Combine 10 g of potassium iodide, 5 g of sodium bicarbonate and 200 mL of water with stirring, then add 7.5 g of vanillin and 12.6 g of iodine in 4 portions over 30 minutes. After all of the iodine is added, leave to stir for 3h. Leave the solution for overnight to precipitate all of the iodovanillin, filter, then wash with very dilute sodium thiosulfate solution followed by 50 mL of cold water. Dry the crude product, recrystallize hot in 1:4 mixture of ethanol and isopropanol or hot ethanol. Let the iodovanillin crystallize for 12 h and then put the solution in a freezer and filter the crystals. Dry the crystals in a vacuum desiccator.
Addition of the iodine
All the iodine was added, vigorous stirring needed
Solution after 2.5h of stirring
The precipitate was washed and dried
Crystals started to precipitate on cooling