a123x
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Strange Reaction and possible accidental Indicator
So, a while ago I tried brominating anisaldehyde with a brominating solution made by reaction NaBr with H2O2 in acidic conditions. The bromination
went pretty slowly but after a day or so there were many water insoluble crystals obtained along with leftover anisaldehyde(recrystalization from
methanol was quite effective for purifying this into nice yellow crystals rather than the thick sludgy sort of mess when dissolved in anisaldehyde). I
was worried that perhaps I had oxidized the carbonyl to a carboxylic acid functional group. Anyway, I didn't get around to testing to make sure
that this wasn't the case until today.
A small amount of the crystals(.05g maybe) was added to some water. It didn't dissolve. NaHCO3 was added, the yellow crystals didn't
dissolve. This satisfied me that it wasn't a carboxylic acid but I decided to try adding some NaOH. The crystals didn't dissolve but the
solution turned pinkish. Upon adding more the crystals still didn't dissolve but the pink color vanished. Sitting for a while resulted in the
yellow crystals dissappearing and being replaced with fluffier white crystals of some sort. Acidifying the solution turned it clear(no more
unidissolved crystals) and violet. Adding NaOH solution makes it colorless again and acidification turned it violet again.
So, I don't think the yellow crystal product of brominating anisaldehyde is a benzoic acid based on failure to dissolve in NaHCO3 and lowish
concentration NaOH. Anyway, what I'm wondering about is what's with the coloration and indicator behavior. It's not really of
importance to my plans with the bromoanisaldehyde but I'm just really curious and puzzled. Any ideas as to what reaction might have happened with
the NaOH and if the pH indicator formed is one which is already known?
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chemoleo
Biochemicus Energeticus
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Location: England Germany
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Interesting.
Could you please state what acid you used, what the final pH was (during the bromination), and how much AA, NaBr, H2O2, water, and 'acid'
you used?
This might help a little.....
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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a123x
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I don't recall all the details of the bromination(it was over a couple months ago). The acid was either H2SO4 or NaHSO4(I've used both in
the past to acidify a solution before oxidizing Br- to Br2). In both cases I've gotten similar bromination results though. I used 4moles of NaBr
per mole of anisaldehyde. I used stoichiometric amounts of H2O2 and of the acid to the amount of Br- for the oxidation to Br2. There was 1g of NaBr
per 10ml of water. Please feel free to criticize such a procedure for bromination as I'm not so sure it worked quite right(hence the qualitative
testing of the product).
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