Cobalt phthalocyanine (CoPc) anchored on Ti3C2 MXene nanosheets for highly efficient selective catalytic oxidation

Abstract

Quinclorac is an important precursor for pharmaceutical, agricultural, and synthetic chemistry. The state-of-the-art synthesis of quinclorac via condensation, chlorination and oxidative hydrolysis often uses homogeneous catalysts and strong acid oxidant agents to promote the catalytic oxidation, which requires huge manpower input for the late-stage purification process and is usually environmentally unfriendly. In this work, we successfully fabricated a stable cobalt phthalocyanine (CoPc) Co-based composite (CoPc/Ti₃C₂) by anchoring CoPc on the surface of Ti₃C₂ nanosheets for the selective oxidation of 3,7-dichloro-8-dichloro methyl quinoline (3,7-D-8-DMQ) into quinclorac. More impressively, CoPc/Ti₃C₂-4.5%–Mn–Br exhibits a high selectivity of 91.8% for the catalytic oxidation of 3,7-D-8-DMQ to quinclorac in acetic acid, with a quinclorac yield of 87.5%, which is approximately 2.46 times higher than that of pristine CoPc–Mn–Br. The obtained heterogeneous catalytic system shows good reusability. Detailed mechanistic investigations reveal that the system works through the free radical mechanism via the formation of Co²⁺/Co³⁺ redox cycles. This work provides a new understanding for the stabilization of reaction intermediates and facilitates the design of catalysts for selective catalytic oxidation.