Hydrazine In Aqueous Solution Research Articles

Palladium Nanoparticles by Electrospinning from Poly(acrylonitrile-co-acrylic acid)−PdCl2 Solutions. Relations between Preparation Conditions, Particle Size, and Catalytic Activity

Catalytic palladium (Pd) nanoparticles on electrospun copolymers of acrylonitrile and acrylic acid (PAN-AA) mats were produced via reduction of PdCl2 with hydrazine. Fiber mats were electrospun from homogeneous solutions of PAN-AA and PdCl2 in dimethylformamide (DMF). Pd cations were reduced to Pd metals when fiber mats were treated in an aqueous hydrazine solution at room temperature. Pd atoms nucleate and form small crystallites whose sizes were estimated from the peak broadening of X-ray diffraction peaks. Two to four crystallites adhere together and form agglomerates. Agglomerate sizes and fiber diameters were determined by scanning and transmission electron microscopy. Spherical Pd nanoparticles were dispersed homogeneously on the electrospun nanofibers. The effects of copolymer composition and amount of PdCl2 on particle size were investigated. Pd particle size mainly depends on the amount of acrylic acid functional groups and PdCl2 concentration in the spinning solution. Increasing acrylic acid concentration on polymer chains leads to larger Pd nanoparticles. In addition, Pd particle size becomes larger with increasing PdCl2 concentration in the spinning solution. Hence, it is possible to tune the number density and the size of metal nanoparticles. The catalytic activity of the Pd nanoparticles in electrospun mats was determined by selective hydrogenation of dehydrolinalool (3,7-dimethyloct-6-ene-1-yne-3-ol, DHL) in toluene at 90 °C. Electrospun fibers with Pd particles have 4.5 times higher catalytic activity than the current Pd/Al2O3 catalyst.

Synthesis of cobalt disulfide nanoparticles in polymer matrix

Amorphous rod-like and needle-like nanoparticles of cobalt disulfide were prepared by the reaction of CoCl 2·6H 2O with thiourea in the presence of some hydrazine in aqueous solution. The reaction was undertaken in an open reflux system at a relatively low temperature. Polycrystalline cobalt disulfide nanorods were obtained by a similar reaction in an alcohol/water mixed solution. The products were characterized by Fourier transform infrared spectrometer (FTIR), X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The effects of solvent, temperature and time of the reaction on the formation of cobalt disulfide nanocrystalline were discussed. It was found that hydrazine played an important role in shaping rod- or needle-like nanoparticles, and the reflux temperature and time mainly influenced the crystallization of nanoparticles. In addition, the microwave (wavelength λ=3 cm) absorption property of this nanocomposite at room temperature was also investigated.

Synthesis and characterization of reduced transition metal oxides and nanophase metals with hydrazine in aqueous solution

Reduction of the first row (3d) transition metal complexes in aqueous solution using hydrazine as the reducing agent has been investigated systematically. Nanoscale reduced metal oxides such as VO 2(B), Cr 2O 3 were obtained through hydrazine reduction followed by proper thermal treatments. Nanocrystalline γ-Mn 2O 3 was synthesized directly through aqueous phase reduction at room temperature. Nanoclusters of cobalt, copper and the one-dimensional single crystal nickel nanowhiskers were synthesized by direct reduction without post-annealing process. All the products were characterized on their structure and micro-morphology. The reaction details and features were described and discussed.

Nitrogen Trioxide in Irradiated Aqueous Nitric Acid Solutions of Hydrazine

The rate constants of reactions of the NO3•radical with hydrazoic acid (7.6 × 106l mol–1s–1) and the hydrazonium ion (2.3 × 106l mol–1s–1) in 6 M nitric acid at 290 ± 2 K were measured by a pulse radiolysis technique. The reaction scheme was refined by the computer simulation of the γ-radiolysis of aqueous nitric acid solutions of hydrazine with the use of the measured rate constants and published data on the reactivity of intermediates. The results of computations were compared with experimental data on the continuous radiolytic degradation of hydrazine in aqueous 2 M nitric acid solutions at 313 K.

Thioureas from 3-aminoquinazolin-4(3H)-one. 2. Unusual alkaline recyclization of 3-(N",N",S-trialkylisothioureido)quinazolin-4(3H)-ones into new 1,3,4-oxadiazoles

3-(N",N",S-trialkylisothioureido)quinazolin-4(3H)-ones obtained by the reactions of 3-(N",N"-dialkylthioureido)quinazolin-4(3H)-ones with alkyl halides undergo unusual recyclization into 5-(2-aminophenyl)-2-dialkylamino-1,3,4-oxadiazoles under the action of aqueous solutions of alkali, hydrazine, and primary aliphatic amines. A plausible mechanism of the recyclization was proposed.

Use of Conducting Electroactive Polymers for Drug Delivery and Sensing of Bioactive Molecules. A Redox Chemistry Approach

We have examined the properties of polypyrrole (PPy) as a model electroactive membrane which can simultaneously serve as a medium sensing, and bioactive molecule releasing, material using optical spectroscopic, potentiometric, and conductometric methods. In particular, PPy membranes can sense hydrazine in aqueous solution with linear logarithmic potentiometric and conductometric responses between 10-4 and 10-1 M. The sensing properties of the PPy membranes are discussed in terms of both its redox properties and specific acid−base behavior. Adenosine triphosphate (ATP) has been used as a model drug which is easily loaded into PPy during electrochemical synthesis. ATP release processes from PPy/ATP membranes have been studied spectroscopically using electrochemical and chemical triggering. Electrochemical triggering allowed ATP to be delivered with a variety of release profiles and adjustable rates (up to 20 μg cm-2 min-1 for a 10 μm thick membrane). The mass transfer through the membranes has been successf...

On the mechanism of the γ-radiolysis of deoxygenated aqueous solutions of hydrazine

A reaction mechanism has been devised by trial and error that accounts for most of the data that have been obtained from γ-radiolysis studies under deaerated conditions and which hitherto have not been satisfactorily explained. The major features of the proposed mechanism are the following. (a) Hydrazyl radicals N2H4•+ and •N2H3 react by disproportionation to form N2H2 and hydrazine, and by combination either as the free radicals or with one of them complexed with a hydrazine molecule, N2H5+ or N2H4, to produce N2 + 2NH3. This accounts for the observed strong dependence of the radiolytic decomposition yields (G-values) on [N2H5+]. (b) Hydrogen atoms (hydrated electrons) are proposed to react with N2H5+ (N2H4) by a split path to form H2 + N2H4•+ (•N2H3) and •NH2 + NH4+ (NH3), which helps to account for the observed values of G(H2); reduction of N2H2 by H• to •N2H3 is also required to explain fully the values of G(H2). (c) In alkaline solution the decrease in decomposition yields is explained in terms of the dissociation of H2O2 to HO2−, which is more readily oxidised to O2•−. This, together with the much longer lifetime of O2•− at high pH, results in the reduction by O2•− of •N2H3 back to N2H4. The effect of added H2O2 in acidic solution can be explained if it forms a complex with N2H4•+ followed by reaction with another N2H4•+ to form N2 + 2H2O.

Application of aqueous hydrazine solution for beta-elimination of O-glycans from gastric mucin.

O-Glycans from pig gastric mucin were released by beta-elimination in 0.2 M triethylamine and 50% aqueous hydrazine solution. The released glycan hydrazides were isolated using Centricon 10 separators, brought to their reducing form and reductive by labelled with p-aminobenzoic acid ethyl ester (ABEE). Labelled products were fractionated into neutral and acid fractions on a Bio-Gel P4 column, calibrated with a mixture of dextran oligosaccharides, labelled according to the same procedure.

Radiation chemistry of aqueous solutions of hydrazine Part 3. The chain reaction in oxygenated solutions irradiated with 60Co γ-rays

The radiation-induced decomposition by 60Co γ-rays of oxygen saturated aqueous solutions of hydrazine has been measured over the pH range 3.5 to 11.7. A reaction set has been devised which accounts for the experimental observations based on decomposition proceeding by a pH-dependent chain reaction propagated by hydrazil radicals (specifically N2H3) reacting with O2 and the resulting HO2/O2- radicals oxidising hydrazine (N2H5+/N2H4) to hydrazil radicals (N2H4+/N2H3). Chain termination is via the self-reactions of HO2-/O2-. The pH dependence of the chain length is consistent with (a) HO2/O2- having different reactivity towards N2H4/N2H5+ in the propagating step, and (b) the known pH dependence of the termination reaction. The values of the rate constants of the propagation reactions that simulate the experimental data quite well are (in units of d mol-1 s-1): k(HO2+N2H5+)=10; k(HO2+N2H4)=70; k(O2-+N2H5+)=100; k(O2-+N2H4)=2.2; each with an estimated uncertainty of ±10%. There is no evidence that N2H4+ is a chain carrier.

Kinetic study of the reaction of pyridoxal 5′-phosphate with hydrazine

The kinetics of the reaction between pyridoxal 5′-phosphate (PLP) and hydrazine in aqueous solution at a variable pH and a constant strength of 0.1 M was studied spectrophotometrically. The rate constants of formation and hydrolysis of the resulting Schiff base and its stability were also determined in a wide range of pH. A comparison of the formation rate constants with those for the models of PLP with n-hexylamine and with poly- l-lysine revealed that hydrazine formed Schiff base more quickly than lysine below pH 7 and than n-hexylamine below pH 8. The reactivity shows the sequence poly- l-lysine> n-hexylamine>hydrazine in whole studied range of pH. Schiff bases formed by hydrazine with PLP are more stable than the ones formed by n-hexylamine in the pH range studied and more stable than the formed by poly- l-lysine at pH<7.0.

A tin-free catalyst for electroless platinum deposition on polyethylene terephthalate

The metallization of polymer materials has many applications in a range of industries for decorative and=or functional purposes, e.g., nickel plating of ABS plastics in automotive parts [1] and copper plating of polyimides in printed-circuit boards [2]. Electroless deposition has attracted a great deal of interest as an economic means of metallization of polymers. Recently, this technique has been shown to have signi®cant potential for the fabrication of a new generation of electrodes used in implantable medical applications, such as de®brillation, pacing and cardiomyoplasty [3]. Since electroless deposition takes place only on conductors, it is necessary to use a catalyst to seed the insulator surface with catalytic metal particles [1]. Traditionally, a two-step treatment is used in which a SnCl2 solution acts as a sensitizer and a PdCl2 solution as an activator to provide catalytic metallic Pd sites [4]. More recently, a one-step treatment has been introduced using a mixed SnCl2 ± PdCl2 solution to yield Pd±Sn alloy as catalyst centres [5±9]. These activation treatments are normally followed by an acceleration treatment to remove excessive Sn ions which inhibit electroless deposition. Both these methods use tin which is known to be toxic and therefore they are not suitable for medical implants. A new method for the activation of a nonconductor which eliminates the use of tin has been invented by our research group [10]. In this letter, we report the use of this new catalyst for electroless platinum deposition on polyethylene terephthalate (PET) surfaces. Platinum and PET are chosen because of their proven suitability for use in implantable medical devices. The results to be discussed were mostly generated from experiments on PET ®lms which facilitates characterization and testing. Preliminary results from PET ®bres are also brie y discussesd. PET ®lms of 0.1 mm thickness were supplied by Goodfellow and PET ®bres of diameter approximately 22 im were supplied by Akzo Fibres. Unless otherwise stated, all chemicals were supplied by Aldrich or Sigma as laboratory reagents with no further puri®cation. A tin-free catalyst was prepared by dissolving 0.2% (w=v) PdCl2 into dimethylsulphoxide (DMSO), which is referred to as DMSO±Pd catalyst in this report. A reducer was formulated with 4% (v=v) hydrazine in aqueous solution. The electroless deposition bath was a proprietary formulation and it was used as recommended, except for some adjustment of the ammonia concentration. The electroless deposition of Pt on PET using the new catalyst method involved the following four steps, with thorough rinsing in de-ionized water between each step. As-received PET ®lms or ®bres were ®rstly washed in hot detergent solution (NewBon at a strength of 0.1%) for 30 min at 80 8C to remove wax and=or oil residues present on the surface. The cleaned samples were then etched in a hot alkaline bath which consisted of NaOH (100 g ly1) and 0.1% surfactant (proprietary product) for 30 min at 80 8C. The etching provided a rough PET surface for better adhesion through the mechanical interlocking of the Pt coating and the PET substrate. Catalysis was achieved by dipping the PET samples into the DMSO±Pd catalyst for a speci®c time and then dipping the samples into the reducer for 1 min, with both the catalyst and the reducer maintained at room temperature. The catalysed samples were immersed into a pre-heated electroless deposition bath at the recommended temperature of 60 8C for the required deposition time. The above cleaning and etching steps were carried out with vigorous mechanical agitation, whereas the catalysis and electroless deposition were conducted with gentle agitation. In addition, some selected ®bre samples, treated under slightly different etching conditions, were electrolessly plated using either the new catalyst or the traditional mixed Sn±Pd catalyst to give a comparative study on the adhesion between the Pt coatings and the PET substrate.

Structural changes induced by chemical reduction of various MnO2 species

Several kinds of MnO2 were progressively reduced by cinnamic alcohol (CA) and aqueous hydrazine solutions (AHS) to compare changes in their structure. With α-MnO2 stabilized by NH+4, the maximum homogeneous degree of H-insertion (MHID) is only 0.62H per Mn, which involves the filling of each NH+4-free tunnel by four protons. This MHID value is consistent with the discharge capacity during the electrochemical reduction in 1m KOH solution and in nonaqueous media (~0.65 and ~0.63 faradays per Mn, respectively). This result shows that Li+ and H+ ions occupy the same sites. The lowest degrees of oxidation are obtained when AHS are used, resulting in progressive appearance of a spinel structure which replaces the original lattice. For degrees of reduction x lower than MnO1.33, pyrochroite exists in a poorly crystallized form since it is not observed in the XRD patterns. The XRD patterns of γ-MnO2 reduced to MnO1.12 usually show the spinel structure while the patterns of the Bi-doped MnO2 reduced to MnO1.14 exhibit peaks corresponding to pyrochroite and bismite (Bi2O3). Thus, the presence of Bi3+ hinders the formation of the nonelectroactive compound Mn3O4 or γ-Mn2O3, but the mechanism to explain this cannot be determined by XRD data alone.

Radiation chemistry of aqueous solutions of hydrazine at elevated temperatures Part 2.—Solutions containing oxygen

The rate of reaction for has been measured by pulse radiolysis up to 110°C in aqueous solutions of hydrazine having a pH of 10.3 at room temperature. The values of the kinetic parameters are k 1 =(3.8±0.1)×10 8 dm3 mol -1 s -1 at 20°C and E act =5.6±2.1 kJ mol -1 . This small activation energy is interpreted in terms of the formation of an intermediate adduct N 2 H 3 O 2 which is in a pre-equilibrium with the reactants and whose stability with respect to dissociation back to the reactants decreases with increasing temperature. The rate of the thermal reaction has also been determined up to 110°C by measuring the decrease in k 1 with increasing age of the oxygenated hydrazine solution in order to monitor the depletion of [O 2 ]. The kinetic parameters are k 12 =(1.2±0.8)×10 -3 dm3 mol -1 s -1 at 20°C and E act =70±5 kJ mol -1 . γ-Radiolysis studies show that N 2 H 4 is destroyed in a short chain reaction in oxygenated hydrazine solutions with G(-N 2 H 4 )∝(dose rate) -0.5 , indicating chain termination by radical–radical reactions. Added EDTA shortens the chain but does not alter the form of the rate law, indicating that metal ions present as impurities accelerate the chain-propagating reactions more than the termination steps. In each case the chain length increases as ca. [N 2 H 4 ] 0.5 .

PK a of the hydrazinium ion and the reaction of hydrogen atoms with hydrazine in aqueous solution

The techniques of electron pulse radiolysis and paramagnetic resonance free induction decay (FID) attenuation measurements have been used to determine Arrhenius parameters for the reaction of the hydrogen atom with N2H5+ and N2H4 in aqueous solution. At 41.6 °C, a scavenging rate constant of (5.8 ± 1.9)× 106 dm3 mol–1 s–1 was directly measured for the N2H5+ reaction, with a corresponding activation energy of 61.4 ± 1.2 kJ mol–1 over the temperature range 41.6–82.1 °C. The pKa of the hydrazinium ion was determined by absorption spectroscopy, and over the temperature range 0–80 °C, this equilibrium was well described by pKa=(2600 ± 30)/T–(0.771 ± 0.099). Using these values, and FID attenuation measurements in borax buffered solution over the temperature range 0.2–83.0 °C, the hydrogen atom rate constant for N2H4 reaction was calculated to be (6.74 ± 0.23)× 107 dm3 mol–1 s–1(24.5 °C), with an activation energy of 16.28 ± 0.80 kJ mol–1. The reaction rate of ˙H with N2H4 is consistent with a hydrogen atom abstraction, giving H2 and ˙N2H3 radical as products, as in the gas phase. Based on the large activation enthalpy and entropy obtained for the reaction of hydrogen atoms with N2H5+, however, we suggest that this is more likely an addition–fragmentation process, to give ˙NH2, NH3 and (H+)aq as products.

Radiation chemistry of aqueous solutions of hydrazine at elevated temperatures. Part 1.—Oxygen-free solutions

Rate constants for the reactions of eaq– and ˙OH with N2H4 and N2H5+ in liquid water up to 200 °C have been measured by pulse radiolysis. Linear Arrhenius plots for the reactions of eaq– gave k(20 °C)= 106 and 1.6 × 108 dm3 mol–1 s–1, and Ea= 13.5 and 18.2 kJ mol–1, respectively. H is the product of the reaction with N2H5+. Non-linear Arrhenius behaviour was observed for the reactions of ˙OH with k(20 °C)= 4.5 × 109 and 8.2 × 107 dm3 mol–1 s–1, respectively. The pKa of N2H5+ decreases linearly with temperature from 8.1 at 20 °C to 4.2 at 200 °C. The products of the ˙OH reactions are ˙N2H3 and ˙N2H4+, respectively, and the pKa of ˙N2H4+ also decreases with increasing temperature. The self-reaction of ˙N2H3 shows the same temperature dependence as that of ˙OH with k(20 °C)= 2 × 109 dm3 mol–1 s–1. The product of this reaction is tetrazene. Up to 200 °C the data are consistent with successive eliminations of NH3 to form triazene and then N2. The pH-dependent kinetics of these processes indicate that the decomposition of N3H3 is acid- and base-catalysed over the whole temperature range.

Density dependence of heat conductivity of aqueous hydrazine solutions within wide ranges of temperature and pressure

Equations are obtained that establish dependence of heat conductivity of hydrazine on density and concentration of water at various values of temperature and pressure.

Viscosity and density of aqueous solutions of hydrazine and phenylhydrazine as functions of temperature at atmospheric pressure

Using the method of hydrostatic weighing and a capillary viscosimeter, we measured the density and viscosity of aqueous solutions of hydrazine and phenylhydrazine in the temperature range from 293 to 353 K and obtained an empirical equation.

Dynamic viscosity of aqueous solutions of hydrazine with high state parameters

We report the results of measurements of the dynamic viscosity of aqueous solutions of hydrazine with a molar concentration of water ranging from 10 to 90%, in the temperature interval 293–558.4 K and the pressure interval 0.101–58.86 MPa.

A study by pulse radiolysis of the radiation-chemical transformation of aqueous solutions of hydrazine in the presence of oxygen

It is shown by pulse radiolysis that in aqueous solutions of hydrazine containing oxygen the radical N2H3 reduces oxygen to O2− at pH > 7 (k ≥3·109 dm3· mole−1·sec−1), while this reaction does not occur for the protonated form N2H4+ at pH < 7 (k≤, 5·106 dm3·mole−1·sec−1). The rate constants for the disappearance of O2− have been determined in the pH range from 4 to 12. Rate constants have been calculated for the reaction of O− with N2H4 [k=(1.6 ±0.2)·109 dm3·mole−1·sec−1] and of O3with N2H4 [k=(1.2 ±0.2)·106 dm3· mole−1·sec−1].

Glass of the past: The degradation and deterioration of medieval glass artifacts

Medieval artifacts made of glass are at a serious disadvantage concerning the chemical stability compared with ancient or common modern glasses. The total amount of silica and other network formers such as alumina is very low and potassium instead of sodium was introduced into the silicate structure by using local raw material. By means of scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS) and nuclear reaction analysis (NRA) a weathering mechanism governed by an ion exchange process could be determined for medieval glass paintings exposed to the ambient air for centuries. Additionally, the leached glass surface of medieval hollow glass artifacts found in a well and exposed to moist earth show a brown discoloring due to the oxidation of Mn(II) to Mn(IV) oxide. That process can be converted by a treatment of the glass objects in an aqueous hydrazine solution.