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Agha Agha

Solubility of Iodine in Some Organic Solvents

David Petersen  Follow

Iodine forms charge transfer complexes, most notably with starch. In these complexes, a fraction of the electronic charge is transferred to the other molecule. The formation of these complexes increase the solubility of iodine. This has also been called solvation, see for instance this article.

One effect of the formation of these complexes is the change in colour. When there is no interaction with the solvent, the colour of the solutions is violet. This colour changes to red-violet and brown when there is increasing charge transfer.

The order of solubility in the different solvents can be rationalized to some extent looking at the relative permittivity (also known as dielectric constant):

compound               solubility  permittivity   colour------------------------------------------------------------carbon tetrachloride       19          2.24       violethexane                     16          0.44       violetdiethyl ether             337          9.83       browntoluene                   182          2.4        red-violet

Of course, carbon tetrachloride seems an outlier. What happens here is that the dielectric constant is high due to the high $\delta+$ on the carbon. But, since the $\delta-$ is shared by four chlorine atoms and the molecule is symmetrical, there is no effect on the iodine.

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Cherie Valeithian  Follow

Iodine as a halogen has the strong electron affinity, what is the best met by the free electron pair of diethylether, then by $\pi$ electron density of toluene.

Note that iodine is also well soluble in ethanol, commercially used in medical treatment of skin injuries.

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