Organic Reactions in Sub- and Supercritical Water in the Absence of Any Added Catalyst

Recent interest in the use of sub- and supercritical water as alternative media for various organic reactions lies in the enhanced solubility and reaction rate of organic substrates, and the increase in the dissociation of water into H3O  and OH  under these conditions. If properly chosen, organic reactions could take place under homogeneous conditions with no other additives at high temperature and yet the reaction products separate out of the aqueous phase when cooled to ambient conditions, thereby reducing the environmental burden of the workup processes. After short surveys of the preceding studies, we report in this comprehensive paper on our recent collaborative work directed toward the mechanistic and exploratory investigations of organic reactions in sub- and supercritical water in the absence of any added catalyst. They cover the formations of polyacenequinones via crossed aldol condensation of 1,4-cyclohexanediones with arene-o-dicarboxyaldehydes, 1,3,5-triaroylbenzenes by means of Michael-type cyclotrimerization of 1-aryl-2-propyn-1-ones, and 1,3,5-triacetylbenzenes by cyclotrimerization of 4-methoxy-3-buten2-one, all leading to important intermediates for synthesizing materials of nanotechnological importance. Some experimental and recommended methods and future directions are discussed.