Direct self-condensation of bio-alcohols in the aqueous phase

Bio-alcohols (e.g. ethanol, butanol) are primarily obtained as diluted aqueous solutions from biomass fermentation, and thus the subsequent isolation is a very costly process. So the direct transformation of bio-alcohols in water will have great advantages. This study describes the development of catalysts used for the self-condensation of bio-alcohols in water (that mimic the primary fermentation solutions). Efficient iridium catalysts have been developed rationally from homogeneous to heterogeneous, and the immobilized catalysts could be reused without any loss of activity, which is very important for the development of practical processes. The expected self-condensation could be realized with 80–90% selectivity in water and air. Such a protocol might be used for producing butanol from ethanol solution directly, which is an improved higher-alcohol biofuel. Other useful chemicals, such as 2-ethylhexanol, could also be obtained from renewable resources through this condensation reaction.