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Author Topic: performic ketone color change?  (Read 157 times)

akcom

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performic ketone color change?
« on: May 10, 2011, 06:58:14 PM »
I've been getting a curious result with my last two performic runs and I'm hoping someone can tell me whats happening.  The last two times I've distilled MDP2P after buffered performic followed by HCl hydrolysis my ketone is initialize pale yellow but shortly after standing takes on a very red color.  The ketone reacts properly, I haven't had time to TLC it, but I'm wondering if anyone here has experienced this?

shroomedalice

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Re: performic ketone color change?
« Reply #1 on: May 10, 2011, 07:21:08 PM »
I would say red ketone is from left over acid in your cleanup.

its probably an aldol like condensation product.

thats one good thing about sulfuric it can not gas over with the tone if its
not removed properly

akcom

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Re: performic ketone color change?
« Reply #2 on: May 10, 2011, 07:50:32 PM »
ah, good to know shroom.  I'll have to be more careful next time in my work up.  I just did one brine wash.  I'm getting lazy ;)

shroomedalice

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Re: performic ketone color change?
« Reply #3 on: May 10, 2011, 07:56:53 PM »
thats the one two or three bicarb washes and you will be fine.

jon

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Re: performic ketone color change?
« Reply #4 on: May 10, 2011, 11:17:12 PM »
another yeild killer is that the ketone is partially soluble in the water used in the washes.
it is advisable to back extract the washes.

akcom

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Re: performic ketone color change?
« Reply #5 on: May 11, 2011, 06:38:56 AM »
I didn't notice that chromic mentioned the exact same phenomena when he used HCl the first time.  I'm going to wash this red oil with sodium bicarb as shroom suggested then redistill.  jon, I'd be a schmuck would I be if I wasn't backwashing already.  Didn't know the ketone was extra soluble though?  Good to know.

You know its funny.  I think it came over extra red because I had to stop the distillation an hour or so in.  I turned off the vac and left the flask to cool from ~120C.  I'm guessing led to a lot of the aldol dehydration product because I noticed water condensed on the inside of the flask when I came back...

edit: After 2 washes of sat sodium bicarb the oil has gone from candy apple red to dull yellow/orange, I think this is a good sign.  Jon was right.  Each wash was back extracted with a small portion of DCM and each time the first back extraction has a noticeable yellow color.  Will distill and report back.

The distillate is very clean.  I've never seen ketone quite this pale before.  I guess that's what you get when you double distill.  Thanks for the help guys!
« Last Edit: May 11, 2011, 04:19:05 PM by akcom »

salat

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Re: performic ketone color change?
« Reply #6 on: April 26, 2012, 03:52:48 AM »
Is it possible that differences in ketone color are due to something simple like the fact that bicarbonate is whitish and tints things lighter?

Salat

RoidRage

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Re: performic ketone color change?
« Reply #7 on: April 26, 2012, 07:33:57 AM »
How does that translates to distilled ketone , especially considering bicarbonates boiling points?

salat

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Re: performic ketone color change?
« Reply #8 on: April 26, 2012, 01:33:14 PM »
Doesn't after distillation if you truly separated everything out.  Vacuum tends to make things a little fuzzier as far as separation goes.  I've been learning microscale and it tends to change a LOT of stuff like colors and ratios.

Salat
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