[cth]

Hello everyone.

I am trying to do a ketal reaction:
-   Dissolve 500mg of catechol (2-hydroxyphenol) in 10mL of acetone.
-   Then add 3 or 4 drops of concentrated sulfuric acid.
-   Use aluminium foil to protect it from light, let it rest for 2 or 3 hours.
-   Evaporate the acetone to dryness: white crystalline solids form.
Everything is done at room temperature. What I want to achieve is:



Do you think it should be working?


Ultimately, I wish to synthesise the ligand hexahydroxytriphenylene (http://www.chemicalbook.com/ChemicalProductProperty_EN_CB0245984.htm). I know synthetic methods have been published for this ligand, mainly involving oxidative trimerisation of 1,2-dimethoxybenzene and removal of the methyl groups. Unfortunately, I do not have access to the dimethoxybenzene. I used to work in university labs a few years ago, but not anymore. Thus, I can only use chemicals available on ebay or local stores. For the same reason, I don’t have IR spectroscopy to tell me if what I got is the catechol starting material or the ketal product (or something else).

I would appreciate if you have any help or comment about the ketal reaction. Thank you very much
Also, if you happen to have worked with a similar ketal, do you know how long it takes in water before it gets hydrolysed, especially at basic pH? Thank you

[rolnor]

The cathecol is sensitive to electrophilic attac, acetone could attac the aromatic ring in presence of acid. Difficult for you when you are limited in so many ways. If you whant to get NMR I can recomend ChemAnalytical.

[kamiyu]

For this type of reaction, it is crucial to remove the water by-product to drive the equilibrium to the right.

The concentrated sulphuric acid is a catalyst here, but not desiccant.

One very typical way is to use toluene and p-TsOH refluxing (not sure about the stability of your catechol) with Dean-and-Stark apparatus. The merit of this apparatus to allow to see the amount of water thus formed. When this amount matches the theoretical amount of water formed, you can stop the reaction.

Other means include added molecular sieves and anhydrous MgSO4, this approach is compatible with room-temp reaction

[Dan]

How dry is your acetone?

Here is a simple prep using  acetone (1.3 equiv) in benzene with PCl₃ (0.4 equiv):

http://link.springer.com/article/10.1023%2FA%3A1011387916186#enumeration

You can substitute benzene for toluene:

http://www.mdpi.com/1420-3049/20/5/8654

I think catechol ketals are very sensitive to acid hydrolysis, more so than ketals derived from aliphatic diols, so it is vital to have a water scavenger (like PCl₃) present, or use a Dean-Stark setup etc.

Alternatively, 2,2-dimethoxypropane may be a better option (since it does not generate water as it condenses).

[cth]

Thank you a lot for your answers and help. 

Clearly the acetone is too wet, so the next step is to dry it. I’ll find some molecular sieve.

Thanks as well for chemanalytical.com, I’ll contact them when ready.