Ball-Milling: A Productive, Economical, and Widely Applicable Method for Condensation of Biomass-Derived Aldehydes and Ketones at Mild Temperatures

For the first time, ball-milling was introduced as an efficient process for the condensation of biomass-derived cyclopentanone using commercial CaO as a catalyst. Compared with traditional magnetic stirring methods ("heat input" methods), ball-milling is an alternative "energy input" method. CaO dosage, rotation speed, and reaction time were investigated for optimal condition screening, and the ball-milling method could achieve a high yield (98.9%) and a high selectivity (99.2%) under lower energy demand conditions at mild temperature (∼40 °C). Moreover, the power hypothetically needed for dimer per mole (E2) of the ball-milling method was comparable or even lower than that for the magnetic stirring method after our assessment. In addition, we also explored the applicability of the ball-milling method for the condensation of other biomass-derived aldehydes and ketones. Competitive yield was obtained using heterogeneous CaO as a catalyst. Due to the intense stirring in ball-milling, the CaO catalyst was mixed uniformly with reactants, and higher surface area was also obtained due to the decrease of the particle size during the ball-milling method, which may also benefit the reaction and increase the catalytic activity. This way would tally with the concept of green chemistry and economic efficiency, which has the potential for industrial applications.