The aqueous-biphasic hydroformylation of higher alkenes catalyzed by Rh/TPPTS has been carried out in the presence of imidazolium, pyridinium and triethylammonium salts. High reaction rates are achieved with imidazolium and triethylammonium salts provided that their alkyl âtailâ is â¥C8. Fast and complete phase separation, and good retention of the metal in the aqueous phase could be achieved with an octyl âtailâ. Imidazolium salts were found to give the highest rate enhancement. The nature of the anion showed a moderate influence on the reaction. Evidence suggests that the additive can act as weak surfactant allowing emulsions to be formed and broken by simply switching the stirring on and off.
Rh/
TPPTS催化的高烯烃
水相双相合成反应已在
咪唑盐、
吡啶盐和
三乙胺盐的存在下进行。使用
咪唑盐和
三乙胺盐时,只要它们的烷基“尾部”不小于C8,就能获得高反应速率。采用辛基“尾部”可实现快速且完全的相分离,以及
金属在
水相中的良好保持。研究发现,
咪唑盐可提供最高的反应速率增强。阴离子的性质对反应有适度影响。证据表明,添加剂可以作为弱表面活性剂,通过简单地切换搅拌的开关来形成和破坏乳状液。