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COOH synthesis

  1. Jan 20, 2005 #1
    Having trouble with this one; I've tried working backwards from the three carbon carboxylic acid product, but to no avail. Please help!! I can not figure out 'K'.


    "A hydrocarbon K adds one equivalent of H2 upon hydrogenation over a Pt catalyst. When K is oxidized vigorously with hot KMnO4, a single three carbon carboxylic acid is obtained. Give the structures of K and the carboxylic acid."

    This seems simple but K is giving me a lot of grief.
     
  2. jcsd
  3. Jan 20, 2005 #2

    chem_tr

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    Well, vigorous reaction with hot permanganate is not still enough for pure hydrocarbons, this is an alkene with single double bond, this is okay. Since decarboxylation won't occur with KMnO4, I think the K hydrocarbon has three carbons. The vinylic hydrocarbon [tex]H_3C-CH=CH_2[/tex] may be the structure for K and the corresponding carboxylic acid may be [tex]HOOC-CH=CH_2[/tex]. I think the carboxylic acid should be like this, since it is principally similar with an aromatic alkane, say, toluene, which can also be oxidized with permanganate to the acid.

    I may be wrong, so you will have to finish the remaining work by yourself.
     
  4. Jan 20, 2005 #3

    movies

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    Sounds like a symmetrical alkene to me. Probably 3-hexene.
     
  5. Jan 20, 2005 #4

    chem_tr

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    Hmm, does permanganate cleave double bonds to give carboxylic acid? I couldn't remember this one. However, this is logical. I remember ozonolysis to produce ketones or aldehydes, so this sounds okay to me.

    EDIT: I looked up my textbook and saw the example with cyclohexene to give adipic acid with hot permanganate. So your assumption is okay, I think.
     
    Last edited: Jan 20, 2005
  6. Jan 20, 2005 #5
    I'll play around with both ideas and get back to you on my answers. Thank you both for all your help!!!
     
  7. Jan 20, 2005 #6

    movies

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    Yeah, I think KMnO4 first does a dihydroxylation, much like OsO4, and then cleaves the diol, much like NaIO4 does. The resulting aldehydes are then oxidized to the acids.
     
  8. Feb 23, 2005 #7
    sorry i never got back to writing my answer. I waited for it to be graded.
    This is what I did and it was marked correct:

    K ____H2/Pt___K ____Oxidized___KMnO4/heat___ 3-hexene___H2/Pt___hexane w/carbocation on the 3carbon_____warm KMnO4/-OH___>> HO-C-CH2-CH3
    ll
    O

    Thanks for your help!
     
  9. Feb 23, 2005 #8
    i don't know why my answer posted that way, but the =O is supposed to be on the Carbon attached to the -OH.
     
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