AbstractThe dissolving properties of softwood in an aqueous solution of the ionic liquid tetra-n-butylphosphonium hydroxide ([P4,4,4,4]OH) were studied. Cedar wood meal and 40% [P4,4,4,4]OH aqueous solution were mixed in a glass tube and treated at 121 °C and 2 atm in an ordinary autoclave. As the treatment time increased, the residue content decreased to 68.7%, 49.4%, and 37.0% after 1, 5, and 20 h, respectively. Following the 20-h treatment time, 97.0% of the residue was determined to be holocellulose and 96.3% of the constituent monosaccharide in the residue was glucose. UV analysis showed that most of the lignin had dissolved in the [P4,4,4,4]OH solution. Phenolic hydroxyl group analysis of the dissolved lignin suggested that the macromolecular structures of the lignin were considerably degraded. The results of this study suggest the possibility of developing a simple multi-sample analysis method for lignin content using a single-step autoclave treatment in a glass tube using an aqueous solution of [P4,4,4,4]OH.