Kinetic and radical mechanism of potassium ions promoted 2,6-Dimethylnaphthalene oxidation

2,6-Naphthalenedicarboxylic acid (2,6-NDA) is one of the key monomers for the synthesis of high-performance polyesters such as polyethylene naphthalate (PEN), liquid crystalline polymers (LCP) and high-performance polyurethane elastomers. 2,6-NDA is typically produced via liquid-phase oxidation of 2,6-dimethylnaphthalene (2,6-DMN) that catalyzed via Co-Mn-Br ternary system, which proceeds through a complex free-radical chain oxidation mechanism. However, this catalytic system is limited by inherent radical chain-transfer efficiency, causing accumulation of intermediates prone to side reactions and restricting further yield improvement. In this study, an efficient Co-Mn-Br-K catalytic system was constructed by introducing potassium ions as a promoter, and the promotion mechanism of potassium ions was revealed by a combined analysis of a fractional kinetic model and the hyperfine structure of the Co-Mn-Br catalytic system. The results indicate that the introduction of potassium ions promotes the oxidation reaction by accelerating the Mn³⁺ to Mn²⁺ electron transfer process without altering the coordination sphere of Mn species and reaction activation energy. This acceleration enhances the initiation and propagation of the radical chains, thereby increasing the concentration of acylperoxy radicals and improving the 2,6-NDA yield by 6.05%. This work provides new mechanistic insights into optimizing the liquid-phase oxidation of 2,6-DMN.