Effect of substitution degree of 2-hydroxypropyl-β-cyclodextrin on the alkaline hydrolysis of cinnamaldehyde to benzaldehyde

The yield of benzaldehyde in the 2-hydroxypropyl-beta-cyclodextrin (2-HP-beta-CD), with a low degree of substitution (DS = 3.9), catalytic system was 70%, which was higher than that of the system with 8.8 DS under the optimised conditions (323 K, 2% NaOH (w/v), cinnamaldehyde: 2-HP-beta-CD = 1:1 (molar ratio)). Due to the structural complementary effects of the host and guest, cyclodextrins (CDs) played the catalysis role in the reaction, which was confirmed by kinetic studies and solubilisation. The characterisation of NMR and fluorescence measurement suggested that the extent of hydroxypropyl substitution affected the cavity structure of the CD molecule. The hydroxypropyl groups at O-2 positions were spatially spread out but restricted, which affected the molecular encapsulation capabilities.