This study re-examines the widely touted thermostability of deep eutectic solvents (DESs) using novel stability indicators. Thermostability is critical for the application of thermochemical reactions. Type II and Type III DESs receive the most attention due to their versatility, with Type II DES demonstrating superior thermostability, often remaining stable at temperatures up to 200 °C. Of the Type II DES, ChCl:CoCl₂·6H₂O was the most thermostable at 250 °C, followed by ChCl:MgCl₂·6H₂O and ChCl:ZnCl₂·2H₂O that showed moderate stability at 200 °C. Type III DESs typically exhibited thermolability at 150 °C, although ChCl:Lac, ChCl:Gly, and ChCl:Ur were capable of retaining their liquid state even after heating. It was through simple visual observation that out of the 10 DESs studied, we were able to exclude DESs that were no longer liquid after heating. Visual observation is an important complement to TGA and DSC, as most of the DESs we examined were previously reported to be stable within the 150 to 200 °C range. The other part of our study is to quantitatively measure changes to the molar ratio post-heat using GC-FID and to identify possible decomposition products using GC-MS. Determining the molar ratio is crucial, as it facilitates the molar adjustment of DES for reuse, an area that presently receives less attention.

中文翻译：

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用于热化学反应的热稳定低共熔溶剂：新型稳定性指标

这项研究使用新颖的稳定性指标重新检验了广受好评的低共熔溶剂 (DES) 的热稳定性。热稳定性对于热化学反应的应用至关重要。 II 型和 III 型 DES 由于其多功能性而受到最多关注，其中 II 型 DES 表现出卓越的热稳定性，通常在高达 200 °C 的温度下保持稳定。在 II 型 DES 中，ChCl:CoCl ₂ ·6H ₂ O 在 250 °C 时最稳定，其次是 ChCl:MgCl ₂ ·6H ₂ O 和 ChCl:ZnCl ₂ ·2H ₂ O，在 200 °C 时表现出中等稳定性。尽管 ChCl:Lac、ChCl:Gly 和 ChCl:Ur 即使在加热后也能够保持液态，但 III 型 DES 通常在 150 °C 下表现出热稳定性。通过简单的目视观察，我们在研究的 10 种 DES 中排除了加热后不再呈液态的 DES。目视观察是 TGA 和 DSC 的重要补充，因为我们检查的大多数 DES 此前均报告在 150 至 200 °C 范围内稳定。我们研究的另一部分是使用 GC-FID 定量测量加热后摩尔比的变化，并使用 GC-MS 识别可能的分解产物。确定摩尔比至关重要，因为它有助于调整 DES 的摩尔比以供重复使用，而这一领域目前受到的关注较少。