-
Inorganic Chemistry Apr 2010Recently extensive research has focused on replacing toxic hydrazine, monomethylhydrazine, and unsymmetrical dimethylhydrazine as liquid propellant fuels....
Recently extensive research has focused on replacing toxic hydrazine, monomethylhydrazine, and unsymmetrical dimethylhydrazine as liquid propellant fuels. 2-Azido-N,N-dimethylethylamine (1) is a good candidate to replace hydrazine derivatives in certain hypergolic fuel applications. Energetic ionic liquids that contain the 2-azido-N,N,N-trimethylethylammonium cation with nitrocyanamide, dicyanamide, dinitramide, or azide anion have been successfully synthesized in good yields by metathesis reactions. Ionic liquids have received considerable attention as energetic materials. The replacement of hydrazine with tertiary ammonium salts is especially attractive since many ionic liquids are models for green chemistry. In this work, new azide-functionalized ionic liquids are demonstrated to exhibit hypergolic activity with such oxidizers as 100% nitric acid or nitrogen tetraoxide (NTO).
PubMed: 20175509
DOI: 10.1021/ic902224t -
The Journal of Physical Chemistry. B Aug 2009We report reactive dynamics (RD) studies on: the decomposition of bulk hydrazine (N(2)H(4)); the decomposition of bulk monomethyl-hydrazine (CH(3)N(2)H(3)), hereafter...
We report reactive dynamics (RD) studies on: the decomposition of bulk hydrazine (N(2)H(4)); the decomposition of bulk monomethyl-hydrazine (CH(3)N(2)H(3)), hereafter referred to simply as methyl-hydrazine; the decomposition of hydrazine in the presence of hydrogen peroxide (H(2)O(2)); and decomposition hydrazine on catalytic surfaces Pt[100] and Pt[111] under various conditions. These studies use the ReaxFF reactive force field to describe the multitude of chemical reactions in these systems for a variety of reaction conditions in order to show that this approach leads to realistic decomposition mechanisms and rates. In particular, we determined how the decomposition of hydrazine is affected by temperature, pressure, and heating rate. We analyzed chemical reaction mechanism of the decomposition of hydrazine at the studied conditions and found that at lower temperatures the initial product from hydrazine decomposition is NH(3), whereas at higher temperatures H(2) and N(2) are the dominant early products. Prominent intermediates observed during these decompositions include N(2)H(3), N(2)H(2,) and NH(2), in agreement with quantum mechanical studies (7.3 ps at 3000 K). As the heating rate is decreased, the onset for hydrazine decomposition shifts to lower temperatures. Using a constant heating rate, we found that higher pressure (increased density) favors formation of NH(3) over N(2) and H(2). In studies of the catalytic decomposition of hydrazine on surfaces Pt[100] and Pt[111], we found that the presence of a Pt-catalyst reduces the initial decomposition temperature of hydrazine by about 50%. We found that the Pt[100]-surface is 20 times more active for hydrazine decomposition than the Pt[111]-surface, in qualitative agreement with experiments. These studies indicate how ReaxFF RD can be useful in understanding the chemical processes involved in bulk and catalytic decomposition and in oxidation of reactive species under various reaction conditions.
PubMed: 19601597
DOI: 10.1021/jp900194d -
Journal of Computational Chemistry Nov 2009A direct dynamics study was carried out for the multichannel reaction of CH(3)NHNH(2) with OH radical. Two stable Conformers (I, II) of CH(3)NHNH(2) are identified by...
A direct dynamics study was carried out for the multichannel reaction of CH(3)NHNH(2) with OH radical. Two stable Conformers (I, II) of CH(3)NHNH(2) are identified by the rotation of the -CH(3) group. For each conformer, five hydrogen-abstraction channels are found. The reaction mechanisms of product radicals (CH(3)NNH(2) and CH(3)NHNH) with OH radical are also investigated theoretically. The electronic structure information on the potential energy surface is obtained at the B3LYP/6-311G(d,p) level and the energetics along the reaction path is refined by the BMC-CCSD method. Hydrogen-bonded complexes are presented at both the reactant and product sides of the five channels, indicating that the reaction may proceed via an indirect mechanism. The influence of the basis set superposition error (BSSE) on the energies of all the complexes is discussed by means of the CBS-QB3 method. The rate constants of CH(3)NHNH(2) + OH are calculated using canonical variational transition-state theory with the small-curvature tunneling correction (CVT/SCT) in the temperature range of 200-1000 K. Slightly negative temperature dependence of rate constant is found in the temperature range from 200 to 345 K. The agreement between the theoretical and experimental results is good. It is shown that for Conformer I, hydrogen-abstraction from -NH- position is the primary pathway at low temperature; the hydrogen-abstraction from -NH(2) is a competitive pathway as the temperature increases. A similar case can be concluded for Conformer II. The overall rate constant is evaluated by considering the weight factors of each conformer from the Boltzmann distribution function, and the three-term Arrhenius expressions are fitted to be k(T) = 1.6 x 10(-24)T(4.03)exp (1411.5/T) cm(3) molecule(-1) s(-1) between 200-1000 K.
Topics: Computer Simulation; Hydrogen Bonding; Hydroxyl Radical; Models, Chemical; Monomethylhydrazine; Quantum Theory; Temperature
PubMed: 19242961
DOI: 10.1002/jcc.21228 -
Physical Chemistry Chemical Physics :... Aug 2008The complications during flight 510 of the Ariane Project were ascribed to problems in the upper stage engine that employs the bipropellant monomethylhydrazine (MMH) and...
The complications during flight 510 of the Ariane Project were ascribed to problems in the upper stage engine that employs the bipropellant monomethylhydrazine (MMH) and nitrogen tetroxide (NTO). This has led to the question what conditions or reactions possibly cause an uncontrolled behaviour in the combustion process of MMH/NTO. We use first-principles molecular dynamics to investigate the reactions of the hypergolic mixture in different chemical situations. It was possible to observe the ultrafast redox reaction between the reactants on the timescale of an unconstrained simulation. We show that electrostatic attraction is crucial for the understanding of this reaction. Besides a cold reaction preceding the ignition, a reaction path leading to the highly reactive compound dimethyltetrazane could be identified.
Topics: Computer Simulation; Models, Molecular; Molecular Structure; Monomethylhydrazine; Nitrogen Oxides; Oxidation-Reduction; Quantum Theory; Static Electricity
PubMed: 18654677
DOI: 10.1039/b715740a -
The Journal of Physical Chemistry. A May 2007The reaction kinetics for the thermal decomposition of monomethylhydrazine (MMH) was studied with quantum Rice-Ramsperger-Kassel (QRRK) theory and a master equation...
The reaction kinetics for the thermal decomposition of monomethylhydrazine (MMH) was studied with quantum Rice-Ramsperger-Kassel (QRRK) theory and a master equation analysis for pressure falloff. Thermochemical properties were determined by ab initio and density functional calculations. The entropies, S degrees (298.15 K), and heat capacities, Cp degrees (T) (0 < or = T/K < or = 1500), from vibrational, translational, and external rotational contributions were calculated using statistical mechanics based on the vibrational frequencies and structures obtained from the density functional study. Potential barriers for internal rotations were calculated at the B3LYP/6-311G(d,p) level, and hindered rotational contributions to S degrees (298.15 K) and Cp degrees (T) were calculated by solving the Schrödinger equation with free rotor wave functions, and the partition coefficients were treated by direct integration over energy levels of the internal rotation potentials. Enthalpies of formation, DeltafH degrees (298.15 K), for the parent MMH (CH3NHNH2) and its corresponding radicals CH3N*NH2, CH3NHN*H, and C*H2NHNH2 were determined to be 21.6, 48.5, 51.1, and 62.8 kcal mol(-1) by use of isodesmic reaction analysis and various ab initio methods. The kinetic analysis of the thermal decomposition, abstraction, and substitution reactions of MMH was performed at the CBS-QB3 level, with those of N-N and C-N bond scissions determined by high level CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) calculations. Rate constants of thermally activated MMH to dissociation products were calculated as functions of pressure and temperature. An elementary reaction mechanism based on the calculated rate constants, thermochemical properties, and literature data was developed to model the experimental data on the overall MMH thermal decomposition rate. The reactions of N-N and C-N bond scission were found to be the major reaction paths for the modeling of MMH homogeneous decomposition at atmospheric conditions.
PubMed: 17388291
DOI: 10.1021/jp067591l -
Journal of the American Society For... May 2007Protonated ammonia and hydrazines (MH(+)) form complexes with ketones and the differences in masses and mobilities of the resulting ions, MH(+)(ketone)(n), are...
Protonated ammonia and hydrazines (MH(+)) form complexes with ketones and the differences in masses and mobilities of the resulting ions, MH(+)(ketone)(n), are sufficient for separation in an ion mobility spectrometer at ambient pressure. The highest mass ion for any of the protonated molecules is obtained when the ketone is present at elevated concentrations in the supporting atmosphere of both the source and drift regions of the spectrometer so that an ion maintains a discrete composition and mobility. The sizes of the ion-molecule complexes were found to depend on the number of H atoms on the protonated nitrogen atom--four for ammonia, three for hydrazine, two for monomethylhydrazine, and one for 1,1-dimethylhydrazine, and the drift times of these ions were proportional to the size of the ion-molecule complex. Unexpected side products, including protonated hydrazones and azines, and associated ketone clusters, were isolated to a single drift tube containing ceramic parts and could not, from CID studies, be attributed to gas-phase ion chemistry. These findings illustrate that mobility resolution of ions in IMS and IMS/MS experiments can be enhanced through chemical modification of the supporting gas atmosphere without changes in the core ion.
Topics: Air; Air Pressure; Ammonia; Hydrazines; Ketones; Mass Spectrometry; Protons
PubMed: 17376700
DOI: 10.1016/j.jasms.2007.01.014 -
The Journal of Emergency Medicine Aug 2006Normobaric supplemental oxygen can prolong seizures not caused by hyperbaric oxygen therapy. In addition, hyperbaric oxygen therapy can cause seizures. The mechanism of...
Normobaric supplemental oxygen can prolong seizures not caused by hyperbaric oxygen therapy. In addition, hyperbaric oxygen therapy can cause seizures. The mechanism of hyperbaric oxygen-induced seizures is unknown. We hypothesized that pretreatment with pyridoxine may delay the onset of hyperbaric oxygen-induced seizures, recognizing that pyridoxine is already an antidote for some epileptogenic poisons such as isoniazid and monomethylhydrazine. Therefore, rats were pretreated with intraperitoneal injections of pyridoxine at 48, 24, and 2 h before undergoing hyperbaric oxygen (HBO) treatment at 3 atmospheres absolute with 100% oxygen and were compared to a control group of HBO-treated rats for time to onset of seizures. There was no difference in onset of seizure time between the pyridoxine-treated group of rats and the control rats. Supplemental pyridoxine pretreatment did not alter the time to onset of seizures during HBO treatment in this study.
Topics: Animals; Hyperbaric Oxygenation; Injections, Intraperitoneal; Male; Premedication; Pyridoxine; Random Allocation; Rats; Rats, Sprague-Dawley; Seizures
PubMed: 17044573
DOI: 10.1016/j.jemermed.2005.09.011 -
Journal of Chromatography. A Sep 2006The main toxic compound found in false morel (Gyromitra esculenta) is acetaldehyde-N-methyl-N-formylhydrazone (gyromitrin). This paper describes a method of determining...
Gas chromatography-mass spectrometry determination of the pentafluorobenzoyl derivative of methylhydrazine in false morel (Gyromitra esculenta) as a monitor for the content of the toxin gyromitrin.
The main toxic compound found in false morel (Gyromitra esculenta) is acetaldehyde-N-methyl-N-formylhydrazone (gyromitrin). This paper describes a method of determining the total hydrazones content based on acid hydrolysis of gyromitrin and other related hydrazones in air-dried false morel followed by derivatisation of methylhydrazine with pentafluorobenzoyl chloride. The derivative, tris-pentafluorobenzoyl methylhydrazine (tris-PFB-MH) is analyzed by gas chromatography-mass spectrometry. The overall precision of the method is better than 10% (relative standard deviation) for 0.5 ng/microl methylhydrazine in solution. The minimum detectable concentration of methylhydrazine (tris-PFB-MH) by this method is estimated to be approximately 12 pg/microl, which is equal to 0.3 microg/g dry matter (DM) of false morel.
Topics: Acetaldehyde; Ascomycota; Benzoates; Gas Chromatography-Mass Spectrometry; Hydrolysis; Monomethylhydrazine; Mycotoxins
PubMed: 16782115
DOI: 10.1016/j.chroma.2006.05.040 -
The Journal of Physical Chemistry. A May 2006Stationary points of paths for H atom abstraction from CH(3)NHNH(2) (monomethylhydrazine) by NO(2) were characterized via CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p)...
Stationary points of paths for H atom abstraction from CH(3)NHNH(2) (monomethylhydrazine) by NO(2) were characterized via CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) and CCSD(T)/6-311+G(2df,p)//CCSD/6-31+G(d,p) calculations. Five transition states connecting CH(3)NHNH(2)-NO(2) complexes to a manifold that includes CH(3)NHNH-HONO, CH(3)NNH(2)-HONO, CH(3)NNH(2)-HNO(2), and CH(3)NHNH-HNO(2) complexes were identified. Transition states that connect CH(3)NHNH-HONO, CH(3)NNH(2)-HONO, CH(3)NNH(2)-HNO(2), and CH(3)NHNH-HNO(2) complexes to each other via H atom exchange and/or hindered internal rotation were also identified. The high point in the minimum energy path from the CH(3)NHNH(2) + NO(2) reactant asymptote to the manifold of HONO-containing product states is a transition state 8.6 kcal/mol above the reactant asymptote. From a kinetics standpoint, this value is considerably higher than the 5.9 kcal/mol value that was estimated for it based on theoretical results for H atom abstraction from NH(3) by NO(2).
PubMed: 16671684
DOI: 10.1021/jp060210j -
Electrophoresis Sep 2005The present study is concerned with the application of nonaqueous capillary electrophoresis (NACE) with electrochemical detection (ED) to the separation and quantitative...
The present study is concerned with the application of nonaqueous capillary electrophoresis (NACE) with electrochemical detection (ED) to the separation and quantitative determination of hydrazine (Hy) and its methyl derivatives. The best performance of NACE-ED was found when using 4 mM sodium acetate/10 mM acetic acid/methanol: acetonitrile = 1:2 as the running buffer, with a bare platinum working electrode set at +1.0 V in an end-column amperometric detection cell. The choice and ratio of suitable solvents for the separation and injection media played an essential role for the performance characteristics of the method. The limits of detection for Hy, methylhydrazine, symmetrical dimethylhydrazine, and unsymmetrical dimethylhydrazine were 5, 2, 12, and 1 ng/mL, respectively. This is between one and two orders of magnitude lower than that achieved by previously reported CE-ED methods in aqueous buffer systems in conjunction with various types of chemically modified electrodes. The practical utility of the new NACE-ED methodology is demonstrated in terms of the determination of traces of Hys in spiked environmental samples containing a wide range of explosives and related compounds.
Topics: 1,2-Dimethylhydrazine; Dimethylhydrazines; Electrochemistry; Electrophoresis, Capillary; Hydrazines; Monomethylhydrazine
PubMed: 16097027
DOI: 10.1002/elps.200500188