Synthesis of biofuel precursors from benzaldehyde and cyclopentanone via aldehyde–ketone condensation in a deep eutectic solvent system

Production of biofuel precursors from biomass-derived platform compounds (BDPC) has a profound influence on biofuel industries. Herein, an efficient catalytic system composed of the deep eutectic solvent (DES, i.e., ChCl/Fa) and SnCl(4) (ChCl/Fa–SnCl(4)) was developed to produce biofuel precursors (C12 and C19) through aldehyde–ketone (A–K) condensation of benzaldehyde (BD) and cyclopentanone (CPO). ChCl/Fa–SnCl(4) exhibited the prospective catalytic performance and given the high selectivity (S(C12) = 49.20%, S(C19) = 15.20%) and total yield (Y(C12+C19) = 64.37%) of C12 and C19, as well as 99.96% BD conversion under the optimized conditions (BD : CPO molar ratio of 1 : 6, ChCl : Fa molar ratio of 1 : 12, 4 mmol SnCl(4), 80 °C for 120 min). Subsequently, the C12 and C19 precursors were successfully applied to generate cyclic alkanes (C(12)H(14) and C(19)H(18)) by hydrodeoxygenation with selectivity of 37.61% and 24.10%, respectively. Finally, the potential catalytic mechanism was explored by density functional theory (DFT) calculations. The results unveiled that the formation of a stable structure for the ChCl/Fa–SnCl(4) system was ascribed to the viable interactions among ChCl, Fa and SnCl(4) by coordination bonds, electrostatic interactions and H-bonds, which decreased reaction energy barriers and drove the condensation of BD and CPO. In this case, the catalytic reactions between BD and CPO were enhanced to promote the synthesis of C12 and C19. This work provides a novel strategy for the applicability of different BDPC to synthesize fuel precursors for the development of liquid biofuels.