硫醇类硫化物与H^+相互作用的分子模拟

Molecular simulation for the interaction between mercaptan sulfide and H^+

为了研究催化裂化、加氢等工艺过程中,硫醇类硫化物与固体酸性催化剂的B酸中心之间的相互作用机理,采用动力学和半经验量子力学方法,对几种典型硫醇类硫化物与H^+之间的相互作用进行了研究。以2-戊硫醇、环己硫醇和硫酚为模型化合物,模拟计算了各硫醇类硫化物的最高占据轨道(HOMO)以及H^+进攻硫位及不同碳位时所形成中间体的生成热及键长变化,进而讨论H^+的优先进攻位置以及反应中间体的稳定性。结果表明,H^+的进攻位置对形成的中间体的稳定性有很大影响。当H^+进攻硫醇类硫化物中的碳位时,反应中间体的生成热远大于或接近于H^+直接进攻硫位所形成的中间体的生成热;对于反应中间体的生成热同进攻硫位所形成的中间体的生成热相近的碳原子上的质子化反应,其实质与直接进攻硫原子时相一致,并生成硫化氢,这说明H^+将优先进攻硫醇类硫化物中的硫原子。由此可以认为,硫醇类硫化物在固体酸性催化剂的作用下,由于B酸中心的给质子性质,较容易在硫位上发生质子化反应,以生成硫化氢的形式转化脱除。

The protonation of mercaptan sulfides over acidic catalyst was studied by molecular simulation technique.2-pentanethiol,cyclohexanethiol and thiophenol were selected as model compounds of mercaptan sulfide.The highest occupied molecular orbital of model compounds,heat of formation and bond length change of reaction intermediates were calculated by molecular kinetics method and semi-empirical quantum mechanical method.According to the heat of formation and bond length change of intermediates formed by the protonation of mercaptan sulfides at S atom and different carbon atoms,it was found that the stability of intermediate was greatly relative to the position attacked by H~＋,and the advantageous reaction site of protonation occurred at S atom of mercaptan sulfides,and H_2S would be formed.The result showed that mercaptan sulfide had a better protonation over the acidic catalyst,the reaction took place easily at S atom,and the sulfur would be removed by H_2S.