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For example, consider radical bromination of toluene: [5] bromination of toluene with hydrobromic acid and hydrogen peroxide in water. This reaction takes place on water instead of an organic solvent and the bromine is obtained from oxidation of hydrobromic acid with hydrogen peroxide. An incandescent light bulb suffices to radicalize.
In chemistry, halogenation is a chemical reaction which introduces one or more halogens into a chemical compound. 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.
In this way the two halogens add in an anti addition fashion, and when the alkene is part of a cycle the dibromide adopts the trans configuration. For maximum overlap of the C–Br σ* antibonding molecular orbital (the LUMO , shown to the right in red) and the nucleophile (X − ) lone pair (the HOMO , shown to the right below in green), X − ...
Halogenation of phenols is faster in polar solvents in a basic environment due to the dissociation of phenol, with phenoxide ions being more susceptible to electrophilic attack as they are more electron-rich. Chlorination of toluene with chlorine without catalyst requires a polar solvent as well such as acetic acid.
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.
For alkylbenzene derivatives, e.g. toluene, the alkyl positions tend to be halogenated by free radical conditions, whereas ring halogenation is favored in the presence of Lewis acids. [6] The decolouration of bromine water by electron-rich arenes is used in the bromine test. Reaction between benzene and halogen to form an halogenobenzene
Benzyl bromide is used in organic synthesis for the introduction of the benzyl groups when the less expensive benzyl chloride is insufficiently reactive. [6] [7] Benzylations are often achieved in the presence of catalytic amounts of sodium iodide, which generates the more reactive benzyl iodide in situ. [3]
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.