Bleaching is a process in which the colors of the treated substance disappear and are whitened by using reactants called as bleaching agents. Cl₂ was discovered by Swedish chemist Carl Wilhelm Scheele in 1774, which is used as a bleaching agent in pulp industry. Claude Louis Berthelot was the first to use Cl as a bleaching agent.

Cl₂ is produced in-situ along with sodium hydroxide using electrolysis of aqueous NaCl

The oxidation state of Cl₂ is zero, while that in the hypochlorite ion is +1, thus undergoing oxidation. This method is used to remove color or whiten the wood pulp in paper industry. This chlorine generated oxidizes the chromopohores present in wood pulp, which are the main color substances that can reflect, transmit or absorb wavelengths in the visible spectrum present in living things.

Note: In the above mentioned reaction, Cl₂ is an oxidizing agent which in presence of hydroxide forms a hypochlorite which is harmful substance. Along with it, 2,3,7,8 – tetrachlorodibenzo-p-dioxin (TCDD), which is the most harmful substance produced in the process, so now the practice of Totally Chlorine Free (TCF) bleaching methods are used i.e. by using ClO₂.