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Topic: Aldehyde impurity removal via Bisulfite Adduct  (Read 6928 times)

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Offline curiouscat

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Aldehyde impurity removal via Bisulfite Adduct
« on: August 30, 2013, 12:41:12 PM »
For removal of a few percent of aromatic aldehyde impurity the bisulfite adduct is a standard procedure and it works well too. Problem is, this time around I'm trying to get rid of a few percent of aromatic aldehyde from an aromatic epoxide and I wasn't getting the desired results. I mean the aldehyde percent does reduce but I start losing my epoxide too.

I didn't expect this (silly me) but on some literature searching I find that the epoxide-bisulfite reaction seems well known.

Question: Any workarounds? Conditions? pH? etc. Can anyone think of a way to make this work by tweaking conditions?

If not, any other reagents (not too expensive hopefully) that are aldehyde specific but won't react with epoxides?

One idea I had was oxidising the aldehyde to a carboxilic acid and then extracting it into water . Thoughts? What may be good oxidizing agents? KMnO4?
« Last Edit: August 30, 2013, 01:00:37 PM by curiouscat »

Offline Archer

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Re: Aldehyde impurity removal via Bisulfate Adduct
« Reply #1 on: August 30, 2013, 01:06:38 PM »
What about Bayer-Villager oxidation? Using buffered peracetic acid. You can buy commercial quantities of this as an aqueous solution. (two phase with vigorous mixing works well.

This won't effect the epoxide but should make the formate ester which should hydrolyse much more easily than the epoxide.

Just a thought, not sure what the outcome would be upon work up.
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Offline curiouscat

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Re: Aldehyde impurity removal via Bisulfate Adduct
« Reply #2 on: August 30, 2013, 01:11:43 PM »
What about Bayer-Villager oxidation? Using buffered peracetic acid. You can buy commercial quantities of this as an aqueous solution. (two phase with vigorous mixing works well.

Thanks @archer! I hadn't thought of this.  I'll try.

Offline curiouscat

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Re: Aldehyde impurity removal via Bisulfite Adduct
« Reply #3 on: September 04, 2013, 04:06:23 AM »
As an aside, would H2O2 potentially be a reagent that might oxidize an aldehyde? If so, is that worth  a shot too here?

The thought of organic peroxides & detonation made me a bit cautious.

Offline Archer

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Re: Aldehyde impurity removal via Bisulfite Adduct
« Reply #4 on: September 04, 2013, 04:25:55 AM »
I've used both for this reaction, however when I used H2O2 I used basic conditions (so it was actually a Dakin Oxidation) this would not be suitable for your purposes.

Probably best to start with hydrogen peroxide and see what happens.
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

Denis Leary.

Offline curiouscat

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Re: Aldehyde impurity removal via Bisulfite Adduct
« Reply #5 on: September 04, 2013, 04:31:35 AM »
I've used both for this reaction, however when I used H2O2 I used basic conditions (so it was actually a Dakin Oxidation) this would not be suitable for your purposes.

Probably best to start with hydrogen peroxide and see what happens.

Thanks! I'll use 30% H2O2 & do it below 60 C. Do I have to take any precautions to avoid the explosive peroxides?

Or is that only an issue if I try to distill them to dryness? Protocol is to test with Starch Iodide paper I recall?

The detonating organic peroxide business is hugely confusing to me.

Offline Archer

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Re: Aldehyde impurity removal via Bisulfite Adduct
« Reply #6 on: September 04, 2013, 09:48:11 AM »

Thanks! I'll use 30% H2O2 & do it below 60 C. Do I have to take any precautions to avoid the explosive peroxides?

Or is that only an issue if I try to distill them to dryness? Protocol is to test with Starch Iodide paper I recall?

The detonating organic peroxide business is hugely confusing to me.

I have only ever done this on small scale so any peroxide formation has not been an issue.

I wouldn't like to advise on this on large scale. I would consult the literature, normally these reactions are carried out in dichloromethane.
“ I love him. He's hops. He's barley. He's protein. He's a meal. ”

Denis Leary.

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