Molecular Oxygen In Aqueous Solution Research Articles

Bis(pyridine-2-carboxaldehyde oxime)copper(II) sulphate as catalyst precursor in the oxidation of veratryl alcohol by dioxygen

In situ generated [Cu II(pyridine-2-carboxaldehyde oxime) 2] complex catalyses selective oxidation of veratryl alcohol (3,4-dimethoxybenzyl alcohol) to aldehyde by molecular oxygen in aqueous solution. Under alkaline conditions, the catalyst has both oxime groups deprotonated and the solid state structure of the complex reveals a square pyramidal geometry established by two pyridine-2-carboxaldehyde oxime ligands and sulphate as a counter anion.

Electron transfer in environmental systems: a frontier for theoretical chemistry

The advances in understanding the kinetic behavior of certain environmental electron transfer (ET) systems are presented. Emphasis is placed on the homogeneous ET chemistry of transition metals, particularly the FeII/III system, in various relevant forms. In the context of modern ET theory, we examine the utility of computational chemistry methods for the calculation of ET quantities such as the reorganization energy and electronic coupling matrix element. We discuss successful application of the methods to topics of homogeneous oxidation of dissolved metal ions by molecular oxygen in aqueous solution, as well as the prediction of electron mobility in solid phase iron oxide crystals. The examples illustrate the significant potential for many more advances in understanding environmental ET systems through the combination of ET theory and computational chemistry.

Theoretical study of hypericin

Electronic properties and phototoxic reactions of the hypericin molecule are explored by the use of density functional theory, integral equation formalism polarised continuum model (to include solvent effects) and a time-dependent formalism for the study of singlet and triplet excited states. Our structural and vibrational data are in very good agreement with previous calculated and experimental results. The results suggest a hypericin (triplet state) reduction and subsequent electron transfer from the drug to molecular oxygen in aqueous solution. The most probable source of singlet molecular oxygen is a transfer of triplet excitation energy from hypericin to molecular oxygen. Direct radiation induced electron transfer between hypericin and oxygen is also explored, as well as the effect of triplet excitation on hypericin auto ionization reactions.

Parallel Screening of Homogeneous Copper Catalysts for the Oxidation of Benzylic Alcohols with Molecular Oxygen in Aqueous Solutions

A simple and efficient parallel screening method to evaluate the catalytic activities of homogeneous copper complexes for the oxidation of benzylic alcohols in aqueous solutions with molecular oxygen is reported. Copper(II) sulfate was treated in situ with 22 nitrogen donor ligands, and the catalytic activities of these combinations were studied at four different pH values with two substrates (benzyl alcohol and 3,4-dimethoxy benzyl alcohol (veratryl alcohol)), resulting in 176 oxidation experiments in the primary screening stage. Copper complexes based on N,N,N',N'-tetramethyl ethylenediamine (TMEDA), 9,10-diaminephenanthrene (DAPHEN), and 1,2-diaminocyclohexane (DACH) were determined to be the most active catalysts. In the second screenings, the influence of reaction conditions on Cu(DACH)-, Cu(TMEDA)-, and Cu(DAPHEN)-catalyzed reactions were investigated in more detail. It was found that highly basic reaction conditions favor the reaction with the exception of Cu(TMEDA), which is active at a lower pH range. Under optimized conditions, Cu(DAPHEN) catalyzes the transformation of veratryl alcohol to the corresponding aldehyde with 100% conversion.

Kinetics of the Catalytic Oxidation Reactions of Thiol Compounds in Aqueous Solutions in the Presence of Copper Ions

The kinetics of the catalytic oxidation reactions of thiol compounds with molecular oxygen in aqueous solutions in the presence of copper ions was studied in relation to the structures of oxidized thiols and the pH of the solution. A modified procedure used for the determination of [O2] allowed us to obtain the kinetic characteristics of more than 30 thiols over a wide pH range. We found that weakly chelating thiols exhibited a first order of reaction with respect to [Cu+] and [O2] under conditions when the [(Cu+)(RS–)2] complex occurred. In the oxidation of strongly chelating thiols in an alkaline medium, the order of reaction with respect to [Cu+] was equal to 2, and the rate of reaction was independent of [O2]. We found that the introduction of small amounts of strongly chelating thiols into Cu+ solutions containing difficult-to-oxidize mercaptans resulted in a dramatic acceleration of mercaptan oxidation. We hypothesized that O2 was effectively bound to the [(Cu+)(RS–)2] complexes in an alkaline medium in the case of strongly chelating thiols, and this was not the case with the complexes of weakly chelating thiols.

Energy transfer between singlet (1Delta(g)) and triplet (3Sigma(g)-) molecular oxygen in aqueous solution.

We clearly demonstrate the occurrence of energy transfer between 18O2 (1Deltag) and 16O2 in the ground state (3Sigmag-) with subsequent conversion of the latter species into its singlet excited state (1Deltag) in aqueous solution. This was inferred from the results of incubation experiments involving DHPN18O2 as a chemical generator of 18O2 (1Deltag) and the water-soluble disodium salt of anthracene (EAS) used as a chemical trap of singlet oxygen. The products of the reaction were accurately analyzed by HPLC-ESI-MS.

Oxidation of veratryl alcohol by molecular oxygen in aqueous solution catalyzed by cobalt salen-type complexes: the effect of reaction conditions

A series of Schiff-base salen-type cobalt complexes Co(salen) (1) [salen=N,N′-bis(salicylidene)ethylenediamine], Co(α-CH3salen) (2) [α-CH3salen=N,N′-bis(α-methylsalicylidene)ethylenediamine], Co(4-OHsalen) (3) [4-OHsalen=N,N′-bis(4-hydroxosalicylidene)ethylenediamine], Co(sulfosalen) (4) [sulfosalen=N,N′-bis(5-sulfonatosalicylidene)ethylenediamine], Co(acacen) (5) [acacen=N,N′-bis(acetylacetone)ethylenediamine)] and Co(N-Me-salpr) (6) [N-Me-salpr=bis(salicylideniminato-3-propyl)methylamine] were studied as catalysts for dioxygen activation in the oxidation of 3,4-dimethoxy benzylalcohol (veratryl alcohol) in basic aqueous conditions. The oxidation occurs selectively at benzylic position as in all experiments veratraldehyde was the only observed product. The highest catalytic activity was reached with the unsubstituted complex (1), which was used for further studies on the effect of temperature, pressure, time and pH. The effect of pH was noted to be critical and the reaction proceeds up to 72 h if the pH is kept at about 12.5. The need for higher temperatures (over 60 °C) was also confirmed. Reactivity of the catalyst increase linearly with increased O2 pressure, the best turnover numbers (TON=moles of veratryl aldehyde produced per mole of complex) reached in similar conditions were 58 for ambient pressure and 103 for oxygen pressure of 10 bar. The catalytic activity can be further enhanced if the catalyst:substrate ratio is increased. Turnover numbers as high as 330 were detected with catalyst:substrate ratio 1:5950 at ambient pressure.

Complexes of Copper(I) with Dimercapto Compounds as Catalysts for Oxidation of Mercaptans and Hydrogen Sulfide with Molecular Oxygen in Aqueous Solutions

The conditions for formation of complexes of copper(I) with mercapto compounds in aqueous- alkaline solutions and the catalytic activity of these complexes in oxidation of mercaptans and hydrogen sulfide was studied. The kinetic characteristics of these catalysts were compared with those of catalysts based on cobalt phthalocyanines. A method was proposed for suppressing formation of the thiosulfate ion in oxidation of H2S to elemental sulfur.

Oxidation of thiol compounds by molecular oxygen in aqueous solutions

Side self-oxidation of thiols was studied. It was found that these reactions in neutral and alkaline solutions are induced by impurities of variable-valence metals. The ability of transition metals to catalyze oxidation of thiols changes in the order Cu > Mn > Fe > Ni ≫ Co. The plot of the self-oxidation rate vs. pH passes through a maximum whose position on the pH scale depends on both the nature of metal and the structure of the thiol oxidized. For thiols having different structures, the kinetic orders in reactions catalyzed by copper ions differently vary with pH, which is apparently associated with the formation of complexes possessing different catalytic activity.

CdS Nanoparticle Photocatalysis of the Chain Oxidation of Sulfite Ions by Molecular Oxygen

High photocatalytic activity was found for colloidal cadmium sulfide nanoparticles in the radical chain oxidation of sulfite ions by molecular oxygen in aqueous solution. The kinetics of this reaction was studied and a mechanism was proposed, which is in satisfactory accord with the experimental data.

Application of gold catalysts to selective liquid phase oxidation

New applications of gold catalysts for selective oxidation of organic molecules are reported. All reactions investigated were performed using molecular oxygen in aqueous solution under mild conditions. Polyhydroxylated aliphatic molecules can be oxidised to monocarboxylates with high selectivity towards the primary alcoholic group in the presence of alkali, whereas the phenyl group enhances the reactivity of a benzylic alcoholic group as it limits the selectivity to mandelate starting from phenyl-1,2-ethanediol. α- and β-aminoalcohols react slowly with oxygen in the absence and quickly in the presence of alkali to produce the corresponding aminoacid derivatives. Aliphatic aldehydes and glucose are easily oxidised to free carboxylic acid. A comparison of gold catalysts and conventional Pd and Pt monometallic, bimetallic and tricomponent catalysts has, in some cases, been done.

Radiation-induced autoxidation of bisulfite catalyzed by manganese (II) ions

Manganese (II) is shown to be an efficient catalyst for radiation-induced HSO 3 − chain oxidation by molecular oxygen in aqueous solutions. The catalytic activity of Mn(II) is explained in terms of a free radical chain mechanism. The rate-determining step with a rate constant of k 9 ⩾ 1×10 6 M −1 s −1 is a reaction between SO 5 − radical and a manganese (II) bisulfite complex.

A possible path for mercury in biological systems: the oxidation of metallic mercury by molecular oxygen in aqueous solutions

Metallic mercury has been assumed by several authors as not very reactive and, as a consequence, with little or no toxicity. The toxicity of this element is usually ascribed to alkyl-mercury ions considered to be formed by some microorganisms. In this work, we describe experiments that clearly show that metallic mercury can be easily oxidized by molecular oxygen in aqueous solution in the presence of species such as chloride, which complex Hg(II). The experiments were carried out using metallic mercury in NaCl aqueous solution under ‘open air’ (temperature and agitation rate maintained constant) and under more controlled conditions (CO2 rate bubbling, i.e. pH = 4.2; air rate bubbling, i.e., O2 constant concentration, temperature, agitation rate). The reactions were monitored spectrophotometricaly at 230 nm (HgCl42−). Significative values of the concentration of Hg(II) in the form of HgCl42− were soon attained in those solutions. For example, in ‘open air’ conditions, at 25°C and [NaCl] = 30 g/l (0.51 mol/dm3), the maximal concentration of 13 ppm (6.44 × 10−5 mol/dm3) of Hg(II) in the form of HgCl42− was reached in 120 min; for [NaCl] = 5 g/l at 25°C, (0.085 mol/dm3) the maximal concentration of 0.3 ppm (1.53 × 10−6 mol/dm3) of Hg(II) in the form of HgCl42− was reached in 10 min. The rate constants, kobs, of the oxidation of the metallic mercury under the studied conditions are pseudo zero-order at 25°C, and under more controlled conditions have ranged from 1.0 × 10−7 mol/min ([NaCl] = 5 g/l ≡ 0.085 mol/dm3) to 20.0 × 10−7 mol/min ([NaCl] = 300 g/l ≡ 5.12 mol/dm3). The rate constant increases with temperature, up to 25°C, from where kobs remains constant up to 40°C. From the analysis of the experimental results it was possible to propose a mechanism of oxidation of metallic mercury by O2 in aqueous solution containing NaCl. This oxidation is proposed as a possible route for the introduction of mercury into biological systems.

Auto-sensitized oxidation of Ru(II) complexes I. Studies on the stability of two Ru(II) complexes ([Ru(NH 3) 5NCPyR] 3+, RCH 3 and C 6H 5CH 2) in a medium containing singlet oxygen

The generation of singlet oxygen by a photochemical pathway, involving the excited state of a pentaammine Ru(II) complex containing an N-substituted 4-cyanopyridine ligand and molecular oxygen in aqueous solution, is reported in this work. A two-step degradation process occurs by virtue of the action of singlet oxygen. This species promotes the oxidation of Ru(II) to Ru(III) in the ground state of the complex. The cyanopyridine ligand then suffers hydrolysis, resulting in an Ru(III) complex containing a carboxyamidopyridine ligand. The influence of the substituent on the stability of the complex in the presence of singlet oxygen is studied, showing that a methyl substituent leads to a more stable complex than a benzyl substituent. A kinetic treatment of this process shows that the quenching of singlet oxygen by the complex has diffusional character, and is predominantly physical. Chemical quenching is related to the electron transfer process between Ru(II) and singlet oxygen.

Sunlight-initiated partial inhibition of the dissolved iron(III)-catalysed oxidation of S(IV) species by molecular oxygen in aqueous solution

The dissolved Fe(III)-catalysed oxidation of S(IV) species [SO 2(aq), HSO 2 −/HOSO 2 −, SO 3 2−] by molecular oxygen is partially inhibited by sunlight, relative to dark controls, under conditions that are realistic for tropospheric clouds and fogs {initial [S(IV] = 4.0–68 μM, total [Fe(III)] = 38–750 nM, pH = 2.8–4.6}. Due to the unusual effect of sunlight on this reaction, empirical rate expressions for the Fe(III)-catalysed oxidation of S(IV) by O 2 should not be used to predict daytime rates of H 2SO 4 formation in atmospheric hydrometeors via this pathway.

Heterogeneous electron transfer to molecular oxygen in aqueous solutions

Heterogeneous electron transfer to molecular oxygen in aqueous solutions

ChemInform Abstract: Copper(II)‐Catalyzed Oxidation of Catechol by Molecular Oxygen in Aqueous Solution

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Copper(II)-catalyzed oxidation of catechol by molecular oxygen in aqueous solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCopper(II)-catalyzed oxidation of catechol by molecular oxygen in aqueous solutionJozsef Balla, Tamas Kiss, and Reginald F. JamesonCite this: Inorg. Chem. 1992, 31, 1, 58–62Publication Date (Print):January 1, 1992Publication History Published online1 May 2002Published inissue 1 January 1992https://doi.org/10.1021/ic00027a012RIGHTS & PERMISSIONSArticle Views1584Altmetric-Citations124LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (535 KB) Get e-Alerts Get e-Alerts

Kinetics of the reactions between alkyl radicals and molecular oxygen in aqueous solution

The rate constant for the reaction R{sup {sm bullet}} + O{sub 2} {yields} ROO{sup {sm bullet}} in aqueous solution was determined for 18 alkyl radicals by laser flash photolysis. The values are all at the diffusion-controlled limit and lie in the range (1.6-4.9) {times} 10{sup 9} L mol{sup {minus}1} s{sup {minus}1}. The radicals studied are primary, substituted primary, secondary, and benzyl radicals.

Electrochemical catalytic reduction of molecular oxygen by iron porphyrin ion-complex modified electrode

The iron porphyrin ion-complex, which is electrostatic aggregate of iron meso-tetrakis- (N-methyl-4-pyridyl)porphyrin (FeTMPyP, cationic) and iron meso-tetrakis( p-sulfophenyl)porphyrin (FeTPPS, anionic), has a catalytic activity for the reduction of molecular oxygen in aqueous solutions. Rotating ring—disk voltammetric measurements show the two different reaction pathways for the oxygen reduction; one is in a lower and other in a higher overpotential region. The main product in lower overpotentials is hydrogen peroxide but 12% of molecular oxygen is reduced to water directly via four-electron process. In higher overpotentials, the iron porphyrin ion-complex also acts as a catalyst for the reduction of hydrogen peroxide. The four-electron process and the two step pathway through intermediate hydrogen peroxide occur. From these results, it can be presumed that some of iron porphyrin aggregates form a “face-to-face”-like structure by the electrostatic interaction and provide the effective sites for the reduction of molecular oxygen.