Syn the Sizer
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KMnO4 and glycerine, no reaction
About a month ago I purchased some KMnO4 and today decided I would start playing around with it. My ultimate goal was to try and oxidize
1-butano and 1-pentanol to their respective carboxylic acids. But never personally playing with it I decided to get out some glycerine. I put a small
amount on a dish and dropped a couple drops of glycerine on. No reaction. I waited 5min, no reaction. so I grabbed a 2nd dish and put a bit more on
there, grabbed my sufuric acid and put 2 drops of that on the KMnO4. There was a bit of bubbling and smoke, so I added some acid to the
glycerine mixture and a few brown bubbles formed. It is only 4C outside right now could that be what is causing no reaction, the glycerine is from the
pharmacy USP, or did I get ripped off?
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mackolol
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It's quite hard to promote that reaction. Sometime ago I tried it with my chemistry teacher for the school show few times, it has never worked and she
told me that this reaction often doesn't ignite.
Maybe your glycerine is a little bit wet or maybe KMnO4 not fine enough. Maybe just add more H2SO4 to KMno4 and then drip it. I don't think I have to
tell you that it's dangerous though.
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Syn the Sizer
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Quote: Originally posted by mackolol  | It's quite hard to promote that reaction. Sometime ago I tried it with my chemistry teacher for the school show few times, it has never worked and she
told me that this reaction often doesn't ignite.
Maybe your glycerine is a little bit wet or maybe KMnO4 not fine enough. Maybe just add more H2SO4 to KMno4 and then drip it. I don't think I have to
tell you that it's dangerous though. |
Awesome good to know, thank you very much.
As for the danger it never hurts to reiterate it even if it known, better to over state than under protect.
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Syn the Sizer
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I believe you are right about glycerine nor being dry, I added sulfuric acid first than glycerine and it ignited.
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Sulaiman
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try warming the glycerine before adding to the permanganate,
e.g. candle flame heating glycerine in a table spoon
CAUTION : Hobby Chemist, not Professional or even Amateur
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Syn the Sizer
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| Quote: Originally posted by Sulaiman | try warming the glycerine before adding to the permanganate,
e.g. candle flame heating glycerine in a table spoon |
That makes sense. I am going to give it a try in a bit
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woelen
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This reaction works best with finely divided KMnO4 and glycerine, which has a little water in it. Very dry glycerine makes it less reactive. The
amount of water in the glycerine must be a few percent, not more. Where I live, standard glycerine has a density of 1.23 g/ml, while pure glycerine is
1.26 g/ml. The standard glycerine works quite well with KMnO4, while the sg 1.26 material works not as well. Probably a little amount of water makes
the KMnO4 more soluble and allows the reaction to start easier.
The phenomenon that the presence of a little amount of water is beneficial is quite common though. Some other examples:
- Mix powdered AgNO3 and Mg. On addition of a small drop of water, the mix inflames with a bright white flame.
- Mix powdered Mg and crushed I2. On addition of a small drop of water you get a puff of iodine vapor.
- Mix powdered Zn and NH4NO3. On addition of a small drop of water the mix ignites with a greenish/grey flame.
- Mix powdered NaClO2, acetone and sulfuric acid. On addition of a single drop of water the mix explodes with a bright orange flash.
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Syn the Sizer
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| Quote: Originally posted by woelen | This reaction works best with finely divided KMnO4 and glycerine, which has a little water in it. Very dry glycerine makes it less reactive. The
amount of water in the glycerine must be a few percent, not more. Where I live, standard glycerine has a density of 1.23 g/ml, while pure glycerine is
1.26 g/ml. The standard glycerine works quite well with KMnO4, while the sg 1.26 material works not as well. Probably a little amount of water makes
the KMnO4 more soluble and allows the reaction to start easier.
The phenomenon that the presence of a little amount of water is beneficial is quite common though. Some other examples:
- Mix powdered AgNO3 and Mg. On addition of a small drop of water, the mix inflames with a bright white flame.
- Mix powdered Mg and crushed I2. On addition of a small drop of water you get a puff of iodine vapor.
- Mix powdered Zn and NH4NO3. On addition of a small drop of water the mix ignites with a greenish/grey flame.
- Mix powdered NaClO2, acetone and sulfuric acid. On addition of a single drop of water the mix explodes with a bright orange flash.
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Ok, that also makes sense, that could be why warming the glycerine also could work, the increased heat could also increase solubility, as well as
adding sulfuric acid dissolving the KMnO4 prior to adding the glycerine.
I was innitially curious before posting here if it did have something to do with lack of H2O much like concentrated nitric acid won't
dissolve copper well but if you dilute it with water it works better, I believe due to increasing solubility of the produced salts allowing the
reaction to progress.
[Edited on 11-5-2020 by Syn the Sizer]
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