Showing papers on "Reagent published in 1996"

Chemical Redox Agents for Organometallic Chemistry

Abstract: 1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

2,4-Dichlorophenol Oxidation Kinetics by Fenton's Reagent

Abstract: Oxidation kinetics and mechanisms of 2,4-dichlorophenol (2,4-DCP) by Fenton's reagent were studied. The effect of pH, concentration of H2O2, and Fe2+, and 2,4-DCP on both oxidation and dechlorination kinetics was investigated. A mathematical model was developed to describe the kinetics of 2,4-DCP oxidation and chloride ion production at constant concentrations of H2O2 and Fe2+. The optimal ratio of H2O2 to Fe2+ for the oxidation of 2,4-DCP was determined to be 11 which is the same as predicted by the previously developed kinetic model.

A Novel Oxidizing Reagent Based on Potassium Ferrate(VI)(1).

Abstract: A new, efficient preparation has been devised for potassium ferrate(VI) (K(2)FeO(4)). The ability of this high-valent iron salt for oxidizing organic substrates in nonaqueous media was studied. Using benzyl alcohol as a model, the catalytic activity of a wide range of microporous adsorbents was ascertained. Among numerous solid supports of the aluminosilicate type, the K10 montmorillonite clay was found to be best at achieving quantitative formation of benzaldehyde, without any overoxidation to benzoic acid. The roles of the various parameters (reaction time and temperature, nature of the solvent, method of preparation of the solid reagent) were investigated. The evidence points to a polar reaction mechanism. The ensuing procedure was applied successfully, at room temperature, to oxidation of a series of alcohols to aldehydes and ketones, to oxidative coupling of thiols to disulfides, and to oxidation of nitrogen derivatives. At 75 degrees C, the reagent has the capability of oxidizing both activated and nonactivated hydrocarbons. Toluene is turned into benzyl alcohol (and benzaldehyde). Cycloalkanes are also oxidized, in significant (30-40%) yields, to the respective cycloalkanols (and cycloalkanones). Thus, potassium ferrate, used in conjunction with an appropriate heterogeneous catalyst, is a strong and environmentally friendly oxidant.

Handbook of Grignard Reagents

Abstract: Part 1 Methods of Grignard reagent preparation: common method of Grignard reagent preparation preparation of Grignard reagents from olefins and acetylenes magnesium activation. Part 2 Safe handling practices: safe handling practices of industrial scale Grignard reagents. Part 3 Analyses of Grignard reagents: wet analyses of Grignard reagents infrared and raman spectroscopy nuclear magnetic resonance analysis of Grignard reagents crystal structures of Grignard reagents. Part 4 Mechanisms and structure-reactivity relationships: mechanism of Grignard reagent formulation mechanism of reactions in Grignard reagents structure-reactivity relationships the composition of Grignard reagents in solution - the Schlenk equilibrium and its effect on reactivity effect of tris(pyrazolyl)hydrobotato ligation. Part 5 General reactions of Grignard reagents: nucleophilic substitution with electrophilic organic, main group and transition metal species nucleophilic addition to unconjugated C-C multiple bond nucleophilic addition of C-C multiple bonds - O, S, N, P nucleophilic addition to conjugated carbon-carbon bonds nucleophilic addition to conjugated carbon-heteroatom multiple bonds - O, S, N nucleophilic addition to organometallic vinylidene and allyl complexes. Part 6 Special topics - applications and reactions of Grignard reagents: the Barbier reaction Grignard reagents as bases Sn2 versus Sn21 dihalide-derived di-Grignard reagents - preparation and reactions formation and reactions of substituted (2-butene-1,4-diyl)magnesium complexes spiroannulations using substituted (2-butene-1,4-diyl)magnesium complexes asymmetric synthesis using Grignard reagents metal-catalyzed reactions the preparation of 1,1-bimetallics of magnesium and zinc alkynyl Grignard reagents and their uses Grignard reagents and silanes Ziegler-Natta catalysis organomagnesium compounds as polymerization initiators.

A low-temperature solution phase route for the synthesis of silicon nanoclusters

Abstract: We report here a new solution phase synthesis for producing crystalline silicon nanoclusters at significantly lower temperatures than previously required. In addition, it is performed at ambient pressure and yields a particle surface that can be modified by chemical methods. This method has the potential to yield large amounts of silicon nanocrystals in addition to providing reliable control over size distribution and surface termination. In this synthesis we use the Zintl salt KSi as a starting reagent. KSi is synthesized by reacting excess K with silicon at 650{degree}C for three days and subliming off the excess K at 275{degree}C under vacuum. The purity of the air-sensitive, black solid is verified by powder X-ray diffraction. 23 refs., 1 fig.

Identification of Cu+ as the effective reagent in nitric oxide formation from S-nitrosothiols (RSNO)

Abstract: Decomposition of S-nitrosothiols (RSNO) in aqueous solution at pH 7.4 is brought about by copper ions, either present as an impurity or specifically added. The primary products are nitric oxide and the disulfide. In the presence of the specific Cu+ chelator, neocuproine, reaction is progressively inhibited as the [neocuproine] is increased, the reaction eventually stopping completely. The characteristic UV–VIS spectrum of the Cu+ adduct can be obtained from the reaction solutions. This shows clearly that Cu+ and not Cu2+ is the effective catalyst. Two limiting kinetic conditions can be identified for a range of S-nitrosothiols at specific copper ion concentrations (a) a first-order dependence and (b) a zero-order dependence upon [RSNO]. Normally both situations also have a short induction period. This induction period can be removed by the addition of the corresponding thiol RSH. A mechanism is proposed in which Cu+ is formed by reduction of Cu2+ by thiolate anion via an intermediate, possibly RSCu+. Loss of nitric oxide from RSNO is then brought about by Cu+, probably via another intermediate in which Cu+ is bound to the nitrogen atom of the NO group and another electron-rich atom (such as nitrogen from an amino group, or oxygen from a carboxylate group) involving a six-membered ring. As well as NO this produces both RS– and Cu2+ which then are part of the cycle regenerating Cu+. Thiolate ion is oxidised to RS˙ which dimerizes to give the disulfide. Depending on the structure (and hence reactivity) of RSNO either Cu+ formation or its reaction with RSNO can be rate-limiting. Computer modelling of the reaction scheme allows the generation of absorbance time plots of the same forms as those generated experimentally, i.e. first- or zero-order, both with or without induction periods. We suggest that the thiolate ion necessary to bring about Cu2+ reduction is either present as a thiol impurity or is generated in small quantities by partial hydrolysis of the nitrosothiol, which results in an induction period. Addition of small quantities of thiol removes the induction period and leads to catalysis but larger quantities bring about a rate reduction by, it is suggested, complexation of the Cu2+. For two very unreactive substrates, S-nitrosoglutathione and S-nitroso-N-acetylcysteine very large induction periods were observed, typically three hours. This results, we suggest, from competitive re-oxidation of Cu+ to Cu2+ by the dissolved oxygen. Experiments carried out anaerobically confirm this, since there is then no induction period. Addition of hydrogen peroxide extends the induction period ever further. The results are discussed in terms of the biological properties of S-nitrosothiols which are related to nitric oxide release.

Detection of transmembrane potentials by optical methods

Abstract: Methods and compositions are provided for detecting changes in membrane potential in membranes biological systems. In one aspect, the method comprises: a) providing a living cell with a first reagent comprising a charged hydrophobic molecule which is typically a fluorescence resonance energy transfer (FRET) acceptor or donor, or is a quencher and is capable of redistributing within the membrane of a biological membrane in response to changes in the potential across the membrane; b) providing the cell with a second reagent that can label the first face or the second face of a biological membrane within the cell; c) detecting light emission from the first reagent or the second reagent. One aspect of this method involves monitoring membrane potential changes in subcellular organelle membranes in a living cell. Another aspect of the invention is the use of certain embodiments of the method for the screening of test chemicals for activity to modulate the activity of a target ion channel. Another aspect of the present invention is a transgenic organism comprising a first reagent that comprises a charged hydrophobic fluorescent molecule, and a second reagent comprising a bioluminescent or naturally fluorescent protein.

Sensor and production method of and measurement method using the same

Abstract: There is provided a sensor for the measurement of a content of a material in liquid which material is oxidized with an oxidase enzyme in which sensor a reagent layer is formed on an electrode system composed of a measuring electrode and a counter electrode both of which are formed on an insulating substrate, the reagent layer is composed of a hydrophilic polymer layer comprising a hydrophilic polymer and a reactive layer comprising the oxidase enzyme and an electron carrier, and the reagent layer further comprises a phosphate.

Degradation/decoloration of concentrated solutions of Orange II. Kinetics and quantum yield for sunlight induced reactions via Fenton type reagents

Abstract: Light and thermal processes involving Fenton reagent are shown to be effective in the mineralization/decoloration of concentrated Orange II solutions. Light activation accelerates the observed degradation and the UV component of natural sunlight is sufficient to promote the reaction leading to the azo-dye abatement. The degradation involves dark and light steps. Kinetic information on these steps is reported. The results obtained in this study suggests that the thermodynamic potential for the redox couple in a Fenton-like reagent is not the most important factor controlling ther degradation of this dye. A quantum yield of 0.10 was observed for Orange II disappearance. Decoloration of a 2.9 mM dye solution (450 mg Cl−1) is achieved in less than 2 h via photo-Fenton reactions and mineralization is completed to 95% in less than 8 h. A turnover number of 4.7 was estimated for light induced processes in the model system used. Cyanuric acid added to the Fenton system suggests that besides the OH radicals, highly stable Fe-complexes in combination with H2O2 are active in the abatement of this azo-dye. Near surface radical formation is shown to be important during the observed photocatalysis. No activation energy was detected during the mineralization suggesting a radical mechanism for this reaction. The quantum yields observed as a function of wavelength during Orange II disappearance corresponds in experimental error to the point-by-point addition of the absorbance of the Fe3+ and H2O2 solutions used in the photolysis.

Cationic Derivatization of Oligosaccharides with Girard's T Reagent for Improved Performance in Matrix-assisted Laser Desorption/Ionization and Electrospray Mass Spectrometry

Abstract: Oligosaccharides were derivatized by hydrazone formation with Girard's T reagent in order to introduce a cationic site for detection by matrix-assisted laser desorption/ionization (MALDI) and by electrospray mass spectrometry. The derivative was prepared in high yield and did not require extensive clean-up prior to mass spectrometric examination, unlike the products of the more commonly used reductive amination derivatization. The derivatives gave a ten-fold increase in detection sensitivity over that afforded by the underivatized oligosaccharides and provided intense spectra in positive-ion electrospray without the need to add cations to the solvent. In addition, the use of these derivatives removed ambiguities caused by the presence of MK+ ions that accompany the MNa+ ions formed from the underivatized sugars in MALDI. Furthermore, Girard's T derivatization overcame problems associated with the presence of reducing-terminal, N-acetylamino groups that were often introduced when the oligosaccharides were prepared by cleavage from glycoproteins with hydrazine.

Hypervalent Iodine Chemistry: New Oxidation Reactions Using the Iodosylbenzene−Trimethylsilyl Azide Reagent Combination. Direct α- and β-Azido Functionalization of Triisopropylsilyl Enol Ethers

Abstract: Treatment of triisopropylsilyl (TIPS) enol ethers with PhIO/TMSN3/at −18 to −15 °C rapidly (5 min) gave β-azido TIPS enol ethers in high yields, with only traces of the α-azido adduct. The reaction...

Remotely-controlled production of the 5-HT1A receptor radioligand, [carbonyl-11C]WAY-100635, via 11C-carboxylation of an immobilized Grignard reagent

Abstract: WAY-100635 [N-(2-(1-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl))-N-(2-pyridyl)-cyclohexanecarboxamide], when labelled in its carbonyl position with carbon-11 (t 1/2 = 20.4 min), is an effective radioligand for the study of 5-HT 1A receptors in human brain with positron emission tomography (PET). A simple remotely-controlled procedure was developed for the routine synthesis of [carbonyl- 11 C]WAY-100635. Thus, cyclohexylmagnesium chloride is coated onto the inner surface of a narrow polypropylene tube. Cyclotron-produced [ 11 C]carbon dioxide is passed into the tube in a nitrogen stream. A solution of thionyl chloride in tetrahydrofuran is then passed through the tube to convert the trapped radioactive adduct into [carbonyl- 11 C]cyclohexanecarbonyl chloride and to release this labelling agent into a vial containing 1-(2-methoxyphenyl)-4-(2-(2-pyridylamino)ethyl)piperazine plus triethylamine. The vial is sealed and heated to 70'C for 5 min. [carbonyl 11 C]WAY-100635 is isolated by sample-enrichment and reverse phasc HPLC and formulated for human intravenous injection by evaporation of solvent and dissolution in 'saline for injection'. The novel use of the immobilized Grignard reagent has the advantages that only small quantifies of all reagents are required so simplifying product purification. Moreover, the procedure was readily adapted for operation in a shielded hot-cell with remote control for radiation safety. The remotely-controlled radiosynthesis takes 45 min and gives high radioactivities (2.96-5.92 GBq) of formulated [carbonyl- 11 C]WAY-100635 in > 99% radiochemical purity and high specific radioactivity (average, 192 GBq/μmol).

Chemical vapor deposition and powder formation using thermal spray with near supercritical and supercritical fluid solutions

Abstract: A method for chemical vapor deposition using a very fine atomization or vaporization of a reagent containing liquid (T) or liquid-like fluid (T) near its supercritical temperature, where the resulting atomized or vaporized solution (N) is entered into a flame or a plasma torch (170), and a powder is formed or a coating is deposited onto a substrate (190). The combustion flame (170) can be stable from 10 torr to multiple atmospheres, and provides the energetic environment in which the reagent contained within the fluid (T) can be reacted to form the desired powder or coating material on a substrate (190). The plasma torch likewise produces the required energy environment, but, unlike the flame, no oxidizer is needed so materials stable in only very low oxygen partial pressures can be formed. Using either the plasma torch or the combustion flame (170), coatings can be deposited and powders formed in the open atmosphere without the necessity of a reaction chamber, but a chamber may be used for various reasons including process separation from the environment and pressure regulation.

An Oxidative Intramolecular Phenolic Coupling Reaction for the Synthesis of Amaryllidaceae Alkaloids Using a Hypervalent Iodine(III) Reagent

Abstract: The oxidative intramolecular phenolic coupling reaction of norbelladine derivatives (1) was investigated with the aim of preparing amaryllidaceae alkaloids. Spirodienone compounds (2), which are intermediates for the synthesis of an amaryllidaceae alkaloid, (+)-maritidine, or phenol ether derivatives containing the 5,6,7,8-tetrahydrobenzazocine systems (9), were selectively obtained by the reaction of 1 and the hypervalent iodine(III) reagent, phenyliodine(III) bis(trifluoroacetate) (PIFA). Both p−p‘ coupling (11) and p−o‘ coupling spirodienone compounds (12) were obtained by the reaction of phenol derivatives having an alkoxy group at the C-3‘ position (10) with PIFA.

Decomposition of hydroxybenzoic and humic acids in water by ultrasonic irradiation

Abstract: Sonochemical decomposition of a series of hydroxybenzoic acids such as monohydroxy-, 3,4-dihydroxy-, 3,4,5-trihydroxybenzoic acids, tannic acid, and reagent and prepared humic acids in water under argon or air atmosphere was investigated. The decomposition followed first-order kinetics at initial stage, and initial rates were in the range of 1.9−5.1 μM min-1 under argon and 1.9−16.4 μM min-1 under air. The rates of OH radical formation in the sonolysis of water were estimated to be 20 μM min-1 under argon and 15 μM min-1 under air from the yield of Fe(III) formed by the sonication of Fe(II) solution. The decomposition of 3-hydroxybenzoic acid was almost completely inhibited by the addition of 0.1 mM t-BuOH, which is an effective scavenger of OH radicals. It is suggested that, in sonolysis under argon, the main sonochemical decomposition of the substances employed in this study proceeds via reactions with OH radicals in the bulk solution and that the contribution of thermal decomposition in cavitation bubb...

Release tag compounds producing ketone signal groups

Abstract: A release tag reagent suitable for use in the chemical analysis of a substance to be detected comprises signal, release, and reactivity groups. A class of release tag compounds that are cleaved to release as signal groups very stable electrophoric ketones which are sufficiently volatile for determination in the gas phase of an analytical reaction mixture is disclosed.

Nanoscale Metal Oxide Particles/Clusters as Chemical Reagents. Adsorption of Hydrogen Halides, Nitric Oxide, and Sulfur Trioxide on Magnesium Oxide Nanocrystals and Compared with Microcrystals

Abstract: Adsorption of HCl, HBr, NO and SO3 on nanoscale MgO (autoclave prepared = AP-MgO) and microscale MgO (conventionally prepared = CP-MgO) has been studied. The higher surface area of AP-MgO allows a higher capacity of these gases to be adsorbed/mol MgO. However, at pressures of 100 Torr or higher, the amounts adsorbed/nm2 for HX and SO3 are larger on the microcrystals. This is explained as due to the formation of ordered multilayers of adsorbate on the more perfect crystals of CP-MgO (adsorption on flatter, more extended planes). In the case of NO, the different surface chemistry of AP-MgO vs CP-MgO is again demonstrated. In this case, AP-MgO adsorbed more NO/nm2, and NO2, N2, and N2O were formed on the surface. The high surface area and unusual surface reactivity of nanoscale MgO allows it to be considered as a new type of adsorbent as well as a near-stoichiometric chemical reagent.

Chemical Redox Agents for Organometallic Chemistry

Abstract: 1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

A model for prediction of selective noncatalytic reduction of nitrogen oxides by ammonia, urea, and cyanuric acid with mixing limitations in the presence of co

Abstract: A reduced chemical kinetic mechanism for the prediction of selective noncatalytic reduction (SNCR) chemistry has been developed and incorporated into a three-dimensional. CFD-based turbulent reacting flow model. The model can be used for prediction and investigation of thermal and mixing effects as well as the influence of CO on the SNCR process in practical systems. The model accurately describes the SNCR chemistry as indicated by comparisons of NO reduction efficiency, ammonia slip, and N2O emissions with predictions using a complete chemical mechanism (70 species, 327 reactions) and experimental measurements from independent investigators. The reduced mechanism (6 species, 7 reactions) and individual rate constants are provised so that the mechanism could be incorporated into any CFD-based computer code. The effects of thermal environment (injection temperature and quench rate), reactant ratios (initial NO and NH3/NO), and reagent mixing on NO reduction by ammonia were investigated in the presence and absence of CO using a pilot-scale facility. Comparison with the coupled CFD/chemistry model predictions indicated good agreement, and both suggest that SNCR effectiveness is critically influenced by (1) finiterate chemistry, (2) imperfect reagent dispersion, (3) mixing delay times, (4) local CO concentrations, and (5) nonisothermal temperature profile.