Green transformations of bio-based chemicals

Abstract

This thesis work was focused on the development of green chemical technologies for the upgrading of platform molecules obtainable from renewable feedstocks through a biorefinery scheme. The feedstocks were chosen among those considered as the most promising for the development a new, sustainable, chemical industry. Levulinic acid (LA) can be converted into new derivatives with a higher degree of oxigenation (methyl levulinate and its 4,4-dimethyl ketal, dimethyl succinate and dimethyl 3-methylsuccinate), without actually using oxidizing agents. This result was achieved by using dimehtyl carbonate (DMC), a green reagent and solvent, in conditions of basic catalysis (K2CO3). Bio-derived lactones such as gamma-valerolactone, gamma-butyrolactone, delta-valerolactone and epsilon-caprolactone were reacted with three dialkylcarbonates (DMC, diethyl- and dibenzylcarbonate). The five-membered ring lactones yielded the corresponding alpha-alkylated derivatives with high selectivity and yields. The six- and seven-membered ringed lactones afforded highly oxygenated acyclic monomeric derivatives otherwise hardly accessible by previous chemistry. Gamma-valerolactone was chosen as a model to study acid catalyzed ring-opening reactions. A novel reactivity of the molecule was discovered in the presence of DMC. The 4-methoxy pentanoyl moiety was thus accessible by a green route. A reaction mechanism, supported by experimental and computational data, was proposed. The reaction was then extended to a continuous flow process, with solid acid catalysts. In such conditions, the selectivity towards methyl 4-methoxy pentanoate or methyl pentenoate, monomer for the production of polymers, can be tuned by optimising the operating parameters: Bio-derived diols were efficiently upgraded using organic carbonates in tandem with ionic liquids as organocatalysts. The study investigated the parameters that control the selectivity towards cyclic- or linear di-carbonates. The derivatisation of fatty acids methyl ester in conditions of on-water catalysis was investigated whilst at the University of Sydney, with the aim of developing a green strategy to reduce the cloud point of biodiesels. A new branched additive was synthesised, the thermal characteristics of which were analysed, both pure and blended with biodiesel. The study of on-water catalysis continued by investigating the mechanism and the effect of reagent structure on on-water catalysis. It was demonstrated, by using the model reactions between cyclopentadiene (cp) and alkyl vinyl ketones, that little changes of the alkyl chain of a reactant have a dramatic influence on the catalytic effect. In particular, the reaction between ethyl vinyl ketone and cp was demonstrated to be on-water catalysed. When vinyl ketones bearing a longer or bulkier alkyl chain were tested, the catalytic effect was not observed, and the reactions were as fast as in neat conditions.