环烷酸催化脱羧机理的研究

为深入认识环烷酸催化脱羧的反应机理，选取具有代表性的带有较长侧链的9 环己基壬酸为模型化合物，采用基于密度泛函理论的量子化学从头计算方法研究了该分子的电荷分布和前线轨道分布，发现分子中的羰基O原子更易受到B酸和L酸进攻。在此基础上，进一步分析了该分子与B酸和L酸作用前后的键长、键级等变化，推演出了羧基β位碳碳键发生断裂生成小分子的石油酸和直接脱羧生成CO2 2条反应路径。比较2条反应路径的反应能垒后，提出了在B酸作用下，9 环己基壬酸分子更容易发生的是生成小分子石油酸的反应，而在L酸作用下，9 环己基壬酸分子更容易发生直接脱羧生成CO2反应的观点。

Study on the Mechanism of Catalytic Decarboxylation of Naphthenic Acid

To deeply elucidate the mechanism of catalytic decarboxylation of naphthenic acids, density functional theory based ab initio quantum method was selected, and 9 cyclohexylnonanoic acid with a long chain was used as model compound, to study the charge distributions and frontier orbital of molecule, and its elementary reaction steps under catalysis of Brnsted and Lewis acids. Calculated results showed that the carbonyl oxygen atom in the molecule was more susceptible to be attacked by B acid and L acid. Then the bond length and bond order of this molecule before and after being attacked by B acid and L acid were calculated and two reaction paths were deduced, in which one is the cracking of β C—C bond in carboxyl group to generate small acid molecule and the other is direct decarboxylation to generate CO2.From the comparison of energy barriers for the two reaction paths in the presence of B acid and L acid, it is found that 9 cyclohexylnonanoic acid was more likely to generate small acid in the presence of B acid, while more likely to generate CO2 in the presence of L acid. These theoretical insights may greatly promote the development of more selective decarboxylation catalysts.