Acetalization of carbonyl compounds catalyzed by acidic ionic liquid immobilized on silica gel

Imidazolium-silica heterogeneous catalyst (SG-[(CH2)3SO3H-HIM]HSO4) was prepared by immobilization of acidic ionic liquid 1-(propyl-3-sulfonate) imidazolium hydrosulfate ([(CH2)3SO3H-HIM]HSO4) on silica–gel using tetraethoxysilane (TEOS) as silica source in this study. The properties of the samples were characterized by FT-IR, SEM and TG/DSC. The results suggested that [(CH2)3SO3H-HIM]HSO4 had been successfully immobilized on the surface of silica–gel and the immobilized ionic liquid catalyst SG-[(CH2)3SO3H-HIM]HSO4 had good thermal stability. The original smooth surface of silica–gel was covered with [(CH2)3SO3H-HIM]HSO4 and a rough surface of SG-[(CH2)3SO3H-HIM]HSO4 was formed, but the size of particles had no obvious change. Moreover, SG-[(CH2)3SO3H-HIM]HSO4 exhibited high catalytic activity for a series of acetalization and could be recovered easily. After reused for 10 times in the synthesis of benzaldehyde ethanediol acetal, the catalyst could still give satisfactory catalytic activity.

The original smooth surface of silica–gel was covered with [(CH2)3SO3H-HIM]HSO4 resulting in a rough surface of SG-[(CH2)3SO3H-HIM]HSO4, but the size of particles had no obvious change. The whole and magnified SEM images of silica–gel (A and B), and SG-[(CH2)3SO3H-HIM]HSO4 (C and D).Figure optionsDownload high-quality image (190 K)Download as PowerPoint slideHighlights
► Immobilized [(CH2)3SO3H-HIM]HSO4 prepared by using TEOS as silica source was prepared.
► SG-[(CH2)3SO3H-HIM]HSO4 exhibited high catalytic activity for acetalization.
► SG-[(CH2)3SO3H-HIM]HSO4 could be recycled easily and exhibited excellent reusability.