| Issue |
J. Chim. Phys.
Volume 74, 1977
|
|
|---|---|---|
| Page(s) | 767 - 777 | |
| DOI | https://doi.org/10.1051/jcp/1977740767 | |
| Published online | 29 May 2017 | |
A dielectric investigation on water-pyridine system
Department of Chemistry, Faculty of Science, University of Cairo, Egypt.
The property-composition curves in water-pyridine mixtures in the full concentration range at 283 to 333 K for volume and « free volume » contraction, viscosity, relaxation lime, and dielectric constant and refractive index diverge from the additive law : they were all found to heve a maximum in the vicinity of 30 mole percent of pyridine. The evidence for the existence of the hydrogen-bonded complex C5H5X, 2H2O in solution to which this maximum is due, was subsequently justified by molecular beam experiments.
The relation of relaxation time to viscosity, and the temperature and « free volume » dependence of both are discussed, A model is proposed to account for the observed properties, and comparison is made between the water-pyridine and water- loxane systems in regard to interactions between unlike molecules.
The behaviour of water protons in a series of organic sol- vent which are proton acceptors, such as pyridine and dio- xane was studied some fifteen years ago by NMR- and infrared techniques (1-6). Rizk (7) extended the research into complex formation by density, dielectric constant and viscosity determinations for the water-dioxane system. In continuation of this work, the same lines of evidence completed by molecular beam experiments were used to investigate water- pyridine mixtures.
Résumé
Entre 283 et 333 K aucune des grandeurs suivantes : volume, viscosité, temps de relaxation diélectrique, constante diélectrique statique et indice de réfraction ne suit une loi additive en fonction de la concentration : elles présentent toutes un maximum vers 30 mole % de pyridine. Ainsi ces études, étendues à tout le domaine de concentration, mettent en évidence un complexe C5H5N, 2H2O, maintenu par liaisons hydrogène. Récemment des expériences de jets moléculaires confirment l’existence d'un tel complexe.
La relation entre temps de relaxation et viscosité, ainsi que la variation de ces deux grandeurs en fonction de la température et du « volume libre » sont discutées. Enfin un modèle est proposé pour rendre compte des propriétés observées et une comparaison sur l’interaction entre molécules dissemblables dans les mélanges eau-pyridine et eau-dioxane clôt l'article.
© Paris : Société de Chimie Physique, 1977