Sciencemadness Discussion Board

Help with Acetylation of Catechol

Maui3 - 2-1-2025 at 09:17

Today, I attempted to acetylate catechol by first adding catechol to a NaOH solution at room temperature, followed by the addition of acetic anhydride. It seems like the reaction worked, but I observed two distinct layers: a yellowish oil at the bottom and a white layer on top. The white layer did not contain a precipitate and was likely just a suspension of a small amount of the yellow oil from the bottom. However, I'm unsure of the whereabouts of my catechol diacetate, which is a solid at room temperature.

If anyone with more experience could help me understand what might have happened, I'd appreciate it! :p

Boffis - 2-1-2025 at 10:51

@ Maui3; the usual method of preparing phenolic acetates is to use excess acetic anhydride and a little sulphuric acid as a catalyst.

From your current mixture I suggest that you just dilute it with water until the sodium acetate/water layer separates from the catachol acetate. If it dissolves completely then you probably don't have any catechol ester.

Maui3 - 2-1-2025 at 11:00

Thank you Boffis!

I have been searching a lot for a procedure for catechol diacetate, and did not find one, so your response definitely helps me a lot!

Do you know if it is possible to use sodium bisulfate instead of sulfuric acid? Or another alternative? Sulfuric acid is very hard to get where I am.

jackchem2001 - 2-1-2025 at 18:05

Impure solids have a depressed melting point and may oil out instead of crystalizing

AvBaeyer - 2-1-2025 at 21:07

Google search "1,2-diacetoxybenzene synthesis" seems to be an obvious place to start. One hit that pops up is

https://www.guidechem.com/encyclopedia/synthesis_635-67-6-p1...

Lots of references to explore eg: https://journals.sagepub.com/doi/pdf/10.3184/030823401103169...

Avb

Maui3 - 3-1-2025 at 03:23

Thank you all very much! That is very helpful :P

I think I might try a esterification similar to this post on here:
https://www.sciencemadness.org/talk/files.php?pid=304709&...

.. of course using catechol instead of phenol, and adjusting the amount of catechol, acetic acid and sodium bisulfate.
If you think this will work..

jackchem2001 - 3-1-2025 at 04:02

Not sure what product you want but I imagine with catechol and one equivilant of Ac2O you can selectively acylate once but I think that will be much harder with acetic acid reflux with H2SO4.
Edit: Nevermind, I see you want the diacylated product. Ignore this post

[Edited on 3-1-2025 by jackchem2001]

clearly_not_atara - 3-1-2025 at 06:09

Quote: Originally posted by Boffis  
@ Maui3; the usual method of preparing phenolic acetates is to use excess acetic anhydride and a little sulphuric acid as a catalyst.

From your current mixture I suggest that you just dilute it with water until the sodium acetate/water layer separates from the catachol acetate. If it dissolves completely then you probably don't have any catechol ester.

Wouldn't that give the FC product? I would have guessed you want basic conditions for an ester.

Maui3 - 3-1-2025 at 06:26

Jackchem2001, Yeah I am making the diacetate :-)
Do you think NaHSO4 can be used instead of H2SO4 for this esterification? - I have done many esterifiactions before with NaHSO4 sucessfully, but I just want to be sure - catechol is expensive..

jackchem2001 - 3-1-2025 at 15:34

The only way to really know is to do the experiment. Electronically I would expect diacylation to be easier than with phenol but sterically more difficult, and if I had to guess the steric effect is probably more important given the favoured flat conformation of a phenyl ester. Overall I would guess that you won't get as good as a result as in the paper (yield 50-60%) with the same conditions.

If you are going to use a weaker acid then I would suggest using more so there is a greater concentration of protonated carbonyl in the reaction mixture. Maybe more time at reflux as well since your mixture is slower to equilibriate. Ultimately these are just guesses. Good luck with the experiment :)
Quote: Originally posted by clearly_not_atara  

Wouldn't that give the FC product? I would have guessed you want basic conditions for an ester.

I think FC is much slower due to loss of aromaticity

Maui3 - 4-1-2025 at 03:15

Yeah, that's true. I will probably try it soon, and report back! I might also try with acetyl chloride - like the paper AvBaeyer posted.