Effect of structure and acidity of acid modified clay materials on synthesis of octahydro-2H-chromen-4-ol from vanillin and isopulegol

• Montmorillonite, kaolin and, metakaolin were modified by 0.5 mol/dm3 HCl.
• The acid-activated clays were used as catalyst for the Prins cyclization reaction.
• Activity of the materials depended on their structural and textural properties.
• Activity of the materials depends on their acid–base properties.

The Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2H-chromen-4-ol was studied in the presence of natural layered aluminosilicates modified by 0.5 mol/dm3 HCl, such as montmorillonite, kaolin, and metakaolin obtained by the calcination of kaolin at 650 °C. According to infrared spectroscopy using pyridine as probe molecule, the amount and strength of Brønsted acid sites depend on the type of clay and decrease in the following order HCl-montmorillonite > HCl-kaolin > HCl-metakaolin. The difference in Brønsted acidity and textural properties of clays affected the reaction rate and the selectivity towards octahydro-2H-chromen-4-ol.

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