FCC汽油噻吩类硫化物烷基化硫转移反应机理的量子化学

Quantum Chemistry Research in Alkylation Sulfur Transfer Reaction Mechanism of Thiophene Sulfide in FCC Gasoline

以各种甲基噻吩与2-甲基丁烯-2在催化剂作用下的烷基化反应为模型反应,对FCC汽油的噻吩类硫化物的定位效应和烷基化反应机理进行了从头算的量子化学研究。采用LST/QST/CG进行过渡态搜索,验证仲正碳离子进行重排转变为叔正碳离子的可行性和具体途径。结果表明,计算得到的叔正碳离子的能量低于仲正碳离子的,仲正碳离子重排为叔正碳离子是放热过程,该反应的能垒仅19.74kJ/mol。2-甲基噻吩的烷基化反应是典型的亲电取代反应,对中间体IM及产物P进行结构优化,以分子复合物R和IM为起点进行LST/QST/CG过渡态搜索,所得过渡态TS1经优化后的几何构型的能量为-2.072×106 kJ/mol,在132cm-1有唯一的虚频;以IM和P为起点进行LST/QST/CG过渡态搜索,所得过渡态TS2经优化后的能量为-2.071×106 kJ/mol,在128.9cm-1处有唯一虚频。

With the catalytic alkylation of methyl-thiophene and 2-methybutene-2 as the model reaction,the alkylation mechanism and the orientation effect of thiophenes in FCC gasoline were theoretically studied by ab initio quantum chemistry.LST/QST/CG was used to search the transition state to prove the feasibility and specific path of 2′-carbonium to 3′-carbornium by rearrangement.The results showed that the energy of 3′-carbonium was lower than that of 2′-carbonium,reaction active energy released by 2′-carbonium rearrangement to 3′-carbonium was only 19.74 kJ/mol,meaning that the rearrangement was a exothermic process.Alkylation reaction of 2-methyl-thiophene was typical electrophilic substitution reaction.The geometry structures of reactants,intermediates,transition states and products were optimized by searching for transient with LST/QST/CG.Energy of transition TS1 with R and IM as starting point was-2.072×106 kJ/mol,with only virtual frequency of 132 cm-1.Energy of transition TS2 with IM and P as starting point was-2.071×106 kJ/mol,with only virtual frequency of 128.9 cm-1.