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Here we present analysis of a novel reactive material system that employs dinitrogen tetroxide (N 2 O 4) 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/N 2 O 4 reactivity was found to be most likely limited by the vaporization of the metal from the particle surface and Zr/N 2 O 4 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 N 2 O 4 can be added remotely and driven to evaporate via vacuum or purge of inert gases to return it to a safe condition. [ABSTRACT FROM AUTHOR]

A new solvate of a powerful explosive 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (CL‐20) and liquid oxidizer N2O4 has been synthesized. When stored at room temperature, the white crystals turn yellowish brown, which indicates partial dissociation of N2O4 with the formation of a stable NO2 free radical, which is confirmed by ESR spectroscopy. The resulting solvate was analyzed by powder X‐ray diffraction, IR‐spectroscopy, differential scanning calorimetry and thermogravimetric analysis. The vapor pressure of NO2 above the solvate crystals is similar to the pressure above common hydrates. The presence of the NO2 radical does not affect the thermal stability of CL‐20. However, under closed conditions, NO2 increases the rate of the autocatalytic decomposition reaction. The kinetics of this reaction at the surface temperature determine the burning rate of the solvate. The novel solvate has a high density (1.98 g cm−3), a high predicted detonation velocity and pressure, and sensitivity to impact slightly higher to that of ϵ‐CL‐20. [ABSTRACT FROM AUTHOR]

Highlights • Pure N 2 O 4 and N 2 O 4 /CO 2 mixtures are investigated as working fluid in CSP plants. • Two simple regenerative cycles using pure N 2 O 4 and N 2 O 4 /CO 2 mixtures are designed. • The N 2 O 4 /CO 2 composition is optimised for the considered application. • Two solar fields with maximum temperatures of 565 °C and 715 °C are designed with dedicated tools. • The overall solar-to-electric efficiency is determined for all the studied cases. Abstract The competitiveness of concentrated solar power technology in the near-future electricity generation scenario, requires a substantial reduction of the Levelized Cost of Energy which can be achieved with an increase of the energy conversion efficiencies while maintaining or reducing the investment costs. This paper discusses the use of pure Dinitrogen tetroxide N 2 O 4 , and N 2 O 4 /CO 2 mixture, as working fluids in supercritical Brayton cycles applied to solar tower power plants. When N 2 O 4 is combined with CO 2 , the resulting mixture has a comparatively higher critical temperature than pure CO 2 , allowing a condensing cycle even at the fairly high ambient temperatures of desert areas, where solar power plants are typically installed. This allows the adoption of simpler cycle configurations than the one used in sCO 2 cycles (cost reduction) while achieving very high thermodynamic efficiency (47% at 700 °C). The N 2 O 4 /CO 2 mixture with optimized composition, integrated in a solar tower unit, increases the solar-electric efficiency by 1% with respect to commercial plants based on steam cycle with 550 °C maximum temperature (22.3% vs. 21.3%). At 700 °C, the overall solar-electric efficiency can reach 24.5% which is slightly higher than supercritical CO 2 cycles, yet with a foreseeable reduction of the investment costs as consequence of the simpler plant lay-out. [ABSTRACT FROM AUTHOR]

The oxidation of hexane-2,3,4,5-tetraone tetraoxime with dinitrogen tetroxide was studied in different solvents. The primary furoxan ring closure was found to occur involving either two central or two terminal oxime groups to form 4,7-dimethyl[1,2,5]oxadiazolo[3,4-d]pyridazine 1,5,6-trioxide and the previously unknown 4,4′-dimethyl-[3,3′-bi(1,2,5-oxadiazole)] 5,5′-dioxide. The structure of the latter compound was established by X-ray diffraction. [ABSTRACT FROM AUTHOR]

An efficient method for nitration of aliphatic and heterocyclic nitromethyl- ONN-azoxy derivatives with a mixture of concentrated nitric acid and dinitrogen tetroxide to give the corresponding dinitromethyl- ONN-azoxy compounds was developed. [ABSTRACT FROM AUTHOR]

Highlights: [•] The UV spectra of the reaction of 2NO2 ↔N2O4 with (CF3) n C(CH3) m OH were registered. [•] The rate constant of the reaction in the temperature range 298–358K was obtained. [•] Activation energies for the forward and for the reverse reaction were calculated. [•] The mechanism of the reaction involving N2O4 was proposed. [•] The DFT calculations of UV–Vis spectra and reactions were studied. [ABSTRACT FROM AUTHOR]

Highlights: [•] Products spectra of reactions of 2NO2 ↔N2O4 with some fluorobutanols were registered. [•] The rate constants of the reactions in the temperature range of 298–358K were obtained. [•] The activation energies for the reactions were calculated. [•] The mechanism of the reaction involving N2O4 was proposed. [•] The DFT calculations of UV–Vis spectra and reactions was studied. [Copyright &y& Elsevier]

Abstract: Nitrogen dioxide is formed endogenously via the oxidation of NO by O2 or O2 − and from NO2 − via peroxidases, among other pathways. This radical has many potential biological targets and its concentration, like that of NO and other reactive nitrogen species, is thought to be elevated at sites of inflammation. To investigate the specific cytotoxic or mutagenic effects of NO2, it is desirable to be able to maintain its concentration at constant, predictable, and physiological levels in cell cultures, in the absence of NO. To do this, a delivery system was constructed in which NO2-containing gas mixtures contact a liquid within a small (110ml) stirred reactor. In such gas mixtures NO2 is present in equilibrium with its dimer, N2O4. The uptake of NO2 and N2O4 was characterized by measuring the accumulation rates of NO2 − and NO3 −, the stable products of N2O4 hydrolysis, in buffered aqueous solutions. In some experiments NO2-reactive 2,2′-azino-bis(3-ethyl-benzothiazoline-6-sulfonate) (ABTS) was included and formation of the stable ABTS radical was measured. A reaction–diffusion model was developed that predicts the accumulation rates of all three products to within 15% for gas-phase concentrations of NO2 spanning 3 orders of magnitude. The model also provides estimates for the NO2 concentration in the liquid. This system should be useful for exposing cells to NO2 concentrations similar to those in vivo. [Copyright &y& Elsevier]

Abstract: We present novel measurements of the refractive index, density and integrated band strengths of mid-infrared features of solid N2O at 16K and of NO2 and N2O4 in two frozen NO2:N2O4 mixtures deposited at 16 and 60K. The refractive index and density measurements were performed also for frozen O2 deposited at 16K. In this case, the integrated band strength values could not be determined since O2 is a homonuclear molecule and therefore its fundamental mode is not infrared active. The solid samples were analysed by infrared spectroscopy in the 8000÷800cm−1 range. The sample thickness was measured by the interference curve obtained using a He–Ne laser operating at 543nm. The refractive index at this laser wavelength was obtained, by numerical methods, from the measured amplitude of the interference curve. The density values were obtained using the Lorentz–Lorenz relation. Integrated band strength values were then obtained by a linear fit of the integrated band intensities plotted versus column density values. The astrophysical relevance of these novel measurements is briefly discussed. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical synthesis of dinitrogen pentoxide (N2O5) by oxidation of dinitrogen tetroxide (N2O4) in a plate-and-frame electrolyzer was investigated. As the separator, different porous polytetrafluoroethylene (PTFE) membranes were tested in this process and the effects of hydrophilicity and of hydrophobicity on the electrolysis were discussed. The transport of N2O4 and water from catholyte to anolyte through membrane occurred in the electrolysis, especially at the end of the electrolysis. The water transport had a much more effect on the electrolysis than that of the N2O4 diffusion. The hydrophobic PTFE membranes had better performance on control of water transport from catholyte to anolyte than that of the hydrophilic ones. Hydrophobicity can increase the chemical yield of N2O5. The membranes with a low hydrophobic surface were preferred. All the hydrophobic PTFE membranes with low resistance have the specific energy of 1.1–1.5kWhkg−1 N2O5. The current efficiency of 67.3–80.2% and chemical yield of 58.9–60.9% were achieved in production of N2O5. The technique of replacing the catholyte with fresh nitric acid can minimize the transport of N2O4 and water to a great extent, it can further improve the chemical yield and reduce the specific energy. [Copyright &y& Elsevier]

Selective oxidation of thiols to disulfides (RSSR) was performed by using catalytic amounts of dinitrogen tetroxide/charcoal in chloroform at r.t. while the reaction of thiols with four molar equivalents of the reagent in dichloromethane afforded thiosulfonates (RSO 2 SR) with excellent yields. [ABSTRACT FROM AUTHOR]

Efficient N -nitrosation of amines, amides, and ureas, and also S -nitrosation of thiols were performed with dinitrogen tetroxide impregnated on activated charcoal (N 2 O 4 /charcoal) in CH 2 Cl 2 at room temperature. High selectivity was observed for N -nitrosation of dialkyl amines, N -alkylamides and N -alkylureas. Dealkylation and N -nitrosation of trialkylamines were also performed by this reagent. [ABSTRACT FROM AUTHOR]

Zn(NO3)2 N2O4 and its charcoal supported system were found to be efficient nitrating agents. Mononitration of aromatic compounds such as benzene, alkyl benzenes, halobenzenes, nitrobenzene, anisol, and the highly selective mono-, di-, and trinitration of phenol, and dinitration of substituted phenols were also performed in the presence of these reagents. [ABSTRACT FROM AUTHOR]

The oxidation of thiols with N2O4 to sulfonic acids is presented. One compound 5b shows lyotropic liquid crystalline properties. [ABSTRACT FROM AUTHOR]

G3(MP2)//B3LYP calculations on the unknown tetracyanohydrazine are reported and compared with the results for the known hydrazine, tetramethylhydrazine, tetrafluorohydrazine, and dinitrogen tetroxide. Contrary to previous calculations, tetracyanohydrazine is predicted to have a positive dissociation enthalpy. The energetic and geometric properties of this series of compounds, which vary widely, are analyzed qualitatively using an internally consistent mix of the Weinhold ‘natural-bond-order’ scheme, extended Hu¨ckel theory, and classical electrostatics. The interplay of these factors produces a striking variation in the properties of the hydrazines and demonstrate that these hydrazines are not just another series of analogous compounds. [Copyright &y& Elsevier]

Gaseous N2O4 was immobilized on polyvinylpyrrolidone to give a stable polymeric reagent. Thiols were converted to S-nitrosothiols (thionitrites) using this new nitrosating agent in n-hexane or CHCl3 at 10°C. With this reagent, thiols were also converted into their corresponding disulfides. Selective oxidation of sulfides to sulfoxides and disulfides to thiosulfonates can also be achieved by this reagent at room temperature. By using an excess of the reagent, the selective one-pot synthesis of thiosulfonates from thiols at room temperature was also performed. [Copyright &y& Elsevier]

Various hydrazines such as aryl-, carbonyl-, and sulfonyl-hydrazine were reacted with dinitrogen tetroxide to give the corresponding azides in excellent yields under mild conditions at low temperature (−20-−40°C) in acetonitrile. The reaction appears to be initiated by formation of the β-nitroso hydrazine intermediate which converts into the azide product. [ABSTRACT FROM AUTHOR]

A new method of generation of nitrile oxides through interaction of NO with salts of substituted dinitromethanes ( 1) has been worked out. It has been shown byH,C,N NMR spectroscopy that this reaction proceeds via dinitronitrosomethyl intermediates (one of these has been isolated), and that the reaction is feasible only for substituents capable of conjugation with the nitrile oxide fragment. On the basis of cyclodimerization of the obtained nitrile oxides, preparative methods of synthesis of symmetrically substituted furoxans have been developed. [ABSTRACT FROM AUTHOR]

The C-2 lithiation of N-Boc- and N-(phenylsulfonyl)indoles (4–7) followed by reaction with dinitrogen tetroxide at low temperature affords the corresponding 2-nitroindoles 10–13 in 63–78% yields. Deprotection of the N-Boc-2-nitroindoles (10, 11) with trifluoroacetic acid gives 2-nitroindole (3) and 3-methyl-2-nitroindole (14) in essentially quantitative yields. [Copyright &y& Elsevier]

A new solvate of a powerful explosive 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and liquid oxidizer N 2 O 4 has been synthesized. When stored at room temperature, the white crystals turn yellowish brown, which indicates partial dissociation of N 2 O 4 with the formation of a stable NO 2 free radical, which is confirmed by ESR spectroscopy. The resulting solvate was analyzed by powder X-ray diffraction, IR-spectroscopy, differential scanning calorimetry and thermogravimetric analysis. The vapor pressure of NO 2 above the solvate crystals is similar to the pressure above common hydrates. The presence of the NO 2 radical does not affect the thermal stability of CL-20. However, under closed conditions, NO 2 increases the rate of the autocatalytic decomposition reaction. The kinetics of this reaction at the surface temperature determine the burning rate of the solvate. The novel solvate has a high density (1.98 g cm -3 ), a high predicted detonation velocity and pressure, and sensitivity to impact slightly higher to that of ϵ-CL-20., (© 2020 Wiley-VCH GmbH.)