Halogenaatioreaktiot

Halogenaatioreaktiot are chemical reactions in which one or more halogen atoms are introduced into an organic molecule. Halogens commonly used in these reactions are fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). These reactions can occur through various mechanisms, including free radical substitution, electrophilic addition, and electrophilic substitution.

Free radical halogenation typically occurs with alkanes. It involves a chain reaction initiated by light or heat, where a halogen radical abstracts a hydrogen atom from the alkane, creating an alkyl radical. This alkyl radical then reacts with a halogen molecule to form a halogenated alkane and regenerate a halogen radical, continuing the chain.

Electrophilic addition of halogens to alkenes and alkynes involves the addition of a halogen molecule across a double or triple bond. The pi bond of the unsaturated system attacks the halogen molecule, leading to the formation of a cyclic halonium ion intermediate, which is then attacked by a halide ion to yield a vicinal dihalide.

Electrophilic aromatic substitution (EAS) is another important type of halogenation reaction, where a halogen atom replaces a hydrogen atom on an aromatic ring. This reaction requires a Lewis acid catalyst, such as iron(III) bromide or aluminum chloride, to polarize the halogen molecule and generate a strong electrophile. The electrophile then attacks the electron-rich aromatic ring, forming a sigma complex, which subsequently loses a proton to restore aromaticity and yield the halogenated aromatic compound. The position of halogenation on the aromatic ring is influenced by existing substituents.