Sciencemadness Discussion Board

Dichromate overoxidation

mr_bovinejony - 23-4-2021 at 08:17

Nile red has a video on making propionaldehyde but uses some heated condenser water which adds more complication to the setup. I've made acetaldehyde by dripping in ethanol to the dichromate solution and the acetaldehyde evaps off as it's formed. This can be done too with propionaldehyde if the solution is heated below the bp of propanol I assume? Is there a reason nile red does it the opposite way?

Another small dichromate question, can the same system of dilute h2so4 be used to oxidize indole 3 carbinol to indole 3 carboxaldehyde? I've tried this oxidation with bleach and gaa but got some weird colors, I was thinking this was from impurities in the bleach but maybe too strong of an acid will hurt the indole somehow

njl - 23-4-2021 at 08:27

I think you will want a much milder oxidant for indole 3 carbinol since indoles are notoriously sensitive to oxidation, even by atmospheric oxygen.

mr_bovinejony - 23-4-2021 at 08:34

I was thinking of using IBX but I have very little and it took a while to make. Might not have a choice though

Oxy - 23-4-2021 at 11:48

Quote: Originally posted by mr_bovinejony  
Is there a reason nile red does it the opposite way?

Adding the dichromate to ethanol reduces the amount of side-products. Propanol (which is in high excess during addition) is being oxidized and quickly removed from from reaction mixture so the risk of over-oxidation is reduced. There are just many alcohol molecules which will undergo the oxidation instead of aldehyde. When you add alcohol to dichromate it's totally opposite. An excess of oxidizer attacks both alcohol and produced aldehyde and it results in over oxidation

[Edited on 23-4-2021 by Oxy]

zed - 24-4-2021 at 02:07

Bovinejony... Indoles are a horse of different color.

They don't take kindly to being oxidized, and they are finicky in general. They hate acidic condition.

There have been reports of Indole-3-Acetaldehyde being produced from Tryptophan by the bleach-method

you tried to employ, and maybe those reports are accurate. Maybe.

That procedure, relies on extracting the aldehyde into a non-water solvent, as it it formed. Preventing

further oxidation.

But, I'm gonna think on about that carbinol.

mr_bovinejony - 24-4-2021 at 07:23

Are there any more mild oxidizing agents other than IBX/DMP/TEMPO that might work for it then? Maybe pyridinium chloro chromate would work?

karlos³ - 24-4-2021 at 09:37

I don't have the paper on me, but I told you definitely about it, maybe even showed it already to you: IBX gives 98% of the aldehyde on indole-3-carbinol in just 30min.
Its to me the ideal choice of reagent here, no doubt.

@zed I doubt those methods very much, this aldehyde is very unstable and I don't think this can easily be reproduced in an amateur setting.
Yet the oxidation of indole-3-carbinol to the aldehyde can be very well.

Damn, wish I would remember where I got this paper... I'll ask a friend who might has an idea, otherwise it has to be re-found... :o
But for everyone ready to look for it, its IBX and indole-3-methanol among many other alcohols to aldehydes.

clearly_not_atara - 24-4-2021 at 10:52

It seems like activated manganese dioxide would be the first port of call for indole-3-carbinol, since it is also used for the oxidation of indolines to indoles.

mr_bovinejony - 24-4-2021 at 10:58

@carl I do have that paper downloaded like 3 times on my phone, ill have to dig for it. The only reason I don't want to use ibx at this point is because my potassium iodide is low and don't want to use it all right now

@atara thanks for this! I think I saw a video about activated manganese dioxide somewhere, might be worth a try

The manganese dioxide method has intrigued me even more now that I see it can oxidize benzyl alcohol. Everything is so cheap, it'd be dumb not to try it. Heres the easiest preparation I found

Well that excitement was short lived. The addition of carbon to the boiling permanganate solution didn't produce any frothing at all, even though the bottle says "laboratory grade activated carbon". On to the next one

[Edited on 24-4-2021 by mr_bovinejony]

xdragon - 24-4-2021 at 12:49

Quote: Originally posted by karlos³  
I don't have the paper on me, but I told you definitely about it, maybe even showed it already to you: IBX gives 98% of the aldehyde on indole-3-carbinol in just 30min.

98 %, 8 h. I think this is the one you meant, but the reaction time is longer.

karlos³ - 24-4-2021 at 15:48

Yeah, must be it.
I was quite certain about the reaction time though, seems I remembered that wrong :D

@mr bj, if you try it with something manganese based, you can at least use the overoxidised indole-3-carboxylic acid for esterification, followed by 5,6-dibromination :D

mr_bovinejony - 24-4-2021 at 16:10

Oooo don't give me any more ideas! There's already too much on the list :P