半乳糖氧化酶模型化合物对乙苯选择性氧化制备苯乙酮的催化性能及机理

Properties and mechanisms of selective oxidation of ethylbenzene to acetophenone by GOase model compound

摘要:

温和条件下实现C-H键的选择性氧化在精细化学品的生产中发挥重要作用。受到半乳糖氧化酶(galactose oxidase,GOase)活性中心结构和催化循环启发,仿生其模型化合物CuL为催化剂,N-羟基邻苯二甲酰亚胺(N-Hydroxyphthalimide,NHPI)为助催化剂,在温和条件下(氧气1.0 MPa,75 °C,反应6 h),乙苯转化率高达99%,其中氧化产物苯乙酮选择性高达99%。机理研究表明CuL与NHPI形成活性中间体,通过电子转移高效促进NHPI生成PINO(phthalimide N-oxyl)自由基,并用于底物C-H键活化。KIE实验(K_NHPI-H/K_NHPI-D ≈ 3.4)指出NHPI的活化可能为决速步骤。电子顺磁共振(EPR)和高分辨质谱指出反应过程中存在烷基自由基,过氧自由基和羟基自由基。

Abstract:

Selective oxidation of C?H bonds under mild conditions plays an important role in the production of fine chemicals. Inspired by the active center structure and catalytic cycle of galactose oxidase (GOase), the biomimetic model compound CuL was used as a catalyst and N-Hydroxyphthalimide (NHPI) was used as a co-catalyst. Under mild conditions (O₂ 1.0 MPa, 75 °C, 6 h), the conversion of ethylbenzene was as high as 99%, and the selectivity of the oxidation product acetophenone was as high as 99%. Mechanistic studies showed that CuL forms an intermediate with NHPI, which efficiently promotes NHPI to generate PINO (phthalimide N-oxyl) radicals through electron transfer. PINO radical was used to activate C?H bonds. KIE experiment (K_NHPI-H/K_NHPI-D ≈ 3.4) indicated that the activation of NHPI was the rate-determining step. Electron paramagnetic resonance (EPR) and high-resolution mass spectrometry pointed out that the existence of alkyl radicals, peroxy radicals and hydroxyl radicals during the reaction.