The Mechanism for the Thermal Decomposition of E-Aldoxime Carbonates

1975 ◽  
Vol 53 (22) ◽  
pp. 3481-3486 ◽  
Author(s):  
J. M. Prokipcak ◽  
P. A. Forte
Keyword(s):  
Low Temperatures ◽  
Solvent Polarity ◽  
Decomposition Rates ◽  
Cyclic Transition ◽  
First Order ◽  
First Order Kinetics ◽  
Inductive Effects ◽  
Cyclic Transition State ◽  
E And Z Isomers ◽  
Low Entropy

Pyrolysis of aldoxime carbonates at relatively low temperatures (100–120 °C) produced nitriles in excellent yields. These decompositions followed first-order kinetics and the decomposition rates showed little dependence on inductive effects or solvent polarity. Low entropy values along with the fact that the E and Z-isomers behaved quite differently led to the proposal of a cyclic transition state for the decompositions.

Kinetic Studies of [4n+2]π-Thermal Cyclodimerization of 1-(3-Pyridazinyl)-3-oxidopyridinium Betaines

1992 ◽  
Vol 57 (9) ◽  
pp. 1951-1959 ◽  
Author(s):  
Madlene L. Iskander ◽  
Samia A. El-Abbady ◽  
Alyaa A. Shalaby ◽  
Ahmed H. Moustafa
Keyword(s):  
Energy Gap ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Cyclic Transition ◽  
Concerted Mechanism ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Cyclic Transition State ◽  
Complete Dissociation ◽  
Homo Lumo

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

scholarly journals Influence of Radiation Damage and Isochronal Annealing on the Magnetic Susceptibility of Pu1-xAmx Alloys

2008 ◽  
Vol 1104 ◽  
Author(s):  
Scott K McCall ◽  
Michael J Fluss ◽  
Brandon W. Chung ◽  
Richard G. Haire
Keyword(s):  
Magnetic Susceptibility ◽  
Radiation Damage ◽  
Low Temperatures ◽  
Metastable Phase ◽  
Magnetic Measurement ◽  
Isochronal Annealing ◽  
Magnetic Susceptibility Data ◽  
First Order ◽  
Susceptibility Data ◽  
First Order Kinetics

AbstractResults of radiation damage in Pu and Pu1-xAmx alloys studied with magnetic susceptibility, χ(T), and resistivity are presented. Damage accumulated at low temperatures increases χ(T) for all measured alloys, with the trend generally enhanced as the lattice expands. There is a trend towards saturation observable in the damage induced magnetic susceptibility data. that is not evident in similar damage induced resistivity data taken on the same specimen. A comparison of isochronal annealing curves measured by both resistivity and magnetic susceptibility on a 4.3at% Ga stabilized δ-Pu specimen show that Stage I annealing, where interstitials begin to move, is largely transparent to the magnetic measurement. This indicates that interstitials have little impact on the damage induced increase in the magnetic susceptibility. The isochronal annealing curves of the Pu1-xAmx alloys do not show distinct annealing stages as expected for alloys. However, samples near 20% Am concentration show an unexpected increase in magnetization beginning when specimens are annealed to 35K. This behavior is also reflected in a time dependent increase in the magnetic susceptibility of damaged specimens indicative of first order kinetics. These results suggest there may be a metastable phase induced by radiation damage and annealing in Pu1-xAmx alloys.

scholarly journals Reaction of caa3-type terminal cytochrome oxidase from the thermophilic bacterium PS3 with oxygen and carbon monoxide at low temperatures

1984 ◽  
Vol 221 (2) ◽  
pp. 529-533 ◽  
Author(s):  
N Sone ◽  
A Naqui ◽  
C Kumar ◽  
B Chance
Keyword(s):  
Activation Energy ◽  
Carbon Monoxide ◽  
Cytochrome Oxidase ◽  
Low Temperatures ◽  
Thermophilic Bacterium ◽  
Reduced Form ◽  
Compound A ◽  
First Order ◽  
First Order Kinetics ◽  
Higher Temperature

Reaction of O2 and CO with a caa3-type terminal cytochrome oxidase (EC 1.9.3.1) from the thermophilic bacterium PS3 grown with high aeration was studied at low temperatures. The CO recombination at the temperature range studied (−50 degrees C to −80 degrees C) followed first-order kinetics with an activation energy of 29.3 kJ/mol (7.0 kcal/mol). In the presence of O2 at −113 degrees C the photolysed reduced form binds O2 to form an ‘oxy’ intermediate similar to Compound A. At a higher temperature (-97 degrees C) another intermediate, similar to Compound B, is formed as a result of electron transfer from the enzyme to the liganded O2.

Mechanism of SNi reactions. The effect of the base strength of the anionic fragments

1978 ◽  
Vol 56 (19) ◽  
pp. 2582-2589 ◽  
Author(s):  
D. J. Verrinder ◽  
M. J. Hourigan ◽  
J. M. Prokipcak
Keyword(s):  
Thermal Decomposition ◽  
Optical Activity ◽  
Ion Pair ◽  
Decomposition Rates ◽  
First Order ◽  
First Order Kinetics ◽  
Cyclic Mechanism ◽  
Base Strength ◽  
Oxygen Bond ◽  
Anionic Fragment

The kinetics and stereochemical aspects of the thermal decomposition of aralkyl carbonates, thiocarbonates, and carbamates were examined. The rates for the decompositions as well as the rates of loss of optical activity followed first-order kinetics. The decompositions appear to involve the heterolysis of the aralkyl–oxygen bond followed by the breakdown of the subsequent ion pair via a cyclic mechanism. However, it was found that this ion pair could return to covalency without completely decomposing to products leading to the racemization of the starting materials. This type of racemization occurred more readily in the case of the carbamates than in the thiocarbonates and carbonates. The dependence of the decomposition rates and the loss of optical activity on the nature of the hetero atom of the anionic fragment of the starting material is discussed.

Mechanisms of SNi Reactions. The Kinetics of the Decomposition of Aralkyl Carbonates

1972 ◽  
Vol 50 (11) ◽  
pp. 1770-1774 ◽  
Author(s):  
J. M. Prokipcak ◽  
T. H. Breckles
Keyword(s):  
Structural Changes ◽  
Elevated Temperatures ◽  
Ion Pair ◽  
Decomposition Rates ◽  
First Order ◽  
First Order Kinetics ◽  
Cyclic Mechanism ◽  
Alkyl Chloroformates ◽  
Kinetics Of ◽  
Oxygen Bond

Anisylic phenyl carbonates decomposed at elevated temperatures to give CO2 and the corresponding anisylic phenyl esters. The decomposition follows first order kinetics very similar to those found for alkyl chloroformates. The decompositions involve the heterolysis of the aralkyl oxygen bond followed by the breakdown of the subsequent ion pair via a cyclic mechanism. The dependence of the decomposition rates on the nature of the solvent and structural changes of the starting carbonates is discussed.

scholarly journals Mechanism of the First Order Decay of 2-Hydroxy-propyl-2-peroxyl Radicals and of O2~ Formation in Aqueous Solution

1977 ◽  
Vol 32 (8) ◽  
pp. 886-889 ◽  
Author(s):  
Eberhard Bothe ◽  
Günther Behrens ◽  
Dietrich Schulte-Frohlinde
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Kinetic Isotope Effect ◽  
Peroxyl Radicals ◽  
Time Resolved ◽  
Cyclic Transition ◽  
Methyl Substitution ◽  
First Order ◽  
Kinetic Isotope ◽  
Cyclic Transition State

Using time resolved ESR spectroscopy and photoflash conductivity the uncatalysed, first order decay of 2-hydroxy-propyl-2-peroxyl radicals and the uncatalysed, first order generation of O2·̅ and H+ were measured to have the same rate constants. The formation of O2·̅ and H+ was measured in H2O and D2O and a kinetic isotope effect of kH/k =D3.5 was obtained. Comparing the rate constants of the peroxyl radicals derived from methanol, ethanol and 2-propanol it was shown that the rate constant increases with increasing methyl-substitution. In 2-propanol water mixtures the rate constant of the 2-hydroxy-propyl-2-peroxyl radical increases only slightly with increasing polarity of the solvent. The experimental results are in accord with a mechanism which involves a cyclic transition state leading to a concerted elimination of HO2· followed by dissociation into H+ and O2·̅.

Kinetics and mechanism of the thermal decomposition of N-nitrosodiphenylmethylimine

1981 ◽  
Vol 59 (3) ◽  
pp. 559-562 ◽  
Author(s):  
Michael T.H. Liu ◽  
Toshikazu Ibata
Keyword(s):  
Thermal Decomposition ◽  
Transition State ◽  
Experimental Evidence ◽  
Kinetics And Mechanism ◽  
Ring Closure ◽  
Decomposition Products ◽  
Cyclic Transition ◽  
First Order ◽  
Closure Mechanism ◽  
Cyclic Transition State

The thermal decomposition of N-nitrosodiphenylmethylimine has been investigated in various solvents. The decomposition products are benzophenone and nitrogen. The ΔH†and ΔS† parameters for these first-order decompositions have been determined. The experimental evidence is consistent with the hypothesis that the thermolysis of N-nitrosodiphenylmethylimine involves the formation of a cyclic transition state via an electrocyclic ring closure mechanism.

Photo-catalytic degradation of gaseous pollutants in paper mills of southern China

TAPPI Journal ◽  
2018 ◽  
Vol 17 (03) ◽  
pp. 167-178 ◽  
Author(s):  
Xin Tong ◽  
Jiao Li ◽  
Jun Ma ◽  
Xiaoquan Chen ◽  
Wenhao Shen
Keyword(s):  
Degradation Rate ◽  
Southern China ◽  
Catalytic Degradation ◽  
Pulp And Paper ◽  
Gaseous Pollutants ◽  
Pulp And Paper Mills ◽  
Paper Mills ◽  
Initial Concentration ◽  
First Order ◽  
First Order Kinetics

Studies were undertaken to evaluate gaseous pollutants in workplace air within pulp and paper mills and to consider the effectiveness of photo-catalytic treatment of this air. Ambient air at 30 sampling sites in five pulp and paper mills of southern China were sampled and analyzed. The results revealed that formaldehyde and various benzene-based molecules were the main gaseous pollutants at these five mills. A photo-catalytic reactor system with titanium dioxide (TiO2) was developed and evaluated for degradation of formaldehyde, benzene and their mixtures. The experimental results demonstrated that both formaldehyde and benzene in their pure forms could be completely photo-catalytic degraded, though the degradation of benzene was much more difficult than that for formaldehyde. Study of the photo-catalytic degradation kinetics revealed that the degradation rate of formaldehyde increased with initial concentration fitting a first-order kinetics reaction. In contrast, the degradation rate of benzene had no relationship with initial concentration and degradation did not conform to first-order kinetics. The photo-catalytic degradation of formaldehyde-benzene mixtures indicated that formaldehyde behaved differently than when treated in its pure form. The degradation time was two times longer and the kinetics did not reflect a first-order reaction. The degradation of benzene was similar in both pure form and when mixed with formaldehyde.

Kinetic of oxidation of methyl orange by vanadium(V) under conditions VO2+ and decavanadates coexist: Catalysis by Triton X-100 micellar medium

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Methyl Orange ◽  
Solution Ph ◽  
Vanadium Concentration ◽  
Limiting Behavior ◽  
First Order ◽  
First Order Kinetics ◽  
Ph Range ◽  
Kinetic Pattern ◽  
Triton X ◽  
Kinetics Of

The kinetics of oxidation of methyl orange by vanadium(V) {V(V)} has been investigated in the pH range 2.3-3.79. In this pH range V(V) exists both in the form of decavanadates and VO2+. The kinetic results are distinctly different from the results obtained for the same reaction in highly acidic solution (pH < 1) where V(V) exists only in the form of VO2+. The reaction obeys first order kinetics with respect to methyl orange but the rate has very little dependence on total vanadium concentration. The reaction is accelerated by H+ ion but the dependence of rate on [H+] is less than that corresponding to first order dependence. The equilibrium between decavanadates and VO2+ explains the different kinetic pattern observed in this pH range. The reaction is markedly accelerated by Triton X-100 micelles. The rate-[surfactant] profile shows a limiting behavior indicative of a unimolecular pathway in the micellar pseudophase.

Biodegradation rates of aromatic contaminants in biofilm reactors

1995 ◽  
Vol 31 (1) ◽  
pp. 117-128 ◽  
Author(s):  
Jean-Pierre Arcangeli ◽  
Erik Arvin
Keyword(s):  
Aromatic Hydrocarbons ◽  
Competitive Inhibition ◽  
Removal Rate ◽  
First Order ◽  
Biofilm Reactors ◽  
First Order Kinetics ◽  
Reducing Conditions ◽  
Low Concentrations ◽  
Degradation Rates ◽  
Order Surface

This study has shown that microorganisms can adapt to degrade mixtures of aromatic pollutants at relatively high rates in the μg/l concentration range. The biodegradation rates of the following compounds were investigated in biofilm systems: aromatic hydrocarbons, phenol, methylphenols, chlorophenols, nitrophenol, chlorobenzenes and aromatic nitrogen-, sulphur- or oxygen-containing heterocyclic compounds (NSO-compounds). Furthermore, a comparison with degradation rates observed for easily degradable organics is also presented. At concentrations below 20-100 μg/l the degradation of the aromatic compounds was typically controlled by first order kinetics. The first-order surface removal rate constants were surprisingly similar, ranging from 2 to 4 m/d. It appears that NSO-compounds inhibit the degradation of aromatic hydrocarbons, even at very low concentrations of NSO-compounds. Under nitrate-reducing conditions, toluene was easily biodegraded. The xylenes and ethylbenzene were degraded cometabolically if toluene was used as a primary carbon source; their removal was influenced by competitive inhibition with toluene. These interaction phenomena are discussed in this paper and a kinetic model taking into account cometabolism and competitive inhibition is proposed.

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