Solubility of Iodine in Glycol-Water Solutions*

The solubility of iodine at 25° in ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and dipropylene glycol increases in the order of solvents named, reaching a concentration of 88.16 Gm. of iodine in 100 cc. of dipropylene glycol solution. Addition of water to the respective glycols markedly reduces the solubility of iodine. Absorption spectra of iodine in the glycols, as well as in glycerin, indicate the presence of solvate complexes analogous to triiodide ion. The mechanism of solution of iodine in the solvents studied may involve a Lewis type of acid-base interaction, the iodine functioning as the acid and the solvent as the base.