while performing the experiment of benzoin condensation using thiamine as catalist(without heating, just leaving the reaction for a few days).
i have noticed that the solution of thiamin hidrochloride in water was colorless. but when adding the NaOH the solution became yellowish. i guess that the tihamine changed it's color but i'm not sure for the reason. could it be that because of the deprotonation of the amine group in basic conditions from NH3 to NH2 and consequently conjugation, there is a change in color? (notice that in the attached picture the amine group appears as NH2 even in the accidic form, shouldn't it be NH3+ WHILE acidic?)
another question- we had to put the reaction mixture in a sealed container in a dark room for at least 2 days. why dark room? what is sensitive to light here and why? i mean, could it be that the thiamine is sensitive to light? and how can you see that from it's structure?