(589f) Understanding Reaction Networks for the Ring Opening of Lactones on Supported Oxide Catalysts

Improvements in enzymatic and genetic engineering capabilities have enabled biological engineers to synthesize high titers of a diverse range of novel platform chemicals.  These feedstocks have opened new avenues for researchers in the area of heterogeneous catalysis to apply and expand upon knowledge from the petrochemical industry to upgrade these highly functionalized molecules.¹

2-Pyrones, specifically triacetic acid lactone (TAL), can be synthesized enzymatically or by S. cerevisiae and allow for multiple upgrading routes.²  After consecutive hydrogenation and dehydration reactions, TAL can be converted into delta-hexalatone, which provides a route to synthesize alpha,omega-functionalized molecules.  Upon reaction with methanol over a supported cesium catalyst, the lactone undergoes ring-opening and esterification to form an unsaturated ester.  We have probed lactones of different ring size and carbon number to understand the selectivity to the unsaturated isomers.  To elucidate the mechanism of ring-opening over a supported base catalyst, we performed weight hourly space velocity studies, apparent activation energy studies, and studies of alcohol dehydration reactions.  Our results show that lactones that pass through a hydroxy ester intermediate produce lower yields to the terminal unsaturated esters.

The production of linear alpha olefins (LAO) is another target for the upgrading of lactones.  The lactone undergoes ring-opening and decarboxylation to form LAO over solid acids. Lewis acids, such as gamma-alumina, produce higher selectivities to the alpha olefins than Brønsted acid catalysts, such as silica-alumina.  By impregnating alumina with tungsten, the selectivities to the alpha olefin increase as a result of the decreased basic site density.³  We have studied the reaction network with weight hourly space velocity studies and probe molecules to elucidate the mechanisms for ring-opening and decarboxylation.

(1)      Shanks, B. H. Ind. Eng. Chem. Res. 2010, 49, 10212–10217.

(2)      Cardenas, J.; Da Silva, N. A. Metab. Eng. 2014, 25, 194–203.

(3)      Wang, D.; Hakim, S. H.; Alonso, D. M.; Dumesic, J. A. Chem. Commun. (Camb). 2013, 49, 7040–7042.