The photochemical reaction between benzene and chlorine in the presence of sunlight is known as the photochlorination of benzene. This reaction involves the substitution of one hydrogen atom in the benzene ring with a chlorine atom. The mechanism of this reaction can be described in the following steps:1. Initiation: In the presence of sunlight UV light , the chlorine molecule Cl2 absorbs energy and undergoes homolytic fission, resulting in the formation of two chlorine radicals Cl .Cl2 + h sunlight 2 Cl2. Propagation: The chlorine radical generated in the initiation step reacts with the benzene molecule by attacking one of its hydrogen atoms. This leads to the formation of a benzene radical C6H5 and a molecule of hydrogen chloride HCl .C6H6 + Cl C6H5 + HClNext, the benzene radical reacts with another chlorine molecule, resulting in the formation of chlorobenzene C6H5Cl and another chlorine radical.C6H5 + Cl2 C6H5Cl + ClThe overall propagation step can be summarized as:C6H6 + Cl2 C6H5Cl + HCl3. Termination: The reaction can be terminated when two radicals react with each other, forming a stable molecule. This can occur in several ways, such as:Cl + Cl Cl2C6H5 + Cl C6H5ClC6H5 + C6H5 C6H5-C6H5 biphenyl The main product of this reaction is chlorobenzene, but minor amounts of biphenyl and unreacted chlorine may also be formed during the termination step.