(713c) Selective Removal of Protecting Groups Using Water At Elevated Temperatures

Protecting groups are frequently used in multistep syntheses of chemicals and generally require the utilization of strong acids or bases for the removal of these protecting groups.  Hot water is an ideal solvent for the development of sustainable, environmentally green processes for the removal of protecting groups.  At temperatures and pressures higher than ambient (150-275°C), the physical and chemical properties of water change drastically compared to common polar organic solvents.  This change in the properties is due to the decrease of hydrogen bonding, which ultimately results in enhanced solubility of nonpolar organic species.  In addition the auto-ionization constant (K_W) of water increases by three orders of magnitude compare to ambient conditions, making hot water a source of hydronium and hydroxide ions.  These ions are available to act as catalysts for an acid- and/or base- catalyzed reaction; these currently require additional, mineral acid or base, and the subsequent catalyst neutralization creates a problem of salt disposal.   By employing hot water as the reaction solvent and catalyst simultaneously, the need for environmentally hazardous solvents and acid catalysts is eliminated.   The efficient water-mediated selective removal of removal of protecting groups will be discussed for a variety of organic substrates.