I added solid KMnO4 in watter solution ascorbic acid. The solution begins to turn yellow when I shake it. What happened with ascorbic acid (vitamine
C)? What is product of the decomposition ascorbic acid?Nerro - 10-2-2006 at 12:13
dehydroascorbic acid
The ascorbic acid is reduced to release two hydrogen ions and two electrons. The yellow colour is probably MnO2.nuclear - 10-2-2006 at 13:20
Quote:
Originally posted by Nerro
The yellow colour is probably MnO2.
Solution begins yellow-orange when I add KMnO4, or when add KNO3 and heat.
(sorry for my spelling english. I learn it... )woelen - 10-2-2006 at 14:31
Quote:
Originally posted by Nerro
dehydroascorbic acid
The ascorbic acid is reduced to release two hydrogen ions and two electrons. The yellow colour is probably MnO2.
I also noticed the yellow color of the oxidized form of ascorbic acid. I'm quite sure the yellow color is not due to MnO2, because it is formed with
any oxidizer.
Take some ascorbic acid, dissolve in excess solution of NaOH and let stand in contact with air for several days. The solution slowly turns yellow.
Take a solution of deep blue copper (II) tetrammine sulfate in excess ammonia (can be made by dissolving copper sulfate in household ammonia) and add
some ascorbic acid. The liquid becomes yellow quickly and remains clear. The copper is present as colorless copper (I) diammine complex, the ascorbic
acid again forms a yellow compound.
A picture of such a yellow alkaline oxidized ascorbic acid solution is given here:
I'm not sure what the yellow compound is. It is formed from ascorbic acid with any oxidizer which works at not too low a pH. Can someone shed some
light on this?
[Edited on 10-2-06 by woelen]Sriraman - 28-3-2006 at 06:57
The path way of decomposition of Ascorbic acid is Ascorbic acid to Dehydroascorbic acid to 2,5 Diketogulonic acid and then to oxalic acid and
L-threonic acid. you can guess which gives yellow colour-possibly 2,5 diketogulonic acid due to its two ketonic functions
SriramanNerro - 28-3-2006 at 09:11
I never noticed it before but WOW! I added ascorbic acid to Na2CO3 solution (both pretty concentrated) and I could SEE! it turn yellow. Cool
With some CuSO4 added to it a yellow precipitate of CuOH formed which meant I probably hadnt used enough ascorbic acid.
I also tried adding Mg flakes to ascorbic acid in water, I boiled down the solution to a syrupy consistency, If I dissolve a fat droplet of that in
~100mL of water and I add a chunk of CuSO4.5H2O the solution becomes yellow like in the second paragraph but then the solution clears as Cu is
precipitated.
just adding ascorbic acid to CuSO4 soln. gives a green solution which only extremely slowly precipitates copper.
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