When glycerol is treated with excess of HI, it produces
2-iodopropane
Allyl iodide
Propene
Glycerol triiodide
When glycerol is treated with an excess of HI, it produces 2-iodopropane.
In the first step, a molecule of glycerol reacts with 3 HI molecules to form an unstable 1,2,3-triiodopropane. This loses a molecule of iodine to form allyl iodide.
Allyl iodide adds a molecule of HI to obtain an unstable molecule which loses a molecule of iodine to form propene.
A molecule of HI is added to propene to form 2-iodopropane.