Kinetics of the oxygenation of unsaturated organics with singlet oxygen generated from H2O2 by a heterogeneous molybdenum catalyst.

A heterogeneous catalyst containing MoO42- exchanged on layered double hydroxides (Mo-LDHs) is used to produce 1O2 from H2O2, and with this dark 1O2, unsaturated hydrocarbons are oxidized in allylic peroxides. The oxidation kinetics are studied in detail and are compared with the kinetics of oxidation by 1O2, formed from H2O2 by a homogeneous catalyst. A model is proposed for the heterogeneously catalyzed 1O2 generation and peroxide formation. The model divides the reaction suspension in two compartments: (1) the intralamellar and intragranular zones of the LDH catalyst; (2) the bulk solution. The 2-compartment model correctly predicts the oxidant efficiency and peroxide yield for a series of olefin peroxidation reactions. 1O2 is generated at a high rate by the heterogeneous catalyst, but somewhat more 1O2 is lost by quenching with the heterogeneous catalyst than using the homogeneous catalyst. Quenching occurs mainly as a result of collision with the LDH hydroxyl surface, as is evidenced by using LDH supports containing strong 1O2 deactivators such as Ni2+. A total of 15 organic substrates were peroxidized on a preparative scale using the best Mo-LDH catalyst under optimal conditions.