Analysis of polycyclic aromatic hydrocarbon sequences in a premixed laminar flame by on-line time-of-flight mass spectrometry

A time-of-flight mass spectrometer in reflectron configuration has been used for the real-time detection of combustion products. The products of a premixed laminar C2H4/O2 flame at atmospheric pressure were sampled along its axis, diluted with inert gas and carried to the ion source as a molecular beam under minimal perturbation. Electron ionization and different optical ionization sources are compared. Photoionization was achieved with laser radiation from a Nd:YAG nanosecond pulsed laser at two different wavelengths in the UV range (266 and 355 nm). The mass spectra obtained using laser wavelength of 355 nm and electron ionization present a series of ions regularly spaced by 18 m/z units up to m/z 2000. This series allowed precise calibration of the instrument for compounds of high molecular weight. Information on the chemical nature of the analyzed species has been obtained by comparing mass spectra produced with different ionization methods. In order to better understand the growth mechanisms, polycyclic aromatic hydrocarbon sequences have been analyzed by fast Fourier transform of the mass spectra.     

Multi-diagnostic approach to characterize the onset of formation of nanoparticles in a premixed laminar ethylene/air flame

The onset of formation of nanoparticles in a premixed laminar ethylene/air flame was studied using optical and non-optical diagnostic techniques. The optical techniques (Visible Imaging, Spectroscopic analysis of optical emission, Laser Induced Incandescence and Optical Extinction) were checked against the direct measurement of particles size distribution done with a commercial sampler. The diagnostic techniques were set up on a standard burner (McKenna). The combustion conditions were varied by tuning two experimental parameters: the equivalent ratio Φ and the cold gases velocity v. Values of Φ were investigated in the range 1.3 to 2.2, in combination with cold unburned gas velocities of 5, 7 and 10 cm/s. By varying the combustion conditions, a transition in the signal detected by the different techniques was observed. The transition was put in correspondence with the sensitivity of the given technique to the onset of the nanoparticles formation. A comparison of the sensitivity of the different techniques was performed.     

A numerical study on the acoustic forcing of a laminar premixed saturated spray flame

Journal of Thermal Analysis and Calorimetry - This paper presents a numerical investigation into the interaction between a laminar premixed saturated spray flame and periodic acoustic forcing. A...     

Experimental study of laminar lean premixed methylmethacrylate/oxygen/argon flame at low pressure

A fuel-lean laminar premixed methylmethacrylate/oxygen/argon flame at 2.67 kPa with an equivalence ratio (phi) of 0.75 has been investigated with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular beam sampling mass spectrometry techniques. Isomers of most observed species in the flame have been identified by measurements of photoionization mass spectra and the near-threshold photoionization efficiency spectra. Mole fraction profiles for about 42 flame species are displayed. Free radicals such as CH3, C2H3, C2H5, C3H3, C3H5, C2H3O, C4H7, C3H5O, C3H7O, C4H3O, C4H9O, C4H5O2, C4H7O2, and C5H7O2, which should be of importance in understanding the formation mechanism of some toxic substances, were detected in the flame. Moreover, no isomers of any PAHs have been detected in the lean flame. Combined with the mole fraction profiles, the formation mechanisms of the free radicals, oxygenated compounds, and other molecular intermediates are proposed and will provide important information on modeling the combustion kinetics of methylmethacrylate (MMA).     

Free-atom formation processes in premixed fuel-rich and stoichiometric oxygen-acetylene flames employed in atomic emission and absorption spectroscopy

Detailed observations on the atomic and molecular absorption and emission spectra of the various zones of premixed oxyacetylene flames are presented. Spatial flame profile data for both the natural flame species and those formed when solutions of metallic salts are nebulized into the flame are interpreted in terms of: (a) the relative concentrations of reactive intermediate and stable species in the various zones; (b) the mechanism of free-atom formation from aerosol droplets; and (c) free-atom depopulation processes. The results of this study clearly show that the striking enhancement in atomic spectra observed in either absorption or emission for many elements in the fuel-rich oxyacetylene flame originate in the favorable chemical environment provided by the interconal zone for the formation and existence of free-atoms.     

On the role of transport in the combustion kinetics of a steady-state premixed laminar CO + H2 + O2 flame

The role of mechanistic steps, diffusion, and their interrelation is explored in a steady-state premixed laminar CO + H₂ + O₂ flame using a numerical model. Sensitivity coefficients and Green's functions calculated for this system offer systematic characterization of the role of diffusion and exothermicity in carbon monoxide oxidation kinetics. The results reveal that the uncertainties in transport parameters are as important to the model predictions as those in the kinetic steps. The rate controlling steps of the CO + H₂ + O₂ reaction are found to be different for adiabatic and nonadiabatic premixed flames, and also for systems with and without transport. In particular, the reactions of the hydroperoxyl radical with hydrogen, oxygen, and hydroxyl radicals are found to be important at all temperatures in the fuel lean (40 torr) adiabatic flame studied here. The diffusive mixing of chemical species from the low and the high temperature portions of the flame and the larger heats of reaction associated with the hydroperoxyl radicals are found to be responsible for the increased importance of these reactions. © 1994 John Wiley & Sons, Inc.     

Specificity in the formation of a seven-membered ring in the synthesis of dihydro-1.5-benzodiazepinones from aromatic diamines

It is shown that a mixture of 7- and 8-substituted 2,3-dihydro-1,5-benzodiazepinones is formed in the reaction of unsymmetrical aromatic diamines (4-chloro-,4-methyl-, and 4-methoxy-o-phenylenediamines) with acetoacetic and benzoylacetic esters under severe conditions. The corresponding anilide of benzoylacetic acid, the cyclization of which again leads to a mixture of isomeric dehydrobenzodiazepinones, can be isolated (in the case of benzoylacetic ester) when the concentrations of the reacting substances and the reaction time are decreased; this makes it possible to assume amidation of the -keto acids as one of the steps in the high-temperature synthesis of dihydrobenzodiazepinones. The quantitative ratio of the isomers formed in the reaction was determined by UV spectroscopy. The UV, IR, and PMR spectral data are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 834–838, June, 1977.     

A laminar flame separate aerosol injection burner for use in atomic absorption flame spectroscopy

The construction of a laminar flame long-path burner facilitating the separate introduction of aerosol into the flame is described. The use of severalThe more efficient sample transport through the flame, combined with an increased sample flow rate from the ultrasonic nebulizer are shown to be advant     

Numerical study of the laminar flame propagation in ethane-air mixtures

The structure of premixed free one-dimensional laminar ethane-air flames was investigated by means of numerical simulations performed with a detailed mechanism (GRI-Mech version 3.0) by means of COSILAB package. The work provides data on ethane-air mixtures with a wide range of concentrations ([C₂H₆] = 3.0–9.5 vol.%) at initial temperatures between 300 and 550 K and initial pressures between 1 and 10 bar. The simulations deliver the laminar burning velocities and the profiles of temperature, chemical species concentrations and heat release rate across the flame front. The predicted burning velocities match well the burning velocities measured in various conditions, reported in literature. The influence of initial concentration, pressure and temperature of ethane-air mixtures on maximum flame temperature, heat release rate, flame thickness and peak concentrations of main reaction intermediates is examined and discussed.      

New aromatic systems having a fused thiazolium ring

The method developed for the synthesis of thiazolo[3,2-a]pyridinium salts has been extended to the first synthesis of simple thiazolo[3,2-a]pyrimidinium, thiazolo[3,2-a]-pyrazinium and thiazolo[2, 3-b]benzo[d]thiazolium salts. No method could be found for the cyclization of 4′-bromo-2-(2-benzoxazolylthio)acetophenone to the thiazolo[2,3-b]-benzoxazolium system.     

The ring opening of cyclopentene oxides by pyrimidines and purines as a pathway to carbocyclic nucleoside analogues

Summary Various carbocyclic nucleosides withxylo-configuration have been synthesized using ring opening of 5-O-acetyl-1,2-anhydro-3-O-benzylcarba--DL-xylo-pentofuranose (6) by thymine, uracil, 4-N-benzoylcytosine, adenine, 6-N-benzoyladenine, and 2-amino-6-chloropurine in alkaline medium. For this purpose, the use of triethylaluminum is introduced into carbanucleoside chemistry. The new method proved to be superior over the application of sodium hydride and potassium or caesium carbonate.

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Ringöffnung von Cyclopentenoxiden mit Pyrimidinen und Purinen als Syntheseweg zu carbocyclischen Nucleosidanalogen

Zusammenfassung Ringöffnung von 5-O-Acetyl-1,2-anhydro-3-O-benzylcarba--DL-xylo-pentofuranose (6) mit Thymin, Uracil, 4-N-Benzoylcytosin, Adenin, 6-N-Benzoyladenin und 2-Amino-6-chlorpurin in alkalischem Medium ergab die entsprechendenxylo-konfigurierten carbocyclischen Nucleoside. Als Hilfsbase wurde Triethylaluminium verwendet, was deutliche Vorteile gegenüber der Verwendung von Natriumhydrid und Kalium- oder Cäsiumcarbonat bezüglich Produktreinheit und Ausbeute bietet.

     

A new method for installation of aryl and alkenyl groups onto a cyclopentene ring and synthesis of prostaglandins

To construct a new strategy for synthesis of cyclopentanoids, the transition metal-catalyzed coupling reaction of cis 4-cyclopentene-1,3-diol monoacetate 1 with hard nucleophiles, R(T)-m, was investigated (eq 1 in Chart 1). Although preliminary experiments using PhZnCl, PhSnMe(3), [Ph-B(Me)(OCH(Me)CH(Me)O)]-Li(+) (6a) (derived from boronate ester 4a (R(T) = Ph) and MeLi) in the presence of a palladium or a nickel catalyst resulted in production of unidentified compounds, enone 16, and/or ketone 17 or recovery of 1, a new borate 5a (derived from 4a and n-BuLi) in the presence of a nickel catalyst (NiCl(2)(PPh(3))(2)) in THF at room temperature furnished the trans coupling products 2a (R(T) = Ph) and 3a (R(T) = Ph) in high combined yield, but with a low product ratio of 0.9:1. The ratio was improved to 13:1 by addition of t-BuCN and NaI into the reaction mixture. This is the first successful example of the reaction of 1 with a hard nucleophile, and the increase in the ratio, realized with the additives, is unprecedented. This reagent system (borate 5 (1.2-1.8 equiv), NiCl(2)(PPh(3))(2) (5-10 mol %), t-BuCN (2-5 equiv), NaI (0.5-1 equiv), THF, room temp) was further investigated with aryl borates 5b-g and alkenyl borates 5h-n to afford 2b-n in moderate to good yields (52-89%) with practically acceptable levels of the regioselectivity (5 approximately 21:1), thus establishing the generality of the reaction (Table 2, eqs 6 and 7). Starting with the products of the coupling reaction, syntheses of the prostaglandin intermediates 13 and 14 (for 11-deoxy-PGE(2) and PGA(2)) and Delta(7)-PGA(1) methyl ester (15) were accomplished efficiently. During these investigations, LDA, LiCA, and LHMDS were found to be equally efficient bases for aldol reaction at the alpha' (alpha prime) position of cyclopentenones 39, 40, and 41 (Table 3).     

Access to a new family of medium ring aromatic lactones

We report a new method for preparation of hydroxyacids as precursors of benzolactones using a simple and an efficient electrochemical step. This gives in only four steps six- to eleven-membered lactones with high isolated yields from conveniently substituted aryl bromides. The lactonisation was performed according to the Yamamoto's process.