Hydroformylation comparative rate studies

The formation of multinuclear clusters is much more favorable for rhodium than for cobalt. Additional evidence was obtained in comparative hydroformylation rate studies of 1-heptene and of cyclohexene at 75°C and 150 atm 1/1 H2/CO (19). For the acyclic olefin the kinetics followed the kinetic expression (except at low olefin) ... 

Phosphacyclic diphosphines (73a) and (73b) with wide natural bite angles were synthesized and the effect of the phosphacyclic moieties on the coordination chemistry in the [(diphosphine) Rh(CO)2H] complexes was studied. Both NMR and IR spectroscopy showed that the phosphacyclic xantphos ligands exhibit an enhanced preference for diequatorial chelation compared to the diphenylphosphino-substituted parent compound. In the hydroformylation of 1-octene the introduction of the phosphacyclic moieties leads to higher reaction rates. The dibenzophospholyl- and phenoxaphosphino-substituted xantphos ligands exhibit a high activity and selectivity in the hydroformylation of trans-2- and 4-octene to linear nonanal. CO dissociation rates from the... 

Kinetics of hydroformylation of styrene using HRhCO(TPPTS)3 catalyst in a bi-phasic system with various co-solvents was investigated by Nair [25]. He reported that 50% aqueous (v/v) N-methyl pyrrolidone (NMP) solution showed much better performance in comparison to ethanol as a co-solvent due to its non-reactive nature towards the aldehyde products. The rate was found to increase by seven times compared to that in the absence of any co-solvent. Kinetic study at 373 K revealed that the rate was first order dependent with catalyst concentration, fractional order with CO and first order tending to zero order with styrene concentration. 

The cavitron device was used to study the conversion rate of n-l-hexene hydroformylation under biphasic conditions. Under standard reaction conditions, but at a lower pressure of lObar, a conversion of 17% (n/iso ratio 99 1) was reached in this unit compared with 12% in a regular stirred autoclave. 

Hydroformylation involves the addition of H2 and CO to a C=C bond to yield aldehydes, and is one of the most important industrial processes [60]. The first example of the homogeneous hydroformylation in SCCO2 was described by Rathke [61.]. The solubility of rhodium catalysts is better in SCCO2 (also in conventional solvents) compared with the cobalt systems. Leitner and Koch studied the Rh-catalyzed hydroformylation of various alkenes in SCCO2 and found a higher reaction rate compared to that in organic solvents [62]. A maximum turnover frequency (TOF) of 1345 h could be achieved (Scheme 13.11). 

HCo(CO)4 is held below its equilibrium value for the reaction in eq (3.2-1), which is only achieved after the alkene is fully consumed. The results for propylene hydroformylation in supercritical CO2 have been compared [53] with those of Mirbach [55] for the reaction of 1-octene in methylcyclohexane solution. Under comparable conditions, the steady-state concentrations of the intermediates do not differ greatly (i.e. by little more than a factor of three), and the overall hydroformylation rates are quite similar, d[aldehyde]/dt = 1.2 x 10" M s and 0.77 x 10 M s , for the methylcyclohexane and CO2 systems, respectively. Although different alkenes were used in the two studies, the comparisons are believed to be meaningful, as Wender et al. [56] have shown that hydroformylation rates for a wide range of straight-chain terminal alkenes vary only slightly with chain length for cobalt catalysts. 

Webb et al. [20] used this approach to study alkene hydroformylations. They found a lower rate, yet higher selectivity towards the desired products, when compared to the reaction in IL alone. This increase in selectivity can be attributed to the partitioning of the product to the gas phase, which reduces its contact with the catalyst, and prevents further reaction. In order to have higher reaction productivity it is necessary to obtain a higher substrate concentration in the IL phase. This can be achieved by decreasing the CO2 partial pressure, which decreases its solvent power, and leads to reactant partitioning more into the IL phase. Webb et al. also found that, under certain conditions, the system could operate continuously for several weeks without detectable catalyst degradation. 

The solubilities of H2 [181] and CO [182] in many different ionic hquids have been measured in this context by Dyson and coworkers using high-pressure H- or C-NMR spectroscopy. CO solubility at ambient conditions (Henry s law constants) were found to be in the range of 8.05-0.67 x 10 MPa which were in the same range than those measured for H2 in the same ionic hquids (about 6.6-0.7 X 10 MPa). In order to establish the effect of the CO solubihty on the rate of hydroformylation reactions, the same authors studied the [RhH(CO)(PPhj)3] catalyzed hydroformylation of 5-hexen-2-one comparing catalyst activities in the different ionic liquids with the determined gas solubilities. 

Bulky monophosphite hgands proved to be very useful for the functionalization of very unreactive substrates. Already in their first study van Leeuwen and Roobeek obtained relatively high rates for the hydroformylation of substrates such as cyclohexene and limonene. [8]. Van Rooy performed a systematic study to the rhodium catalyzed hydroformylation of substituted alkenes and compared the reaction rates with the triphenylphosphine system [42]. The bulky monophosphite derived catalyst was up to two orders of magnitude faster and gave acceptable rates using substrates for which the Wilkinson hydrofomylation catalyst gave hardly any activity. 

This observation is somewhat in contrast to the results of Kandanarachchi and coworkers [33], who studied the kinetics of hydroformylation of triglycerides with oleic and linoleic functionalities as a model for soybean oil. In the presence of a homogeneous Rh catalyst modified with PPhj and P(OPh)j, comparable initial rates and TOFs were observed with both ligands. In comparison to individual fatty... 

The hydroformylation of vegetable oils (soybean, high oleic safflower, safflower, and linseed) using Rh(CO)2(acac) as the catalyst precursor in the presence of PPhs or (PhOlsP was studied. The ligand (PhO)3P resulted in a lesser reactivity compared to TPP in contrast to the rates of bulky phosphite ligands reported in the literature [16]. 

The rhodium/TPPTS-catalyzed hydroformylation of higher olefins in organic/ aqueous biphasic system in the presence of double long-chain cationic surfactants (37) was studied at 100 °C and 20 bar CO H2 = 1 1 pressure. The reaction rate was comparable with that in homogeneous catalysis system [111]. 

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