(375e) Continuous Piancatelli Rearrangement of Furfuryl Alcohol: Kinetics and Reactor Modelling

In the last few years the focus of research has been in the use of lignocellulosic biomass as an alternative feedstock for fuels, pharmaceuticals and platform chemicals. Although there has been much interest in this field of research, the subsequent valorization steps after the conversion of cellulose to various platform molecules have to be explored thoroughly. In most of these reactions in aqueous mixtures, humins often emerge as undesired polymeric by-products. In this study the Piancatelli Rearrangement to 4-hydroxycyclopent-2-enone (4HCP) starting from furfuryl alcohol as a commonly used platform molecule was investigated.

The reaction can be carried out continuously in a capillary microreactor, utilizing an acidic water-toluene two-phase system.^[1,2] The major challenge of this reaction system is the formation of the undesired polymers (humins), or the high dilution of the substrate to avoid this, thus resulting in an expensive workup. Both of these issues were investigated by kinetic experiments in a tubular reactor and associated simulations.

The kinetic studies showed that the product formation can be assumed as first order, and the by-product formation as higher order, in the substrate. A corresponding system analysis revealed that the selectivity towards the product can be enhanced by diluting the substrate. Simulations and corresponding experiments could demonstrate that the use of a reactor system with better back-mixing, like a Continuously Ideally Stirred Tank Reactor (CSTR) or a fed-batch reactor, instead of a plug flow tubular reactor (PFTR) improves the selectivity towards the desired 4HCP significantly. Additionally, through the switch from a tubular to a better mixed reactor, the high dilution of the substrate in water can be circumvented, resulting in a significant cheaper downstream processing. This shows that although the current trend in flow chemistry is to apply tubular reactors, and since the choice of the reactor is a valuable tool to improve the performance of a reaction, it should be attended at an early stage.

Finally, using the example of the Piancatelli Rearrangement of furfuryl alcohol to 4HCP we demonstrated that it is possible to enhance the selectivity towards the desired product by a simple utilization of the reactionâ??s kinetics. Simultaneously, the solvent demand was reduced and the work-up simplified by decreasing the amount of polymeric humin-like by-product. Literature

[1] K. Ulbrich, P. Kreitmeier, O. Reiser, Synlett2010, 13, 2037â??2040.

[2] M. Nettekoven, B. Püllmann, R. E. Martin, D. Wechsler, Tetrahedron Lett.2012, 53, 1363â??1366.