Attempts towards the catalytic ketonization of levulinic acid to 2,5,8-nonanetrione
The ketonization of carboxylic acids to ketones has been explored since the mid 1800’s. However, the vast majority of studies focus on the use of carboxylic acids that do not possess any additional functional groups. Levulinic acid (LA), an important biomass derived platform chemical, presents both a carboxylic acid and a ketone functionality, which considerably increases the self-reactivity of this molecule. This is especially apparent at the high temperatures (300-400 °C) required for ketonizations over solid catalysts like CeO2/Al2O3 or ZrO2. The primary product of the ketonization of LA would be 2,5,8-nonanetrione (NTO) – which due to its structure – could be hydrogenated to the corresponding triol and applied as a 3D-crosslinker in the polymer industry. Prior attempts to produce this molecule required very complex synthetic routes and processes that could not be applied on industrial scale. Our goal was to develop a fixed-bed flow reactor that would promote the ketonization of LA in a one-step process; however, all attempts to obtain NTO in useful yields resulted in the formation of angelica lactones – the products of the self-reaction of LA – and 3-methyl-2-cyclopenten-1-one (3-MCP) which is the product of self-aldol condensation of the transient NTO, followed by further elimination of H2O and acetone. The mechanism and thermodynamic parameters of these reactions will be discussed in this thesis.