Heck reactions in hydrothermal, sub-critical water: water density as an important reaction variable

Heck coupling reactions of iodobenzene and cyclohexene in sub-critical water illustrate the importance of water density as a reaction variable. Altering the water density from 0.03 to 0.84 g/mL and the reaction pressure from 30 to greater than 213 bar at 225°C changed both product and isomer yields. The multiple physical effects of water density were also explored by the addition of ionic salts. Changing the isothermal state of the liquid water, measurably altered coupling reaction pathways suggesting that changes in solvent–solute interactions can influence transition states favoring some configurations and disfavoring others.