咪唑类离子液体催化合成正龙脑

Catalytic synthesis of n-borneol by imidazole ionic liquid

摘要:

通过两步法合成了四种阴离子不同的咪唑类离子液体，并采用FT-IR、1H NMR、13C NMR、TG、Hammett酸度函数对其结构和酸度进行表征。以α-蒎烯酯化-皂化反应为探针反应，考察了四种离子液体对正龙脑的选择性，结果表明阴离子为[HSO4]-对正龙脑的选择性最好，与Hammett酸度函数计算的结果吻合。选取[Bmim-SO3H]HSO4作进一步的工艺研究，优化得到的工艺条件为：环己烷用量35ml，反应温度为120℃，离子液体为松节油质量的8%，n(松节油):n(乙酸)=1:3，反应时间8h。在该条件下，α-蒎烯的转化率为100%，正龙脑选择性为39.83%，占总龙脑的92.58%。其中离子液体的作用是提供H ，使α-蒎烯质子化形成正碳离子，HSO4-稳定非经典正碳离子，与乙酸根形成络合物，使生成龙脑的反应更容易发生。[Bmim-SO3H]HSO4重复使用四次仍具有较高的活性，α-蒎烯的转化率仍达99.76%，正龙脑的选择性为35.45%。

Abstract:

Four imidazole ionic liquids with different anions were synthesized by a two-step method, and their structure and acidity were characterized by FT-IR, 1H NMR, 13C NMR, TG, Hammett acidity function. Using α-pinene esterification-saponification reaction as a probe reaction, the selectivity of four ionic liquids to n-borneol was investigated. The result shows that the anion is [HSO4]-the best selectivity for borneol, which is consistent with the result calculated by Hammett's acidity function. [Bmim-SO3H]HSO4 for further process research, and the optimized process conditions are: ionic liquid is 8% of the mass of turpentine, n(turpentine):n(acetic acid)=1:3, reaction temperature is 120℃, reaction time is 8h, and the amount of cyclohexane is 35ml. Under these conditions, the conversion rate of α-pinene was 100%, and the selectivity of n-borneol was 39.83%, accounting for 92.58% of the total borneol. Among them, the role of ionic liquid is to provide H to protonate α-pinene to form carbanion, HSO4- stabilizes non-classical carbanion, and forms a complex with acetate, making the reaction to generate borneol more easily. [Bmim-SO3H]HSO4 has high activity after repeated use for three times, the conversion rate of α-pinene is still 99.76%, and the selectivity of borneol is 35.45%.