Selective oxidation of ethyl lactate to ethyl pyruvate by a photocatalytic strategy under room temperature

Selective oxidation of ethyl lactate (EL) with molecular oxygen as oxidant is an alternative route to produce ethyl pyruvate (EP). However, to obtain pyruvate with high yield under mild conditions remains challenging due to the troublesome over oxidation issue. Here, a highly efficient photocatalytic strategy was firstly developed to obtain EP at room temperature. ZnIn sulfides (ZIS) with different Zn/In ratios were synthesized as the catalysts. Under the irradiation of visible light, 100% EL conversion with 88.4% EP yield could be obtained. The optimized ZIS catalyst shows the highest surface area (215.7 m2 g−1) as well as much higher separation and transport efficiency of the electron-hole pairs. Combining radical trapping experiments with characterization results, a reaction mechanism was proposed. The mild reaction conditions with efficient generation of singlet oxygen contribute the high yield of EP. Kinetic isotope experiments indicate that the cleavage of C(OH)−H bond probably was involved in the rate determining step.