TheLibertineBell
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Red benzaldehyde
After an HN03 driven oxidation of benzyl alcohol to benzaldehyde, I began cleaning the aldehyde up for storage. The solution always starts out creamy
yellow before workup, but then immediately turns reddish/orange upon the NaHCO3 washes. The color seems to deepen somewhat over time, even when stored
in an airtight container with antioxidant stabilizers. I'm sure with vacuum distillation or adduct purification it would disappear, but I haven't
tried that yet.
Just curious what the speculated reason is for the red colour?
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happyfooddance
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Just relatively small amounts of organic impurities and carbonized junk, just like you would get from most organic reactions.
It might disappear upon bisulfite adduct purification, depending on your technique (always good to practice), but it will definitely disappear with a
vacuum distillation. Benzaldehyde reacts quickly with light (may start to turn yellowish in the recieving flask over the course of a few hours, even
under vacuum), so it is a good idea to exclude light from your stillhead, condenser, take off, and receiver. BzH residue on glassware will oxidize to
benzoic acid which appears as a white crust, if left overnight in open air. I find that it is best to distill it immediately prior to use, for most
purposes.
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TheLibertineBell
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Makes sense. Thanks. I took your advice and changed the storage container to a brown glass bottle. Going to do the bisulfite purification today and
wash/filter the adduct with some toluene to see if the colour clears up a bit.
I originally made 300ml of the benzaldehyde to practice vacuum distillation (just bought my first pump, and need to learn the nuances) because of all
the possible aromas to have floating through the air, it's the only one I think my significant other would appreciate. She thinks it smells like I'm
baking cookies. :-)
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