% at 60°C under 0.1 mmol of cis-MoO 2(SAL-SH)(DMF), 0.3 mmol of cyclooctene and under oxygen saturated conditions. The turnover with respect to Mo in the complex is eight. The percent conversion improved to 75% and the turnover increased nine times when complex-NaY composite is used under the same conditions. The oxidation reaction showed first order dependence with respect to the concentrations of catalyst and cyclooctene. The reaction is endothermic with an activation energy of 25.8 kcal mol −1. A reaction scheme for oxidation of cyclooctene using cis-MoO 2(SAL-SH)(DMF) is proposed and the higher activity observed with complex-NaY composite is attributed to absence of μ-oxo dimer formation in this case. The intermediate Mo(IV)O complex reacts with O 2, regenerating the parent Mo(VI)O 2 complex, which participates cyclically in the reaction.

Kinetics and Process Parameter Studies in Catalytic Air Oxidation of Veratraldehyde to Veratric Acid

Kinetics and different process parameters for the air oxidation of veratraldehyde to veratric acid were studied. At a temperature of 130 °C, air pressure of 1 MPa, cobalt acetate loading of 0.03 mol/L, and an initial concentration of 30% w/v of veratraldehyde, the reaction was found to be first order with respect to veratraldehyde. In 3 h at an aldehyde conversion level of 100%, as high as 99% selectivity was achieved.

Wastewater control and management in a leather tanning district

Initial assessment of industrial structure and wastewater characteristics is important for successful environmental management in an industrial district. This is particularly important for the cases where highly polluting industries such leather tanners are of concern. In this study, Biga Leather Tanners District was evaluated. The process characteristics, wastewater amounts, wastewater quality and their variations with time were defined. The district housed 46 tanning plants, processing mainly sheepskins with a total capacity of 66.5 tons skin per day. Process profile was prepared and checked with experimental data. Chemical treatability experiments were conducted to assess the pretreatment alternatives. Chemical precipitation preceded by catalytic air oxidation of sulfide was found to be an optimum pretreatment system providing COD and TKN removals up to 80% together with complete chromium removal, Results of the study were evaluated and discussed.

Oxygen atom transfer reaction involving oxomolybdenum complexes with sterically bulky thiocarboxylate ligands and biochemical interesting substrates in methanol at neutral pH

Oxidation–reduction reactions of substrates in systems containing the complex [Mo VIO 2(O 2CC(S)CH 3Ph) 2] 2− in methanol have been investigated as models of oxo-transfer reactions. At neutral pH, the [Mo VIO 2(O 2CC(S)CH 3Ph) 2] 2− reacts with Me 2PhP or n-butanethiol to yield a [Mo IVO(O 2CC(S)CH 3Ph) 2] 2− species and Me 2PhPO or disulfide, respectively. The Mo IVO complex reduces a variety of substrates XO = Me 2SO and pyridine N-oxide conducing formation of X = Me 2S and pyridine. The occurrence of these reactions produces a catalytic system Me 2PhP + XO → Me 2PhPO + X and 2BuSH + XO → [BuS] 2 + X + H 2O. In this work we have also included the study of the reaction with biochemical interesting substrates, such as the reduction of nitrobenzene to aniline and catalytic air oxidation of benzoin to benzil.

Wastewater control and management in a leather tanning district

Initial assessment of industrial structure and wastewater characteristics is important for successful environmental management in an industrial district. This is particularly important for the cases where highly polluting industries such leather tanners are of concern. In this study, Biga Leather Tanners District was evaluated. The process characteristics, wastewater amounts, wastewater quality and their variations with time were defined. The district housed 46 tanning plants, processing mainly sheepskins with a total capacity of 66.5 tons skin per day. Process profile was prepared and checked with experimental data. Chemical treatability experiments were conducted to assess the pretreatment alternatives. Chemical precipitation preceded by catalytic air oxidation of sulfide was found to be an optimum pretreatment system providing COD and TKN removals up to 80% together with complete chromium removal, Results of the study were evaluated and discussed.

Heterogenized polymetallic catalysts: Part III . Catalytic air oxidation of alcohols by Pd(II) complexed to a polyphenylene polymer containing β-di- and tri-ketone surface ligands

This paper describes further studies on mono- and bi-metallic catalysts attached to a polymer support by β-di- and tri-ketone surface ligands. The previous two papers described the oxidation of catechol by the heterogeneous catalysts using Cu(II), Fe(III) and Pd(II) as the metal species. The present study expands these studies to a series of mono- and polyfunctional alcohols using Pd(II) as the metal species. The final catalytic surfaces were prepared by treatment of the modified polymer with a very reactive form of Pd(II), [Pd(CH 3CN) 4] 2+. The simple alcohols gave increases in rates of up to 5-fold for the bimetallic systems. As might be expected glycols and α- d-glucose gave even higher increases in rate in going from the mono- to the bi-metallic catalyst. For ethylene glycol the factor was 30. Unsaturated alcohols gave the most dramatic results. With the monometallic catalyst, the products from allyl alcohol consisted of 25% acrolein resulting from direct alcohol oxidation and 75% 3-hydroxypropanal resulting from Wacker-type oxidation of the double bond. With the bimetallic catalyst the overall rate increased by a factor of 10 and the products consisted of 80% acrolein and 20% 3-hydroxypropanal. The actual rate increase for the direct alcohol oxidation is calculated to be a factor of 32. 4-Penten-2-ol and 4-penten-1-ol gave rates that were lower than the monofunctional alcohols. This is attributed to inhibition by olefin π-complex formation with the Pd(II).

Heterogenized polymetallic catalysts. Part I. Catalytic air oxidation of 3,5-di- t-butylphenol by Cu(II) and Fe(III) complexed to a polyphenylene polymer containing β-di-and tri-ketone surface ligands

Catalysis preparation involves the cyclic trimerization polymerization of acetylated aromatics. The polymer is coated on a high surface area support, Celite, and cured to give insoluble high molecular weight polymer. Reaction of the remaining acetyl end groups with base and methyl acetate gave β-diketone groups on the surface of the polymer. A second reaction with base and methyl acetate places β-triketones on the surface. The β-triketones can bind two metal ions in a known geometry. The chemically modified surfaces containing β-diketone and β-triketone surface ligands were reacted with Cu(OAc) 2 and FeCl 3 to give mono- and bi-metallic surface complexes. The oxidation of 3,5-di- t-butylcatechol was studied with all the surfaces. The monometallic catalysts gave only the ortho-quinone as product. The bimetallic catalysts absorbed about twice as much dioxygen as the monometallic catalysts and gave ring cleaved products. Both gave induction periods before dioxygen uptake began. With the bimetallic catalysts the dioxygen uptake stopped at about the ratio: 2 O 2 1 catechol . This is twice as much dioxygen as that required for ring cleavage so H 2O 2 may be the dioxygen reduction product rather than water. The monomeric Cu(OAc) 2 dioxygen uptake curve reached a maximum and then released gas. This could result from Cu(II) catalyzed decomposition of H 2O 2.

Catalytic Air Oxidation of Thiols Mediated at a Mo(VI)O 2 Complex Center Intercalated in a Zn(II)-Al(III) Layered Double Hydroxide Host

While bis(2-mercapto-2,2-diphenyl-ethanoate) dioxomolybdate (VI), {MoO 2[OOCC(S)(C 6H 5) 2] 2} 2− (I), ethanolic solutions stoichiometrically react with aromatic and aliphatic thiols to give the corresponding disulfides, the intercalation of I within a Zn(II)-Al(III) layered double hydroxide (LDH) allows their catalytic oxidation by dioxygen. A reaction scheme is proposed in which a (Mo IVO species activates O 2, regenerating the parent (Mo VIO 2 complex (I), which then acts as a true catalyst. Kinetic data far the thiol oxidation reaction have been determined. The results obtained here demonstrate that the intercalation of I into a Zn(II)-Al(III) LDH host inhibits the formation of catalytically inactive (Mo VO species that are always formed under homogeneous conditions.

Co(II)-catalysed allylic oxidation of α-pinene by molecular oxygen; synthesis of verbenone

A facile, high-yield, catalytic air-oxidation entry to verbenone ( 2) from α-pinene ( 1) is presented.

Intermediate filament-like network formed in vitro by a bacterial coiled coil protein.

The TlpA protein encoded by the virulence plasmid of Salmonella enterica is an alpha-helical 371-amino acid protein possessing characteristics similar to eukaryotic coiled coil proteins (Koski, P., Saarilahti, H., Sukupolvi, S., Taira, S., Rikkonen, P., Osterlund, K., Hurme, R., and Rhen, M. (1992) J. Biol. Chem. 267, 12258-12265). In this paper we have investigated inter- and intramolecular associations and the morphology of structures formed by TlpA. Dynamics and temperature stability of TlpA dimers were studied by examining the feasibility and conditions in which TlpA would form an artificial heterodimer with its truncated derivative. Formation of heterodimers, bridged by Cu(2+)-catalyzed air oxidation of adjacent Cys residues, showed that TlpA dimers are dynamic chain exchanging structures at 37 degrees C, whereas they were nonexchanging at room temperature or on ice. Chemical cross-linking suggested higher order interaction between TlpA dimers. Electron microscopy studies revealed two levels of TlpA organization in vitro: thin filaments and rods, 2-5 nm in diameter, and a higher ordered filament network consisting of tonofilament-like formations with a diameter of 8-15 nm. Electron microscopy of thin-sectioned Escherichia coli over-producing TlpA showed an extraordinary intracellular assembly of proteinacious lamellae with a striated appearance and a 38-nm periodicity. This study describes for the first time a bacterial protein capable of organizing itself into an ordered and suspectedly dynamic intermediate filament-like architecture.

Methanol oxidation on semiconducting oxides

Correlations between reaction rates and selectivities vs. Egap (eV) of the semiconducting oxides Co3O4, CuO, NiO, Cr2O3, α-Fe2O3, TiO2 and MoO3 were obtained for the catalytic air oxidation of methanol at 573 K. Higher and lower selectivities to formaldehyde for Egap>2 n-type, and Egap >2 p-type semiconducting oxides, are observed, respectively.

Oxidation of benzoin to benzil and of p-substituted benzyl alcohol to the corresponding benzaldehyde catalyzed by iron(II) thiolate complexes. A proposed reaction mechanism

The catalytic p-benzoquinone or air oxidation of benzoin to benzil was carried out in the presence of [Fe II(S 2- o-xyl) 2] 2- ( o-xyl = o-xylene-α, α′-dithiolate) or [Fe II(S- t-Bu) 4] 2- in a ratio [benzoin]/[catalyst] = 20/1 in DMF at 25 °C. Under such mild reaction conditions, the Fe(II) thiolate complex exhibited high catalytic activity. In the reaction catalyzed by [Fe II(S 2- o-xyl) 2] 2-, 64% and 93% of benzoin was oxidized to benzil in 25 h by air and p-benzoquinone, respectively. In the air oxidation of benzyl alcohol catalyzed by [Fe II(S 2- o-xyl) 2] 2-, benzaldehyde was formed specifically without formation of benzoic acid. Furthermore, p-substituent effect (Cl > H > OMe) was found in the catalytic air oxidation of p-substituted benzyl alcohol. The catalytic oxidation is first order with respect to each of substrate and the catalyst at initial stage. A reaction mechanism was proposed and the rate-determining step is at the release of the methine hydrogen as a proton which is based on the kinetic isotope effect (k H/k D was 4.3 by p-benzoquinone oxidation and 5.0 by air oxidation, respectively) and p-substituent effect of substrate in the presence of [Fe II(S 2- o-xyl) 2] 2-.

Catalytic air and amine N-oxide oxidation of p-substituted benzoin by molybdenum(VI) complexes. Identification of the deactivation process by dioxygen

The catalytic oxidation of benzoin and two p-substituted benzoins, e.g. 4,4′-dimethoxy- and 4,4′-dichloro derivatives, by dioxygen or pyridine N-oxide, in the presence of [MoO2(cysS-OMe)2](cysS-OMe = S-deprotonated cysteinate methyl ester) and [MoO2(S2CNEt2)2] was studied kinetically. The catalytic oxidation rates indicate a trend, MeO > H > Cl, which is related to the ease in apparent hydride release from the C–H group of benzoin derivatives. The stoicheiometric oxidation indicates a similar oxo-transfer reactivity of the above complexes towards the three p-substituted benzoins. Only one 18O atom from [18O] dioxygen was found in one of the benzil carbonyl groups. The catalytic dioxygen oxidation by [MoO2(S2CNEt2)2] suffers from deactivation through the formation of [MoVO(S2CNEt2)2] formed by a one-electron-transfer reaction from [MoIVO(S2CNEt2)2] to dioxygen.

Oxidation of exogenous substrates by the O 2-evolving center of photosystem II and related catalytic air oxidation of secondary alcohols via a tetranuclear manganese(IV) complex.

The O 2-evolving center of Photosystem II (PSII) contains atetranuclear Mn complex that acts as the catalyst for photosynthetic H 2O oxidation. The catalytic cycle for H 2O oxidation is thought to involve the light-driven generation of a very strongly oxidizing state of the Mn complex prior to the formation of the OO bond. However, the Mn complex also exhibits oxidation chemistry in its lower oxidation states. Exogenous ligands, such as primary amines and hydroxylamines, have been shown previously to interact with the O 2-evolving center in the dark S 1 oxidation state by coordinating to a Cl −-binding site near the Mn complex. In this paper, we present evidence that primary and secondary amines irreversibly inactivate the Mn complex in the S 1 state by a reductive mechanism, leading to the liberation of Mn(II) ions and a concomitant loss of O 2-evolution activity. Hence, the Mn complex in the O 2-evolving center acts as a strong oxidant even in the dark-stable S 1 state. The synthetic tetranuclear Mn(IV) complex [(TACN) 4Mn 4O 6]Br 4, which has been suggested as a model for the Mn complex in the O 2-evolving center, is a strong oxidant as well. We find that it catalyzes the air oxidation of secondary alcohols to ketones and triphenylphosphine to triphenylphosphine oxide.

Mn11-thiophenolate and -selenophenolate complexes as catalyst in air oxidation of benzoin, benzaldehyde and hydrazobenzene

Catalytic air oxidation of benzoin to benzil in N,N-dimethylformamide (DMF) occurred in the presence of [Mn(SePh)4]2- or [Mn(SPh)4]2- (with conversion of 70% and 45%, respectively ([complex]/[benzoin] =1/20, 50 h, 20 °C)). Similar oxidation of other substrates, e.g. hydrazobenzene, benzaldehyde, and benzhydrol, was also found.