Association in dilute aqueous solution of pyridine and its methyl derivatives studied by cryoscopic method

Pyridine and its methyl derivatives form complexes with water due to hydrogen bonds. The co-operative nature of the hydrogen bonds leads to the association of the complexes and to various modes of hydration. The degrees of association of monohydrate complexes have been calculated for liquid dilute aqueous solutions of pyridine, 2-, 3-, 4-methylpyridine, and 2,6-dimethylpyridine at temperatures from 273K to 268.5K. The association number increases with an increase of the amine concentration. Positive correlation was found between the degree of association of the 1:1water–amine complexes and the size ofmicroheterogeneities. Itwas shown that the mechanics of this process involves hydrogen bonding and van derWaals interactions