Iodine solubility, organic solvents solutions, colour

Like bromine, iodine is soluble in organic solvents, for example chloroform, which can be used to extract it from an aqueous solution. The iodine imparts a characteristic purple colour to the organic layer this is used as a test for iodine (p. 349). NB Brown solutions are formed when iodine dissolves in ether, alcohol, and acetone. In chloroform and benzene a purple solution is formed, whilst a violet solution is produced in carbon disulphide and some hydrocarbons. These colours arise due to charge transfer (p. 60) to and from the iodine and the solvent organic molecules. 

In the presence of a small excess of iodide, Pd gives Pdt which is sparingly soluble in acidic media. When shaken with benzene or DIPE, PdE passes into the organic phase it has been the basis for a sensitive indirect determination method. The suspension of Pdh in the organic solvent is stripped by dilute ammonia. The aqueous solution is acidified, then the iodide is oxidized by bromine to IO3. This iodate reacts with added T to liberate iodine, which is determined as its coloured complex with starch (see Section 25.2.1). One Pd atom in PdE is equivalent to twelve atoms of iodine. 

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