Untersuchungen zur Synthese linearer Aldehyde durch isomerisierende Hydroformylierung innenständiger n-Alkene petro- und oleochemischer Herkunft (English shop)

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The objective of the research presented in this thesis was to develop a reaction sequence—comprising isomerization and hydroformylation—that converts internal olefins into linear aldehydes, while minimizing hydroformylation at internal positions along the carbon chain. Furthermore, the catalysts developed were intended to operate effectively and with high selectivity within a recyclable reaction system, thereby meeting modern ecological and economic standards.
Internal olefins can be obtained, for example, through the metathesis of 1-olefins. It was demonstrated that the heterogeneously catalyzed metathesis of 1-pentene to 4-octene can be achieved using a Re2O7/Al2O3 catalyst, with a product selectivity of up to 98%. The catalyst system could be reactivated via oxidation in an oxygen stream, allowing it to be used for several months without any decline in activity or product selectivity.
The isomerizing hydroformylation of 4-octene was successfully carried out using a homogeneous catalyst system consisting of Rh(acac)(CO)2 and BIPHEPHOS in propylene carbonate, achieving a 96% selectivity for n-nonanal. The solvent, propylene carbonate, accelerates the isomerization process, which results in a higher yield of n-aldehydes. Moreover, the use of propylene carbonate facilitates the recycling of the homogeneous catalyst through the application of a liquid-liquid biphasic technique. In a series of five recycling runs using the same catalyst, the reaction was carried out without any measurable decline in activity or selectivity. Starting from a C8-olefin fraction rich in n-octene, the production of n-nonanal for the fragrance industry is economically viable, provided the cost of the starting material does not exceed €1.71/kg.
Compared to unsubstituted octenes, fatty acid derivatives are ten times less reactive, and a high degree of hydrogenation occurs. Comparative experiments with model compounds have shown that this high level of hydrogenation is attributable to the high thermodynamic stability of an (α,β,γ,δ)-unsaturated carboxylic acid ester moiety.