Catalytic hydroformylation reaction isomerization

In the case of 38, a significant amoimt of olefin was foimd to isomerize. This observation implies that the isomerization and hydroformylation reactions take place simultaneously. The former process results in the formation of internal olefins which are ultimately converted into aldehydes in the case of 36 and 37. However, the hydroformylation process of the internal olefins is apparently less effective with the indium-containing catalyst 38. This property allows the isolation of substantial yields of internal olefins in catalytic reactions (17-37% after 18 h). It can be explained by a simple reaction scheme involving the individual rate constants of the various processes, as shown in Scheme 18. It appears from the data presented in Table 7 that the rate constants 2 and are larger than fci in the case of the aluminum- and gallium-containing catalysts 36 and 37, whereas the reverse is true for indium-containing 38. 

Treatment of 1-alkenes with a cobalt catalyst under high pressures (100-200 atm) of synthesis gas (CO + H2) at 120-150 C (catalytic hydroformylation) seldom leads to the isolation of isomerized olefins even when the reaction is interrupted before all of the olefin disappears. The appearance of the formyl group on a carbon atom other than those involved in the carbon-carbon double bond of the starting alkene arises because of successive 1,2-addition-eliminations, which move the cobalt down the chain without dissociation of coordinated HM. That such a sequence of reactions occurs was demon-... 

Pd showed significantly promotional effect than Pt and Ru for Co/Si02 catalyst in hydroformylation of 1-hexene [4], Cobalt free lwt% Ru, Pt and Pd supported on active carbon were prepared and tested in hydroformylation reaction. As shown in Table 1, these kinds of catalysts showed very low activity for 1-hexene hydroformylation. For the Ru catalyst, the 1-hexene eonversion was 81.3%, but the 1-hexene was only converted to isomerization produets. For the Pt and Pd catalysts, both the 1-hexene conversion and oxygenates selectivity were very low. Results show in Table 1 indicate that the noble metal/active carbon catalysts themselves had no catalytic activity of 1-hexene hydroformylation to form oxygenates. 

Based on the activation and elementary steps outlined, a variety of catalytic reactions can be better understood and catalytic cycles defined. We consider a few major classes of reactions isomerization, hydrogenation, carbonylation, hydroformylation, oxidation, and metathesis. 

The desired reaction in catalytic hydroformylation is the addition of carbon monoxide and dihydrogen to the olefin substrate usually to obtain aldehyde. To some extent, however, concurrent reactions of the olefin (substrate) such as hydrogenation, isomerization, and special carbonylations, and consecutive reactions of the aldehyde product such as hydrogenation to alcohol, aldol reaction, trimer-ization, and formate formation take place under the reaction conditions of hydroformylation, which affect both yield and selectivity of the aldehyde products. For an example of product composition obtained using an unmodified cobalt catalyst in the BASF process, see Table 3. 

To achieve a considerable result for internal olefin hydroformylation, it is generally accepted that the catalytic system should meet the following requirements (i) the isomerization of the internal olefin to the terminal olefin must be faster than the hydroformylation reaction (ii) the hydroformylation of the terminal olefin must be faster than any other hydroformylation reaction and (iii) the activity and selectivity of the catalyst for the hydroformylation of the terminal olefin must be really good. 

The reverse reaction (formation of metal alkyls by addition of alkenes to M-H) is the basis of several important catalytic reactions such as alkene hydrogenation, hydroformylation, hydroboration, and isomerization. A good example of decomposition by y3-elimination is the first-order intramolecular reaction ... 

The formation of isomeric aldehydes is caused by cobalt organic intermediates, which are formed by the reaction of the olefin with the cobalt carbonyl catalyst. These cobalt organic compounds isomerize rapidly into a mixture of isomer position cobalt organic compounds. The primary cobalt organic compound, carrying a terminal fixed metal atom, is thermodynamically more stable than the isomeric internal secondary cobalt organic compounds. Due to the less steric hindrance of the terminal isomers their further reaction in the catalytic cycle is favored. Therefore in the hydroformylation of an olefin the unbranched aldehyde is the main reaction product, independent of the position of the double bond in the olefinic educt ( contrathermodynamic olefin isomerization) [49]. 

Propylene carbonate is a good solvent of the rhodium precursor [Rh(acac) (00)2] and the phosphite ligand BIPHEPHOS and can thus be used as the catalyst phase in the investigation of the isomerizing hydroformylation of trans-4-octene to n-nonanal in a biphasic system [24]. As already mentioned, the reaction products can be extracted with the hydrocarbon dodecane. Instead of an additional extraction after the catalytic reaction, we carried out in-situ extraction experiments, where the products are separated from the catalytic propylene carbonate phase while the reaction is still in progress. Conversion of 96% and selectivity of 72% was achieved under comparably mild conditions (p(CO/H2) = 10 bar, T = 125 °C, 4 h, substrate/Rh = 200 1). 

In the previous chapters we discussed alkene-based homogeneous catalytic reactions such as hydrocarboxylation, hydroformylation, and polymerization. In this chapter we discuss a number of other homogeneous catalytic reactions where an alkene is one of the basic raw materials. The reactions that fall under this category are many. Some of the industrially important ones are isomerization, hydrogenation, di-, tri-, and oligomerization, metathesis, hydrocyana-tion, hydrosilylation, C-C coupling, and cyclopropanation. We have encountered most of the basic mechanistic steps involved in these reactions before. Insertions, carbenes, metallocycles, and p -allyl complexes are especially important for some of the reactions that we are about to discuss. 

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