Dissolve 5 g of vanillin in 20 mL of acetone, dissolve 2 g of sodium hydroxide in 20 mL of cold water and slowly pour it to the solution. After the solution becomes dark stir it for 48 h and pour 100 mL of 10 % HCI to it with stirring. Stir for 10 minutes and filter, wash with 50 mL of water and crystallize in hot ethanol.
The solution gradually darkens
The solution needs to be stirred for 48h
Addition of the HCl
Washing with water
The recrystallized product