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Does KMnO4 really cleave double/triple bonds?

Discussion in 'MCAT Study Question Q&A' started by thebillsfan, Jul 21, 2009.

  1. thebillsfan

    thebillsfan Unseasoned Veteran 5+ Year Member

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    Dec 22, 2008
    I thought it only oxidized to alcohols...under what conditions can it cleave pi bonds?

    Also, what's the different between hot/acidic KMnO4 and cold/dilute KMnO4?
     
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  3. G1SG2

    G1SG2 5+ Year Member

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    Hot/acidic KMnO4-cleaves double bonds to their carbonyl products, and even oxidizes the aldehydes to carboxylic acids.

    Cold/dilute KMnO4-makes a glycol/diol.
     
  4. thebillsfan

    thebillsfan Unseasoned Veteran 5+ Year Member

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    Dec 22, 2008
    pookiez,

    so wouldnt it always oxidize to carboxylic acids, since cleavage of a double bond would always lead a terminal carbonyl (ie aldehyde)
     
  5. G1SG2

    G1SG2 5+ Year Member

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    No, cleavage of a double bond does not always lead to an aldehyde. Consider R2C=CRH. The KMnO4 cleaves the double bond to give R2C=O, a ketone and RCH=O, an aldehyde, which then gets oxidized to RCOOH, a carboxylic acid. Just picture yourself erasing the double bond and replacing it with two O's (that are not attached to each other, of course).
     
  6. loveoforganic

    loveoforganic -Account Deactivated- 2+ Year Member

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    For terminal alkynes, it oxidizes to a carboxylic acid and CO2. For an internal alkyne, it oxidizes to two carboxylic acids. ('it' being hot, acidic kmno4).
     
  7. G1SG2

    G1SG2 5+ Year Member

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    Yeah, also if it's neutral, then it'll oxidize an internal alkyne to a diketone.
     
  8. loveoforganic

    loveoforganic -Account Deactivated- 2+ Year Member

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    Cool, never knew that :p
     

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