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.

中文翻译：

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从精油成分 α,β-不饱和醛直接合成全生物基纤维素酯

为了独立于石油资源，社会必须开发直接从天然产物合成全生物基聚合物的方法。在这项研究中，在作为溶剂和催化剂的离子液体中，通过纤维素和天然 α,β-不饱和醛之间的氧化酯化过程合成了全生物基纤维素酯。系统研究了离子液体在该纤维素改性体系中的作用，并开发了一种新设计的非羧酸盐型离子液体，即 1-乙基-3-甲基咪唑鎓 2-吡啶醇盐 (EmimOPy)，以防止发生严重的副反应，其中羧酸根型离子液体的羧酸根阴离子作为产物上的酯基引入纤维素的羟基中。在优化条件下，EmimOPy 中的这种氧化酯化反应系统提供了完全取代的纤维素酯（最高取代度 = 3.0）。此外，纤维素与几种类型的醛底物反应，甚至是生物基低反应性 α- 或 β- 取代的不饱和醛（例如柠檬醛和紫苏醛）。因此，该合成在不含金属的条件下无需使用任何额外的催化剂或活化剂就展示了出色的原子经济性。