CATALYTIC ALDOL CONDENSATIONS OF BIO-DERIVED ALDEHYDES AND KETONES
In response to the environmental changes due to the utilization of fossil fuels for the production of energy and chemicals, biomass has been proposed as an alternative and sustainable raw material. The chemical differences between the two feedstocks make bio-derived platform molecules more suitable for low-temperature processing via reactions such as aldol condensation that rely on oxygen-containing functional groups. In this thesis, aldehydes (furfural and HMF) and ketones (acetone and derivatives of levulinic acid) that can be obtained from biomass are combined into their corresponding aldol condensation products, which may serve as intermediates in the production of biofuels, polymeric materials and organic dyes. The developed processes have been designed by following the principles of Green Chemistry, especially for the use of environmentally benign solvents, the avoidance of protecting groups and the use of basic catalysts such as Mg-Al hydrotalcites and derivatives, and sodium hydroxide. After developing microwave-assisted protocols to selectively condensate furfural and HMF with acetone, the same reactions were studied with a number of spectroscopic techniques and catalyst characterizations to elucidate various aspects of the reaction mechanism such as the behaviour of the intermediates and the catalyst deactivation. Finally, the possibility of using ethyl levulinate in aldol condensations with furfural, as a substitute of sodium levulinate, was assessed. In conclusion, catalytic aldol condensation processes were successfully developed, implementing catalyst recovery and recycling, and the fundamental understanding of the reactions was increased.
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