evil_lurker
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toluene --> benzoic acid...
I'm looking for a good cheap method of turning toluene into benzoic acid in kilogram size quantities.
KMnO4 is basically out of the question due to cost, although it might be used to create some MnO2.
Any suggestions?
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Sergei_Eisenstein
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Another route might be the oxidation with Chromium salts, but it might be a problem with the cost as well. If I was asked to synthesize a few kilo of
benzoic acid in a cost effective way, I'd try adding solid CO2 to phenylmagnesium bromide.
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budullewraagh
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direct oxidation with KMnO4 or CrO3 or CrO4-2 salts wouldnt work, as there are no pi electrons connected to the methyl group of toluene. free
radicals wouldnt work.
you could try using chlorine radicals to chlorinate the methyl group of toluene, then react with hydroxide to form benzyl alcohol, then oxidize to
benzoic acid with chromic acid
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Sergei_Eisenstein
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| Quote: | Originally posted by budullewraagh
direct oxidation with KMnO4 or CrO3 or CrO4-2 salts wouldnt work, as there are no pi electrons connected to the methyl group of toluene. free
radicals wouldnt work. |
As far as my chemistry knowledges reaches, potassium permanganate and chromic acid are strong enough to oxidize alkyl side chains of an arene. The
only condition is that the benzylic carbon has at least one hydrogen, i.e. -CH3, -CH2R and -CHR2 can be oxidized but -CR3 cannot.
I'm pretty sure this works. For instance, p-nitrobenzoic acid is prepared by Na2Cr2O7-oxidation of p-nitrotoluene (nitration of benzoic acid
gives the m-isomer), and terephthalic acid (PET precursor) is made in the lab by KMnO4-oxidation of p-xylene (aerobic oxidation in the industry).
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Eclectic
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There is a lab scale prep for phthalic anhydride from napthaline that involves passing air and naphthaline vapours through a V2O5 catalyst. The same
setup would probably work for toluene...
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Sandmeyer
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| Quote: | Originally posted by budullewraagh
direct oxidation with KMnO4 or CrO3 or CrO4-2 salts wouldnt work, as there are no pi electrons connected to the methyl group of toluene. free
radicals wouldnt work. |
http://www.orgsyn.org/orgsyn/RxnTypes/section.asp?section=18...
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WizardX
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BENZIL http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0087
Oxidative cleaverage of Benzil gives 2 moles of Benzoic acid.
CARBOXYLIC ACIDS FROM THE OXIDATION OF TERMINAL ALKENES BY PERMANGANATE
http://www.orgsyn.org/orgsyn/prep.asp?prep=cv7p0397
Styrene ==> Benzoic acid 96%
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budullewraagh
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can somebody show me a mechanism for this oxidation? i can see this working if an alcohol were an intermediate, but it is a stretch to see the
initial oxidation occur
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evil_lurker
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Actually any oxidation for benzaldehyde would work, its just a matter of pushing it hard enough so that the end product is the acid.
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Eclectic
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There are some liquid phase toluene oxidations to benzoic acid that just involve bubbling air through toluene in the presence of a transition metal
catalyst.
just throw in some copper, manganese,cobalt, and iron acetate. Any or all of the above. I don't think it's too picky. A patent search
should turn up details...
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sparkgap
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Anyone recall what catalyst(s) are used in air-oxidizing alkylbenzenes to their corresponding acids? May take a while, but most certainly useful in
evil_lurker's scenario.
sparky (~_~)
"What's UTFSE? I keep hearing about it, but I can't be arsed to search for the answer..."
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budullewraagh
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permanganate or chromic acid work well for the oxidation of aldehydes to carboxylic acids. you could try that.
also you could use thionyl chloride to form the acyl halide, then just convert to the acid
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evil_lurker
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I tried the KMnO4 oxidation of toluene last night and let me tell ya, toluene is some tough stuff to oxidize!!!
Even after 5 hours of reflux, I still had a toluene layer floating on top of the reaction vessel. I did manage to get a little yield though.
But all things considered, the time and effort in using that synth it is just not worthwhile especially when you can purchase it off the net for less
than $10 a pound.
As far as the catalystic air oxidation, I recall seeing something that called for I believe cobalt acetate at 10 atmospheres. Yields were crappy
though at 14% total product conversion, but it was meant for producing benzaldehyde. If you could just get it out in the open, hook up a good reflux
condensor on it and bubble the crap outta some air thru it for 24 hours, it might actually be worth it.
Anyways, I just stumbled onto something interesting.
http://pubs.acs.org/cgi-bin/abstract.cgi/iecred/2001/40/i26/...
Talks about electrochemically oxidizing toluene using cobalt acetate. Benzyl Acetate would be a useful byproduct, if
If I'm thinking correctly it could be decarboxylated (correct term)? to benzene?
[Edited on 21-8-2005 by evil_lurker]
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mick
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Oxidising toluene to benzoic acid would involve
alcohol and aldehyde intermediates which could react with each other so the yields could be low because of dimeric compounds such as ketones,
something like benzophenone.
If you can convert to a CN group. H2O2 and NH3 should give you the amide which should give the acid with water
mick
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unionised
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Benzopheneone? where did the other carbon go?
Among the compounds that you might get from coupling 2 benzaldehydes together is benzoin. That's easily oxidised to benzil and that in turn (as
has been pointed out) gives benzoic acid on oxidation anyway. Losses by coupling this way will be small because many of the products will get cleaved
and oxidised to the right product in the end.
If you can turn the methyl group into a CN then you only have to hydrolyse it to get the acid. I wouldn't waste H2O2 or NH3 on it.
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