Synthesis Of Thermoregulated Polyether Modified Quaternary Ammonium Ionic Liquid And Its Application In Hydroformylation Of 1-Octene

The ionic liquids applied in liquid-liquid two-phase systems provide a novel route for the separating and recycling of catalysts. Based on the concept of Thermoregulated Ionic Liquid Biphasic System (TRILC), a series of quaternary ammonium ionic liquids which were modified by introducing the polyethylene glycol chain and n-octyl have been designed and prepared, of which the structures are shown below:These four ionic liquids were characterized by ¹H-NMR and API-MS accordingly. The melting points and glass transition temperatures of them have been studied by DSC (Differential Scanning Clorimetry). The results show that their melting points are all less than 100℃. The IL₁ and IL₄ are both liquids under room temperature while the IL₂ and IL₃ are both solids. A decrease of melting points of the salts with an increase in the length of polyethylene glycol chain was observed, meanwhile, the melting points were influenced by the position of n-octyl substitution in the cation. All. of the compounds show the glass transition temperature except for IL₃. The TGA (Thermogravimetric Analysis) shows that these molten were stable up to 210℃. The solubility of these ionic liquids in different solvents was investigated under different temperature. It is found that the two phase system composed of IL₃ or IL₄ with cyclohexane possesses the property of "mono-phase under high temperature, bi-phase under low temperature" respectively. The phase diagram for IL₄ with cyclohexane was then described. The thermoregulated ionic liquid biphasic system was applied in the hydroformylation of 1 -octene catalyzed by Rh/TPPTS complex. The effects of different reaction conditions have been tested and discussed in detail. With a system consisting of 1.0g IL₄, 4.0g cyclohexane the optimum condition is, T=120℃, P(CO:H₂=1:1)=5.0MPa, t=10h, S/C=1000(molar ratio), P/Rh=8(molar ratio). Under this condition, the conversion of 1-octene and yield of nonanal are 99.3% and 98.5% respectively. After six times of the catalyst recycle, the conversion of 1-octene and yield of nonanal are still above 98%. The results show the good catalytic activity of RhCl₃·3H₂O/TPPTS complex for hydroformylation of 1-octene in thermoregulated ionic liquid/cyclohexene biphasic system. It is a well-established method for effective catalyst separation and recycling.