A method for producing p-dichlorobenzene using a reactor containing a catalyst/reagent to convert chlorobenzene (or benzene) to p-dichlorobenzene, the reactor having an inlet and an outlet for introducing reactants and removing product; introducing a pulse of gaseous chlorobenzene (or benzene) into the reactor and reacting the chlorobenzene with the catalyst/reagent whereby p-dichlorobenzene is formed; introducing a pulse of inert gas into the reactor; introducing a pulse of gaseous chlorine into the reactor and reacting the chlorine with the catalyst/reagent; introducing a pulse of inert gas into the reactor; repeating the pulsing steps in a sequential manner, whereby mixing of the vaporized benzene or chlorobenzene, and the chlorine gas is prevented; and continuously removing product containing p-dichlorobenzene from the outlet of the reactor.