Hydroformylations to linear aldehydes

Other alternative reaction pathways to AA or MAA via hydroformylation of 7-octenoic acid or the respective ester and consecutive oxidation of the formed aldehydic group may fail due to the poor accessibility of the C8 compound needed as starting material. This is unfortunate because recent development in the selective hydroformylation to linear aldehydes using sophisticated phosphite ligands [134,135] may enable such reaction sequence. 

Often the aldehyde is hydrogenated to the corresponding alcohol. In general, addition of carbon monoxide to a substrate is referred to as carbonylation, but when the substrate is an olefin it is also known as hydroformylation. The eady work on the 0x0 synthesis was done with cobalt hydrocarbonyl complexes, but in 1976 a low pressure rhodium-cataly2ed process was commerciali2ed that gave greater selectivity to linear aldehydes and fewer coproducts. 

The rate of hydroformylation was found to vary in a nonlinear fashion as a function of triphenylphosphine concentration. A maximum in rate was noted at a triphenylphosphine/HRh(CO)(PPh3)3 weight ratio of (5-10) 1, as illustrated in Fig. 7. A maximum in selectivity to linear aldehyde was noted at about a 5 1 ratio, and no significant further increase was noted up to a 50 1 ratio of triphenylphosphine to rhodium complex. 

The linear olefins are used in the production of biodegradable detergents. The Cq to cuts are fed to alkylation units where the olefins react with benzene to form alkylbenzenes which are subsequently sulphonated. The paraffins present in the feed pass through unconverted. These are then chlorinated and used as plasticizers. The linear olefins can also be converted to linear aldehydes and alcohols by hydroformylation. 

A relatively weak rate enhancement was observed in the biphasic hydroformylation of 1-octene using Rh/tppts catalysts in the presence of cosolvents such as ethanol to enhance the solubility of the olefin in the aqueous phase and with addition of buffers (Na2C03/NaHC03) to eliminate side reactions such as the formation of acetals.31,365,366 Similarly, addition of ethanol improved the yields in the hydroformylation of 1-octene catalysed by Rh2(p-S-tBu)2(CO)2(tppts)2 species in an aqueous/organic two phase system.367 However, the high selectivity to linear aldehyde observed for neat olefin in the biphasic system (97%) decreased (to 83%) in the presence of the cosolvent.367... 

Replacement of tppts by the fluoro substituted sulfonated ligand 4 [Table 2 94% (n=l) and 6% (n=0)] in the rhodium-catalysed hydroformylation of 1-hexene in a two phase system increased the selectivity to linear aldehyde n-heptanal from 86% to 93% at the low P/Rh molar ratio of 7.5/1.75,76 The Rh/4 catalyst was quantitatively recovered after the reaction by simple decantation.75,76 The moderate increase of the n/i ratio is of interest when one considers that ligand 4 is mainly present as the disulfonated species (94%) compared to the trisulfonated compound tppts and that tris(4-fluorophenyl)phosphine is less basic (pKa=1.97) than triphenylphosphine (pKa=2.73).376 In rhodium-catalysed hydroformylation reactions in organic solvents it is known that electron withdrawing substituents, which increase the -acidity of the ligand, give rise to an increase in the n/i ratio.377 379... 

An interesting new concept of catalyst immobilization is the use of supported aqueous phase catalysts. Here, the catalyst is immobilized in a thin water layer adhered within the pores of a high-surface-area porous support. A new Rh catalyst of this class with ligand 11 is stable, recyclable, and highly selective in the hydroformylation of higher alkenes to linear aldehydes.236... 

The plot of data for the carbonyl, Rh6(CO)i6, (Figure 1) shows that the rate of 1-hexene isomerization exceeds that of hydroformylation. At olefin conversion in excess of 50%, little 1 isomer remains. An increase in branched aldehyde relative to linear aldehyde accompanies the change in isomer distribution. The absence of aldehyde hydrogenation is complete even at very high conversion levels using the conditions cited. 

Using the complexes in hydroformylation not only increased the reaction rate in comparison with their analogues produced as mixtures but also improved the selectivity with respect to linear aldehyde owing to the orientation of the substrate in cyclodextrin. Unlike catalysis by low molecular weight analogues, the reaction involves even alkenes with an internal double bond (trans-3-octene). The catalyst was highly soluble in water, mainly remained in the aqueous phase after the reaction and can be reused. 

Industrially, the rhodium-catalyzed hydroformylation is normally operated at about 100°, at pressures up to 50 atm and in the presence of a large excess of added phosphorus ligand, it can be carried out in molten PPhs. Under these conditions, a terminal olefin can be converted in over 90% yield to linear aldehyde. By-products include branched aldehydes as well as small amounts of alkanes and isomerized olefins. Advantages over the more conventional cobalt catalysts include lower temperatures and pressures, higher ratios of linear to branched products, and less hydrogenation of aldehyde products to alcohols. 

The constant selectivity for linear aldehyde in the hydroformylation of 1 -octene implies that for the basic ligands the l b ratio reflects the regioselectivity of the formation of the rhodium alkyl species. For the less basic ligands the increase in 1 b ratio results from the different behavior of branched and linear rhodium alkyls toward -hydrogen elimination, as was already reported by Lazzaroni and co-workers for the deuteriofomylation of 1-hexene [57]. The linear alkyl is mainly converted to linear aldehyde, while... 

A similar synthesis strategy was employed to construct high-weight catalysts carrying multiple catalytic centers in the outer core of the dendrimer [137]. The catalyst depicted below is characterized by 16 catalytic centers. It was found to be more active in the hydroformylation of vinyl arenes than its synthetic precursor carrying only four catalytic units. The ratio of branched to linear aldehydes ranged from 36 1 to 39 1 at >99% conversion. By simple filtration, the dendrimeric catalyst was separated from the product. Even the 10th hydroformylation cycle proceeded without loss of activity and selectivity. 

Mein, H., Jackstell, R., Wiese, K.-D., Borg-mann, C., and BeDer, M. (2001) Highly selective catalyst systems for the hydroformylation of internal olefins to linear aldehydes. Angew. Chem. Int. Ed., 40 (18), 3408-3411. 

Replacement of tppts by the fluoro substituted sulfonated ligand 4 [Table 2 94% (n=l) and 6% (n=0)] in the rhodium-catalysed hydroformylation of 1-hexene in a two phase system increased the selectivity to linear aldehyde n-heptanal from 86% to 93% at the low P/Rh molar ratio of The Rh/4 catalyst was... 

The hydroformylation of alkenes is one of the most extensively applied homogeneous catalytic processes in industry. More than 9 million tons of aldehydes and alcohols are produced annually [13]. Many efforts have been devoted in the last few years to the development of systems with improved regioselectivity toward the formation of the industrially more important linear aldehyde. Both phosphine- and phosphite-based systems giving high regioselectivities to linear aldehyde for the hydroformylation of terminal and internal alkenes have been reported [1,2,14—16] (Scheme 1.1). 

Several synthetic approaches toward 3,3-diarylpropyl- or 4,4-diarylbutylamines (Figure 12.2) comprise hydroformylation as the key step. One possible route involves the reaction of the (D.co-diarylalkylhalide, obtained in a few steps from the hydroformylation product linear aldehyde, with an appropriate amine [19]. On the contrary, the aldehydes can be converted directly into the amines via a transition metal catalyzed reductive amination reaction [20]. Although these methods have heen employed efficiently for the synthesis of compounds 10,11 [19], and 12 [20], the most elegant solution is the direct hydroaminomethylation where the initial hydroformylation of the alkene is followed by the condensation of the intermediate aldehyde with the amine present in the reaction mixture and a final hydrogenation to give a saturated secondary or tertiary amine. 

Hydroformylation reactions of C2-C4 Olefins By applying silica gel-supported BMIm-n-C8Hi70S03 IL phase containing Rh(acac)(CO)2 and xanthene-based biphosphine ligand sulfoxantphos (SX), Scheme 2.21 [89], as catalyst (Rh-1), the hydroformylation of propene was successfully realized under fixed-bed gas-phase reaction conditions. The addition of the ligand SX promoted the formation of linear aldehyde product. Under optimized reaction conditions, the selectivity to linear aldehyde reached 96% with about 1% propene conversion. However, deactivation occurred if the flow reaction was prolonged to 24 h. Subsequently,... 

Pla.tinum. Platinum catalysts that utilize both phosphine and tin(Il) haUde ligands give good rates and selectivities, in contrast to platinum alone, which has extremely low or nonexistent hydroformylation activity. High specificity to the linear aldehyde from 1-pentene or 1-heptene is obtained using HPtSnClgCO(1 1P) (26), active at 100°C and 20 MPa (290 psi) producing 95% -hexanal from 1-pentene. 

The linear aldehyde usually is the desired product. Often, this aldehyde is converted to the corresponding alcohol. Both Co and Rh complexes are used in hydroformylation. In general, Rh catalysts are more active and produce a higher n/wo-ratio. Co catalysts have higher... 

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