Halogenation means the replacement of one or more hydrogen atoms in an organic compound by a halogen like fluorine, chlorine, bromine or iodine. Unlike the complex transformations of combustion, halogenation of an alkane appears to be a simple substitution reaction in which a C-H bond is broken and a new C-X bond is formed. The chlorination of methane
, shown below, provides a simple example of this reaction.
CH4 + Cl2 + energy → CH3Cl + HCl
Since only two covalent bonds are broken (C-H & Cl-Cl) and two covalent bonds are formed (C-Cl & H-Cl). However, one complication is that all the hydrogen atoms of an alkane may undergo substitution, resulting in a mixture of products, as shown in the following unbalanced equation. The relative amounts of the various products depend on the proportion of the two reactants used. In the case of methane, a large excess of the hydrocarbon favours the formation of methyl chloride as the chief product; whereas, an excess of chlorine favours the formation of chloroform and carbon tetrachloride.
CH4 + Cl2 + energy → CH3Cl + CH2Cl2 + CHCl3 + CCl4 + HCl
Methane gas makes you go into halogenation.