Decomposition of diphenylamine in nitrocellulose based propellants-I. Optimization of a numerical model to concentration-time data for diphenylamine and its primary degradation products determined by liquid chromatography with dual-amperometric detection

The consumption of diphenylamine (DPA) in two nitrocellulose (NC) based propellants subjected to a heat storage test at 85 degrees has been studied. A previously developed method based on reversed-phase liquid chromatography with dual-amperometric detection was used to monitor the concentrations of DPA, 2-nitro-DPA and 4-nitro-DPA during the test. A numerical model based on first order rate equations was fitted to the obtained analytical data with the use of a specially written curve fitting program. The model implemented in the program describes the initial nitrosation and nitration steps of DPA in aging NC propellants. The use of matrices in the calculation of concentration-time (CT) curves enables the introduction of a general algorithm which can be readily changed in order to simulate any system of first order reactions. The program can therefore be used in other applications such as mechanistic studies in organic synthesis. The general simulation algorithm allows inclusion of unknown (not analysed) components in the reaction mechanism. In this application, it was possible to simulate the course of N-nitroso-DPA which is not detectable by the amperometric principle.     

Effect of mechanical grinding on the reaction pathway and kinetics of the thermal decomposition of hydromagnesite

Effect of mechanical grinding of hydromagnesite on the reaction pathway and kinetic behaviors of the thermal decomposition process was investigated by means of thermoanalytical techniques, together with crystallographic and morphological measurements. A crystalline hydromagnesite, the as-received sample, was decomposed in two distinguished mass loss steps of overlapped dehydration-dehydroxylation and dehydroxylation-decarbonation via an amorphous intermediate of carbonate compound. Thermal decomposition of an amorphous hydromagnesite, obtained by mechanical grinding of the as-received sample, was characterized by three well-separated decomposition processes of dehydration, dehydroxylation and decarbonation. The kinetic behaviors of the respective decomposition steps were estimated separately using a mathematical deconvolution of the partially overlapped reaction steps. From the formal kinetic analyses of the respective reaction processes, it was revealed that the dehydration and dehydroxylation processes indicate the decelerate rate behaviors controlled by diffusion, while the rate behavior of nucleation limited type is predominant for the decarbonation process.     

Pyrolysis of Nickel Zirconyl Oxalate

Nickel zirconyl oxalate hexahydrate (NiZrOx) is δ prepared and characterised by I.R. spectral and chemical analysis. Its thermal decomposition has been investigated by employing TG, DTG, DTA and chemical analysis. End product was identified by X-ray diffraction studies. The decomposition proceeds through four steps i) dehydration of NiZrOx in two steps, ii) partial decomposition of oxalate to give an oxalate carbonate intermediate, iii) decomposition of oxalate to give a non-stoichiometric carbonate and iv) decomposition of this non-stoichiometric carbonate to give the end product a mixture of NiO+ZrO₂. On the basis of the results obtained, a tentative scheme for the decomposition of NiZrOx is proposed.     

The electrophilic reactions of pentacyanonitrosylferrate(II) with hydrazine and substituted derivatives. Catalytic reduction of nitrite and theoretical prediction of eta(1)-, eta(2)-N(2)O bound intermediates

The electrophilic reactivity of the pentacyanonitrosylferrate(II) ion, [Fe(CN)(5)NO](2)(-), toward hydrazine (Hz) and substituted hydrazines (MeHz, 1,1-Me(2)Hz, and 1,2-Me(2)Hz) has been studied by means of stoichiometric and kinetic experiments (pH 6-10). The reaction of Hz led to N(2)O and NH(3), with similar paths for MeHz and 1,1-Me(2)Hz, which form the corresponding amines. A parallel path has been found for MeHz, leading to N(2)O, N(2), and MeOH. The reaction of 1,2-Me(2)Hz follows a different route, characterized by azomethane formation (MeNNMe), full reduction of nitrosyl to NH(3), and intermediate detection of [Fe(CN)(5)NO](3)(-). In the above reactions, [Fe(CN)(5)H(2)O](3)(-) was always a product, allowing the system to proceed catalytically for nitrite reduction, an issue relevant in relation to the behavior of the nitrite and nitric oxide reductase enzymes. The mechanism comprises initial reversible adduct formation through the binding of the nucleophile to the N-atom of nitrosyl. The adducts decompose through OH(-) attack giving the final products, without intermediate detection. Rate constants for the adduct-formation steps (k = 0.43 M(-)(1) s(-)(1), 25 degrees C for Hz) decrease with methylation by about an order of magnitude. Among the different systems studied, one-, two-, and multielectron reductions of bound NO(+) are analyzed comparatively, with consideration of the role of NO, HNO (nitroxyl), and hydroxylamine as bound intermediates. A DFT study (B3LYP) of the reaction profile allows one to characterize intermediates in the potential hypersurface. These are the initial adducts, as well as their decomposition products, the eta(1)- and eta(2)-linkage isomers of N(2)O.     

Density functional theory studies of negishi alkyl-alkyl cross-coupling reactions catalyzed by a methylterpyridyl-Ni(I) complex

Density functional theory calculations were done to examine the potential energy surfaces of Ni(I)-catalyzed Negishi alkyl-alkyl cross-coupling reactions by using propyl iodide and isopropyl iodide as model alkyl electrophiles and CH 3ZnI as a model alkyl nucleophile. A four-step catalytic cycle involving iodine transfer, radical addition, reductive elimination, and transmetalation steps were characterized structurally and energetically. The reaction mechanism for this catalytic cycle appears feasible based on the calculated free energy profiles for the reactions. The iodine transfer step is the rate-determining step for the Ni(tpy)-CH 3 (tpy = 2,2'6',2'-terpyridine) reactions with alkyl iodides. For secondary alkyl electrophiles, the oxidative addition intermediate, Ni(III), prefers to undergo decomposition over reductive elimination, whereas for the primary alkyl electrophiles, Ni(III) prefers to undergo reductive elimination over decomposition based on comparison of the relative reaction rates for these two types of steps. In addition, thermodynamic data were employed to help explain why the yield of the coupled product is very low from the Ni(II)-alkyl halide reactions with organozinc reagents.     

On the reported emission from the T2 state during ECL of 9,10-diphenylanthracene

The long wavelength component of the emission occurring during the electron transfer reaction of the electrogenerated radical ions of 9,10-diphenylanthracene (DPA) in acetonitrile and 1,2-dimethoxyethane solutions, previously attributed to T₂ → T₁ emission, was investigated. Several sources contributing to detection of emission at wavelengths beyond 620 nm are discussed and the major source is attributed to a stable product formed by a small amount of decomposition of DPA radical cation.     

Reaction of a copper(II)-nitrosyl complex with hydrogen peroxide: putative formation of a copper(I)-peroxynitrite intermediate

The reaction of a Cu(II)-nitrosyl complex (1) with hydrogen peroxide at -20 °C in acetonitrile results in the formation of the corresponding Cu(I)-peroxynitrite intermediate. The reduction of the Cu(II) center was monitored by UV-visible spectroscopic studies. Formation of the peroxynitrite intermediate has been confirmed by its characteristic phenol ring nitration reaction as well as isolation of corresponding Cu(I)-nitrate (2). On air oxidation, 2 resulted in the corresponding Cu(II)-nitrate (3). Thus, these results demonstrate a possible decomposition pathway for H(2)O(2) and NO through the formation of a peroxynitrite intermediate in biological systems.     

Mechanistic and spectroscopic identification of initial reaction intermediates for prenal decomposition on a platinum model catalyst

The prediction of a reaction mechanism and the identification of the corresponding chemical intermediates is a major challenge in surface science and heterogeneous catalysis, due to a complex network of elementary steps and surface species. Here we demonstrate how to overcome this difficulty by tracking the temperature dependent formation of the initial reaction intermediates and identifying the decomposition pathways in the case of prenal, an α,β-unsaturated aldehyde, on the Pt(111) model catalyst surface by combining vibrational spectroscopy, thermal reaction/desorption spectroscopy (TPRS) experiments and detailed theoretical analysis. TPRS characterization of this reaction up to 600 K shows a series of desorption states of H(2) (～280 K, 410 K and 473 K) and CO (～414 K), giving valuable insights into the sequence of elementary steps suggesting that the loss of hydrogen and the carbonyl functions are among the first elementary steps. HREELS experiments recorded after annealing to specific temperatures result in complex spectra, which can be assigned to several subsequently formed and transformed surface intermediates. Starting from stable prenal adsorption structures, complementary DFT calculations allow the determination of the most likely reaction pathway for the initial decomposition steps and the identification of the corresponding intermediates by comparison with HREELS. The decomposition occurs from the strongly bonded prenal adsorption structures via a dehydro-η(3)-triσ(CCC)-H1 intermediate to the highly stable η(1)-isobutylidyne species at high temperatures.     

Ru(3)(CO)(12) in Acidic Media. Intermediates of the Acid-Cocatalyzed Water-Gas Shift Reaction (WGSR)

The elucidation of the WGSR promoted by ruthenium carbonyls in acidic media started with the detection of the Ru(0), Ru(I), and Ru(II) intermediate complexes, namely Ru(3)(CO)(12), Ru(2)[&mgr;-eta(2)-OC(CF(3))O](2)(CO)(6), and fac-[Ru(CF(3)COO)(3)(CO)(3)](-), which accumulate when CF(3)COOH is employed as an acid cocatalyst. Under catalytic conditions, the three were found to interconvert through elementary steps which produce CO(2) and H(2). In fact, Ru(0) is oxidized by H(+) to Ru(I) and half the hydrogen of the catalytic cycle is supplied by this reaction. On the other hand, Ru(I) disproportionates to Ru(0) and Ru(II), and this latter species undergoes nucleophilic attack by H(2)O. The decomposition of the metallacarboxylic acid intermediate gives back Ru(I), while H(2) and CO(2) are produced in a 1/2 molar ratio. The two alternating pathways for dihydrogen formation, namely Ru(0) oxidation by H(+) and the decomposition of a metallacarboxylic acid intermediate, involve H(2) reductive elimination from the same RuHCF(3)COO(CO)(2)L(2) intermediate (L = H(2)O, ethers). These findings define an acid-cocatalyzed WGSR whose distinctive features are (i) the intervention of a disproportionation reaction to generate a Ru(II) electron poor complex, whose CO ligands can undergo nucleophilic attack by water, (ii) the generation of the hydrido intermediate for dihydrogen production through two distinct reaction patways, and (iii) the reductive elimination of H(2) from the hydrido intermediate without involving H(+) from the medium.     

16-脱氢孕烯醇酮醋酸酯的环境友好合成法

Instead of environmentally toxic chromium oxidant, singlet oxygen generated photcchemically was used as environmentally friendly and benign oxidizing agent to accomplish the transformation of pseudodiosgenin diacetate to diosone efficiently in a low toxic and less expensive solvent acetone. Accordingly 16-dehydropregnenolone acetate(16-DPA), an important intermediate for preparation of steroidal drugs, was prepared in good yield (75%) when photoreaction was run in acetone/acetic anhydride/pyridine system. The mild reaction condition as well as simple and environmentally friendly process made the method commercially viable and important for production of 16-DPA in industrial scale.     

Peroxyoxalate High‐Energy Intermediate is Efficiently Decomposed by the Catalyst Imidazole

The peroxyoxalate reaction is a highly efficient chemiluminescence system, its chemiexcitation process involving the intermolecular interaction between an activator (ACT) and the high‐energy intermediate (HEI) of the reaction. Typically, the HEI is generated through the reaction of an oxalate ester with H₂O₂, in the presence of a basic/nucleophilic catalyst, such as imidazole (IMI‐H). IMI‐H, besides catalyzing the formation of the HEI, is also known to decompose this peroxidic intermediate. Despite that, up to now, no rate constant value has been determined for such significant interaction. Through kinetic measurements, we have observed that IMI‐H is roughly four times more efficient than 9,10‐diphenylanthracene (DPA), a classic ACT, in catalyzing the decomposition of the HEI by a bimolecular electron transfer reaction through a Chemically Initiated Electron Exchange Luminescence‐like process. For instance, when IMI‐H and DPA are at the same concentration, 78% of the generated HEI is actually consumed by the nonemissive bimolecular interaction with IMI‐H. We have obtained an average singlet excited state formation quantum yield, at infinite ACT concentration, of (5.5 ± 0.5) × 10^?2 E mol^?1, determined at five different IMI‐H concentrations. This ultimately suggests that the yield of formation of HEI actually does not depend on the IMI‐H concentration.     

Online kinetic studies on intermediates of laccase-catalyzed reaction in reversed micelle

Using water/AOT/n-octane reversed micelle as the medium, the optical signal of the reactive intermediate of laccase-catalyzed oxidation of o-phenylenediamine, which was indetectable in aqueous solutions, was successfully captured. Thus online kinetic studies of the intermediate were accomplished. Two-way kinetic spectral data were acquired with stopped-flow technique. By resolving the data with global analysis software, both the kinetic curves and the absorption spectra of the components involved in the reaction process were simultaneously obtained. The whole reaction in the reversed micelle was proved to be composed of two successive steps, an enzymatic generation of the intermediate and a following nonenzymatic decay of the intermediate. A consecutive first-order kinetic model of the whole reaction was confirmed. The influences of microenvironmental factors of the medium (such as the pH value of the water pool and the water/AOT ratio) on the detection of the intermediate were also investigated.     

Kinetic Modelling of the Concentrations of the Stabilizer DPA and Some of Its Consecutive Products as Function of Time and Temperature

By kinetic modelling of the possible reactions of diphenylamine (DPA) and its nitrated consecutive products used to stabilize cellulose nitrate (CN), one can get reactivities for the nitrated DPA compounds for the situation inside a real CN formulation and therewith determine their stabilizing contribution. Concentration data of DPA and seven of its consecutive products have been determined by HPLC from isothermal ageing of a CN formulation at temperatures between 65 and 90°C for up to 344 days. A comparison between the modelling presented and modellings published in the literature using the steady-state approximation is made. The steady-state approximation oversimplifies the stabilizer reaction behaviour in a CN formulation. From the applied modelling the question about N—NO—DPA as a key intermediate can be answered.This revised version was published online in November 2005 with corrections to the Cover Date.     

Media effects on the kinetics of anthracene photo-oxidation in polymers

An improved quantitative analysis of the photochemical reaction of diphenylanthracene (DPA) in thin films of poly(ethyl methacrylate) (PEMA) is reported. This analysis confirms the previous suggestion (J.R. Sheats, J. Phys. Chem., 94 (1990) 7194) that the rate of reaction between singlet oxygen and DPA decreases as the reaction proceeds, consistent with the hypothesis that the free volume is decreased by endoperoxide formation. For [DPA]≈30 wt.%, the rate constant decreases by approximately 50% for complete conversion. The initial value is 25-fold smaller than in fluid solution, and decreases slightly as [DPA] is increased.     

Diisopropyl fluorophosphate (DFP) degradation activity using transition metal–dipicolylamine complexes

Transition metal complexes have been extensively used as catalysts for organophosphorus agent decomposition to reduce their toxicity with their performance being strongly dependent on the nature of the metal ion. To investigate this dependence, we prepared dipicolylamine (DPA)‐containing complexes of Cu(II), Zn(II), Ni(II), Co(II), and Fe(II) and analyzed their activities for the degradation of diisopropyl fluorophosphate (DFP), a nerve agent surrogate compound. Cu(II)‐DPA complex showed fastest reaction kinetics while Zn(II)‐DPA and Ni(II)‐DPA exhibited more slower reactions. This observation can be explained using frontier molecular orbital (FMO) theory, which revealed that the nucleophilicity of the oxygen atom in water molecules in these transition metal complexes was well matched with reactivity order observed in experiments. These investigations combined with theoretical study provide valuable information for designing and predicting the activity of new transition metal–organic ligand complexes as a catalyst to decompose and reduce toxicity of organophosphorus nerve agents.     

Determination of haloperidol and reduced haloperidol in human serum by liquid chromatography after fluorescence labeling based on the Suzuki coupling reaction

A simultaneous method for the determination of haloperidol (HP) and its metabolite, reduced haloperidol (RHP), in human serum was developed by means of high-performance liquid chromatography (HPLC) with fluorescence detection. Suzuki coupling reaction with a fluorescent arylboronic acid, 4-(4,5-diphenyl-1H-imidazol-2-yl)phenylboronic acid (DPA), was employed to convert HP and RHP into highly fluorescent compounds. HP and RHP were extracted from human serum by liquid-liquid extraction with a mixture of n-hexane and isoamyl alcohol (99:1, v/v) and subsequently labeled by reaction with DPA. Separation of DPA derivatives of HP and RHP was performed on a silica column with a mixture of acetonitrile and H(2)O (90:10, v/v) containing triethylamine and acetic acid as a mobile phase. The proposed method allowed sensitive detection of HP and RHP in human serum with a detection limit (at a signal to noise ratio of 3) of 0.22 and 0.20 ng/mL, respectively. The applicability of the method for therapeutic drug monitoring (TDM) was demonstrated by analyzing human serum samples from schizophrenic patients receiving HP.     

Effect of diphenylamine on photodissociation of aryl azides

The charge-transfer complexes of aromatic azides with diphenylamine (DPA) were studied. Irradiation of 4-nitrophenyl azide in the presence of DPA was found not to give rise to the dissociation of the azido group in the azide radical anionvia intracomplex electron transfer. The photodissociation slows down due to both the static (the formation of a photostable complex with diphenylamine) and dynamic quenching. When 4-azidoacetophenone is irradiated in the presence of DPA, the amine-sensitized decomposition of azide and the photodecomposition of the azide—DPA complex occur along with the direct photolysis of azide, which results in acceleration of the photodissociation due to an increase in the efficiency of the light absorption by the reaction system. A possible sensitization of photodecomposition of aromatic azidesvia an electron transfer mechanism by irradiation of the azide-donor complex is shown.     

Density-dependent liquid nitromethane decomposition: molecular dynamics simulations based on ReaxFF

The decomposition mechanism of hot liquid nitromethane at various compressions was studied using reactive force field (ReaxFF) molecular dynamics simulations. A competition between two different initial thermal decomposition schemes is observed, depending on compression. At low densities, unimolecular C-N bond cleavage is the dominant route, producing CH(3) and NO(2) fragments. As density and pressure rise approaching the Chapman-Jouget detonation conditions (～30% compression, >2500 K) the dominant mechanism switches to the formation of the CH(3)NO fragment via H-transfer and/or N-O bond rupture. The change in the decomposition mechanism of hot liquid NM leads to a different kinetic and energetic behavior, as well as products distribution. The calculated density dependence of the enthalpy change correlates with the change in initial decomposition reaction mechanism. It can be used as a convenient and useful global parameter for the detection of reaction dynamics. Atomic averaged local diffusion coefficients are shown to be sensitive to the reactions dynamics, and can be used to distinguish between time periods where chemical reactions occur and diffusion-dominated, nonreactive time periods.     

CL-20热分解反应机理的ReaxFF分子动力学模拟

为探究固相CL-20热分解反应机理,本文采用反应分子动力学ReaxFF MD模拟研究了含有128个CL-20分子的超胞模型在800–3000 K温度下的热分解过程。借助作者所在课题组研发的反应分析及可视化工具VARxMD得到了热分解过程中多种反应中间物和较为全面的反应路径。氮氧化物是CL-20初始分解的主要中间产物,其中NO₂是数量最多的初始分解产物,观察到的中间物NO₃的生成量仅次于NO₂。统计CL-20初始分解的所有反应后发现,在所有考察温度下CL-20初始分解路径主要是N―NO₂断裂反应和C―N键断裂引起开环的单分子反应路径。N―NO₂断裂反应数量在高温下显著增多,而C―N键断裂引起的开环反应数量随温度升高变化不大。在低温热分解模拟中还观察到CL-20初始分解阶段生成的NO₂会发生双分子反应—从CL-20分子中夺氧生成NO₃。对CL-20热分解过程中环结构演化进行分析后发现,CL-20分解的早期反应中间物主要为具有3元或2元稠环结构的吡嗪衍生物,随后它们会分解形成单环吡嗪。吡嗪六元环结构在热分解过程中非常稳定,这一模拟结果支持Py-GC/MS实验中提出吡嗪存在的结论。CL-20中的咪唑五元环结构相对不稳定,在热分解过程中会发生开环分解而较早消失。由ReaxFF MD模拟得到的3000 K高温热分解产物N₂,H₂O,CO₂和H₂的数量与爆轰实验的测量结果定量吻合。本文获得的对CL-20热分解机理的认识表明ReaxFF MD结合VARxMD有可能为深入了解热刺激下含能材料复杂化学过程提供一种有前景的方法。     

Antibody-catalyzed benzoin oxidation as a mechanistic probe for nucleophilic catalysis by an active site lysine

Aldolase antibody 24H6, which was obtained by reactive immunization against a 1,3-diketone hapten, is shown to catalyze additional reactions, including H/D exchange and oxidation reactions. Comparison of the H/D exchange reaction at the alpha-position of a wide range of aldehydes and ketones by 24H6 and by other aldolase antibodies, such as 38C2, pointed at the significantly larger size of the 24H6 active site. This property allowed for the catalysis of the oxidation of substituted benzoins to benzils by potassium ferricyanide. This reaction was used as a mechanistic probe to learn about the initial steps of the 24H6-catalyzed aldol condensation reaction. The Hammett correlation (rho=4.7) of log(k(cat)) versus the substituent constant, sigma, revealed that the reaction involves rapid formation of a Schiff base intermediate from the ketone and an active site lysine residue. The rate-limiting step in this oxidation reaction is the conversion of the Schiff base to an enamine intermediate. In addition, linear correlation (rho=3.13) was found between log(K(M)) and sigma, indicating that electronic rather than steric factors are dominant in the antibody-substrate binding phenomenon and confirming that the reversible formation of a Schiff base intermediate comprises part of the substrate-binding mechanism.