Synthesis of advanced fuel with density higher than 1 g/mL by photoinduced [2 + 2] cycloaddition of norbornene
High-energy–density (HED) fuels have attracted extensive attention for volume-fixed aerospace vehicles because they can provide more propulsion energy to increase the payload and range of aerospace vehicles. Herein, we report a route for synthesis of HED fuel, pentacyclo[8.2.1.1 4,7 .0 2,9 .0 3,8 ]tetradecane (PCTD) with strained structure, by photoinduced intermolecular [2 + 2] cycloaddition of norbornene (NBE). The triplet quenching and phosphorescence quenching results indicate that NBE cycloaddition is conducted through the photosensitized processes containing triplet–triplet energy transfer, cyclization and relaxation. The reaction conditions are optimized to obtain the high photocatalytic activity, with the NBE conversion and PCTD selectivity reaching 78.7% and 94.4%, respectively. Moreover, a kinetic model is proposed with the reaction rate equation being correlated with the incident light flux, with the pseudo reaction kinetics parameters and reaction rate equations obtained. Importantly, PCTD shows high density of 1.024 g/mL and high volumetric net heat of combustion of 42.98 MJ/L, much higher than those of JP-10. In addition, blending with JP-10 or QC can significantly improve cryogenic properties of blended fuels, which is very promising for the practical application.
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