Physical Inorganic Chemistry
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ChemInform Abstract: Thermodynamics of Ionization of Hypophosphorous and Phosphorous Acids. Substituent Effects on Second Row Oxy Acids.
First published: May 30, 1989
Abstract
The pKa values of H3PO2 and H3PO3 at 5, 25, 45, 65, and 85 °C are determined using an NMR method.
ChemInform Abstract
The pKa values of H3PO2 and H3PO3 at 5, 25, 45, 65, and 85 °C are determined using an NMR method. These data allow calculation of the ΔH° and ΔS° of ionization to be -12.69 kJ and -66.3 J/K for H3PO2, -14.86 kJ and -73.8 J/K for H3PO3, and -7.74 kJ and -67.1 J/K for H3PO4. It is seen that the acidity trend of this series is due primarily to the change in enthalpy. Substitution of OH for H leads to decreased acidity in the phosphorous oxy acid series. This trend is opposite the inductive effect observed in other acids and can be interpreted in terms of backbonding.
