Alcohols are important class of products that find application as intermediates in organic synthesis for agrochemicals, detergents, plasticizers, or as oxygen containing compounds blended into fuels. In most of the cases, these valuable materials are produced in separate steps from terminal alkenes, namely by a hydroformylation reaction followed by aldol condensation of the resulting aldehyde to higher aldehydes and its subsequent hydrogenation to alcohols [1]. We reported supported catalysts for gas phase hydroformylation reactions of propene to butanals [2] and the objective of this work was to explore a C-C bond forming catalyst that can be used for the tandem conversion of propene to 2-ethylhexenal. Conventionally, n-butanal is quantitatively converted to 2-ethylhexenal using 2% sodium hydroxide solution or using basic ion exchange resins [3]. To mitigate the problems related to homogenous catalysts, we synthesized and characterized various metal substituted mesoporous SBA-15 silica supported primary, secondary and tertiary amine catalyst for the gas phase self-condensation of n-butanal to 2-ethyl hexenal. The activity and stability of amine-supported catalysts are strongly influenced on the nature of amine species, density of amine sites on the support material, support pore size, nature of metal site introduced and the spatial separation between the acid and amine groups. For instance, secondary amine supported on Ti-SBA-15 showed the best catalytic performance and are nearly two times more active than amine supported Si-SBA-15. These results suggest that an increase in Bronsted acidity and their spatial separation play an important role in in the self-condensation of n-butanal to 2-ethylhexenal. A mechanism for aldol condensation is proposed and then analyzed using density functional theory (DFT). DFT analysis of the reaction pathway suggests that the rate-limiting step in aldol condensation is carbon-carbon bond formation, which is consistent with the observed kinetics. [1] C. Kohlpaintner, M. Schulte, J. Falbe, P. Lappe, J. Weber, Ullmann's Encyclopedia of Industrial Chemistry, 2008, Wiley-VCH, Weinheim.[2] S. Shylesh, D. Hanna, S. Werner, A. T. Bell, ACS Catal. 2 (2012) 487-493.[3] F. King, G. J. Kelly, Catal. Today 73 (2002) 75-81.

Tailored acid-base groups on silica supports: Applications in the self condensation of n-butanal

248th National Meeting (2014)

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