Esterification of glycerol and solketal by oxidative NHC-catalysis under heterogeneous batch and flow conditions†,Reaction Chemistry & Engineering

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Esterification of glycerol and solketal by oxidative NHC-catalysis under heterogeneous batch and flow conditions†
Reaction Chemistry & Engineering ( IF 3.4 ) Pub Date : 2018-09-18 00:00:00 , DOI: 10.1039/c8re00143j
Daniele Ragno _{1,

2,

3,

4} , Arianna Brandolese _{1,

2,

3,

4} , Daniele Urbani _{1,

2,

3,

4} , Graziano Di Carmine _{1,

2,

3,

4} , Carmela De Risi _{1,

2,

3,

4} , Olga Bortolini _{1,

2,

3,

4} , Pier Paolo Giovannini _{1,

2,

3,

4} , Alessandro Massi _{1,

2,

3,

4}

Affiliation

The design and synthesis of a set of supported azolium salt pre-catalysts is presented along with their utilization in the production of monoesters of glycerol and solketal by oxidative N-heterocyclic carbene (NHC)-catalysis through batch and continuous-flow approaches. After a propaedeutic study with soluble NHCs, the heterogeneous analogues (silica and polystyrene supports) were tested in a model monoesterification of glycerol using either the Kharasch oxidant or air (in the presence of electron transfer mediators) as the terminal oxidants. The best performing polystyrene-supported triazolium salt pre-catalyst afforded monoacylglycerols (MAGs) in high yields (up to 95%) and almost complete selectivity (monoester/diester >95 : 5) using air and the green solvent Me-THF. The synthesis of fully bio-based MAGs from furfural, 5-hydroxymethylfurfural (HMF), citronellal, and vanillin is also reported. Continuous-flow experiments have been finally performed by fabricating the corresponding packed-bed microreactor, which could be operated for ca. 120 hours with maintenance of conversion efficiency and selectivity.

中文翻译：

在非均相批料和流动条件下，通过氧化性NHC催化将甘油和Solketal酯化†

介绍了一组负载型偶氮盐预催化剂的设计与合成，以及它们在氧化N-杂环卡宾（NHC）催化下通过间歇和连续流方法生产甘油和Solketal单酯的应用。在使用可溶性NHC进行辅助研究之后，使用Kharasch氧化剂或空气（在电子转移介质存在下）作为末端氧化剂，在甘油模型单酯化中测试了非均相类似物（二氧化硅和聚苯乙烯载体）。使用空气和绿色溶剂Me-THF，性能最好的聚苯乙烯负载的三唑盐预催化剂可提供高收率（高达95％）和几乎完全的选择性（单酯/二酯> 95：5）的单酰基甘油（MAGs）。由糠醛合成完全基于生物的MAG，还报道了5-羟甲基糠醛（HMF），香茅醛和香兰素。通过制造相应的填充床微反应器，最终进行了连续流实验，该反应器可用于约。120小时，保持转化效率和选择性。

更新日期：2018-09-18

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