Synthesis of Isopulegol Through Cyclisation of Citronellal Using Solid Acid Catalysts: Catalytic Reaction Performance Evaluation and Process Parameters Optimization

Abstract

The cyclisation of citronellal to isopulegol is a significant intermediate stage in the production of menthols. In this research work, the effects of acid treatment on montmorillonite clay have been investigated and used in citronellal cyclisation reactions. Furthermore, the effects of acid treatment and hetero-poly acid impregnation have been determined on the textural and catalytic properties of montmorillonite clay. The designed catalysts were characterized by XRD, N2 sorption, and NH3- TPD techniques. Acid treatment of montmorillonite resulted in the enhancement of surface area and pore volume. The catalytic activity and selectivity parameters were lessened due to the severe leaching of Al ions from tetrahedral crystalline structures (e.g., weakened structure and loss of acidity). Among all prepared materials, the heteropoly acid supported HCl treated montmorillonite catalyst was observed as a more active, stable, and selective catalyst that showed the highest catalytic performance in citronellal cyclisation under optimized process parameters. The catalytic activity and selectivity were enhanced with rising mesoporosity and acidity parameters due to HCl acid treatment and HPA impregnation.

A Green and Efficient Cyclization of Citronellal into Isopulegol: A Guided-Inquiry Organic Chemistry Laboratory Experiment

“…Both mono- and bifunctional catalytic systems were observed in the literature. The cyclization has been successfully carried out with silica-supported catalysts − and clay catalysts, − of interest to the student researcher due to their benign nature, often with organic solvents ,,,, and temperatures ranging from room temperature to 120 °C. ,− Most catalyst preparations included acid-loading of the silica or clay solid catalysts, usually by refluxing or mixing the support with acids and then drying at 60–150 °C for 15–24 h. ,− , Some procedures involved additional calcination. ,,, …”

“…The cyclization has been successfully carried out with silica-supported catalysts 33−36 and clay catalysts, 37−44 of interest to the student researcher due to their benign nature, often with organic solvents 35,36,38,39,42 and temperatures ranging from room temperature to 120 °C. 8,34−36 support with acids and then drying at 60−150 °C for 15−24 h. 35,[37][38][39]42 Some procedures involved additional calcination. 35,38,39,42 Given this foundational research, the student revised the literature search to focus on silica and clay-supported catalysts and greener cyclization reactions.…”

“…8,34−36 support with acids and then drying at 60−150 °C for 15−24 h. 35,[37][38][39]42 Some procedures involved additional calcination. 35,38,39,42 Given this foundational research, the student revised the literature search to focus on silica and clay-supported catalysts and greener cyclization reactions. However, the uses of Reaction conditions: 0.0013 mol of citronellal; 2 mL solvent; catalyst was stirred in the buffer for 15 minutes before adding citronellal; room temperature stirring; characterization by 1 H NMR spectroscopy.…”