THE THERMAL DECOMPOSITION OF HEXAFLUOROAZOMETHANE

1962 ◽  
Vol 40 (5) ◽  
pp. 930-934 ◽  
Author(s):  
Elizabeth Leventhal ◽  
Charles R. Simonds ◽  
Colin Steel
Keyword(s):  
Thermal Decomposition ◽  
High Pressure ◽  
Rate Constant ◽  
Static System ◽  
Homogeneous Reaction

The pyrolysis of hexafluoroazomethane has been studied in a static system between 0.3 mm and 73 mm and 572 °K and 634 °K by measuring the rate of nitrogen formation. The rate constant of the high-pressure homogeneous reaction is given by k = 1016.17±0.15 exp (−55,200 ± 400/RT) sec−1

Die unimolekulare thermische Spaltung von Äthylchlorid-2-d3 und Äthylchlorid-2-d1 nach einem Vierzentrenmechanismus

1968 ◽  
Vol 23 (11) ◽  
pp. 1407-1411 ◽  
Author(s):  
G. W. Völker ◽  
H. Heydemann
Keyword(s):  
Thermal Decomposition ◽  
High Pressure ◽  
Rate Constants ◽  
Mass Spectrometric ◽  
Spectrometric Analysis ◽  
Static System ◽  
Pressure Limit ◽  
Reaction Complex ◽  
Elimination Mechanism ◽  
Two Temperatures

The unimolecular thermal decomposition of chloroethane-2-d3 and chloroethane-2-d1 was studied in a static system at two temperatures and at pressures between 0.1 and 10 mm Hg. The rate constants for the high pressure limit were obtained from these measurements and used to calculate the Arrhenius equations. The decomposition of chloroethane-2-d3 was also studied at high conversions and yielded almost exclusively (97%) DCl and CD2CH2 as shown by mass spectrometric analysis thus proving a molecular elimination mechanism via a four-centered reaction complex.

The thermal decomposition of methane. III. Methyl radical exchange in CH4–CD4 mixtures

1977 ◽  
Vol 55 (10) ◽  
pp. 1624-1628 ◽  
Author(s):  
C.-J. Chen ◽  
M. H. Back ◽  
R. A. Back
Keyword(s):  
Thermal Decomposition ◽  
Shock Tube ◽  
Exchange Reaction ◽  
Rate Constant ◽  
Average Rate ◽  
Static System ◽  
Chain Mechanism ◽  
Methyl Radical ◽  
Radical Chain ◽  
Decomposition Of Methane

The thermal methyl-radical exchange reaction, CH4 + CD4 → CH3D + CD3H, has been studied in a static system at temperatures from 880 to 1103 K, with equimolar mixtures at a pressure of 440 Torr. The exchange occurs by a methyl-radical chain mechanism, propagated by the reactions CH3 + CD4 → CH3D + CD3, and CH3 + CD4 → CH3H + CD3. Values of an average rate constant for these reactions have been estimated; kx = 1.42 × 106 ℓ mol−1 s−1 at 995 K. Comparison with shock tube data and photochemical measurements, at higher and lower temperatures respectively, indicates pronounced non-Arrhenius behaviour.

High-Resolution Electron Microscopy Studies of Faults and Intergrowth in Nb3O7F

1990 ◽  
Vol 183 ◽  
Author(s):  
Lotta permér ◽  
Monica Lundberg
Keyword(s):  
Electron Microscopy ◽  
Thermal Decomposition ◽  
High Pressure ◽  
High Resolution Electron Microscopy ◽  
Two Dimensions ◽  
Resolution Electron ◽  
Shear Type ◽  
Pressure Form ◽  
The Common ◽  
Shear Planes

AbstractHREM studies of the low-pressure form of Nb3O7F, obtained by thermal decomposition of NbO2F or by reacting stoichiometric amounts of NbO2F and Nb2O5, confirmed that the crystals are built up of a shear-type structure in which slabs of ReO3 type, infinite in two dimensions and three octahedra wide, separate the shear planes. Most of the crystals were well-ordered, although faults could occasionally be detected. However, some crystals were found to be intergrown with a structure closely related to the high-pressure form of Nb3O7F. The latter structure is composed of wavy rows of edge-sharing NbX7 pentagonal bipyramids, joined to each other by NbX6 octahedra. The connection between the two atomic arrangements can be understood in terms of the common c-axes and a slight distortion of the polyhedra along the boundary.

Pressure effect on hydrogen isotope exchange kinetics in chymotrypsinogen investigated by FT-IR spectroscopy

1991 ◽  
Vol 69 (11) ◽  
pp. 1699-1704 ◽  
Author(s):  
P. T. T. Wong
Keyword(s):  
High Pressure ◽  
Exchange Rate ◽  
Rate Constant ◽  
Bound Water ◽  
Pressure Effects ◽  
Protein Molecules ◽  
Fast Exchange ◽  
Exchange Rate Constant ◽  
Hydrogen Deuterium ◽  
Exchange Kinetics

Hydrogen/deuterium (H/D) exchange rate constants in chymotrypsinogen have been determined at several pressures up to 28.9 kbar by FTIR spectroscopy. The secondary structure of the protein molecules was monitored simultaneously at the corresponding pressures by the intensity redistribution of the infrared amide I band at these pressures. As in other proteins, the labile protons on the amide groups in chymotrypsinogen can, to a good approximation, be separated into two classes, each with distinct first order H/D exchange rates constants in the time period from 10 min to ~24 h. The fast exchange rate constant increases while the slow exchange rate constant decreases with increasing pressure. The increase in the fast exchange rate constant at high pressure is largely associated with the pressure-induced unfolding of the protein molecules. At extremely high pressure (12.8 kbar), in addition to the unfolding of protein molecules, pressure induced a distortion and weakening of the hydrogen bonds of the fold protein segments also contribute to an increase in the overall H/D exchange rate. The present results confirm that when chymotrypsinogen is dissolved in D2O, a considerable amount of D2O molecules is bound to the protein molecules on the surface as well as in the interior cavities of the molecules. The H/D exchange takes place between these bound D2O and the protons in the protein molecules. The mechanism of the H/D exchange and the interior dynamics in proteins are discussed on the basis of the present results. Key words: hydrogen/deuterium exchange, exchange kinetics, rate constant, pressure effects, infrared spectroscopy, protein, conformation structure, bound water.

THE THERMAL DECOMPOSITION OF PERACETIC ACID IN AROMATIC SOLVENTS

1963 ◽  
Vol 41 (7) ◽  
pp. 1826-1831 ◽  
Author(s):  
F. W. Evans ◽  
A. H. Sehon
Keyword(s):  
Thermal Decomposition ◽  
Rate Constant ◽  
Peracetic Acid ◽  
First Order ◽  
Aromatic Solvents ◽  
Temperature Range ◽  
Polymeric Compounds

The thermal decomposition of peracetic acid in toluene, benzene, and p-xylene was studied over the temperature range 75–95°C. The main products of decomposition were found to be CH4, CO2, CH3COOH; small amounts of methanol, phenols, and polymeric compounds were also detected.The rate of the overall decomposition was first order with respect to peracetic acid, and the results could be explained by postulating the participation of the two simultaneous reactions:[Formula: see text] [Formula: see text]The rate constant of reaction (1) was independent of the solvent, whereas k2 was dependent on the solvent. The ratio k2/k1 was about 10.

scholarly journals Thermal decomposition of mercerized linter cellulose and its acetates obtained from a homogeneous reaction

Polímeros ◽  
2011 ◽  
Vol 21 (2) ◽  
pp. 111-117 ◽  
Author(s):  
Daniella L. Morgado ◽  
Elisabete Frollini
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Quantitative Methods ◽  
Homogeneous Medium ◽  
Solvent System ◽  
Homogeneous Reaction ◽  
Reactive Site ◽  
Cellulose Decomposition ◽  
Mechanism Of Thermal Decomposition ◽  
Cellulose Acetates

Cellulose acetates with different degrees of substitution (DS, from 0.6 to 1.9) were prepared from previously mercerized linter cellulose, in a homogeneous medium, using N,N-dimethylacetamide/lithium chloride as a solvent system. The influence of different degrees of substitution on the properties of cellulose acetates was investigated using thermogravimetric analyses (TGA). Quantitative methods were applied to the thermogravimetric curves in order to determine the apparent activation energy (Ea) related to the thermal decomposition of untreated and mercerized celluloses and cellulose acetates. Ea values were calculated using Broido's method and considering dynamic conditions. Ea values of 158 and 187 kJ mol-1 were obtained for untreated and mercerized cellulose, respectively. A previous study showed that C6OH is the most reactive site for acetylation, probably due to the steric hindrance of C2 and C3. The C6OH takes part in the first step of cellulose decomposition, leading to the formation of levoglucosan and, when it is changed to C6OCOCH3, the results indicate that the mechanism of thermal decomposition changes to one with a lower Ea. A linear correlation between Ea and the DS of the acetates prepared in the present work was identified.

Substituent effects of rate constants for thermal [4π + 2π] cycloreversion of spiro-fused β-lactam oxadiazolines

1993 ◽  
Vol 71 (6) ◽  
pp. 907-911 ◽  
Author(s):  
Michel Zoghbi ◽  
John Warkentin
Keyword(s):  
Thermal Decomposition ◽  
Rate Constant ◽  
Rate Constants ◽  
Transition States ◽  
Substituent Effects ◽  
Ground States ◽  
Phenyl Substituent ◽  
First Order ◽  
Average Value ◽  
Carbonyl Ylide

Twelve Δ3-1,3,4-oxadiazolines in which C-2 is also C-4 of a β-lactam moiety (spiro-fused β-lactam oxadiazoline system) were thermolyzed as solutions in benzene. Substituents in the β-lactam portion affect the rate constant for thermal decomposition of the oxadiazolines to N2, acetone, and a β-lactam-4-ylidene. The total spread of first-order rate constants at 100 °C was 47-fold and the average value was 6.7 × 10−4 s−1. A phenyl substituent at N-1 or at C-3 was found to be rate enhancing, relative to methyl. At C-3, H and Cl were also rate enhancing, relative to methyl. The data are interpreted in terms of the differential effects of substituents on the stabilities of the ground states, and on the stabilities of corresponding transition states for concerted, suprafacial, [4π + 2π] cycloreversion. The first products, presumably formed irreversibly, are N2 and a carbonyl ylide. The latter subsequently fragments to form acetone (quantitative) and a β-lactam-4-ylidene.

The gas-phase photochemistry and thermal decomposition of glyoxylic acid

1985 ◽  
Vol 63 (2) ◽  
pp. 542-548 ◽  
Author(s):  
R. A. Back ◽  
S. Yamamoto
Keyword(s):  
Thermal Decomposition ◽  
Carbon Monoxide ◽  
Absorption Spectrum ◽  
Gas Phase ◽  
Singlet State ◽  
Glyoxylic Acid ◽  
Static System ◽  
First Order ◽  
Increasing Temperature ◽  
Homogeneous Formation

The photolysis of glyoxylic acid vapour has been studied at five wavelengths, 382, 366, 346, 275, and 239 nm, and pressures from about 1 to 6 Torr, at a temperature of 355 K. Major products were CO2 and CH2O, initially formed in almost equal amounts, while minor products were CO and H2. Except at 382 nm, the system was complicated by the rapid secondary photolysis of CH2O. Three primary processes are suggested, each involving internal H-atom transfer followed by dissociation.The absorption spectrum is reported and shows the three distinct absorption systems. A finely-structured spectrum from about 320 to 400 nm is attributed to a transition to the first excited π* ← n+ singlet state; a more diffuse absorption ranging from about 290 nm to a maximum at 239 nm is assigned to the π* ← n− state, while a much stronger absorption beginning below 230 nm is attributed to the π* ← π transition. Product ratios vary with wavelength and depend on which excited state is involved.The thermal decomposition was studied briefly in a static system at temperatures from 470 to 710 K and pressures from 0.4 to 8 Torr. Major products were again CO2 and CH2O, but the latter was always less than stoichiometric. First-order rate constants for the apparently homogeneous formation of CO2 are described by Arrhenius parameters log A (s−1) = 7.80 and E = 30.8 kcal/mol. Carbon monoxide and H2 were minor products, and the CO/CO2 ratio increased with increasing temperature and showed some surface enhancement at lower temperatures. The SF6-sensitized thermal decomposition of glyoxylic acid, induced by a pulsed CO2 laser, was briefly studied, with temperatures estimated to be in the 1100–1600 K range, and the CO/CO2 ratio increased with increasing temperature, continuing the trend observed in the static system.

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