Synthesis and Performance of Strained Multicyclic Hydrocarbons as Highly Potential High-Energy-Density Fuels

Abstract

The rapid development of aerospace technology puts forward the urgent needs for fuels with higher energy density and good cryogenic and ignitable properties. Herein, we applied an RCOOZnCH2I-mediated cyclopropanation to synthesize four three-membered cyclic fuels with ca. 100% yield through optimizing the reaction conditions including substituent groups in zinc carbenoids, carbenoid/substrate ratio, and solvents. The fuels show the volumetric heat of combustion to be 3.6–11.7% higher than the currently used fuel JP-10 and low freezing point and viscosity. The advantages of strained fuels with regard to increasing the energy density while maintaining good low-temperature fluid properties are illustrated through comparison with conventional cyclic fuels. Moreover, the strained fuels exhibit low ignition temperature and short ignition delay. This work suggests that the strained fuels are highly promising as advanced high-energy-density fuels.

High-Energy-Density Liquid Spiro-Norbornanes from Methylenenorbornane

“…Moreover, Q v L of 16 is also higher than those of the related hydrocarbons obtained from VNB and containing one or two norbornane moieties (hydrocarbons 17 and 18, Table 2 32 ). The dependence of Q v L on the density was opposite to the same dependence for Q m L (Figure 6b 35 ). Q v L increased quickly with the density of the prepared hydrocarbons, and this relationship was stronger for synthesized strained hydrocarbons compared to conventional fuels.…”

“…Structure of spiro-hydrocarbons studied earlier − and in this work as potential high-energy-density fuels.…”

“…Nevertheless, the highest Q m L values were obtained for hydrocarbons 4 and 8, for which the H/C ratios are the highest among the synthesized cycloalkanes. Interestingly, Q m L values for most of the studied hydrocarbons were higher than that of JP-10 (Figure 6a 35 ). Another feature is the dependence of Q m L values on the density of the synthesized hydrocarbons.…”

“…This is due to a higher optimal H/C ratio and the presence of small strained rings in the case of cyclopropanated hydrocarbons. 35 Therefore, the cyclopropanated norbornanes are more attractive as liquid fuels with enhanced Q m L , I s1/s , and I s2/s values. At the same time, I v depends on the fuel density, and thus compounds 3, 5, 9, and 16 with high densities exhibit higher I v than that of JP-10 and the related norbornanes (Table 3 and Figures S25b and S26).…”

“…Moreover, after the introduction of a certain amount of such motifs into a molecule, the volumetric heat of combustion also ceases to increase. 32 A combination of three-or four-membered cycles with norbornane moiety in one molecule has been found to be a very fruitful strategy for the development of new HED fuels possessing high volumetric heats of combustion, high densities, and good cryogenic properties (e.g., quadricyclane, 33 dicyclopropanated dienes like dicyclopentadiene, 34 norbornadiene-2,5, 34 VNB, 31 or ENB 35 ). A promising development of this strategy is the synthesis of related hydrocarbons with spirocarbon atoms (i.e., spirocycloalkanes).…”