Liu Xiaozhong, Wang Yanhua, Jiang Jingyang, Jin Zilin
(State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116012, China)

Received Nov.24,1999; Supported by the National Natural Science Foundation of China and SINOPEC(Grant No. 29792074).

Abstract A novel water-soluble Rh complex modified by Octyl polyethylene glycol phenylenephosphite has been applied in the biphasic hydroformylation of higher olefins. A conversion of 99.3% and aldehyde yield of 97.3% were obtained when 1-decene was employed as substrate. The catalyst exhibited high activity and was recoverable.
Keywords hydroformylation, higher olefins, biphasic catalysis

Up to now, about 90% of higher oxo products are manufactured by processes using unmodified or trialkylphosphine- modified cobalt catalyst^[1]. Low activity was usually observed in the aqueous/organic system which facilitates the product/catalyst separation in the hydroformylation of higher olefins because of mass-transfer limitations resulted due to very slight water-solubility of such long-chain olefins. Different approaches to overcome these problems have been reported in recent literatures, such as addition of surfactant or by a co-solvent to the commercially employed RCH/RP system suitable for lower olefins^[2,3], and supported aqueous-phase catalysis^[4,5]. However, so far, no catalytic system has been found industrially achieving sufficient high conversion and yet bringing a complete catalyst separation by decantation or simple phase separation. Thermoreg-ulated Phase-Transfer Catalysis(TRPTC) proposed by Jin and co-workers^[6-8] provides a perspective future in a path to aqueous/organic biphasic hydroformylation of water-immiscible olefins. According to the principle of TRPTC, Rh complexes modified with polyalkyl glycol ether derived phosphine, which gives precise cloud point(Cp) similar to nonionic surfactant could precipitate from the aqueous phase at a temperature higher than Cp of the phosphine and then transfer into organic phase to catalyze the reaction. After the reaction , the complexes return to the aqueous phase and separated by simple phase separation from the product at a temperature below Cp and could be employed in the successive reaction runs.
    A novel polyalkyl glycol ether derived phosphite (Octyl polyethyleneglycol phenylene-phosphite,OPGPP) with precise cloud point was synthesized according to the following equation:

    The structure(R=n-C₈H₁₇,n=13) was confirmed by IR and ¹HNMR spectra( ¹H-NMR/CDCl₃: d(ppm) 0.8(3H, CH₃), 1.0-1.3(14H, CH₂), 3.5(52H, OC₂H₄,), 6.8-7.2(4H, Ph); FT-IR(cm^-1):u(C-O-C)1116,u(P-O-C(alkyl)) 1035, u(P-O-C(arom)) 975.) and its cloud point was determined to be 57.5°C (3wt% aqueous solution). Its Rh complex was employed in the aqueous/organic biphasic hydroformylation of higher olefins. Under the selected conditions of T=80°C, P=5.0MPa, P/Rh(mol)=13, Sub/Rh(mol)=1000, n-heptane as a solvent and Rh(acac)(CO)₂ as precursor, the reaction was completed in 6 hrs. A conversion of 99.3% was achieved with 97.3% of aldehyde yield and the ratio of n/i of the aldehydes amounted to 0.91. It was observed that 88.5% of the hydroformylation products were n-undecanal and 2-methyl-decanal which would provide a potential application in perfume industry.
    Effect of temperature on this reaction was shown on Table1. In the range of 60~100°C, conversion increases as temperature rises, there was a sharp change of conversion between 60°C and 50°C. It could be elucidated from the principle of TRPTC that when the temperature is higher than Cp of the ligand, the catalyst would likely be precipitated from aqueous phase and transferred into the organic phase to catalyze the reaction. The low conversion at temperature below the Cp was ascribed to the formation of micelles resulted from the polyethylene glycol moiety of the phosphine.

Table 1 Effect of temperature on the hydroformylation of 1-decene

Reaction conditions:1-decene 1.0ml,n-Heptane 2.0ml,H₂O 3.0 ml Ligand/Rh(mol):13, Sub/Rh(mol):1000,Synthesis-gas pressure: 5.0MPa,reaction time:6h.
*Aldehyde content:(n-undecanal+ 2-methyl decanal)/total aldehydes

    After the reaction, the catalyst in aqueous phase was easily recovered by simple phase separation and could be applied in the successive reaction runs(as shown in Table2). The catalyst can be reused twice without decrease in activity. The reason for the decrease in activity after three reaction runs may be attributed to the partial hydrolysis of the phosphite.

Table 2 Recycling use of the aqueous catalyst

Reaction conditions:1-decene 1.0ml,n-Heptane 2.0ml, H₂O 3.0 ml Ligand/Rh(mol):13, Sub/Rh(mol):1000, Synthesis-gas pressure: 5.0MPa,t:80ºC,reaction time:6h.

    The above catalyst has also been applied in the hydroformylation of other higher olefins(1-hexene, 1-octene, 1-dodecene, 1-tetradecene). Under the same conditions, more than 95% of conversions were obtained. The results got the core of TRPTC that thermoregulated phase-transfer catalyst catalyzes the reaction in the organic phase in terms of classic homogeneous catalysis. Accordingly high conversions of higher olefins were obtained regardless of their water-immiscibility.

Table3 Biphasic hydroformylation of higer olefins catalyzed by OPGPP/Rh

Reaction conditions : olefin 1.0 ml,n-heptane 2.0 ml,P/Rh(mol):13, Olefin/Rh(mol):1000,T:80ºC, Synthesis-gas pressure:5.0MPa,reaction time: 6 hrs.

    In conclusion, Rh complexes, modified with a novel polyalkyl glycol ether derived phosphite(OPGPP), was applied in the hydroformylation of higher olefins and the catalyst could be high activity. Different from previously reported phosphite, the phosphite(OPGPP) presented in this paper could be employed in the aqueous/organic catalysis and the Rh complex was recoverable. The results from this communication are an extension to application of TRPTC in the hydroformylation of higher olefins.

REFERENCES
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