Heterogeneous Catalytic Conversion of Citronellal into Isopulegol and Menthol: Literature Review

Abstract

The conversion of citronellal into isopulegol is a key route in the production of a number of important chemicals. In the perspective of green conversion, the use of a heterogeneous catalyst is superior due to its ease in separation and reusability, so it facilitates a highly economical conversion. In this review, we examine the use of some transition metals in cyclization reactions, which are suitable for citronellal conversion into isopulegol, and consider the potential progress in clay-based catalysts. The structure of clay which potentially provides the porosity by modification and supporting active metal is proposed to be the low-cost catalyst for the conversion. As other mechanism by porous materials-supported metal, the porosity of clay support contributes to conduct thesurface adsorption mechanism and the Broensted acid supply, meanwhile the metal acts as active site for cyclization, and in the one-pot conversion into menthol, as both cyclization and hydrogenation.

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

“…Moreover, the citronella essential oil is rich in citronellal and exhibits insecticidal properties. Isopulegol is commercially important as a chemical precursor for menthol and use in the preparation of fragrances and food flavourings; additionally, isopulegol has been reported to have anti-inflammatory, antioxidant, antitumor, antihyperlipidemic, and analgesic properties . The cyclization of citronellal to isopulegol provides an ideal system to explore green chemistry in the context of an undergraduate research project.…”

“…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 dry lab and prelab assignment walked students through tasks 1–4; the wet lab covered task 5, and students completed task 6 after the laboratory experience. As recommended in previous literature, , discussion between students was highly encouraged and required at numerous steps. Furthermore, the student researcher and faculty supervisor were both present in laboratories to provide clarification.…”

The Increase in Kaffir Lime Leaf Production Due to Gibberellin Is Diminished by Pruning

“…Aside from essential oils, the main economic organ of kaffir lime cultivation is its aromatic leaves [3], with the major metabolites being citronellal [10]. Citronellal-rich leaves display various beneficial properties, i.e., an intense lemony scent [12,13], antifungal [14,15], antibacterial [16], anti-inflammatory [17], and mosquito-repellent [18][19][20], and they are the raw material for synthesizing citronellol, isopulegol, and menthol [21][22][23]. Numerous beneficial properties of kaffir lime leaves make them a promising commodity for the global growing market.…”