高密度高热安定烷基金刚烃燃料的合成及性质研究进展

烷基金刚烃具有高密度和高热安定性等特点,可为航空航天飞行器提供充足的推进能量和冷却能力。综述了烷基金刚烃燃料的合成进展,包括多环烷烃重排反应和金刚烷基化合物烷基化反应。分析了重排反应受热力学控制的特性,结合量子化学计算与实验产物分布推测重排反应路径;讨论了以金刚烷基化合物为原料烷基化反应具有区域选择性,能够实现定向合成指定烷基结构(甲基、乙基、丙基、丁基等)的金刚烃。同时,总结了烷基金刚烃燃料性质,归纳了针对烷基金刚烃燃料热安定性的评价方法和结果,分析了构效关系。其中,烷基金刚烃的密度和分子结构的紧凑程度有关,取代烷基链越长,密度越低,黏度越大;烷基金刚烃碳环数越多,密度越大。燃料的冰点和分子结构对称性有关,对称度越低,冰点越低。碳氢燃料热安定性主要由分子结构中包含的碳原子的种类及数量决定,其中各种碳原子稳定性顺序为季碳原子>伯碳原子>仲碳原子>叔碳原子。因此,未来有望采用具有区域选择性的高效合成方法,将烷基定向取代于金刚烃母体的叔碳原子上,实现从叔碳原子到季碳原子的转变,提升热安定性的同时保持烷基金刚烃较高的密度,这为未来定向高通量合成高密度、高热安定烷基金刚烃燃料提供了新的思路。

Progress on Synthesis and Performance of High-Density and High-Thermal-Stability Alkyl Diamondoid Fuels

High-density and high-thermal-stability alkyl diamondoid fuels have drawn tremendous attention since they can provide more propulsion energy and remove excess heat for aerospace vehicles. Recent progress on synthesis of alkyl diamondoid fuels via rearrangement and alkylation is summarized in this review. Proposed rearrangement pathway is put forward by density functional theory calculation and reaction results. Also, regioselective synthesis of alkyl diamondoids with specific alkyl group (methyl, ethyl, propyl, butyl) is conducted via alkylation of adamantane derivatives. The performance of alkyl diamondoid fuels is highlighted including density, low-temperature performance and especially thermal stability, and correlated with the hydrocarbon structure. The compact structure with short alkyl substituents and more rings of carbon leads to a high density, while the low-temperature performance is dependent on the symmetry of molecular structure. The thermal stability is mainly related to the type of carbon contained in the molecule structure, in the order of quaternary carbon > primary carbon > secondary carbon > tertiary carbon. Through the regioselective and high throughput synthesis method which is expected to be applied in the future, the alkyl group can be orientatedly substituted on the tertiary carbon atom of the adamantane core, and then converted to the quaternary carbon atom, improving thermal stability while maintaining higher density of alky diamondoid.