Hydroformylation, aldehydes from, with alkenes

The synthesis of aldehydes from alkenes known as hydroformylation using CO and hydrogen and a homogeneous catalyst is a very important industrial process [204]. Today, over seven million tons of oxoproducts are formed each year using this procedure, with the majority of butanal and butanol from propene. To further increase the efficiency of this process it can be combined with other transformations in a domino fashion. Eilbracht and coworkers [205] used a Mukaiyama aldol reaction as a second step, as shown for the substrate 6/2-63 which, after 3 days led to 6/2-65 in 91% yield via the primarily formed adduct 6/2-64 (Scheme 6/2.13). However, employing a reaction time of 20 h gave 6/2-64 as the main product. 

In contrast to the normal-scXcctwc hydroformylation mainly developed in industry, asymmetric hydroformylation, which requires /i o-aldehydes ( branched aldehydes) to be formed from I-alkenes, was first examined in the early 1970s by four groups independently, using Rh(i) complexes of chiral phosphines as catalysts. " Since then, a number of chiral ligands have been employed for asymmetric hydroformylation and used in combination with transition metal ions, especially Pt(ii) and Rh(i). Asymmetric hydroformylation of I-alkenes is most extensively studied. 

It was discovered by Roelen in 1938 and is the oldest and largest volume catalytic reaction of alkenes, with the conversion of propylene to butyraldehyde being the mosi important. About 5 million tons of aldehydes and aldehyde derivatives (mostly alcohols) are produced annually making the process the most important industrial synthesis using a metal carbonyl complex as a catalyst. The name hydroformylation arises from the fact that in a formal sense a hydrogen atom and. formyl group are added across a double bond. The net result of the process is extension of (he carbon chain by one and introduction of oxygen into the molecule. 

The hydroformylation reaction or 0x0 process is an important industrial synthetic tool. Starting from an alkene and using syngas, aldehydes with one or more carbon atoms are obtained. In almost all industrial processes for the hydroformylation of alkenes, rhodium or cobalt complexes are used as catalysts [33]. A number of studies on ruthenium complex-catalyzed hydroformylation have been reported [34]. One of the reasons for the extensive studies on ruthenium complex catalysts is that, although the rhodium catalysts used in industry are highly active, they are very expensive, and hence the development of a less-expensive catalytic system is required. Since inexpensive ruthenium catalysts can achieve high selectivity for desired u-alde-hydes or n-alcohols, if the catalytic activity can be improved to be comparable with that of rhodium catalysts, it is possible that a ruthenium-catalyzed 0x0 process would be realized. 

The hydroformylation reaction or oxo synthesis, discovered in 1938 by O. Roelen in the laboratories of Ruhr Chemie in Germany, is of great importance as a synthetic tool. Starting from an alkene and using syn-gas (Hj/CO = 1/1), aldehydes with one more carbon are obtained, according to Eq. (1). More than 5 million tons of aldehydes are produced in the... 

As far as is known, the only industrial application of the water-soluble catalyst for the hydroformylation of 5 -functionalized alkenes has been developed by Kura-ray [17]. In this process, 7-octen-l-al is hydroformylated into nonane-1,9-dial, a precursor of nonene-l,9-diol, by using a rhodium catalyst and the monosulfonated tri-phenylphosphine as water-soluble ligand in a 1 1 sulfolane/water system. At the completion of reaction, the aldehydes are extracted from the reaction mixture with a primary alcohol or a mixture of primary alcohol and saturated aliphatic hydrocarbon (cf. Section 6.9). 

Hydroformylation is a useful catalytic method for the synthesis of aldehydes from alkenes and alkynes. There are no other methods that compete directly with hydroformylation for the synthesis of alkyl aldehydes. However, when the desired compounds are carboxylic acids or esters, and aldehydes are used as their... 

The inertness of SC-CO2 is also useful for metal-catalyzed hydroformylations and hydrogenations of alkenes to the corresponding aldehydes. Selective hydroformylations were obtained with Co catalysts. [26] They profit from the good miscibility in SC-CO2 (Scheme... 

The n i ratio of aldehydes formed by the hydroformylation of a 1-alkene with rhodium catalysts containing PPhj varies from 3 to 12. The highest regioselectivity is obtained at high concentrations of PPhj and low pressures of CO. As depicted in Scheme 17.10, at high concentrations of PPhj, n-aldehydes are formed selectively through diphosphine intermediates. At lower concentrations of PPh, more reactive and less selective monophosphine intermediates are responsible for the lower n i ratios. 

In the hydroformylation of terminal olefins, superior results in comparison to BISBI at higher temperature were noted l/b = 54.2 in comparison to BISBI Hb = 2.4) [66]. Moreover, with these tetraphosphines more than 95% linear selectivity and up to 94% yield of total aldehydes starting from 2-alkenes (2-pentene, 2-hexene, 2-octene) were observed in isomerizing hydroformylation [67]. The M-regioselectivity increased in relation to the nature of Ar in the following order, indicating a remarkable electronic effect ... 

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