A new finding in selective Baeyer-Villiger oxidation of α-fluorinated ketones; a new and practical route for the synthesis of α-fluorinated esters

α-Fluorinated esters were effectively prepared by the Baeyer-Villiger oxidation of α-fluorinated ketones with m-chloroperbenzoic acid (m-CPBA) under mild conditions. The yield of the esters was influenced by the choice of solvent, base, and substituent on the aryl group of the ketones. 4-Methoxyphenyl substituted fluoroketones were oxidized almost quantitatively with m-CPBA within 10 min to 12 h at room temperature using 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a cosolvent with CH₂Cl₂ (1:1, v/v) and aqueous buffer (KH₂PO₄-NaOH, pH 7.6) as an additive base. The oxidation reaction rates of α-fluorinated ketones were higher than those of the corresponding non-fluorinated ketones. The fluorine atom at α-position of fluoromethyl aryl ketones enhanced the reactivity in the Baeyer-Villiger oxidation.     

Nutritional consequences of sun-drying,freezing, and frying of Lates calcarifer on human health

Asian Sea bass (Lates calcarifer), a popular fish, is cultured and consumed in several countries for its commercial benefits and delectable taste. In this study, the biochemical parameters and fatty acids (FA) composition of Lates calcarifer in raw and fried (with mustard oil) conditions were compared for samples treated under three different ways: fresh, frozen, and sun-dried. From the final outcome, it was observed that after frying the protein content deteriorated significantly for all experimental conditions. Scrutiny of fried sample pointed to an increment in neutral lipid content (4.91%) along with trans FA that may pose a threat to health of the consumers. Contrastingly, after frying the loss of saturated FA to a great extent was countered by the increment of beneficial monounsaturated and polyunsaturated FA (MUFA and PUFA). From the nutritional view point, it was revealed that frying improved the nutritional quality indices (NQI) not only for sun-dried or frozen samples but also for fresh samples nullifying the adverse effect of trans FA because of the presence of low concentration of saturated FA along with high percentage of MUFA and PUFA. However, NQI deteriorated typically after sun-drying and freezing. Principal component analysis (PCA) bi-plot further suggested high positive correlation of fried condition to lipid profile but none of the NQI were significantly affected either on sun-drying or on freezing. From the present study, finally it can be recommended that frying is a suitable method to preserve the nutritional values of L. calcarifer.     

Catalytic elimination of carbon monoxide in gas streams by thermal and ozone oxidations

Summary The catalytic activities of Pt-Pd, 0.25 wt.% Mn and 0.56 wt.% Mn coated on Al₂O₃ pellets during catalytic thermal oxidation and catalytic ozone oxidation were investigated. The results reveal that the activity of catalysts in catalytic ozone oxidation differed substantially from that in catalytic thermal oxidation.      

Kinetics of the individual and joint oxidation of dihydroquercetin and potassium ferrocyanide in the presence of horseradish peroxidase

The study-state kinetics of individual and cooxidation of ferrocyanide and dihydroquercetin catalyzed by horseradish peroxidase is studied. It is shown that ferrocyanide and dihydroquercetin are slowly oxidized substrata peroxidase. In an interval of pH 4.5–8.0, sizes k _cat and K _m for these substrata peroxidase are certain. In reactions of cooxidation substrata, it was revealed that, at pH 4.5–7.0, dihydroquercetin accelerated oxidation ferrocyanide. At pH 7.5 oxidation only dihydroquercetin was observed. Mechanisms of reactions of combined oxidation ferrocyanide and dihydroquercetin are offered.     

Decomposition of hydrogen peroxide catalyzed by vanadium(v) compounds: the pathways for the formation of ozone

Reactions of H₂O₂ in trifluoroacetic acid catalyzed by vanadium(v) compounds were studied. The system under study exhibits unusual behavior: along with oxygen, large quantitaties (10–15 %) of ozone are found in the products of hydrogen peroxide decomposition; difficultly oxidizable compounds (alkanes, arenes, and perfluoroalkenes) are oxidized under mild conditions. The rates of the oxidation of individual substrates are commensurable. However, when two compounds are simultaneously present in the reaction mixture, cyclohexane stops the oxidation of all of the other substrates, arenes suppress the oxidation of perfluoroolefins, and perfluoro-1-octene stops the consumption of internal perfluoroolefins. The effect of the oxidizable substrates on the amount of ozone evolved was studied. Based on the kinetic data obtained, a mechanism that involves the consecutive formation of several active complexes of vanadium(v) responsible for the oxidation of substrates and for the formation of ozone is suggested. In terms of the scheme suggested, the inner-sphere oxidation of the peroxo ligand by the coordinated peroxotrifluoroacetic acid affords a complex incorporating O ₃ ^2– as a ligand. The latter acts as the precursor of the ozone. A mathematical model that adequately describes the experimental data is proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 605–619, April, 1995.     

Effects of humidity and temperature on laser-assisted dip-pen nanolithography array using molecular dynamics simulations

Reactions of As(III) and As(V) with pyrite were investigated using pristine pyrite (produced and reacted in a rigorously anoxic environment with P_O2 < 10⁻⁸ atm) and using surface-oxidized pyrite (produced under anoxic conditions, exposed to air, then stored and reacted under rigorously anoxic conditions). Results with surface-oxidized pyrite were similar to previously reported arsenic-pyrite results. However As(III) adsorbed over a broader pH range on pristine pyrite than on surface-oxidized pyrite, As(V) adsorbed over a narrower pH range on pristine pyrite than on surface-oxidized pyrite, and adsorbed As(V) on pristine pyrite was reduced to As(III) but adsorbed As(V) was not reduced with surface-oxidized pyrite. Reduction of As(V) with pristine pyrite was first-order in total As(V), Fe(II) was released, and sulfur was oxidized. The proposed mechanism for pyrite oxidation by As(V) was similar to the published mechanism for oxidation by O₂ and rates were compared. The results can be used to predict the removals of As(V) and As(III) on pyrite in continuously anoxic environments or on pyrite in intermittently oxic/anoxic environments. Rigorous cleanup and continuous maintenance of strictly anoxic conditions are required if commercial or produced pyrites are to be used as surrogates for pristine pyrite.     

Chronoamperometric evaluation of the antioxidant capacity of tea on a polyquercetin-modified electrode

It was established that the components of tea are oxidized on a glassy carbon electrode modified with carbon nanotubes and electropolymerized quercetin in a phosphate buffer solution (pH 7.0) as a supporting electrolyte under conditions of differential pulse voltammetry. The oxidation potentials of the individual phenolic antioxidants of tea (gallic acid, rutin, quercetin, catechin, epigallocatechin gallate, and tannin) on the modified electrode were found. A method for the chronoamperometric determination of the antioxidant capacity (AOC) of tea was developed based on the oxidation of tea antioxidants at a potential of 0.20 V. The AOC of tea was evaluated using а difference between the oxidation currents of the analyte and a supporting electrolyte after 50 s of electrolysis in terms of gallic acid. The analytical range of gallic acid was 0.25?750 μM with a detection limit of 0.063 μM. Positive correlations of the AOC with antioxidant activity in a reaction with 2,2-diphenyl-1-picrylhydrazyl and the total phenolic content were found (r = 0.700 and 0.647 at r _crit = 0.396, respectively).     

Oxidation of wood cellulose using 2-azaadamantane N-oxyl (AZADO) or 1-methyl-AZADO catalyst in NaBr/NaClO system

A wood cellulose was oxidized with catalytic amounts of 2-azaadamantane N-oxyl (AZADO) or 1-methyl-AZADO, in an NaBr/NaClO system, in water at pH 10. The oxidation efficiency, carboxylate/aldehyde contents, and degree of polymerization (DP_v) of the oxidized celluloses thus obtained were evaluated in terms of the amount of AZADO or 1-methyl-AZADO catalyst added, in comparison with those prepared using the TEMPO/NaBr/NaClO system. When the AZADO/NaBr/NaClO and 1-methyl-AZADO/NaBr/NaClO oxidation systems were applied to wood cellulose using the same molar amount of TEMPO, the oxidation time needed for the preparation of oxidized celluloses with carboxylate contents of 1.2–1.3 mmol/g was reduced from ≈80 to 10–15 min. Moreover, the molar amounts of AZADO and 1-methyl-AZADO that had to be added for the preparation of oxidized celluloses with carboxylate contents of 1.2–1.3 mmol/g were reduced to 1/32 and 1/16 of the amount of TEMPO added, respectively. The DP_v values for the AZADO- and 1-methyl-AZADO-oxidized celluloses after NaBH₄ treatment were in the range of 600–800. This indicated that not only C6-carboxylate groups but also C2/C3 ketones were formed to some extent on the crystalline cellulose microfibril surfaces during the AZADO- and 1-methyl-AZADO-mediated oxidation. When the AZADO-oxidized wood cellulose, which had a carboxylate content of 1.2 mmol/g, was mechanically disintegrated in water, an almost transparent dispersion consisting of individually nano-dispersed oxidized cellulose nanofibrils was obtained, with a nanofibrillation yield of 89 %.     

The effect of oxidation and reduction on thermal expansion of magnetite from 298 to 1173 K at different vacuum conditions

Three thermal expansion curves of natural and synthetic magnetite (Fe₃O₄) have been measured under different vacuum conditions (10⁻⁴ and 10⁻⁶ mbar). The different behavior in thermal expansion depends on vacuum level, which controls the partial oxidation of the sample. If the vacuum is poor, that is in mildly oxidizing conditions, the thermal expansion curve presents a discontinuity at 875 K and the samples oxidizes. In non-oxidizing conditions the discontinuity is not present and the thermal expansion coefficient is markedly smaller. The experimental curves indicate that virtually all thermal expansion data on magnetite in the literature were measured on oxidized or partially oxidized samples.     

Surface ozonation and photooxidation of polyethylene film

High-density polyethylene (HDPE) and low-density polyethylene (LDPE) films were oxidized by treatment with ozone and by photooxidation with a low-pressure mercury lamp. The changes that resulted in the surfaces of the films were followed by ESCA. On ozonation, the surface of LDPE initially is oxidized more rapidly than that of HDPE; however, extended ozonation produces a surface composition that corresponds to C₈O for HDPE and to C₁₈O for LDPE. The surface oxidation products are mainly carboxyl groups, with lower levels of carbonyl and C? O groups. For both polymers photooxidation provides more extensively oxidized surfaces than ozonation, although the surface of HDPE oxidizes slightly faster than that of LDPE treated under identical conditions. In both cases the surface stoichiometry after extensive photoxidation is C₆O. The functional groups formed are mainly carboxyl and C? O. The effects of ozonation and photooxidation on the polyethylene surfaces are compared with those produced by several other means of surface oxidation.     

Structure Selectivity of Alkaline Periodate Oxidation on Lignocellulose for Facile Isolation of Cellulose Nanocrystals

Reported here for the first time is the alkaline periodate oxidation of lignocelluloses for the selective isolation of cellulose nanocrystals (CNCs). With the high concentrations as a potassium salt at pH 10, periodate ions predominantly exist as dimeric orthoperiodate ions (H₂I₂O₁₀^4?). With reduced oxidizing activity in alkaline solutions, dimeric orthoperiodate ions preferentially oxidized non‐ordered cellulose regions. The alkaline surroundings promoted the degradation of these oxidized cellulose chains by β‐alkoxy fragmentation and generated CNCs. The obtained CNCs were uniform in size and generally contained carboxy groups. Furthermore, the reaction solution could be reused after regeneration of the periodate with ozone gas. This method allows direct production of CNCs from diverse sources, in particular lignocellulosic raw materials including sawdust (European beech and Scots pine), flax, and kenaf, in addition to microcrystalline cellulose and pulp.     

Some aspects of the ozone degradation of poly(vinyl alcohol)

Poly(vinyl alcohol) (PVAL) forms a strong hydrogen-bond complex with ozone. The interaction energy is of the order of 47.3 kJ/mol as calculated from the blue shift undergone by the ozone absorption band in the UV after its complexation with PVAL. This fact may have many important practical implications in the application of PVAL in wastewater treatment both in terms of O₃ dissolution and persistence in water. Furthermore, PVAL is easily biodegradable but it is also slowly degraded by ozone. It is shown by viscometry, electrical conductimetry and by pH measurements that PVAL is degraded by ozone attack with extensive chain breaking. By FT-IR spectroscopy it has been shown that the final product is a PVAL oligomer with numerous ketonic groups along the main oligomer backbone and with carboxylic end groups. A mechanism of ozone degradation of PVAL has been presented and discussed. The chain scission is based on the ozone oxidation of the alcoholic groups of PVAL with formation of ketonic groups which in turn are the source of a keto-enol tautomerism which leads to random chain scission by further O₃ attack. Viscometric measurements show that the main viscosity drop of PVAL is achieved when a nominal stoichiometric ratio of O₃/PVAL < 0.05 is reached which means one ozone molecule for every >20 PVAL monomeric units. For comparison PVAL has been oxidized also with paraperiodic acid.Ozonized PVAL has been studied by thermal analysis (TGA, DTG and DTA) in comparison to a reference untreated PVAL under N₂. The oxidation of PVAL causes its complete amorphization since the crystalline melting point of PVAL at 235 °C is no longer detectable in the case of ozonized PVAL. In any case ozonized PVAL shows a better thermal stability which can be confirmed for instance by a higher maximum decomposition rate temperature as measured by DTG. This result is in agreement with theoretical calculations made by group increments according to Van Krevelen's method which predicts a higher decomposition temperature for a PVAL having ketonic groups in place of alcoholic moieties in the main polymer backbone.     

Photocatalytic oxidation of arsenite by a composite of titanium dioxide and activated carbon fiber

Preoxidation process is usually needed in the treatment of arsenic-containing drinking water because arsenite (i.e. As[III]) is less easily removed by adsorption. Nano-scale titanium dioxide is an efficient photocatalyst for arsenite oxidation but its application in water treatment is limited due to the difficulty of separation or packed-bed application of the tiny particles. This study synthesized a composite photocatalyst by loading titanium dioxide onto activated carbon fiber (TiO₂/ACF). The effects of calcination temperature, photocatalyst dosage, pH, initial concentration of As(III) and common anions on the oxidation of As(III) were studied. Photocatalytic oxidation of As(III) took place in minutes and followed first-order kinetics. 0.80 mg L⁻¹ of As(III) could be entirely oxidized to As(V) within 30 min in the presence of 3.0 g L⁻¹ photocatalyst and under UV-light irradiation. The oxidation of As(III) occurred in a wide range of pH as examined from 2 to 10 with the oxidation efficiency increasing markedly with pH. The presence of phosphate and silicate significantly decreased As(III) oxidation at pH 7, while the effect of sulfate and chloride was small.     

Degradation of paracetamol in a bubble column reactor with ozone generated in electrolyte-free water using a solid polymer electrolyte filter-press electrochemical reactor

A porous anode composed of β-PbO₂ was electrochemically deposited onto a carbon cloth substrate (e.g., CC/β-PbO₂) aiming for the electrochemical ozone production (EOP) in electrolyte-free water using a solid polymer electrolyte (SPE) filter-press reactor. Scanning electron microscopy (SEM) images revealed the presence of a three-dimensional oxide structure necessary to obtain a fluid-permeable anode. X-ray analysis showed the predominance of the β-PbO₂ phase. The maximum current efficiency for the EOP was 9.5% with an ozone production rate of 1.40 g h^?1. Using a constant ozone production rate of 0.5 g h^?1, the oxidative degradation of paracetamol (PCT) dissolved in water was accomplished as a function of the PCT concentration (20, 30, and 50 mg L^?1) and the pH (acid, natural (without adjustment), and alkaline). The UV-Vis spectrophotometric analysis showed that the degradation process is more pronounced in alkaline media with a strong reduction in the electrical energy per order (E _EO). A reduction of the chemical oxygen demand (COD) of up to 80% was observed. A linear correlation between data referring to COD and HPLC measurements with the UV absorbance measured at 243 nm (UV₂₄₃) was verified indicating that these different techniques can be complementary to each other. The nuclear magnetic resonance (NMR) study of the ozonation by-products revealed that the oxidation of PCT occurred through the rupture of the aromatic ring. The major part of phenol’s ring was oxidized to CO₃ ^2? while no reaction occurs in the acetamide group of paracetamol during the ozonation reaction.     

Mechanistic study of homogeneous reactions coupled with electrochemical oxidation of catechols

The electrochemical oxidation of catechols was described and has shown that these compounds can be oxidized to related o-benzoquinones. The electrochemically generated o-benzoquinones are quite reactive and can be attacked by a variety of nucleophiles under various mechanistic disciplines such as CE, EC, EC′, ECE, ECEC, ECEC ₂, ECECE, ECECEC, ECECECE and trimerization, in which E represents an electron transfer at the electrode surface, and C represents a homogeneous chemical reaction. The mechanistic pathways and final products are depending on some parameters such as electron withdrawing or donating properties of nucleophile, electrolysis medium (solvent, acidity or pH) and nature of catechol.     

Surface modification of poly(methyl methacrylate) for improved adsorption of wall coating polymers for microchip electrophoresis

The development of rapid and simple wall coating strategies for high-efficiency electrophoretic separation of DNA is of crucial importance for the successful implementation of miniaturized polymeric DNA analysis systems. In this report, we characterize and compare different methods for the chemical modification of poly(methyl methacrylate) (PMMA) surfaces for the application of wall coating polymers. PMMA surfaces coated with 40 mol% diethylacrylamide and 60 mol% dimethylacrylamide are compared to the PMMA surfaces first oxidized and then coated with hydroxypropylmethyl-cellulose or poly(vinyl alcohol) (PVA). PMMA oxidation was accomplished with UV/ozone or an aqueous solution of HNO(3) to yield hydrogen-bond donors for the spontaneous adsorption of the coating polymers. Contact angle measurements of UV/ozone exposed PMMA surfaces indicate increase in hydrophilicity, and polymer coated surfaces show a strong dependence on the coating polymer and the oxidation method. Fast and repeatable electrophoretic separations of a 10-base and 20-base DNA ladder were performed in PMMA micro CE devices. All analyses were completed in less than 10 min, resulting in the number of theoretical plates as high as 583 000 in a 7.7 cm long separation channel. The duration of UV/ozone treatment was found to have a considerable impact on separation performance. The microchips irradiated with UV for 10 min and coated with PVA as well as the microchips treated with HNO(3) and coated with HPMC were found to have the best separation performance. These results demonstrate facile and robust methods for the surface modification of PMMA enabling low-cost single use devices for electrophoretic DNA separations.     

Highly efficient degradation of emerging contaminants by magnetic CuO@FexOy derived from natural mackinawite（FeS） in the presence of peroxymonosulfate

In this study,natural mackinawite （Fe S）,a chalcophilic mineral,was utilized to prepare iron/copper bimetallic oxides （Cu O@Fe_xO_y） by displacement plating and calcination process.Various characterization methods prove that Cu⁰is successfully coated on the surface of Fe S,which were further oxidized to Cu O,Fe₃O₄and/or Fe₂O₃during calcination process,respectively.Cu O@Fe_xO_yperformed highly efficient...     

Ozonocatalytic decomposition of glyoxal and glyoxylic and formic acids in the presence of iron(III) ions

Rate constants of reactions of ozone with glyoxal, glyoxylic and formic acid in aqueous solutions at pH 1.5 were determined. It was shown that iron(III) in the form of ions accelerates oxidation of glyoxal and glyoxylic acid, but does not influence reaction between ozone and formic acid. It was established that the catalyst acts effectively if its concentration is comparable to the concentration of the oxidized substrate, the optimal stoichiometric ratio (Fe³⁺/substrate) being close to 1/3. The catalytic reaction mechanism was studied using a competitive chelate ligand, oxalic acid. We concluded that the catalytic activity of iron(III) in the investigated reaction was due to its ability to form chelate complexes in which the substrate was more easily oxidized by molecular ozone.     

Enhanced oxidase-like activity of g-C3N4 nanosheets supported Pd nanosheets for ratiometric fluorescence detection of acetylcholinesterase activity and its inhibitor

The undesirable enzymatic activity of nanozymes under near neutral p H condition and the traditional single signal output always restrict the analytical application of nanozyme-based biosensors.Herein,graphitic carbon nitride nanosheets supported palladium nanosheets composite （Pd/g-C₃N₄） with both oxidase-like activity and fluorescent property is synthesized.Notably,Pd/g-C₃N₄exhibits enhanced oxidase-like activity compared to Pd NSs under p H 7.4.By c...     

Transformations of C<Subscript>2</Subscript>-C<Subscript>4</Subscript> alcohols on the surface of a copper catalyst

The interaction of monoatomic alcohols C₂-C₄ with the surface of a copper catalyst preliminarily oxidized under various conditions was studied by the temperature-programmed reaction method to determine the detailed mechanism of partial oxidation. The conditions of oxygen preadsorption on the surface of copper for the preparation of the desired products were determined. The selective formation of carbonyl compounds was shown to occur at the boundary between reduced and oxidized copper surface regions. The role played by Cu₂O was the deep oxidation of alcohols to CO₂. Alcohols with branched hydrocarbon structures experienced parallel partial oxidation and dehydrogenation, which was related to the high stability of intermediate keto-type compounds.