Extraction of Eugenol from Essential Oils by In Situ Formation of Deep Eutectic Solvents: A Green Recyclable Process

Eugenol is extensively utilized in chemical industry. In actual production, it is mainly separated from clove essential oils (EOs) through acid–base solutions. In this work, a simple, rapid and effective extraction process was developed for the extraction of eugenol from EOs samples by directly forming deep eutectic solvents (DESs) without using acid–base solutions. The proposed process is designed to dissolve EOs in n-hexane and eugenol was highly selective extracted into DESs with tetrabutylammonium chloride (TBAC). Hydrogen bonds in DESs can be broken by addition of water, resulting in a separation of the two phases, thus obtaining a hydrophobic yellowish eugenol in the upper layer. The quaternary ammonium salt in the lower aqueous solution can be reused after recovery. The most determining influence factors such as the structure of quaternary ammonium salt, the mole ratio of quaternary ammonium salt to eugenol and the amount of n-hexane were investigated. The forming conditions of DESs were studied by Box–Behnken design (BBD). Experiment was carried out under the optimal conditions and good experimental result was demonstrated by the developed process, a high extraction recovery of 92.51% and the purity was about 98.50%, which verifies the excellent performance for the proposed process.