(684d) Acid-Catalyzed Rearrangement of Tetrahydrotricyclopentadiene: Synthesis of High-Density Alkyl-Diamondoid Fuel

Since aerospace vehicles like missiles and spacecrafts are always volume-limited, often operated in cold climates and at high altitudes, some features of the fuels such as high density, large volumetric energy content, low freezing point, and low viscosity become considerable important. In the development of fuels for aerospace vehicles, synthesis of alkyl-diamondoid fuels has fascinated scientists for many years. Here we reported a facile route to synthesize alkyl-diamondoids (methyl-1,2-tetramethyleneadamantane is the primary product) via solvent-free rearrangement of tetrahydrotricyclopentadiene simply catalyzed by acid. Different from previous ionic liquid catalysis with tremendous dosage, acid catalysis (simply use AlCl₃) makes the synthesis of alkyl-diamondoid fuels more facile and feasible. The two-step catalysis and solvent-free condition are favorable to the reaction towards alkyl-diamondoids, and the supreme content of alkyl-diamondoids in the liquid phase can reach 85.6% with carbon yield of alkyl-diamondoids of 60.5% catalyzed by low dosage of catalyst (10.7wt%). The reaction kinetics of rearrangement has been investigated, and the reaction rate constants and apparent activation energies were calculated based on the experimental kinetic data. And the rearrangement pathway of endo-THTCPD to alkyl-diamondoids is easier to take place while exo-THTCPD to alkyl-diamondoids is harder to occur. The resultant diamondoid-based product shows excellent low-temperature performance (freezing point less than -70°C) and a higher energy content (0.976 g/mL, 40.6 MJ/L) than reported diamondoids and widely used JP-10 fuel, thus is superior as a high-energy-density fuel.