Direct Synthesis of Full-Biobased Cellulose Esters from Essential Oil Component α,β-Unsaturated Aldehydes
Samuel Budi Wardhana Kusuma, Daisuke Hirose, Akina Yoshizawa, László Szabó, Daiki Ina, Naoki Wada, Kenji Takahashi
Abstract
To become independent of petroleum resources, societies have to develop methods to synthesize full-biobased polymers from natural products directly. In this study, full-biobased cellulose esters were synthesized by the oxidative esterification process between cellulose and natural α,β-unsaturated aldehydes in an ionic liquid working as solvent and catalyst. The role of the ionic liquid in this cellulose-modification system was systematically investigated, and a newly designed noncarboxylate-type ionic liquid, 1-ethyl-3-methylimidazolium 2-pyridinolate (EmimOPy), was developed to prevent a serious side reaction in which the carboxylate anion of the carboxylate-type ionic liquid is introduced into the hydroxyl group of cellulose as an ester group on the products. Under optimized conditions, this oxidative esterification-reaction system in EmimOPy afforded fully substituted cellulose ester (up to the degree of substitution = 3.0). Furthermore, cellulose reacted with several types of aldehyde substrates, even biobased low-reactive α- or β-substituted unsaturated aldehydes (e.g., citral and perillaldehyde). Thus, this synthesis demonstrates excellent atom economy without using any additional catalysts or activators under metal-free conditions.