摘要
应用原位红外光谱,研究了以正丁醛为溶剂的丙烯醛化反应过程,采用反应气逐个引入的方法,当催化剂母体活化生成活性组分HRh(CO)_2(PPh_3)_2 后.检测到它与丙烯配位后生成的烷基物C_3H_7Rh(CO)_2(PPh_3)_2;引入CO后.可检测出生成的酰基物(C_3H_7CO)Rh(CO)_2(PPh_3)_2;并证明.酰基物可与H_2发生氧化加成和还原消除反应.因而生成正丁醛与异丁醛,同时.催化剂恢复其活性组分.实验证明.该过程可反复进行.由此.初步验证了铑膦络合物催化丙烯醛化反应的缔合型反应机理;实验结果也支持体系中存在另一种解离(CO)机理的观点.
For the hydroformylation reaction of olefin, Wilkinson and coworkers have proposed an association and a dissociation mechanism. In this paper we attempt to prove the correctness of these mechanisms by experiments.
In order to observe and identify the reaction intermediates and the change of the catalysts under reaction conditions, we have used a high temperature and high pressure IR spectrophotometric cell constructed from stainless steel with NaCl or CaF2windows. The cell can withstand 18 MPa pressure at 260 ℃, and its thickness can be adjusted continueously from 0 to 30 mm under high pressure and high temperature. The IR spectra are recorded on a 5DX FT-IR spectrophotometer. In this work, the reaction pressure were from 0.6 to 5.0 MPa, and the temperature were from 100 to 140 ℃.
For the studies on hydroformylation reaction of propylene with Rh-phosphine complex catalyst, the catalyst precursor Rh(acac) (CO) (PPh3), were activated in the in situ IR cell under activation conditions (100 ℃, 2.0 MPa CO / H2, CO / H2 = 1 / 1). The appearance of carbonyl peak at 1940 cm-1 indicates the formation of active species RhH (CO) 2 (PPh3) 2.
When propylene was introduced into the reaction system and its pressure was maintained at 2.0 and 5.0 MPa, the peak of active species (1940 cm-1) was reduced in intensity and new peaks developed at 2018 and 1961 cm-1, and their intensity increased gradually, which could be attributed to the Rh-alkyl complex C3H7Rh(CO)2(PPh3)2.The experimental
46results also indicate that the coordination rate of propylene with Rh-phosphine complex is related to the reaction temperature and pressure. Raising the reaction temperature and propylene pressure is favourable to the coordination of propylene with rhodium.
When the reactant carbon monoxide was introduced into the Rh-alkyl complex system, new characteristic peaks arising at 1990 and 1943 cm-1, could be attributed to the end carbonyl groups of Rh-phosphine-butyryl complex. In experiments under somewhat different conditions, another two carbonyl peaks at 1658 and 1647 cm-1 were detected. All these results showed the formation of Rh-phosphine-butyryl complex C3H7CORh(CO)2(PPh3)2.
When hydrogen ( 2. 0 MPa) was introduced into the reaction system with Rh-phosphine-butyryl complex, the characteristic peaks of n-butyraldehyde(1720 cm-1) and iso-butyraldehyde (1707 cm-1) appear, and peaks of the active species ( 1940 and 1998 cm-1) reappear again.
To sum up, the abovementioned experimental results verified the association mechanism of hydroformylation reaction of olefin proposed by Wilkinson. But it can be also indicated that in our reaction system the dissociation (CO dissociation) reaction mechanism takes place to some extent also. The experiments showed that the oxidative addition of H2 to Rh-butyryl complex is the reaction rate control step. Based on these experimental results, a mechanism of propylene hydroformylation reaction catalyzed by Rh- phosphine complex catalyst was suggested (see Fig.6 on p. 45 )
出处
《分子催化》
EI
CAS
CSCD
1989年第1期41-46,共6页
Journal of Molecular Catalysis(China)
