LD5050
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Need pointers on seperating benzaldehyde from benzyl alcohol
I have a mixture of Benzaldehyde and benzyl alcohol probably around 150-200ml worth. I'm looking to separate the two by fractional vacuum
distillation. Boiling point of benzaldehyde is 178.1c and BP of benzyl alcohol 205c and 26.9 degree difference. I suspect the separation will be
difficult, I own a 400mm vigreux column but there is a pin hole size crack in it that I wrapped with teflon tape and seems to hold up alright but I
would rather use my other vigreux column that is much smaller I think like 100-200mm (not positive the correct size but much smaller) would this be OK
to use instead? I know I can make an adduct of the benzaldehyde but I ran out of sodium bisulfite so it isn't an option. So if anyone has experience
separating this mixture with good results please shoot some pointers my way I would really appreciate the help.
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Magpie
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Check out my prep of benzaldehyde in Prepublication. The preliminary separation using steam distillation may facilitate this separation:
http://www.sciencemadness.org/talk/viewthread.php?tid=26075
The single most important condition for a successful synthesis is good mixing - Nicodem
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LD5050
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Thanks magpie, a question I have is what byproducts would likely come from oxidation of benzyl alcohol with 95% nitric acid? This is the method I
used. I got some benzoic acid as a by product but is there any other byproducts I should be aware of using this method?
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Magpie
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I could only guess at your side-products, if any. If you really want pure benzaldehyde I suggest you buy some potassium or sodium meta-bisulfite. It
should be available cheaply at your local brewing supplies vendor.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Texium
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Thread Moved
1-3-2017 at 17:21 |
LD5050
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Thanks Magpie I will check with the local brewing vendors.
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chemplayer...
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Reduced pressure distillation or the bisulfite addition-product method are really your two options. Don't try to distill without reduced pressure
because you'll see vast amounts of white benzoic acid crystals being formed in the condenser as you proceed.
With the bisulfite method the trick is to go slowly, use a saturated solution (take your time to make this properly), and stir really well once you've
added the crude benzaldehyde mixture and be sure to break up any lumps. Take a good 40 minutes to stir and react properly.
You can use some DCM to wash the adduct once you've filtered it to remove any other organic impurities and get it nice and white, but spend some time
after that to dry it carefully and get rid of any residual solvent before you do the hydrolysis step. Saturated sodium carbonate is good for this
(sodium hydroxide runs a risk of killing your benzaldehyde), and use a large excess and again take time and patience to do it.
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LD5050
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Thanks Chemplayer, BTW are you the infamous youtube Chemplayer??? lol?? but anyway for forming an adduct I use 52g of bisulfite mixed in about 120ml
of water with around 70ml of denatured alcohol for every .25mol of benzaldehyde. I then filter and wash with denatured alcohol and air dry it
completely. When recovering the Benzaldehyde I use a 10% sodium hydroxide and water solution. I always wondered if it would be better to use sodium
bicarbonate and you just answered that question for me so thank you.
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chemplayer...
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Something like that... Be careful with using alcohol as it might just be the sort of thing that could dissolve the adduct (check if you can find about
solubilities). The hydrolysis needs to be done with carbonate rather than bicarbonate because it needs a high pH (bicarbonate is not basic enough).
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