| Near-critical water (NCW) has been investigated as a green chemistry alternative to organic solvents. The development of new methodologies using water as a solvent and reagent, has provided an array of important, standard organic reactions in water below the critical point without organic solvents, corrosive acids, bases or environmentally unfavorable metal catalysts such as Hg. A number of these key transformations have been investigated in NCW and afford the expected (predicted) organic product(s).; Functional group transformation of organic systems investigated in water below the critical point (∼325°C, 1200 psi) has shown terminal alkynes hydrate to give methyl ketones and internal alkynes give mixtures of ketones. Olefin migration, alcohol dehydration, hydrolysis of nitriles to acids (and amides), intramolecular cyclodehydration, Diels-Alder, and lactonization have also been realized.; In the presence of sodium formate, aldehydes are reduced to alcohols in near-critical water at temperatures and pressures below those required to reduce cyclic ketones. Acyclic ketones afford only minor amounts of alcohol with sodium formate even under more forcing conditions; therefore providing a green route to the chemio-selective reduction of aldehydes in the presence of ketones. The use of other formates such as ammonium formate provides a green route to the amination of aldehydes.; The introduction of metal catalysts such as palladium or rhodium on carbon in near-critical water employing sodium formate as a hydrogen source provided a “green” procedure for the hydrogenation of olefins and acetylenes. Palladium on carbon with and without sodium formate also dehalogenates aromatic rings.; The replacement of H2O with D2O allows for the introduction of deuterium labels into organic reagents through electrophilic aromatic substitution, hydration and dehydration, acid/base equilibria, and catalytic reduction. |
