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Alcohols + non-organic acids = ?

  1. Jun 24, 2005 #1
    Let's say you mixed propanol and HCl, would you just get water and 1-chloro-propane?
     
  2. jcsd
  3. Jun 24, 2005 #2
    Yes. O-chem 101 predicts that you should get the alkylhalide via a Sn2 mechanism.
     
  4. Jun 24, 2005 #3

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    You might also make a lot of diisopropyl ether.
     
  5. Jun 24, 2005 #4
    I believe the because CL- is a poor nucleophile (given it's electronegativity and size), HCL by itself only reacts with Tertiary alcohols which is by the SN1 mechanism where the hydrogen protonates the -OH group, the water leaves, and the CL- attacks the carbocation. For primary and secondary alcohols you need the lucas reagent (ZnCl2) with HCL and for the secondary you get the same type of SN1 mechanism. The primary alcohol is not substituted enough to form a carbocation, so it is SN2, but is very slow.

    HBr would be a beter hydrohalide to work with because Br- is a better nucleophile (larger molecule doesn't hold electrons so close, etc.) The same rules apply here with the primary being the only alcohol to undergo Sn2 displacement, secondary and tertiary go Sn1.

    In short, if you mixed 1-propanol with HCl it may not react (maybe with excess acid and heat??) and you would probably need the ZnCl2 to promote the reaction and it would go Sn2. If you mixed 2-propanol you would probably still need the ZnCl2 but it would go Sn1. (There is an intermediate with the ZnCl2 where it binds to the Oxygen, OH-ZnCl2 is the leaving group.)

    -A
     
  6. Jun 24, 2005 #5
    Cool, I didn't even think of ether formation (doh!) So, how does this work? For 1-propanol I could see it would be hard to get a carbocation for the hydride shift necessary to make the isopropyl ether, no? And, even then, wouldn't you get isopropyl-propyl ether because the n-propyl would attack? I could see via Sn2 getting propyl ether, though, because isn't n-propyl alcohol a better nucleophile than Cl-?

    Or, were you speaking of 2-propanol?

    -A
     
  7. Jun 24, 2005 #6

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    Oh yeah, I thought it was just isopropanol in the original question. My bad. Anyway, yes, if you had 1-propanol you'd just make the carbocation and then probably undergo a hydride shift followed by attack of another 1-propanol molecule.

    This the way that they make diethyl ether industrially (using ethanol and H2SO4.)
     
  8. Jun 24, 2005 #7
    Cool, Thanks for the info on the industrial synthesis.

    I am going to try to hang out in here and take in some of the knowledge before the ACS exam.... I might post a few questions maybe you can help me on later:)

    thx!
    Angela.
     
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