Catalytic Modulation on the Regioselectivity of the Photosensitized Oxidation of α-Pinene with Molecular Oxygen under Sodium Lamp Irradiation

A simple and efficient photosensitized catalytic oxidation approach for α-pinene with molecular oxygen in a temperature-controlled reactor with sparged dioxygen as oxidant and an immersed high-pressure sodium lamp as a green irradiation light source was developed. The effects of various catalysts and reaction parameters on reaction performance were studied. The results indicated that 98% conversion with 84% total selectivity for verbenone and verbenol was obtained when N,N'-dimethylformamide (DMF) was used as a solvent. The product distributions were remarkably affected by the reaction media and DMF was found to especially modulate the regioselectivity of the products. Moreover, a possible photosensitized catalytic oxidation reaction mechanism in DMF is proposed and a clear acid-base synergetic catalysis effect was evident. The relationship between chemical reactivity and selectivity was modeled using density functional theory at the B3LYP/6-311+G(d) level from optimized molecular configurations.

摘要发展了一种简单有效的 α-蒎烯光敏催化氧化方法, 该方法以高压钠灯为绿色光源, 内循环氧气作为氧化剂和搅拌气, 自制水浴式光化学反应器. 考察了催化剂种类和反应条件对 α-蒎烯转化率和产物选择性的影响. 结果表明, α-蒎烯可通过催化一步生成单萜醇、醛和酮, 且通过催化剂的酸碱协同作用可调节产物的区域选择性. 当以 N,N-二甲基甲酰胺为溶剂时, α-蒎烯的转化率可达 98%, 主产物马鞭草烯酮和马鞭草烯醇的总选择性达到了 84%. 此外, 还探讨了 N,N-二甲基甲酰胺酸碱协同催化的作用机理, 并利用密度泛函计算结果对 α-蒎烯分子中化学反应活性和产物选择性之间的对应关系进行了合理的解释.

Graphical abstractAn efficient catalytic modulation approach for the photosensitized oxidation of α-pinene with molecular oxygen was developed. A relationship between the chemical reactivity and selectivity was modeled using density functional theory.Figure optionsDownload full-size imageDownload as PowerPoint slide