伪质子离子液体中可能的质子传导机制：特定质子传导的概念,The Journal of Physical Chemistry B

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伪质子离子液体中可能的质子传导机制：特定质子传导的概念
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2019-07-16 , DOI: 10.1021/acs.jpcb.9b03185
Hikari Watanabe ₁ , Tatsuya Umecky ₂ , Nana Arai ₁ , Andreas Nazet ₃ , Toshiyuki Takamuku ₂ , Kenneth R. Harris ₄ , Yasuo Kameda ₅ , Richard Buchner ₃ , Yasuhiro Umebayashi ₁

Affiliation

在先前的工作中，我们发现伪质子离子液体乙酸N-甲基咪唑鎓盐[C ₁ HIm] [OAc]或[Hmim] [OAc]主要由电中性分子物质N-甲基咪唑C _1组成。即使混合物具有显着的离子电导率，Im和乙酸AcOH也是如此。通过使用同位素置换拉曼光谱（ISRS）和脉冲场梯度（PFG）NMR自扩散测量，对该系统进行了重新研究。获得的ISRS和PFG-NMR结果充分证实了我们先前的发现。特别地，在实验不确定性范围内，AcOH中羟基氢原子的自扩散系数与甲基氢原子的自扩散系数相同，这与极少的电离一致。因此，假设类似于酸水溶液的格罗特斯（Grotthuss）机理的质子传导机理是所观察到的电导率的原因。耐纬度系数（r _ij）是根据传输性质计算得出的，并且类似离子相互作用获得的负值与假离子液体描述相符，也就是说，混合物确实是一种非常弱的电解质。还使用高能X射线总散射实验，分子动力学模拟和介电弛豫谱对混合物的结构和旋转动力学进行了研究。基于活化能的比较和公知的线性动力学和质子自迁移反应的热力学之间自由能关系，我们提出了[C ₁他] [OAC]一个GROTTHUS型质子传导机制涉及快速的AcOH / ACO ^-旋转如决定性的一步。

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Possible Proton Conduction Mechanism in Pseudo-Protic Ionic Liquids: A Concept of Specific Proton Conduction

In a previous work, we have found that the pseudo-protic ionic liquid N-methylimidazolium acetate, [C₁HIm][OAc] or [Hmim][OAc], mainly consists of the electrically neutral molecular species N-methylimidazole, C₁Im, and acetic acid, AcOH, even though the mixture has significant ionic conductivity. This system was revisited by employing isotopic substitution Raman spectroscopy (ISRS) and pulsed field gradient (PFG) NMR self-diffusion measurements. The ISRS and PFG-NMR results obtained fully confirm our earlier findings. In particular, the self-diffusion coefficient of the hydroxyl hydrogen atom in AcOH is identical to that of the methyl hydrogen atoms within the experimental uncertainty, consistent with very little ionization. Therefore, a proton conduction mechanism similar to the Grotthuss mechanism for aqueous acid solutions is postulated to be responsible for the observed electrical conductivity. Laity resistance coefficients (r_ij) are calculated from the transport properties, and the negative values obtained for the like-ion interactions are consistent with the pseudo-ionic liquid description, that is, the mixture is indeed a very weak electrolyte. The structure and rotational dynamics of the mixture were also investigated using high-energy X-ray total scattering experiments, molecular dynamics simulations, and dielectric relaxation spectroscopy. Based on a comparison of activation energies and the well-known linear free energy relationship between the kinetics and thermodynamics of autoprotolysis, we propose for [C₁HIm][OAc] a Grotthus-type proton conduction mechanism involving fast AcOH/AcO⁻ rotation as a decisive step.

更新日期：2019-07-17

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