Abstract
The essential oils of hinoki (Chamaecyparis obtusa) leaves have anti-bacterial, anti-fungal, and relaxation properties that are likely associated with the major components such as sabinene, α-terpinyl acetate, limonene, elemol, myrcene, and hibaene. The present study describes the use of a cellulose-dissolving ionic liquid (IL) [C2mim][(MeO)(H)PO2] and low-toxicity solvents called betaine-based deep eutectic solvents (DESs) for the efficient extraction of hinoki essential oils. As a control method, organic solvent extraction was performed using either hexane, ethyl acetate (EtOAc), or acetone at 30 °C for 1 h. Both the experimental and control methods were conducted under the same conditions, which relied on partial dissolution of the leaves using the IL and DESs before partitioning the hinoki oils into the organic solvent for analysis. Quantitative analysis was performed using gas chromatography–mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode. The results indicated that extraction using the [C2mim][(MeO)(H)PO2]/acetone bilayer system improved the yields of limonene and hibaene, 1.5- and 1.9-fold, respectively, when compared with the control method. In addition, extraction using betaine/l-lactic acid (molar ratio 1:1) gave the greatest yields for both limonene and hibaene, 1.3-fold and 1.5-fold greater, respectively, than when using an organic solvent. These results demonstrate the effective extraction of essential oils from plant leaves under conditions milder than those needed for the conventional method. The less toxic and environmentally begin DESs for the extraction are also applicable to the food and cosmetic industries.
Highlights
Hinoki (Chamaecyparis obtusa) is a conifer of the Cupressaceae family distributed in Japan, China, and other Asian countries
Limonene and hibaene were chosen as the target compounds for quantitative analysis
Organic solvent extractions using hexane, EtOAc, and acetone were used as controls
Summary
Hinoki (Chamaecyparis obtusa) is a conifer of the Cupressaceae family distributed in Japan, China, and other Asian countries. The major components of the essential oil in hinoki leaves are sabinene, α-terpinyl acetate, limonene, elemol, myrcene, and hibaene (Figure 1) [1]. ILs can dissolve these biopolymers, which are generally considered waste products [5,6] The dissolution of these materials enables more time-efficient and milder methods of refinement into valuable and sustainable materials. The conventional method for dissolving cellulose is the viscose process, which requires large amounts of carbon disulfide, Molecules 2021, 26, x FOR PEER REVIEW sodium hydroxide, sulfuric acid, and fresh water This process generates large quantities of wastewater and alkali and acidic pollution [6,7]. To develop a more eco-friendly method for leaves, essential oil extraction [C2mim][(MeO)(H)PO2] and betaine-based DESs were used to extract hinoki oils. When IL was used, the average yield of hibaene was slightly greater in IL/acetone than in IL/EtOAc, perhaps because the IL mixed more with acetone than with ethyl acetate, enabling a better stirring efficiency
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