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Topic: Oxidation of ketone  (Read 4607 times)

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Offline UG

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Oxidation of ketone
« on: April 12, 2010, 02:18:03 AM »
I am a bit confused about this question:
Harsh oxidation of a certain asymmetric ketone with potassium dichromate in the presence of sulfuric acid produces a mixture of two carboxylic acids whose molar masses are in a 1:1.234 ratio.
So I have worked out that one is ethanoic acid, molar mass = 45 g mol-1 and the other is propanoic acid, molar mass = 74 g mol-1
The second question was, What ketone was used?
The answer said butanone, but how can that be? Shoudn't there be five carbons? Is the answer wrong?
Just on a side note, how does the mechanism for this reaction work?
Thanks for your help.

Offline azmanam

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Re: Oxidation of ketone
« Reply #1 on: April 12, 2010, 06:04:48 AM »
the problem didn't say that the two products came from the same ketone at the same time. 
Knowing why you got a question wrong is better than knowing that you got a question right.

Offline UG

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Re: Oxidation of ketone
« Reply #2 on: April 12, 2010, 06:06:46 AM »
the problem didn't say that the two products came from the same ketone at the same time.  
Ah, so you think then that we're going to get a lot more acetic acid than propanoic acid?

Offline UG

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Re: Oxidation of ketone
« Reply #3 on: April 12, 2010, 07:36:49 AM »
If I was to make butanone using only inorganic materials and reagents, would this be a good option?


Offline azmanam

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Re: Oxidation of ketone
« Reply #4 on: April 12, 2010, 08:17:38 AM »
I don't know which acid will be produced preferentially.  But butanone can be oxidized to acetic acid.  Butanone can also be oxidized to propionic acid.  Just not on the same molecule of butanone.  It's not like ozonolysis where the alkene gets fragmented into two aldehydes which contain the same total carbon atoms as the original alkene.  You'll need two different reactions here: one on butanone to produce acetic acid, and one on a different butanone to produce propionic acid.

as to your route, I don't know if coal counts as an inorganic reagent.  And the hydration of the enyne will probably not be selective, and you may get significant quantities of the alpha-hydroxy ketone.  Creative though :)
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Offline UG

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Re: Oxidation of ketone
« Reply #5 on: April 12, 2010, 05:45:00 PM »
as to your route, I don't know if coal counts as an inorganic reagent. 
Is there another way to get a carbon chain then? Maybe there's some fancy trick you can do with carbon dioxide or something?

Offline orgopete

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Re: Oxidation of ketone
« Reply #6 on: April 12, 2010, 06:00:28 PM »
Re: the oxidation.

I agree with UG, based upon the data given, it implies that it should have been 3-pentanone (except it has been specified as an asymmetric ketone). What was left would was the carbon dioxide as the missing carbon. If it were my problem, I would have given that as information for the problem.
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