HBeta沸石高效催化醇/酚酯化

Acidic HBeta zeolite catalyzed the acylation reaction of aryl alcohol and phenol

摘要:

以酸性HBeta沸石为催化剂，以芳基醇/酚和脂肪族酸酐为原料，在清洁、温和的反应条件下通过酯化反应，合成一系列芳香族酯化反应产物。对模型反应条件进行研究，确定最优条件为：HBeta沸石催化剂（10 mg）、4-甲基苯甲醇（Ⅰa，0.5 mmol）、乙酸酐（Ⅱa，0.5 mmol）、环己烷（1.5 mL），惰性氛围中室温反应1 h，以>99%的产率合成4-甲基苄醇乙酯（Ⅲaa）。同时探索了底物的普适性，以较广的底物范围合成32种芳香族酯化反应产物。并在沸石中掺入不同质量分数的磷（质量分数：0.2%-1%），通过XRD、N2-吸附、NH3-TPD、Py-IR等测试对催化剂的织构参数和酸性特征进行表征，发现随HBeta强Br?nsted酸位点（SBAS）浓度降低，芳基醇/酚酯化反应速率从>99%逐渐降低到57%，说明催化剂上的SBAS是芳基醇/酚反应的活性中心。此外，HBeta催化剂在醇/酚的酯化反应中表现出良好的结构稳定性，能够循环使用5次而没有明显活性损失（>98%）。最后，根据表征和实验结果提出芳基醇/酚在催化剂的SBAS上首先转化成对应的碳正离子中间体，随后与酸酐中富电子氧发生亲核加成反应，从而生成目的产物的反应机理。

Abstract:

A series of aromatic esterification products were synthesized from aryl alcohol and phenol with aliphatic anhydride using acidic HBeta zeolite as a catalyst under clean and mild reaction conditions. The optimal reaction conditions were determined as follows: HBeta zeolite catalyst (10 mg), 4-methylbenzyl alcohol (Ⅰa, 0.5 mmol), acetic anhydride (Ⅱa, 0.5 mmol), cyclohexane (1.5 mL), reaction at room temperature in an inert atmosphere for 1 h, the yields of 4-methylbenzyl acetate (Ⅲaa) reached over 99%. Then, 32 kinds of aromatic esterification products were synthesized from a wide range of substrates. The catalysts were characterized by XRD, N2-adsorption, NH3-TPD, and Py-IR, the structure parameters and acidity of the catalysts were determined. It was found that the esterification rate of aryl alcohol and phenol gradually decreased from >99% to 57%, with the concentration of HBeta's strong Br?nsted acid sites (SBAS) decreased, indicating that the SBAS of the catalysts are the active sites for converting aryl alcohols and phenols into carbon cations. No significant activity loss was observed with product yield still up to 98% after being recycled 5 times. Finally, based on the characterization and experimental results, it is suggested that aryl alcohols and phenols first undergoed transformation into the corresponding carbocation intermediates on the strong Br?nsted acid sites (SBAS) of HBeta zeolite, which is then followed by a nucleophilic addition reaction with electron-rich oxygen in acid anhydride to yield the target products.