The reaction between chlorine and butane is a free radical substitution reaction. In this type of reaction, a chlorine atom replaces a hydrogen atom in the butane molecule. The reaction is initiated by the formation of a chlorine radical, which is a highly reactive atom with an unpaired electron. This radical can then react with a hydrogen atom in the butane molecule, forming a hydrogen chloride molecule and a butyl radical. The butyl radical can then react with another chlorine molecule, forming a butyl chloride molecule and a new chlorine radical. This process can continue until all of the hydrogen atoms in the butane molecule have been replaced by chlorine atoms.

The rate of a free radical substitution reaction is influenced by a number of factors, including the concentration of the reactants, the temperature, and the presence of inhibitors or catalysts. The reaction is also more likely to occur if the hydrogen atom that is being replaced is located on a tertiary carbon atom (a carbon atom that is bonded to three other carbon atoms).

The reaction between chlorine and butane is an important industrial process for the production of chlorinated hydrocarbons, which are used as solvents, refrigerants, and plastics.