Abstract: A mass stream comprising mesityl oxide may be reacted with water in an acidic medium, a basic medium, or in the presence of an acidic catalyst, to convert the mesityl oxide to acetone. This process may be used in conjunction with the Hock process for manufacturing phenol and acetone to decrease the amount of mesityl oxide by-product, and increase the yield of acetone. Thus, cumene is oxidized to form cumene hydroperoxide, which is then cleaved in the presence of an acidic catalyst to form a cleavage product phase comprising phenol, acetone, and mesityl oxide. The cleavage product phase may then be distilled to provide a mass stream comprising mesityl oxide. At least some of the mesityl oxide of the mass stream is then, according to the process of the present invention, reacted with water, in an acidic medium, a basic medium, or in the presence of an acidic catalyst, thereby producing acetone.