Role of solvents in fine-tuning the selectivity of geraniol transformation using 20% FeCl3/MCM-41

Abstract

The nature-inspired selective synthesis of linalool and the role of solvents in the selectivities of the products linalool, digeranyl ether (DGE) and geranyl linalyl ether (GLE) using a 20% FeCl₃/MCM-41-supported solid acid catalyst are reported in this research work. The textural and microscopic properties of the catalyst contributing to its acidity and stability were revealed using SAXRD, WAXRD, PyIR, TEM and XPS studies, which were further exploited for the transformation of geraniol into rearranged and etherification products. In this work, 100% selectivity for linalool was achieved in only petroleum ether owing to the Brønsted acidity of the catalyst, which was further established by the catalyst masking studies with 2,6-lutidine. The Lewis as well as Brønsted acidity of the catalyst in polar aprotic DCM solvents accounts for product distribution to give 76% conversion and linalool (37%), DGE (35%) and GLE (18%) selectivities. The meticulous and detailed optimization studies contributed in condensing the accurate quantification of the reaction conditions and suggested the role of the Lewis and Brønsted acidity of catalysts in deciphering the plausible mechanism. The sustainability of the 20% FeCl₃/MCM-41 catalyst was well established by confirming the speciation of Fe(III) by XPS after the recycling studies.