Flow Pickering Emulsion Interfaces Enhance Catalysis Efficiency and Selectivity for Cyclization of Citronellal.
Cyclization of citronellal is a necessary intermediate step to produce the important flavor chemical (-)-menthol. Here, a continuous-flow Pickering emulsion (FPE) strategy for selective cyclization of citronellal to (-)-isopulegol by using water droplets hosting a heteropolyacid (HPA) catalyst to fill a column reactor is demonstrated. Owing to the large liquid-liquid interface and the excellent confinement ability of droplets toward HPA, the FPE system exhibited a much higher catalysis efficiency than its batch counterpart (2-5-fold) and an excellent durability (two months). Moreover, a remarkably enhanced selectivity was observed from 34.8 % for batch reactions to 64 % for the FPE reactions. It was found that the water droplet size and the flow rate significantly impact the catalysis selectivity and efficiency. This study not only represents an unprecedented and sustainable process for the selective cyclization of citronellal but also demonstrates a new flow-interface catalysis effect that can be useful for designing innovative catalysis systems in the future.
School of Chemistry and Chemical Engineering, Shanxi University, 92 Wucheng Road, Taiyuan, 030006, P.R. China.
Huan
H
Chen
School of Chemistry and Chemical Engineering, Shanxi University, 92 Wucheng Road, Taiyuan, 030006, P.R. China.
Houbing
H
Zou
School of Chemistry and Chemical Engineering, Shanxi University, 92 Wucheng Road, Taiyuan, 030006, P.R. China.
Yajuan
Y
Hao
School of Chemistry and Chemical Engineering, Shanxi University, 92 Wucheng Road, Taiyuan, 030006, P.R. China.
Hengquan
H
Yang
D000080462:Acyclic Monoterpenes; D000447:Aldehydes / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D004655:Emulsions / Q000737:chemistry*; D008610:Menthol / Q000138:chemical synthesis; D039821:Monoterpenes / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D000080462:Acyclic Monoterpenes; D000447:Aldehydes; D004655:Emulsions; D039821:Monoterpenes; D014867:Water; D008610:Menthol; C108217:citronellal
Pickering emulsion; biphasic catalysis; citronellal; continuous-flow process; cyclization