Radical chain reductive dehalogenation of hetaryl halides promoted by methoxide ion

1975 ◽  
Vol 97 (20) ◽  
pp. 5889-5896 ◽  
Author(s):  
John A. Zoltewicz ◽  
Terence M. Oestreich ◽  
Alan A. Sale
Keyword(s):  
Reductive Dehalogenation ◽  
Radical Chain ◽  
Methoxide Ion

ChemInform Abstract: RADICAL CHAIN REDUCTIVE DEHALOGENATION OF HETARYL HALIDES PROMOTED BY METHOXIDE ION

1975 ◽  
Vol 6 (50) ◽  
pp. no-no
Author(s):  
JOHN A. ZOLTEWICZ ◽  
TERENCE M. OESTREICH ◽  
ALAN A. SALE
Keyword(s):  
Reductive Dehalogenation ◽  
Radical Chain ◽  
Methoxide Ion

Sulfamides Direct Radical-Mediated Chlorination of Aliphatic C–H Bonds

2019 ◽  
Author(s):  
Melanie Short ◽  
Mina Shehata ◽  
Matthew Sanders ◽  
Jennifer Roizen
Keyword(s):  
Hydrogen Atom ◽  
Transfer Reaction ◽  
Hydrogen Atom Transfer ◽  
Chain Propagation ◽  
Propagation Mechanism ◽  
Atom Transfer ◽  
Radical Chain ◽  
Radical Intermediates ◽  
Transfer Processes ◽  
Unusual Position

Sulfamides guide intermolecular chlorine transfer to gamma-C(sp<sup>3</sup>) centers. This unusual position-selectivity arises because accessed sulfamidyl radical intermediates engage in otherwise rare 1,6-hydrogen-atom transfer processes. The disclosed chlorine-transfer reaction relies on a light-initiated radical chain-propagation mechanism to oxidize C(sp<sup>3</sup>)-H bonds.

Sulfamides Direct Radical-Mediated Chlorination of Aliphatic C–H Bonds

2019 ◽  
Author(s):  
Melanie Short ◽  
Mina Shehata ◽  
Matthew Sanders ◽  
Jennifer Roizen
Keyword(s):  
Hydrogen Atom ◽  
Transfer Reaction ◽  
Hydrogen Atom Transfer ◽  
Chain Propagation ◽  
Propagation Mechanism ◽  
Atom Transfer ◽  
Radical Chain ◽  
Radical Intermediates ◽  
Transfer Processes ◽  
Unusual Position

Sulfamides guide intermolecular chlorine transfer to gamma-C(sp<sup>3</sup>) centers. This unusual position-selectivity arises because accessed sulfamidyl radical intermediates engage in otherwise rare 1,6-hydrogen-atom transfer processes. The disclosed chlorine-transfer reaction relies on a light-initiated radical chain-propagation mechanism to oxidize C(sp<sup>3</sup>)-H bonds.

Catalyst- and Silane- Controlled Enantioselective Hydrofunctionalization of Alkenes by Cobalt-Catalyzed Hydrogen Atom Transfer and Radical-Polar Crossover

2020 ◽  
Author(s):  
Kousuke Ebisawa ◽  
Kana Izumi ◽  
Yuka Ooka ◽  
Hiroaki Kato ◽  
Sayori Kanazawa ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Absolute Configuration ◽  
Kinetic Resolution ◽  
Hydrogen Atom Transfer ◽  
Biologically Active ◽  
Atom Transfer ◽  
High Concentration ◽  
Chain Reaction ◽  
Radical Chain ◽  
Radical Chain Reaction

Catalytic enantioselective synthesis of tetrahydrofurans, which are found in the structures of many biologically active natural products, via a transition-metal catalyzed-hydrogen atom transfer (TM-HAT) and radical-polar crossover (RPC) mechanism is described herein. Hydroalkoxylation of non-conjugated alkenes proceeded efficiently with excellent enantioselectivity (up to 94% ee) using a suitable chiral cobalt catalyst, <i>N</i>-fluoro-2,4,6-collidinium tetrafluoroborate, and diethylsilane. Surprisingly, absolute configuration of the product was highly dependent on the steric hindrance of the silane. Slow addition of the silane, the dioxygen effect in the solvent, thermal dependency, and DFT calculation results supported the unprecedented scenario of two competing selective mechanisms. For the less-hindered diethylsilane, a high concentration of diffused carbon-centered radicals invoked diastereoenrichment of an alkylcobalt(III) intermediate by a radical chain reaction, which eventually determined the absolute configuration of the product. On the other hand, a more hindered silane resulted in less opportunity for radical chain reaction, instead facilitating enantioselective kinetic resolution during the late-stage nucleophilic displacement of the alkylcobalt(IV) intermediate.

Reductive Dehalogenation of Environmental Contaminants: A Critical Review

1989 ◽  
Vol 24 (2) ◽  
pp. 299-322 ◽  
Author(s):  
R. M. Baxter
Keyword(s):  
Hydrogen Atom ◽  
Aromatic Compounds ◽  
Reductive Dechlorination ◽  
Halogen Atom ◽  
Environmental Contaminants ◽  
Methanogenic Bacteria ◽  
Photochemical Reactions ◽  
Reductive Dehalogenation ◽  
Iron Porphyrins ◽  
Aliphatic Compounds

Abstract It is generally recognized that reductive processes are more important than oxidative ones in transforming, degrading and mineralizing many environmental contaminants. One process of particular importance is reductive dehalogenation, i.e., the replacement of a halogen atom (most commonly a chlorine atom) by a hydrogen atom. A number of different mechanisms are involved in these reactions. Photochemical reactions probably play a role in some instances. Aliphatic compounds such as chloroethanes, partly aliphatic compounds such as DDT, and alicyclic compounds such as hexachlorocyclohexane are readily dechlorinated in the laboratory by reaction with reduced iron porphyrins such as hematin. Many of these are also dechlorinated by cultures of certain microorganisms, probably by the same mechanism. Such compounds, with a few exceptions, have been found to undergo reductive dechlorination in the environment. Aromatic compounds such as halobenzenes, halophenols and halobenzoic acids appear not to react with reduced iron porphyrins. Some of these however undergo reductive dechlorination both in the environment and in the laboratory. The reaction is generally associated with methanogenic bacteria. There is evidence for the existence of a number of different dechlorinating enzymes specific for different isomers. Recently it has been found that many components of polychlorinated biphenyls (PCBs), long considered to be virtually totally resistant to environmental degradation, may be reductively dechlorinated both in the laboratory and in nature. These findings suggest that many environmental contaminants may prove to be less persistent than was previously feared.

Biotreatability test of bleach wastewaters from pulp and paper mills

1997 ◽  
Vol 35 (2-3) ◽  
pp. 101-108
Author(s):  
X. Wang ◽  
T. H. Mize ◽  
F. M. Saunders ◽  
S. A. Baker
Keyword(s):  
Wastewater Treatment ◽  
Pulp And Paper ◽  
Reductive Dehalogenation ◽  
Continuous Reactor ◽  
Batch Reactors ◽  
Aerobic Treatment ◽  
Pulp And Paper Mills ◽  
Paper Mills ◽  
Degradation Rates ◽  
Adsorbable Organic Halide

Research is focused on an integrated way to simultaneously optimize the bleaching operations and subsequent wastewater treatment for pulp and paper mills. Bleach wastewaters from ClO2-bleached pulping studies at Institute of Paper Science and Technology (IPST) were used as the feed for batch reactors to test and rank the treatability and kinetics. The key aspect of the system is the use of sequential anaerobic/aerobic phases to enhance reductive dehalogenation of chloro-organic materials. Two continuous reactor systems, one operated in an anaerobic-aerobic mode and a second in an aerobic-aerobic mode, received bleaching wastewater obtained from a full-scale plant. Acclimated cultures from both continuous reactors were used to quantify the AOX (Adsorbable Organic Halide) and COD removal from various bleaching wastewaters. In general, the sequential anaerobic/aerobic treatment of bleach wastewater can improve both biotreatability and degradation rates.

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