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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Carbon dioxide in 1-butyl-3-methylimidazolium acetate. I. Unusual solubility investigated by Raman spectroscopy and DFT calculations
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Carbon dioxide in 1-butyl-3-methylimidazolium acetate. I. Unusual solubility investigated by Raman spectroscopy and DFT calculations

机译：乙酸1-丁基-3-甲基咪唑鎓盐中的二氧化碳。 I.通过拉曼光谱和DFT计算研究异常溶解度

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The unusual solubility of carbon dioxide in 1-butyl-3-methylimidazolium acetate (Bmim Ac) has been studied by Raman spectroscopy and DFT calculations. It is shown that the solubility results from the existence of two distinct solvation regimes. In the first one (CO _2 mole fraction ≥ 0.35), the usual Fermi dyad is not observed, a fact never reported before for binary mixtures with organic liquids or ionic liquids (IL). Strong experimental evidence complemented by effective DFT modeling shows that this regime is dominated by a chemical reaction leading to the carboxylation of the imidazolium ring accompanied by acetic acid formation. The reactive scheme proposed involves two concerted mechanisms, which are a proton exchange process between the imidazolium cation and the acetate anion and the carboxylation process itself initiated from the formation of "transient" CO _2-1-butyl-3-methylimidazole 2-ylidene carbene species. In that sense, CO _2 triggers the carboxylation reaction. Moreover, this dynamic picture circumvents consideration of a long-lived carbene formation in dense phase. The second regime is characterized by the detection of the CO _2 Fermi dyad showing that the carboxylation reaction has been strongly moderated. This finding has been interpreted as due to the interaction of the acetic acid molecules with the COO group of acetate anions involved in monodentate forms with the cation. The observation of the Fermi doublet allows us to infer that CO _2 essentially preserves its linear geometry and that the nature and strength of the interactions with its environment should be comparable to those existing in organic liquids and other IL as well. These results have been supported by DFT calculations showing that the CO _2 molecule interacts with energetically equivalent coexisting structures and that its geometry departs only slightly from the linearity. Finally, we find that the CO _2 solvation in Bmim Ac and 1-butyl-3-methylimidazolium trifluoroacetate (Bmim TFA) cannot be straightforwardly compared neither in the first regime due to the existence of a chemical reaction nor in the second regime because CO _2 interacts with a variety of environments not only consisting of ions pairs like in Bmim TFA but also with carboxylate and acetic acid molecule.
机译：通过拉曼光谱和DFT计算研究了二氧化碳在乙酸1-丁基-3-甲基咪唑鎓盐（Bmim Ac）中的异常溶解度。结果表明，溶解度是由于存在两种不同的溶剂化方案而产生的。在第一个（CO _2摩尔分数≥0.35）中，未观察到通常的费米二元组，以前从未与有机液体或离子液体（IL）形成二元混合物的报道。强有力的实验证据与有效的DFT建模相辅相成，表明该方案主要由化学反应主导，该化学反应导致咪唑环的羧化反应伴随着乙酸的形成。提出的反应方案涉及两个协同的机理，即咪唑阳离子与乙酸根阴离子之间的质子交换过程和羧化过程本身是由“瞬态” CO _2-1-丁基-3-甲基咪唑2-亚烷基卡宾的形成引发的。种类。从这个意义上讲，CO _2触发了羧化反应。此外，该动态图规避了稠密相中长寿命卡宾形成的考虑。第二种方案的特征在于检测到CO _2 Fermi dyad，表明羧化反应已被强烈调节。该发现被解释为是由于乙酸分子与以单齿形式与阳离子结合的乙酸根阴离子的COO基团的相互作用。通过费米二重峰的观察，我们可以推断出CO _2基本上保留了其线性几何形状，并且与其环境相互作用的性质和强度也应与有机液体和其他IL中的存在相当。这些结果得到了DFT计算的支持，该计算表明CO _2分子与能量等效的共存结构相互作用，并且其几何形状与线性仅略有偏离。最后，我们发现由于化学反应的存在，在第一方案中和第二方案中都无法直接比较Bmim Ac和1-丁基-3-甲基咪唑三氟乙酸盐（Bmim TFA）中的CO _2溶剂化，因为CO _2与各种环境相互作用，不仅包括Bmim TFA中的离子对，而且还与羧酸盐和乙酸分子相互作用。

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