A kinetic study of the reaction of adamantanethione with 2-adamantanethiol

1976 ◽  
Vol 54 (21) ◽  
pp. 3407-3411 ◽  
Author(s):  
J. C. Scaiano ◽  
J. P.-A. Tremblay ◽  
K. U. Ingold
Keyword(s):  
Benzene Solution ◽  
Hydrogen Abstraction ◽  
Chain Process ◽  
Radical Chain ◽  
Diffusion Controlled ◽  
Carbon Centered Radical ◽  
Photochemical Initiation ◽  
Kinetics Of ◽  
Radical Chain Process ◽  
Termination Process

The title reaction is a free radical chain process which yields di(2-adamantyl)disulfide(2). The kinetics of this reaction have been studied in benzene solution at 50 °C using both thermal and photochemical initiation. Thermal initiators which yield resonance stabilized carbon-centered radicals were surprisingly inefficient at starting the reaction. The kinetics indicate that the rate controlling propagation step is hydrogen abstraction from the thiol, AdHSH, by the carbon-centered radical, AdHSSAd•. Rotating sector studies gave a rate constant for this step, k2 = 4 × 104 M−1 s−1. There is some kinetically first order chain termination, but the predominant termination process involves the diffusion-controlled bimolecular self-reactions of AdHSSAd• radicals, 2kt = 1.8 × 1010 M−1 s−1.

Forskolin Editing via Radical Iodo- and Hydroalkylation

Synthesis ◽  
2021 ◽  
Author(s):  
Elena Pruteanu ◽  
Nicholas D. C. Tappin ◽  
Veaceslav Kulciţki ◽  
Philippe Renaud ◽  
Vladilena Gîrbu ◽  
...  
Keyword(s):  
Iodine Atom ◽  
Cyclic Ether ◽  
Radical Addition ◽  
Chain Process ◽  
Radical Chain ◽  
Radical Process ◽  
Atom Transfer Radical Addition ◽  
Carbon Centered Radical ◽  
Radical Chain Process

AbstractThe modification of highly oxygenated forskolin as well as manoyl and epi-manoyl oxide, two less functionalized model substrates sharing the same polycyclic skeleton, via intermolecular carbon-centered radical addition to the vinyl moiety has been investigated. Highly regio- and reasonably stereoselective iodine atom transfer radical addition (ATRA) reactions were developed. Unprotected forskolin afforded an unexpected cyclic ether derivative. Protection of the 1,3-diol as an acetonide led the formation of the iodine ATRA product. Interestingly, by changing the mode of initiation of the radical process, in situ protection of the forskolin 1,3-diol moiety as a cyclic boronic ester took place during the iodine ATRA process without disruption of the radical chain process. This very mild radical-mediated in situ protection of 1,3-diol is expected to be of interest for a broad range of radical and non-radical transformations. Finally, by using our recently developed tert-butyl­catechol-mediated hydroalkylation procedure, highly efficient preparation of forskolin derivatives bearing an extra ester or sulfone group was achieved.

The pyrolytic reactions of acetaldehyde in presence of nitric oxide

1958 ◽  
Vol 245 (1243) ◽  
pp. 456-469 ◽  
Keyword(s):  
Nitric Oxide ◽  
Hydrogen Abstraction ◽  
Chain Process ◽  
Molecular Rearrangement ◽  
Radical Chain ◽  
Low Concentrations ◽  
Rearrangement Mechanism ◽  
A Chain ◽  
Induced Decomposition ◽  
Radical Chain Process

Except at very low concentrations where a slight inhibition is observable nitric oxide strongly catalyses the decomposition of acetaldehyde. The rate of the induced reaction is approximately proportional to [aldehyde] 3/2 [NO] ½ . The ratio of nitric oxide consumed to aldehyde decomposed remains small even in conditions where the corresponding ratio for the nitric-oxide-induced ether decomposition approaches unity. The induced decomposition is reduced in rate to a limit by the addition of propylene. From kinetic and analytical measurements it is concluded that the thermal acetaldehyde decomposition occurs partly by a molecular rearrangement mechanism and partly by a radical chain process. The catalysis by nitric oxide involves a chain reaction initiated by hydrogen abstraction, and probably also an acceleration of the molecular process under the influence of collisions with the nitric oxide. The steps of the nitric-oxide-induced chain process are discussed.

Free Radical Bromination of Saturated Hydrocarbons using Bromine and Mercuric Oxide

1972 ◽  
Vol 50 (19) ◽  
pp. 3109-3116 ◽  
Author(s):  
N. J. Bunce
Keyword(s):  
Free Radical ◽  
Hydrogen Abstraction ◽  
Chain Process ◽  
Mercuric Oxide ◽  
Saturated Hydrocarbons ◽  
Radical Chain ◽  
Radical Bromination ◽  
Mercury Oxide ◽  
Alkyl Bromides ◽  
Radical Chain Process

The reaction of alkanes with a mixture of bromine and mercuric oxide gives alkyl bromides in preparatively useful yields. The reagent is significantly more reactive than elemental bromine, and it is believed that bromine monoxide, formed insitu by the interaction of bromine and mercury oxide, is the reactive intermediate. Bromination by bromine monoxide is a free radical chain process in which hydrogen abstraction is carried out predominantly by bromoxy (BrO•) radicals, and to a lesser extent by bromine atoms.

Sign in / Sign up

Export Citation Format

Share Document