苯甲醇的绿色选择性氧化

Green and Selective Oxidation of Benzyl Alcohol

醇的氧化是制备醛和酮的重要反应之一,也是有机化学理论教学和实验教学的一个重点内容。目前,大多数本科生实验教材安排了环己醇氧化合成环己酮的实验。虽然现有实验教材提供了一例将伯醇氧化为醛的方案,即采用Na_(2)WO_(4)×2H_(2)O/(C_(4)H_(9))_(4)NHSO_(4)催化体系,在90℃用H_(2)O_(2)将苯甲醇选择性氧化为苯甲醛,但是存在着产率低、安全性不高和重金属污染等问题。本文采用Fe(NO_(3))_(3)×9H_(2)O、4-羟基-2,2,6,6-四甲基哌啶氧化物(4-OH-TEMPO)和乙酸(HOAc)为催化剂、O_(2)为氧化剂,以H_(2)O为溶剂,在温和的反应条件下高选择性地将苯甲醇氧化为苯甲醛,分离产率可达91%,这为伯醇的选择性氧化提供了一个低成本且高效绿色的实验教学新方案。同时,在实验过程中引入薄层色谱、气相色谱、快速制备液相色谱和核磁共振氢谱等手段对产物进行分离、提纯和表征,有效提升了本科生的综合实验技能和科研素养。

Oxidation of alcohols is an important method to produce aldehydes and ketones,and is an important component in organic chemistry theory and practical teaching.Currently,oxidation of cyclohexanol to cyclohexanone is commonly introduced in practical undergraduate textbooks.The only experiment designed for the preparation of aldehydes from primary alcohols in current practical textbooks is using the oxidant H_(2)O_(2) for the selective oxidation of benzyl alcohol to benzaldehyde at 90℃ in the presence of a catalytic amount of Na_(2)WO_(4)×2H_(2)O/(C_(4)H_(9))_(4)NHSO_(4).However,this reaction has low-yields,potential safety issues,and concerns with environmental pollution.Here,we present a practical alternative reaction involving the mixed catalytic system of Fe(NO_(3))_(3)×9H_(2)O,4-hydroxy-2,2,6,6-tetramethyl-piperidinooxy(4-OH-TEMPO),and acetic acid(HOAc).This reaction allowed for a highly selective oxidation of benzyl alcohol to benzaldehyde with an isolated yield of up to 91% using O_(2) as the oxidant and H_(2)O as the solvent under mild conditions.This new strategy for the selective oxidation of primary alcohols is a low-cost,and more importantly,highly efficient and green strategy.Additionally,several techniques such as thin layer chromatography,gas chromatography,flash preparative liquid chromatography,and 1H NMR spectroscopy were used to detect and purify products,to improve experimental techniques,and to enhance the scientific literacy of undergraduate students.