Thermal decomposition of phosphonium salicylate and phosphonium benzoate ionic liquids
Thermal decomposition of phosphonium salicylate and phosphonium benzoate ionic liquids
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DOI：
10.1016/j.molliq.2022.118700
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发表时间：
2022-02
影响因子：
6
通讯作者：
A. Khajeh;M. Rahman;T. Liu;Pawan Panwar;P. Menezes;A. Martini
中科院分区：
文献类型：
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作者：
A. Khajeh;M. Rahman;T. Liu;Pawan Panwar;P. Menezes;A. Martini
离子液体的热稳定性对于它们在各种应用中的应用是很重要的。采用反应分子动力学模拟和热重分析方法对水杨酸膦和苯甲酸膦的热分解机理进行了研究。在不同升温速率下进行的实验表明，在等温高温条件下，水杨酸膦和苯甲酸膦的分解温度相当，但苯甲酸膦的稳定性不如水杨酸膦。反应分子动力学模拟表明，与水杨酸酯相比，苯甲酸酯的热稳定性较低。模拟结果还表明，阳离子链长对热稳定性影响不大。模拟结果表明，水杨酸膦和苯甲酸膦的热分解都通过许多不同的途径进行，这些途径大致可分为质子转移反应、缔合反应和解离反应。与水杨酸膦相比，苯甲酸膦经历了更多的这些反应，并且在每一类反应中都表现出了广泛的反应途径。人们探索了多种可能的机制来解释这种差异，结果发现，主导因素是水杨酸盐中羟基的存在，它影响了氧原子参与质子转移反应的能力，这是所有后续反应的第一步。这些发现表明，即使是阴离子化学中的细微差异也可能显著影响离子液体的热稳定性，这为通过分子设计调整这些性质提供了途径。
The thermal stability of ionic liquids is important for their use in a variety of applications. Here, reactive molecular dynamics simulations and thermogravimetric analyses were used to explore the thermal decomposition mechanisms of phosphonium salicylate and phosphonium benzoate. Experiments performed at different heating rates indicated that the decomposition temperatures of phosphonium salicylate and phosphonium benzoate were comparable, but phosphonium benzoate was less stable than phosphonium salicylate under isothermal high temperature conditions. The lower thermal stability of the benzoate compared to the salicylate was reproduced in reactive molecular dynamics simulations. The simulations also showed that cation chain length had little effect on thermal stability. The simulations revealed that thermal decomposition for both phosphonium salicylate and phosphonium benzoate occurred through many different pathways that could be broadly categorized as proton-transfer, association, and dissociation reactions. The phosphonium benzoate underwent more of these reactions and exhibited a wide range of reaction pathways in each category than the phosphonium salicylate. Multiple possible mechanisms were explored to explain this difference and it was found that the dominant factor was the presence of the hydroxyl group in salicylate that affects the ability of oxygen atoms to take part in proton-transfer reactions that are the first step of all subsequent reactions. These findings demonstrate that even subtle differences in anion chemistry may significantly affect the thermal stability of ionic liquids, suggesting avenues for tuning these properties through molecular design.