Review of C-C Coupling Reactions in Biomass Exploitation Processes

Biomass represents the type of renewable energy source that will play a substantial role in the future global energy balance, as it is the only renewable source with the potential to be converted to liquid, solid and gaseous fuels. Today lignocellulosic biomass appears to be the cheapest and most abundant biomass feedstock, yet no economically and technologically feasible process is developed for its conversion to fuels, at least competitive with the currently used petroleum fuels. Biomass pyrolysis is an emerging thermochemical conversion process that leads to the production of bio-oil. Bio-oil however, presents several undesired properties that do not permit its direct exploitation. On the other hand, sugars derived from lignocellulosic biomass make up the predominant class of compounds, also exhibiting undesired properties. In both cases presence of oxygen in biomass derived copounds seems the major problem. Recently the targeted pathways for the conversion of lignocellulose-derived carbohydrates to liquid transportation fuels involve the partial removal of oxygen, CC bond formation of functional molecules, and removal of the remaining oxygen. The formation of C-C bonds between these oxygenated molecules can take place by aldol condensation, alkylation, or ketonization as will be described in the present review study.