Kinetics and mechanism of dealkylation of coordinated isocyanide in Fe(PMe3)2(t-BuNC)3

2005 ◽  
Vol 83 (6-7) ◽  
pp. 626-633 ◽  
Author(s):  
Christine L Tennent ◽  
William D Jones
Keyword(s):  
Hydrogen Atom ◽  
Iron Complex ◽  
Kinetics And Mechanism ◽  
Zerovalent Iron ◽  
Mechanistic Studies ◽  
First Order ◽  
Tert Butyl ◽  
Preferential Formation ◽  
First Order Kinetics ◽  
Thermal Cleavage

The zerovalent iron complex Fe(PMe3)2(t-BuNC)3 undergoes thermal cleavage of the C—N bond to give Fe(PMe3)2(t-BuNC)2(H)(CN) and isobutylene. The reaction follows first order kinetics, and addition of the hydrogen-atom donor 1,4-cyclohexadiene leads to the preferential formation of isobutane rather than isobutylene. Mechanistic studies are consistent with a rate determining homolysis of the C—N bond, giving rise to tert-butyl radicals.Key words: iron, isocyanide, elimination, C—N cleavage.

Cytochrome P-450 mediated biotransformation of organic nitrates

1990 ◽  
Vol 68 (12) ◽  
pp. 1552-1557 ◽  
Author(s):  
Bernard J. McDonald ◽  
Brian M. Bennett
Keyword(s):  
Glyceryl Trinitrate ◽  
Microsomal Fraction ◽  
Direct Interaction ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Aerobic Conditions ◽  
First Order ◽  
Preferential Formation ◽  
First Order Kinetics ◽  
Cytochrome P 450

The vascular biotransformation of organic nitrates appears to be a prerequisite for their action as vasodilators. In the current study, we assessed the involvement of cytochrome P-450 in the denitration of glyceryl trinitrate and the enantiomers of isoidide dinitrate. Denitration of organic nitrates by the microsomal fraction of rat liver was NADPH dependent and followed apparent first-order kinetics. Under aerobic conditions, the t1/2 of D-isoidide dinitrate was significantly shorter than that of L-isoidide dinitrate (11.9 vs. 14.1 min, p ≤ 0.05), which is consistent with the greater potency of the D-enantiomer for vasodilation. Under anaerobic conditions, the denitration of glyceryl trinitrate was very rapid (t1/2 approximately 30 s). Organic nitrate biotransformation was inhibited by carbon monoxide, SKF 525A, and dioxygen. This suggests that the biotransformation of organic nitrates can occur through the direct interaction with the heme moiety of cytochrome P-450. The biotransformation of glyceryl trinitrate was catalyzed preferentially by those isoenzymes induced by phenobarbital. The biotransformation of glyceryl trinitrate was regioselective for 1,3-glyceryl dinitrate formation except in phenobarbital-induced microsomes under aerobic conditions, in which preferential formation of 1,2-glyceryl dinitrate occurred. These data suggest that cytochrome P-450 is involved in the biotransformation of organic nitrates and raises the possibility that vascular cytochrome P-450 may play a role in the mechanism-based biotransformation of organic nitrates, the result of which is vascular smooth muscle relaxation.Key words: cytochrome P-450, glyceryl trinitrate, isoidide dinitrate, biotransformation, liver.

Di-tert-butyl peroxide decomposition behind shock waves

1976 ◽  
Vol 54 (4) ◽  
pp. 581-585 ◽  
Author(s):  
David K. Lewis
Keyword(s):  
Thermal Decomposition ◽  
Gas Phase ◽  
Single Pulse ◽  
First Order ◽  
Tert Butyl ◽  
First Order Kinetics ◽  
Peroxide Decomposition ◽  
Butyl Peroxide ◽  
Temperature Work ◽  
Lower Temperature

The homogeneous, gas phase thermal decomposition of di-tert-butyl peroxide has been studied in a single pulse shock tube. Samples containing 0.05% to 0.5% reactant in argon were heated to 528–677 K at total pressures of about 1 atm. Acetone and ethane were the only significant products. The reaction obeyed first order kinetics. The Arrhenius parameters, log A (s−1) = 15.33 ± 0.50, Eact (kJ/mol) = 152.3 ± 5.8, are in agreement with the bulk of the earlier reported results of lower temperature work, and with a recently reported result obtained via the very low pressure pyrolysis technique. Indications from some of the earlier work that the A factor may decline at high temperatures are not supported by the present study.

An Electron Spin Resonance Study of the Arylsilyl Adducts of Phenyl tert-Butyl Nitrone and Their Decomposition Kinetics

1974 ◽  
Vol 52 (16) ◽  
pp. 2901-2905 ◽  
Author(s):  
Babatunde B. Adeleke ◽  
Sau-King Wong ◽  
Jeffrey K. S. Wan
Keyword(s):  
Decomposition Kinetics ◽  
Electron Spin Resonance Study ◽  
Silyl Group ◽  
First Order ◽  
Tert Butyl ◽  
First Order Kinetics ◽  
Spin Resonance ◽  
Butyl Peroxide ◽  
The Stability ◽  
Spin Resonance Study

The formation and the stability of some arylsilyl adducts of phenyl tert-butyl nitrone were studied in a photochemical system using di-tert-butyl peroxide as solvent. The β-proton splittings of all the arylsilyl adducts, ranging from 5.6 to 8.3 G, are relatively larger than their carbon analogs, which are usually less than 4 G. The arylsilyl adducts are found to decompose in di-tert-butyl peroxide solvent by a first-order kinetics. The activation energy involved in the decomposition of a series of arylsilyl adducts varies from about 14 to about 9 kcal/mol, as the size of the silyl group increases. In all cases, very low values of the A factors (between 106 and 1010) were observed.

scholarly journals The kinetics and mechanism of the organo-iridium-catalysed enantioselective reduction of imines

2016 ◽  
Vol 14 (14) ◽  
pp. 3614-3622 ◽  
Author(s):  
Matthew J. Stirling ◽  
Gemma Sweeney ◽  
Kerry MacRory ◽  
A. John Blacker ◽  
Michael I. Page
Keyword(s):  
Enantiomeric Excess ◽  
Zero Order ◽  
Kinetics And Mechanism ◽  
First Order ◽  
Enantioselective Reduction ◽  
First Order Kinetics

The enantiomeric excess (ee) for the organo-iridium catalysed reduction of imines decreases during the reaction because the rate of formation of the (R)-product amine follows first-order kinetics whereas that for the (S)-enantiomer is zero-order.

Kinetics and mechanism of substitution reactions of (N,N-dimethylformamide)pentaammine–cobalt(III) and –rhodium(III) ions in DMF as solvent

1978 ◽  
Vol 56 (20) ◽  
pp. 2609-2615 ◽  
Author(s):  
S. T. Danny Lo ◽  
Margaret J. Sisley ◽  
Thomas W. Swaddle
Keyword(s):  
Exchange Rate ◽  
Rate Coefficient ◽  
Kinetics And Mechanism ◽  
Rate Data ◽  
Substitution Reactions ◽  
First Order ◽  
Order Rate ◽  
First Order Kinetics ◽  
Simple Substitution ◽  
Pseudo First Order

The exchange of N,N-dimethylformamide (DMF) between M(NH3)5DMF3+ and solvent in acidic DMF solutions proceeds with pseudo-first-order kinetics governed by the parameters kex(55 °C) = 8 × 10−5 and 1.1 × 10−4 s−1, ΔHex* = 113 and 99 kJ mol−1, ΔSex* = +22 and −20 J K−1 mol−1, and ΔVex* = +3.2 and −1.4 cm3 mol−1 for M = Co and Rh respectively. For M = Co (but not Rh), the exchange rate was much faster in the absence of acid, and reduction of Co(III) to Co(II) was significant at low acidities. Solubility problems precluded the measurement of meaningful rate data for the reactions of M(NH3)5DMF3+ with nucleophiles X− in acidic DMF solution except for the case M = Co with X = Br−, for which a limiting first-order rate coefficient 2.5 times kex was obtained for the formation of Co(NH3)5Br2+ at high [Br−] at 55 °C. Despite this last result, the mechanism of simple substitution reactions is evidently dissociative interchange (Id) for pentaamminecobalt(III) complexes in general, but associative interchange (Ia) for pentaamminerhodium(III) analogues.

Reversible pH-Induced Dissociation of Glucose Dehydrogenase from Bacillus megaterium II. Kinetics and Mechanism

1987 ◽  
Vol 42 (7-8) ◽  
pp. 907-915 ◽  
Author(s):  
Eberhard Maurer ◽  
Gerhard Pfleiderer
Keyword(s):  
Bacillus Megaterium ◽  
Specific Activity ◽  
Glucose Dehydrogenase ◽  
Kinetics And Mechanism ◽  
First Order ◽  
First Order Kinetics ◽  
Activity Measurements ◽  
Nacl Concentration ◽  
Reaction Orders ◽  
Association Equilibrium

Glucose dehydrogenase from Bacillus megaterium exists as a stable, active tetramer at pH 6.5. By shifting the pH to 9. the enzyme is. completely and reversibly, dissociated into four inactive protomers. Kinetics and mechanism of this pH-induced dissociation have been studied, at various enzyme concentrations, by ultraviolet absorption, circular dichroism, normal and stopped-flow fluorescence as well as by light scattering and activity measurements. Dissociation of the fully active tetramer proceeds via three distinct kinetic steps: (1) fast conformational rearrangement of the tetramer, without any loss of activity (t1/2 0.0075 sec); (2) slow isomerization to a tetramer with lower specific activity (t1/2 27 sec): (3) subsequent dissociation of this rearranged tetramer into inactive monomers (t1/2 114 sec) with still intact native secondary structure. All three processes follow first-order kinetics. Both rate and extent of the dissociation are reduced, with a concomitant shift to higher reaction orders, by increasing the NaCl concentration in the buffer. This suggests the establishment of a dissociation/association equilibrium, due to the concentration- dependent stabilization of the tetrameric enzyme state by NaCl.

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.

Recent advances in Minisci-type reactions and applications in organic synthesis

2020 ◽  
Vol 24 ◽  
Author(s):  
Wengui Wang ◽  
Shoufeng Wang
Keyword(s):  
Free Radical ◽  
Hydrogen Atom ◽  
Organic Synthesis ◽  
Radical Reactivity ◽  
Atom Loss ◽  
Radical Generation ◽  
In Situ Generation ◽  
Thermal Cleavage ◽  
Synthetic Chemist

Abstract:: Minisci-type reactions have become widely known as reactions that involve the addition of carbon-centered radicals to basic heteroarenes followed by formal hydrogen atom loss. While the originally developed protocols for radical generation remain in active use today, in recent years by a new array of radical generation strategies allow use of a wider variety of radical precursors that often operate under milder and more benign conditions. New transformations based on free radical reactivity are now available to a synthetic chemist looking to utilize a Minisci-type reaction. Radical-generation methods based on photoredox catalysis and electrochemistry, which utilize thermal cleavage or the in situ generation of reactive radical precursors, have become popular approaches. Our review will cover the remarkably literature that has appeared on this topic in recent 5 years, from 2015-01 to 2020-01, in an attempt to provide guidance to the synthetic chemist, on both the challenges that have been overcome and applications in organic synthesis.

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