Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Cosmic on March 05, 2008, 08:13:08 PM
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When I was 15, I dropped into a lab in a big city hospital.. The fellow there was doing illegal isotope experiments there... He took me under his wing to teach me some of the strange chemistry things he new... The one that still puzzles me today is his silly little acid/alcohol/p. permanganate in a test tube thing...
He took a thick walled test tube, and gently added two inches of conc. sulphuric acid...
He carefully floated two inches of ethyl alcohol on the acid...
He He dropped half a gram of crystals of potassium permanganate into the mix, set a loose ball of cotton in the mouth of the tube to prevent splash, and a safety-glass shield between us and the tube.. and waited...
The salt dropped to the bottom of the tube.. and the crystals released a few bubbles for a minute.. then crystals, attached to bubbles, rose to the seam of the liquids layer, and detonated one by one when the new compound contacted the alcohol... The reaction continued for approx. five minutes... The odor the tube gave off was delightful...
Questions: What are the chemical properties of that scent..? I figure it is partly due to burned hydrocarbons, plus something..? It might even be a good scent additive in a perfume..?
What compound is created to make the p. permanganate in sulphuric react violently in ethyl..?
What is the resultant brown p. compound in the alcohol..? Umm..? Umm..? Umm..?
"potassium brownate"..?
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I'm guessing the smell was ethyl acetate, that's an ester, many people say the smell of ethyl acetate, in small amounts, is nice, a light fruity scent, 'tho in large amounts it smells like nail polish remover. Many esters are used as artificial flavorings and scents.
You can watch the permanganate and ethanol reaction here:
http://www.youtube.com/watch?v=KaXQpdQ0Trk
Permanganate is an oxidizing agent, it rapidly oxidizes ethanol into acetic acid, acetic acid and ethanol in the presence of sulfuric acid yield ethyl acetate.
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You can make ethyl acetate that way!?
I would've thought that the permanganate would have just flat out oxidized the ethyl alcohol to the point where it was basically just burning forming CO2 and H2O.
I wouldn't believe it, though, if it weren't for the fact that you said you were getting a pleasant smell, which hints to the presence of an ester (most likely ethyl acetate like Arkcon said) since you have an alcohol and an acid present to act as a catalyst.
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My organic chemistry is a little rusty, but a little Googling makes me feel a little secure that's what's happening. Permanganate + ethanol should rapidly produce nothing but acetic acid. I don't know if the sulfuric acid can catalyze ester formation before all the ethanol is gone 'tho. I'm mostly going by the observation of the odor.
But other things can happen too, permanganate in sulfuric can produce ozone, which some people like in small doses, like the fresh smell after a thunderstorm. {wikipedia} (http://en.wikipedia.org/wiki/Potassium_permanganate#Acids_and_KMnO4) It can even produce Mn2O7 {click} (http://en.wikipedia.org/wiki/Mn2O7), which is a new favorite around here. http://www.chemicalforums.com/index.php?topic=23388.msg88794#msg88794