Study of the 4:1 inclusion compound between deoxycholic acid and (E)-p-dimethylaminoazobenzene by vapour pressure measurements

Vaporization studies on pure (E)-p-dimethylaminoazobenzene (hereafter indicated as DAB) and the DAB-choleic acid (DCADAB) were accomplished by means of the torsion effusion method. The pressure of the vapour in equilibrium with the solid phase was determined for DAB as log P (kPa) = (15.05±0.18)−(6887±500)/T and by the second-law treatment of the vapour pressure data a ΔH°381 = 132±8 kJ mol−1 was obtained for DAB vaporization from the pure compound. Since the tensimetric data of DCADAB lie at the limit of the instrument's working range only a rough value of ΔH°435 = 138 kJ mol−1 was obtained for DAB vaporization from DCADAB. This finding agrees with the strong DAB-DCA interactions found in the DCADAB crystal structure.