Preparation of chlorine by Deacon’s process : By oxidation of hydrogen chloride gas by atmospheric oxygen in the presence of $\mathrm{CuCl}_2$ at 723 K $4\mathrm{HCl} + \mathrm{O}_2 \xrightarrow{\mathrm{CuCl}_2} 2\mathrm{Cl}_2 + 2\mathrm{H}_2\mathrm{O}$ Preparation of HCl : Cl$2$ can be reduced to HCl by reaction of H$2$ in thepresence of diffused sunlight. $\mathrm{H}_2 + \mathrm{Cl}_2 \xrightarrow[\mathrm{Sunlight}]{\mathrm{Diffused}} 2\mathrm{HCl}$