Pumukli
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Model reaction uncertainties
I've been thinking about monitoring and following the O-alkylation of phenols in an amateur setting.
What I came up with so far: mix a phenol with a base, an alkylating agent in excess, with stirring and thermal control, and from time to time take out
a sample, mix it with acid and Fe(III)-chloride, and record the absorbance of the complex under "standardized" conditions.
The alkylation probably works, the photometry of the Fe-complex too. "The science" behind the method is the supposed (expected) decrease of absorbance
due to less and less phenol would be available for complex-forming as the alkylation progresses.
My main concern is centered around the susceptibility of phenols towards oxidation and the formation of coloured side products. At high pH (alkylation
medium) this is just worse.
I'm wondering if there were some special phenols that were not really susceptible to this oxidation. What if I used specially substituted phenols,
where positions 2-4-(6) were occupied (hence prevented from chinon-formation). Maybe, 2,4-DNP would be a good candidate. The nitro-groups may be just
deactivating enough towards oxidation... Would they?
Would a 2,4,6-trisubstituted phenol sterically too hindered for alkylation of the OH-group? I know 2,6-disubstituted benzoic acids are (very)hard to
esterify with common methods (Fisher). How about the alkylation of a similarly substituted phenol?
Tips, hints would be warmly appreciated!
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goldberg
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You would like to monitor synthesis of phenolic ethers right?
How about TLC? Since phenols are easily oxidized You could visualise your plates with basic KMnO4 or FeCl3 as you said.
you can also consider using amperometry. I didn't heard about problems with oxidation of phenols during etherification.
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Pumukli
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Thanks for the ideas.
I'd prefer something more quantitative than TLC and as I have an old but working photometer (and found references for determination of phenol via VIS
photometry) I thought it may do.
Amperometry? Hm, probably some sort of electrochemical method would be my next choice anyway.
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