Scientists have helped solve an 80-year-old puzzle about a widely used chemical process. The Fenton reaction involves iron and hydrogen peroxide and is used to treat wastewater worldwide. Does the reaction involve a radical intermediate? Or, is it the non-radical, iron species known as Fe(IV)? The exact nature of the intermediate has been debated for decades with data to support both theories. The problem is both intermediates will react to form the same products in most cases making the reaction intermediate hard to pin down. Researchers have now proved that both intermediates can be involved — it just depends on the pH. They carefully studied a reaction for which the two intermediates would form different products. They showed that in an acidic environment, the intermediate is an hydroxyl radical, whereas at near neutral pH the intermediate is Fe(IV). This discovery explains the differences in products formed under certain reaction conditions and clears up a decades-old mystery.
pH-induced Mechanistic Changeover from Hydroxyl Radicals to Iron(IV) in the Fenton Reaction