Ionic Liquid-Assisted Extraction of Essential Oils from Thujopsis dolobrata (Hiba)

Aomori hiba (Thujopsis dolobrata) has been used as a building material for centuries because of the wood's resistance against fungi and termites. In addition, the essential oil of hiba wood has a relaxing woody fragrance and antifungal properties and is composed mainly of (-)-thujopsene, cedrol, and hinokitiol. Steam distillation is the main industrial method for obtaining the oil but requires large amounts of water and heating energy. The present study describes the use of a cellulose-dissolving [C₂mim][(MeO)(H)PO₂] ionic liquid (IL) for efficient extraction of hiba oil. As a control method, organic solvent extraction using either hexane, Et₂O, or EtOAc was conducted at 80 °C for 1 h. The method developed in this study using an IL was conducted at the same temperature and time as the control method and relied on partial dissolution of the wood using the IL before partitioning the hiba oil into the organic solvent for analysis. Quantitative analysis was performed using gas chromatography-mass spectrometry in selected ion-monitoring mode. The results showed that extraction using the [C₂mim][(MeO)(H)PO₂] IL/hexane biphasic system improved the yields of (-)-thujopsene, cedrol 1.2- and 2.3-fold, when compared with the control method. Furthermore, extraction at a lower temperature (30 °C) did not significantly change the yield. The IL could be recovered with high purity, while the cellulose-rich material and lignin were regenerated. This study demonstrates the ability to effectively extract wood essential oil more quickly and under milder conditions than the conventional method, with subsequent separation and regeneration of wood biopolymers using an IL.