careysub - 9-1-2016 at 15:17
I have become curious about the actual benzaldehyde content of various almond flavoring products and would like an easy assay procedure to determine
what that content is.
My strategy: oxidize the benzaldehyde to benzoic acid (with KMnO4 perhaps), then add NaOH till neutralized to form sodium benzoate, and then evaporate
to dryness. Evaporating an unmodified sample to dryness would check for any other solids. I would subtract the mass of the reduced permanganate to get
the final mass with enough precision for my curiosity.
Is there a better oxidation procedure that would just use atmospheric oxygen reliably?
Any suggests or comments?
Oscilllator - 9-1-2016 at 16:25
I can't immediately think of a better way, but I don't think this one will work very well because of how strong an oxidiser KMnO4 is. It would very
easily oxidise other things (Sugar, glycerin etc), providing a bad result. Perhaps using a weaker oxidation agent would be better. I don't think the
silver mirror test will work either, as these mixtures often contain inverted(hydrolysed) fructose which also reduces silver(I).
Sadly I think you will need a fairly precise test for this as I don't think the benzandehyde content goes above a few %.
Etaoin Shrdlu - 9-1-2016 at 16:41
Why not form the bisulfite adduct?
careysub - 9-1-2016 at 20:58
Clearly if there is a lot of other stuff in it then the job gets a lot harder.
I was thinking of almond flavorings which are usually water, alcohol, and almond extract, or artificial flavoring. Real almond extract would contain
some phenolics and fatty acids. Artificial flavoring is probably just benzaldehyde and maybe an antioxidant (a role played by phenolics in natural
extract).
For a milder oxidant, how about H2O2? Then there is no added solid to the mix. I do have 30% H2O2 if that helps.
I think the bisulfite suggestion is probably the way to go, looks like a standard aldehyde assay technique.
semesa - 9-1-2016 at 21:03
Isolate aldehydes/methyl ketones by their bisulfite adduct.
Take an Rf.
Compare against known concentration.
gdflp - 9-1-2016 at 21:06
Problem with the bisulfite adduct is that it is still slightly soluble in water so the result won't be quantitative, it depends on how accurate you
want the result to be. Another option is the 2,4-dinitrophenylhydrazone adduct, which precipitates more quantitatively(and has a precipitate which is
much easier to filter), though 2,4-dinitrophenylhydrazine can be a bit hard to come by. Another benefit of the 2,4-dinitrophenylhydrazone is that the
adducts have well defined and recorded melting points, the MP of the benzaldehyde adduct in question is 237°C. Do note that both of these adducts
aren't terribly selective, they will both precipitate any aldehydes and ketones present in the mixture(The purity can be checked via MP if the
hydrazone is used).
byko3y - 11-1-2016 at 20:30
Bisulfite adduct is not slightly soluble in water. It is VERY SOLUBLE in water - this is a main misconception with bisulfite extraction. Although,
it's not miscible and its solubility is lower than the solubility of the original sodium bisulfite.
You can't use oxidation of benzaldehyde to benzoic acid, because benzyl alcohol and sodium benzoate are common preservatives that will interfere,
until you know there's not acids and alcohols in the mixture.
UC235 - 11-1-2016 at 20:38
Almond flavoring is usually water, alcohol (or propylene glycol), and benzaldehyde. That's all. The "natural" version uses rectified oil of bitter
almond which is like 98% benzaldehyde so the composition is effectively identical. Benzaldehyde oxidizes pretty easily to benzoic acid on air exposure
and some is likely present in these products unintentionally.
KMnO4 titration will not work unless you remove the alcohol (and the benzaldehyde is volatile with steam so you'd need a column). You're out of luck
if it's propylene glycol.
phlogiston - 12-1-2016 at 04:04
If you can obtain dinitrophenylhydrazine (DNPH), it yields a highly colored derivative that should be straightforward to separate from unreacted DNPH
with TLC.
[Edited on 12-1-2016 by phlogiston]
chemrox - 12-1-2016 at 16:23
Become an analytical lab. Spend $250K on gear and hire an analytical chemist to teach you how to use the equipment. Otherwise send a sample to a well
equipped lab and pay for the report. Much cheaper. There is no quick and dirty way to get quantitative results. Weight the bisufite adduct is the
closest you might come with fore mentioned issues. Oil of bitter almond is almost pure benzaldehyde which is why fascist, overprotective countries
make it hard to buy.
byko3y - 12-1-2016 at 16:38
Some of you just forgot that 80 years ago there was no equipment $250K worth, there was no widespread NMR, IR, HPLC still it was sophisticated enough
to determine structure of morphine or LSD. There was already existing chromatography, elemental analysis, distillation, extraction, and a lot of
reactive quantitative and qualitative methods.
The main reason for the modern analytical instruments to exist is a speed and convenience. Some complicated molecule or a mixture will take day or two
to be analyzed, while decades ago you would need weeks or months for the same task, and you would few grams of the compounds, while NMR requires
something like 10 mg.
careysub - 12-1-2016 at 17:50
Also, there is such a thing as "semiquantitative analysis" where you get rough estimates of how much of a thing is present.
I am not going to be publishing any papers, I am just satisfying my curiosity about the strength of products that I buy while doing a little hobby
chemistry (also a thing).
I will probably try both bisulfite, and my original oxidation-to-benzoic schemes to see what happens.
Thanks, this thread gave me the type of feedback I was looking for.