Tandem Reactions for the Synthesis of High-Density Polycyclic Biofuels with a Double/Triple Hexane Ring

Synthesizing high-density fuels from non-food biomass is of great interest in the field of biomass conversion because they can increase the loading capability and travel distance of vehicles and aircraft as compared to conventional low-density biofuels (<0.78 g/cm³). In this work, we reported a new and facile strategy for the synthesis of high-density biofuels with polycyclic structures from lignocellulose-derived 5,5-dimethyl-1,3-cyclohexanedione and different aldehyde derivatives in two steps under mild reaction conditions, including a developed tandem reaction and a hydrodeoxygenation reaction. Theoretical approaches were used to estimate the fuel properties, which indicate that the obtained biofuels have a high density of 0.78-0.88 g/cm³ and high net heat of combustion (NHOC) values of 44.0-46.0 MJ/kg. A representative biofuel 3c was measured to have a high NHOC of 43.4 MJ/kg, which matched well with the calculated NHOC value of 44.4 MJ/kg, indicating the high accuracy of the theoretical approaches. This work is expected to provide a green strategy for the synthesis of polycyclic high-density biofuels with platform chemicals.