Showing papers on "Hydrazine published in 2006"

Carbon Nanotubes Contain Metal Impurities Which Are Responsible for the “Electrocatalysis” Seen at Some Nanotube-Modified Electrodes

Abstract: Its all done with metals: The title statement is confirmed by comparing the electrocatalytic oxidation of hydrazine at a basal-plane pyrolytic-graphite (BPPG) electrode treated with iron (III) (blue) with that at a multiwalled-carbon-nanotube (MW-CNT)-modified BPPG electrode (red) and at an edge-plane pyrolytic graphite electrode (black; ••••• and -•-• are the responses of iron(III)-treated and MW-CNT-modified BPPG electrode, respectively, in the absence of hydrazine). (Figure Presented) © 2006 Wiley-VCH Verlag GmbH and Co. KGaA.

Quantification of Surface Oxides on Carbonaceous Materials

Abstract: X-ray photoelectron spectroscopy (XPS) in conjunction with chemical derivatization has been developed to quantify the concentrations of hydroxyl, carboxylic acid, and carbonyl groups on carbonaceous surfaces, specifically black carbons (BCs). Control studies on polymers and graphite were performed to establish the selectivity and stoichiometry of each derivatization reaction toward the targeted oxide. Hydroxyl groups were successfully derivatized with trifluoroacetic anhydride. Derivatization strategies using trifluoroethanol, however, had to be modified from protocols used in polymer studies in order to effectively derivatize carboxylic acid groups on BCs. Derivatizing agents previously used to target carbonyl groups on polymers were found unsuitable for BC materials because of nonspecific adsorption interactions between the phenyl ring of the derivatizing agent and the extended graphene sheets of the BCs. These complications were overcome by employing trifluoroethyl hydrazine as a new derivatizing agent...

Electrocatalytic oxidation of ammonia on Pt(111) and Pt(100) surfaces.

Abstract: The electrocatalytic oxidation of ammonia on Pt(111) and Pt(100) has been studied using voltammetry, chronoamperometry, and in situ infrared spectroscopy. The oxidative adsorption of ammonia results in the formation of NHx (x = 0–2) adsorbates. On Pt(111), ammonia oxidation occurs in the double-layer region and results in the formation of NH and, possibly, N adsorbates. The experimental current transients show a hyperbolic decay (t−1), which indicates strong lateral (repulsive) interactions between the (reacting) species. On Pt(100), the NH2 adsorbed species is the stable intermediate of ammonia oxidation. Stabilization of the NH and NH2 fragments on Pt(111) and Pt(100), respectively, is in an interesting agreement with recent theoretical predictions. The Pt(111) surface shows extremely low activity in ammonia oxidation to dinitrogen, thus indicating that neither NH nor N (strongly) adsorbed species are active in dinitrogen production. Neither nitrous oxide nor nitric oxide is the product of ammonia oxidation on Pt(111) at potentials up to 0.9 V, as deduced from the in situ infrared spectroscopy measurements. The Pt(100) surface is highly active in dinitrogen production. This process is characterized by a Tafel slope of 30 mV decade−1, which is explained by a rate-determining dimerization of NH2 fragments followed by a fast decay of the resulting surface-bound hydrazine to dinitrogen. Therefore, the high activity of the Pt(100) surface for ammonia oxidation to dinitrogen is likely to be related to its ability to stabilize the NH2 adsorbate.

Trace Hydrazine Detection with Fluorescent Conjugated Polymers: A Turn‐On Sensory Mechanism

Abstract: Hydrazine, a heavily used industrial chemical, has been implicated as a carcinogen and is readily absorbed through the skin. Its strong reducing power has led to its use as an oxygen scavenger and corrosion inhibitor in various applications involving water-heating systems, as well as a fuel in rocketpropulsion systems. As a result of its toxicity and reactivity, facile detection of hydrazine is also relevant to homeland security. Traditional analytical methods utilized for hydrazine detection include spectrophotometric detection, as well as assorted electrochemical schemes. The expansion of conjugated polymer sensory materials has also led to their application towards the detection of hydrazine. Of primary interest have been the conducting properties of polypyrrole, polythiophene, and polyaniline. To our knowledge, however, amplifying fluorescent polymers (AFPs) have not been explored for hydrazine detection. AFPs show very high sensitivities to quenching analytes such as 2,4,6trinitrotoluene (TNT) via a photoinduced electron-transfer quenching (“turn-off”) mechanism. This sensitivity of fluorescence quenching is due to a combination of interand intrachain exciton transport in thin films. Herein we report a “turn-on” fluorescence detection method for hydrazine vapor with AFPs. We investigated several polymers (P1–P3) for hydrazine detection. These conjugated polymers are structurally related poly(phenylene ethynylene)s (PPEs), varying in their degree of electron density along the polymer chain. The response of P3 to saturated hydrazine vapor (10 s exposure) is given in Figure 1. It is clear from Figure 1 that no new emitting species were generated by exposure to hydrazine since the spectral shape does not change. In addition, the excitation spectrum of the polymer remained the same after the introduction of hydrazine. The other conjugated polymers investigated also showed no change in the shape of their emission spectra upon exposure to hydrazine vapor (see Supporting Information).

Synthesis of FeNi3 alloyed nanoparticles by hydrothermal reduction.

Abstract: The present paper presents a facile and low-cost hydrothermal method to synthesize stoichiometric FeNi3 alloy nanoparticles by reducing Ni(NO3)2·6H2O and Fe(NO3)2·9H2O with hydrazine hydrate in str...

New Practical Synthesis of Indazoles via Condensation of o-Fluorobenzaldehydes and Their O-Methyloximes with Hydrazine

Abstract: The reaction of o-fluorobenzaldehydes and their O-methyloximes with hydrazine has been developed as a new practical synthesis of indazoles. Utilization of the methyloxime derivatives of benzaldehydes (in the form of the major E-isomers) in this condensation effectively eliminated a competitive Wolf−Kishner reduction to fluorotoluenes, which was observed in the direct preparations of indazoles from aldehydes. Reaction of Z-isomers of methyloximes with hydrazine resulted in the formation of 3-aminoindazoles via a benzonitrile intermediate.

Characterization of Iridium Catalyst for Decomposition of Hydrazine Hydrate for Hydrogen Generation

Abstract: A catalyst with an ultra high iridium load was prepared using a method involving multiple impregnations. The obtained iridium catalyst contained between 29 and 35 wt% of 2 nm-sized nanoparticles dispersed on a support such as reinforced alumina, bauxite and precipitated alumina. XAFS suggested a possible structural model of Ir4 surrounded by oxygen. The decomposition of hydrazine hydrate to its elements was used as a probe reaction. The results showed that a catalyst support with a high mechanical strength such as reinforced alumina and bauxite is essential for sustaining the decomposition reaction of hydrazine hydrate where there is a high degree of mechanical and thermal shock. The decomposition reaction of hydrazine monohydrate (N2H4 · H2O) proceeded rapidly to generate a CO x -free hydrogen-rich gas through contact with the iridium catalyst at room temperature.

Pure nickel coating on a mesoporous alumina membrane: Preparation by electroless plating and characterization

Abstract: This work concerns the preparation and characterization of a composite inorganic membrane based on nickel supported on a tubular porous ceramic for use in high temperature hydrogen separation. The characteristics required of this material for a high hydrogen permselectivity are a defect-free coating and thermal stability. Thus, electroless plating of nickel using hydrazine as reducing agent enables a metallic nickel coating to be deposited directly on an asymmetric alumina support having a mesoporous top layer composed of γ-alumina. To optimize conditions for reduction of the metal ion, variables including the temperature, the nature of the nickel salt, the choice of stabilizer and the hydrazine concentrations in the plating bath were studied. Metallic nickel was found to be dispersed both in and on the γ-alumina. After heat treatment at high temperature, a thin and uniform pure Ni˙ layer (thickness ≈ 1–1.5 μm), characterized by scanning electron microscopy (SEM) and X-ray Diffraction (XRD), was formed. The separation performance of the Ni/ceramic membrane was investigated using single gases (hydrogen, nitrogen, carbon dioxide and methane) at room temperature. The results indicate that the mechanism of hydrogen transport is related to the Knudsen diffusion.

Hydrazine determination in sludge samples by high‐performance liquid chromatography

Abstract: A relatively simple and cost-effective method utilizing HPLC with UV detection was developed to detect and quantify hydrazine in sludge samples. The method was developed primarily for sludge samples, but it can also be applicable to soil and other environmental samples. The hydrazines in the matrices were derivatized to hydrazones with benzaldehyde. The hydrazones were separated using HPLC with an RP C-18 column in an isocratic mode with methanol-water (95:5 v/v) and detected with UV detection at 313 nm. The detection limit (25 microL injection) for the method is 0.02 microg/mL of hydrazine.

Solution-Based Deposition Process for Metal Chalcogenides

Abstract: A solution of a hydrazine-based precursor of a metal chalcogenide is prepared by adding an elemental metal and an elemental chalcogen to a hydrazine compound. The precursor solution can be used to form a film. The precursor solutions can be used in preparing field-effect transistors, photovoltaic devices and phase-change memory devices.

Electrochemistry and electrocatalytic activity of catechin film on a glassy carbon electrode toward the oxidation of hydrazine

Abstract: A very stable electroactive film of catechin was electrochemically deposited on the surface of activated glassy carbon electrode. The electrochemical behavior of catechin modified glassy carbon electrode (CMGCE) was extensively studied using cyclic voltammetry. The properties of the electrodeposited films, during preparation under different conditions, and the stability of the deposited film were examined. The charge transfer coefficient (α) and charge transfer rate constant (ks) for catechin deposited film were calculated. It was found that the modified electrode exhibited excellent electrocatalytic activity toward hydrazine oxidation and it also showed a very large decrease in the overpotential for the oxidation of hydrazine. The CMGCE was employed to study electrocatalytic oxidation of hydrazine using cyclic voltammetry, rotating disk voltammetry, chronoamperometry, amperometry and square-wave voltammetry as diagnostic techniques. The catalytic rate constant of the modified electrode for the oxidation of hydrazine was determined by cyclic voltammetry, chronoamperometry and rotating disk voltammetry and was found to be around 10−3 cm s−1 . In the used different voltammetric methods, the plot of the electrocatalytic current versus hydrazine concentration is constituted of two linear segments with different ranges of hydrazine concentration. Furthermore, amperometry in stirred solution exhibits a detection limit of 0.165 μM and the precision of 4.7% for replicate measurements of 40.0 μM solution of hydrazine.

On the mechanism of nitrogen photofixation at nanostructured iron titanate films.

Abstract: The photofixation of dinitrogen to ammonia at a nanostructured iron titanate thin film, prepared from iron(III) chloride and titanium tetraisopropylate, was established by isotopic labeling employing 15,15N2. It is found that traces of iron chloride in the film are required to observe significant amounts of ammonia. It is therefore proposed that the photogenerated hole oxidizes chloride to an adsorbed chlorine atom and the latter subsequently oxidizes ethanol, the reducing agent necessary for ammonia formation. However, thin films obtained from a chloride-free precursor like iron tris-acetylacetonate are also active. Upon prolonged irradiation ammonia is oxidized to nitrate by traces of oxygen. It is found that this final reaction step does not require photoexcitation of the iron titanate thin film but occurs thermally. Titania films exhibit about the same catalytic activity in ammonia oxidation whereas iron oxide films are much less active. Contrary to this thermal reaction step, the reduction of intermediate hydrazine by ethanol occurs only photochemically.

Thermal decomposition of ammonia. N2H4-an intermediate reaction product

Abstract: The paper reports the thermal decomposition of ammonia under dynamic conditions at 800°C in a quartz reactor. Its purpose is to confirm the homogeneous-heterogeneous degenerated branched chain mechanism established in previous studies, which assume the formation of N2H4 as a molecular intermediate; this paper identifies hydrazine as a product of thermal decomposition using FT-IR and UV-VIS spectroscopies.

Aqueous dispersions of polyurethane compositions

Abstract: An aqueous dispersion of polyurethane composites is made by forming a mixture of urethane prepolymer or polymer, ketone functional molecule/oligomers, and hydrazine functional molecular/oligomers; and dispersing the mixture so made in aqueous medium.

Reduction of Ni2+ by hydrazine in solution for the preparation of nickel nano-particles

Abstract: The reduction of Ni2+ by hydrazine in solution for the preparation of nickel nano-particles has been studied It was found that the reactions occur in two stages The first stage is the reduction of Ni2+ by N2H4 according to 2Ni2+ + N2H4 + 4OH− = 2Ni↓ + N2↑+ 4H2O, while the second stage consists of two side reactions, the decomposition of hydrazine (N2H4 = N2↑ + 2H2↑) and the disproportionation of hydrazine (3N2H4 = N2↑ + 4NH3↑) catalyzed by the formed nickel nano-particles The reaction for the formation of nickel is also catalyzed by nickel as an autocatalytic reaction Accordingly, a small amount of inducing agent, NaBH4 can be added to initiate the reaction that can then proceed continuously at 288 K Kinetic study reveals that the reaction orders with respect to Ni2+, N2H4 and Ni are 1, 0 and 1, respectively Thus, the increase of the initial concentration of Ni2+ and the amount of inducing agent used accelerate the reaction rate and decrease the consumption of N2H4 significantly Pure nickel nano-particles with high surface areas are produced and the surface area can increase from 18 to 79 m2/g with the increase of concentration of Ni2+ used The fully understanding of the reaction between Ni2+ and hydrazine in solution may provide a new optimized technique to prepare the nickel catalysts with high surface areas, in addition to the currently available techniques for the preparation of Raney nickel and supported nickel catalysts

Synthesis of some new testosterone derivatives fused with substituted pyrazoline ring as promising 5alpha-reductase inhibitors.

Abstract: Condensation of 3beta-hydroxy-16-[(4-chlorophenyl)methylene]androst-5-en-17-one (1) with hydrazine hydrate in acetic acid afforded N-acetyl pyrazoline derivative 2, while condensation of 1 with semicarbazide afforded compound 3. Also, compound 1 was treated with hydrazine hydrate in absolute methanol or ethanol to afford the corresponding alpha-methoxy (4) and alpha-ethoxy (5) derivatives, which were cyclized with etherated boron trifluoride to the pyrazoline derivative 6. The latter could be prepared directly by refluxing 1 with hydrazine hydrate in dioxane. Oxidation of compound 6 with Oppenour or Moffat oxidizing agents yielded 3-oxo-derivatives 7 and 8, respectively. On the other hand, condensation of compound 1 with substituted hydrazines, gave the corresponding 3beta-hydroxyandrostenopyrazolines 9a,b, which were oxidized using the Moffat method to give 3-oxo-androstenopyrazolines 10a,b, which were condensed with ethylene triphenyl-phosphorane in DMSO to yield 3-ethylene androstenopyrazolines 11a,b. Dehydrogenation of 9a,b with Wettestein oxidation afforded Delta4,6-diene-3-one analogues 12a,b, which were treated with chloranil to yield Delta(4,6,8(14))-tri-ene-3-one analogues 13a,b. Oppenour oxidation of 9a,b afforded Delta4-ene-3-one analogues 14a,b, which were treated with dichlorodicyanoquinone (DDQ) in dioxane to give Delta1,4,6-triene-3-one analogues 15a,b. Pharmacological screening showed that many of these compounds inhibit 5alpha-reductase activity.

Catalytic reduction of hydrazine to ammonia by a vanadium thiolate complex.

Abstract: Vanadium(III) thiolate complexes, [V(PS3‘ ‘)(Cl)]- [1a; PS3‘ ‘ = P(C6H3-3-Me3Si-2-S)33-] and [V(PS3‘)(Cl)]- [1b; PS3‘ = P(C6H3-5-Me-2-S)33-], were synthesized and characterized. Complex 1a serves as a precursor for the catalytic reduction of hydrazine to ammonia. The spectroscopic and electrochemical studies indicate that hydrazine is bound and activated in a VII state.

1,3‐Diketones from Acid Chlorides and Ketones: A Rapid and General One‐Pot Synthesis of Pyrazoles.

Abstract: [reaction: see text] 1,3-Diketones were synthesized directly from ketones and acid chlorides and were then converted in situ into pyrazoles by the addition of hydrazine. This method is extremely fast, general, and chemoselective, allowing for the synthesis of previously inaccessible pyrazoles and synthetically demanding pyrazole-containing fused rings.

Microwave-Assisted Preparations of Amidrazones and Amidoximes

Abstract: In an operationally straightforward and efficient method, amidrazones 1a−h and amidoximes 2a−h are prepared in yields of 65−87% from imidoylbenzotriazoles 3a−h by microwave heating for 5−20 min with the appropriate hydrazine or hydroxylamine.

Aqueous Polyurethane Compositions

Abstract: An aqueous polyurethane composition comprising a polyurethane which is the reaction product of: (A) an isocyanate-terminated prepolymer and (B) at least one active- hydrogen chain-extending compound comprising at least 0.20 stoichiometric equivalents with respect to the isocyanate content of the isocyanate-terminated prepolymer (A), of an active-hydrogen chain-extending compound selected from the group consisting of hydrazine, hydrazine derivatives and mixtures thereof; and wherein at least 0.2 stoichiometric equivalents of the anionic or potentially anionic water-dispersing groups are neutralised with ammonia.