TOPOLOGICAL INVESTIGATIONS ON THE ASSOCIATION OF ALKANOLS - EXCESS VOLUME OF PYRIDINE-ALKANOL (C1-C10) MIXTURES

The excess volume (V(E)) has been determined dilatometrically for 10 binary pyridine-alkanol mixtures over the whole composition range at 298.15 K. The V(E) values were negative for pyridine-alkanol (C1-C6) mixtures, sigmoid for pyridine-heptanol mixtures (with negative V(E) values at lower mole fractions of pyridine) and positive for pyridine-alkanol (C8-C-10) mixtures over the complete mole fraction range. V(E) values increased in a positive direction with increase in chain length of the alkanol (C1-C-10). Experimental V(E) data have been analysed in terms of graph theory which utilises the concept of the third-degree molecular connectivity index. The results obtained from graph theory have been used to predict the association of pyridine and alkanols in the pure and mixed states. The V(E) data have also been analysed using the Prigogine-Flory-Patterson theory. An analysis of each of the three contributions viz. interactional, free volume and P* to V(E) shows that the interactional contribution and the free volume effects are negative for all systems, whereas the P* contribution is negative for methanol and ethanol and positive for remainder of the alkanols.