Today I tried your method...
250 mL RB flask was charged with 5 g vanillin, 6.2 g KI and 100 mL MeOH and the resulting homogenous mixture was vigorously stirred.
60 mL household-toilet bleach (~5% NaOCl, product w/ pH ~12 is importnant, see the mechanism) was added to the reaction flask from an ordinary sep. funnel at such a rate that the addition took 20 minutes. No condenser/cooling were required as originally recommended since no temperature rise could be felt. Throughout the addition of NaOCl the colour in the flask changed from light yellow to deeply red and back to cloudy, coffee-with-milk coloured at the end of the addition. Some precipitate could bee seen at this stage.
The stirring was continued (cover the flask with foil to prevent MeOH evaporation) for 6 more hours after the addition was complete, (6 h is overkill but I had to leave to school).
Content of the RB flask was now transferred to a bigger 500 mL e-flask and ~150 mL 10% sodium dithionite was added, rinse the RB with it. [I didn’t had sodium thiosulfate, Nicodem suggests ascorbic acid, which is also cheap, OTC and works as good]. Then there was added ~150 mL 10% HCl, until the colour shifted back to light-yellow. Throughout the addition of HCl colour changes from yellow to deaply red and back to yellow, stop adding the HCl at when it turns yellow again. I felt it unnescessary to strip off the alcohol as originally suggested, maybee this affected my yield as the product is s a bit soluble in MeOH esp this volume, but not much more than in water so I didn't care. The neck of the Erlenmeyer was wrapped in foil, the flask sealed in a plastic bag (stinks SO2) and put in food-freezer for 40 minutes. In the meantime improvised vac-filtration setup was assembeled.
The thick, off-white precipitate was vac-filtered, washed with ~100 mL cold H2O and dried under a desktop lamp for 3.5-4 h. Dry, clean white crystals weighed 6.5 g (71 %). Interestingly, there was no smell of vanillin coming from this batch of crystals. Recrystallisation is not necessary but will be attempted from MeOH.
Comments:
The procedure is easy if you are in ghetto situation and gives very clean product; my yield went down the drain during the wash I think. Last time I iodinated vanillin I used the KI/I2/baking powder method, it is pretty messy compared to this, and in my hands it yielded the same as this. However I saved liquor phases from that synth becouse of need to regenrate iodine and I see now a a share of crystals have formed in those, so the yield is not too bad. I bet same holds here, but this time I didn’t save mother liquors. Noteworthy is that KI/I2 method give, even after the recrystallisation from MeOH, a tan product that smelled a bit vanillin. Pablos, this method is recommended, try it.