I was doing a high school lab, and according to my expectations for organic chemistry reactions, the following reaction of potassium permanganate and tert-butyl alcohol (t-butanol) should occur:

KMnO4 + C4H10O -> No Reaction

This is because, as far as I understand, while primary alcohols produce aldehydes and secondary alcohols produce ketones, tertiary alcohols do not react in standard oxidation.

My issue is that when I combined 3mL of t-butanol and 1mL of potassium permanganate, plus an H2SO4 (sulfuric acid) catalyst, a visible reaction did occur, turning the solution Orange.

For reference, the initial colour of t-butanol is clear, and KMnO4 is a clear but pink colour.

My initial thoughts are there must be some sort of contaminant. That being said, the only other chemicals nearby that COULD have possible contaminated the solution if someone mixed pipettes werea sec-butyl alcohol and 1-butanol, and I already know the reaction for those with potassium permanganate produces a clear product.

This is my first time using the chemistry StackExchange but I'm used to using StackOverflow, so please feel free to let me know if there is anything missing in my question and I will put it in an addendum in my post. All help appreciated.


Maybe it formed formaldehyde?


2 Answers 2


Normally, the tertiary alcohols do not react with potassium permanganate. However, you added a strong acid (H2SO4). So, the sulfuric acid can react with the alcohol, generating an alkene, and then the alkene could oxidize with potassium permanganate. enter image description here

  • 1
    $\begingroup$ I think I understand: The acid generated isobutylene, which in turn was oxidized by the potassium permanganate originally intended to prove that tert-butyl alcohol doesn't react. This is then oxidized into water, carbon dioxide, and 2-propanone (acetone). This makes sense. But my understanding of acetone is that it's clear (as is water and carbon dioxide obviously). What's the cause of the colour change? $\endgroup$
    – Isaac K
    Nov 14, 2021 at 22:19
  • 2
    $\begingroup$ It is probably $\ce{MnO2}$. $\endgroup$
    – M.L
    Nov 16, 2021 at 6:19
  • $\begingroup$ When I ran reactions with KMnO4, the reaction media became slightly yellow due to the MnO2... I agree with M.L. It could be the MnO2. Or it's other impurities, I guess. $\endgroup$
    – Koba
    Nov 16, 2021 at 9:25

Given time and heat acidic permanganate will oxidize almost anything even water! The Baeyer reagent, cold alkaline permanganate was originally a test for alkenes, isolated double bonds; it oxidizes a double bond to a glycol in decent yield giving a copious MnO2 precipitate. As a test when run properly the end result is a mess and obvious. Unfortunately, other moieties such as primary-, secondary-alcohols, amines, sulfides react. Confirmatory tests or analyses are necessary.

Acidic permanganate [or an intermediate MnO2] is reduced to Manganous ion. The yellow color is not likely to be a manganese compound, unless a complex is formed or a reaction step is inhibited. What is needed here is a more complete stoichiometric analysis. It seems that you reacted an excess of alcohol with a very dilute [pink] permanganate solution and an indefinite amount of acid and got either a pale yellow or orange solution. Possibly a small amount of impurity was reacted with the permanganate and the reaction halted at some intermediate stage. You may be on to something.

First be certain of the purity of the alcohol and the cleanliness of the glassware. Second do a careful account of the amounts possibly a titration with the permanganate instead of a gross addition; control the temperature; an ice bath might be appropriate. The reductions of ions such as MnO4- and CrO4= are stepwise and complicated involving intermediates and intermediate reactions that are sensitive to acidity and concentrations. Add in a secondary reaction such as carbocation formation, makes it more interesting. Careful observation is essential. Have fun and good luck.

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    $\begingroup$ I suspect the color us MnO2. Sulfuruc acid was added as a "catalyst", thus a small amount, and permanganate reductions consume acid. So you msy have gotten the neutral reduction product instead of the acidic one. $\endgroup$ Jul 22, 2023 at 10:45
  • $\begingroup$ MnO2 is "insoluble" in water. You are suggesting the amount of acid was such to neutralize the solution to give a colloidial suspension of MnO2. The info given is insufficient to make conclusions; it is a poorly thought out experiment altho the results are intriguing and invite some serious experimentation not specious conclusions. Also a catalyst is not consumed so the use of the word is amusing at best. The PINK permanganate[have you ever seen pink MnO4- solution?] raises question if there was enough to do anything. $\endgroup$
    – jimchmst
    Jul 23, 2023 at 23:39
  • $\begingroup$ So I said "may". The kay mistake may really have been made by tge book saying there is no reaction with the tertiary alcohol. Some sort of reaction evidently did occur. $\endgroup$ Jul 24, 2023 at 0:15
  • $\begingroup$ True something happened but not what happens with primary and secondary alcohols at least in the end product. We might be seeing a first step in a sequence or just an impurity. Without more data specific speculation is futile. Permanganate and chromate reductions are complex and varied. I see a possible research topic here. $\endgroup$
    – jimchmst
    Jul 24, 2023 at 22:02

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