Primary Oxidant Research Articles

Effects of O2 and H2O2 on TiO2 Photocatalytic Efficiency Quantified by Formaldehyde Formation from Tris(hydroxymethyl)aminomethane

AbstractThe impact of O

A sustainable two-phase procedure for V-catalyzed toluene oxidative bromination with H2O2–KBr

A sustainable V(V) and Mo(VI) catalysed two-phase procedure for bromination of toluene under quite mild conditions is proposed; H2O2 is the primary oxidant and KBr is the bromine source; metal precursors are commercially available salts. The reaction is efficient without any additional solvent. By using PhCH3 as a solvent/substrate good yields, together with interesting selectivity toward the formation of PhCH2Br, are obtained with both metal ions. Recycling of the catalytic phase is also possible. Useful information on the V-peroxido chemistry was obtained.

Comparison of primary oxidants for water-oxidation catalysis

In this tutorial review, we compare chemical oxidants for driving water-oxidation catalysts, focusing on the advantages and disadvantages of each oxidant.

Synthesis of 2′‐Deoxy‐1′‐homo‐N‐nucleosides with Anti‐Influenza Activity by Catalytic Methyltrioxorhenium (MTO)/H2O2 Oxyfunctionalization

This paper describes a new route for the synthesis of 1'-homo-N-nucleoside derivatives by means of either methyltrioxorhenium (MTO) or supported MTO catalysts, with H(2)O(2) as the primary oxidant. Under these selective conditions, the oxyfunctionalization of the heterocyclic ring and the N heteroatom oxidation were operative processes, regardless of the type of substrate used, that is, purine or pyrimidine derivatives. In addition, the oxidation of 1'-homo-N-thionucleosides, showed the occurrence of site-specific oxidative nucleophilic substitutions of the heterocyclic ring. The MTO/H(2)O(2) system showed, in general, high reactivity under both homogeneous and heterogeneous conditions, affording the final products with high conversion values of substrates and from medium to high yields. Many of the novel 1'-homo-N-nucleoside analogues were active against the influenza A virus, without any cytotoxic effects, retaining their activity in both protected and unprotected forms.

Reaction of zero-valent magnesium with water: Potential applications in environmental remediation

This study examined the dissolution kinetics of granular zero-valent Mg (ZVMg) at pH 7 in water that was open to the atmosphere and buffered with 50mM Na–MOPS. The oxidative dissolution of ZVMg was rapid; the initial amount of ZVMg (10–50mg/L) dissolved completely within 200min. The rate and extent of ZVMg dissolution was not affected by atmospheric oxygen. Although the oxidation of ZVMg is thermodynamically more feasible by dissolved oxygen or proton ions (H+), the primary oxidants are water molecules. The initial rate of ZVMg dissolution obeys first order kinetics with respect to ZVMg concentration with an observed rate constant, kMg,7=1.05±0.06×10−2min−1. Model calculations using the rate constant perfectly predict the extent of ZVMg dissolution for an extended time period at lower [Mg0]0 but underestimate at 50mg/L [Mg0]0. The offset is likely attributed to the rapid dissolution of ZVMg particles, which could cause a substantial increase in the specific surface area. As to the reactivity of Mg–water system, we suggest that the hydrated electron (eaq-), the most powerful reducing agent, would probably be the major reactive entity under neutral and alkaline conditions. In addition, we discuss briefly the factors affecting the rate and extent of the Mg–water reaction such as background electrolytes, ZVMg impurities, surface passivation, solution pH and temperature based on literature review.

ChemInform Abstract: Development and Application of New Oxidation Systems Utilizing Oxometalate Catalysts

AbstractReview: 228 refs.

Biochemical activities of 6-carboxy β-chitin derived from squid pens

TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated 6-carboxy β-chitin derivatives (T-chitin) with different carboxylate content were successfully synthesized by controlling the addition level of NaClO as the primary oxidant. The structural and biochemical properties of the derivatives were investigated. The carboxylate contents of the derivatives calculated by electrical conductivity titration were 1.33, 1.68, 1.80, and 2.08mmol/g, respectively. The yield of T-chitin with carboxylate content of 2.08mmol/g reached 74.55%. T-chitin exhibited stronger bile acid binding capacities than that of β-chitin. The scavenging ability of T-chitin against hydroxyl radicals improved with increasing concentration, and EC50 values were below 1.2mg/mL. All T-chitin exhibited a strong ferrous ion chelating effect. At 8mg/mL, the chelating effects of T-chitin with carboxylate content of 0.81mmol/g reached 80.15%. These results showed that T-chitin had good bile acid binding capacity and antioxidant activities and it may be a potential antioxidant in vitro.

Bromide-free oxidizing system for carboxylic moiety formation in cellulose chain

NHPI (N-hydroxyphthalimide) was used to mediate the oxidation of cellulose fibers in the absence of sodium bromide, as traditionally was used in this kind of transformations, solely using sodium hypochlorite (NaOCl) as the primary oxidant. Avoiding the use of NaBr is highly desired from both environmental and corrosion concerns. The non-persistent PINO (phthalimide-N-oxy) radical, the key species in the oxidation reaction, has been in situ generated from NHPI and copper (II) chloride. The reaction was performed at room temperature at pH=10.5. The carboxylic moiety formation was evidenced by FTIR and X-ray photoelectronic spectroscopy (XPS) and the content of the negatively charged groups determined by potentiometric titration. The changes appeared in crystallinity were evidenced by X-ray diffraction technique.

ChemInform Abstract: Molybdenum‐Oxo and Peroxo Complexes in Oxygen Atom Transfer Processes with O2 as the Primary Oxidant

AbstractReview: 62 refs.

Particle Formation during Oxidation Catalysis with Cp* Iridium Complexes

Real-time monitoring of light scattering and UV-vis profiles of four different Cp*Ir(III) precursors under various conditions give insight into nanoparticle formation during oxidation catalysis with NaIO(4) as primary oxidant. Complexes bearing chelate ligands such as 2,2'-bipyridine, 2-phenylpyridine, or 2-(2'-pyridyl)-2-propanolate were found to be highly resistant toward particle formation, and oxidation catalysis with these compounds is thus believed to be molecular in nature under our conditions. Even with the less stable hydroxo/aqua complex [Cp*(2)Ir(2)(μ-OH)(3)]OH, nanoparticle formation strongly depended on the exact conditions and elapsed time. Test experiments on the isolated particles and comparison of UV-vis data with light scattering profiles revealed that the formation of a deep purple-blue color (~580 nm) is not indicative of particle formation during oxidation catalysis with molecular iridium precursors as suggested previously.

Cellulose nanofibrils prepared from softwood cellulose by TEMPO/NaClO/NaClO2 systems in water at pH 4.8 or 6.8

Catalytic oxidation of softwood cellulose using NaClO and either 2,2,6,6-tetramethylpiperidine-1-oxyl (4-H-TEMPO) or 4-acetamido-TEMPO (4-AcNH-TEMPO) was applied with NaClO2 used as a primary oxidant in an aqueous buffer at pH 4.8 or 6.8. When the 4-AcNH-TEMPO-mediated oxidation was applied to softwood cellulose in water at pH 4.8 and 40°C, the carboxylate content rose to ∼1.3mmol/g after reaction for 48h and the DPv value was more than 1100. This 4-AcNH-TEMPO-oxidized softwood cellulose was mostly converted to individual nanofibrils by mechanical disintegration in water, with uniform widths of 3–4nm and lengths greater than 1μm.

Sodium Periodate as a Primary Oxidant for Water-Oxidation Catalysts

Sodium periodate was characterized as a primary chemical oxidant for the catalytic evolution of oxygen at neutral pH using a variety of water-oxidation catalysts. The visible spectra of solutions formed from Cp*Ir(bpy)SO(4) during oxygen-evolution catalysis were measured. NMR spectroscopy suggests that the catalyst remains molecular after several turnovers with sodium periodate. Two of our [Cp*Ir(bis-NHC)][PF(6)](2) complexes, along with other literature catalysts, such as the manganese terpyridyl dimer, Hill's cobalt polyoxometallate, and Meyer's blue dimer, were also tested for activity. Sodium periodate was found to function only for water-oxidation catalysts with low overpotentials. This specificity is attributed to the relatively low oxidizing capability of sodium periodate solutions relative to solutions of other common primary oxidants. Studying oxygen-evolution catalysis by using sodium periodate as a primary oxidant may, therefore, provide preliminary evidence that a given catalyst has a low overpotential.

Water Oxidation Catalyzed by the Tetranuclear Mn Complex [MnIV4O5(terpy)4(H2O)2](ClO4)6

The tetranuclear manganese complex [Mn(IV)(4)O(5)(terpy)(4)(H(2)O)(2)](ClO(4))(6) (1; terpy = 2,2':6',2″-terpyridine) gives catalytic water oxidation in aqueous solution, as determined by electrochemistry and GC-MS. Complex 1 also exhibits catalytic water oxidation when adsorbed on kaolin clay, with Ce(IV) as the primary oxidant. The redox intermediates of complex 1 adsorbed on kaolin clay upon addition of Ce(IV) have been characterized by using diffuse reflectance UV/visible and EPR spectroscopy. One of the products in the reaction on kaolin clay is Mn(III), as determined by parallel-mode EPR spectroscopic studies. When 1 is oxidized in aqueous solution with Ce(IV), the reaction intermediates are unstable and decompose to form Mn(II), detected by EPR spectroscopy, and MnO(2). DFT calculations show that the oxygen in the mono-μ-oxo bridge, rather than Mn(IV), is oxidized after an electron is removed from the Mn(IV,IV,IV,IV) tetramer. On the basis of the calculations, the formation of O(2) is proposed to occur by reaction of water with an electrophilic manganese-bound oxyl radical species, (•)O-Mn(2)(IV/IV), produced during the oxidation of the tetramer. This study demonstrates that [Mn(IV)(4)O(5)(terpy)(4)(H(2)O)(2)](ClO(4))(6) may be relevant for understanding the role of the Mn tetramer in photosystem II.

Development and Application of New Oxidation Systems Utilizing Oxometalate Catalysts

This review describes our recent efforts in the development and application of new oxidation systems utilizing oxometalate catalysts. The novel use of heteropoly acid (HPA), an acidic oxometalate catalyst, in hypervalent iodine-mediated oxidations provided an effective strategy to generate cation radical species that enables a variety of direct C-H functionalizations of aromatic compounds. This strategy brought a facile biaryl synthesis and new spirodienone syntheses in aromatic oxidation chemistry. Moreover, this strategy opens up a facile synthetic route to morphinandienone alkaloids. On the other hand, the use of oxometalate catalyst together with poly(N-isopropylacrylamide) (PNIPAAm)-based polymer in the development of new solid-phase catalyst provided a novel reaction system in water. Due to the characteristic temperature-responsive intelligence of PNIPAAm, this reaction system brought a remarkable acceleration of the reactivity and ease of catalyst recovering in catalytic oxidation that uses hydrogen peroxide or oxygen gas (O<inf>2</inf>) as primary oxidant. In addition, the recovered solid-phase catalyst could be used for consecutive reactions without any significant loss of its catalytic efficacy.

Molybdenum-Oxo and Peroxo Complexes in Oxygen Atom Transfer Processes with O2as the Primary Oxidant

The chemistry of Oxygen Atom Transfer catalyzed by metal-dioxo and metal-oxo-peroxo complexes, described in this mini review is limited to processes in which the primary oxidant is dioxygen. Contrary to the vast majority of OAT catalytic systems reported in the literature and involving oxidant such as hydroperoxide, peracid, hydrogen peroxide, DMSO or N2O, the use of dioxygen is certainly more arduous since it brings up more constraints. First, experimental conditions must minimize free radical chain pathways in order to avoid unselective product formation. Second, it is essential that the catalytic system be able , not only, to activate O2 but also transfer both oxygen atoms to a substrate. Examples from the literature and from our laboratory are given for systems under homogeneous conditions and with recently reported more performant solid matrix anchored catalysts. Keywords: Dioxygen, Molybdenum-dioxo, Oxygen atom transfer, Titania anchored catalyst, OAT processes, transition metals, Goddard, TRANSFER REACTIONS, HOMOGENEOUS CONDITIONS, oxygen atoms

Molybdenum-Oxo and Peroxo Complexes in Oxygen Atom Transfer Processes with O2 as the Primary Oxidant

Molybdenum-Oxo and Peroxo Complexes in Oxygen Atom Transfer Processes with O2 as the Primary Oxidant

Long-Term Temporal Variability in Hydrogen Peroxide Concentrations in Wilmington, North Carolina USA Rainwater

Measurements of hydrogen peroxide (H(2)O(2)), pH, dissolved organic carbon (DOC), and inorganic anions (chloride, nitrate, and sulfate) in rainwater were conducted on an event basis at a single site in Wilmington, NC for the past decade in a study that included over 600 individual rain events. Annual volume weighted average (VWA) H(2)O(2) concentrations were negatively correlated (p < 0.001) with annual VWA nonseasalt sulfate (NSS) concentrations in low pH (<5) rainwater. Under these conditions H(2)O(2) is the primary aqueous-phase oxidant of SO(2) in the atmosphere. We attribute the increase of H(2)O(2) to decreasing SO(2) emissions which has had the effect of reducing a major tropospheric sink for H(2)O(2). Annual VWA H(2)O(2) concentrations in low pH (<5) rains showed a significant increase over the time scale of this study, which represents the only long-term continuous data set of H(2)O(2) concentrations in wet deposition at a single location. This compositional change has important implications because H(2)O(2) is a source of highly reactive free radicals so its increase reflects a higher overall oxidation capacity of atmospheric waters. Also, because rainwater is an important mechanism by which H(2)O(2) is transported from the atmosphere to surface waters, greater wet deposition of H(2)O(2) could influence the redox chemistry of receiving watersheds which typically have concentrations 2-3 orders of magnitude lower than rainwater.

‘Old’ Clusters with New Function: Oxidation Catalysis by High Oxidation State Manganese and Cerium/Manganese Clusters Using O2 Gas

The family of polynuclear manganese clusters of formula [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(4)] (R = Et, Ph, etc.) has been investigated in great detail over the years for their ability to function as single-molecule magnets (SMMs), but they have not been employed as oxidation catalysts. In the present report, the ability is described of these clusters to act as catalysts in the selective oxidation of benzyl alcohol to benzaldehyde using molecular O(2) as the primary oxidant and the nitroxyl radical TEMPO as a cocatalyst. A systematic investigation of Mn clusters varied in their R group, oxidation state, and size was conducted in order to realize the electronic requirements that will lead to the best catalytic activity. The best reactivity (>99%) was obtained when the catalyst was the mixed-metal cluster [CeMn(6)O(9)(O(2)CMe)(9)(NO(3))(H(2)O)(2)], which contains Ce(4+)Mn(4+)(6) ions; in this case, lower loadings of catalysts (cluster and TEMPO) are required and the reaction can proceed even without a solvent. In addition, it has been demonstrated that the high efficiency can be only achieved when both high oxidation Ce(4+) and Mn(4+) ions are present within the same cluster.

An experimental aluminum-fueled power plant

An experimental co-generation power plant (CGPP-10) using aluminum micron powder (with average particle size up to 70μm) as primary fuel and water as primary oxidant was developed and tested. Power plant can work in autonomous (unconnected from industrial network) nonstop regime producing hydrogen, electrical energy and heat. One of the key components of experimental plant is aluminum–water high-pressure reactor projected for hydrogen production rate of ∼10nm3h−1. Hydrogen from the reactor goes through condenser and dehumidifier and with −25°C dew-point temperature enters into the air-hydrogen fuel cell 16kW-battery. From 1kg of aluminum the experimental plant produces 1kWh of electrical energy and 5–7kWh of heat. Power consumer gets about 10kW of electrical power. Plant electrical and total efficiencies are 12% and 72%, respectively.

Wilkinson's iridium acetate trimer as a water-oxidation catalyst

The catalytic water-oxidation activity of Wilkinson's iridium acetate trimer (1) has been characterized electrochemically and by using chemical oxidants. We show that 1 can function as an operationally homogeneous water-oxidation catalyst when driven with sodium periodate as a primary oxidant, but rapidly decomposes using Ce(IV) as a primary oxidant.