- Aromatic substitution in ball mills: Formation of aryl chlorides and bromides using potassium peroxomonosulfate and NaX
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Aryl chlorides and bromides are formed from arenes in a ball mill using KHSO5 and NaX (X = Cl, Br) as oxidant and halogen source, respectively. Investigation of the reaction parameters identified operating frequency, milling time, and the number of milling balls as the main influencing variables, as these determine the amount of energy provided to the reaction system. Assessment of liquid-assisted grinding conditions revealed, that the addition of solvents has no advantageous effect in this special case. Preferably activated arenes are halogenated, whereby bromination afforded higher product yields than chlorination. Most often reactions are regio- and chemoselective, since p-substitution was preferred and concurring side-chain oxidation of alkylated arenes by KHSO5 was not observed. The Royal Society of Chemistry.
- Schmidt, Robert,Stolle, Achim,Ondruschka, Bernd
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p. 1673 - 1679
(2013/02/22)
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- Regio- and Stereochemistry of Bromochlorinations of Alkynes with molecular Bromine Chloride and Dichlorobromate(1-) Ion
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The bromochlorination of phenyl- and alkyl-substituted acetylenes with tetrabutylammonium dichlorobromate(1-) (1) in dichloromethane was found to be anti-stereospecific and nonregiospecific (regiospecific in the case of phenylacetylene).Whereas the addition of molecular bromine chloride (2) to phenyl-substituted acetylenes was found to give nonstereospecific and regiospecific adducts, the reaction of alkyl-substituted acetylenes gave anti-stereospecific and nonregiospecific adducts.These results suggest that the addition of 1 involves an attack of chloride ion to a three-centered ?-complex in the product-forming stage, and that the addition of 2 to phenyl-substituted acetylenes involves a vinyl cation intermediate (but a bridged bromonium ion intermediate in the case of alkyl-substituted acetylenes).
- Negoro, Takeshi,Ikeda, Yoshitsugu
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p. 3515 - 3518
(2007/10/02)
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- Reaction of Phosphorus Pentachloride with 2-Acetylthiophene and Acetophenone
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The treatment of 2-acetylthiophene with PCl5, followed by dehydrochlorination, is known to be a poor method for synthesizing 2-ethynylthiophene (1a).Reinvestigation of the reaction showed the major products to be the E- and Z- isomers of 1,2-dichloro-1-(2-thienyl)ethylene (7a), with minor amounts of 1,1-dichloro-1-(2-thienyl)ethane (3a), 1-chloro-1-(2-thienyl)ethylene (4a), 2-(chloroacetyl)thiophene, and 2-(dichloroacetyl)thiophene.The treatment of acetophenone with PCl5 yielded similar products, and the mechanism of these reactions is discussed.The major product 7a could be converted into 1a by reaction with magnesium.The yield of 4a was increased when pyridine was also used, when only 1 equiv of PCl5 was added by portions to the ketone, or when catecholphosphorus trichloride was used instead of PCl5.The best method for converting 2-acetylthiophene into 1a goes through the enol phosphonate of 2-(bromoacetyl)thiophene, which is treated with sodium amide.
- Kagan, Jaques,Arora, Sudershan K.,Bryzgis, Marius,Dhawan, Som N.,Reid, Kevin,et al.
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p. 703 - 706
(2007/10/02)
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- Formation of Disubstituted Chloro-olefins by Treatment of Substituted 1,2-Dichloroethylenes with Hydrocarbons in the Vapour Phase
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Disubstituted chloro-olefins RCH=CR1Cl together with hydrogen chloride have been formed by treatment of substituted 1,2-dichloroethylenes with hydrocarbons in the gas phase in a flow system at 500 to 600 deg C.Some stereoselectivity towards formation of the Z isomers was observed.The results are interpreted in terms of a free-radical chain mechanism.
- Milner, David J.
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p. 3241 - 3255
(2007/10/02)
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