The cumene process, i. e., the proton-catalyzed cleavage of cumene hydroperoxide to and acetone, was discovered by Hock and Lang in 1944. Although the earliest commercialization was in an 8000 tonne-per-year Gulf plant in Canada in 1953. about 97% of the total synthetic phenol production in the USA until 1987, and 100% in Japan until 1990, was manufactured by this process. At that time, a new process based on toluene was introduced and this route is now used for ahout 91% of phenol production in Western Europe. The world production capacity for phenol using the Hock process is currently about 5×10⁶ tonnes per year. Despite the 0.62 tonnes of acetone produced per tonne phenol, this process has dominated because of its economics.

The principle of the combined phenol/acetone manufacture by the Hock Drocess is based on the oxidation of cumene to cumene hydroperoxide and its subsequent cleavage in acidic media to phenol and acetone:

In the industrial process, cumene from benzene propylation can be oxidized to the hydroperoxide in a bubble column either by the BP (formerly Distillers), Hercules and Kellogg process with air in an aqueous emulsion containing Na₂CO₃ at pH 8.5-10.5, 90-130°C and 5-10 bar, or undiluted in a homogeneous phase at 120 °C by the Hercules process. Cu, Mn, or Co salts can be used as catalysts. Although these catalysts can decrease the induction period at the start of the reaction, a lower hydroperoxide concentration may result due to its further oxidation to CO₂; thus catalysts have not been used commercially. The oxidation is discontinued when the hydroperoxide content is 35-40% in order to ensure low formation of byproducts such as dimethylphenylcarbinol and acetophenone. The oxidized product is concentrated to about 65-90% in vacuum columns and cleaved to phenol and acetone.

The cleavage can be conducted either in homogeneous solution with 0.1 -2% H₂SO₄ at 60-65°C in acetone according to the BP and Hercules processes or in phenol, according to the Rhône-Poulenc approach. Phenolchemie operates a two-phase process with 40% H₂SO₄ at about 50 °C.