Ether when treated with HI produces both benzyl iodide or phenol. Under acidic conditions (i.e., with a small amount of HI), the ether can undergo an acid-catalyzed cleavage to form phenol and benzyl iodide. In this reaction, the HI acts as a catalyst, and the protonation of the ether oxygen atom makes it a good leaving group, which then departs to form benzyl carbocation. The carbocation can then react with the iodide ion to form benzyl iodide, while the protonated oxygen atom can undergo deprotonation and form phenol.
