A review of the reactivity of organic compounds with oxygen-containing functionality in superheated water

Abstract

Understanding the reactivity of organic molecules in pure superheated water is developing from studies aimed at explaining how organic matter (kerogen) forms and then breaks down, in low temperature (<150°C) natural environments, into energy source materials. In natural systems where kerogens are depolymerized to generate petroleum, superheated water is ubiquitous. Organic compounds, especially those with oxygen-containing functionality, can participate in reactions such as ionic condensations, additions, cleavages and hydrolyses. These reactions are discussed with an awareness to their facilitation by changes in the chemical and physical properties of water as temperature increases. It is emphasized that these changes make the solvent properties of liquid water at high temperature similar to those of polar organic solvents at room temperature, thus favoring ionic versus thermal free radical solution phase reactions with organic compounds. Examples illustrate that in this aquathermolysis chemistry, water can participate in one or more roles: as a catalyst, reactant, and solvent. It is often not necessary to add acid, base, or other catalysts. We point out how an understanding of the aqueous chemistry of a wide range of organic molecules may lead to environmentally friendly potential applications in areas as diverse as recycling of plastics, syntheses of chemicals, and generation of liquid fuels from natural resource materials.