Thermodynamic properties of 1,4-benzoquinone (BQ), 1,4-hydroquinone (HQ), 1,4-naphthoquinone (NQ), 1,4-naphthohydroquinone (NHQ), and the complexes BQ–HQ 1:1, NQ–HQ 1:1, NQ–NHQ 2:1, and NQ–NHQ 1:1

Abstract

Simultaneous torsion and mass loss effusion techniques are applied to measure vapor pressure as a function of temperature. The enthalpy of sublimation is derived from the temperature dependence of vapor pressure. Overall mean values for both techniques are as follows: 1,4-benzoquinone, ΔH°s(261.50 K) = (68.0±0.5) kJ mol−1; 1,4-hydroquinone, ΔH°s(342.37 K) = (103.9±1) kJ mol−1; 1,4-naphthoquinone, ΔH°s(313.21 K) = (90.7±2) kJ mol−1; 1,4-naphthohydroquinone, ΔH°s(381.09 K) = (119.0±1) kJ mol−1. The complexes evaporate incongruently. The enthalphies of sublimation of the first mentioned constituent when evaporated are found as follows: BQ–HQ 1:1, ΔH°s(312.97 K) = (88.6±1) kJ mole−1; NQ–HQ 1:1, ΔH°s(324.03 K) = (98.7±1) kJ mole−1; NQ–NHQ 2:1, ΔH°s(328.49 K) = (88.7±3) kJ mol−1; NQ–NHQ 1:1, ΔH°s(342.36 K) = (102.3±2) kJ mol−1. The temperatures given are midrange values at which the saturation vapor pressure of each substance is 0.4 Pa. From the measured vapor pressures and the enthalphies the sublimation of Gibbs energies and enthalpies of complexation are calculated: BQ–HQ 1:1, 295 K, ΔG°compl = (−13.8±1) kJ mol−1, ΔH°compl = (−20.6±1) kJ mol−1; NQ–HQ 1:1, 320 K, ΔG°compl = (−3.2±2) kJ mol−1, ΔH°compl = (−8.0±2) kJ mol−1; NQ–NHQ 2:1, 320 K, ΔG°compl = (−12.9±1) kJ mol−1, ΔH°compl = (−9.6±4) kJ mol−1; NQ–NHQ 1:1, 330 K, ΔG°compl = (−8.6±1) kJ mol−1, ΔH°compl = (−11.6±2) kJ mol−1.