Near-critical water (liquid water between 200 and 374 °C) offers an environmentally benign
alternative for the replacement of undesirable solvents and catalysts. This work characterizes
the solvent strength of liquid water at saturation pressure from ambient temperature to 275 °C
in terms of its Kamlet−Taft dipolarity/polarizability, hydrogen-bond-donating acidity, and
hydrogen-bond-accepting basicity using in situ UV−vis spectroscopy. The results suggest that
near-critical water exhibits a wide range of polarity and hydrogen-bond-donor ability for tailoring
chemical reactions and separations. These Kamlet−Taft solvent parameters can be used to
correlate kinetic properties for reactions in water. As model reactions, the temperature-dependent
kinetics of the hydrolyses of two nitroaromatic compounds, 4-nitroaniline and N,N-dimethyl
nitroaniline, were determined in NCW in the temperature range of 200−275 °C. The hydronium
ion dissociated from water promotes the initial hydrolysis reaction without the addition of any
acid. Solvent effects on the rate constant were correlated with Kamlet−Taft solvent parameters
based on a linear solvation energy relationship (LSER).
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