Optimized Cellulose Nanocrystal Organocatalysts Outperform Silica-Supported Analogues: Cooperativity, Selectivity, and Bifunctionality in Acid-Base Aldol Condensation Reactions
Optimized Cellulose Nanocrystal Organocatalysts Outperform Silica-Supported Analogues: Cooperativity, Selectivity, and Bifunctionality in Acid-Base Aldol Condensation Reactions
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DOI：
10.1021/acscatal.8b05180
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发表时间：
2019-04-01
期刊：
影响因子：
12.9
通讯作者：
Jones, Christopher W.
中科院分区：
文献类型：
--
作者：
Ellebracht, Nathan C.;Jones, Christopher W.
纤维素纳米晶体（CNCs）被证明是一种有效的，有序的支持合作的酸碱非均相有机催化，提供了一个替代典型的二氧化硅载体。CNC催化剂表面化学通过定量控制羧酸、伯胺和硫酸半酯的负载量来优化，其特征在于元素分析、电导滴定和FT-IR光谱。在4-硝基苯甲醛或糠醛与丙酮的液相羟醛缩合中评价催化剂。羧基是CNC有机催化剂中有效的合作酸伴侣，并且位点特异性活性与COOH：NH 2比率强烈相关。在催化剂合成中去除部分硫酸酯半酯、高酸/碱比和使用未保护的二胺导致优化的CNC催化剂功能（现场-时间产率= 1.0 x 10（-4）s（-1））。由于CNC催化剂的酸含量，实现了脱水羟醛产物的高选择性（>80%）。CNC催化剂在活性和选择性方面优于类似的SBA-15负载的氨基二氧化硅催化剂。CNCs的晶体表面结构和有序的化学功能化有利于精确设计和控制双功能酸碱协同催化剂。
Cellulose nanocrystals (CNCs) are demonstrated as effective, ordered supports for cooperative acid-base heterogeneous organocatalysis, offering an alternative to typical silica supports. CNC catalyst surface chemistry is optimized through quantitative control of the loadings of carboxylic acids, primary amines, and sulfate half-esters, as characterized by elemental analysis, conductometric titration, and FT-IR spectroscopy. Catalysts are evaluated in the liquid phase aldol condensation of 4-nitrobenzaldehyde or furfural with acetone. Carboxylic are effective cooperative acid partners in CNC organocatalysts, and site-specific activity is strongly correlated with the COOH:NH2 ratio. Partial sulfate half-ester removal, high acid/base ratios, and use of unprotected diamines in the catalyst synthesis lead to optimized CNC catalyst function (site-time yield = 1.0 x 10(-4) s(-1)). High selectivities to dehydrated aldol products (>80%) are achieved due to the acid content of the CNC catalysts. CNC catalysts outperform analogous SBA-15-supported aminosilica catalysts in regard to both activity and selectivity. Crystalline surface structures and ordered chemical functionalization in CNCs appear advantageous for precise design and control of bifunctional acid-base cooperative catalysts.