Hydroformylation product distribution

Effect of Carbon Monoxide Partial Pressure on Isomeric Distribution of the Hydroformylation Products of Olefins (30)a... 

General Procedure for the Hydroformylation/Electrophilic Substitution. Synthesis of 5,6-dihydroindolizines. A solution of 1-allylpyrroles (leq) and Rh4(CO)i2 (lmol%) in toluene was introduced by suction into an evacuated stainless-steel reaction vessel. CO (60 bar) was introduced, the autoclave was then rocked, heated to the desired temperature and H2 (60 bar) was introduced rapidly. When the gas absorption reached the value corresponding to the fixed conversion, the reaction mixture was siphoned out. The degree of conversion and the product distributions were determined by GC and GC-MS, by using acetophenone as an internal standard. 

With an annual production of up to 9.3 million tons in 1998, hydroformylation is the most important homogeneously catalyzed reaction [20,21], The reaction is performed almost exclusively by the use of cobalt or rhodium catalysts. The advantages of rhodium catalysts are milder reaction conditions and better n/iso ratios in product distribution. The toxicity of rhodium compounds as well as the high rhodium price [22] (between 20 and 75 g during the last five years) demand an efficient catalyst recycling. 

Fig. 22 Conversion and product distribution by the hydroformylation of 1-octene in SCCO2 with Co2(CO)s and 8 with different P Co atomic ratios. Initial conditions 53 mmol of 1-octene, 106 mmol syngas (H2/CO = 1), 0.106 mmol Co2(CO)8, T 393 K. C Conversion, S selectivity, la 1-nonanal, lb 2-nonanal, 2 nonanols, 3 octenes (without 1-octene), 4 n-octane...

Initial studies showed that the encapsulated palladium catalyst based on the assembly outperformed its non-encapsulated analogue by far in the Heck coupling of iodobenzene with styrene [7]. This was attributed to the fact that the active species consist of a monophosphine-palladium complex. The product distribution was not changed by encapsulation of the catalyst. A similar rate enhancement was observed in the rhodium-catalyzed hydroformylation of 1-octene (Scheme 8.1). At room temperature, the catalyst was 10 times more active. For this reaction a completely different product distribution was observed. The encapsulated rhodium catalyst formed preferentially the branched aldehyde (L/B ratio 0.6), whereas usually the linear aldehyde is formed as the main product (L/B > 2 in control experiments). These effects are partly attributed to geometry around the metal complex monophosphine coordinated rhodium complexes are the active species, which was also confirmed by high-pressure IR and NMR techniques. 

The effect of DMBA and polyDMBA on the hydroformylation of 1-hexene is shown in Table I. Product distributions are reported at 80% total olefin conversion for various rhodium sources and olefin concentrations. As shown, olefin isomerization is complete in all cases. In the presence of 2M DMBA, significant aldehyde hydrogenation occurred producing nearly 30% alcohol. With the exception of RhCl3 3H20 which is inactive, no differences were found between various rhodium sources. 

The resulting noncovalently immobilized complexes have been used as ligand systems for both the Pd-catalyzed allylic amination reaction and the Rh-catalyzed hydroformylation. A glycine-urea functionalized PPh3 ligand, 4(S), was noncovalently attached to the immobilized dendritic support, and the application of this system in the Pd-catalyzed allylic amination attains similar yields and product distributions as the homogeneous analogue for the... 

In addition to the hydroformylation reactions, side reactions of the product alcohols and aldehydes occur to form heavy ends, particularly at higher reaction temperatures, and usually account for 9% of the product distribution. Industrial reactors usually start using high boiling solvents, but after a while these heavy ends become the solvents. 

Cesar et al. have investigated the Berry pseudorotation prevalent in five coordinate rhodium complexes [93] (see Figure 3.27). The product distribution in the rhodium catalysed hydroformylation of 1-olefins is often dependant on the coordination pattern of the bidentate spectator ligand [53], i.e. whether it coordinates equatorial/equatorial or... 

Under these conditions, the linear to branched aldehyde ratio for the hydroformylation of 1-octene was 1.9 1. Starting with 4-octene one still gets a 1.2 1 linear to branched ratio. Thus, one can start with a considerably less-expensive mixture of terminal and internal alkenes and get a product distribution favoring the linear aldehyde. The product distribution in Scheme 3 can be nicely explained by invoking facile alkene isomerization, with the fastest hydroformylation occurring for double bonds in the 1-position. Labeling studies have shown that alkene isomerization generally occurs without dissociation of the alkene from the cobalt catalyst. ... 

Based on their chain length, olefins converted in commercial oxo plants are divided into four groups ethylene (C2), propene (C3), butene to dodecene (C4 to Cl2) and longer-chain olefins (> C12). The factors influencing product distribution and reaction rates in the hydroformylation of olefins will be discussed in Section 2.1.1.3.3. The economical aspects of 0x0 processes are described in Section 2.1.1.4.1. The share of various products in the overall olefin hydroformylation capacity is C2 2%), C3 (73%), C4-C12 (19%) and >Ci2 (6%). 

Ph2PCH2CH2PPh2), the ligand bite angle (see structure 6.16) can significantly influence the product distribution. For example, the n i ratios in the hydroformylation of... 

These Reppe systems could warrant further investigation as changing the catalyst and operating conditions, especially the pH of the solution, can give rise to different product distributions ranging from high yields of aldol condensation products of -aldehydes in one step (compared to two steps for conventional Rh catalysed hydroformylation of propene) to high yields of alcohols in one step (similar to the phosphine-modified Co process). In this respect these systems are similar to the Exxon Aldox system. 

Biphasic hydroformylation is a typical and complicated gas-liquid-liquid reaction. Although extensive studies on catalysts, ligands, and catalytic product distributions have appeared, the reaction mechanism has not been understood sufficiently and even contradictory concepts of the site of hydroformylation reaction were developed [11, 13, 20]. Studies on the kinetics of hydroformylation of olefins are not only instructive for improvement of the catalytic complexes and ligands but also provide the basic information for design and scale-up of novel commercial reactors. The kinetics of hydroformylation of different olefins, such as ethylene, propylene, 1-hexene, 1-octene, and 1-dodecene, using homogeneous or supported catalysts has been reported in the literature. However, the results on the kinetics of hydroformylation in aqueous biphasic systems are rather limited and up to now no universally accepted intrinsic biphasic kinetic model has been derived, because of the unelucidated reaction mechanism and complicated effects of multiphase mass transfer (see also Section 2.4.1.1.2). 

Scheme 6.7 Hydroformylation of 1-octene a) within nanoreactor [G z> Rh] and b) within nanoreactor [I 3 RhJ. Product distribution of the aldehyde products...

With olefins, CO, and H2 catalytic hydroformylation takes place even at 25 and subatmospheric pressure. Rates and product distributions depend on substrate type, [S], [H2], [CO], ligand type, [L], [Rh], and temperature. Rates with selected olefins are given in Table 10. Note that 2-pentenes react about 25 times slower than 1-pentene, and that 2-methyl-1-pentene (a hindered terminal olefin) is slower still. Cyclooctene is much faster than cyclohexene, presumably because of ring strain effects on olefin coordination, t Butadiene reacts rapidly with the catalyst to form an inert (tt-crotyl)Rh(CO)L2 complex and no gas uptake occurs at 25 . 1,5-Hexadiene can be successfully hydroformylated, because the hydroformylation rate (to primarily linear dialdehyde) is fast compared to the rate of isomerization... 

Isomerization probably occurs primarily via i Rh(CO)L2 prior to capture by CO in step 9. After i CORh(CO)2L2 forms by further steps 10 and 14, getting back to i Rh(CO)L2 by the reverse of steps 14, 10, and 9 seems unlikely, especially under CO and H2 pressure. This conclusion is supported by isotopic-labeling studies by Pino. If steps 9 and 4 are essentially irreversible, then the RCHO/R CHO ratio will primarily depend on the steady-state concentration ratio of i Rh(CO)L2 to i Rh(CO)L2. If 4 and kg are similart, then fcs, kg, and the relative stabilities (K /Kg) of i Rh(CO)L2 and R Rh(CO)L2 will determine the aldehyde product distribution. Steric crowding in the branched alkyl complex is no doubt a major factor in destabilizing it compared to the linear alkyl as early recognized by Evans, Osborn, and Wilkinsonthe increased crowding of phosphines relative to carbonyls accounts for the increased yields of desired linear products in both the Rh and Co hydroformylation systems. Electronic factors no doubt also play a role, and in fact most dominate the product distribution with styrene, where R Rh(CO)L2 capture by CO is favored over R Rh(CO)L2. The question is, to what extent is the ratio [R Rh(CO)L2]/[R Rh(CO)L2] kinetically or thermodynamically controlled under steady-state conditions ... 

Table 13. Dependence of Product Distribution on L Rh Ratio for PfOPhJs in 1-Octene Hydroformylation ...

Structure (ATO) gives a product distribution that is dominated by adipic acid. This is thought to result because the narrower channels inhibit the release of cyclohexanol and cyclohexanone and the reaction proceeds further to the more mobile linear products, such as adipic acid. Selectivity is also observed in the aerial oxidation of linear alkanes. If the reaction is performed over large-pore solids, w-alkanes are oxidised preferentially at carbon atoms at C2 and C3 positions in the chain, in accordance with the C-H bond strengths at these positions. If a small-pore structure such as CoAPO-18 is used, however, the product selectivity favours Cl oxyfunctionalised products. The synthesis of terminally oxidised alkanes would be of use for many applications, because linear terminal alcohols could be prepared from alkane feedstocks, rather than from a-olefins (via hydroformylation). 

Cobalt. Solvent effects on hydroformylation of propene and of pent-l-ene catalysed by CoH(CO)4 have been investigated by product distribution analysis. Effects of temperature and pressures of hydrogen and carbon monoxide on the mechanism of hydroformylation of propene in the presence of Co2(CO)8(PBu8)a have similarly been probed by product analysis. The reaction of (36) with methanol or ethanol (R OH) produces CHR(COaRi)2. ... 

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