A Theoretical and Experimental Investigation of the Kinetics of Ring Closure of the 3-Methyl-3-azahex-5-enyl Radical

1995 ◽  
Vol 48 (12) ◽  
pp. 2047 ◽  
Author(s):  
EW Della ◽  
AM Knill
Keyword(s):  
Activation Energy ◽  
Experimental Investigation ◽  
Force Field ◽  
Activation Barrier ◽  
Ring Closure ◽  
Force Field Calculations ◽  
Arrhenius Parameters ◽  
A Value ◽  
Kinetics Of

Evaluation of the Arrhenius parameters for ring closure of the 3-methyl-3-azahex-5-enyl radical is reported. Cyclization of the radical is found to occur with high regioselectivity giving the exo -trig product exclusively with an activation energy of 22 kJ mol-1 and log A value of 11.1. The experimental activation barrier compares favourably with that determined by force field calculations which predict a value of 21 kJ mol-1. The 3-methyl-3-azahex-5-enyl radical is therefore found to undergo ring closure some 70 times faster than the parent hex-5-enyl radical, in accord with predictions based upon geometrical considerations.

scholarly journals The kinetics of colour degradation, chlorophylls and xanthophylls loss in pistachio nuts during roasting process

2019 ◽  
Author(s):  
Ali Dini ◽  
Soudeh Khanamani Falahati-Pour ◽  
Khosro Behmaram ◽  
Nasser Sedaghat
Keyword(s):  
Activation Energy ◽  
B Value ◽  
Order Kinetic ◽  
Air Velocity ◽  
Carotenoid Concentration ◽  
Hot Air ◽  
A Value ◽  
Pistachio Nuts ◽  
Roasting Temperature ◽  
Kinetics Of

Abstract Objectives Colour is amongst the parameter which is used for process control during roasting. Materials and Methods In this study, the effects of hot air roasting temperature (120, 130, 145, 160, and 170°C) and hot air velocity (0.6, 1.3, and 2 m/s) on colour change kinetics of pistachio nuts were investigated by employing image analysis and simultaneously chlorophylls and xanthophylls (lutein and β-carotenoid) concentration were determined by spectrophotometric measurement method. Results We found that roasting temperature and hot air velocity had significant effect on colour changes. There is a correlation between a- and b-value with chlorophylls and xanthophylls concentration, respectively. The roasting temperature was found to be the main factor affecting colour development. The variations in the pigments concentration and colour parameters of pistachio nuts were adequately simulated by quadratic and cubic polynomials. The changes in L-, b-values, and xanthophylls degradation were well-fitted to the first-order kinetic model while a-value and chlorophylls degradation followed the zero-order kinetic. The activation energy was determined at 113.9, 116.7, and 117.2 kJ/mol with R2 ≥ 99.9 and 191, 195, and 163.2 kJ/mol with R2 ≥ 99.5 and 73.7, 71.3, and 81.6 kJ/mol with R2 ≥ 99.9 for L-, b-, and a-value in hot air velocity of 0.6, 1.3, and 2 m/s, respectively. Conclusions Activation energy of chlorophylls and xanthophylls degradation were in the range of the activation energy for the yellowness (b-value) and redness (a-value) reactions.

Determination of Recrystallization Kinetics and Activation Energy of Grain Growth Process of Cu-14Al-4Ni Shape Memory Alloy

2015 ◽  
Vol 1765 ◽  
pp. 127-132 ◽  
Author(s):  
Emmanuel P. R. Lima ◽  
Pedro C. de Lima ◽  
Marcelo Nava
Keyword(s):  
Activation Energy ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Grain Growth ◽  
Growth Process ◽  
Treatment Time ◽  
Mechanical Tests ◽  
A Value ◽  
Kinetics Of

ABSTRACTThe non-ferrous shape memory alloys have, normally, two problems that hinder its use in industrial scale: the natural aging and grains growth. The first degrades the memory effect, while the second, observed during the processing of alloy, modifies the temperatures which the transformations occur. Thus, the study of kynetic of recrystallization is important for enabling the control of hardened state in function of treatment time, without causing excessive grain growth. Therefore, the objective of this study is to determine the kinetics of recrystallization of Cu-14Al-4Ni shape memory alloy, based on an empirical law of the formation of Jonhson-Mehl-Avrami, as well as their activation energies for grain growth process according to the empirical Arrhenius law. The alloy was vacuum melted in an induction furnace. After casting, the bulk samples of the alloy were homogenized for 24 hours, solubilized and hot rolled followed by water-quenching to initiate the recrystallization. Then, different samples were annealed at temperatures close to the peak, start and end of the DSC curve. Following the heat treatments, the samples were submitted to mechanical tests and the values of the properties were correlated to the fraction transformed for determination of recrystallization’s kinetic. For the characterization of the grain growth process, analyses in optical microscopy were accomplished and all annealed samples were examined by statistical metallography and the grain sizes were measured. After measurements, the ln[-ln(1-Yrec)] x ln(t) and the ln [D-Do] x 1/T diagrams were plotted to determine the parameters of Jonhson-Mehl-Avrami equation and the activation energy of the process, respectively. The results showed that the equation of the recrystallized fraction follows the empiric law of the formation of Jonhson-Mehl-Avrami for the considered property, as well as, also showed that the alloy Cu-14Al-4Ni is extremely sensitive to temperature variation in which the alloy is treated, having a dual kinetics of grain growth. In the first domain, between 670 and 710°C, the diagram provides a value for the activation energy equal to 39.32 KJ/mol, in the second domain, between 710 and 790°C, the diagram provides a value for the activation energy equal to 9.01 KJ/mol.

Kinetics of the Mercury-Photosensitized Decomposition of Propane. Part II. Reactions of the Propyl Radicals

1971 ◽  
Vol 49 (4) ◽  
pp. 549-554 ◽  
Author(s):  
M. M. Papic ◽  
K. J. Laidler
Keyword(s):  
Activation Energy ◽  
High Pressure ◽  
Kinetic Parameters ◽  
Dissociation Energy ◽  
Heat Of Formation ◽  
Entropy Changes ◽  
A Value ◽  
Yield Information ◽  
Temperature And Pressure ◽  
Kinetics Of

The results of the previous paper are analyzed to yield information about the reactions of the n-propyl and i-propyl radicals. The various combination and disproportionation reactions are considered. The rate of decomposition of the n-propyl radical was determined as a function of temperature and pressure, and limiting high-pressure and low-pressure kinetic parameters were obtained. The high-pressure activation energy is 32.6 kcal mol−1, and this leads to a value of 24.3 kcal mol−1 for the dissociation energy of the C—C bond in the n-propyl radical, to 22.2 kcal mol−1 for its heat of formation, and to 99.1 kcal mol−1 for the primary C—H dissociation energy in propane. Entropy changes are also calculated from the results.For the decomposition of the i-propyl E∞ = 38.7 kcal mol−1, and this leads to 37.7 kcal mol−1 for the C—H bond dissocation energy in this radical and to 19.3 kcal mol−1 for its heat of formation. The secondary C—H dissociation energy in propane is calculated to be 96.2 kcal mol−1. Corresponding entropy changes are calculated.

Kinetic Study of the Pyrolysis of Formaldehyde

1972 ◽  
Vol 50 (7) ◽  
pp. 992-998 ◽  
Author(s):  
C. J. Chen ◽  
D. J. McKenney
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Carbon Monoxide ◽  
Kinetic Study ◽  
Pressure Range ◽  
Heterogeneous Reaction ◽  
Experimental Results ◽  
Arrhenius Parameters ◽  
Rate Laws ◽  
Kinetics Of

Kinetics of the thermal decomposition of pure formaldehyde were studied over a temperature range of 466–516 °C and a pressure range of ~ 50–160 Torr. Arrhenius parameters and rate laws were determined for carbon monoxide, hydrogen and methanol as follows:[Formula: see text]A mechanism is postulated which is qualitatively consistent with the experimental results but the activation energy for reaction 1[Formula: see text]is ~15 kcal/mol lower than predicted from recent thermochemical data, suggesting the possibility of a heterogeneous reaction.

The Kinetics of the Reaction 2C3H6 → C3H5 + C3H7

1973 ◽  
Vol 51 (17) ◽  
pp. 2934-2939 ◽  
Author(s):  
M. Simon ◽  
M. H. Back
Keyword(s):  
Activation Energy ◽  
Rate Constant ◽  
Radical Scavenger ◽  
A Value ◽  
Kinetics Of

An attempt has been made to measure the rate constant for the bimolecular process[Formula: see text]using acetaldehyde as a radical scavenger. The rate constant obtained may be expressed as follows:[Formula: see text]This activation energy corresponds to a value of 36 kcal/mol for ΔHf(allyl).

KINETICS OF THE DECOMPOSITIONS OF ETHANE AND PROPANE SENSITIZED BY AZOMETHANE: THE DECOMPOSITION OF THE NORMAL PROPYL RADICAL

1966 ◽  
Vol 44 (24) ◽  
pp. 2927-2940 ◽  
Author(s):  
M. C. Lin ◽  
K. J. Laidler
Keyword(s):  
Activation Energy ◽  
Satisfactory Agreement ◽  
Rate Constant ◽  
Dissociation Energy ◽  
Low Temperatures ◽  
Heats Of Formation ◽  
Kcal Mole ◽  
Energy Diagram ◽  
A Value ◽  
Kinetics Of

The azomethane-sensitized pyrolysis of ethane was studied at low temperatures from 280 to 350 °C. Measurements were made of initial rates of formation of methane, nitrogen, and butane. From the rate of nitrogen production the rate constant for the azomethane decomposition into 2CH3 + N2 was[Formula: see text]A similar study of the propane decomposition, at temperatures from 260 to 300 °C, led to the value[Formula: see text]in satisfactory agreement. The rate of decomposition of the n-propyl radical into CH3 and C2H4 was obtained by comparing the rates of formation of C2H4 and n-C6H14; the rate constant was[Formula: see text]The activation energy of 31.4 kcal/mole, together with that of 8.9 kcal/mole for the reverse reaction obtained by Brinton, leads to a value of 20.3 kcal/mole for the dissociation energy of n-CH3—CH CH2 at 0 °K, and to a value of 22.8 at 25 °C. The corresponding values for the heats of formation 2of the n-propyl radical are 28.4 kcal/mole at 0 °K, and 23.1 kcal/mole at 25 °C. The dissociation energy of n-CH3CH2CH2—H is deduced to be 99.4 kcal/mole at 0 °K and 99.9 kcal/mole at 25 °C. An energy diagram is constructed for the various reactions of n-C3H7 and i-C3H7.

The kinetics of the reaction between O 2 ( 1 ∆ g ) and ozone

1970 ◽  
Vol 317 (1530) ◽  
pp. 407-416 ◽  
Keyword(s):  
Activation Energy ◽  
Rate Constant ◽  
Room Temperature ◽  
Published Data ◽  
Temperature Range ◽  
A Value ◽  
Kinetics Of

The kinetics of the reaction O 2 ( 1 ∆ g ) + O 3 k 2 → 2O 2 + O have been investigated in the temperature range 195 to 439 K by using the kinetic photo­ionization technique to follow [O 2 ( 1 ∆ g )]. In Arrhenius form, the rate constant, k 2 ,'is given by k 2 = 4.0 ± 1.5 x 10 8 exp (13000 /RT) 1 mol -1 s -1 (joule units) ( = 4.0 ± 1.5 x 10 8 exp (3100/RT) 1 mol -1 s -1 (calorie units)). At room temperature (292 K) k 2 = 2.1 ± 0.3 x 10 6 1 mol -1 s -1 . The activation energy of 13 ± 1.6 kJ mol -1 suggests that there is virtually no barrier to the reaction other than that provided by its endothermicity (12.1 kJ mol -1 ). The results are used to derive, from pre­viously published data, a value of the rate constant for the reaction O + O 3 k 3 → 2O 2 of 4 ± 2 x 10 6 1 mol -1 s -1 at room temperature.

Kinetics of the recombination of methyl radicals with benzyl radicals

1967 ◽  
Vol 45 (6) ◽  
pp. 575-578 ◽  
Author(s):  
R. J. Kominar ◽  
M. G. Jacko ◽  
S. J. Price
Keyword(s):  
Frequency Factor ◽  
Ethyl Benzene ◽  
Recombination Reaction ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
Arrhenius Parameters ◽  
Temperature Range ◽  
A Value ◽  
Benzyl Radicals ◽  
Kinetics Of

The recombination of methyl and benzyl radicals has been studied over the temperature range 529 to 799 °K. The Arrhenius parameters for the recombination reaction are log A (cc mole−1 s−1) = 11.20, E = 0.20 kcal mole−1. The frequency factor at 1 000 °K for the reverse reaction, the dissociation of ethyl benzene, is calculated to be log A (s−1) = 14.9. A value of 70.5 kcal mole−1 has been estimated for D(C6H5CH2—CH3).

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