Mechanistic Study on the Production of Hydrogen Peroxide in the Anthraquinone Process

Hydrogen peroxide is produced from hydrogen gas and air in industry by using the anthraquinone process. The mechanism for the production of hydrogen peroxide in this process is studied by using DFT calculations and reaction rate measurements. A hydrogen atom of anthrahydroquinone (AHQ) is directly abstracted by triplet dioxygen to produce a hydroperoxide radical (HOO center dot) and a 10-hydroxy-9-anthroxyl radical (AQH(center dot)), followed by subsequent hydrogen atom abstraction that leads to the formation of hydrogen peroxide and anthraquinone (AQ). Hydrogen atom abstraction was found to be the rate-determining step in this process. Tetrahydro-anthrahydroquinone (THAHQ) is also used in this process in a similar way to AHQ, but a higher activation energy is required for the rate-determining step when THAHQ is used, which would lead to a 25-fold rate deacceleration compared with AHQ at 27 degrees C. The reactivities of AHQ and THAHQ are not significantly influenced by effects of side alkyl chain that is used in the industrial process for increasing the solubility of AHQ and AQ in working solution. The relative reaction rate of AHQ and THAHQ is measured under laboratory conditions. The computational results are consistent with an observed lower rate of the oxidation process of THAHQ.