zhiang0113 - 13-6-2016 at 21:39
Hello all, I have a bottle of imitation almond flavour containing propylene glycol, water, and benzaldehyde (it's labeled as "permitted flavouring",
but seeing as most almond flavours are made from benzaldehyde, I'll assume it's the same).
I was wondering how I can extract the benzaldehyde from this? I was thinking of two methods: liquid-liquid extraction using ethyl
acetate/toluene/hexane, or formation of the bisulfite adduct with aqueous sodium bisulfite, followed by hydrolysis using sodium carbonate solution.
Which method is better? The former is more straightforward, but I don't know the solubility of benzaldehyde and propylene glycol (I assume this will
be much more hydrophilic than benzaldehyde though) in ethyl acetate. Or are there any better methods to extract the benzaldehyde?
Thank you! 
[Edited on 14-6-2016 by zhiang0113]
[Edited on 14-6-2016 by zhiang0113]
[Edited on 14-6-2016 by zhiang0113]
macckone - 14-6-2016 at 07:48
Vacuum distillation should remove the water.
propylene glycol and benzaldehyde have similar boiling points at normal pressure.
forming a bisulfite addition product seems the most feasible.
there should be a benzaldehyde thread here somewhere.
search.
careysub - 14-6-2016 at 09:44
Forming the bisulfite adduct is the common method of isolating and purifying aldehydes, the adduct can be split after separation:
http://chem2all.blogspot.com/2009/03/addition-of-bisulfite-t...
http://www.sciencemadness.org/talk/viewthread.php?tid=27476
http://www.orgsyn.org/demo.aspx?prep=cv5p0437
A paper discussing the conditions (and rates) for dissociating the adduct:
Attachment: stewart1932.pdf (407kB)
This file has been downloaded 603 times
zhiang0113 - 15-6-2016 at 05:13
Thank you for the responses! However I don't have a vacuum distillation setup, but I did try making the bisulfite addition product. However, the
mixture just turned cloudy, and no visible precipitate was formed. Could it be that the adduct is soluble in the propylene glycol, or was I doing
something wrong?
zed - 17-6-2016 at 16:54
Steam distillation is possible.
Crowfjord - 17-6-2016 at 18:04
Bisulfite adducts tend to be water soluble. You should get a precipitate if you add the benzaldehyde solution to a large excess of strong, preferably
saturated sodium bisulfite or metabisulfite solution. If using metabisulfite, let the solution stand for a few minutes before using so the
metabisulfite has time to hydrolyze to bisulfite.
draculic acid69 - 25-9-2018 at 03:55
So does anyone know if the bisulfite adduct is soluble in propylene glycol?
What about ethanol? These are 2 of the ingredients in almond essence apart from water.what about acetone? Could the adduct be formed by pouring the
essence into the bisulfite solution and then boiling to near dryness followed by acetone or xylene washing?