Calorimetric investigations of hydrogen bonding in binary mixtures containing pyridine and its methyl-substituted derivatives. I. The dilute solutions of water

摘要

Enthalpies of solution of water in pyridien and its methyl derivatives were investigated at T = 298.15 K with a titration calorimeter. The effects of solution are exothermic and increase in the following order: pyridine < 3-methylpyridine < 4-methylpyridine < 2-methylpyridine < 2,6-dimethylpyridine < 2,4,6-trimethylpyridine. As expected, the negative enthalpies of solution are fairly large, especially those for pyridine derivatives with a methyl group in the ortho position, due to the formation of hydrogen bonds between water and amine. Thus, the energy of the N...H-O bond, strengthened by the ortho methyl group, overcomes the hindering effect of that group. The experimental results were correlated with the association energies of the 1:1 (water + amine) complexes and with the net charges on the nitrogen atom reported in the literature. Although model based on the hydrogen bond interactions was found to be too simple to account for the measured heat effects.