Tables for Chemistry

Iodine

Iodine

Iodine vapour is a very versatile and unselective reagent. It reacts forms addition compounds even with very unreactive compounds such as hydrocarbons.
Many compounds adsorb iodine giving brown spots. These are particularly intense for quartenary ammonium salts and sulphonium salts (e.g. choline, thiamine). Other compounds may prevent the formation of complexes with the solid phase or react with the iodine to produce white spots on a light brown background.
Most spots will disappear fairly rapidly as the iodine evaporates.

Reagent

Iodine is placed in a beaker covered with a glass plate. To speed up the formation of vapour the beaker may be heated slightly.

Reagent Iodine on celite

An alternative to iodine vapour is iodine adsorbed on celite. The bottom of a wide necked plastic container is covered with celite and iodine is added (approx. 20:1). The TLC plate is placed in the container, the lid tightened, and the container rotated or shaken for a few seconds. On removal the plate shows dark or light spots as above.