Recipe notes:
Mix 1g thiamine HCl, 4g water, 6g EtOH, 5g BzO and stir while cold (below 20 degC).
Add 3M NaOH dropwise until soln turns yellow (~1.8g)
Heat to max 60deg C for at least 1-2 hours
Cool down and filter of benzoin crystals.

I have tried about 3 procedures from YT and 1 from sciencemadness article multiple times and they all failed. Not entirely sure why. I was using benzaldehyde that I have sythetized so this was immensly time consuming until I have found method that worked. benzaldehyde quality wasn't the issue though, I am certain it was bug in condensation procedure.

When this reaction fails, usually there is residual unreacted benzaldehyde that will somehow separate from solution. Color of reactants goes to deep red and the smell... The smell is unbelievable - extremely sweet but also combined with strong rotten egg stentch quite similar to natural gas odorant but ramped up to 11. Sometimes it is possible to recover this by diluting the mixture and checking if crystals will percipitate. If there is some thiamine left, reaction may start after this dilution and you get crystals after some time (~24h). If reaction fails completely, after dilution a polymerized goo will percipitate that is very sticky and extremely hard to clean with soap (use acetone or EtOH).

Oh and I forgot to mention - you can get thiamine tablets for human consumption, but extracting pure thiamine is extremely difficult. You should be able to use these for condensation without extraction, or try to extract with soxhlet and 50/50 ethanol.

Another question is if you can reuse thiamine solution by adding more benzaldehyde. In theory yes, but there is definitely something that does decompose there and it may not be worth doing this but I can check this.

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