Polar species, high pressure chemical reactions

Hot compressed water can be generally described as water at temperature above 150°C and various pressures. Depending upon the temperature and pressure, hot compressed water can exhibit stimulating physical and chemical properties. Water plays a very active role as its dielectric constant sharply decreases and helps the reaction to proceed. Low relative dielectric constant in this state enhances the ionic reaction suitable for a variety of syntheses or some degradation reactions. Depending on the temperature and pressure, hot compressed water supports either free radical or ionic reactions. At high pressures and below the critical temperature, ionic reactions dominate and thus ionic and polar species of biomass are extracted. At high temperatures and low pressures, free-radical reactions are superior and non-polar substances are readily dissolved and extracted (Mohanty et al., 2014). 

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