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Author: Subject: Demethylation of Vanillin and Eugenol
nimgoldman
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[*] posted on 24-9-2018 at 07:48


Today I prepared some Py.HCl and it seems to be impossible to store it properly. Even in dry bottle with desiccant packets, it clumped and turned into droplets on the walls. Maybe I should have flame dried the bottle beforehand...

Prolonged drying under vacuum is not an option as pyridine.HCl volatilizes easily.

I think the only sensible way is to prepare Py.HCl on demand - fortunately the preparation is easy (bubbling HCl into a cold solution of pyridine in ether, filtering and putting the solids in a vacuum desiccator without applying vacuum or maybe only very slight vacuum - we just want to remove the ether).

I plan to keep distilled eugenol reacting with excess Py.HCl at 190 °C for 3 hours under argon.

I think the demethylated product (hydroxychavicol) can be distilled under vacuum - is it possible?

I have no idea how hydroxychavicol (i.e. allylcatechol) looks like - a crystalline solid?

[Edited on 24-9-2018 by nimgoldman]
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clearly_not_atara
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[*] posted on 24-9-2018 at 18:37


There's another method I forgot but which is worth considering, particularly since it doesn't smell like pyridine. The attached paper reports a demethylation of eugenol (Page 3742, left side) by extended reflux with lithium chloride in DMF. LiCl is much easier to handle than aluminium halides or PyHCl. I speculate that LiBr may be more effective.

Attachment: kraft2003.pdf (217kB)
This file has been downloaded 226 times

[Edited on 25-9-2018 by clearly_not_atara]




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 25-9-2018 at 01:42


Here is that synthesis step for conveniece:

Quote:
LiCl (292 g, 6.89 mol) was
added to a solution of eugenol (354 mL, 2.30 mmol) in DMF
(3.7 L), and the mixture was refluxed for 44 h, with additional portions of LiCl (292 g, 6.89 mol) being added after 4 h, 22 h and 29 h.
The reaction mixture was allowed to cool down to room temp.,
and diluted with toluene (2 L). The formed precipitate was filtered
off and washed with toluene, the washings were combined with the
organic solution and concentrated in a rotary evaporator. Silicagel FC (Et2O/pentane, 1:1, Rf = 0.37) provided 4-allylpyrocatechol
(173 g, 50%)


50% yield is better than the procedure I found.

I will try the AlCl3/DMF approach after the Py.HCl.

My pyridine hydrochloride sort of caked overnight (see photos) and there are droplets of the liquefied stuff on the glass. The silicagel packet look soaking wet.

I don't think this is all water, the Py.HCl more likely just melted in a presence of minuscule amount of H2O.

It however stays white and fluffy in a desiccator (it seems to be then filled with pyridine vapour) but as long as exposed to the air, it quickly evaporates and liquefies before your eyes.

DSC_0808.JPG - 130kBDSC_0813.JPG - 124kB
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[*] posted on 25-9-2018 at 02:57


The LiCl route is one I've considered, I have some LiCl (made from Li2ClO3 and HCl aq) and about 500ml DMF. LiCl is a little on the expensive side, but I see no reason why the litium couldn't be recovered and recycled. I could give this a try in the near future.

I wonder if the more commonly available DMSO would work instead of DMF.
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[*] posted on 27-9-2018 at 03:59
Disappointing results.


I attempted a 13g eugenol demethylation (slight deficiency compared with the vanillin patent). Reaction seemed to run very well, instead of pyro grade aluminum I used cut up pie tins and then superficially activated with copper. This just involved a short NaOH solution wash then a several minute dilute CuSO4 solution soak, and finally oven dried. Everything was dried well before the reaction.




Reaction was quite vigorous, when the eugenol addition was begun, the ice cooled reaction mix temperature increased from 10 C to 20 C in about 15 seconds, took 55 minutes to complete the addition (maintaining below 20 C).
The reaction was run according to the patent, including an extra hour at 100 C before cooling down.


Interestingly, the final mix turned into milkshake during the complex decomposition with the ice/water. After external heating was applied (I estimate above 50 C or so), the viscosity rapidly dropped off and the mixture settled and the two phases quickly separated.





By morning there was just a clear water phase and organic phase, with a thin emulsion later in the middle.

For the workup, I just steam distilled the lot (could have separated the emulsion layer, but I included that too). The purpose of this was to test for compatibility. There was only a little foaming. All foaming disappeared completely after most of the toluene had been driven off.
A lot of oil came over too, some solidifying in the condenser and receiver (hydroxychavicol mp is ~49 C). It was looking very promising.





The steam distillate (about 2.5 litres) contained about 200ml of toluene in the first litre. I used that to extract the rest of the distillate later on, with another 100ml makeup toluene also.

Working under very non-ideal circumstances, since lacking much analytical data, one has to make some best guess judgements based on limited info available.
That said, whilst I'm confident there was some hydroxychavicol produced the amount "seemed" to diminish later on with the workup, only to be replaced with something else. A fragrant chemical that smells like a lemon/spring cleaning product, a lot like urinal cakes/tabs or floor cleaner. I don't know what it is. It may have just become more noticeable later in the workup as the smoke hydroxychavicol aroma (once dominant) seemed to become less and less. All very subjective.

I'd imagine the o-quinone to have a disagreeable odor, whereas this product isn't disagreeable at all (also reminds me a little of methyl benzoate aroma). Whatever it is, the eugenol appears to have been largely converted to it one way or another.

The aqueous steam distillate (after workup) tested very alkaline on litmus paper, I was expecting it to be acidic (given the post-reaction mix is acidic). Not sure if that's a relevant detail or not.

Before beginning the steam distillation, I took a small sample from the organic phase, and added it to 4% NaOH solution, and it appeared to polymerize immediately.
Organic phase sample is on the right.


A few drops of the organic phase into the alkaline yields this.


Forming a sticky mess that sticks to the sides of the container, but is easily cleaned with isopropyl alcohol.

The final majority oil product after steam distillation does not polymerise with NaOH solution (though a small amount reacts, it reversible with acidification), so it seems logical to assume something has changed.

On the next run, I'll get samples at varying stages. The purpose being to discern if the product is indeed rearranging or degrading, because if it is then that potentially could affect all synthesis/workup attempts not just this approach. Prudent to rule that out if possible.


[Edited on 27-9-2018 by CycloKnight]
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[*] posted on 27-9-2018 at 08:58


After cleaning up all the glassware, work area smells like a freshly cleaned public restroom. Can almost hear the janitor's trolley squeaking in the distance. That lemon/naphthalene fragrance isn't quite the one I was aiming for.
Any suggestions before the next run are most welcome, running out of ideas as far as this particular aluminum bromide approach goes. I was considering using a eugenol excess next time, to perhaps rule out the possibility of a secondary reaction occurring to the demethylated product (assuming it existed). Another idea is to ease up on the reaction conditions a bit, maybe the reaction temp at 100 C for an hour is a little too aggressive for eugenol? I only did the toluene workup (K2CO3) on 100ml of the steam distillation toluene extracts, still have 200ml toluene extracts that I plan to just vacuum distill and collect the individual fraction(s).
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[*] posted on 30-9-2018 at 12:22
Update


Further from the last run, the workup on the remaining 200 ml of the toluene extractions and vacuum distillation has mostly been completed.
Quite unexpected results.

Toluene distilled off using vigreux column.

Vacuum distilled (smaller vigreux column used), vacuum was consistent throughout the entire vacuum distillation.

3 fractions collected.
Residual toluene, came off at 20 C.

Second fraction, 30 - 50 C. Most came over at 49 C. This is the fragrant compound described in my last post. Yield = 28.62g.

I can only assume this has been formed in some way from the toluene during the demethylation. Any guesses what this compound is? Its the main side product so understanding how it's formed might help improve this method later.

Third fraction, 110 - 144 C. Yield = 3.85 g. Plus another few grams solidified in the column and condenser.

Second fraction on the left. Yet to be identified.


Third fraction, with a little carry over from the last.


Third fraction crystallizing in the apparatus.






Isopropyl alcohol solution evaporating in a pyrex dish. Product forms crystalline needles. You can see from the crystal mass on the edge that the solution is fully saturated, a good few grams in there. This is only the column and condenser washings, it does not include any of the 3.85 grams in the final fraction.




The waxy crystalline solid in the pyrex dish appeared to collect some water under the waxy surface (I assumed from the cooling effect from the fan blowing on the alcohol solution pulling humidity from the air), so I applied gentle heat on the hotplate and the crystals melted at around the hyrdoxychavicol melting point (49 C), and color began to slowly change to a browner shade. Not a particularly stable compound. Didn't get a photo unfortunately.

Therefore I was unable to isolate all of the pure solid for a yield measurement.
The product was reacted with potassium carbonate solution to form the salt, to try and prevent any further decomposition. It reacts instantly and the solution turns pink, but when acidified it turns clear again and the solidified oil forms on the surface. I don't have any reason (yet) to conclude any significant decomposition has taken place.

Potassium salt/catecholate solution


This appears to be the target compound, 4-allylcatechol (hydroxychavicol).
No final yield yet, this is only about half to 2/3rds of the actual yield, since I took a large sample of the toluene steam distillation extracts for workup testing (not included in these results). However, considering that the steam distillation wasn't quite completed since it was only desired to have enough product for testing and for product fraction isolation, the yields could've been somewhat higher.

Will be isolating the potassium salt in the next few days or so. I'm hoping this compound is stable in the salt form, will make things a lot easier.
Still early days yet, but this now looks to be headed in the right direction at least.


[Edited on 1-10-2018 by CycloKnight]
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[*] posted on 30-9-2018 at 14:29


BTW there are claims from the betel-growing areas of over 25% (really) yield of AC/APC/HC from dried and ground betel leaf, with alcoholic extracting...lots of interest lately except for methylenating.



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CycloKnight
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[*] posted on 30-9-2018 at 18:13


Recovered salt from the first of two extractions.



There's a good tablespoon of crude chunky potassium catecholate there, haven't weighed it yet. Will weigh it all together when the rest of the work up is complete. So far it isn't looking too bad from a mere 13 g eugenol, all considering! Lots of refinements in the pipeline.

Oven dried it at 60 C. Seems stable, no obvious signs of decomposition so far. I don't know what the other extraction contains yet.

As an aside, I've been unable to find much useful data (solubility, solvent compatibility, etc) for this salt nor the hydroxychavicol, and it's not from lack of trying. So I'll determine and provide it. Tests planned, consider this yield expendable for said purpose. No doubt the data will come in useful for formulating an efficient workup.
Any requests, let me know.

I neglected to mention earlier that the pink catecholate solution also contained about 10 ml of isopropyl alcohol. When the alcohol was evaporated off it changed from pink to a light brown/beige color.

[Edited on 1-10-2018 by CycloKnight]
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[*] posted on 1-10-2018 at 09:30


A few words about product purity, I can't offer any guarantees as it hasn't been thoroughly analysed yet. However, I'm certain at least there isn't any discernible quantity of eugenol in the workup. I've completed this reaction about 15 times (in varying renditions) over 20 days, with experience its quite easy to tell what's eugenol and what isn't. The final product reacts like a catechol should, it decomposes rapidly when melted and exposed to air, and it melts at around 49 C. Can do an accurate mp test later. Crystallizes in needles and has a waxy appearance (as hydroxychavicol does). It smells like diesel and tastes like soap, not easily confused with an obvious workup contaminant such as eugenol.

Today I've been busy trying to wrap up the second extraction. Some product appears to be trapped in about 20 ml of toluene. Rather than waste any more time on it, I might just acidify, rinse, and throw it in with the next vacuum distillation (or vac distill on its own). Either way, there's a small amount I've recovered (still evaporating now), but nowhere as much as the first extraction. So the total second extraction yield is as yet still undetermined, and might remain so.

The first extraction potassium catecholate dried yield is just over 4 g. As that is only from as much as, but no more than 2/3rd of the total steam distillation toluene extractions, then the total yield would extrapolate to at least 5.3 g of catecholate. Add on to that any yield from the second extraction if and when it materializes.

The best workup strategy so far seems to be to run the demethylation reaction, then after the water/ice/HCl aluminum bromide decomposition step, save the organic phase, separate the aqueous layer and extract with toluene.
(Save the aqueous layer for later bromide recovery.)
Steam distill the organic phase (also throw in the toluene from the aqueous phase extraction). Product is the last fraction to come over, so put a lot of steam through it.
Use the toluene that steam distilled in the first litre or so, to back extract the rest of the steam condensate, also extract with extra toluene to get the rest of the product out. Can also add salt to the condensate prior to toluene extractions.

Distill off the toluene using a short column and vacuum distill what remains. The last fraction is the final product, it is then combined with water and isopropyl alcohol and basified with K2CO3 solution. Evaporate to dryness, and then you have your potassium catecholate for whatever purpose you had in mind.
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[*] posted on 1-10-2018 at 12:35
HCl acidified sample


This is about a gram of assumed potassium catecholate, several drops of HCl were added directly without any solvent.
There was some effervescence, indicating some residual K2CO3 contamination with my final yields.



The (assumed) catechol is released as a waxy oil immediately and solidifies on cooling.
Afterwards it was all dissolved by adding a few ml of isopropyl alcohol and then K2CO3 solution added to convert it back to the salt, it was simply dripped in until the effervescence ceased. The catechol is extremely soluble in isopropyl alcohol.
The solution will then be evaporated to recover the salt along with KCl contamination, but can always clean it up later.
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[*] posted on 1-10-2018 at 15:48


BTW Perkin and Trikojus and Schöpf (hive post 507775, UTFSE) note a green color with ferric chloride and allylcatechol.

I suspect one might want to extract such a diol from an aqueous phase with something a bit more polar than toluene.




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[*] posted on 1-10-2018 at 16:25


I would recommend extraction with ethyl acetate- worked very nicely for 5-hydroxyvanillin, might work for any substituted catechol.

(The paper I listed earlier calls for extracting the benzene with water, then washing the water with ethyl acetate, fyi)
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[*] posted on 1-10-2018 at 16:27


Thanks for the suggestion, I'll try that test after the next run. I had a mishap a short while ago. Whilst trying to remove the excess K2CO3 all at once, the product became degraded during the workup. Oops, or something like that.

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[*] posted on 9-10-2018 at 05:35


FeCl3 solution test of assumed hydroxychavicol.



Eugenol yields a yellow-orange color.

Potassium carbonate solutions have proved nearly useless for extracting the product from toluene. It extracts, but only a small percentage per separating funnel extraction using 5% K2CO3 aq. solution. Not proving to be a viable workup strategy unfortunately.

I did manage to isolate some of the product from the completed reaction mixture using solvents and vacuum filtration only.

I removed about 4 ml at round 80 C, evaporated most of the toluene on a glass sample dish, then added a >15 ml of water to decompose the Al Br2 aryl complex. While stirring on the hotplate, several ml of isopropyl alcohol was added, then it was basified with K2CO3. The precipitate was vac filtered (with difficulty as the product was very fine). The gray clay-like precipitate (assumed to contain a lot of aluminum hydroxide) was acidified with 36% HCl (aq) and a little water and extracted with ethyl acetate. 3 extractions of a few ml ethyl acetate removed all of the detectable hydroxychavicol product (using FeCl3 indicator test). The golden yellow ethyl acetate combined extracts were then carefully evaporated in a desiccator with full vacuum applied. Yielding a golden yellow viscous/waxy oil.

The filtrate from the previous filtration step also tested green for some (assumed) hydroxychavicol product also. But, at least this is one way to isolate some product (albeit with impurities) from the reaction mix, without having to steam distill nor vacuum distill.

[Edited on 9-10-2018 by CycloKnight]
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[*] posted on 9-10-2018 at 07:35


Do you have the capacity to carry out TLC plates?
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[*] posted on 9-10-2018 at 10:43


Not difficult to do but I don't have any TLC plates I'm afraid. Its on my list of things still to acquire.
I'm currently building a small standalone recirculating steam distillation and decanting rig that I think might extract the product with minimal hassle. Aiming to have it finished soon. I'm running a little short on extra clamps and fittings so having to improvise a bit.
Steam distillation is the only extraction method I've tried that's produced an extract free of the tar and discoloration, one which can be reliably vac distilled to yield a pure white product that crystallizes.

Once I have a larger pure quantity without the contamination, I imagine it should be a lot easier to positively identify.

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[*] posted on 21-11-2018 at 09:52


Finally have some results to update on.

The fragrant compound I described as a major side product of my previous demethylation attempts using the Al Br method, appears to be none other than bromotoluene (ortho meta para). Same density and boiling point(s) for the isomers. I measured the boiling point mixture ranging between 178 and 184 C, and the density around 1.37 g/ml, which ties in quite closely with that for bromotoluene.

The crystalline substance I isolated before isn't pure 4-allylcatechol, but I assume mostly the dibenzoyl with some 4-allylcatechol. I measured the melting point as being 72 deg C. The reference I have for the dibenzoyl, mentions the melting point as being 72 deg C.

This would explain why the crystals were turning brown when heated to the melting point as I mentioned previously, but it wasn't the main crystalline product that was degrading. The pure dibenzoyl (assumed based on melting point) I've isolated can be melted without obvious signs of decomposition.

From the last steam distillation.
3L beaker as steam condensate receiver, covered in crystals.


Condenser


Crystals in FeCl3 solution, an impurity in the crystals is giving green indication, but not the bulk of the crystal mass.


Ethyl acetate containing hyroxychavicol (presumably) extract.


About half the above solution was evaporated in a glass dish at 6 C with no heating applied. It was an ethyl acetate extract of an acidifed, 5% NaOH extract of the final fraction from vacuum distillation of the steam distillation extracts.
Turned black in air, though this may have been accelerated due to impurities, or decomposition with the NaOH. The NaOH extract was dark red, and then a light yellow/beige upon acidification .


This is an ethyl acetate extract of the steam condensate that's been lying open in the air for about 4 days now. Exposed surfaces turning black.


Its mostly the product that melts at 72 C (dibenzoyl or otherwise), but clearly there is another product in there that degrading on exposure to air.

I've learned that the Al Br demethylation reaction can be run far more concentrated for eugenol than for vanillin. Presumably the dilution for the vanillin demethylation is due to the relatively poor solubility of vanillin in the aromatic solvents referenced in the patents. The last demethylation reaction used 100ml solvent, 26g eugenol, 12g aluminum and 100g bromine. Overhead stirring was used.

I've tweaked the reaction conditions somewhat from the original vanillin demethylation patent procedure, getting better results now.


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[*] posted on 22-11-2018 at 18:11


Results from latest vac distillation.

I see we now have a new player in town. This is the fraction after the dibenzoyl fraction, coming over at >160 C at 24 mbar abs (18 mmHg).






Started off white but soon discolored. The solids shown here solidified in the condenser, nearly completely blocked it (even though I stopped the water flow) but came out mostly in one piece. Turning dark in air, FeCl3 test yields green.

Crystalline solid yield is just under 12 g (including final fraction receiver), and there's a bit more in the glassware alcohol rinsings. This from a 26 g eugenol demethylation run. Steam distillation was run for 10 hours, but was incomplete. Will directly vac distill the organic phase next time.

I've wrapped in foil and put it all in the freezer for safe keeping.

[Edited on 23-11-2018 by CycloKnight]
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[*] posted on 22-11-2018 at 19:00


Final fraction receiver is on the right. Still crystallizing when the image was taken, soon after completely solidifying.
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[*] posted on 23-11-2018 at 07:47


Final fraction mp: 38 C
Condenser solids mp: 48-51 C (some dibenzoyl crystals remained solid)

In the final fraction, there was a drip of clear oil that separated from the crystal mass at room temperature that I hadn't noticed before, so this sample will most likely need to be refined for a more accurate mp test.

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[*] posted on 23-11-2018 at 07:55


Just a short update on the procedure I'm now using.

A while back I had the idea of running the eugenol demethylation reaction using the main side product, bromotoluene, in place of toluene. I've been doing that and it appears to be working so much better as an improved substitute for toluene/xylene complex solvent for this eugenol demethylation approach. It fulfill's the same function (complex formation) just as toluene does. The last two runs have been with bromotoluene (still using toluene as eugenol solvent for the eugenol addition step)

The heating step is now avoided altogether, so after the eugenol addition is complete, only stirring up to 20 deg C but no higher.

This has been working so well, that after the reaction completion and then the complex decomposition step, there is very little tar. Vac distillation of the organic phase looks to be worth trying.

Steam distillation is acceptable for small quantities, but for say a 50 g eugenol demethylation run, it would be necessary to steam distill for perhaps several days just to get the product out.

The bromotoluene is simple to prepare, the reaction conditions (Al Br + HBr) catalyze its formation, so that any excess bromine reacts with available toluene in solution and yields the bromotoluene, which remains after the complex decomposition step, and can be extracted with toluene, then vacuum distilled to separate.
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[*] posted on 23-11-2018 at 08:24


Complex decomposition step.
Final reaction mix in the 500 ml RBF. About a third already added to the beaker.



Note the color after decomposition, much cleaner than before.
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[*] posted on 24-11-2018 at 07:05


http://shodhganga.inflibnet.ac.in/bitstream/10603/161518/4/0...

"The work on betel leaf (Piper betle) consisted of
heating the chopped leaves with groundnut oil at 200°/5»6 mm.
for 5 min. and of obtaining the essential oil by solvent
extraction as well as by steam distillation. The essential
oil was sepeur-ated into phenolic and non-phenolic constituents*
The former on careful distillation under vacuum gave solid
and liquid fractions* The solid fraction on recrystallisation
from benzene-petrol ether melted at 48.5°C. and gave a
dibenzoyl derivative melting at 72°C. On further
examination, it was found to be identical to 4-allyl
catechol (hydroxy-chavicol), the presence of which in Java
betel leaf oil had been reported earlier by Schimmel^and
its presence in Indian betel leaf oil has sincee been
confirmed by Dutt"

----------------
(page 261 of attached pdf)

THE CONSTITUENTS OF ESSENTIAL OILS 261
ALLYL-PYROCATECHOL.
Allyl-pyrocatechol, C9H10O2, exists in betel leaf oil. It is a crystalline
body melting at 48° to 49° and boiling at 139° at 4 mm. It yields a
dibenzoyl derivative melting at 71° to 72°. Its constitution is as follows :—

By methylation with dimethyl sulphate and potash, it yields methyleugenol,
boiling at 248° to 249°;

---------------


Could use a little help. I'm looking for information on this dibenzoyl derivative, its probable structure, etc, and if it can be easily reverted to the 4-allylcatechol. Any feedback appreciated, thanks.



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[*] posted on 24-11-2018 at 09:20


The alcohol part(s) is being converted to benzoate ester, perhaps with benzoyl chloride. Hydrolysis might be a challenge if AC is a little sensitive to everything, so it's hard to say without some investigation.

Thanks for letting us know what's going on.




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