Flame structure and flame reaction kinetics - V. Investigation of reaction mechanism in a rich hydrogen+nitrogen+oxygen flame by solution of conservation equations

1970 ◽  
Vol 317 (1529) ◽  
pp. 235-263 ◽  
Keyword(s):  
Reaction Mechanism ◽  
Hydrogen Atom ◽  
Reaction Zone ◽  
Rate Constant ◽  
Rate Constants ◽  
Time Dependent ◽  
Flame Velocity ◽  
Atom Concentration ◽  
Comparison With Experiment ◽  
Oxygen Flame

A powerful combination of two computational methods has been used to investigate the reaction mechanism in a fuel-rich hydrogen+nitrogen+oxygen flame. The first of these involves the solution of the time-dependent heat conduction and diffusion equations by finite difference methods. It allows a preliminary assessment of reaction mechanisms and rate constants which must be used to reproduce the observed flame velocity. However, the transport fluxes are only represented approximately in this time-dependent model, so that a precise calculation of flame profiles cannot be made. The second computational method uses a Runge–Kutta procedure to calculate the steady-state flame profiles, and is an extension of the methods discussed by Dixon-Lewis (1968). It incorporates detailed transport property calculations, and thus allows computation of detailed flame profiles for comparison with experiment. Application of the methods to the rich hydrogen+nitrogen+oxygen flame and subsequent comparison with experiment has established the participation of hydroperoxyl in the flame mechanism, and has shown the principal reactions in the flame to be: OH + H 2 = H 2 O + H, (i) H + O 2 =OH + O, (ii) O + H 2 =OH + H, (iii) H + O 2 + M = HO 2 + M, (iv) H + HO 2 = OH + OH, (vii) H + HO 2 = H 2 + O 2 , (xii) H+ H + M = H 2 + M. (xv) It was found that the interplay between these reactions is such that it is impossible to use the atmospheric pressure flame for an independent, precise determination of the hydrogenoxygen chain branching-rate constant k 2 . Another property of the mechanism is that the hydrogen atom concentration profile in the flame is not very dependent on the precise rate constants employed, so that the profile itself can be computed probably to better than ±10%. The reaction zone of the very rich flame commences at about 550 K, the maximum overall reaction rate is at about 900 K, and the maximum hydrogen atom concentration is at 1030 to 1040 K. The rate constant ratio k 7 / k 12 is found to lie in the range 5±1, assumed independent of temperature over the reaction zone. Assuming equal efficiencies of all the molecules in the flame as third bodies in the hydrogen atom recombination, the rate constant k 15 is estimated to lie in the range 4.5±1.5 x 10 15 cm 6 mol -2 s -1 .

Radiolysis studies on the corrosion inhibitors 1 -hexyn-3-ol, cinnamonitrile, and 1,3-diethyl-2-thiourea

1995 ◽  
Vol 73 (12) ◽  
pp. 2137-2142 ◽  
Author(s):  
A.J. Elliot ◽  
M.P. Chenier ◽  
D.C. Ouellette
Keyword(s):  
Hydrogen Atom ◽  
Hydroxyl Radical ◽  
Temperature Dependence ◽  
Rate Constant ◽  
Rate Constants ◽  
Corrosion Inhibitors ◽  
Hydrated Electron

In this publication we report: (i) the rate constants for reaction of the hydrated electron with 1-hexyn-3-ol ((8.6 ± 0.3) × 108 dm3 mol−1 s−1 at 18 °C), cinnamonitrile ((2.3 ± 0.2) × 1010 dm3 mol−1 s−1 at 20 °C), and 1,3-diethyl-2-thiourea ((3.5 ± 0.3) × 108 dm3 mol−1 s−1 at 22 °C). For cinnamonitrile and diethylthiourea, the temperature dependence up to 200 °C and 150 °C, respectively, is also reported; (ii) the rate constants for the reaction of the hydroxyl radical with 1-hexyn-3-ol ((5.5 ± 0.5) × 109 dm3 mol−1 s−1 at 20 °C), cinnamonitrile ((9.2 ± 0.3) × 109 dm3 mol−1 s−1 at 21 °C), and diethylthiourea ((8.0 ± 0.8) × 108 dm3 mol−1 s−1 at 22 °C). For cinnamonitrile, the temperature dependence up to 200 °C is also reported; (iii) the rate constant for the hydrogen atom reacting with 1-hexyn-3-ol ((4.3 ± 0.4) × 109 dm3 mol−1 s−1 at 20 °C). Keywords: radiolysis, corrosion inhibitors, rate constants.

scholarly journals Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction

2021 ◽  
Author(s):  
Bernard Stevenson ◽  
Ethan Spielvogel ◽  
Emily Loiaconi ◽  
Victor M. Wambua ◽  
Roman Nakhamiyayev ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Absorption Spectroscopy ◽  
Rate Constant ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Transient Absorption ◽  
Coupling Reaction ◽  
Time Dependent ◽  
Transient Absorption Spectroscopy ◽  
Mechanistic Investigations

We present time-dependent percent and quantum yield measurements of a photoredox-catalyzed coupling reaction between 1,4-dicyanobenzene and N-phenylpyrrolidine. We also use transient absorption spectroscopy to examine the kinetics within the reaction and use kinetic modeling to extract rate constants and predict how changes in rate constant will impact the quantum yield.

An anomalous effect of methyl group on acidity of acylthioureas

1987 ◽  
Vol 52 (8) ◽  
pp. 1992-1998 ◽  
Author(s):  
Jaromír Kaválek ◽  
Josef Jirman ◽  
Vladimír Macháček ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Acetyl Derivative ◽  
Methyl Groups ◽  
Anomalous Effect ◽  
Methyl Group ◽  
Methyl Derivatives

Dissociation constants and methanolysis rate constants have been measured of 1-acetyl- and 1-benzoylthioureas and their N-methyl derivatives. Replacement of hydrogen atom at N(1) (next to the acyl group) by methyl group increases the acidity of the benzoyl derivative by one order, that of the acetyl derivative by as much as two orders of magnitude. Replacement of both hydrogens at N(3) by methyl groups lowers the methanolysis rate constant by more than two orders, whereas the replacement of hydrogen atom at N(1) by methyl group increases the methanolysis rate by the factor of 30.

scholarly journals A computer-enhanced pH study of the formaldehyde–sulphite clock reaction

1992 ◽  
Vol 14 (3) ◽  
pp. 79-83 ◽  
Author(s):  
F. T. Chau ◽  
K. W. Mok
Keyword(s):  
Reaction Mechanism ◽  
Theoretical Model ◽  
Data Acquisition ◽  
Rate Constant ◽  
Rate Constants ◽  
Empirical Expression ◽  
Instantaneous Rate ◽  
Data Treatment ◽  
First Time ◽  
Clock Reaction

The formaldehyde-sulphite clock reaction was studied using an Orion SA 720 pH/ISE meter interfaced to an IBM PC. The laboratory software ‘ASYST’ was employed to facilitate data acquisition and data treatment. Experimental pH profiles thus obtained for the first time were simulated by invoking a theoretical model based on the reaction mechanism suggested by Burnett [1]. The variation of rate constants with compositions of reaction mixtures was also discuseed in light of the empirical expression proposed by Bell and Evans [2] for instantaneous rate constant of the clock reaction.

BrHgO• + C2H4 and BrHgO• + HCHO in Atmospheric Oxidation of Mercury: Determining Rate Constants of Reactions with Pre-Reactive Complexes and a Bifurcation

2019 ◽  
Author(s):  
Khoa T. Lam ◽  
Curtis J. Wilhelmsen ◽  
Theodore Dibble
Keyword(s):  
Hydrogen Atom ◽  
Quantum Chemistry ◽  
Transition State ◽  
Rate Constant ◽  
Rate Constants ◽  
Minimum Energy ◽  
Atmospheric Oxidation ◽  
Minimum Energy Path ◽  
Oh Radical ◽  
Hydrogen Atoms

Models suggest BrHgONO to be the major Hg(II) species formed in the global oxidation of Hg(0), and BrHgONO undergoes rapid photolysis to produce the thermally stable radical BrHgO•. We previously used quantum chemistry to demonstrate that BrHgO• can, like OH radical, readily can abstract hydrogen atoms from sp<sup>3</sup>-hybridized carbon atoms as well as add to NO and NO<sub>2</sub>. In the present work, we reveal that BrHgO• can also add to C<sub>2</sub>H<sub>4</sub> to form BrHgOCH<sub>2</sub>CH<sub>2</sub>•, although this addition appears to proceed with a lower rate constant than the analogous addition of •OH to C<sub>2</sub>H<sub>4</sub>. Additionally, BrHgO• can readily react with HCHO in two different ways: either by addition to the carbon or by abstraction of a hydrogen atom. The minimum energy path for the BrHgO• + HCHO reaction bifurcates, forming two pre-reactive complexes, each of which passes over a separate transition state to form a different product.

The mechanism of the pyrolysis of 2, 2, 3, 3-tetramethylbutane

1978 ◽  
Vol 363 (1715) ◽  
pp. 503-523 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Rate Constants ◽  
Volume Ratio ◽  
Reaction Scheme ◽  
Secondary Source ◽  
Kinetic Characteristics ◽  
Hydrogen Atoms ◽  
Reaction Conditions ◽  
Total Product

The pyrolysis of 2, 2, 3, 3-tetramethylbutane (TMB) was investigated in the ranges 699-735 K and 3-19 Torr (0.4-2.5 kPa) at up to 4% decomposition. The reaction is strongly self-inhibited and sensitive to the surface/volume ratio of the reaction vessel. A simple Rice-Herzfeld chain terminated by the heterogeneous removal of hydrogen atoms is proposed for the initial, uninhibited reaction generating isobutene and hydrogen in a 2:1 ratio. Self-inhibition is due to abstraction by hydrogen atoms of hydrogen atoms from product isobutene giving resonance-stabilized 2-methylallyl radicals which participate in homogeneous termination reactions. The kinetic characteristics of the major primary products (> 95% on a mole basis), isobutene and hydrogen, are accounted for when reasonable values are assumed for the rate constants for hydrogen atom abstraction by hydrogen atoms from TMB and from isobutene and for initiation and heterogeneous termination of the chain reaction. The kinetic characteristics of the formation of methane and propene (2-4% of total product) are accounted for by the secondary reaction scheme H + i-C 4 H 8 → i-C 4 H 9 , i-C 4 H 9 → CH 3 + C 3 H 6 , CH 3 + TMB → CH 4 + C 8 H 17 , when a reasonable value for the rate constant for the hydrogen atom addition to isobutene is assumed. The kinetic characteristics of the formation of ethene ( ca . 0.1% of total product) are accounted for by the tertiary reaction scheme H + C 3 H 6 → n -C 3 H 7 n -C 3 H 7 → CH 3 + C 2 H 4 , when a reasonable value for the rate constant for the hydrogen atom addition to propene is assumed. The kinetic characteristics of the formation of isobutane ( ca . 1% of total product) are much less affected by an increase in surface/volume ratio of the reactor than are those of the other products. A heterogeneous, secondary source is suggested, viz. 1/2H 2 ( g ) ⇌ H (wall), H (wall) + t-C 4 H 9 ( g ) ⇌ i-C 4 H 10 ( g ), which can generate the observed dependence of the isobutane yield on the reaction conditions but the reasonableness or otherwise of the values of the equilibrium and rate constants it is necessary to postulate is impossible to assess without further work designed specifically to investigate this problem.

Enzyme-induced coagulation of casein micelles: a number of different kinetic models

1993 ◽  
Vol 60 (4) ◽  
pp. 517-533 ◽  
Author(s):  
Douglas B. Hyslop
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Energy Barrier ◽  
Time Dependent ◽  
Series Expansions ◽  
Simple Relationship ◽  
Casein Micelles ◽  
Functional Sites ◽  
The Third ◽  
Flocculation Rate

SummarySeveral mathematical models are presented in an attempt to describe the kinetics of the enzyme-induced coagulation of casein micelles. In each model the primary phase of the clotting reaction is assumed to follow first order kinetics. The only differences amongst the various models centre on the definition of the flocculation rate constant, which is defined in seven different ways. The rate constants are defined and discussed in terms of activation energy and functionality theory. The first model is such that the number of functional sites is two. The second is such that the number is much larger. The third and fourth are such that there is an exponential energy barrier, one which has a magnitude proportional to the extent of proteolysis caused by the clotting enzyme. These two definitions differ only in the pre-exponent. In one case the pre-exponent is a constant, whereas in the other it is dependent on the size of clotting particles. The fifth and sixth definitions are also energy barrier rate constants, but the energy barrier changes in an arbitrary fashion with respect to time during proteolysis. The seventh definition assumes a large number of functional sites, but such that the number increases with extent of proteolysis. In the Payens nomenclature (Payens, 1989), all models could be considered to be ‘source’ models, and all are derived using the Drake moment equation (Drake, 1972). Only the first model has a truly constant flocculation rate parameter, and only this model has a relatively simple analytical solution. All other models yield analytical solutions only by way of infinite series expansions. Thus, all models are presented in terms of power series expansions, and only through the first five time-dependent coefficients. This confines all models to the early stages of coagulation. In all cases the first three coefficients are virtually the same. The first two coefficients involve only proteolysis, and the third includes initial flocculation information. Time-dependent changes in the flocculation rate constant begin to take effect in the fourth coefficient. When the fourth coefficients of the third and seventh models are compared, a simple relationship is suggested between free energy barrier removal and functional site generation, but only assuming that the number of functionalities is large.

Mesure de la constante de vitesse de réaction des atomes d'hydrogène sur l'éthane et le propane en réacteurs tubulaire et parfaitement agité ouverts

1978 ◽  
Vol 56 (3) ◽  
pp. 392-401 ◽  
Author(s):  
Jacques Lede ◽  
Jacques Villermaux
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Electrical Discharge ◽  
Room Temperature ◽  
Hydrogen Atoms ◽  
Atom Concentration ◽  
Sensitive Method ◽  
Good Agreement

The rate constant for the reaction of hydrogen atoms, generated by electrical discharge, with ethane and propane has been studied in tubular and perfectly stirred open reactors. Measurements are made with a new and very sensitive method of analysis of the hydrogen atom concentration. The results obtained near room temperature are in good agreement with those of other authors operating at much higher temperatures. The following estimates may be made:[Formula: see text]

scholarly journals Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction

2020 ◽  
Author(s):  
Bernard Stevenson ◽  
Ethan Spielvogel ◽  
Emily Loiaconi ◽  
Victor M. Wambua ◽  
Roman Nakhamiyayev ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Absorption Spectroscopy ◽  
Rate Constant ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Transient Absorption ◽  
Coupling Reaction ◽  
Time Dependent ◽  
Transient Absorption Spectroscopy ◽  
Mechanistic Investigations

We present time-dependent percent and quantum yield measurements of a photoredox-catalyzed coupling reaction between 1,4-dicyanobenzene and N-phenylpyrrolidine. We also use transient absorption spectroscopy to examine the kinetics within the reaction and use kinetic modeling to extract rate constants and predict how changes in rate constant will impact the quantum yield.

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