High temperature pyrolysis of formaldehyde in shock waves

Thermal decomposition of formaldehyde diluted with Ar was studied behind reflected shock waves in the temperature range of 1200–2000 K at total pressures between 1.3 and 3.0 atm. The study was carried out for compositions from the concentrated mixture, 4% CH₂O, to the highly dilute mixture, 0.01% CH₂O by using time-resolve IR-laser absorption and IR-emission, and a single-pulse technique. From a computer-simulation study, the mechanism and the rate-constant expressions that could explain all of our data and previously reported ARAS data were discussed. This data obtained over a wide concentration range from 50 ppm CH₂O to 4% CH₂O were satisfactorily modeled by a five-reaction mechanism. © 1993 John Wiley & Sons, Inc.     

The three corrugated surfaces of 1,4-divinyltetramethylene diradical intermediates and their connections to 1,2-divinylcyclobutane, 4-vinylcyclohexene, 1,5-cyclooctadiene, and two butadienes

The three potential energy surfaces of the trans-trans, cis-trans, and cis-cis divinyltetramethylene diradicals have been located with DFT calculations at the BPW91/6-311+G levels. The three surfaces account well for the experimental results reported for the thermolysis of optically active trans-1,2-divinylcyclobutane and optically active and deuterated 4-vinylcyclohexene. The surfaces account also for the outcome of the dimerization of butadiene and the thermolysis of cis,cis-1,5-cyclooctadiene. The three diradical intermediates are connected to the cyclization and dissociation products through conformations that are explored fully here.     

1,5-环辛二烯阳离子型跨环齐聚合反应

本文系统地研究了1,5-环辛二烯(COD)在BF3.OEt2和AlCl3催化下的阳离子型跨环聚合. 考察了引发剂、助催化剂以及溶剂等因素对单体转化率的影响. 得到的齐聚物数均分子量为1000左右, 软化温度为140-160℃. 采用裂解色谱-质谱证明产物具有1的结构.     

High temperature pyrolysis of methane in shock waves. Rates for dissociative recombination reactions of methyl radicals and for propyne formation reaction

The pyrolysis of 2% CH₄ and 5% CH₄ diluted with Ar was studied using both a single–pulse and time–resolved spectroscopic methods over the temperature range 1400–2200 K and pressure range 2.3–3.7 atm. The rate constant expressions for dissociative recombination reactions of methyl radicals, CH₃ + CH₃ → C₂H₅ + H and CH₃ + CH₃ → C₂H₄ + H₂, and for C₃H₄ formation reaction were investigated. The simulation results required considerably lower value than that reported for CH₃ + CH₃ → C₂H₄ + H₂. Propyne formation was interpreted well by reaction C₂H₂ + CH₃ → P-C₃H₄ + H with ?? = 6.2 × ¹⁰12 exp(?17 kcal/RT) ^cm3 mol^?1 s^?1.     

Homogeneous pyrolysis of acetylacetone at high temperatures in shock waves

The kinetics of the thermal decomposition of acetylacetone has been studied in a shock tube in the temperature range of 1120–1660 K. Detailed analyses of CO and H₂O formation data indicate that H₂O is formed by a four-center molecular channel, whereas CO is formed by the rapid dissociation of CH₃CO produced by the C? C bond dissociation of acetylacetone. The Arrhenius equations for H₂O and CH₃CO formation channels are ??₂ = 10^14.24±0.21 exp(?60,800 ± 1,220/RT)sec^?1 and ??₃ = 10^17.05±0.28 exp(?74,600 ± 1,680/RT) sec^?1, respectively. The results of the study suggest that the six-center molecular channel for the production of acetone and ketene is not important under the condition used in this investigation.     

Quantum-mechanical and molecular mechanics conformational analysis of 1,5-cyclooctadiene

The 1,5-cyclooctadiene (COD) molecule can easily form complexes with transition metals with the molecular structure of various of these complexes being proposed with the aid of X-ray diffraction methods. The fact that the complexes exhibit weak metal-COD bonds makes it very important in inorganic synthesis and catalysis. In this work the potential energy surface (PES) for the COD molecule was comprehensively investigated: first with molecular mechanics (using the MM3 force field); and, in a second stage, at the ab initio Hartree-Fock level of theory employing the 3-21G^*, 6-31G, and 6-31G^* basis sets and also including electron correlation effects at the Moller-Plesset second-order perturbation theory level. This work revealed that there are three distinct conformers of the COD molecule with the predicted lowest energy conformation being in agreement with the proposed structure based on experimental electron diffraction data. © 1997 by John Wiley & Sons, Inc.     

On the Interesting Course of Dichloroketene Addition to 1,5-Dimethyl-1,5-cyclooctadiene

Reaction of dichloroketene with 1,5-dimethyl-1,5 COD 6 charters an eventful course to furnish novel tricyclic ketone 10, through the intermediacy of tricyclic hydroxy olefin 9, in which the two carbon atoms of dichloroketene form a bridge across the eight mem-bered ring.     

Carbon-13 nuclear magnetic resonance spectra and conformations of cis,cis-1,5-cyclooctadiene monoepoxide and cis,syn,cis-1,5-cyclooctadiene diepoxide

The natural-abundance ¹³C NMR spectra of cis,cis-1,5-cyclooctadiene monoepoxide and cis,syn,cis-1,5-cyclooctadiene diepoxide have been investigated over the temperature range of – 10 to – 180°C. Whereas the spectra of the former showed no dynamic NMR effect, two different conformations in the ratio of 3:1 were observed at low temperatures for the latter. The free-energy barrier (ΔG^≠) for conversion of the major conformation to the minor conformation is calculated to be 5.9°0.2 kcal mol^?1 from a line-shape analysis of spectra obtained at intermediate temperatures. It is shown that cis,syn,cis-1,5-cyclooctadiene diepoxide exists in solution in chair (major) and in twist-boat (minor) conformations of slightly different energies. Interconversion paths between these conformations are discussed. The monoepoxide is suggested to have a twist-boat conformation that is rapidly pseudorotating via a boat conformation even at – 180°C.     

Further experiments on pyrolysis of 2,2-dimethylpropane behind shock waves

Pyrolysis of a dilute mixture of neopentane (2,2-dimethylpropane) has been studied behind incident shock waves at an average pressure of 0.35 atm; the reaction was followed by absorption spectroscopy for H atoms. In the temperature range 1230–1455 K, the rate constant for dissociation of neopentane to t-butyl and methyl radicals is 1.1 E 13 exp(?62 kcal/RT) s^?1. These data and some of the literature results, between 1000 and 1450 K, can be fitted by an RRKM model of the hindered Gorin type, with five active internal rotors in the complex. To match our data with other literature data down to 800 K, a vibrational model was more satisfactory, but this did not fit very low pressure pyrolysis data in the 1000–1100 K range. Apparently, the VLPP data are too high because of heterogeneous processes or chain reactions.     

Synthesis of alicyclic derivatives of spiropentane based on 1,5-cyclooctadiene

Methods for the synthesis of alicyclic derivatives f spiropentane by ]1 +2] cycloaddition of halo- and dihalocarbenes to 1,5-cyclooctadiene followed by dehydrohalogenation and cyclopropanation of the olefins formed are described.Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya No. 7, no, 1753–1757 July 1996.     

Reactions of (1,5-cyclooctadiene)duroquinonenickel with electron donors

Conclusions Electron transfer from the reducing agent to the complex occurs when the electron donors, sodionaphthalene and sodiomalonic ester, act on (1,5-cyclooctadiene)duroquinonenickel, with the formation of the [(C₈H₁₂)(DQ)Ni]^–· anion radicals, which proved to be thermally less stable and more reactive than the anion radicals of bis(duroquinone)nickel.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2320–2322, October, 1975.     

Cyanogen pyrolysis and the CN + NO reaction behind incident shock waves

The reaction chemistry of C₂N₂? Ar and C₂N₂? NO? Ar mixtures has been investigated behind incident shock waves. Progress of the reaction was monitored by observing the cyano radical (CN) in absorption at 388.3 nm. A quantitative spectroscopic model was used to determine concentration histories of CN. From initial slopes of CN concentration during cyanogen pyrolysis, the rate constant for C₂N₂ + M → 2CN + M (1) was determined to be k₁ = (4.11 ± 1.8) × 10¹⁶ exp(?47,070 ± 1400/T) cm³/mol · s. A reaction sequence for the C₂N₂? NO system was developed, and CN profiles were computed. By comparison with experimental CN profiles the rate constant for the reaction CN + NO → NCO + N (3) was determined to be k₃ = 10^{(14.0 ± 0.3)} exp(?21,190 ± 1500/T) cm³/mol · s. In addition, the rate of the four-centered reaction CN + NO → N₂ + CO (2) was estimated to be approximately three orders of magnitude below collision frequency.     

Complexation and C-H bond activation of 1,5-cyclooctadiene on triosmium carbonyl clusters

Reaction of Os₃(CO)₁₀(NCMe)₂ and 1,5-cyclooctadiene (C₈H₁₂) affords the diene complex Os₃(CO)₁₀(η⁴-C₈H₁₂) (1) with the two alkene moieties coordinated to an equatorial and an axial positions of one osmium atom. Thermolysis of 1 in refluxing n-hexane results in a vinylic C-H bond activation to form (μ-H)Os₃(CO)₉(μ,η⁴-C₈H₁₁) (2) in good isolated yield. The crystal structures of 1 and 2 have been established by an X-ray diffraction study.     

Formation of H and D atoms in pyrolysis of 1,3-butadiene and 1,3 butadiene-1,1,4,4,-d4 behind shock waves

Highly dilute mixtures of 1,3-butadiene and 1,3-butadiene-1,1,4,4-d₄ were pyrolyzed behind reflected and incident shock waves, respectively. Concentrations of H and D atoms were measured by resonance absorption spectroscopy. In the early stages of the reaction, nearly equal amounts of H and D were formed from CD₂CHCHCD₂, indicating that loss of H from C₂ followed by loss of D from C₁ is a more important reaction than breaking of the central C? C bond. Overall, rate constants for atom-forming reactions are much slower than rate constants for disappearance of butadiene in earlier experiments, suggesting that most of the butadiene disappears by processes that do not involve H or D atoms or by radicals that produce them rapidly.     

Soot formation in the pyrolysis of benzene,methylbenzene, and ethylbenzene in shock waves

Soot formation in the pyrolysis of benzene, methylbenzene, and ethylbenzene and in the oxidative pyrolysis of benzene in shock waves has been investigated using an absorption-emission technique. Even in the presence of small amounts of oxygen, soot formation in the pyrolysis of these hydrocarbons is accompanied by a decrease in the temperature of the reacting mixture. The soot yield has been measured as a function of temperature over wide initial reactant concentration ranges. A new, larger value was obtained for the coefficient of light absorption by soot particles at a wavelength of 632.8 nm. A revised, substantially modified kinetic model is suggested for soot formation. This model has been verified against experimental data available from the literature on the time profiles of the concentrations of some key components at the early stages of pyrolysis and oxidation of various hydrocarbons in a wide range of process conditions. The model reproduces fairly well the time dependences of the soot yield and soot particle temperature measured in this study for benzene, methylbenzene, and ethylbenzene pyrolysis.     

Nonisothermal effects in the process of soot formation in ethylene pyrolysis behind shock waves

The nonisothermal nature of hydrocarbon pyrolysis explains the differences in the critical temperatures of soot formation in the experimental studies of these processes. When reaction heats are taken into account, the critical temperatures become close to 1600 K for all the systems studied. The estimated standard enthalpy of carbon atom formation in the composition of soot particles is δH_{f, z}. ≈ 11 ±6 kJ/mol. A kinetic model is proposed for soot formation in ethylene pyrolysis that describes the experimental data. The calculated temperature of soot particles may differ substantially depending on the choice of a model for energy exchange in collisions.     

High temperature pyrolysis of novolac resin biomass composites

Composites of novolac resin (N.R.) and biomass derived from olive stones (OL.B.), in various proportions, were cured with hexamethylenetetramine (HTA) and pyrolyzed up to 900°C. The pyrolysis mechanism was monitored using TGA and gas chromatography. The pyrolysis regions, as well as important pyrolysis parameters of the materials used, were determined. Cured and pyrolyzed composites of N.R./OL.B. varied from 20/80 to 75/25, exhibiting at temperatures up to approx. 600°C lower weight losses than expected by the rule of mixtures, owing to additional cross linkages of lignin with HTA. This stabilization effect vanished during pyrolysis at higher temperatures because of the breaking of other chemical bonds, e.g. cross linkages. The release of CH₄ during the pyrolysis of OL.B. is derived from the lignin contained in OL.B. The other gases, CO, CO₂ and H₂, could be formed from celluose, hemicellulose and lignin which are the main components of OL.B. The use of N.R. in the initial mixture with OL.B. reduces the weight losses during pyrolysis compared with OL.B. alone. A heating rate of 10°C/min was necessary for the carbonization processes of OL.B. and its mixtures with N.R. in order to promote minimum weight loss of material and minimum pyrolysis time.     

顺, 顺-1,5-环辛二烯的单重态氧反应及其产物的重排

本文报道用竹红菌甲素作光敏剂匹配高压钠灯光源, 对1,5-环辛二烯(1)进行单重态氧氧化反应, 高产率和立体选择性地得到顺-5,8-二(氢过氧基)-1,3-环辛二烯(7). 证明了7还原产物顺-5,8-二烃基-1,3-环辛二烯(8)热重排的产物是6-羟基-4-环辛烯酮(3). 而不是6-羟基-3-环辛烯酮(6). 并讨论了热重排过程的机理.