Kinetics and thermochemistry of the acetyl radical: study of the acetyl + hydrogen bromide .fwdarw. acetaldehyde + bromine atom reaction

1992 ◽  
Vol 96 (14) ◽  
pp. 5881-5886 ◽  
Author(s):  
Jukka T. Niiranen ◽  
David Gutman ◽  
L. N. Krasnoperov
Keyword(s):  
Hydrogen Bromide ◽  
Bromine Atom ◽  
Acetyl Radical

The relative rates of bromination of cyclohexane and cyclopentane with molecular bromine. Comparison of the reactions in solution and in vapor phase

1981 ◽  
Vol 59 (9) ◽  
pp. 1368-1374 ◽  
Author(s):  
Dennis D. Tanner ◽  
Tomoki C-S. Ruo ◽  
Hideki Takiguchi ◽  
Andre Guillaume
Keyword(s):  
Vapor Phase ◽  
Hydrogen Bromide ◽  
Bromine Atom ◽  
Relative Rate ◽  
Solution Phase ◽  
Molecular Bromine ◽  
Transfer Rates ◽  
Relative Rate Constants ◽  
Halogenated Alkanes ◽  
Relative Transfer

The relative rates of transfer of the cyclopentyl radical with molecular bromine and hydrogen bromide (k2′/k−1′) and with hydrogen tribromide and hydrogen bromide (k3′/k−1′) have been determined. The relative transfer rates are compared with the analogous values previously reported for the reactions of cyclohexyl radicals (k2/k−1 and k3/k−1). Utilizing the values of k2′/k−1 and k2/k−1 the competitive vapor phase rates of bromine atom abstraction of hydrogen from the two substrates could be obtained. An expression using a combination of the five sets of relative rate constants was used to determine the effect of competitive cage reversal which occurs in the solution phase bromination of the two substrate radicals with caged hydrogen bromide. For two structurally similar radicals, cage reversal (internal return) was found to affect the relative rates of bromination by 30%, while the relative transfer rates, although differing each by a factor of two, fortuitously nearly cancel each other's effect.The effect of both internal and external reversal reactions on the relative rates of bromination of structurally dissimilar substrates, halogenated alkanes and their parent hydrocarbons, is discussed.

The thermal decomposition of n-propyl bromide

1968 ◽  
Vol 21 (4) ◽  
pp. 973 ◽  
Author(s):  
JTD Cross ◽  
VR Stimson
Keyword(s):  
Thermal Decomposition ◽  
Rate Constant ◽  
Hydrogen Bromide ◽  
Bromine Atom ◽  
Order Reaction ◽  
Chain Mechanism ◽  
Initial Concentration ◽  
First Order ◽  
Reaction Proceeds ◽  
Atom Chain

Mechanisms already proposed or formally possible for the decomposition of n-propyl bromide as a 312-order reaction are shown to be unsatisfactory, and the reaction has been reinvestigated. Two reactions occur simultaneously: (a) a first-order reaction identifiable with the maximally inhibited reaction and presumably molecular; (b) a reaction second order in the initial concentration and somewhat autocatalysed as the reaction proceeds. The rate constant is given by k2 == 1018.1exp(-49300/RT)sec-1ml mole-1 Reaction (b) is catalysed by hydrogen bromide and inhibited by propene, and a bromine atom chain mechanism with hydrogen bromide catalysed initiation is proposed. Bromine-catalysed decomposition has also been studied. The mechanism of the inhibition is discussed.

The gas-phase decomposition of ethyl bromide

1971 ◽  
Vol 24 (10) ◽  
pp. 2031
Author(s):  
DA Kairaitis ◽  
VR Stimson
Keyword(s):  
Gas Phase ◽  
Initial Rate ◽  
Hydrogen Bromide ◽  
Bromine Atom ◽  
Ethyl Bromide ◽  
Phase Decomposition ◽  
Unimolecular Decomposition ◽  
Chain Reaction ◽  
Insight Into

The gas-phase decomposition of ethyl bromide at 423� in the presence of both ethylene and hydrogen bromide has been investigated. These additives, which are also the products, each influence the rate strongly but in opposite ways. The variation of initial rate with reactant pressure is given by (P in cm) ������������� k1 (min-1) = 15.2x10-3+19.5x10-3(PEtBrPHBr/PEne)1/2 This has been interpreted in terms of a unimolecular decomposition together with a bromine atom carried chain reaction with simple steps that involve the products. Some insight into the unaccompanied decomposition has been gained. Some remarks about the role of olefinic inhibitors in reactions producing hydrogen bromide have been made.

Metabolic Activation of Xenobiotics: Ethylene Dibromide and Structural Analogs

1983 ◽  
Vol 2 (3) ◽  
pp. 73-83 ◽  
Author(s):  
Peter J. van Bladeren
Keyword(s):  
Sulfur Mustard ◽  
Hydrogen Bromide ◽  
Bromine Atom ◽  
Parent Compound ◽  
Reactive Intermediates ◽  
The Body ◽  
Decisive Factor ◽  
Carcinogenic Effect ◽  
Enzyme Systems

A large number of compounds which can enter living organisms are relatively harmless as such, but are transformed by the body into reactive agents. The structure of such a compound is the factor determining its disposition in the organism. Its physicochemical characteristics determine the overall fate in terms of absorption, distribution and excretion, while the chemical structure is the decisive factor in its biotransformation. Whether formation of reactive intermediates occurs depends on what points of attack it has to offer to the different enzyme systems. The extent to which alkylation of cellular macromolecules by reactive intermediates occurs in turn depends on the balance of activating and detoxifying enzymes in the particular cell and on the reactivity of the intermediates towards critical targets in the cell macro-molecules. Many chemicals undergo several concurrent metabolic pathways. The ratio between these pathways may be a decisive factor determining the extent of adverse effects caused by these chemicals. Small variations in structure may have a drastic effect on the activation and detoxification by competing enzyme systems. These concepts are elucidated using the examples of ethy-lene dibromide and some structural analogs. Apart from the parent compound itself, two alkylating species may be responsible for the toxic effects of these compounds. Bromo-acetaldehyde is formed by oxidation, catalyzed by cyto-chrome P-450, followed by spontaneous loss of hydrogen bromide; S-2-bromoethylglutathione results from replacement of a bromine atom by glutathione, catalyzed by the glutathione transferases. The latter intermediate possesses a reactivity comparable to sulfur mustard. Results indicate that the reactive glutathione conjugate is responsible for the mutagenic and possibly also the carcinogenic effect of ethy-lene dibromide. However, in vivo, oxidation is quantitatively much more important as a primary process.

Free radical hydrobromination of propargyl bromide and bromoallene

1969 ◽  
Vol 47 (17) ◽  
pp. 3153-3165 ◽  
Author(s):  
Karl R. Kopecky ◽  
Shima Grover
Keyword(s):  
Free Radical ◽  
Kinetic Study ◽  
Addition Reaction ◽  
Hydrogen Bromide ◽  
Bromine Atom ◽  
Liquid Hydrogen ◽  
Major Product ◽  
Propargyl Bromide ◽  
Solvent Cage ◽  
Ether Solution

Rearrangement is observed in the free-radical hydrobromination of propargyl bromide. Between −20 and +30 °C in n-pentane or ether solution, 1,2-dibromopropene is the major product. A detailed stereochemical and kinetic study of the reaction indicates that the 1,2-dibromopropene is formed via bromoallene which results from the loss of a bromine atom from the first formed 1,3-dibromo-2-propenyl radical. Only 1/3 to 1/2 of the bromoallene diffuses away from its bromine atom partner. The remainder of the bromoallene recombines within the solvent cage with its bromine atom partner at a rate which is competitive with its rate of rotation with respect to the bromine atom. When the free radical hydrobromination of propargyl bromide is carried out at −78° in liquid hydrogen bromide, the 1,3-dibromo-2-propenyl radical can be trapped to a large extent by the hydrogen bromide to form cis-1,3-dibromopropene. The stereochemistry of this addition reaction >99% trans. A small amount of 1,2-dibromopropene which is 77% trans is also formed. Under the same conditions a 3:1 mixture of 1,2- and 1,3-dibromopropenes is produced from bromoallene. The 1,3-dibromopropene produced from bromoallene is >95% cis, while the 1,2-dibromopropene consists of a 49:51 cis:trans mixture of isomers.

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