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A hydrohalogenation reaction is the electrophilic addition of hydrogen halides like hydrogen chloride or hydrogen bromide to alkenes to yield the corresponding haloalkanes. [ 1 ] [ 2 ] [ 3 ] If the two carbon atoms at the double bond are linked to a different number of hydrogen atoms, the halogen is found preferentially at the carbon with fewer ...
In hydrohalogenation, an alkene reacts with a dry hydrogen halide (HX) electrophile like hydrogen chloride (HCl) or hydrogen bromide (HBr) to form a mono-haloalkane. The double bond of the alkene is replaced by two new bonds, one with the halogen and one with the hydrogen atom of the hydrohalic acid.
Dehydrohalogenation to give an alkene. In chemistry, dehydrohalogenation is an elimination reaction which removes a hydrogen halide from a substrate. The reaction is usually associated with the synthesis of alkenes, but it has wider applications.
The addition of halogens to alkenes proceeds via intermediate halonium ions. In special cases, such intermediates have been isolated. [5] Bromination is more selective than chlorination because the reaction is less exothermic. Illustrative of the bromination of an alkene is the route to the anesthetic halothane from trichloroethylene: [6]
The reaction mechanism for an alkene bromination can be described as follows. In the first step of the reaction, a bromine molecule approaches the electron-rich alkene carbon–carbon double bond. The bromine atom closer to the bond takes on a partial positive charge as its electrons are repelled by the electrons of the double bond.
Arrow-pushing mechanism for the Darzens reaction. If the starting halide is an α-halo amide, the product is an α,β-epoxy amide. [8] If an α-halo ketone is used, the product is an α,β-epoxy ketone. [2] Any sufficiently strong base can be used for the initial deprotonation.
The necessary α-halo sulfones are accessible through oxidation of the corresponding α-halo sulfides with peracids such as meta-chloroperbenzoic acid; oxidation of sulfides takes place selectively in the presence of alkenes and alcohols. α-Halo sulfides may in turn be synthesized through the treatment of sulfides with halogen electrophiles such as N-chlorosuccinimide or N-bromosuccinimide.
In chemistry, the haloform reaction (also referred to as the Lieben haloform reaction) is a chemical reaction in which a haloform (CHX 3, where X is a halogen) is produced by the exhaustive halogenation of an acetyl group (R−C(=O)CH 3, where R can be either a hydrogen atom, an alkyl or an aryl group), in the presence of a base.