Showing papers on "Hydrazine published in 1996"

Detection of hydrazine, methylhydrazine, and isoniazid by capillary electrophoresis with a palladium-modified microdisk array electrode.

Abstract: A palladium particle-modified carbon fiber microdisk array electrode was designed and employed in capillary electrophoresis for the simultaneous detection of hydrazine, methylhydrazine, and isoniazid. The Pd-modified microdisk electrode had high catalytic ability for hydrazines and exhibited good reproducibility and stability. The response for hydrazine was linear over 3 orders of magnitude with a correlation coefficient of 0.993. The detection limits for hydrazine, methylhydrazine, and isoniazid were 1.2, 2.1, and 6.2 pg, respectively.

Conductive polymer films as ultrasensitive chemical sensors for hydrazine and monomethylhydrazine vapor.

Abstract: Thin films of the electrically conductive polymer poly(3-hexylthiophene) were investigated as ultrasensitive chemical sensors for hydrazine and monomethylhydrazine vapor. The threshold limit value for these highly toxic species, which are used extensively as rocket fuels, has recently been lowered to 10 ppb for 8-h exposure, necessitating the development of instrumentation with improved sensitivity. The present study describes the fabrication, calibration, and testing of simple, rugged, polymer-based sensors for detection of hydrazines in both ambient and vacuum environments. For reasonable choices of film thickness, initial resistance, and integration time, it is demonstrated that concentrations in the 0.1-100 ppb range can be monitored with an accuracy of ±20%. The sensor can be utilized for both dosimetric and real-time detection. Reproducible fabrication was achieved using standard spin-coating techniques. The polymer sensors exhibit good specificity to hydrazines in the presence of NH(3), amines, and ambient H(2)O and have a shelf-life of several years when stored in cold, dry conditions.

One-pot synthesis of tetrasubstituted pyrazoles—proof of regiochemistry

Abstract: 1-Alkyl-5-amino-3-aryl-4-cyanopyrazoles, useful intermediates for fused heterocyclic systems, are synthesised by a one-pot three-step procedure from acid chlorides, malononitrile and alkylhydrazines. The regiochemistry of the hydrazine incorporation was proved in each case by X-ray crystallography and NMR spectroscopy.

1,1,1-Trimethylhydrazinium Iodide: A Novel, Highly Reactive Reagent for Aromatic Amination via Vicarious Nucleophilic Substitution of Hydrogen.

Abstract: 1,1,1-Trimethylhydrazinium iodide, TMHI, has been shown to be a novel vicarious nucleophilic substitution aminating reagent. It can be used to obtain isomers not produced by reaction with other nucleophilic aminating reagents. It is easily prepared from 1,1-dimethylhydrazine, or directly from hydrazine. Further studies on the use of TMHI and related quaternary hydrazines as nucleophlic aminating reagents are in progress. 1 tab.

Functional analogs for the reduction of certain nitrogenase substrates. Are multiple sites within the Fe/Mo/S active center involved in the 6e – reduction of N 2 ?

Abstract: Reactivity studies of clusters that contain the MFe3S4 cores (M = Mo, V) with catecholate, multicarboxylate (or DMF) ligands coordinated to the Mo (or V) atoms, and Cl ligands coordinated to the Fe atoms have been carried out. These studies show the M/Fe/S single cubane clusters to be effective catalysts in the reduction of nitrogenase substrates such as hydrazine, acetylene and protons to give ammonia, ethylene and dihydrogen respectively. The same molecules do not activate or catalyze the reduction of dinitrogen. The results indicate that the observed catalyses are occurring at the Mo (V) sites by a process that, in the case of hydrazine, involves substrate protonation prior to reduction. The facile catalytic reduction of hydrazine by clusters that contain coordinatively saturated polycarboxylate-bound Mo atoms is rationalized in terms of a possible protonation/proton delivery function of the coordinated polycarboxylate ligands. The reactivity characteristics of the M/Fe/S clusters (structurally quite similar to the nitrogenase cofactor) have led to the suggestion that the Mo (V) atoms may be involved in the reduction of hydrazine in the later stages of dinitrogen reduction.

Catalytic and stoichiometric multielectron reduction of hydrazine to ammonia and acetylene to ethylene with clusters that contain the MFe3S4 cores (MMo, V). Relevance to the function of nitrogenase

Abstract: A functional model for nitrogenase is currently sought in our laboratory in reactivity studies using various single cubane clusters that possess the [MFe 3 S 4 ] n + core, (MMo, n = 3; MV, n = 2). These clusters are used as catalysts for the reduction of enzymatically relevant substrates. Substrates such as hydrazine and acetylene are catalytically reduced by (NEt 4 ) 2 [(Cl 4 -cat) (CH 3 CN) MoFe 3 S 4 Cl 3 ], I , to ammonia and ethylene respectively, in the presence of added protons and reducing equivalents. Hydrazine also is catalytically reduced by the (NEt 4 ) [(DMF) 3 VFe 3 S 4 Cl 3 ] cubane under similar conditions. Gas chromatography was employed to monitor the reduction of acetylene to ethylene and a trace of ethane. Catalysis in excess of 100 turnovers (for hydrazine reduction) and in excess of 15 turnovers (in acetylene reduction) has been demonstrated over a period of 24 h. A study of the acetylene reduction reveals saturation kinetics to be operating at high substrate concentrations. A variable temperature kinetic study of acetylene reduction shows a moderate activation energy ( E act = 9(1) kcal mol −1 ) but a large entropy of activation ( ΔS ‡ = −32(2) cal K −1 mol −1 ) which extrapolates to a significant Gibbs free energy ( ΔG ‡ = 19(1) kcal mol −1 ). These results are consistent with an ordered transition state. Considerable evidence has been amassed which directly implicates the Mo and V atoms as the primary catalytic sites. Replacement of the Mo or V bound, kinetically labile, solvent molecules with non-labile ligands acts to suppress the observed rates of reaction. The Fe sites on I are totally inactive in the reduction of hydrazine, however they have been found to effect acetylene reduction albeit at a markedly reduced rate compared to the Mo site. Catalyst integrity has also been demonstrated by a variety of techniques, primarily EPR spectroscopy which identifies the characteristic S = 3 2 signals of the Mo and V cubanes after at least 18 h reaction time.

Kinetic Studies on the Hydrazine and Phenylhydrazine Reductions of the Escherichia coli R2 Subunit of Ribonucleotide Reductase

Abstract: Samples of the Escherichia coli R2 protein of ribonucleotide reductase (RNR) normally have two components, the fully active tyrosyl radical (Tyr•) and FeIII2-containing protein (∼60%) and the FeIII2-only met-R2 form (∼40%). Reaction with the 1- or multi- (maximum 4-) equiv reagent hydrazine under anaerobic conditions gives biphasic kinetics. From UV−vis absorbance changes, the first stage of reaction corresponds unexpectedly to reduction of the FeIII2 met-R2 component, rate constant 7.4 × 10-3 M-1 s-1 (25 °C) at pH 7.5. The slower second stage is assigned as net reduction of Tyr• and one FeIII of the FeIII2 center, rate constant 1.7 × 10-3 M-1 s-1. Separate experiments with met-R2 protein, and previous evidence from EPR spectroscopy for the formation of an FeIIFeIII intermediate, support such a mechanism. Reduction of the second FeIII is then rapid. The corresponding reduction of the Tyr122Phe R2 variant gives a rate constant of 7.7 × 10-4 M-1 s-1, which is substantially (×10) less than that for met-R2. T...

Gas-phase chemical sensing using electrochemiluminescence

Abstract: Tris (2,2'-bipyridine) ruthenium (III) (Ru(bpy) 3 3+ ), an electrogenerable, chemiluminescent reagent which is electrochemically reversible, has been demonstrated to be a suitable reagent for the sensitive detection of gas-phase hydrazine, and its derivatives dimethyl hydrazine and monomethyl hydrazine. The electrochemical oxidation of Ru(bpy) 3 2+ to Ru(bpy) 3 3+ creates a strong oxidizer, whose reduction back down to Ru(bpy) 3 2+ by reaction with a reducing analyte is typified by the emission of a photon of light centered at 610 nm. A portable and semiportable instrument which rely upon the chemiluminescent reactivity and reversibility of the Ru(bpy) 3 3+ reagent have been designed and tested. Detection limits for hydrazine and its derivatives have been obtained in the low ppb regime, while response times are on the order of seconds to several minutes, depending upon the analyte being examined. The sensitivities of these devices are strongly pH-dependent due to the effect pH has on both the lifetime of the Ru(bpy) 3 3+ reagent, as well as on the reactivity of the hydrazine derivatives.

Hydroxy-group containing acylated nitrogen compounds useful as additives for lubricating oil and fuel compositions

Abstract: Compositions comprising hydroxyl group containing acylated nitrogen compounds, a process for reacting certain carboxylic reactants with olefinic compounds then reacting the product prepared thereby with ammonia, a hydrazine or an amine, products prepared thereby and lubricating oil and fuel compositions.

Electrocatalysis and measurements of hydrazine compounds at glassy carbon electrodes coated with electropolymerized 3,4-dihydroxybenzaldehyde films

Abstract: Chemically modified electrodes exhibiting electrocatalytic response towards hydrazine compounds were prepared by electroxidation of 3,4-dihydroxybenzaldehyde (3,4-DHB) on glassy carbon electrodes. The surface-confined quinone moiety accelerates the slow oxidation of hydrazine or its methylated analogs, and allows their convenient quantitation at very low potentials. Cyclic voltammetry offers useful insights into the catalytic behavior. The electrocatalytic response is evaluated with regard to pH, scan rate, applied potential, hydrazine concentration, flow rate and other variables. When used as flow-injection detector, the 3,4-DHB modified electrode yields an extremely low detection limit of 5 × 10 −8M (32 pg) hydrazine. Applicability to thick-film sensor strips is also illustrated.

Preparation of polymer-bound trityl-hydrazines and their application in the solid phase synthesis of partially protected peptide hydrazides

Abstract: Polymer-bound N-tritylhydrazines 4 were easily prepared by reacting polymeric tritylchlorides 3 with hydrazine. Subsequently, compounds 4 have been successfully applied to the solid phase synthesis of partially protected peptide hydrazides using 1-hydroxybenzotriazolyl esters of Fmoc- or Trt-amino acids. The synthesized peptide hydrazides can be quantitatively split off from the resins by mild acidic treatment, while the benzyl- and tert-butyl protecting groups remain unaffected.

Intermolecular Electron-Transfer Reactions Involving Hydrazines

Abstract: The self-exchange electron-transfer (ET) rate constant k22 for 1,2,3,4,5-pentamethylferrocene was determined by NMR line broadening to be 8.5(±0.8) × 106 M-1 s-1 (25 °C, CD3CN/0.09 M Et4NBF4) and k11 for the bis-N,N-bicyclic hydrazine, 9,9‘-bi-9-azabicyclo[3.3.1]nonane, to be 8.7(0.5) × 103 M-1 s-1 (25 °C, CH2Cl2). These self-exchange rate constants are used to analyze cross reactions of these molecules with hydrazines, ferrocenes, and tetramethyl-p-phenylenediamine (TMPD) using Marcus theory. Cross-reaction rate constants for eight reactions are reported. Included are six cross-reactions between methylferrocenes and four cyclic hydrazines, one hydrazine, hydrazine−reaction, and the reduction of TMPD+ by a cyclic hydrazine. These are the first cross-reaction rate constants reported for hydrazine−hydrazine and hydrazine−TMPD+ ET reactions. The cross-reaction rate constants are used to test the application of Marcus theory to hydrazine ET reactions and to extract estimates of hydrazine self-exchange ET rate...

Regioselective deacetylation of fully acetylated mono- and di-saccharides with hydrazine hydrate

Abstract: Selective deacetylation reactions of the peracetylated reducing disaccharides (1), (5), (9), (15), β-D- glucopyranose (17) and 2-acetamido-2-deoxy-β-D-glucopyranose (19), with 1.2 equiv. Of hydrazine hydrate in acetonitrile, gave predominantly the corresponding heptaacetates (2), (6), (10), (16), the tetraacetate (18) and the triacetate (20), with the free hydroxy group at C1. Reaction of (1) with 1.2 equiv. of hydrazine hydrate in N,N- dimethylformamide also afforded the heptaacetate (2), but in lower yield. When reactions of (1), (5) and (9) were performed with 2.5 equiv. of hydrazine hydrate, deacetylation also occurred at other positions to afford the corresponding hexaacetates (3), (7), (11) and (12), with hydroxy groups at C 1,2 or C 1,3, and the pentaacetates (4), (8) and (13), with hydroxy groups at C 1,2,3. Maltose octaacetate (9), in addition, yielded the tetraacetate (14) in which the free hydroxy groups were located at C1,2,2',3. Compound (15) on treatment with 2.5 equiv. of hydrazine hydrate afforded an intractable mixture. The reaction of methyl 2,3,4,6-tetra-O-acetyl-α-D-glucopyranoside (21) with 2.5 equiv. of hydrazine hydrate gave the 3,4,6-triacetate (22), a mixture of the 2,6- and the 3,6-diacetates (23) and (24), respectively, the 4,6-diacetate (25), and the 6-acetate (26).

Synthesis and reactions of 2-mercaptomethyl-1,3,4-oxadiazolin-5-one

Abstract: The title compound (4) was synthesized from thioglycolic acid hydrazide and ethyl chloroformate. The reactions of4 with aromatic amines, amino derivatives, hydrazine hydrate, hydroxylamine, and formamide were studied. Addition of compound4 to α,β-unsaturated compounds,i.e. chalcones, maleic anhydride, quinones, and acrylonitrile, was investigated.

On the mechanism of electrooxidation of hydrazine on platinum electrodes in acidic solutions

Abstract: A systematic study of the electrooxidation mechanism of hydrazine on Pt electrodes in 0.5 M H2SO4 solutions has been made. The experimental rate equation found is This can be theoretically explained by a five step mechanism. The log I vs. log Chyd linear plot that results in the determination of the reaction order respect to hydrazine concentration can be used as a working curve for quantitative analytical determination of hydrazine concentrations. A mechanistic explanation has been found for the unusual dependence of the Tafel slope with the pH value.

Spectrophotometric Study of the Reaction between Hydrazine and p. dimethylaminobenzaldehyde

Abstract: In order to realize an optical fibre chemical sensor for hydrazine in the Purex process, the reaction between hydrazine and p.dimethylaminobenzaldehyde (p.DMAB) in nitric acid medium was studied by spectrophotometry and 1H.NMR. The effect of temperature and acidity were determined. The equilibrium constant is of 7,800l/mol at 15°C and decreases to 600 at 55°C. The reaction is fully reversible. In order to keep p.DMAB out of damage, the acidity working range has to be within 0.1 to 1.0M nitric acid medium. This reaction is suitable for the application of optical fibre chemical sensors because direct reversibility or regeneration by temperature or acidity may be possible.

Thermal, spectral and magnetic studies on glycine complexes of cobalt(II), nickel(II) and zinc(II) with hydrazine

Abstract: Hydrazinium metal glycinates [(N2H52M(NH2CH2COO)4] and bis(hydrazine)metal glycinates, [M(NH2CH2COO)2(N2H4)2], whereM=Co, Ni or Zn have been prepared and characterized by chemical analyses, magnetic moments and vibrational and electronic spectra. The thermal behaviour of these compounds has been studied by thermogravimetry and differential thermal analyses. These complexes decompose with high exothermicity giving metal powder as the final residue. The X-ray powder data of each set of complexes show isomorphism among themselves.

Optical waveguide fabrication using a polymeric azine containing the 3-dodecylthiophene moiety

Abstract: New polymeric azines, DOZ and DOPh, containing the 3-dodecylthiophene moiety, have been obtained by the condensation reactions of 2,5-diformyl-3-dodecylthiophene with hydrazine and p-diaminobenzene, respectively. Their average molecular masses depend on the preparation conditions. Using DOZ polymers, which are completely soluble in common organic solvents, we were able to demonstrate channel waveguide formation and function. The waveguide losses could be separated into intrinsic absorption losses and scattering contributions.

Method for producing copper powder

Abstract: A method for stably producing a copper powder having a low degree of oxidation comprises generating copper hydroxide by adding an alkali to an aqueous solution containing copper ions, and reducing the copper hydroxide to obtain copper powder as a precipitate by adding hydrazine or a hydrazine compound to the aqueous solution until the aqueous solution yield a pH value in a range of from about 7 to 9.

Recovery of platinum family elements from waste catalysts

Abstract: The process for recovering Pt-family metals from waste catalyst includes such steps as dissolving waste catalyst in solution of sulfuric acid, hydrochloric acid, sodium chlorate and sodium chloride, adsorbing anions of Pt-family metals in solution by using anionic exchange resin, washing the resin with hydrochloric acid or perchloric acid, and reducing the washing liquid with hydrazine hydrate, and features high recovery rate and low cost.