Theoretical kinetics of HO2 + C5H5: A missing piece in cyclopentadienyl radical oxidation reactions

The resonantly-stabilized cyclopentadienyl radical (C₅H₅) is a key species in the combustion and molecular growth kinetics of mono and poly-aromatic hydrocarbons (M/PAHs). At intermediate-to-low temperatures, the C₅H₅ reaction with the hydroperoxyl radical (HO₂) strongly impacts the competition between oxidation to smaller products and growth to PAHs, precursors of soot. However, literature estimates for the HO₂ + C₅H₅ reaction rate are inaccurate and inconsistent with recent theoretical calculations, thus generating discrepancies in global combustion kinetic models. In this work, we perform state-of-the-art theoretical calculations for the HO₂ + C₅H₅ reaction including variable reaction coordinate transition state theory for barrierless channels, accurate thermochemistry, and multi-well master equation (ME) simulations. Contrary to previous studies, we predict that OH + 1,3-C₅H₅O is the main reaction channel. The new rate constants are introduced in two literature kinetic models exploiting our recently developed ME based lumping methodology and used to perform kinetic simulations of experimental data of MAHs oxidation. It is found that the resonantly-stabilized 1,3-C₅H₅O radical is the main C₅H₅O isomer, accumulating in relevant concentration in the system, and that the adopted lumping procedure is fully consistent with results obtained with detailed kinetics. The reactivity of C₅H₅O with OH and O₂ radicals is included in the kinetic mechanisms based on analogy rules. As a result, C₅H₅O mostly reacts with O₂ producing smaller C₃/C₄ species and large amounts of C₅H₄O, suggesting that further investigations of the reactivity of both C₅H₅O and C₅H₄O with oxygenated radicals is necessary. Overall, this work presents new reliable rate constants for the HO₂ + C₅H₅ reaction and provides indications for future investigations of relevant reactions in the sub-mechanisms of cyclopentadiene and MAH oxidation.     

Lean or ultra-lean stretched planar methane/air flames

Lean premixed combustion has potential advantages of reducing pollutants and improving fuel economy. In some lean engine concepts, the fuel is directly injected into the combustion chamber resulting in a distribution of lean fuel/air mixtures. In this case, very lean mixtures can burn when supported by hot products from more strongly burning flames. This study examines the downstream interaction of opposed jets of a lean-limit CH₄/air mixture vs. a lean H₂/air flame. The CH₄ mixtures are near or below the lean flammability limit. The flame composition is measured by laser-induced Raman scattering and is compared to numerical simulations with detailed chemistry and molecular transport including the Soret effect. Several sub-limit lean CH₄/air flames supported by the products from the lean H₂/air flame are studied, and a small amount of CO₂ product (around 1% mole fraction) is formed in a “negative flame speed” flame where the weak CH₄/air mixture diffuses across the stagnation plane into the hot products from the H₂/air flame. Raman scattering measurements of temperature and species concentration are compared to detailed simulations using GRI-3.0, C₁, and C₂ chemical kinetic mechanisms, with good agreement obtained in the lean-limit or sub-limit flames. Stronger self-propagating CH₄/air mixtures result in a much higher concentration of product (around 6% CO₂ mole fraction), and the simulation results are sensitive to the specific chemical mechanism. These model-data comparisons for stronger CH₄/air flames improve when using either the C₂ or the Williams mechanisms.     

A statistical model for the product energy distribution in reactions leading to prompt dissociation

Direct dynamics calculations have been performed for three reactions: C₃H₈ + H → i-C₃H₇ + H₂, C₃H₈ + H → n-C₃H₇ + H₂, and C₂H₃ + O₂ → HCO + CH₂O. The fraction of the population for the radical products that promptly dissociates is computed. The results for C₃H₈ + H are qualitatively similar to previous results for C₃H₈ + OH, but the new results exhibit a slightly higher branching fraction for prompt dissociation products, owing to the fact that a greater fraction of the internal energy in the transition state ends up in the radical. For C₂H₃ + O₂ → HCO + CH₂O, the fraction of HCO that promptly dissociates is in excess of 99%. Consequently, the main product for C₂H₃ + O₂ at lower temperatures should be written as H + CO + CH₂O and not HCO + CH₂O. These results are then compared with four previous systems: CH₂O + H → HCO + H₂, CH₂O + OH → HCO + H₂O, C₃H₈ + OH → i-C₃H₇ + H₂O, and C₃H₈ + OH → n-C₃H₇ + H₂O. Based upon these seven system, several statistical models are presented. The goal of these statistical models is to predict the fraction of the transition state energy that ends up in the rovibrationally excited radical. On average, these statistical models provide an excellent prediction of product energy distribution. Consequently, these models can be used instead of costly trajectory simulations for predicting prompt radical dissociation for larger species.     

An experimental study of the premixed benzene/oxygen/argon flame with tunable synchrotron photoionization

A comprehensive experimental study of the premixed benzene/oxygen/argon flame at 4.0 kPa with a fuel equivalence ratio (?) of 1.78 has been performed with the tunable synchrotron photoionization and molecular-beam sampling mass spectrometry. Isomers of most observed species in the flame have been unambiguously identified by measurements of the photoionization efficiency spectra. Mole fraction profiles of species up to C₁₆H₁₀ have been measured at the selective photon energies near ionization thresholds, and the flame temperature profile is obtained using Pt/Pt-13%Rh thermocouple. Compared with previous studies on benzene flames by Bittner and Howard, and by Defoeux et al., a number of new species are observed in the present work. These new combustion intermediates should be included in the kinetic models of the growth of polycyclic aromatic hydrocarbons (PAHs) and benzene oxidation. Free radicals detected in the flame include CH₃, C₂H, C₂H₃, C₂H₅, C₃H, C₃H₃, C₃H₅, C₄H, C₄H₃, C₄H₅, C₄H₇, C₅H₃, C₅H₅, C₅H₇, C₆H₅, C₆H₅O, C₇H₇, and C₉H₇. More significantly, isomers of some PAHs have been identified, which should be of importance in understanding the mechanism of soot formation.     

Flame structure studies of rich ethylene-oxygen-argon mixtures doped with CO2, or with NH3, or with H2O

Structures of several premixed ethylene-oxygen-argon rich flat flames burning at 50 mbar have been established by using molecular beam mass spectrometry in order to investigate the effect of CO₂, or NH₃, or H₂O addition on species concentration profiles. The aim of this study is to examine the eventual changes of profiles of detected hydrocarbon intermediates which could be considered as soot precursors (C₂H₂, C₄H₂, C₅H₄, C₅H₆, C₆H₂, C₆H₄, C₆H₆, C₇H₈, C₆H₆O, C₈H₆, C₈H₈, C₉H₈ and C₁₀H₈). The comparative study has been achieved on four flames with an equivalence ratio (f) of 2.50: one without any additive (F2.50), one with 15% of CO₂ replacing the same quantity of argon (F2.50C), one with 3.3% of NH₃ in partial replacement of argon (F2.50N) and one with 13% of H₂O in replacement of the same quantity of argon (F2.50H). The four flat flames have similar final flame temperatures (1800 K).CO₂, or NH₃, or H₂O addition to the fresh gas inlet causes a shift downstream of the flame front and thus flame inhibition. Endothermic processes CO₂ + H = CO + OH and H₂O + H = H₂ + OH are responsible of the reduction of the hydrocarbon intermediates in the CO₂ and H₂O added flames through the supplementary formation of hydroxyl radicals. It has been demonstrated that such processes begin to play at the end of the flame front and becomes more efficient in the burnt gases region.The replacement of some Ar by NH₃ is responsible only for a slight decrease of the maximum mole fraction of C₂H₂, but NH₃ becomes much more efficient for C₄H₂ and C₅ to C₁₀ species. Moreover, the efficiency of NH₃ as a reducing agent of C₅ to C₁₀ intermediates is larger than that of CO₂ and H₂O for equal quantities added.     

Quantitative NH measurements by using laser-based diagnostics in low-pressure flames

NH is a key short-lived radical involved in the prompt-NO formation. Quantification of NH is thus particularly important for testing the NO kinetic mechanisms. However, quantitative measurements of native NH in hydrocarbon/oxygen/nitrogen flames remain very scarce. Therefore, in this work, the mole fractions of native NH were obtained using a combination of laser-based diagnostics; Laser Induced Fluorescence (LIF) and Cavity Ring-Down Spectroscopy (CRDS). The NH species was probed after exciting the transition R₁(6) in the A³Π-X³Σ^? (0-0) system at 333.9?nm. The mole fraction profiles of NH were successfully obtained in premixed low-pressure flames of CH₄/O₂/N₂ and C₂H₂/O₂/N₂ at two equivalence ratios of 1.00 and 1.25. The estimated detection limit for the NH radical was around 4.5?×?10⁸ molecule cm^?3 (i.e. 2 ppb in mole fraction at 1600?K), which is nearly 2 orders of magnitude lower than previous values reported in the literature. These new experimental results were compared with predictions by a recently developed NO model (namely NOMecha2.0). In the case of the CH₄ flames, a satisfying agreement between the experiment and model was observed. However, in the case of the C₂H₂ flames, some discrepancies were observed. Model analysis has highlighted the importance of the HCCO radicals in the NH formation through the HCNO→HNCO→NH₂ reactions pathway. Modification of the rate constant values of the reactions C₂H₂+?O and HCCO?+?O₂, which are key reactions for both the acetylene laminar flame speed and the HCCO predictions, has enabled the model to satisfactorily predict the experimental NH and NO profiles also in the C₂H₂ flames.     

A study of the relative brönsted acidities of surface complexes on Ag(110)

The relative acidities of a number of Brönsted acids have been established on the Ag(110) surface under UHV conditions. For acids which react completely with adsorbed oxygen atoms on this surface to form H₂O, relative acidities were determined by means of acid-base titration reactions. Adsorbed species such as carboxylates, alkoxides, etc., were formed by reaction of the parent acids with O(a) and then displaced from the surface by titration with stronger acids. Relative acidities of the acids which did not react to completion with O(a) were established on the basis of their relative extents of reaction. The relative acidity scale on Ag(110), according to the reaction BH(g) + B'(a) B'H(g) + B(a) was found to be HCOOH ≈ CH₃COOH>C₂H₅OH> C₂H₂>CH₃OH>C₃H₆, H₂O>C₂H₄, C₂H₆, H₂. This order is in excellent agreement with the acidity scale for these species in the gas phase according to BH(g)B^?(g) + H⁺ (g); it cannot be explained by aqueous dissociation constants or homolytic bond dissociation energies. This result is in accord with the appreciable anionic character of the adsorbed species, since the electron affinity of the base, B, is a strong thermodynamic factor in the acidity in the gas phase. Both XPS and UPS results for adsorbed species on the Ag(110) surface are consistent with this interpretation.     

Temperature and carbon source effects on methane–air flame synthesis of CNTs

We have conducted experimental and numerical studies on flame synthesis of carbon nanotubes (CNTs) to investigate the effects of three key parameters – selective catalyst, temperature and available carbon sources – on CNT growth. Two different substrates were used to synthesize CNTs: Ni-alloy wire substrates to obtain curved and entangled CNTs and Si-substrates with porous anodic aluminum oxide (AAO) nanotemplates to grow well-aligned, self-assembled and size-controllable CNTs, each using two different types of laminar flames, co-flow and counter-flow methane–air diffusion flames. An appropriate temperature range in the synthesis region is essential for CNTs to grow on the substrates. Possible carbon sources for CNT growth were found to be the major species CO and those intermediate species C₂H₂, C₂H₄, C₂H₆, and methyl radical CH₃. The major species H₂, CO₂ and H₂O in the synthesis region are expected to activate the catalyst and help to promote catalyst reaction.     

An experimental and kinetic modeling study of a premixed nitromethane flame at low pressure

A premixed nitromethane/oxygen/argon flame at low pressure (4.67 kPa) has been investigated using tunable vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry. About 30 flame species including hydrocarbons, oxygenated and nitrogenous intermediates have been identified by measurements of photoionization efficiency spectra. Mole fraction profiles of the flame species have been determined by scanning burner position at some selected photon energies. The results indicate that N₂ and NO are the major nitrogenous products in the nitromethane flame. Compared with previous studies on nitromethane combustion, a number of unreported intermediates, including C₃H₄, C₄H₆, C₄H₈, C₂H₂O, C₂H₄O, CH₃CN, H₂CNHO, C₃H₃N and C₃H₇N, are observed in this work. Based on our experimental results and previous modeling studies, a detailed oxidation mechanism including 69 species and 314 reactions has been developed to simulate the flame structure. Despite some small discrepancies, the predictions by the modeling study are in reasonable agreement with the experimental results.     

The 275-nm absorption system of anisole

The 275-nm absorption systems of anisole (methoxybenzene) and three deuterated derivatives have been photographed at medium to high resolution. The origin bands lie at 36 386.4, 36 389.6, 36 557.2, and 36 560.4 cm^?1 for C₆H₅OCH₃, C₆H₅OCD₃, C₆D₅OCH₃, and C₆D₅OCD₃. The vibrational structure, which was analyzed in some detail, was found to be very similar to that of the analogous system of phenol. The spectrum consists of both allowed and forbidden components although the forbidden component, principally evident through activity of vibrations 18b and 6b, is relatively weak.     

Effect of ammonia addition on suppressing soot formation in methane co-flow diffusion flames

Due to issues surrounding carbon dioxide emissions from carbon-containing fuels, there is growing interest in ammonia (NH₃) as an alternative combustion fuel. One attractive method of burning NH₃ is to co-fire it with hydrocarbons, such as natural gas, and in this case soot formation is possible. To begin understanding the influence of NH₃ on soot formation when co-fired with hydrocarbons, soot volume fractions and mole fractions of gas-phase species were computationally and experimentally interrogated for CH₄ flames with up to 40% NH₃ by volumetric fuel fraction. Mole fractions of gas-phase species, including C₂H₂ and C₆H₆, were measured with on-line electron impact mass spectrometry, and soot volume fractions were obtained via color-ratio pyrometry. The simulations employed a detailed chemical mechanism developed for capturing nitrogen interactions with hydrocarbons during combustion. The results are compared to findings in N₂CH₄ flames, in order to separate thermal and dilution effects from the chemical influence of NH₃ on soot formation. Experimentally, C₂H₂ concentrations were found to decrease slightly for the NH₃CH₄ flames relative to N₂CH₄ flames, and a stronger suppression of C₆H₆ was found for NH₃ relative to N₂ additions. The measured results show a strong suppression of soot with the addition of NH₃, with soot concentrations reduced by over a factor of 10 with addition of up to 20% or more NH₃ by mole fraction. The model satisfactorily captured relative differences in maximum centerline C₂H₂, C₆H₆, and soot concentrations with addition of N₂, but was unable to match measured differences in NH₃CH₄ flames. These results highlight the need for an improved understanding of fuel-nitrogen interactions with higher hydrocarbons to enable accurate models for predicting particulate emissions from NH₃/hydrocarbon combustion.     

Nitromethane pyrolysis in shock tubes and a micro flow reactor with a controlled temperature profile

Nitromethane has many applications, such as in racing, as a gasoline fuel additive, and as a monopropellant. Despite a large number of studies and the small size of the molecule, the combustion chemistry of nitromethane is still not well understood. To improve models, the pyrolysis of nitromethane (CH₃NO₂) was investigated experimentally in shock tubes and in a micro flow reactor with a controlled temperature profile (MFR), under dilute conditions. Several spectroscopic diagnostics were used in the shock tubes to follow the concentration time histories of CO, H₂O (both using IR laser absorption), and CH₃NO₂ (UV light absorption). A quadrupole mass spectrometer was used to measure CH₃NO₂, NO₂, CH₄, C₂H₄, and C₂H₂ at various temperatures with the MFR. These unique experimental results were compared to modern, detailed kinetics models from the literature, and no mechanism was able to reproduce these data over the wide range of conditions investigated. Predictions for the CO and H₂O levels were generally inaccurate, and the CH₄, C₂H₄, and C₂H₂ predictions were poor in most cases for the MFR data. Importantly, all models largely differ in their predictions. A numerical analysis was performed to identify ways to improve the next generation of nitromethane models. Results indicate that nitromethane decomposition needs to be improved below 1050 K, and that hydrocarbon-NOx interactions still need to be further investigated.     

Oxidation of H2/CO2 mixtures and effect of hydrogen initial concentration on the combustion of CH4 and CH4/CO2 mixtures: Experiments and modeling

An experimental investigation of the oxidation of hydrogen diluted by nitrogen in presence of CO₂ was performed in a fused silica jet-stirred reactor (JSR) over the temperature range 800-1050 K, from fuel-lean to fuel-rich conditions and at atmospheric pressure. The mean residence time was kept constant in the experiments: 120 ms at 1 atm and 250 ms at 10 atm. The effect of variable initial concentrations of hydrogen on the combustion of methane and methane/carbon dioxide mixtures diluted by nitrogen was also experimentally studied. Concentration profiles for O₂, H₂, H₂O, CO, CO₂, CH₂O, CH₄, C₂H₆, C₂H₄, and C₂H₂ were measured by sonic probe sampling followed by chemical analyses (FT-IR, gas chromatography). A detailed chemical kinetic modeling of the present experiments and of the literature data (flame speed and ignition delays) was performed using a recently proposed kinetic scheme showing good agreement between the data and this modeling, and providing further validation of the kinetic model (128 species and 924 reversible reactions). Sensitivity and reaction paths analyses were used to delineate the important reactions influencing the kinetic of oxidation of the fuels in absence and in presence of additives (CO₂ and H₂). The kinetic reaction scheme proposed helps understanding the inhibiting effect of CO₂ on the oxidation of hydrogen and methane and should be useful for gas turbine modeling.     

Potential Energy Surface for Oxidation of Indenyl C<Subscript>9</Subscript>H<Subscript>7</Subscript>

Ab initio calculations were performed to obtain local energy extrema, including an effect of reagents, intermediates, and reaction products on the potential energy surface for the C₉H₇+O₂ reaction, playing a significant role in oxidation of polycyclic aromatic hydrocarbons at combustion conditions. The final products, determined as a result of the calculations are styrenyl radical C₈H₇+CO₂, ortho-vinyl phenyl radical C₈H₇+CO₂ and 1-H-inden-1-one C₉H₆O+OH, which is predicted to be the prevailing reaction product.     

O,O′-Dimethyl diphenyldithiophosphates of titanium(IV): synthesis,spectroscopic, DFT and biological studies

Dimethyl diphenyldithiophosphate complexes of titanium(IV), [(C₅H₅)₂Ti{S₂P(OAr)₂}_nCl_2-n] (Ar?= 2,4-(CH₃)C₆H₃, 2,5-(CH₃)C₆H₃, 3,4-(CH₃)C₆H_3, 3,5-(CH₃)C₆H_3, 3-CH₃-4-Cl-C₆H₃O; n?=?1 and 2) have been synthesised and characterised by various physicochemical techniques along with computational analysis of the complexes (2), (9) and (10) using density functional theory (DFT) and time-dependent DFT (TDDFT). Comparison of antimicrobial activity of the free ligands and complexes has shown that the complexes are more effective than the free ligands. The in vitro cytotoxic by using a MTT staining method with RAW 264.7 cells (mouse macrophages) have been investigated. On the basis of analytical and DFT data, a distorted trigonal bipyramidal around titanium(IV) may be assigned to the complexes (1–5) and distorted octahedral geometries for the complexes (6–10).     

Benzene formation in premixed fuel-rich 1,3-butadiene flames

Detailed kinetic modeling and flame-sampling molecular-beam time-of-flight mass spectrometry are combined to unravel important pathways leading to the formation of benzene in a premixed laminar low-pressure 1,3-butadiene flame. The chemical kinetic model developed is compared with new experimental results obtained for a rich (? = 1.8) 1,3-butadiene/O₂/Ar flame at 30 Torr and with flame data for a similar but richer (? = 2.4) flame reported by Cole et al. [Combust. Flame 56 (1) (1984) 51-70]. The newer experiment utilizes photoionization by tunable vacuum-ultraviolet synchrotron radiation, which allows for the identification and separation of combustion species by their characteristic ionization energies. Predictions of mole fractions as a function of distance from the burner of major combustion intermediates and products are in overall satisfactory agreement with experimentally observed profiles. The accurate predictions of the propargyl radical and benzene mole fractions permit an assessment of potential benzene formation pathways. The results indicate that C₆H₆ is formed mainly by the C₃H₃ + C₃H₃ and i-C₄H₅ + C₂H₂ reactions, which are roughly of equal importance. Smaller contributions arise from C₃H₃ + C₃H₅. However, given the experimental and modeling uncertainties, other pathways cannot be ruled out.     

The research on the synthesis and structure of some new ferrocene derivatives

The reaction of C₅H₄RLi with FeCl₂ gave nine new compounds of Fe(C₅H₄R)₂ [R=C(CH₃)₂C₆H₄CH₃-p(-m,-o), C₆H₁₀C₆H₅, C(Me)₂C₆C₄OCH_3-o, C₆H₁₀C₆H₄CH₃-p(,-m,-o), C₆H₁₀C₆H₄OCH₃-p]. The compositions of compounds were determined through elementary analysis. The structural determination was made by IR and H²NMR. Mossbauer spectia were taken at room temperature. The IS and QS values are 0.41–0.45mm/s and 2.3–2.5mm/s., respectively. The solid state structure of the complex has been determined by a single crystal x-ray diffraction study, crystal data for Fe[C₅H₄C(CH₃)₂C₆H₅]₂: a=17.988(2)A, b=17. 411(2)A, c=7.496(1)A, α=β=90°, r=112.23°, Z=4, monoclinic form, space group C2/c. Our conclusions are: in π-acceptor ligand, the nucleophilic substituents decrease and the electrophilic substituts increase the metal to ligand electron cloud shift, which results in a decrease or an increase in the strength of the coordinate bonds and in the stabilization of the complexes by their steric effect.     

A combustion chemistry study of tetramethylethylene in a laminar premixed low-pressure hydrogen flame

The combustion chemistry of tetramethylethylene (TME) was studied in a premixed laminar low-pressure hydrogen flame by combined photoionization molecular-beam mass spectrometry (PI-MBMS) and photoelectron photoion coincidence (PEPICO) spectroscopy at the Swiss Light Source (SLS) of the Paul Scherrer Institute in Villigen, Switzerland. This hexene isomer with the chemical formula C₆H₁₂ has a special structure with only allylic CH bonds. Several combustion intermediate species were identified by their photoionization and threshold photoelectron spectra, respectively. The experimental mole fraction profiles were compared to modeling results from a recently published kinetic reaction mechanism that includes a TME sub-mechanism to describe the TME/H₂ flame structure. The first stable intermediate species formed early in the flame front during the combustion of TME are 2-methyl-2-butene (C₅H₁₀) at a mass-to-charge ratio (m/z) of 70, 2,3-dimethylbutane (C₆H₁₄) at m/z 86, and 3-methyl-1,2-butadiene (C₅H₈) at m/z 68. Isobutene (C₄H₈) is also a dominant intermediate in the combustion of TME and results from consumption of 2-methyl-2-butene. In addition to these hydrocarbons, some oxygenated species are formed due to low-temperature combustion chemistry in the consumption pathway of TME under the investigated flame conditions.     

The reaction of allyl radicals with oxygen atoms—rate coefficient and product branching

The primary product formation of the C₃H₅ + O reaction in the gas phase has been studied at room temperature. Allyl radicals (C₃H₅) and O atoms were generated by laser flash photolysis at λ = 193 nm of the precursors C₃H₅Cl, C₃H₅Br, C₆H₁₀ (1,5-hexadiene), and SO₂, respectively. The educts and the products were detected by using quantitative FTIR spectroscopy. The combined product analysis of the experiments with the different precursors leads to the following relative branching fractions: C₃H₅ + O → C₃H₄O + H (47%), C₂H₄ + H + CO (41%), H₂CO + C₂H₂ + H (7%), CH₃CCH + OH and CH₂CCH₂ + OH (<5%). The rate of reaction has been studied relative to CH₃OCH₂ + O and C₂H₅ + O in the temperature range from 300 to 623 K. Here, the radicals were produced via the fast reactions of propene, dimethyl ether, and ethane, respectively, with atomic fluorine. Laser-induced multiphoton ionization combined with TOF mass spectrometry and molecular beam sampling from a flow reactor was used for the specific and sensitive detection of the C₃H₅, C₂H₅, and CH₃COCH₂ radicals. The rate coefficient of the reaction C₃H₅ + O was derived with reference to the reaction C₂H₅ + O leading to k(C₃H₅ + O) = (1.11 ± 0.2) × 10¹⁴ cm³/(mol s) in the temperature range 300-623 K. The C₃H₅ + O rate and channel branching, when incorporated in a suitable detailed reaction mechanism, have a large influence on benzene and allyl concentration profiles in fuel-rich propene flames, on the propene flame speed, and on propene ignition delay times.     

Veredelung industrieller Erzeugnisse durch den Ersatz von Wasserstoff durch Deuterium

Es wurden folgende isotopisomere Formen des Bernsteinsäuredibenzylesters synthetisiert:

C₆H₅CH₂–OOCCH₂CH₂COO–CH₂C₆H₅, (I)

C₆H₅CD₂-OOCCH₂CH₂COO–CD₂C₆H₅, (II)

C₆H₅CH₂–OOCCD₂CD₂COO7ndash;CH₂C₆H₅, (III)

C₆H₅CD₂-OOCCD₂CD₂COO–CD₂C₆H₅. (IV)

Die Gesehwindigkeit der Autoxydation dieser Verbindungen bei 191 °C zeigt Isotopieeffekte der Größe k₁/k₁₁ = 4,3 ± 0,5; k₁/k₁₁₁ = 1,0 und k₁/k_iv = 4,6 ± 0,5, bezogen auf die Maximalgeschwindigkeit. Durch die Anwesenheit des Inhibitors Phenyl-a-naphthylamin (0,1%) werden die maximalen Geschwindigkeiten der Autoxydation nicht beeinflußt. Die Induktionsperioden werden hingegen bei den Verbindungen (I) und (II) in sehr unterschiedlicher Weise verändert, so daß die Induktionsperiode von (II) 40mal länger als die von (I) wild.