GSM Institut des Sciences Moléculaires, CNRS (UMR 5255), Université Bordeaux I, 351, Cours de la Libération, 33405 Talence Cedex, France.
J Phys Chem A. 2012 May 24;116(20):4890-901. doi: 10.1021/jp211689z. Epub 2012 May 10.
The solvation of CO(2) in 1-butyl-3-methylimidazolium acetate (Bmim Ac) has been investigated by (1)H, (13)C, and (15)N NMR spectroscopy at low CO(2) molar fraction (mf) (x(CO(2)) ca. 0.27) corresponding to the reactive regime described in part 1 of this study. It is shown that a carboxylation reaction occurs between CO(2) and Bmim Ac, leading to the formation of a non-negligible amount (~16%) of 1-butyl-3-methylimidazolium-2-carboxylate. It is also found that acetic acid molecules are produced during this reaction and tend to form with elapsed time stable cyclic dimers existing in pure acid. A further series of experiments has been dedicated to characterize the influence of water traces on the carboxylation reaction. It is found that water, even at high ratio (0.15 mf), does not hamper the formation of the carboxylate species but lead to the formation of byproduct involving CO(2). The evolution with temperature of the resonance lines associated with the products of the reactions confirms that they have a different origin. The main byproduct has been assigned to bicarbonate. All these results confirm the existence of a reactive regime in the CO(2)-Bmim Ac system but different from that reported in the literature on the formation of a reversible molecular complex possibly accompanied by a minor chemical reaction. Finally, the reactive scheme interpreting the carboxylation reaction and the formation of acetic acid proposed in the literature is discussed. We found that the triggering of the carboxylation reaction is necessarily connected with the introduction of carbon dioxide in the IL. We argue that a more refined scheme is still needed to understand in details the different steps of the chemical reaction in the dense phase.
CO(2)在 1-丁基-3-甲基咪唑醋酸盐（Bmim Ac）中的溶解作用通过（1）H、（13）C 和（15）N NMR 光谱在低 CO(2)摩尔分数（x(CO(2))约 0.27）下进行了研究，该摩尔分数对应于本研究第 1 部分中描述的反应性区域。结果表明，CO(2)与 Bmim Ac 之间发生了羧化反应，导致形成了相当数量（约 16%）的 1-丁基-3-甲基咪唑-2-羧酸酯。还发现，在该反应过程中产生了乙酸分子，并且随着时间的推移，这些分子倾向于形成存在于纯酸中的稳定的环状二聚体。进一步的一系列实验专门用于表征痕量水对羧化反应的影响。结果发现，即使在高比例（0.15 mf）下，水也不会阻碍羧酸盐的形成，但会导致涉及 CO(2)的副产物的形成。与反应产物相关的共振线随温度的演变证实了它们具有不同的来源。主要副产物已被分配到碳酸氢盐。所有这些结果证实了 CO(2)-Bmim Ac 体系中存在反应性区域，但与文献中报道的形成可逆分子配合物的反应性区域不同，可能伴随着少量化学反应。最后，讨论了文献中提出的解释羧化反应和乙酸形成的反应方案。我们发现，羧化反应的触发必然与二氧化碳在 IL 中的引入有关。我们认为，仍然需要更精细的方案来详细了解密相中的化学反应的不同步骤。
