The Solubility of Iodine in Aqueous Solutions of Non-Ionic Surface-Active Agents

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Abstract
The solubility of iodine in aqueous solutions of Cetomacrogol 1000 B.P.C., polyethylene glycol 1540 and cetyl and lauryl ethers of polyoxyethylene glycol has been determined. In the region of the critical micelle concentration of cetomacrogol the solubility is below that in water. Well above the CMC, the solubility increases linearly with the concentration of cetomacrogol. Over the temperature range 20–50° the solubility of iodine in aqueous cetomacrogol solution increases with rise of temperature. When a solution is heated and cooled the amount of iodine in the cooled solution is greater than can be obtained by equilibration at that temperature alone. Not all the iodine added to the surface-active agent systems is available for titration with sodium thiosulphate; the unavailable iodine can be accounted for as hydrogen iodide. For 200 g./litre solutions of polyoxyethylene glycol cetyl and lauryl ethers, the available iodine in solution decreases with the number of ethylene oxide units of the ether, but the molecular ratio of iodine to ether increases with the number of ethylene oxide units. The evidence indicates that formation of a complex between iodine and the surface-active agents is in some way involved in the mechanism of the solubilisation process.

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