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Author: Subject: benzyl alcohol oxidation
Fyndium
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[*] posted on 7-2-2021 at 09:02


If anyone's interested, I could post detailed synthesis of BzH with HNO3. Did it a couple of times prior.
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Mancival
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[*] posted on 7-2-2021 at 13:52


Fyndium, I’m sure I’m not the only one who will appreciate a lot your contribution. Details coming from actual experience are invaluable. Thanks in advance
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Fyndium
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[*] posted on 10-2-2021 at 11:20


I might do a writeup, but sadly I don't have any pictures. I could, although, to the run again in close future in my sloppy days and take pics too. They tell a lot, considering the process has many shades of yellow.
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draculic acid69
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[*] posted on 12-2-2021 at 01:22


Just to put it out there I've seen new formulation paint stripper has benzyl alcohol
where DCM used to be making bnzOH otc.
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dawt
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[*] posted on 2-4-2021 at 23:54


Small update on the procedure I posted about on the previous page, using dilute H2O2 and an octamolybdate catalyst to oxidise benzyl alcohol:

Yield for the preparation of the catalyst was 93 %. I've also attempted to scale up the reaction 10x using 1.1 eq. of H2O2, and while heating up the mixture kicked off a violent reaction when the bath temperature was only approx. 85–90 °C. Luckily I had my eye on the mixture and was able to remove it from the oil bath the second it started acting up, and I had also used my longest condenser, but the bubbling nearly reached the top nonetheless. The picture below was taken 5-10 min after the erruption started, and you can see the reaction was still quite vigorous. For the workup I followed the same procedure as before and ended up with an 81 % yield, though I did have to abort the distillation with approx. 100 mL left in the pot since it started foaming.

I suspect there's still a significant amount of benzyl alcohol and some benzoic acid in my product, so I'll purify it via the bisulfite adduct next.

IMG_20210402_160057.jpg - 137kB




Check out my ELN - and feel free to register and host your own lab notebook there!
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Keras
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[*] posted on 31-10-2021 at 12:03


Here is another green path from benzyl alcohol to benzaldehyde. It is almost OTC, provided you can put your hands on Oxone (potassium peroxymonosulfate).

Source : Oxone/Sodium Chloride: A Simple and Efficient Catalytic System for the Oxidation of Alcohols to Symmetric Esters and Ketones. Synthetic Communications, 36: 1147–1156, 2006. DOI: 10.1080/00397910500514030

Oxone and sodium chloride can be used to either synthesise symmetric alkyl esters or aromatic aldehydes (non-enolisable).

EXPERIMENTAL:

31 g of Oxone (100 mmol) are dissolved into 150 mL of water in a 250 mL beaker using strong stirring. To this is added 6 g (100 mmol) of NaCl. WARNING: upon addition, chlorine gas in released, so this must be conducted in a well ventilated area. Immediately after the sodium chloride has dissolved, 10,8 mL of benzyl alcohol (d ~ 1, 100 mmol) is added to the mixture, which is left to stir at r.t. for 5 hours under a watch glass or similar loose capping, to avoid sur-oxidation to benzoic acid. After a few minutes, the emulsion becomes greenish in colour, probably due to the presence of dissolved chlorine gas.

After 5 hours of continuous stirring, the mixture is left to stand. The upper yellow layer containing benzaldehyde (strong aroma of almonds) and unreacted benzyl alcohol (total: 11 mL) separates from the bottom aqueous layer containing salt and Oxone. The organic phase is collected, washed with water twice. Pure benzaldehyde can be obtained using the bisulfate adduct method (with ~ 15 ml of a saturated solution of sodium bisulfate or metabisulfate).

Pictures: separated upper layer before purification ; Washing of the bisulfite adduct with ethanol

IMG_0944.JPG - 1.2MB IMG_0945.JPG - 1.3MB

[Edited on 31-10-2021 by Keras]
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