Addition of Hydrogen (Hydrogenation)

Hydrogenation of benzene involves the addition of hydrogen across the double bonds of the benzene ring, converting it into cyclohexane. This reaction requires a metal catalyst called Raney nickel, and it typically occurs at a temperature of 150 °C.

A metal catalyst is essential for facilitating the reaction, providing a surface where the hydrogen molecules dissociate and the addition reaction can proceed efficiently. Note that the process is exothermic, releasing heat as the stable aromatic system of benzene is converted into the less stable cyclohexane structure. Hydrogenation demonstrates the chemical reduction of benzene and serves as a critical step in the industrial production of cyclohexane, a precursor to nylon and other polymers.

Addition of Chlorine

Direct chlorination of benzene to form cyclohexane chlorides (such as 1,2-dichlorocyclohexane, 1,3-dichlorocyclohexane, etc.) is not typically performed due to the stability of benzene and the preference for substitution reactions like the formation of chlorobenzene in electrophilic substitution reactions. However, if the reaction is allowed to proceed in the presence of light, the product is 1,2,3,4,5,6-hexachlorocyclohexane. This reaction can also be done using bromine instead of chlorine.