I was in need of some 5-bromovanillin - a completely useless precursor *ahum* - and decided to scale up my usual procedure. I employed the GAA/bromine method for 0.5 mol vanillin. Addition of bromine was complete in 1.5 hours and reaction allowed to continue a further hour. Subsequently, some water was added and the precipitating reaction mixture stored in the fridge for a few hours. The precipitate was filtered (Buechner) and washed with water. We all know this story, n'est-ce pas?
However, my 5-bromovanillin didn't look very pure: dark yellow, at some points even orange. On a smaller scale, this wasn't really a problem because everything except vanillin and 5-bromovanillin was washed away. I could wash the product with a few liters of water though, but it wouldn't be very practical. Another alternative would be washing with aqueous methanol, but I decided to dissolve the whole crystalline mush in 500 ml methanol and bring it to a soft boiling. When all product was dissolved, heating was continued for about 2-3 min and 400 mL warm water (temperature shouldn't be higher than bp of methanol) was added (with stirring of the solution). This caused the precipitation of a white crystalline product. The reaction mixture was allowed to reach ambient temperature and transferred to the fridge (4°C) to complete crystallization. The mixture was stored overnight, the precipitate filtered (suction) and washed with 200 ml of cold water. Total yield: 91% (based on dried weight of product).
The end product is a crystalline powder, very similar to vanillin itself in both appearance and odour. The colour is slightly off-white. The first crop of precipitate arising from the addition of water to the methanolic solution consists of a white crystalline powder. The second crop, coming forth from storing the reaction mixture in the fridge, consists of much longer needles. Using this procedure, a rather pure 5-bromovanillin can be obtained (GC-FID: 98% 5-bromovanillin, 1% vanillin). And most importantly, it
looks pure
. The look of my intermediary products is important as well, but we all know something is wrong with me, so don't worry if you happen not to care about it
.
There obviously is nothing special about this procedure (educated and self-made chemists use similar methods to find a good recrystallization solvent combination), but I thought it was a good addition for the few psychonauts with less knowledge about chemistry, but very hungry for M.
M!
I have a similar method for the recrystallization of 5-iodovanillin, but substituting MeOH for EtOH. It gives plates/needles.