Environmentally benign chemical reactions in near-critical water and supercritical carbon dioxide

Conventional organic solvents present special challenges when used to carry out reactions. Not only are the solvents expensive to purchase and difficult to remove from the reaction products, but they are also very difficult to dispose without adversely affecting the environment. This work addresses pollution prevention for several industrially important reaction systems by replacing harmful organic solvents with environmentally benign near-critical water and supercritical CO;Chemical processing in near-critical water is possible because of the favorable changes that occur in the chemical and physical properties at high temperatures and pressures. Near-critical water has a density and dielectric constant similar to a polar organic solvent, which allows the dissolution and reaction of both organic and ionic compounds. Also, near-critical water has a strong tendency to ionize and is a source of hydronium and hydroxide ions far better than at ambient conditions, which promotes acid- and base-catalyzed reactions. To demonstrate the feasibility of carrying out typical acid-catalyzed reactions in near-critical water, reaction products of several Friedel-Crafts alkylation reactions are reported. Further, phase-equilibria measurements and detailed kinetic investigations are presented to provide an understanding of the mechanistic features involved in the alkylation reactions.;Supercritical CO...