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Author: Subject: Demethylation of Eugenol
flopfish
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smile.gif posted on 19-8-2024 at 09:05
Demethylation of Eugenol


Well,
This is my first proper attempt at this. And my first post.
I have attached some images for which I have questions:

In the big flask, is 200ml xylene, 25g Eugenol, and 26g AlCl3.
As soon as the AlCl3 touches the eugenol it gets angry and red/brown. Is this normal? I molecular drives the shit out of my xylene so I know it was dry.
When I add the pyridine (60g), it looks like it’s about to explode. And creates quite a bit of smoke.

I did a second attempt with 5g Eugenol in 20ml toluene, which I dried to kingdom come, added 5g AlCl3, and 5ml pyridine.
Again, the reaction was slower to start but after a few mins the AlCl3 seemed to react with the eugenol and turn everything red brown.
I added the pyridine a bit too fast and it created a hell of a lot of smoke.

Anyway, I just wanted to document my progress and compare this to anyone else’s experience.

[Edited on 20-8-2024 by flopfish]
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clearly_not_atara
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[*] posted on 19-8-2024 at 09:18


You basically need an inert atmosphere to do this rxn.



Quote: Originally posted by bnull  
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Mateo_swe
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[*] posted on 29-8-2024 at 06:37


Have you tried the procedure with AlI3?

Gram-Scale Synthesis of 4-Allylcatechol (4)
To a mixture of AlI3 (38.5 mmol, 1.1 equiv) prepared in situ from Al
powder (2.721 g) and I2 (14.657 g, 57.75 mmol) in MeCN (250 mL)
was added DMSO (6.836 g, 87.5 mmol, 2.5 equiv). The mixture was
stirred for 0.5 h at 80 °C, before a solution of eugenol (3; 5.746 g, 35
mmol) in MeCN (20 mL) was added dropwise over 1 h. After stirring
for 18 h at 80 °C, the reaction mixture was quenched with aq 2 M HCl
(50 mL), and extracted with EtOAc (3 × 100 mL). The organic phases
were combined, washed with sat. aq Na2S2O3 and brine, and dried
(anhyd MgSO4). After filtration, the organic solvents were removed on
a rotary evaporator, and the residue was purified through flash column
chromatography (eluent PE/EtOAc 4:1) to give 4; yield: 4.968 g
(94%).

I add the paper.



[Edited on 2024-8-29 by Mateo_swe]
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[Edited on 2024-8-29 by Mateo_swe]

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clearly_not_atara
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[*] posted on 29-8-2024 at 16:52


^well that's certainly something.

So many failures doing this rxn without nitrogen I have to wonder why this version was different. A couple hypotheses:

- heating the MeCN to 80 C (bp 82 C) for 30 minutes before adding eugenol generates a "vapor blanket" that reduces oxygen intrusion into the rxn mixture

- oxygen is generally less soluble in polar solvents like MeCN vs nonpolar solvents like toluene

- iodide is a pretty good antioxidant and radical scavenger




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GhostAliensFromMars
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[*] posted on 4-12-2024 at 21:15


The link contains lots of different demethylation methods, perhaps the most interesting one is the demethylation with just pyridine.hcl and microwave radiation. Only problem is lots of pyridine is needed.

https://www.thevespiary.org/rhodium/Rhodium/chemistry/methyl...
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jackchem2001
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[*] posted on 5-12-2024 at 17:26


Remember that molecular sieves take a while to dry anything (I would guess at least a week is needed for sensitive reactions). Not sure if your problem is water though
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[*] posted on 11-12-2024 at 00:53


"Imoto and Ono, Journal of the Chemical Society of Japan, vol 55, pg 275-9 (1934) (Chemical Abstracts 4048' vol 28) report on cleaving methylene ethers of several compounds by refluxing the compound with AlCl3 in chlorobenzene as solvent. This method should be perfectly applicable to cleaving eugenol's methyl ether (experiment is king). Yields were as high 96% (for piperonylic acid) with chlorobenzene as solvent. 1,2-dichloroethane as solvent gave yields of 90% for demethylation of piperonylic acid, chloroform 70%, and nitrobenzene 3%. Generally the chemist would reflux (with stirring) 164g dried eugenol (1 mole) in 1000g of chlorobenzene and add in several portions AlCl3 (totaling 500g) over 2.5 hours in a reflux apparatus fitted with a calcium chloride tube. After refluxing add dilute hydrochloric acid (15-20%) to the warm solution with stirring until the mixture is definitely acidic to congo red indicator. Extract the aqueous layer with several portions of ether. Extract the ether with portions of dilute 5% sodium hydroxide solution. Acidify the aqueous solution and extract with ether. Separate the layers and distill off the ether and collect the product. The original article will have to be consulted for their exact method and purification scheme"

This seems like a viable route to 4-allylcatechol.
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