Oxidation of Dibenzothiophene Catalyzed by Hemoglobin and Other Hemoproteins in Various Aqueous-Organic Media

Biocatalytic oxidation of dibenzothiophene (a model of organic sulfur in coal) with hydrogen peroxide was investigated. It was found that various hemoproteins, both enzymic (e.g., horseradish peroxidase) and nonenzymic (e.g., bovine blood hemoglobin), readily oxidized dibensothiophene to its S-oxide and, to a minor extent, further to its S-dioxide (sulfone). This process catalyzed by hemoglobin (a slaughterhouse waste protein) was studied in a number of monophasic aqueousorganic mixtures. Although hemoglobin was competent as an oxidation catalyst even in nearly dry organic solvents (with protic, acidic solvents being optimal), the highest conversions were observed in predominantly aqueous media. The hemoglobin-catalyzed oxidation of dibenzothiophene at low concentrations of the protein stopped long before all the substrate was oxidized. This phenomenon was caused by inactivation of hemoglobin by hydrogen peroxide that destroyed the heme moiety. The maximal degree of the hemoglobin-catalyzed dibenzothiophene oxidation was predicted, and found, to be strongly dependent on the reaction medium composition.     

Selective precipitation of rare earth orthophosphates with hydrogen peroxide from phosphoric acid solutions

It has been shown for the first time that the use of hydrogen peroxide allows precipitation of rare earth orthophosphates (La–Tb) from phosphoric acid solutions at temperatures below 100°C. Either anhydrous or hydrated orthophosphates with monazite or rhabdophane structure, respectively, can be obtained depending on rare earth element position in lanthanide series and precipitation conditions (orthophosphoric acid and hydrogen peroxide concentration). Hydrated orthophosphates with rhabdophane structure can be prepared by precipitation with hydrogen peroxide for all studied rare earth elements.     

Determination of Sulfur in Trace Amounts

Abstract

An absolute method for the determination of trace amounts of sulfur in water and organic matrices is described. The method involves decomposition of organic samples in an oxygen bomb or oxidation of water samples with hydrogen peroxide. The resultant sulfates are reduced and distilled as hydrogen sulfide by the action of stannous phosphate in anhydrous phosphoric acid. The evolved hydrogen sulfide is absorbed in zinc acetate solution, converted to methylene blue and measured spectrophotometrically at 665 mm. The range is from 2 to 40 μg of sulfur using 1 cm cells.     

Olefin epoxidation with bis(trimethylsilyl) peroxide catalyzed by inorganic oxorhenium derivatives. Controlled release of hydrogen peroxide.

The replacement of organometallic rhenium species (e.g., CH(3)ReO(3)) by less expensive and more readily available inorganic rhenium oxides (e.g., Re(2)O(7), ReO(3)(OH), and ReO(3)) can be accomplished using bis(trimethylsilyl) peroxide (BTSP) as oxidant in place of aqueous H(2)O(2). Using a catalytic amount of a proton source, controlled release of hydrogen peroxide helps preserve sensitive peroxorhenium species and enables catalytic turnover to take place. Systematic investigation of the oxorhenium catalyst precursors, substrate scope, and effects of various additives on olefin epoxidation with BTSP are reported in this contribution.     

Novel Syntheses of Aryl and Benzyl Selenides Promted by Metallic Zinc in Aqueous Media

Introduction Recently, organometallic-type of reactions in aqueous media have attracted a considerable interest in organic syntheses[1-4]. The main advantage of making organometallic reactions in strictly anhydrous organic solvents took place in aqueous media is the ease of the reactions so as to obviate the need for inflammable anhydrous organic solvents and troublesome inert atmosphere. For some reactions, e.g., the alkylations of the carbonyl group in carbohydrates didnt need to be altered to take place in organic solvents[5]. The most commonly used metals are zinc, tin and indium[1-4].     

Hydrogen peroxide synthesis by direct photoreduction of 2-ethylanthraquinone in aerated solutions

A new synthesis method of hydrogen peroxide was investigated by the photoreduction of 2-ethylanthraquinone (AQ) in water-insoluble organic solvents. Through optimizing the photoreduction condition including solvent, atmosphere and irradiated time, the photolysis system of 1,3,5-trimethylbenzene/trioctyl phosphate (3:1) solvent mixture under oxygen atmosphere was found to give a high yield of hydrogen peroxide. Furthermore, the formation mechanism of hydrogen peroxide was proposed, i.e. photoreduction and subsequent oxidation of AQ. The photoreduction of 2-ethylanthraquinone undergoes the hydrogen abstraction from solvent to form the anthrahydroquinone, which is subsequently oxidized by oxygen to give hydrogen peroxide.     

Oxidation of organic sulfur compounds with hydrogen peroxide in the presence of crown ethers

Hydrogen peroxide oxidizes methyl phenyl sulfide and benzothiophene in the presence of crown ethers to the corresponding sulfoxides and sulfones. The oxidation is retarded by amino acids. UV and NMR spectroscopies show that, at the initial stage of oxidation, complexation occurs between crown ether, hydrogen peroxide, and sulfide, as well as between crown ether and amino acid.     

Organic interferences and their elimination in the 2,4-xylenol spectrophotometric method for nitrate

The 2,4-xylenol spectrophotometric method for nitrate involves formation of 6-nitro-2,4-xylenol, which is steam-distilled into an ammonia—water—isopropanol mixture. The yellow color of the ammonium salt of 6-nitro-2,4-xylenol is measured at 455 nm. A detailed study of the possible interferences from 123 representative organic compounds is described; 61 compounds interfered (when present in amounts of 0.1 g in the original sample). The interfering compounds can be classified according to their mode of interference: (1) compounds that are readily nitrated or oxidized by nitrate in the sulfuric acid medium used cause low results; (2) compounds containing the ONO₂ group that hydrolyze to nitrate cause high results; (3) compounds that steam-distil to produce colored solutions; (4) compounds that steam-distil to produce turbid solutions; (5) compounds that hydrolyze, either in water or sulfuric acid solution, to produce inorganic ions or compounds (e.g. Cl^-, S^2-, and H₂O₂) that repress the color development. Three procedures are described for the elimination of the interferences: (1) oxidation of the organic compound with permanganate, reduction of the excess of permanganate with hydrogen peroxide, and destruction of the peroxide by boiling in the presence of Fe(III) catalyst (this is unsuitable for organic compounds containing nitrogen, as there is invariably some oxidation to nitrate); (2) extraction of interfering organic compounds with methyl isobutyl ketone; (3) precipitation—adsorption method involving treatment with zinc sulfate and sufficient sodium hydroxide to precipitate most of the zinc as zinc hydroxide, addition of 3 g of activated carbon, digestion at 55–65°C for 20 min. cooling, dilution, and filtration. Method (3) is applicable to all organic compounds tested except formaldehyde. The amount of organic compound used to test the methods was normally 0.25 g in the solution being treated.     

Macromolecular N-nitroso-acylamines as initiators for polyreactions. I. Synthesis of block copolymers from polycondensates and olefinic monomers,

The synthesis of block copolymers in three-step reactions from linear polycondensates (e.g., nylon 6. nylon 6,6, nylon 6,10 and polyurethane) and olefinic monomers (e.g., styrene, acrylic acid and acrylonitrile, methyl methacrylate, vinyl acetate, vinyl chloride, and isoprene) is reported. Macromolecular radicals are formed by the thermal decomposition of partly nitrosated peptide group containing polycondensates at elevated temperatures (60–200°C). These polyradicals initiate the copolymerization of the olefinic monomers. The conversion and reaction rates were generally high (up to 100% within a few hours). Most of the block copolymers prepared were soluble in organic solvents. Some, however, were insoluble or rubberlike. The reaction mechanism involved are analyzed. Applications are discussed.     

Exploring molecular recognition pathways within a family of gelators with different hydrogen bonding motifs

We report the synthesis of a family of gelators in which alkyl chains are connected to the amino groups of l-lysine methyl ester using a range of different hydrogen bonding linking groups (carbamate, amide, urea, thiourea and diacylhydrazine) using simple synthetic methodology based on isocyanate or acid chloride chemistry. The ability of these compounds to gelate organic solvents such as toluene or cyclohexane can be directly related to the ability of the linking group to form intermolecular hydrogen bonds. In general terms, the ability to structure solvents can be considered as: thiourea<carbamate<amide<urea∼diacylhydrazine. This process has been confirmed by thermal measurements, scanning electron microscopy (SEM) and infrared and circular dichroism spectroscopies. By deprotecting the methyl ester group, we have demonstrated that a balance between hydrophobic and hydrophilic groups is essential—if the system has too much hydrophilicity (e.g., diacylhydrazine, urea) it will not form gels due to low solubility in the organic media. However, the less effective gelators based on amide and carbamate linkages are enhanced by converting the methyl ester to a carboxylic acid. Furthermore, subsequent mixing of the acid with a second component (diaminododecane) further enhances the ability to form networks, and, in the case of the amide, generates a two-component gel, which can immobilise a wide range of solvents of industrial interest including petrol and diesel (fuel oils), olive oil and sunflower oil (renewable food oils) and ethyl laurate, isopropyl myristate and isopropyl palmitate (oils used in pharmaceutical formulation). The gels are all thermoreversible, and may therefore be useful in controlled release/formulation applications.     

Uptake of methacrolein into aqueous solutions of sulfuric acid and hydrogen peroxide

Multiphase acid-catalyzed oxidation by hydrogen peroxide has been suggested to be a potential route to secondary organic aerosol (SOA) formation from isoprene and its gas-phase oxidation products, but the kinetics and chemical mechanism remain largely uncertain. Here we report the first measurement of uptake of methacrolein into aqueous solutions of sulfuric acid and hydrogen peroxide in the temperature range of 253-293 K. The steady-state uptake coefficients were acquired and increased quickly with increasing sulfuric acid concentration and decreasing temperature. Propyne, acetone, and 2,3-dihydroxymethacrylic acid were suggested as the products. The chemical mechanism is proposed to be the oxidation of carbonyl group and C═C double bonds by peroxide hydrogen in acidic environment, which could explain the large content of polyhydroxyl compounds in atmospheric fine particles. These results indicate that multiphase acid-catalyzed oxidation of methacrolein by hydrogen peroxide can contribute to SOA mass in the atmosphere, especially in the upper troposphere.     

Graft polymerization of methyl methacrylate from silica initiated by peroxide groups introduced onto the surface

The surface grafting onto ultrafine silica by the radical polymerization of methyl methacrylate (MMA) initiated by peroxide groups introduced onto the surface was investigated. The introduction of peroxide groups onto the silica surface was achieved by the reaction of hydrogen peroxide with chlorosilyl groups, which were introduced by the treatment of silica with thionyl chloride. The content of diisopropylbenzene peroxide and tert-butyl peroxide groups introduced onto the silica according to the above method was determined to be 0.11 and 0.08 mmol/g, respectively. It was found that the polymerization of MMA is initiated by silica having these peroxide groups. In the polymerization, polyMMA was grafted onto silica surface: the percentage of grafting reached about 70%. Therefore, it was concluded that the polymerization of MMA is initiated by surface radicals formed by the decomposition of peroxide groups on silica and polyMMA is grafted through the propagation from the surface. During the polymerization, ungrafted polyMMA was also formed because of the formation of initiator fragments by the decomposition of peroxide groups: the grafting efficiency of the graft polymerization was 30–40%. PolyMMA-grafted silica produced a stable colloidal dispersion in organic solvents for polyMMA. © 1992 John Wiley & Sons, Inc.     

The analysis of combustion products : The effect of hydrogen peroxide on the reaction of potassium permanganate with organic peroxides in acid solution

Although methyl and ethyl hydroperoxides alone do not react with potassium permanganate in acid solution at room temperature, they can be oxidised by this reagent in the presence of hydrogen peroxide. The apparent equivalents (as compared with hydrogen peroxide) are much lower than usual but, in the presence of excess hydrogen peroxide, the titre due to the organic peroxide is proportional to its original concentration. This forms the basis of a simple titration method which, though empirical, is both rapid and accurate. Since t-butyl hydroperoxide does not react in this way, it may be possible to differentiate the higher peroxides from lower peroxides.     

Facile Hydrolysis and Alcoholysis of Palladium Acetate

Palladium(II) acetate is readily converted into [Pd₃(μ²‐OH)(OAc)₅] ( 1 ) in the presence of water in a range of organic solvents and is also slowly converted in the solid state. Complex 1 can also be formed in nominally anhydrous solvents. Similarly, the analogous alkoxide complexes [Pd₃(μ²‐OR)(OAc)₅] ( 3 ) are easily formed in solutions of palladium(II) acetate containing a range of alcohols. An examination of a representative Wacker‐type oxidation shows that the Pd‐OH complex 1 and a related Pd‐oxo complex 4 can be excluded as potential catalytic intermediates in the absence of exogenous water.     

Heterogeneous oxidation of pyrimidine and alkyl thioethers in ionic liquids over mesoporous Ti or Ti/Ge catalysts

Heterogeneous catalytic oxidation of a series of thioethers (2-thiomethylpyrimidine, 2-thiomethyl-4,6-dimethyl-pyrimidine, 2-thiobenzylpyrimidine, 2-thiobenzyl-4,6-dimethylpyrimidine, thioanisole, and n-heptyl methyl sulfide) was performed in ionic liquids by using MCM-41 and UVM-type mesoporous catalysts containing Ti, or Ti and Ge. A range of triflate, tetrafluoroborate, trifluoroacetate, lactate and bis(trifluoromethanesulfonyl)imide-based ionic liquids were used. The oxidations were carried out by using anhydrous hydrogen peroxide or the urea-hydrogen peroxide adduct and showed that ionic liquids are very effective solvents, achieving greater reactivity and selectivity than reactions performed in dioxane. The effects of halide and acid impurities on the reactions were also investigated. Recycling experiments on catalysts were carried out in order to evaluate Ti leaching and its effect on activity and selectivity.     

Proton‐Conducting Supramolecular Metallogels from the Lowest Molecular Weight Assembler Ligand: A Quote for Simplicity

Oxalic acid has been proven to be the lowest molecular weight organic ligand able to form robust supramolecular metallogel networks in the presence of metal salts. In particular, two novel multifunctional metallogels were readily prepared at room temperature by simple mixing of stock solutions of Cu^II acetate monohydrate or Cu^II perchlorate hexahydrate and oxalic acid dihydrate. Formation of different polymorphs and unprecedented proton conduction under anhydrous conditions were also demonstrated with some of these materials.     

Mechanism of formation of hydrogen trioxide (HOOOH) in the ozonation of 1,2-diphenylhydrazine and 1,2-dimethylhydrazine: an experimental and theoretical investigation

Low-temperature (-78 degrees C) ozonation of 1,2-diphenylhydrazine in various oxygen bases as solvents (acetone-d(6), methyl acetate, tert-butyl methyl ether) produced hydrogen trioxide (HOOOH), 1,2-diphenyldiazene, 1,2-diphenyldiazene-N-oxide, and hydrogen peroxide. Ozonation of 1,2-dimethylhydrazine produced besides HOOOH, 1,2-dimethyldiazene, 1,2-dimethyldiazene-N-oxide and hydrogen peroxide, also formic acid and nitromethane. Kinetic and activation parameters for the decomposition of the HOOOH produced in this way, and identified by (1)H, (2)H, and (17)O NMR spectroscopy, are in agreement with our previous proposal that water participates in this reaction as a bifunctional catalyst in a polar decomposition process to produce water and singlet oxygen (O(2), (1)delta(g)). The possibility that hydrogen peroxide is, besides water, also involved in the decomposition of hydrogen trioxide is also considered. The half-life of HOOOH at room temperature (20 degrees C) is 16 +/- 1 min in all solvents investigated. Using a variety of DFT methods (restricted, broken-symmetry unrestricted, self-interaction corrected) in connection with the B3LYP functional, a stepwise mechanism involving the hydrotrioxyl (HOOO(*)) radical is proposed for the ozonation of hydrazines (RNHNHR, R = H, Ph, Me) that involves the abstraction of the N-hydrogen atom by ozone to form a radical pair, RNNHR(*) (*)OOOH. The hydrotrioxyl radical can then either abstract the remaining N(H) hydrogen atom from the RNNHR(*) radical to form the corresponding diazene (RN=NR), or recombines with RNNHR(*) in a solvent cage to form the hydrotrioxide, RN(OOOH)NHR. The decomposition of these very labile hydrotrioxides involves the homolytic scission of the RO-OOH bond with subsequent "in cage" formation of the diazene-N-oxide and hydrogen peroxide. Although 1,2-diphenyldiazene is unreactive toward ozone under conditions investigated, 1,2-dimethyldiazene reacts with relative ease to yield 1,2-dimethyldiazene-N-oxide and singlet oxygen (O(2), (1)delta(g)). The subsequent reaction sequence between these two components to yield nitromethane as the final product is discussed. The formation of formic acid and nitromethane in the ozonolysis of 1,2-dimethylhydrazine is explained as being due to the abstraction of a methyl H atom of the CH(3)NNHCH(3)(*) radical by HOOO(*) in the solvent cage. The possible mechanism of the reaction of the initially formed formaldehyde methylhydrazone (and HOOOH) with ozone/oxygen mixtures to produce formic acid and nitromethane is also discussed.     

In situ synthesis of gold and silver nanoparticles by using redox-active amphiphiles and their phase transfer to organic solvents

An in situ reduction approach to synthesizing gold and silver nanoparticles by using a series of newly designed, redox-active amphiphiles at basic pH is described. These amphiphiles are the conjugates of a fatty acid (e.g., oleic acid, stearic acid, and lauric acid) and a redox-active amino acid (e.g., tryptophan or tyrosine). The amphiphile-coated nanoparticles are then efficiently transferred from water to different nonpolar organic media (such as benzene, toluene, xylene, cyclohexane, and hexane) simply by acid treatment. The phase-transfer process was monitored by UV/visible spectroscopy and transmission electron microscopy, and the results showed that the average particle size and size distribution remain almost unchanged after transferring to the organic media. The anchoring of the amphiphile to the nanoparticle surface was confirmed by FTIR spectroscopy and thermogravimetric analysis. A mechanism is proposed to describe the stability of colloidal Au and Ag nanoparticles formed in situ and their phase transfer to organic solvents. The presence of the amphiphile increases the thermal stability of the colloidal gold nanoparticle conjugates in organic solvents.     

Large-Scale Enantiomeric Enrichment via Solid State Extraction Using β-Cyclodextrin Crystalline and Anhydrous Acetonitrile as Solid and Liquid Phases

The process-scale enantiomeric enrichment of several adrenergic β-blockers, atropine, and ruelene was accomplished through solid state extraction using anhydrous acetonitrile and β-cyclodextrin crystalline as liquid and solid phases, respectively. This non-chromatographic method has the advantages of easy, low cost operation, simplicity, and a high percentage of enrichment for some of the β-blockers examined in a single batch. The percentage of enrichment in anhydrous acetonitrile was the best for all the racemates studied; however, it dropped dramatically when the extraction was carried out in a liquid phase of low polarity such as petroleum ether. No enantiomeric enrichment was observed in liquid phases that are polar and capable of participating in hydrogen bonding (e.g., methanol). Introducing additives (e.g., acetic acid, triethylamine) to the liquid phase also decreased the percentage of enrichment. Finally, lowering the operating temperature (0 °C) appeared to retard the enantiomeric extraction process, which could be restored to normal level by elevating liquid phase temperature to 28 °C.     

Extraction-spectrometric determination of lead in high-purity aluminium salts

Trace amounts of lead were determined in high purity aluminium salts (especially in ammonium aluminium sulfate) using inductively coupled plasma-optical emission spectrometry (ICP-OES) after extractive pre-concentration and matrix separation. Metals were extracted from the aluminium matrix in the form of chelates with ammonium pyrolidine dithoocarbamate into methyl isobutyketone. The organic extract was digested with nitric acid and hydrogen peroxide. The limit of detection for the determination of lead in crystalline ammonium aluminium sulfate was ca. 0.044 mug g(-1). The relative expanded uncertainty of the lead determination was ca. 23% at the level of 0.2 mug g(-1) and ca. 16% at the level of 1.0 mug g(-1). The main uncertainty contribution was associated with repeatability of the whole analytical procedure.