Green synthesis of natural benzaldehyde from cinnamon oil catalyzed by hydroxypropyl-β-cyclodextrin

The efficient synthesis of natural benzaldehyde from natural cinnamon oil catalyzed by 2-hydroxypropyl-β-cyclodextrin (2-HPβ-CD) in water under rather mild conditions has been developed. Various analysis methods, e.g., DSC, UV–vis, 1H NMR, ROESY, and fluorescence measurements had been utilized to demonstrate formation of the 1:1 (molar ratio) complexes between 2-HPβ-CD and cinnamaldehyde. The inclusion equilibrium constant Ka was 928 M−1 at 298 K. The inclusion complex activated the substrate and promoted the reaction selectivity. The yield for benzaldehyde could reach 70% under the optimized conditions (323 K, 5 h, 2% NaOH (w/v), cinnamaldehyde: 2-HPβ-CD=1:1 (molar ratio)). Further investigation on kinetics and solubilization revealed that the binding ability between 2-HPβ-CD and cinnamaldehyde is primarily responsible for the catalytic effects.