铑膦配合物在烯烃醛化反应中溶剂效应的原位红外光谱研究

IN SITU INFRARED STUDY ON SOLVENT EFFECTS IN HYDROFORMYLATION OF OLEFIN WITH RHODIUMPHOSPHINE COMPLEX

本文应用原位红外光谱技术,在接近于工业反应条件下(H_2:CO=1:1.1.0MPa.80℃),在四种溶剂(异丁醛、2—乙基已醇、甲苯和环已烷)中考察了铑膦配合物催化剂Rh(acac)(CO)(PPh_3)的烯烃醛化反应.检测到在四种溶剂中的主要中间配合物均为HRh(CO)_2(PPh_3)_2,但在2—乙基己醇溶剂中的烯烃醛化反应速度高于异丁醛、甲苯和环已烷溶剂(约1.2～1.3倍).结果表明,采用2—乙基已醇溶剂替代醛类做反应溶剂,有可能提高工业反应装置的生产能力.

Under reaction condition close to that in industrial production (H2 : CO= 1 : 1 . 1.0 MPa, 80℃), the hydroformylation of olefin with rhodium-phosphine complex catalyst Rh(acac) (CO) (PPh3)in four solvents (isobutyraldehyde, 2-ethylhexyl alcohol, toluene and cyclohexane) is studied by in situ IR spectroscopy. The results show that the rate of olefin hydroformylation in 2-ethylhexyl alcohol as solvent is remarkably higher than those in other solvents (about 1.2-1.3 times). According to the in situ infrared spectra of catalyst system Rh(acac)(CO)(PPh3) / PPh3 under the hydroformylation reaction condition (80 ℃, 1.0 MPa) (see Fig. 6), the main intermediate active complex in four solvents is HRh(CO)2(PPh3)2[1,2]. In nonpolar solvents such as toluene and cyclohexane (see Fig. 3. and Fig. 4) , the content of saturated coordinated dimeric [Rh(CO)2(PPh3)2]2 is higher([Rh (CO)2(PPh3)2)2: HRh(CO) 2(PPh3)2 = 0.6-0.72], which may reduce the relative content of catalytic active species HRh(CO)2 (PPh3)2 and leads to the decrease in catalyst activity. In the high polar solvents suchas isobutyraldehyde (see Fig.2), the wavenumbers of carbonyl bands in IR spectrum of active species HRh(CO)2(PPh3)2(1972 cm-1 and 1940 cm-1)is 5 cm-1 below that in 2-ethylhexyl alcohol solvent (1977 cm-1 and 1945 cm-1), which shows that the solvate can be produced as the coordination ability of solvent is strong[14], and it has some influence on the rate of olefin hydroformylation.According to the in situ infrared spectra of catalytic system at different temperatures, the transformation pathway of catalyst Rh(CO)(acac)(PPh3) in four solvents is different. In isobutyraldehyde, toluene and cyclohexane, the transformation pathway is as follows: Rh (acac) (CO) (PPh3) In 2-ethylhexyl alcohol which has medium polarity , it is evident that nonsaturated coordinated HRh(CO) (PPh3)2(2010 cm-1)and dimeric[Rh(CO) (PPh3)2]2(1965 cm-1)[13]. exist under lower temperature (40℃ , 1.0 MPa) (see Fig.5). With increasing temperature to 80℃ , these bands may appear in the spectra of [Rh(CO)2(PPh3)2]2(2015cm-1)and HRh (CO)2(PPh3)2(1977cm-1). The transformation pathway is as follows: Rh(acac)(CO)(PPh3) In addition, the in situ infrared spectrum of catalyst in 2-ethylhexyl alcohol (80℃ , 1.0 MPa) shows that no solvate is formed, the content of saturated coordinated dimeric [Rh (CO)2(PPh3)2]2 is lower and the active species HRh(CO)2(PPh3)2 is more stable, these factors may increase the catalyst activity. If the aldehyde solvent in industrial production unit would be replaced by 2-ethylhexyl alcohol, the productivity could be raised remarkably. But a further study from the view point of economic balance is necessary.