The 4th State of Matter!
Water near or above its critical point (374 °C, 218 atm) is attracting increased attention as a medium for organic chemistry. Most of this attention is driven by the search for more “green” or environmentally benign chemical processes. Using near-critical or supercritical water (SCW) instead of organic solvents in chemical processes offers environmental advantages and may lead to pollution prevention.
High-temperature water behaves like many organic solvents in that organic compounds enjoy high solubilities in near-critical water and complete miscibility with SCW. Moreover, gases are also miscible in SCW so employing a SCW reaction environment provides an opportunity to conduct chemistry in a single fluid phase that would otherwise occur in a multiphase system under more conventional conditions.
Moreover, The ion product, or dissociation constant (Kw) for water as it approaches the critical point, is about three orders of magnitude higher than it is for ambient liquid water. Additionally, it can also boast a higher H+ and OH- ion concentration than liquid water under certain conditions. As a result, water becomes excellent solvent for organic species.