Search

Here we present analysis of a novel reactive material system that employs dinitrogen tetroxide (N2O4) as a liquid oxidizer with metal powder fuels. The oxidizer was added to micron scale aluminum and zirconium powders by a remote injection system. When ignited with a high voltage spark, the mixtures were observed to possess reactivity comparable to nanocomposite reactive materials, with open-tube flame expansion velocities from 500 to 1400 m/s depending on fuel/oxidizer ratio and tube diameter. Temperatures were observed to range from 3000 to 3500 K as measured with gray body fits to 16-channel time-resolved pyrometer and time-integrated spectrometer data. These values were significantly below calculated adiabatic flame temperatures, which we attribute to local deviations from stoichiometry and kinetic/energetic limitations similar to those observed in studies of particles burning in high pressures gaseous oxidizers. Al/N2O4 reactivity was found to be most likely limited by the vaporization of the metal from the particle surface and Zr/N2O4 was limited by slower burning and complex interactions involving the solubility of nitrogen and oxygen in the molten Zr. We also discuss the potential for these materials to be used to create an “on/off” reactive material, since N2O4 can be added remotely and driven to evaporate via vacuum or purge of inert gases to return it to a safe condition.

Conventional hypergolic propellant combinations, using hydrazine and its derivatives as fuels and dinitrogen tetroxide based oxidizers, have been applied in spacecraft for attitude and roll control systems for more than 50 years. However, due to their high toxicity and carcinogenic potential, investigations into alternative green propellants are an active field in current research efforts. Promising alternative propellant candidates are combinations of hydrogen peroxide and suitable hypergolic room-temperature ionic liquids. In this work, imidazole thiocyanate ionic liquids are tested in drop tests with hydrogen peroxide. For this purpose, a newly developed automated drop test setup was designed and implemented. As a result, 1-ethyl-3-methylimidazolium thiocyanate (EMIM SCN) and 1-butyl-3-methylimidazolium thiocyanate (BMIM SCN) turned out to be hypergolic with highly concentrated hydrogen peroxide (96.1%). The ignition delay time on average is 31.7 ms for EMIM SCN and 45 ms for BMIM SCN. Theoretical performance of the two ionic liquids was calculated with NASA CEA and compared to a conventional hypergolic propellant combination (monomethyl hydrazine/dinitrogen tetroxide). The specific impulse of the green propellants is nearly 5% lower, but the density specific impulse is increased by 10%. Furthermore, the ignition delay time was reduced by dissolving a catalytic additive, copper thiocyanate, in the EMIM SCN. The lowest average ignition delay time of 13.9 ms was achieved for EMIM SCN and 5 wt% of copper thiocyanate. For higher copper concentration the ignition delay time is not further reduced. The fuel with EMIM SCN and 5 wt% of copper thiocyanate and the pure EMIM SCN were further characterized by thermal and spectroscopic methods. Fluid properties like density, viscosity and surface tension were also determined in laboratory investigations.

Regardless of the sustainable development path, today, there are highly demanded chemical productions still operating that bear environmental and technological risks inherited from the previous century. The fabrication of nitro compounds, and nitroarenes in particular, is traditionally associated with acidic wastes formed in nitration reactions exploiting mixed acids. However, nitroarenes are indispensable for industrial and military applications. We faced the challenge and developed a greener, safer, and yet effective method for the production of nitroaromatics. The proposed approach comprises the application of an eco-friendly nitrating agent, namely dinitrogen pentoxide (DNP), in the medium of liquefied 1,1,1,2-tetrafluoroethane (TFE) – one of the most non-hazardous Freons. Importantly, the used TFE is not emitted into the atmosphere but is effortlessly recondensed and returned into the process. DNP is obtained via the oxidation of dinitrogen tetroxide with ozone. The elaborated method is characterized by high yields of the targeted nitro arenes, mild reaction conditions, and minimal amount of easy-to-utilize wastes.

Thermodynamic analysis of the high-toxic substances (hydrazine, dimethylhydrazine and dinitrogen tetroxide) thermal decomposition process contained in liquid mixtures in different concentrations was carried out. Calculations of equilibrium compositions were carried out in a wide temperature range for a steam-water plasmatron. The aim of the study was finding the operational parameter’s optimal range of values ensuring the complete decomposition of primary high-toxic components provided secondary harmful substances minimal formation and obtaining acceptance level of specific energy consumption. The methods of further harmful secondary emissions neutralization have been determined. Bibl. 9, Fig. 7.

Gas-phase diffusion is the first step for all heterogeneous reactions under atmospheric conditions. Knowledge of binary diffusion coefficients is important for the interpretation of laboratory studies regarding heterogeneous trace gas uptake and reactions. Only for stable, nonreactive and nonpolar gases do well-established models for the estimation of diffusion coefficients from viscosity data exist. Therefore, we have used two complementary methods for the measurement of binary diffusion coefficients in the temperature range of 200 to 300 K: the arrested flow method is best suited for unstable gases, and the twin tube method is best suited for stable but adsorbing trace gases. Both methods were validated by the measurement of the diffusion coefficients of methane and ethane in helium and air as well as nitric oxide in helium. Using the arrested flow method the diffusion coefficients of ozone in air, dinitrogen pentoxide and chlorine nitrate in helium, and nitrogen were measured. The twin tube method was used for the measurement of the diffusion coefficient of nitrogen dioxide and dinitrogen tetroxide in helium and nitrogen.

The effect of confinement on the equilibrium reactive system containing nitrogen dioxide and dinitrogen tetroxide is studied by molecular simulation and the reactive Monte Carlo (RxMC) approach. The bulk-phase reaction was successfully reproduced and five all-silica zeolites (i.e. FAU, FER, MFI, MOR, and TON) with different topologies were selected to study their adoption behavior. Dinitrogen tetroxide showed a stronger affinity than nitrogen dioxide in all the zeolites due to size effects, but exclusive adsorption sites in MOR allowed the adsorption of nitrogen dioxide with no competition at these sites. From the study of the adsorption isotherms and isobars of the reacting mixture, confinement enhanced the formation of dimers over the full range of pressure and temperature, finding the largest deviations from bulk fractions at low temperature and high pressure. The channel size and shape of the zeolite have a noticeable influence on the dinitrogen tetroxide formation, being more important in MFI, closely followed by TON and MOR, and finally FER and FAU. Preferential adsorption sites in MOR lead to an unusually strong selective adsorption towards nitrogen dioxide, demonstrating that the topological structure has a crucial influence on the composition of the mixture and must be carefully considered in systems containing nitrogen dioxide.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2017-07-06, 資料番号: PA1810059000

Non-toxic hypergolic propellants have considerably generated recent research interest in the field of green propulsion technology because they can replace highly toxic hypergolic combinations currently used. In this experimental research, sodium borohydride-based non-toxic hypergolic fuel was prepared by blending sodium borohydride in the mixture of energetic hydrocarbon solvents. In a drop test, sodium borohydride as an ignition source enabled the hydrocarbon mixture to initiate hypergolic interactions with H 2 O 2 oxidizer. Two different heating methods were utilized to analyze the characteristics of autoignition and combustion of the hypergolic fuel. As a reference fuel, a non-hypergolic fuel which has the identical chemical compositions to the hypergolic fuel except for sodium borohydride was tested and compared. As a one of the heating methods, thermogravimetric analysis was not suitable for evaluating the inherent thermophysical properties of the hypergolic fuel. In a droplet combustion chamber test, the autoignition and combustion of the hypergolic fuel droplets occurred exposed to elevated temperatures (in a range of 400–800 °C) at atmospheric pressure (1 bar), whereas the non-hypergolic fuel droplet was automatically ignited only at 800 °C. The ignition delay and total combustion time of the hypergolic fuel droplet were lower than those of the non-hypergolic fuel droplet. According to the temporal histories of the droplet size, sodium borohydride-based hypergolic fuel droplets did not obey the d 2 -law of diffusion-controlled combustion, which indicates the droplet evaporation rate was not a controlling factor in the combustion process. Consequently, the addition of sodium borohydride into the hydrocarbon mixture expedited the autoignition and combustion process of the fuel at elevated temperatures.

In this paper, the compatibility of carbon/silicon carbide composite ceramic materials and propellant dinitrogen tetroxide was studied. Referring to similar standards, the test parameters and immersion test scheme were selected. The changes of dinitrogen tetroxide properties and mechanical properties of ceramics before and after the experiment were mainly investigated, which provided theoretical and data basis for the application of this ceramic material in the field of dinitrogen tetroxide.

Apart from the more familiar π-conjugation, there is also significant π–π repulsion which is a kind of unrecognized intramolecular strain and can be quantified with the linear B4H2 model system., Electron conjugation stabilizes unsaturated systems and diminishes the differences among bond distances. Experimentally, Kistiakowsky and coworkers first measured and noticed the difference between the hydrogenation heats of carbon–carbon double bonds in conjugated systems. For instance, the hydrogenation heat of butadiene is 57.1 kcal mol–1, which is less than two times that of the hydrogenation heat of 1-butene (30.3 kcal mol–1), and the difference (3.5 kcal mol–1) is the extra stabilization due to the resonance between two double bonds in the former, and is referred to as the experimental resonance energy. Following Kistiakowsky's definition, Rogers et al. studied the stepwise hydrogenation of 1,3-butadiyne and concluded that there is no conjugation stabilization in this molecule. This claim received objections instantly, but Rogers and coworkers further showed the destabilizing conjugation in 2,3-butanedione and cyanogen. Within resonance theory, the conjugation energy is derived “by subtracting the actual energy of the molecule in question from that of the most stable contributing structure.” The notable difference between the experimental and theoretical resonance energies lies in that the former needs other real reference molecules while the latter does not. Here we propose and validate a new concept, intramolecular multi-bond strain, which refers to the repulsion among π bonds. The π–π repulsion, which is contributed to by both Pauli exchange and electrostatic interaction, is quantified with the B4H2 model system (16.9 kcal mol–1), and is compared with the σ–σ repulsion in B2H4 (7.7 kcal mol–1). The significance of the π–π repulsion can be demonstrated by the much longer carbon–nitrogen bond in nitrobenzene (1.486 Å) than in aniline (1.407 Å), the very long and weak nitrogen–nitrogen bond (1.756 Å) in dinitrogen tetroxide, and the instability of long polyynes. This new concept successfully reconciles the discrepancy between experimental and theoretical conjugation energies. However, we maintain that by definition, electron conjugation must be stabilizing.

Dept. of Aerospace Engineering, Sejong UniversityAbstract : Space propulsion system produces required thrust for satellites and space launch vehicles by using chemical reactions of a liquid fuel and a liquid oxidizer typically. Among several liquid propellants, the monomethylhydrazine-dinitrogen tetroxide is expecially preferred for a GEO satellite propellants due to their better storability in liquid phase during a long mission life under a freezing space environment. Recently, a development of the monomethylhydrazine-dinitrogen tetroxide bipropellant system becomes important as the national space program requires the heavier and the more efficient space system. Thus, the objective of the present study is to review a foreign research trend of a chemical reaction between the monomethyhydrazine fuel and the dinitrogen tetroxide oxidizer to understand a fundamental basis of their characteristics to prepare for domestic development in future.Key Words : Space Propulsion, Bipropellant, Monomethylhydrazine, Dinitrogen Tetroxide, Chemical Reaction

Hochintensive Femtosekundenlaser sind wirkungsvolle Instrumente zur Erforschung von sowohl inter- als auch intramolekularen Dynamiken auf Zeitskalen der Kernbewegung und mit einer Ortsauflösung in der Größenordnung der Molekülbindungen. Die vorliegende Dissertation widmet sich der Studie von Moleküldynamiken mithilfe von Starkfeldionisation durch ultrakurze Laserpulse. Im ersten Teil der Dissertation präsentieren wir eine detaillierte Studie über die verschiedenen Aufbruchkanäle in der durch Starkfeldionisation induzierten Coulomb-Explosion von dreifach positiv geladenem Bromiodmethan. Die Impulse der resultierenden Fragmente wurden mithilfe eines Reaktionsmikroskops in Koinzidenz gemessen. Wir haben fünf verschiedene Fragmentationspfade nachgewiesen: eine nicht sequentielle Coulomb-Explosion in welcher die C-I Bindung und die C-Br Bindung gleichzeitig aufbrechen und zusätzlich vier sequentielle Pfade in welchen die Fragmentierung über einen doppelt geladenen Zwischenzustand abläuft und der Bindungsbruch nacheinander erfolgt. Zudem diskutieren wir sowohl die Möglichkeiten als auch die Beschränkungen, die Ergebnisse der Coulomb-Explosion zur Molekülstrukturbestimmung zu verwenden. Im zweiten Teil der Dissertation stellen wir die Ergebnisse eines zeitaufgelösten Pump-Probe Experiments vor, in welchem die N-N Streckschwingung von Distickstofftetroxid untersucht wurde. Wir haben die Schwingung durch einen impulsiven stimulierten Raman Stoßprozess mit dem Pump-Puls angeregt, um anschließend das oszillierende Molekül mit einem zeitverzögerten Probe-Puls in einem Starkfeldprozess zu ionisieren. Durch die von der Zeitverzögerung abhängige, gemessene kinetische Energie erzeugter einfach positiv geladenener Stickstoffdioxid Fragmente, konnten wir den inneren Umkehrpunkt, die Amplitude und die Phase der Schwingen bestimmen. Wir haben für das Experiment eine Kombination aus einem Velocity-Map Imaging Spektrometer, einem im Vakuum integrierten Pixeldetektor und einem Lasersystem, welches 7 fs kurze Impulse erzeugt, verwendet. Im letzten Teil der Dissertation präsentieren wir eine detaillierte Beschreibung des Designs und der Implementierung eines neuen Messaufbaus. Dieser stellt den ersten Schritt der Entwicklung einer neuen Methode vor, die es ermöglichen soll die zeitabhängige Änderung der Molekülstruktur während einer bimolekularen chemischen Reaktion zu erforschen. Wir wollen dabei zwei etablierte Techniken verbinden: (1) Die Präparation der Ausgangsprodukte einer chemischen Reaktion in kleinen ionischen Clustern und Molekülen und (2) Coulomb-Explosion zur Strukturbestimmung von transienten Molekülkonfigurationen. Der neue Aufbau beinhaltet eine Ionenquelle, ein Flugzeitmassenspektrometer, ein Coulomb-Explosion Imaging Spektrometer und eine zusätzliche neutrale Molekularstrahlquelle., Strong-field femtosecond lasers are powerful tools to explore inter- and intramolecular dynamics on the time scales of the nuclear motion and with a spatial resolution of the molecular bond length. This thesis is dedicated to the investigation of molecular dynamics with strong-field ionization induced by ulta-short laser pulses. In the first part of this thesis, we present a detailed study on the different fragmentation pathways in the Coulomb explosion of triply-charged bromoiodomethane upon strong-field ionization. The momenta of the final fragments were measured in coincidence in a reaction microscope. We detected five different break-up pathways. The non-sequential Coulomb explosion where the C-I and the C-Br bond break at the same time and in addition four sequential channels with a successive bond cleavage and a fragmentation pathway which proceeds via an intermediate doubly-charged state. Furthermore, we discuss the possibilities and limitations of Coulomb explosion imaging as a tool to recover the molecular structure. In the second part of the thesis we present the results of a time-resolved pump-probe experiment exploring the N-N vibration of dinitrogen tetroxide. We excited the vibration in an impulsive stimulated Raman scattering process with the pump pulse and strong-field ionized the vibrating molecule with the time-delayed probe pulse. From the time-dependent kinetic energy release of created singly-charged nitrogen dioxide fragments we could extract the inner turning point, the amplitude, and the phase of the vibration. In the experiment, we used the combination of a velocity map imaging spectrometer, an in-vacuum pixel detector, and a laser system delivering few-cycle 7 fs long pulses. In the last part of the thesis, we present the detailed description of the design and implementation of a new setup. The built machine is the first step towards the development of a new approach to study the time-dependent structural change during bimolecular chemical reactions. We want to combine two established methods: (i) the preparation of reaction precursors in small ionic clusters and molecules (ii) Coulomb explosion imaging to determine the transient molecular structure. The new setup includes an ion source, a time-of-flight mass-spectrometer, a Coulomb explosion imaging spectrometer, and an additional neutral molecular beam source.

The high strength aluminum alloy double cantilever beam (DCB) specimens were corroded under the conditions of different liquid propellant environment. After the stress corrosion exposure, the scanning electron microscopy and energy-dispersal analyses on corrosion damage were carried out. The corrosion damage sensitivity and the stress corrosion character of the LD10 high strength aluminum alloy in N 2 O 4 , UDMH and 3.5% NaCl corrosion solution were analyzed.

N2O4 was easily impregnated on silica gel to give a stable heterogeneous reagent N2O4/SiO2 (I). Chemoselective deprotection of trimethylsilyl ethers to the corresponding alcohols was achieved in the presence of I in CH2Cl2 in excellent yields. The stability, easy preparation and high selectivity of the reagent make this method as a useful procedure for the selective deprotection of TMS ethers at room temperature.

Hydrazine (N2H4) and NTO (dinitrogen tetroxide: N2O4) mixtures are used in spacecraft bipropellant systems, having the advantage, for sampling missions, of having no carbon composition. However, no reasonable hydrazine and NTO combustion model has been developed. To construct a hydrazine and NTO combustion model that is useful for bipropellant thruster CFD simulation, we extracted efficient elementary reactions from detailed kinetic reaction model proposed by Ohminami and Ogawa in 2007. The reduced hydrazine and NTO combustion model was composed of 61 extracted reactions with 23 chemical species and was coincident with the original detailed kinetic reaction model in terms of combustion gas temperatures and ignition delay times over O/F(oxidizer and fuel mass ration) =0.82-1.84. Also the simulated combustion gas temperatures were good agreed with the adiabatic flame temperatures, and the simulated ignition delay time at O/F=1.2 was consistent with the literature value. Chemical reaction paths before and after ignition were showed, and could explain hydrazine and NTO combustion network mechanism change.

The effects of photolysis on frozen, thin films of water-ice containing nitrogen dioxide (as its dimer dinitrogen tetroxide) have been investigated using a combination of Fourier transform reflection-absorption infrared (FT-RAIR) spectroscopy and mass spectrometry. The release of HONO is ascribed to a mechanism in which nitrosonium nitrate (NO+NO3-) is formed. Subsequent solvation of the cation leads to the nitroacidium ion, H2ONO+, i.e., protonated nitrous acid. The pathway proposed explains why the field measurement of HONO at different polar sites is often contradictory.

Nitration of aromatic compounds using a zeolite as a solid inorganic catalyst and a combination of dinitrogen tetroxide and oxygen or air as the nitrating reagent, in open or sealed systems, leads to high yields and significant para selectivities for halogenobenzenes and other aromatics in a relatively clean process. The material used as catalyst has a strong influence on the reaction.

The detailed interactions of nitrogen oxides with ice are of fundamental interest and relevance for chemistry in cold regions of the atmosphere. Here, the interactions of NO, NO2, N2O4, and N2O5 with ice surfaces at temperatures between 93 and 180 K are investigated with molecular beam techniques. Surface collisions are observed to result in efficient transfer of kinetic energy and trapping of molecules on the ice surfaces. NO and NO2 rapidly desorb from pure ice with upper bounds for the surface binding energies of 0.16 ± 0.02 and 0.26 ± 0.03 eV, respectively. Above 150 K, N2O4 desorption follows first-order kinetics and is well described by the Arrhenius parameters Ea = 0.39 ± 0.04 eV and A = 10((15.4±1.2)) s(-1), while a stable N2O4 adlayer is formed at lower temperatures. A fraction of incoming N2O5 reacts to form HNO3 on the ice surface. The N2O5 desorption rates are substantially lower on pure water ice (Arrhenius parameters: Ea = 0.36 ± 0.02 eV; A = 10((15.3±0.7)) s(-1)) than on HNO3-covered ice (Ea = 0.24 ± 0.02 eV; A = 10((11.5±0.7)) s(-1)). The N2O5 desorption kinetics also sensitively depend on the sub-monolayer coverage of HNO3, with a minimum in N2O5 desorption rate at a low but finite coverage of HNO3. The studies show that none of the systems with resolvable desorption kinetics undergo ordinary desorption from ice, and instead desorption likely involves two or more surface states, with additional complexity added by coadsorbed molecules.

The heat capacity of nitrogen tetroxide was measured in the temperature range from 410 to 484 K at densities between 201.21 and 980.39 kg m −3 and for pressures up to 35 MPa using a high-temperature and high-pressure adiabatic calorimeter. The measurements were performed in the one-phase region at 17 isochores (11 liquid and 6 vapor densities) including coexistence curve and critical region. Uncertainties of the measurements are estimated to be 2%. The original temperatures and C V data were converted to the ITS-90. The liquid and vapor one-phase isochoric heat capacities, temperatures and densities at saturation were extracted from experimental data for each measured isochore. Some of the experimental data ( T S , ρ S ), C V along isochores and at saturation are compared with values derived from isobaric heat capacity C P , sound velocity W , and PVT measurements. The values of critical parameters for N 2 O 4 are measured using quasi-static thermograms method.

2-Trimethylstannylated benzo[b]furan, benzo[b]thiophene, N-substituted indoles and pyridine afford the corresponding nitro derivatives in regioselective fashion upon treatment with tetranitromethane (using sun-lamp irradiation in the case of N-containing heterocycles) or with dinitrogen tetroxide.

Conventional N234 carbon black was chemically modified by a low temperature treatment with dinitrogen trioxide (N 2 O 3 ), nitrogen oxide (NO) and dinitrogen tetroxide (N 2 O 4 ). The purpose of this treatment was to increase significantly the fraction of polymer chain segments chemically linked to the filler surface in comparison to a conventional CB after compounding with rubber. The theoretical expectation was to reduce the mechanical hysteresis of a rubber compound. The chemical structure of the resulting carbon black (CB) was studied by FT-IR spectroscopy which revealed that an extensive surface chemical modification had occurred. In fact, extensive surface nitration, nitrosation and oxidation had taken place. Raman spectroscopy of treated CB reveals that the bulk structure of the CB remained substantially unchanged after the treatment. The modified CB was tested in practice in a rubber tread compound formulation, and has substantially confirmed the theoretical expectations by reducing the tan 6 at 70°C by about 14%, which correlates with tire rolling resistance without significant losses in traction performances (as estimated on lab scale by tan 6 at 0°C).

Adsorption or bonding geometries of pure adlayers of several NxOy species, i.e., nitrogen dioxide (NO2), dinitrogen trioxide (N2O3), and dinitrogen tetroxide (N2O4), on Au(111) were determined by utilizing infrared reflection−absorption spectroscopy (IRAS). Dosing NO2 on Au(111) at 85 K produced, in our experiments, mixtures of NO2 and N2O3 (from contaminant NO) at submonolayer coverages and NO2, N2O3, and N2O4 at monolayer coverages. However, a pure adlayer of chemisorbed NO2 could be prepared by forming the monolayer on Au(111) at 85 K and then heating to 185 K or by NO2 exposures on Au(111) at 185 K. Chemisorbed NO2 is bonded to the surface in an O,O‘-chelating geometry with C2v symmetry. A monolayer of adsorbed N2O3 was produced by exposing the pure, chelating NO2 adlayer to NO(g). The adsorbed complex with N2O3 has Cs symmetry, and we believe that N2O3 is bonded to the surface through one oxygen. Large NO2 exposures can be used to produce crystalline N2O4 multilayers that have a preferential orientat...

Previous experiments in the 400–500 nm region (Coquart et al., 1995) have been extended to the 200–400 nm region to determine the absorption cross-sections of NO2 at 220 K. The NO2 and N2O4 cross-sections are obtained simultaneously from a calculation applied to the data resulting from measurements at low pressures. A comparison between the NO2 cross-sections at 220 K and at ambient temperature shows that the low temperature cross-sections are generally lower, except in the region of the absorption peaks. Comparisons are also made with previous data at temperature close to 220 K.

To gain an atomistic-level understanding on physical and chemical processes occurring at the interfaces of hypergolic propellants, we carried out the first reactive dynamic (ReaxFF) simulations to study the reactive hypergolic mixture of monomethylhydrazine (MMH) and dinitrogen tetroxide (NTO), in comparison with the ethanol (EtOH) and NTO mixture that is reactive but nonhypergolic. Our studies show that the MMH-NTO mixture releases energy more rapidly than the EtOH-NTO mixture upon mixing the fuels and oxidizers. We found that the major early chemical reactions between MMH and NTO are hydrogen abstractions and N-N bond scissions. The MMH-NTO mixture has more reaction channels than EtOH-NTO based on statistical analyses of chemical reaction events and channels at early stages of the dynamics. Analyzing the evolution of product distribution over reaction time shows that the oxidizer (NO(2)) diffuses into the fuels (MMH or EtOH) for the occurrence of reactions, demonstrating the influence of physical mixing on chemical reactions. Our simulations suggest that effective hypergolic systems require fuels with low energy barriers of H abstractions and/or bond scissions and oxidizers with large diffusion mobility for efficient physical mixing.

The mechanism of the vapour-phase mononitration of aromatics with dinitrogen tetroxide has been investigated over silica-alumina and the large-pore zeolite β (BEA). A Rideal-Eley rate law is observed in both cases, showing that the reaction occurs between the chemisorbed aromatic and the gaseous nitrating agent. The effects of substituents are better correlated by a relation between the activity and the ionisation potential of the aromatic than by the Hammett equation. Both results conflict with the "classical" electrophilic aromatic substitution (SEAr), but agree with the formation of an aromatic radical cation intermediate at the surface of the catalyst and its reaction with a nitrogen dioxide radical in the rate determining step. The generation of electron-acceptor sites on the catalyst surface by nitrogen dioxide radicals is suggested. Addition of water in the feed inhibits the reaction by competitive adsorption over silica-alumina, but improves the efficiency of BEA, certainly by "steam cleaning" of the surface of this hydrophobic catalyst.

The concept of binding entropy is introduced and information theoretical approach is combined with orbital-free density functional theory. It is shown that binding entropy expresses the deviation of the molecular electron density from the promolecular density and the deviation of the molecular kinetic energy density from the promolecular kinetic energy density. The change of the kinetic energy density during the chemical bond formation explicitly appears in the binding entropy expression. The binding entropy and binding entropy density are analyzed using experimental electron density for solid germanium, gallium arsenide and dinitrogen tetroxide. It is demonstrated that the binding entropy joined with deformation electron density and "deformation" kinetic energy density, carries information about both the bonding and binding details and provides a deeper insight into the nature of chemical bond. Atomic and global binding entropies also appeared to be useful descriptors giving a compact description of chemical binding.

Guanidine condensed with 1,4-diformyl-2,3,5,6-tetrahydroxypiperazine 1 to give 2,6-diiminodecahydro-1H,5H-diimidazo[4,5-b:4′,5′-e]pyrazine 3 isolated as the tetrahydrochloride salt. nitric acid (100%) at −40°C converted the bisguanidine 3 to 2,6-dinitrimino-4,8-dinitrodecahydro-1H,5H-diimidazo[4,5-b:4′,5′-e]- pyrazine 8 isolated as a dihydrate, whereas nitration by nitronium tetrafluoroborate at 0° to 25°C afforded 2,6-diimino-4,8-dinitrodecahydro-1H,5H-diimidazo[4,5-b:4′,5′-e]pyrazine 9 isolate as the monohydrated bistetrafluoroborate salt, and treatmetn with nitric acid (100%) and acetic anhydride or phosphorus pentoxide converted the bisguanidine 3 to 2,6-dioxo-1,3,4,5,7,8-hexanitrodecahydro-1H,5H-diimidazo[4,5-b:4′,5′-e]pyrazine 4, also obtained from the tetra N-nitro compound 8 · 2 H2O and from the dinitramine 9 · 2 BHF4 · H2O after similar treatment. The cis-syn-cis- configuration of the tricyclic bisurea 4 and bisguanidine 9 was confirmed by X-ray crys-tallographic analysis. Nitrosation by nitrous acid or by dinitrogen tetroxide converted the bisguanidine 3 to a hydrated 2,6-dinitrosimino-4,8-dinitrosodecahydro-1H,5H-diimidazo[4,5-b:4′,5′-]pyrazine 10 · 2.5 H2O, whereas treatment with nitrosonium tetrafluo-roborate afforded the bistetrafluoroborate salt of 4,8-dinitroso derivative 11 · 2 BHF 4. The nitrosamines 10 and 11 were converted to the tetranitro compound 8 · 2 H2O on treatment with nitric acid (100%) at −40°C. Treatmnt with fluoroboric acid etherate in acetonitrile converted nitroimino groups in compound 8 · 2 H2O and nitrosimino groups in compound 10 · 2.5 H2O to imino groups in compounds 9 · 2 BHF2 · H2O and 11 · 2 HBF4 respectively.

We have used in this work the crossover soft-SAFT (soft-Statistical Associating Fluid Theory) equation of state to model nitrogen dioxide/dinitrogen tetroxide (NO2/N2O4), carbon dioxide (CO2) and their mixtures. The prediction of the vapor–liquid equilibrium of this mixture is of utmost importance to correctly assess the NO2 monomer amount that is the oxidizing agent of vegetal macromolecules in the CO2 + NO2/N2O4 reacting medium under supercritical conditions. The quadrupolar effect was explicitly considered when modeling carbon dioxide, enabling to obtain an excellent description of the vapor–liquid equilibria diagrams. NO2 was modeled as a self-associating molecule with a single association site to account for the strong associating character of the NO2 molecule. Again, the vapor–liquid equilibrium of NO2 was correctly modeled. The molecular parameters were tested by accurately predicting the very few available experimental data outside the phase equilibrium. Soft-SAFT was also able to predict the degree of dimerization of NO2 (mimicking the real NO2/N2O4 situation), in good agreement with experimental data. Finally, CO2 and NO2 pure compound parameters were used to predict the vapor–liquid coexistence of the CO2 + NO2/N2O4 mixture at different temperatures. Experimental pressure–CO2 mass fraction isotherms recently measured were well described using a unique binary parameter, independent of the temperature, proving that the soft-SAFT model is able to capture the non-ideal behavior of the mixture.

The adsorption of dinitrogen tetroxide (N2O4) on multi‐walled carbon nanotubes (MWCNTs) has been studied by FT‐IR, Raman and X‐ray photoelectron spectroscopy (XPS). The N2O4 adsorption is fully reversible, and after the desorption there is no evidences of MWCNTs nitration. Instead, the MWCNTs have been found oxidized by the action of N2O4. By thermogravimetric analysis (TGA) about 5% by weight of oxygenated groups have been found. Thermal analysis has revealed that MWCNTs having a surface area of 275 m2/g are able to reversibly adsorb about 25% by weight of N2O4, a value comparable to that observed for certain active carbons.

The graft copolymerization of thermomechanical pulp previously oxidized by dinitrogen tetroxide was initiated by the xanthate method. The effects of certain parameters, e.g. level of oxidation of the pulp, nature of metal ions, initial pH of reaction, reaction time and temperature, monomer:pulp ratio as well as nature of monomer (methyl methacrylate, styrene or acrylonitrile), were investigated. Graft copolymerization was conducted using both liquid and vapour phase techniques. Compared to nonoxidized pulps, oxidized pulps offer a significant improvement for all grafting parameters. Furthermore, the vapour phase method (particularly when N2 was used as a carrier to transport the monomer to the pulp) provides much better results than the liquid phase method.

In this paper we report the computational results of a density functional study of 73 UN4O12 isomers containing uranyl nitrate, UO2(NO3)2, as a component. The isomers are grouped into three categories and 19 types. Forty-four isomers of 14 types are dinitrogen tetroxide adducts of uranyl nitrate, UO2(NO3)2.N2O4, 22 are nitrosonium salt adducts of uranyl nitrate, NO+UO2(NO3)3-, NO+UO2(NO3)2O(NO2)-, NO+UO2(NO3)2(ONOO)-, or (NO+)2UO2(NO3)2O22-, and 7 are bis(nitrogen dioxide) adducts of uranyl nitrate, UO2(NO3)2.2NO2. The 22 most stable isomers in solution, representing the 20 most stable gas-phase isomers, were selected for analysis. Of these selected structures only two categories and six types were represented. Structures, frequencies, gas-phase and solution energetics, atomic charges, dipole moments, and the bonding within the N2O4 unit and between NO+ and UO2(NO3)3- components have been analyzed in detail. On the basis of relative Gibbs free energy calculations five isomers (the N2O4 adducts a1, a2, and a3 and the nitrosonium salts b1 and b2) were identified as strong candidates to exist and possibly predominate in the gas phase, with a1 and a2 being the strongest candidates. Similarly, four isomers (a6, a5, a8, and a1, all of them N2O4 adducts) were identified as strong candidates to exist and possibly predominate in a nonaqueous solution of nitromethane/dinitrogen tetroxide. Of these, a6 was determined to be the most likely candidate to predominate in solution. The possibility of dissociation in solution has been addressed briefly. In addition, computational evidence for the existence of four new N2O4 isomers 20, 22, 27, and 28 in both the gas and the solution phases is presented for the first time.

The structures of the nitric oxide and dinitrogen tetroxide sorption complexes of dehydrated fully Cd2+-exchanged zeolite X (FAU) have been determined using single-crystal X-ray diffraction in the cubic space group Fdm at 21(1) degrees C. Ion exchange was accomplished by allowing an aqueous stream 0.05 M in Cd2+ to flow past each crystal for 5 days. Each crystal was then dehydrated at 500 degrees C and 2 x 10(-6) Torr for 2 days, followed by exposure to 100 Torr of zeolitically dry NO or NO2/N2O4 gas. The structures were determined in these atmospheres. The unit cell constants at 21(1) degrees C are 24.877(2) A for the dark-yellow NO complex, |Cd46(NO)16|[Si100Al92O384]-FAU, and 24.735(2) A for the black N2O4 complex, |Cd46(N2O4)25.5|[Si100Al92O384]-FAU. The structure of the NO complex was refined to R1 = 0.072 and wR2 = 0.134. In this structure, Cd2+ ions occupy four crystallographic sites. Fifteen Cd2+ ions occupy site I (at the centers of the double 6-rings (D6Rs)), and one occupies site I' (in the sodalite cavity opposite a D6R). The remaining 30 Cd2+ ions occupy two different sites II (near 6-rings in the supercages): 16 coordinate to nitric oxide molecules and 14 do not. Sixteen NO molecules lie in the supercage where each interacts weakly with a Cd2+ ion: Cd-N = 2.57(22) A. The observed N-O bond distance is 1.28(25) A and Cd-N-O is 118(10) degrees. The structure of the N2O4 complex was refined to R1 = 0.084 and wR2 = 0.216. In this structure, Cd2+ ions occupy only three crystallographic sites. The 16 D6Rs per unit cell are filled with 11.5 Cd2+ ions at site I and 9 Cd2+ ions at site I': 11.5 + 9/2 = 16. The remaining 25.5 Cd2+ ions occupy site II where each coordinates at 2.43(8) A to a nitrogen atom of a N2O4 molecule. At the coordinating nitrogen atom, O-N-O is 147(10) degrees and the N-O bond lengths are 1.07(9) and 1.23(10) A. At the second nitrogen atom, O-N-O is 140(10) degrees, and the N-O bond lengths are 1.03(13) and 1.42(12) A. The imprecisely determined N-N bond length, 2.74(17) A, appears to be very much lengthened by coordination to Cd2+. The Cd-N-N angle is 144(10) degrees. This appears to be the first crystallographic report of the coordination of N2O4 to a cation.

[1] Rockets using unsymmetrical dimethyl hydrazine (N(CH3)2NH2) and dinitrogen tetroxide (N2O4) propellants account for about one third of all stratospheric rocket engine emissions, comparable to the solid-fueled rocket emissions. We use plume and global atmosphere models to provide the first estimate of the local and global ozone depletion caused by NO and H2O emissions from the Proton rocket, the largest hydrazine-fueled launcher in use. NO and H2O emission indices are assumed to be 20 and 350 g/kg (propellant), respectively. Predicted maximum ozone loss in the plume of the Proton rocket is 21% at 44 km altitude. Plume ozone loss at 20 km equals 8% just after launch and steadily declines to 2% by model sunset. Predicted steady state global ozone loss from ten Proton launches annually is 1.2 × 10−4%, with nearly all of the loss due to the NO component of the emission. Normalized by stratospheric propellant consumption, the global ozone depletion efficiency of the Proton is approximately 66–90 times less than that of solid-fueled rockets. In situ Proton plume measurements are required to validate assumed emission indices and to assess the role of rocket emissions not considered in these calculations. Such future studies would help to establish a formalism to evaluate the relative ozone depletion caused by different rocket engines using different propellants.

Nitration of aromatic compounds using a zeolite catalyst and a combination of dinitrogen tetroxide and air in a sealed system leads to high yields and para-selectivities in a clean, solvent-free process.

The vapour-phase nitration of fluorobenzene with dinitrogen tetroxide has been investigated over amorphous silica-alumina and zeolites with various structures and aluminium contents. The activity of the catalysts increases with the number and the strength of the acid sites, but is also very dependent on the accessibility controlled by the pore structure and the size of the crystals. Except, the zeolite BEA which is the most active and the most stable, the deactivation of the catalysts is fast since the activity is high. The addition of water to the feed increases the activity and the stability of all the zeolites, but decreases the activity of amorphous silica-alumina. A large part of deactivation is attributed to the marginal formation of 2,4-dinitrofluorobenzene which stays on the surface of the catalyst, but can be eliminated by ‘steam distillation’. No evidence of shape selectivity was obtained. Zeolite BEA proved to be a remarkably efficient catalyst.

Las reacciones de sodio y potasio con óxido de nitrógeno(IV) líquido fueron realizadas para confirmar la naturaleza del producto, que fue predicha por Nekrasov (1976) como MNO3 (M = Na, K). Tanto reacciones químicas clásicas como espectrometría FT–IR fueron empleadas durante el análisis. Se demostró que el producto era nitrato, con nitrito como impureza, en ocasiones. Palabras clave: Metales alcalinos, óxido de nitrógeno(IV), dióxido de nitrógeno, tetróxido de dinitrógeno, nitratos alcalinos, nitritos alcalinos, espectrometría IR.

The dinitrogen tetroxide homolytical dissociation constants K DIS are determined in organic solvents. The values are the highest in non-donor and the lowest in n-donor solvents. The variations of K DIS with solvent are interpreted in terms of electron donor-acceptor interactions between dinitrogen tetroxide and electron donor molecules.

The electrochemical oxidation of thorium in either nitric acid/tri-n-butyl phosphate (TBP) or dinitrogen tetroxide/ethyl acetate/acetonitrile media gives rise to non-aqueous solutions of thorium(IV) nitrate species. The only neutral adduct which could be obtained from HNO3/TBP solution was Th(NO3)4•8dmso (dmso = dimethylsulphoxide). Salts of [Th(NO3)6]2− with Et4N+, [(bpyH)3NO3]2+, and [(phenH)3NO3]2+ (bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline) were also prepared by this route. Solutions in N2O4/EtOAc/CH3CN yield Th(NO3)4, and neutral adducts with dmso, bpy, phen, Ph3PO, and pyridine-N-oxide.

Many kinds of 1-(2-chloroethyl)-3-substituted-3-β-D-glycopyranosyl-1-nitrosoureas (V) were synthesized and tested for antitumor activities against leukemia L1210 and Ehrlich ascites carcinoma. The reaction of aldohexoses such as D-glucose, D-mannose, and D-galactose with primary amines followed by treatment with 2-chloroethyl isocyanate usually gave a mixture of structural isomers of glycosylureas (III'). Complete isomerization into thermodynamically stable β-D-glycopyranosylureas (III) was observed when the mixture of isomers was dissolved in formic acid. Glycopyranosylureas (III) were nitrosated with 5 equivalents of dinitrogen tetroxide followed by treatment with methanol to give the corresponding nitrosoureas (V) in good yields. Many of the nitrosoureas (V) were remarkably active against both leukemia L1210 and Ehrlich ascites carcinoma and showed greater therapeutic ratios than those of the positive controls, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, 3 [(4-amino-2-methyl-5-pyrimidinyl) methyl]-1-(2-chloroethyl)-1-nitrosourea, and 1-(2-chloroethyl)-3-(β-D-glucopyranosyl)-1-nitrosourea. In particular, some of the galactopyranosylnitrosoureas showed excellent antitumor activities and sixtyday survivors against leukemia L1210 were observed at dose levels of 25, 50 and 100 mg/kg of the compounds. These nitrosoureas (V) appear to be activated nonenzymatically by attack of the hydroxyl group of the sugar moiety on the carbonyl group to give the cyclic carbamate (VI) without generation of the isocyanate (XI).

Rapid expansion of vapour through a nozzle inlet system has been used for the study of some molecular species normally only present at pressures much above those usually obtaining at the ionization region of a photoelectron spectrometer. The He I photoelectron spectra for dinitrogen tetroxide and dinitrogen pentoxide obtained in this way are presented and discussed. Comparison is made with Gaussian ab initio molecular orbital calculations and with the spectra of the dissociated species. The relation to nitric acid is also noted. Several possible geometrical structures are considered in the case of dinitrogen pentoxide. It is shown that a planar form with a N–O–N angle of the order of 120° is most consistent with the p. e. s. results.

Lattice dynamics calculations on the cubic crystal N2O4 are described. The model assumes rigid molecules with Lennard–Jones interactions between atoms. The six parameters of the model are optimized to fit the observed zone-centre frequencies, equilibrium condition, and estimated lattice energy. The form of the calculated eigenvectors and the measured relative Raman intensities of the librational modes are used to estimate the components of the polarizability tensor for the N2O4 molecule. Dispersion curves are presented for the (100), (110), and (111) directions of the Brillouin zone, and no imaginary frequencies are encountered.

Twenty-eight para-substituted and eleven ortho-substituted 1, 3-diarylureas were prepared.Their proton nuclear magnetic resonance (1H-NMR) spectra were measured to evaluate the acidity of the ureido protons in the para-substituted ureas, and to estimate the conformations of ortho-substituted molecules. The chemical shifts and acidities of two ureido protons were additively controlled by the two para-substituents in the 1, 3-diarylureas. The sixteen para-substitued diarylureas were nitrosated with gaseous nitrosating reagents (dinitrogen trioxide, dinitrogen tetroxide or nitroxyl chloride) to give unstable isomeric mixtures of 1, 3-diaryl-1-nitrosoureas [R1-C6H4-N(NO)-CO-NH-C6H4-R2] and 1, 3-diaryl-3-nitrosoureas [R1-C6H4-NH-CO-N(NO)-C6H4-R2]. The isomer ratio of each nitrosated urea was correlated with the difference between the chemical shifts (d[NH]) of the two ureido protons in the 1H-NMR spectrum of the starting urea. When d[NH] was below 0.25 ppm (with NOCl) or 0.45 ppm (with N2O3), good linearity was obtained (r(NOCl)=0.943, n=11; r(N2O3)=0.869, n=15). When d[NH] was over 0.25 ppm (NOCl) or 0.45 ppm (N2O3), the 1-nitrosated isomer [R1-C6H4-N(NO)-CO-NH-C6H4-R2] was the sole product. These principles ould not be extended to dinitrogen tetroxide.Thirteen para-substituted diarylureas gave 1- or 3-nitrosated ureido derivatives as sole products and only four gave nitrosated isomeric mixtures.The 1H-NMR spectra of 5 types of ortho-substituted 1, 3-diarylureas were measured for comformational analysis. Their conformations seem to be different from those of para-substituted diarylureas. Eleven ortho-substituted 1, 3-diarylureas were nitrosated with nitrosyl chloride and dinitrogen tetroxide. In many cases, the nitroso group was predominantly introduced at the ureido nitrogen, which is less hindered sterically, and isomeric mixtures of 1- and 3-nitrosated ureas were obtained.

Many kinds of 3, 3-disubstituted-1-(2-chloroethyl)-1-nitrosourea derivatives (V) of aldopentoses were synthesized and tested for antitumor activities against leukemia L1210 and Ehrlich ascites carcinoma. The reaction of aldopentoses with primary amines followed by treatment with 2-chloroethyl isocyanate usually gave a mixture of two or three structural isomers of glycosylureas (III'). Complete isomerization into thermodynamically stable glycopyranosylureas (III) was observed when the mixture of the isomers was dissolved in formic acid. Glycopyranosylureas (III) were nitrosated with 4 equivalents of dinitrogen tetroxide followed by treatment with methanol to give the corresponding nitrosoureas (V) in good yields. A large number of nitrosoureas (V) were remarkably active against leukemia L1210 and Ehrlich ascites carcinoma and showed greater therapeutic ratios than the positive controls, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, 3-[(4-amino-2-methyl-5-pyrimidinyl) methyl]-1-(2-chloroethyl)-1-nitrosourea, and 1-(2-chloroethyl)-3-(β-D-glucopyranosyl)-1-nitrosourea. In particular, many of the arabinopyranosyl-nitrosoureas had large therapeutic ratios (more than fifty) against leukemia L1210 and even larger ones (more than a hundred) against Ehrlich ascites carcinoma. These nitrosoureas (V) appear to be activated nonenzymatically by attack of the hydroxyl group of the sugar moiety on the carbonyl group to give the cyclic carbamate (VII) without generation of the isocyanate.

Structural determination of the isomeric L-arabinosylureas (1a, 2a, and 3a) and their facile isomerization into the thermodynamically stable isomer (3a) by acid are described. The reaction of L-arabinose with 3-methoxy-n-propylamine followed by treatment with 2-chloroethyl isocyanate gave a mixture of the ureas (1a, 2a, and 3a) in a ratio of 3 : 2 : 1. They were determined to be the β anomer (1a) and the α anomer (3a) of 3-(L-arabinopyranosyl)-1-(2-chloroethyl)-3-(3-methoxy-n-propyl) urea and the β anomer (2a) of the corresponding L-arabinofuranosyl derivative, respectively. Isomerization of these ureas was examined in formic acid solution by monitoring their thin layer chromatography. Complete isomerization of both 1a and 2a into 3a was observed, while 1a isomerized into 3a via 2a. Consequently, the selective isomerization of a mixture of these ureas into 3a could readily be effected by formic acid treatment. The nitrosation of these ureas by the use of dinitrogen tetroxide gave the corresponding nitrosoureas (4a, 5a, and 6a), and their structures are discussed.