Hydroformylation reactions product distribution

Fig. 7 [126]. Reaction product distribution in the hydroformylation of terminal and non-terminal olefins at various reaction temperatures Ho/CO — 3/1, overall pressure 246 atm...

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. 

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 factors affecting the distribution of products formed in the hydroformylation reaction have already received attention in Section II, A,2. The isomerizations of both olefin and acylcobalt carbonyl can be of importance and the extent of these isomerizations will be dependent on carbon... 

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. 

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%). 

Over recent years a steady and continuous growth in production capacity of aldehydes by the hydroformylation reaction has taken place. Table 3 shows the estimated capacities for aldehydes generated by hydroformylation of ethylene, propene, and higher olefins, along with their regional distribution [143]. 

The structure written for I is satisfactory for olefins which can have only internal or only terminal double bonds (ethylene, propylene, cyclohexene). We find, however, that although internal olefins are thermodynamically more stable than terminal olefins under reaction conditions, the products obtained in the hydroformylation reactions are largely derived by addition to the terminal carbons. For example, the distribution of alcohols secured from 1-pentene and 2-pentene is about the same 13, 14), 50-55% of n-hexanol, 35-40% of 2-methylpentanol-l, and 10% of 2-ethylbutanol-l. In each case the chief product can be obtained only by the addition of the formyl group to the No. 1 carbon atom. If we assume that hydroformylation occurs only at the double bond, we may ask how it is possible to form a straight-chain aldehyde from an internal olefin. 

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). 

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. ... 

The technical application of the hydroformylation reaction has developed rapidly due to the industrial importance of its products. Many data were obtained during this development work, which allowed H. J. Nien-burg et aL [236] and A. J. M. Keulemans, A. Kwantes and Th. van Bavel [25] to lay down certain empirical rules for the oxo reaction. For quite some time these rules were the basis for the understanding of the product distribution in the hydroformylation reactions. There was no systematic investigation of the reaction mechanism of this process in the early years. Unsatisfactory analytical results were responsible for many misinterpretations. It was assumed that the hydroformylation proceeds through heterogeneous catalysis, an assumption which is supported by some authors even in the sixties [26, 27] (as to these papers see the critical discussion in the paper of V. Macho et aL [28]). 

There remains one more isomerization to be discussed. The formyl group formed in the hydroformylation of olefins with longer carbon chains need not necessarily be attached to one of the C-atoms having previously formed the double bond but can also be bound to other C-atoms of the carbon chain. This is especially the case if the addition to neither C-atom of the double bond results in the formation of an energetically and steri-cally favored alkylcobaltcarbonyl. As an example internal straight chain olefins may be taken. Under favorable reaction conditions they yield nearly the same isomer distribution as the corresponding terminal olefins do [25]. Another example is ethyl vinylacetate which yields the same reaction products as ethyl crotonate does. 

The hydroformylation of the water-soluble substrates, 4-penten-l-ol and 3-buten-l-ol in aqueous solution using HRh(CO)(TPPTS)3 as the catalyst was investigated. Activation parameters and reaction selectivity for the hydroformylation of 4-penten-l-ol were found to depend on the ionic strength of the solution. As sodium sulfate was added, the activation energy increased. The linear-branched selectivity was strongly influenced by the ionic strength and temperature. The reaction could be directed to yield a product distribution of modest linearity (75%) or an exceptionally high ratio of the branched product (98%) as a cyclic 2-hydroxy-3-methyltetrahydropyran [33]. 

Improvement in the isomer distribution can be achieved by lowering the hydroformylation temperature from the range 150°-170°C, now used industrially, to 100°C. Figure 3 shows an almost constant 2% increase in yield of straight chain products for each 10° decrease in reaction temperature. This increase becomes even more pronounced (4-5%) at higher hydrogen partial pressure (CO H2 = 1 3). 

The reactions of ethyl acrylate and ethyl crotonate were studied (117) in the presence of ethyl orthoformate using 1 1 CO/H2 and 250 and 200 atm pressure. For ethyl acrylate, the distribution of products corresponded to j3-hydroformylation 78.2%, (y,y-diethoxybutyrate and j3-formylpropionic acid), and a-hydroformylation 21.7%, (a-methyl-j8-ethoxyacrylate and -methyl-j3,/3-diethoxypropionate). For ethyl crotonate, y-hydroformyla-tion occurred to the extent of 67-73% (8,8-diethoxyvalerate and y-formyl-butyrate) and a-hydroformylation to the extent of only 13.6% (a-ethyl-/ -ethoxyacrylate and j3-ethyl-j8-diethoxypropionate). 

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