halogenisation

Halogenation is a chemical reaction that involves the introduction of a halogen atom into a molecule. Halogens are elements from Group 17 of the periodic table, specifically fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The process of halogenation can occur through various mechanisms, depending on the substrate and the specific halogenating agent used.

One common method is free radical halogenation, often employed for alkanes. This process typically involves UV light or heat to initiate the formation of a halogen radical, which then abstracts a hydrogen atom from the alkane, creating an alkyl radical. This alkyl radical then reacts with a halogen molecule to form the halogenated alkane and regenerate a halogen radical, continuing the chain reaction.

Another important type of halogenation is electrophilic aromatic substitution, used for aromatic compounds like benzene. In this reaction, an electrophilic halogen species, often generated by a Lewis acid catalyst, attacks the electron-rich aromatic ring, replacing a hydrogen atom with a halogen.

Halogenation reactions are fundamental in organic synthesis and are used to produce a wide range of compounds. Halogenated organic compounds find applications as solvents, refrigerants, pesticides, pharmaceuticals, and flame retardants. However, some halogenated compounds can be persistent environmental pollutants and may pose health risks. The specific conditions and reagents used in halogenation are carefully controlled to achieve desired products and minimize unwanted side reactions or byproducts.