Murexide
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Obtaining Benzaldehyde
Benzaldehyde is used for many applications in organic syntheses (Cannizzaro reaction, condensation with acetone, making anti-seizure medications etc.)
that seem amateur friendly. Obtaining benzaldehyde is however a concern.
Benzaldehyde is available as bitter almond oil (approx. $30 for 100mL online - Australia), and not available OTC. The main concern is the cyanide
present in the sample (it is even advertised to contain cyanide as a toxin). Certainly, performing organic reactions with cyanide is unacceptable due
to the risk of HCN leakage.
Benzaldehyde can also be obtained from retro-aldol reaction (of cinnamaldehyde) or from partial oxidation of benzyl alcohol, both of which are
available at around the same price as benzaldehyde in pure form and without issue. These procedures are however very cumbersome from what I have read
on SM and involve steam distillation procedures (requiring glassware which I do not have).
How significant is this cyanide contamination, and otherwise what routes are viable to benzaldehyde?
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j_sum1
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There is a thread here on toluene to benzaldehyde. Good luck. I thhink it is possible using KMnO4 and a catalyst. But tricky. I have had a go and
obtained an odour but nothing more.
Oxidation of benzyl alcohol using chromyl chloride seems to be reliable. Coincidentally I was watching NileRed on this today. Chromal chloride is not
without its own issues though.
There are probably other routes.
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j_sum1
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Thread Pruned
21-12-2018 at 21:02 |
Tellurium
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I don't think, that there is HCN present, I think it would react with the benzaldehyde to form the corresponding cyanohydrin. Even if it's present
there should just be trace amounts in it, for some applications the benzoic acid, that's formed from the Benzaldehyde due to oxidation would be more
of a concern, especially if the stuff is a bit older it can be quite a lot. So I would advise you to distill the Bitter Almond oil before using.
In terms of the HCN: Bitter almonds don't contain the HCN directly, but around 5% amygdaline, which only contains around 0,3% HCN, also it normal is
just slowly released enzymatic, so that shouldn't be that dangerous. Do the destillation outside or in a well ventilated area and you should be safe.
If you want to be sure maybe test for cyanides using a mix of Fe²⁺ and Fe³⁺ Ions.
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Justin Blaise
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If you can get a hold of benzyl alcohol, then the Anelli oxidation would give you benzaldehyde. You need TEMPO as a catalyst and bleach as the
oxidant. TEMPO can be hard to get a hold of, but Melgar is currently offering it in the Reagents and Apparatus Acquisition forum.
Once, out of curiosity, I ran GCMS on an almond fragrance for making candles and it turned out that it was something like 70% benzaldehyde and 30%
benzyl benzoate. If I can find the brand I'll let you know. But that seems like an easy distillation and that product definitely doesn't contain HCN
(not that I think your product does either. If it's for general consumers I can't imagine HCN being present).
Edit: this is the product that I can confirm the composition of https://keystonecandlesupplies.com/products/almond-pastries?...
[Edited on 23-12-2018 by Justin Blaise]
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deadrush
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Just wondering but could one freeze off the benzyl benzoate from the benzaldehyde? Its melting point is 18C.
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Texium
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Maybe to an extent, but much of it would probably stay dissolved in the benzaldehyde. Vacuum distillation would be much more effective.
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Texium
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Thread Moved
25-3-2024 at 12:47 |
SplendidAcylation
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Two possible methods
Hi,
The oxidation of benzyl alcohol using nitric acid is very effective, there is a photo essay on here somewhere which I have followed successfully.
Also, probably one of the most "OTC" routes is the Sommelet reaction, starting with benzyl chloride and hexamine.
Attached is a nice write-up, a screenshot from the Vespiary, illustrating the procedure.
I have followed this procedure with good results and comparable yields to the ones mentioned.
If you don't have benzyl chloride you can make it from benzyl alcohol and hydrochloric acid.
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Mateo_swe
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Benzaldehyde is avaliable on ebay if you are in Europe or UK.
Just search for benzaldehyde or Bitter Almond.
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thermochromic
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Y'all are over complicating it
it is much easier than the toluene synth. Oxidize benzyl alcohol with KMnO4. Just throw the two together (with care of course). It resists further
oxidation. There is a research paper in Nature that explains why it does but trust me. It works.
Here is paper:
https://www.nature.com/articles/ncomms4332.pdf
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kyfuge
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You can buy a half liter from China for around $6 USD. Though of course you’d have to worry about importing it, which shouldn’t be too hard. And
it may be of questionable grade, though they claim 99% purity.
[Edited on 24-12-2024 by kyfuge]
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Keras
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I’m sure you can get benzaldehyde from benzyl alcohol and bleach, as demonstrated in this old 1922 patent.
[EDIT: Add PDF file.]
[Edited on 24-12-2024 by Keras]
Attachment: US1405261 - Benzaldehyde from Benzyl Alcohol and Bleach .pdf (450kB)
This file has been downloaded 81 times
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moviez
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Benzaldehyde is kind of difficult for amateurs to come by, but in the US, we can get reasonably pure (99%) 4-methyl Benzaldehyde (search tolyl
aldehyde on Amazon) as food additives. If you’re interested in some aldehyde chemistry, I think 4-methyl benzaldehyde should mostly work, too.
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Keras
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If you can get a hand on potassium peroxymonosulfate (also known as Oxone™), which is sold as a pool cleaner, then simply stirring together benzyl
alcohol, KHSO₅ and table salt at r.t. will give you benzaldehyde in 5 hours. See this thread.
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Sir_Gawain
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Should be fairly pure: https://www.etsy.com/listing/1018493553/benzaldehyde-500g?cl...
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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Dr.Bob
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I have small amounts of several benzalehydes, including the parent benzaldehyde, and some oxone as well, if anyone in the US is interested. But I
cannot ship chemicals internationally. Don't have many benzyl alcohols though.
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