myristicinaldehyde
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Preparation of 5-hydroxyvanillin
Attached is my write-up. Other than marveling at my fantastic ineptitude in the lab, any comments would be appreciated. Obviously analysis of the
product is extremely limited.
In case you were wondering, the product smells much like vanillin, but perhaps a bit more like caramel, and not as strong.
Attachment: Hydroxyvanillin Lab.pdf (113kB)
This file has been downloaded 1180 times
If we don't study the mistakes of the future we're doomed to repeat them for the first time.
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chemplayer...
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Very interesting and thanks for the detailed write-up! Our attempts also failed, so we might give this method a try and see if it works for us in the
same way.
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myristicinaldehyde
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Thank you! I am waiting for more vanillin to arrive, so I can try using bromide instead of iodide & also see how reproducible my results are.
If we don't study the mistakes of the future we're doomed to repeat them for the first time.
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Gl3n
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Are you aware of the claimed one pot method beginning with vanillin, followed by an iodination via tri-iodide, then basified and reflexes with Cu?
It’s listed on rhodium chem pages under the M syntheses titled something like iodovanillin and hydroxyvanillin Synthesis? It has interested me for
years but every time I get ready to try I have had to relocate due to education/employment situations. It sounds almost too good to be true and I’m
not sure how the tri-iodide works as it seems like a free radical reaction which in my understanding iodine does not work in but maybe the tri-iodide
gets around this? I know the tri-iodide is claimed to be more effective as a biocide but I certainly am not the one to explain the reaction mechanism.
I was actually interested in applying the method towards non hydroxylated BA’s e.g. veratraldehyde but did not want to waste the materials as the
write up clearly states the “preferred substrate” would be benzaldehyde with at least one hydroxy group on the ring. Given the lack of specificity
as to its use in non hydroxylated molecules it seemed prudent to explore other routes.
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bipolar
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5-hydroxyvanillin preparation from 5-iodovanillin
Following text below is mine very old lab records for the preparation of 5-hydroxyvanillin translated to english.
Procedure is really outdated and it needs optimization.
5-iodovanillin C8H7IO3 MW 278.04, mp. 180-182°C
NaOH FW 40
5-hydroxyvanillin C8H8O4 MW 168.15, lit. mp. 131-134°C
13.5 g CuSO4*5H2O was dissolved in 40 ml of boiling water and resulting solution was added with shaking to a 2000 mL RBF
containing mixture of 5-iodovanillin (80 g, 0.287 mol) and solution of 164 g NaOH in 800 mL H2O. Reflux condenser was set in and then whole
apparatus was filled with butane gas, baloon filled with butane was put on the condenser also. The reaction mixture was boiled for 5 hours.
After that, still hot reaction mixture was subjected to filtration through cotton wool pad on a Büchner funnel (this was my very bad substitute for
celite pad - don't use that). Filtration takes very long time (to avoid that you must use good celite pad). Filter cake was washed with few portions
of boiling water.
Filtrate was acidified with cooling with pre-chilled 50% H2SO4 to pH 2-3. While acidification, temperature of the mixture wasn't
allowed to raise above 50°C. Lots of precipitate was formed after completion of this step, there was also color change of the liquid phase.
Resulting suspension was cooled to room temperature and thoroughly mixed with 250 mL of ethyl acetate; most of the precipitate was dissolved. Mixture
was filtrated through 'celite pad', residue on the filter was washed successively with hot water (3 x 30 mL) and EtOAc (25 mL). Filtrate was
transfered to separatory funnel, top layer of EtOAc was separated and saved. Water layer was additionally extracted with EtOAc (3 x 150 mL).
Combined EtOAc extracts was washed successively with 200 g of 25% NaCl solution and with 50 mL of 2% Na2S2O3, then
dried with anh MgSO4 and filtered into distilling flask.
Solvent was removed, resulting semi-solid black residue was cooled and there was added toluene (450 mL). Resulting mixture was boiled for 5-7 minutes,
then heating was discontinued, and as soon as it stops boiling toluene was decanted from remaining black resins in the flask into a heat-resistant
container. This operation was repeated with another portion of fresh PhMe (about 80 mL), decanting it in the same container.
Combined PhMe extracts was heated to dissolve all of the precipitate and allowed to cool slowly to room temperature, let crystallize for 14 hours at
RT°. Resulting precipitate was filtered and dried at ~40°C.
There was obtained 30.1 g (0.179 mol) of 5-hydroxyvanillin, representing yield of 62.3%. Mp = 131-133°C.
Light-brown fine crystalline solid, with aroma resembling that of vanillin but not that strong (possibly micro impurities of vanillin as by-product?)
and, indeed, with some caramel-like notes.
Again, this was a long time ago (I think I was still in highschool when I did that? :lol:  ), and I was way too sloppy back then.
If I was redoing it now I'd change following things about procedure:
1) Don't filter mixture right after reaction. Let it cool in inert atmosphere and filter only after acidification and dilution with EtOAc.
2) Extract with EtOAc few more times. 
3) You should probably use less copper sulfate, like 2-4 times less. It's just a catalyst, using high amounts of it is probably leads to
lower yield and more impurities also.
Using these three features you can expect yield of 80+% very easily, I think.
I also have some other ideas on how to greatly improve hydroxyvanillin work up, but I'm too lazy  to test them right now.
[Edited on 26-3-2019 by bipolar]
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