Synthesis and characterization of high-density biosynthetic fuels from myrtenal

Apopinene was synthesized from myrtenal by catalytic decarbonylation followed by either hydrogenation to generate dihydroapopinene or Simmons-Smith cyclopropanation to generate exo-(1R,2R)-7,7-dimethyltricyclo[4.1.1.02,4]octane (cyclopropanated apopinene, CPA). Key fuel properties of apopinene and the two derivative fuels were evaluated including density, heat of combustion, and low temperature viscosity. CPA exhibited a density of 0.918 g mL−1 and a volumetric net heat of combustion (NHOC) 20 % higher than the lower limit for conventional jet fuel. This exceptional NHOC is a result of the high density of the tricyclic compound and the ring strain of the bridging cyclobutane and fused cyclopropane groups. Dihydroapopinene exhibited a high freezing point that will limit its applications as a jet fuel blendstock. In contrast, no freezing point down to −80 °C was observed for CPA via differential scanning calorimetry (DSC). In addition, CPA exhibited a moderate kinematic viscosity of 10.11 mm2 s−1 at −20 °C and 22.76 mm2 s−1 at −40 °C. This work demonstrates that fuels with both high energy densities and excellent low temperature properties can be generated from bio-based substrates through cyclopropanation reactions.