Selective isomerization of & alpha;-pinene oxide to trans-carveol by task-specific ionic liquids: mechanistic insights via physicochemical studies

A waste-free chemical process involving comparatively greener solvents with recyclability is one of the desired goals of sustainable development. In this regard, task-specific ionic liquids (TSILs) emerge as groundbreaking solution, acting as both eco-friendly catalysts and reusable solvents in numerous industrial reactions. Herein, we exemplify the use of a family of phosphorus anion-based ionic liquids (ILs) having alkyl ammonium, pyridinium or lutidinium cations for successful isomerization of & alpha;-pinene oxide (APO) to industrially applicable trans-carveol with 74% selectivity and 99% conversion. This is the first time that we achieved isomerization of & alpha;-pinene oxide (APO) to trans-carveol with a very high selectivity as compared to campholeneic aldehyde in ionic liquid media. The mechanism for this conversion is well correlated with the physical properties (conductivity, density, molecular volume, standard entropy, and lattice energy) of the synthesized ionic liquids. The derived parameters from primary physical properties and Kamlet-Taft parameters provide strong support for greater reactivity and selectivity. The synthesized TSILs are chemically stable, easy to separate, and reusable for multiple runs without compromising the conversion of PO. The designed process fulfils the green metrics criteria by having 100% atom economy with an E-factor of 1.

Automated summary

A waste-free chemical process using greener solvents and task-specific ionic liquids (TSILs) as catalysts and reusable solvents is proposed. The isomerization of & alpha;-pinene oxide (APO) to industrially applicable trans-carveol with high selectivity and conversion is achieved using a family of phosphorus anion-based ionic liquids (ILs). The synthesized TSILs show good chemical stability, separability, and reusability.