Catalytic Activity and Mechanism of Co‐Catalysts Used in Combinational Catalysts for Aerobic Oxidation

Abstract

(2,2,6,6‐Tetramethylpiperidin‐1‐yl)oxyl (TEMPO) was immobilized on crosslinked polystyrene (CPS) microspheres by polymer reaction to obtain microspheres of the heterogeneous catalyst TEMPO/CPS. TEMPO/CPS microspheres in combination with different transition metal salts were used in the aerobic oxidation of 1‐phenylethanol. This work focuses on the catalytic activities and mechanisms of various co‐catalysts, and the different behavior of these co‐catalysts is explained for the first time with the theory of redox potentials, so that some important principles for selecting better transition metal salts as co‐catalysts of TEMPO are presented. The experimental results show that 1‐phenylethanol can be oxidized to acetophenone as the sole product with a high conversion of 96 % under mild conditions (at 55 °C and with molecular oxygen at ordinary pressure) by using the combinational catalyst consisting of TEMPO/CPS microspheres and transition metal salts.

Metal Nitrate Catalysis for Selective Oxidation of 5-Hydroxymethylfurfural into 2,5-Diformylfuran under Oxygen Atmosphere

“…These results clearly showed that employing redox-active metals such as Fe and Cu had a better effect on the reaction outcome in CH 3 CN. On the basis of the results of this experiment and the previous reports, 43 a plausible reaction pathway is illustrated in Scheme 2. In this proposed mechanism, by the oxidation action of Fe III or Cu II , TEMPO is transformed into a nitrogen carbonyl cation by a single-electron oxidation, and this cation extracts a hydrogen atom from HMF to transform it to DFF.…”

“…These results clearly showed that employing redoxactive metals such as Fe and Cu had a better effect on the reaction outcome in CH 3 CN. On the basis of the results of this experiment and the previous reports, 43 a plausible reaction pathway is illustrated in Scheme 2. In this proposed − ion is reduced to the NO 2 − ion.…”

Honeycomb reactor: a promising device for streamlining aerobic oxidation under continuous-flow conditions

“…In contrast, at 60 °C, the reaction rate improved greatly with the O 2 balloon, and the reaction was completed in 20 min. The proposed catalytic cycle for aerobic oxidation is shown in Scheme 1 [ 40 , 46 – 47 ]. At room temperature, the solubility of O 2 in the reaction solution is relatively high, and the catalytic cycle A, which is associated with the solubility of O 2 , is not the rate-determining step.…”

Honeycomb reactor: a promising device for streamlining aerobic oxidation under continuous flow conditions

“…In contrast, at 60°C, the reaction rate improved greatly with the O2 balloon, and the reaction was completed in 20 min. The proposed catalytic cycle for aerobic oxidation is shown in Scheme 1 [35,41,42]. At room temperature, the solubility of O2 in the reaction solution is relatively high, and the catalytic cycle A, which is associated with the solubility of O2, is not the rate-determining step.…”