STUDIES ON CHEMISTRY OF HALOGENS AND OF POLYHALIDES .30. INFLUENCE OF SOLVENT PROPERTIES ON FORMATION OF PYRIDINE-IODINE CHARGE-TRANSFER COMPLEXES

Formation constants of the pyridine-iodine charge-transfer complex have been determined at 25° in 12 solvents with dielectric constants varying from 1.92 to 10.36. The Kx values range from 612 in n-hexadecane to 3248 in o-dichlorobenzene. The enthalpies and entropies of the complex formation have been determined in five solvents. Comparison of the data with the solvent properties indicates that an increase in the dielectic constant of the reaction medium leads to the stabilization of the pyridine-iodine complex. The phenomenon is complicated, in some cases, by specific solute-solvent interactions, such as solvation of pyridine by chloroform or by the formation of triiodide ion in polar solvents. © 1969, American Chemical Society. All rights reserved.