HBeta沸石高效催化芳醇/酚酯化

Efficient catalysis of alcohol/phenol esterification by HBeta zeolite

将自制的HBeta用于催化4-甲基苯甲醇与乙酸酐的酯化反应,确定了其最优条件为:以10 mg酸性HBeta沸石为催化剂、0.5 mmol 4-甲基苯甲醇、0.5 mmol乙酸酐、1.0 mL环己烷,N_(2)氛围下室温反应1 h,在该条件下以>99%的产率合成了乙酸4-甲基苄酯。探索了底物的普适性,并以较广的底物范围合成了32种芳香族酯化反应产物。在沸石中掺入不同质量分数的磷(0.2%~1.0%),通过XRD、N_(2)吸附-脱附、NH_(3)-TPD、Py-IR对催化剂的织构参数和酸性特征进行了表征。结果表明,随着HBeta强Br?nsted酸酸性位点(SBAS)酸量的降低,芳醇/酚酯化反应产率从>99%逐渐降至57%,说明催化剂上的SBAS是芳醇/酚反应的活性中心。此外,HBeta催化剂在芳醇/酚的酯化反应中表现出良好的结构稳定性,循环4次而没有明显失活。提出了4-甲基苯甲醇在催化剂的SBAS上首先转化成对应的碳正离子中间体,随后与乙酸酐发生亲核加成反应,从而生成目标产物的反应机理。

The self-made HBeta was used to catalyze the esterification of 4-methylbenzyl alcohol with acetic anhydride.Under the optimal conditions of catalyst acid HBeta zeolite 10 mg,4-methylbenzyl alcohol 0.5 mmol,acetic anhydride 0.5 mmol,cyclohexane 1.0 m L,reaction time 1 h in nitrogen atmosphere at room temperature,the yield of 4-methylbenzyl acetate reached>99%.The universality of substrates was explored and 32 kinds of aromatic esterification products were synthesized with a wide range of substrates.The zeolite was mixed with different mass fractions of phosphorus (0.2%~1.0%),and the texture parameters and acidity characteristics of the catalysts were characterized by XRD,N_(2) adsorption-desorption,NH_3-TPD and Py-IR.The results showed that the esterification rate of aryl alcohol and phenol gradually decreased from>99%to 57%as the acid content of strong Br?nsted acid sites (SBAS) in HBeta zeolite decreased,indicating that the SBAS were the active sites for converting aryl alcohols and phenols.Moreover,the catalyst exhibited excellent structural stability with no significant activity loss observed after being recycled 4 times.The proposed reaction mechanism was that 4-methybenzyl alcohol first underwent transformation into the corresponding carbocation intermediates on the SBAS of HBeta zeolite,followed by a nucleophilic addition reaction with acetic anhydride to yield the target product.