Solvent-free chlorination of biphenyl and naphthalene was performed under mechanochemical stressing by high-energy ball milling (HEM) of a mixture of CuCl2 (95 wt %) and the hydrocarbon (5 wt %). The reactivity of the selected hydrocarbons towards CuCl2 during HEM partially correlates with their ionisation potentials (IP): hexadecane (9.91 eV) > biphenyl (8.27 eV) > naphthalene (8.14 eV).