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Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs. [1] This kind of conversion is in fact so common that a comprehensive overview is challenging. This article mainly deals with halogenation using elemental halogens (F 2, Cl 2, Br 2, I 2). Halides are also commonly ...
[1] The general chemical formula of the halogen addition reaction is: C=C + X 2 → X−C−C−X (X represents the halogens bromine or chlorine, and in this case, a solvent could be CH 2 Cl 2 or CCl 4). The product is a vicinal dihalide. This type of reaction is a halogenation and an electrophilic addition.
Remarkably, ketone halogenation also occurs in biological systems, particularly in marine algae, where dibromoacetaldehyde, bromoacetone, 1, l,l -tribromoacetone, and other related compounds have been found. The halogenation is a typical α-substitution reaction that proceeds by acid catalyzed formation of an enol intermediate. [1]: 846
Other conditions for iodination include I 2, HIO 3, H 2 SO 4, and N-iodosuccinimide, H 2 SO 4. [1] [2] These conditions are successful for highly deactivated arenes, including nitroaromatics. In a series of studies, the powerful reagent obtained by using a mixture of iodine and potassium iodate dissolved in concentrated sulfuric acid was used.
Subsequent halogenation (which usually cannot be stopped by control of stoichiometry) occurs at the position which already has a halogen substituent, until all hydrogens have been replaced by halogen atoms. For methyl alkyl ketones (2-alkanones), the haloform reaction proceeds to give the carboxylic acid selectively. [2]
Regiochemistry follows from the reaction mechanism, which exhibits halogen attack on the least-hindered unsaturated carbon. The mechanism for this chain reaction resembles free radical halogenation, in which the peroxide promotes formation of the bromine radical. However, this process is restricted to addition of HBr.
In organic chemistry, free-radical halogenation is a type of halogenation. This chemical reaction is typical of alkanes and alkyl-substituted aromatics under application of UV light. The reaction is used for the industrial synthesis of chloroform (CHCl 3), dichloromethane (CH 2 Cl 2), and hexachlorobutadiene. It proceeds by a free-radical chain ...
As a halogen source for transhalogenation, metal halides (such as sodium fluoride or lithium fluoride) are often used, but also the use of onium halides is possible. [2] Transhalogenation has been described as a gentle method for the synthesis of fluoroorganylboranes. [ 4 ]