Master Organic Chemistry Reaction Guide

Dihydroxylation of alkenes with cold, dilute KMnO4 to give vicinal diols

Description: Treatment of alkenes with cold, dilute basic KMnO4 leads to 1,2-diols (vicinal diols).

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Comment section

69 thoughts on “Dihydroxylation of alkenes with cold, dilute KMnO4 to give vicinal diols

  1. This website has almost all the fundamentals of organic chemistry, google shows it up all the time, really love it!

  2. What if the solution is not neutral

    Maybe acidic or alkaline.
    What would be the product formed

    Cis or trans

  3. How does cold KMnO4 behave with double bounds conjugated to a benzene ring, such as seen with styrene? I know that KMnO4 will oxidize styrene to benzoic acid, and until I found this page, was under the impression that it would ALWAYS oxidize to benzoic acid. Does this mean that careful temperature control and monitoring of the reaction form the 1,2-diol as the main product?

  4. Hi James,
    I’m wondering why the products of the permanganate oxidation are temperature dependent…By le chateliers, more endothermic reactions should be favored at lower temperatures. But the more exothermic oxidation to form ketones occurs under higher temperatures, while the less exothermic pathway ending in alcohols occurs under lower temperatures?

    1. Refer to this post: https://www.masterorganicchemistry.com/2011/08/01/oxidation-and-reduction-in-organic-chemistry/

      In hydroxylation of alkenes you are breaking C-C and forming C-O . Oxygen is more electronegative than carbon, therefore carbon is increasing its oxidation state. It’s a net oxidation because each carbon is oxidized.
      With hydration, you’re also breaking C-C but one carbon is forming C-O and the other is forming C-H. One carbon is oxidized and one is reduced, it’s not a net oxidation.

  5. If in the reaction equation, all that’s mentioned is ” dilute KMnO⁴, cold ” and no mention of ” NaOH ” whatsoever, are we going to consider the manganate product as the final product? Or is it too unstable to actually be the final product, and hence presence of NaOH is compulsorily required in the reaction?

  6. I don’t understand why when adding KMnO4 /NaOH to 1- cyclohexene you just have one product. Why doesn’t the enantiomer form in this case and in the others it does?

  7. Dude. Thanks a lot. Amazing website and a real help before my hellish examination.

  8. Hi, I wanted to ask you, for how long should the reaction be carried over, to prevent the synthesis of a carboxylic acid?

  9. What is the difference of using cold dilute neutral KMnO4 with using warm dilute neutral KMnO4 and hot acidic KMnO4 ?

  10. will you please tell me the supporting information regarding this reaction i.e. the no. of moles and the exact reaction conditions and the complete process

  11. So if I wanted to convert 4-hexen-1-ol to 4-hexanoic acid, would I use potassium permanganate or potassium dichromate and why?

  12. I am getring confused in the byproduct of the reaction. What will be the difference in byproducts when cis and trans form of aklene is reacted with alkaline KMnO4?

  13. Can you explain to me thoroughly about the reaction between cyclohexene and cold acidified kmno4 and cyclohexene with hot acidified kmno4? Does the temp affect the product? I’m having a lot of trouble with organic chem.

    1. Yes, the temperature greatly affects the product. At low temperatures you will obtain the 1,2-diol (glycol). At higher temperatures the 1,2-diol will cleave and you will get a reaction product essentially equivalent to ozonolysis.

  14. Hi, can you please explain the furthur reaction if temperature is given i.e the formation of carbonyl compounds,Mechanism?

    1. Great question. You’d open it up with aqueous acid (H3O+). That protonates the epoxide oxygen, and then water acts as a nucleophile, opening the epoxide.

  15. I’m getting all confused about the conditions under which KMnO4 reacts.
    For alkynes: I have
    1. water, neutral gives vicinal ketones.
    2. if there’s a base in cold, dilute conditions there’s no reaction.
    3. if there’s a base in warm water you get cleavage. (is this the same as a base in warm and dilute conditions?)

    When you throw in the reactions conditions of alkenes too, I cannot keep all this straight in my head if my life depended on it, which indicates to me that I don’t understand the effect of each of the conditions. Is the difference between the last 2 just dependent on the temperature? What is the significance of the base? How do these compare to reaction conditions of an alkene? Etc., etc. Please help me make sense of all this mess!! Thanks!

  16. Hi James,
    This is very helpful! Thank you.
    So, when KMnO4 is added to an alkene under high temperatures, then it further oxidizes it correct?
    Does it form aldehyde in terminal alkenes and ketones in other alkenes?? (if so, then what happens to the rest of the alkene?)

  17. wud like to know C2H4 + H2O + [O]——-> C2H2(OH)2. Pls explain to me where the water molecule comes from when alkene reacts acidified with potassium manganate (VII). tq

      1. but unless the presence of the two equivalents, the result will sure end up still being just a diol, right?

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