在瓦克尔型氧化过程中,从-OH功能群中消除β-化物的难以获得性
John A Keith1, Jonas Oxgaard, William A Goddard
1Materials and Process Simulation Center, Beckman Institute (139-74), California Institute of Technology, Pasadena, California 91125, USA.
量子力学计算揭示了一个新的,更能量的可行途径,用于酒精脱在瓦克尔过程中. 这种还原性淘汰机制比以前假定的β-化物淘汰要快得多.
科学领域:
- 计算化学计算化学
- 催化剂是一种催化剂.
- 有机化学 有机化学
背景情况:
- 瓦克尔工艺是将基因转化为基因的重要工业方法.
- 酒精脱的机制,一个相关的转化,对于理解催化循环至关重要.
- 目前的理解通常依赖于β-化物消除 (BHE) 作为关键产品形成步骤.
研究的目的:
- 调查与瓦克尔工艺相关的酒精脱的不同反应机制的能量可行性.
- 用量子力学来比较拟议中的路径的激活障碍.
- 评估水在这些转变中的催化作用.
主要方法:
- 使用B3LYP和MPW1K函数的密度函数理论 (DFT) 计算.
- 对拟议反应路径的过渡状态和激活度的分析.
- 在计算模型中将水作为催化物种纳入.
主要成果:
- 通常接受的β-化物清除 (BHE) 途径具有高激活度 (36.2 kcal/mol).
- 一种替代的五体减少性消除 (RE) 途径表现出明显较低的激活 (18.8 kcal/mol).
- 水催化降低了这两种途径的激活障碍,但不会改变它们相对的能量优势,有利于再生能源.
结论:
- 在这种情况下,还原性消除 (RE) 途径在能量方面比BHE对酒精脱更有利.
- 假设BHE机制可能需要重新评估,特别是当β原子不是基时.
- 水起着催化作用,但基本的机械偏好仍然存在.
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