DougTheMapper - 18-12-2010 at 12:29
Hey all, I'm new to organic chemistry and I can't find anything regarding the effect concentrated sulfuric acid has on methyl ethyl ketone.
I performed the following experiment yesterday with some interesting results:
I was experimenting to see whether methyl ethyl ketone could be cleaved by concentrated sulfuric acid and the product nitrated to methyl and ethyl
nitrates. Having a huge amount of methyl ethyl ketone, I decided it was worth a try.
I started with methyl ethyl ketone added dropwise to conc. sulfuric acid, which seemed to have no effect except the lowered viscosity of the acid. I
then added KNO3 to the solution slowly and allowed it to dissolve while keeping the temperature at around 15C. Nothing appeared to happen at all, so I
removed it from the water bath which was stabilizing the temperature (The experiment was performed in a test tube.) I began to heat the tube gradually
in a water bath at about 60C with agitation.
Sometime into the heating a classic nitration "runaway" occurred, turning the solution brown with nitrogen oxides and evolving the characteristc brown
gas.
I repeated the experiment several times and tried crashing the mix into 50mL water both before and after initiating a "runaway" which revealed neither
crystals nor an immiscible liquid in any instance.
I'm at a loss for ideas. Perhaps the MEK is cleaving into methanoic and ethanoic acids which are then attacked by the sulfuric, before the creation of
the in situ nitric? I have no idea. I'd appreciate any insight into what might be going on!
mnick12 - 18-12-2010 at 13:14
I don't quite understand what you are asking, why would H2SO4 cleave any part of 2-butanone molecule? What was you target?
UKnowNotWatUDo - 18-12-2010 at 13:51
I agree. What leads you to believe that sulfuric acid and MEK react in this way? Also, if MEK was cleaved into methyl and ethyl products, what happens
to the 4th carbon? Remember MEK is 2-butanone.
not_important - 18-12-2010 at 14:30
If anything the MEK is self-condensing to give a mix of products. In a similar fashion mesitylene is produced from acetone and H2SO4.
Note : missed the KNO3 addition _before_ heating. Heat w/o nitrate, get condensation; unfortunately way too impure to then add the nitrate to get
trinitromesitylene in useful yields and purity.
[Edited on 18-12-2010 by not_important]
madscientist - 18-12-2010 at 14:55
You're nitrating MEK. You won't get the products you're looking for.
Dinitroacetone is some dangerous stuff and I wouldn't expect nitrated MEK to be much better. I wouldn't repeat your experiment if I were you.
Nicodem - 19-12-2010 at 07:31
Treating such ketones with conc. H2SO4 will only lead to their self condensation via acid catalysed aldol reactions followed by dehydration to various
enones and even alkylbenzenes, but mostly just crap, especially under uncontrolled conditions.
Nitration of ketones is possible in some cases, but it does not give alpha-nitroketones as one might expect (unlike the nitrosation, which proceeds
readily at the alpha position).
For the oxidative cleavage of ketones you need to use plain diluted nitric acid without sulfuric acid. A long reflux of 2-butanone (MEK) in somewhat
diluted HNO3 ought to give a mixture of propanoic and acetic acid as the main products. Isolation and separation of these would then require
fractionation which should not be that hard with a good column (unless there are azeotropes breaking the party). This could actually be a useful
homelab route to propanoic acid. Check the literature for the best reaction conditions for the oxidative cleavage of ketones with HNO3(aq). I
currently don't have the time to do a literature search, though a preliminary 10 sec search gives DOI:10.1016/S0255-2701(00)00099-4 where the
oxidation of 2-octanone with nitric acid is studies (it should point to further articles on the topic).
madscientist - 19-12-2010 at 15:57
Here's an ancient post on the matter:
http://www.sciencemadness.org/talk/viewthread.php?tid=403#pi...
Take note of photoguy's post toward the end. Attempting anything like this is very dangerous indeed...
Ephoton - 19-12-2010 at 19:34
I have heard of this oxidation Nicodem and known a few who have used it.
my thoughts though would be that we would still get some aldol condensation
type reactions though from the acidic hydrogen.
this would not be a problem as they would have a much higher molecular weight
than propanoic acid so would easily seperate when distilling the acid.
not sure though just a though.
Sedit - 19-12-2010 at 21:41
Isn't an acid catalysed Enol behave intermediately like that of an alcohol in some sense? Could it be possible he is just performing an oxidation and
not a nitration simular to experiments performed by me using HNO3 and alcohol to yeild a carboxylic acid?
Out of plain ignorence I would suggest the fellow bases some of the mixture and test for the presence of propanic acid and/or acetic acid salts.