April 25, 2024, 10:51:12 AM
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Topic: primary alcohol oxidation to a carboxylic acid under neutral/acidic conditions?  (Read 14898 times)

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Offline aranel

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i have a compound which is base labile, and i need a way to oxidize the primary alcohol up to a carboxylic acid under neutral or acidic conditions. among the chromium based oxidizing agents, i tried PDC in DMF, which did not really work, plus i find the workup afterwards nasty. 

any ideas?  ???

Offline nox

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1. TEMPO based oxidations (Here's a very nice prep from OrgSyn http://www.orgsyn.org/orgsyn/orgsyn/prepcontent.asp?print=1&showprint=1&prep=v81p0195). TEMPO is pretty pricey though.

2. Heyns Oxidation using platinum black and oxygen. However you need to run this reaction in at least neural (pH 7) if not very slightly basic (pH 8 ) conditions to get reasonable rates and yields. Bicarb is commonly used as a base -- how sensitive is your substrate?

3. Oxidation to the aldehyde with Dess-Martin Periodinane, then Pinnick Oxidation to the acid. This is more roundabout, but probably the mildest out of the 3.

Offline aranel

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ah cool!

i thought tempo oxidized only up to an aldehyde. - i'll see how generous my boss feels himself, and go for this one. looks like 1 g is around 45€.

as for Heyns, i'd rather try it if nothing else works. just to be on the safer side.

Although it adds up one more step to oxidize first to an aldehyde, then to an acid, i know my compound is fine with Dess-Martin and Swern oxidations. So i could go for either one - i like Swern better eventhough it's stinky :) then the Pinnick. never tried that one before.

i'll see how it'll turn out. thanks a lot!! 

Offline Fleaker

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Permanganate?


First thing I'd reach for is the good ol' ceric ammonium nitrate :-)
Neither flask nor beaker.

Offline g-bones

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1. TEMPO based oxidations (Here's a very nice prep from OrgSyn http://www.orgsyn.org/orgsyn/orgsyn/prepcontent.asp?print=1&showprint=1&prep=v81p0195). TEMPO is pretty pricey though.

2. Heyns Oxidation using platinum black and oxygen. However you need to run this reaction in at least neural (pH 7) if not very slightly basic (pH 8 ) conditions to get reasonable rates and yields. Bicarb is commonly used as a base -- how sensitive is your substrate?

3. Oxidation to the aldehyde with Dess-Martin Periodinane, then Pinnick Oxidation to the acid. This is more roundabout, but probably the mildest out of the 3.

I agree with oxidation to the aldehyde then Pinnick oxidation.  common place in our group, never seems to let us down :-P

Offline samir

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Simplest would be to use warm/ hot potassium permanganate.
Fast reaction / no messy residues / solid MnO2 as a bye product.

Offline nox

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KMnO4 is good on simple substrates, but you should never try it on anything even moderately complex (or of significant value to you). Plus the problem with KMnO4 is if you have a 1,2-diol (glycol) in your molecule, more often than not it will lead to glycol cleavage.

Offline movies

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How about Jones' reagent? (CrO3, H2SO4, acetone) 

Conditions are pretty harsh, but it's a really easy reaction to perform!

Offline aranel

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i have tried pdc - pyridinium dichromate - which did not really work. that's why i didn't want to go for another chromium based reagent.

i've ordered tempo. will try that one first.  8)

Offline movies

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I believe Jones' reagent is quite a bit more reactive than either PCC or PDC, both of which are buffered.  PDC tends to give the aldehyde, not the carboxylic acid, as I recall.

Anyway, I am a big fan of the TEMPO oxidation methods as well, so good luck!

Offline stewie griffin

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A modified Ley oxidation: TPAP, NMO, and water will give the acid.
Normal TPAP/NMO with molecular sieves gives the aldehyde, but you add water and you can get the acid.

Offline movies

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Hehe – I was talking to a buddy of mine from the Ley group and he reminded me of the TPAP oxidation (for something unrelated) and I thought I would add it to the list of suggestions here.  Stewie beat me to it though!

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